UN Report (Air Coolers)

WORLD BANK TECHNICAL PAPER NO. 421

(I Eneegy Series

Work in progress WTP421for public discussion

March 1999

EvaporativeAir-ConditioningApplications for EnvironmentallyFriendly Cooling

Gelit Jan BomRobert FosterEbel DijkstraAMIaija Tummer-s

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WORLD BANK TECHNICAL PAPER NO. 421

Energy Series

EvaporativeAir-ConditioningApplicationsfor EnvironmentallyFriendly Cooling

Gert Jan BomRobert FosterEbelD#jkstraMarja Tummers

The World BankWashington, D.C.

Copyright © 1999The International Bank for Reconstructionand Development/THE WORLD BANK1818 H Street, N.W.Washington, D.C. 20433, U.S.A.

All rights reservedManufactured in the United States of AmericaFirst printing March 1999

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ISSN: 0253-7494

Gert Jan Bom, Ebel Dijkstra, and Marja Tummers are development consultants at Ecozone, Haarlem,the Netherlands. Robert Foster is a project engineer at New Mexico State University, Las Cruces.

Library of Congress Cataloging-in-Publication Data

Evaporative air-conditioning: applications for environmentallyfriendly cooling / Gert Jan Bom .. .[et al.].

p. cm. - (World Bank technical paper; 421. Energy series)Includes bibliographical references (p. ).ISBN 0-8213-4334-31. Air conditioning. 2. Evaporative cooling. I. Bom, Gert Jan.

II. Series.TH7687.E94 1998697.9'3-dc2l 98-31273

CIP

ENERGY SERIES

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Contents

Foreword ............................................................. ix

Abstract ............................................................. xi

Acknowledgments ............................................................. xiii

Abbreviations, Symbols, and Glossary ............................................................. xv

1. Introduction ............................................................. l1Benefits of Evaporative Cooling .............................................................. 2Opportunities and Limitations .............................................................. 2Environmental Benefits .............................................................. 2Direct Evaporative Air-Conditioning .............................................................. 3Residential Coolers .............................................................. 3Indirect Evaporative Air-Conditioning .............................................................. 4Desiccant-Assisted Evaporative Air-Conditioning .............................................................. 4Commercial Evaporative Air-Conditioners .............................................................. 5Comparing Vapor-Compression and Evaporative Air-Conditioning .................................................5Outlook .............................................................. 5

2. Opportunities and Constraints .............................................................. 9Climatological Factors ............................................................. 9Comfort Issues ............................................................. 10Expected Performance of Evaporative Air-Conditioning ............................................................. 12Power Supply ............................................................. 13Water Supply ............................................................. 13Advantages of Evaporative Versus Vapor-Compression Air-Conditioning .................................... 13

3. Economics ............................................................. 15Economics of Residential Coolers ............................................................. 15Investment Costs ............................................................. 16Market Situation ............................................................. 18

4. Technology ............................................................. 21Direct Evaporative Air-Conditioning ............................................................. 21Indirect-Direct Evaporative Air-Conditioning ............................................................. 26Desiccant Cooling ............................................................. 29

5. Choosing and Maintaining Equipment ............................................................. 31Available Equipment ............................................................. 31

v

vi Evaporative Air-Conditioning, Applications for Environmentally Friendly Cooling

Direct Evaporative Air-Conditioning Recommended Air Change Ratefor Design Wet-Bulb (WB) Conditions .......................................................... 33

Maintenance .......................................................... 33

6. Solar Evaporative Air-Conditioning .......................................................... 37The Market .......................................................... 37Optimizing Evaporative Air-Conditioning Design for Solar Operation .......................................... 38

7. Introduction and Local Manufacture in Developing Countries ......................................................... 41Maintenance ........................................................... 41Installation and Sizing .......................................................... 41Manufacturing Requirements ........................................................... 41Know-How .......................................................... 43

8. Commercial Evaporative Air-Conditioning .......................................................... 45Commercial versus Residential Cooling .......................................................... 45Commercial Kitchen Evaporative Air-Conditioning .......................................................... 46Laundry and Dry Cleaning .......................................................... 46Extreme Heat Conditions .......................................................... 46Industrial Applications .......................................................... 47Factory Air-Conditioning Design Considerations ........................................................... 47Agricultural Applications-Poultry .......................................................... 48Greenhouses .......................................................... 49

Bibliography .......................................................... . 69

Annexes1. Introduction to Evaporative Cooling .......................................................... 532. Suitability of Evaporative Air-Conditioning in Different Climate Zones ........................................ 573. List of Manufacturers and Suppliers .......................................................... 63

Boxes2.1 Relative Humidity and Wet-Bulb Temperature .......................................................... 105.1 A Simple Sizing Example .......................................................... 32

Figures1.1 Typical Direct Evaporative Air-Conditioner .31.2 Roof-Mounted Downdraft Evaporative Air-Conditioning Unit, El Paso, Texas .41.3 Direct Evaporative Air-Conditioner for Transport Use .72.1 Modified Evaporative Air-Conditioning Comfort Zone Taking into Account

Increased Airflow Compared with ASHRAE Comfort Zone Based on VaporCompression Air-Conditioning .11

2.2 Annual Energy Use Summary: Vapor Compression Air-Conditioning(SEER = 9.5 for Phoenix, Arizona, USA) .14

2.3 Annual Energy Use Summary: Indirect/Direct Evaporative Air-Conditioning(2,000 scfm, for Phoenix, Arizona, USA) .14

3.1 Typical Investment Costs for Evaporative Air-Conditioning in the United States .163.2 Typical Investment Costs for Evaporative Air-Conditioning in India .173.3 Typical Life-Cycle Costs: Evaporative Air-Conditioning versus Air-Conditioning

for the United States .173.4 Typical Life-Cycle Costs: Evaporative Air-Conditioning versus Air-Conditioning for India .184.1 Simplified Evaporative Air-Conditioning Process .224.2 Psychrometric Process for Direct Evaporative Cooling, Mexico .224.3 Comnonly Available Rigid Cellulose Pads Provide Superior Saturation and Cooling

Compared with Ordinary Aspen Pads .244.4 Close-up of Rigid Cellulose Pad Made of Corrugated Paper .244.5 Common Cabinets for Residential Coolers in India .26

Contents v2i

4.6 Cutaway of a Direct Evaporative Air-Conditioning ................................................................... 274.7 Plate-Type Indirect-Direct Evaporative Air-Conditioning ................................................................. 274.8 Indirect-Direct Evaporative Air-Conditioners on a Public School Rooftop,

Colorado Springs, USA .................................................................. 284.9 Indirect-Direct Evaporative Air-Conditioning Process .................................................................. 294.10 Ventilation Cycle Desiccant Cooling System .................................................................. 306.1 A Solar-Powered Evaporative Air-Conditioner .................................................................. 376.2 Evaporative Cooler Coupled with Solar Power (System installed by a homeowner

in Chaparral, New Mexico, USA) .................................................................. 397.1 Evaporative Air-Conditioners in Kamla Market, New Delhi, India ................................................. 428.1 Typical Evaporative Air-Conditioning Application for Poultry Houses .......................................... 498.2 Evaporative Cooling Pad Section of Rigid Cellulose Pads ................................................................. 508.3 External Evaporative Air-Conditioners on a Research Greenhouse, New Mexico

State University, Las Cruces, New Mexico .................................................................. 50A1.1 Psychrometric Chart and Saturation Line .53Al.2 Complete Psychrometric Chart .53A1.3 Wet-Bulb Depression of Ambient Air .54A1.4 Saturation Effectiveness for an 80 Percent Effective Evaporative Cooling Pad .54A1.5 Saturation Effectiveness of 80 Percent for Evaporative Cooling Pads at Different

Ambient Conditions .54A1.6 Effect of Indirect Evaporative Cooling on Ambient Airstream .54Al.7 Effect of Combined Indirect Evaporative Cooling Coupled with Direct Section .55A1.8 Energy-Saving Effect of Using a Smaller Coil Coupled with Indirect and Direct

Evaporative Cooling Sections .55A2.1 Suitability of Evaporative Air-Conditioning: Africa .57A2.2 Suitability of Evaporative Air-Conditioning: Asia .58A2.3 Suitability of Evaporative Air-Conditioning: Australia .59A2.4 Suitability of Evaporative Air-Conditioning: Europe .60A2.5 Suitability of Evaporative Air-Conditioning: North America .61A2.6 Suitability of Evaporative Air-Conditioning: South Arnerica .62

Tables1.1 Vapor-Compression versus Evaporative Air-Conditioning .................................................................62.1 Effectiveness of Evaporative Cooling by Climate Type ....................................................................92.2 Relation between Wet-Bulb Temperatures and Effectiveness of Evaporative

Air-Conditioning .................................................................. 102.3 Evaporative Air-Conditioning Performance in Selected Locations at 1 Percent

Cooling Design Conditions .................................................................. 122.4 Benefits of Evaporative Air-Conditioning Versus Vapor Compression Air-Conditioning ............ 135.1 Available Residential Evaporative Air-Conditioning Equipment ..................................................... 315.2 Useful Cooling Chart: Percentage of Useful Cooling for Direct Evaporative

Air-Conditioning Output ................................................................... 346.1 Available Packaged Solar Evaporative Air-Conditioning Equipment .............................................. 386.2 Design Measures to Optimize Evaporative Air-Conditioning for Solar Power .............................. 387.1 Work Involved in Manufacturing Evaporative Air-Conditioning .................................................... 42

Foreword

Although evaporative coolers cannot be used in all countries and at all times, they are generally verymuch underutilized in places where they can be used successfully. This is unfortunate, both for thepotential user, the country, and the global environment. Benefits include lower cooling equipment costsand a much reduced electricity bill for the user, reduced electrical energy and power demand at peak-times for the country, and lower greenhouse gas and CFC/HFC emissions for us all.

This handbook is designed for those who do not know evaporative coolers, but might be convincedto try using or promoting them. It provides the advantages and disadvantages of using evaporativecoolers while comparing them to the commonly used, energy guzzling, and expensive vapor compres-sion air conditioners. Existing markets where evaporative coolers are currently used, local manufactur-ing possibilities, operational aspects are discussed along economic and global aspects. A world-wide listof manufacturers and suppliers is included in the Annex.

James BondDirectorEnergy, Mining andTelecommunications Department

ix

Abstract

As the harmful environmental effects of chloro-fluorocarbons (CFCs) and greenhouse gases have be-come better known, interest has grown in environmentally friendly cooling technologies. Evaporativeair-conditioning (EAC) is such a technology. Whereas conventional vapor compression air-conditioning(VAC) uses CFCs as cooling liquids, EAC uses water. EAC technology is simple, functional, and has bothresidential and commercial applications in industrialized and developing countries. EAC can providesuperior cooling and ventilation while consuming less energy (and hence contributing less to green-house gas emissions) than VAC. EAC works best in hot, dry climates, but it can be used in more humidclimates as well.

This paper elucidates some of the technical characteristics and fields of application for EAC and out-lines the climatic conditions under which EAC can be most effectively employed. The document beginswith a general outline of the applications and limitations of EAC and explains the differences between"direct" and "indirect" EAC. Chapter 2 discusses the applicability of EAC in different climates and ex-plains the use of wet-bulb temperature as a useful tool for predicting the applicability of EAC. Chapters 3and 4 discuss the economics of EAC versus VAC in terms of energy consumption, required investments,and life-cycle costs. Production costs, the paper points out, are low enough so that EACs can be manufac-tured relatively easily in the developing world, as is now being done in South Asia and the Middle East.

Chapters 5 and 6 review the market for EACs and try to show how EAC can increase individuals'"feeling of comfort."

Chapter 7 explains the basic technology of EAC. The difference between direct and indirect coolers iselaborated on through the use of a psychrometric chart. The hardware components of the EAC are ex-plained: pads, motor, pump, and fan. Chapter 8 lists the equipment available on the market. It also pointsout that the capacity of the cooler and the size of the room to be cooled are key elements in selection of anEAC. A simple example is given to aid in sizing. Like any sort of mechanical equipment, EACs need to bemaintained regularly to perform well and last longer. Maintenance requirements for each component arediscussed in chapter 9. EACs require little energy, and because the presence of strong sunshine coincideswith the need for cooling, a link with solar energy appears to be attractive.

In chapter 10 the usefulness of solar EAC and the present market situation are outlined. EAC is anattractive cooling solution, for industrial as well as for less developed countries too. The requirements forthe introduction of a relatively new technology like EAC are discussed in Chapter 11. In Chapter 12 theusefulness of EAC for commercial applications is outlined. Commercial kitchens, laundry and dry clean-ing and industrial applications are three areas where EAC could be useful.

xi

Abbreviations, Symbols, and Glossary

Design temperatures: outdoor temperatures at a fixed percentage more temperate than worst-case fig-ures, which are a standard air-conditioning system design parameter.

Enthalpy: total heat content of air-water vapor atmospheric gas. Not altered by adiabatic cooling.

Evaporative air-conditioning: lowering of dry-bulb temperature as air passes over water. Two methodsusing evaporating water to cool air: (1) direct, which is adiabatic and humidifies the air; and (2) indirect,which is nonadiabatic and cools the air being treated.

Indirect evaporative air-conditioner. a heat and mass transfer device used to sensibly cool a primaryairstream, without addition of moisture, by means of an evaporatively cooled secondary airstream. Sincethe secondary air provides wet-bulb depression, it represents a heat sink to the primary air.

Latent heat load: heat carried by water vapor in air; varies with humidity. Wet-bulb temperature is anindex to latent heat.

Saturation (cooling) effectiveness: the primary air dry-bulb temperature reduction divided by the pri-mary air entering dry-bulb temperature less the entering secondary wet-bulb temperature.

Temperature, dry-bulb: the air temperature measured by a dry temperature sensor.

Temperature, wet-bulb: the temperature measured by a temperature sensor covered by a water-moist-ened wick and exposed to air in motion. When properly measured, it is a close approximation of thetemperature of adiabatic saturation.

xv

Introduction

Evaporative air-conditioning (EAC) technologies are being used increasingly in residential and com-mercial applications worldwide. EAC technologies-which rely on water as a coolant rather than onchemical refrigerants-are economical to produce and use and have important environmental ben-efits. This paper introduces the technical aspects of EAC, reviews EAC's scope of application, andsurveys the specific climatic conditions under which EAC can be used most effectively in industrial-ized and developing countries.

Under the right conditions and applicafions, EAC can provide excellent cooling and ventilation withminimal energy consumption using water as the working fluid and avoiding the use of ozone-destroyingchlorofluorocarbons (CFCs). Policymakers in particular should become better informed about EAC be-cause of the opportunities it affords to reduce the use and emission of CFCs and hydrofluorocarbons(HFCs), the reduction in CO2 emissions that come from the energy efficiency of the technology, and thepotential for mitigating problems of peak electricity demand during the hot season in many countries.The viability of using EAC will depend on the particular application and on the local climatic conditions.For example, for comfort cooling, EAC is most suited to dry regions, although technical improvementssuch as indirect/direct and desiccant-assisted systems widen the zone of applicability. On the other hand,some commercial applications of EAC are suitable even in humid climates.

In general, several sectors have significant reasons for considering employing EAC technologies:

* Utilities. Dissemination of EAC appliances can serve as a significant demand-side management(DSM) tool for utilities. Power savings of EAC technology versus VAC are on the order of 70percent for direct EAC and 50 percent for indirect EAC. This differential presents substantialpeak-saving opportunities for utilities that can promote the use of EAC within their service areas.

* Governments. For goverrnent agencies and planners, cost savings from reduced electrical con-sumption can be realized directly by incorporating EAC technology into buildings and other in-stallations. In addition, government planners should encourage use of EAC technologies as a rel-evant technology alternative to VAC that will save consumers money, reduce overall electricaldemand, reduce pollution emissions, and help meet international treaty obligations related to re-ducing pollutant emissions.

1

2 Evaporative Air-Conditioning: Applications for Environmentally Friendly Cooling

* Consumers. Consumers who use EAC at home can save money on cooling costs. The typical capi-tal, installation, and operation costs are significantly lower for EAC technologies than for VACtechnologies. Moreover, EAC technology is simple enough so that most homeowners can main-tain their own units.

* Private enterprise. The manufacture and sale of EAC appliances presents significant opportunitiesfor both small and large enterprises. It is particularly suited to manufacture even in relativelypoor developing countries because-unlike the comparatively complex technical requirementsfor production of chemical air-conditioners-EAC production requires only the basic infrastruc-ture and skills mix related to sheet metal, motor, pump, and fan fabrication. Hence, marketers ofEACs can underbid VAC prices while maintaining comparatively high profit margins. In theright climates, EACs can gain far more than a "niche" market: in some of the larger cities in thesouthwestern United States and northern Mexico, for example, 95 percent of the residential air-conditioning market is taken by EAC units, most of them manufactured locally.

Benefits of Evaporative Cooling

The following benefits of EAC can be cited:

* Significant local fabrication and employment* Substantial energy and cost savings* No chlorofluorocarbon (CFC) usage* Reduced peak demand* Reduced CO2 and power plant emissions* Improved indoor air quality* Life-cycle cost effectiveness* Easily integrated into built-up systems* Wide variety of packages available* Provide humidification when needed* Easy to use with direct digital control (DDC)* Greater regional energy independence

Opportunities and Limitations

EAC works best for comfort cooling where it is hot and dry. EACs are widely used in the Middle East,Australia, the Indian subcontinent, Eastern African, northern Mexico, and the southwestern United States.Residential EACs are known in India as desert coolers, and in such desert or dry-steppe climates EACs dogive "significant relief" during the hot months. "Significant relief" is considered to be provided when thefinal supply-air temperature leaving the EAC is about 20' to 250C (680 to 77°F). Even in a tropical savannaclimates such as in the northeast of Brazil, the Sahel region of Africa, the southwest Dominican Republic,EAC can be useful in some comfort cooling applications and also for many commercial applications suchas greenhouses and poultry houses.

A limiting factor for the application of EAC is the definition of comfort. A residential cooler bringingdown the temperature from 450 to 30°C (1130 to 860T) may still be appreciated even if it does not provide"significant" relief.

Environmental Benefits

EAC technologies represent significant enviromnental benefits related to reducing CFC/HCFC use andfor obviating C02 and other emissions, as well as for reducing peak electrical demand. For example, the

Introduction 3

4 million EAC units in operation in the United States provide an estimated annual energy savings equiva-lent to 12 million barrels of oil and an annual reduction of 5.4 billion pounds of CO2 emissions. They alsoavoid the need for 24 million pounds of refrigerant traditionally used in residential VAC systems. Similarenergy savings and environmental benefits are also made by commercial applications of evaporativecooling technologies in the United States and elsewhere. Through increasing use of EAC technologies,countries can save energy, reduce power plant emissions, obviate CFC usage, and improve indoor airquality. Basic air conditioning with water is a relatively simple process.

Direct Evaporative Air-Conditioning

Direct EAC is the simplest, the oldest, and the most widespread form of air-conditioning. This systemtypically uses a fan to draw hot outside air into a dwelling through a porous wetting medium. Heat isabsorbed by the water as it evaporates from the porous wetting medium, and the air thus leaves the EACat a lower temperature. The amount of cooling provided is determined by efficiency of the wetting me-dium, the fan, and the overall design and construction of the unit.

A critical component in EAC is the use of water. This may vary from a few liters per day in smallresidential coolers to perhaps a hundred liters or more in pad-and-fan EAC systems in greenhouses andcomplicated duct-systems in laundries and hotel kitchens.

Residential Coolers

A residential EAC typically consists of a cubical box of sheet metal or plastic containing large verticalfilter "pads," an electric-motor-driven fan, a water pump, a water distribution system, and a water sumpat the bottom. As Figure 1.1 and Figure 1.2 show, the fan draws in warm outside air through the wettedmedia, cooling the air. The water pump lifts the water from the sump through the distribution system tothe top of the pads from where it trickles down by gravity back to the water sump. The cooled air is thendelivered either directly through a grille into a single room or into a duct distribution system.

This is a "direct" EAC in which the cooled and saturated outside air flows into the room, displacingthe hot air. It is simple and cheap but is not sufficient for indoor comfort cooling once ambient wet-bulbtemperatures reach 21°C (69.8°F).

Figure 1.1. Typical Direct Evaporative Air-Conditioner

DistributionManifold

d. ConditionedInlet Wetted AirAir Media

RecirculationPump

Source: Authors.

4 Evaporative Air-Conditioning: Applicationsfor Environmentally Friendly Cooling

Figure 1.2. Roof-Mounted Downdraft Evaporative Air-Conditioning Unit, El Paso, Texas

7."~ ~ ~ ~ ~ ~~~~.

Source: R. Foster.

Indirect Evaporative Air-Conditioning

Indirect-direct EAC is a method established only over the past 15 years. It is not as widely used as directEAC, but it is gaining in popularity because it cools air more than direct EAC, and cools the air downfrom higher wet-bulb temperatures. hindirect EAC accomplishes these effects by building an additionalstep into the cooling process. That is , the incoming air is cooled first with a normal air-to--air heat ex-changer. This is the "indirect" stage because it does not add moisture to the supply air. Instead, only oneside of the heat exchanger is cooled with evaporating water as the supply air passes through the otherside, dropping in temperature as it does. Only then, as it passes through the direct EAC stage, is thesupply air moisturized. The final air leaving an indirect-direct EAC unit is generally 3.5C (6.30F) coolerthan what could be achieved with a direct EAC unit alone.

Because it cools the air first without moisturizing it, the indirect-direct process also allows the EACunit to provide more comfort in slightly more humid areas. Commonly these units achieve 65 percentindirect stage efficiency (performnance factor), which allows an ambient wet-bulb temperature of up to250C to provide acceptable room temperatures for real comfort.

Two-stage air-conditioners combinLing indirect and direct EAC are becoming popular in the UnitedStates and Australia, particularly in locations where slightly higher wet-bulb temperatures (i.e., conditionsof higher ambient humidity) do not permit sufficiently comfortable supply-air temperatures via direct EAC.On the downside, however, the two-stage units have higher construction and maintenance costs.

Desiccant-Assisted Evaporative Air-Conditioning

The use of dehumidifying chemicals (e.g., desiccants such as silica gel) further widens the scope for EAC.Desiccant technologies can widen the scope for comfort cooling to even the most humid regions. In suchsystems, the desiccant is used first to dehumidify the ventilation air to a desired state; then, EAC (eitherdirect or indirect or a combination thereof) is used to cool the air to the desired supply-air temperature.

Introduction 5

Commercial Evaporative Air-Conditioners

Commercial EAC applications are of several types. Commercial comfort cooling applications are usedfor offices, retail establishments, and so on, as determined by local climates and comfort preferences.

In other commercial applications, EAC may be used to moderate the effects of an additional internalheat source that does not depend (only) on the climate or the time of the year. For example, temperaturesmay rise inside warehouses or buildings because of the operation of ovens, machines, or the presence oflivestock. These heat sources sometimes exacerbate already high ambient temperatures. Although thecooling requirements differ as a matter of degree, so to say, cooling of buildings affected by both internaland external sources of heat does require a somewhat different approach from residential cooling tomoderate high outside ambient temperatures. For one thing, such commercial EAC systems may wellneed to be designed for operation the year round rather than just in a "hot season." A commercial kitchenor bakery, for example, might need cooling year-round. Moreover, the internal cooling requirements maybe quite localized within the building (e.g., spot-cooling in a manufacturing plant).

Another difference between commercial and comfort cooling with EAC is that EAC in some com-mercial applications is the only practical alternative; that is, where VAC technologies cannot function orcompete effectively because of high operating costs. The most salient example here is the cooling towersin a power plant, but on a smaller scale, EAC is the only real alternative in agricultural applications suchas greenhouses, where VAC is both inappropriate and far too costly

Common commercial applications for EAC include the following:

* Commercial kitchens• Hotels and restaurants- Hospitals• Other institutions* Laundry and dry cleaning* Industrial applications- Agricultural applications

- Poultry sheds- Greenhouses

* Schools and offices* Transit buses (Figure 1.3)* Industrial applications

- Warehouses- Spot cooling- Factories

Comparing Vapor-Compression and Evaporative Air-Conditioning

Table 1.1 compares the basic characteristics of VAC with those of EAC.

Outlook

Worldwide, the potential for EAC is much greater than is currently realized. Investment, operation, andreplacement costs can be lowered significantly by foregoing or replacing VAC technologies and usingEAC. The potential applications are manifold: from buildings and homes to buses and kitchens. In somedeveloping regions of the world where air-conditioning has scarcely arrived, EAC could bring comfort,as VAC may not be affordable by many because of its high investment and operating costs. Even wherethe conventional electric grid service is available, EAC may be a viable and economically attractive op-tion, particularly in conjunction with the use of solar photovoltaic (PV) modules.


Table 1.1. Vapor-Compression versus Evaporative Air-Conditioning

Basic characteristics Vapor compression AC Evaporative AC

Coolant CFCs/HFCs WaterProduction residential coolers Small and large scale Small and large scaleSensitivity to humidity for Applicable in all climate types Applicable in dry hot climates

comfort cooling applications for comfort coolingVentilation (indoor air quality) 20% outside air 100% outside airEnergy use in a typical residential 1,000 kWh/yr 350 kWh/yr

air conditioner for a 100 m3 room.Investment for a residential cooler Developed country Developed country

US$1,000-1,600 US$200-700Less developed country Less developed country

US$600-1,400 US$60-300Maintenance Change filters every 2 years Annual pad change for aspen

sump coat every 2 yearsAnnual accumulated costs In USA: US$500 In USA: US$170

including power, maintenance, In India: US$500 In India: US$37depreciation

Source: Authors.

Some options expanding and realizing the benefits of EAC are noted below:

Low energy use/solar. Small EAC units using solar photovoltaics (PV) are available in several com-mercial and prototype models. Manufacture and dissemination could be done through commer-cial channels providing cost-efficient cooling in grid-and non-grid settings.I Transfer of technology. EAC technologies are a fertile field for South-South transfer of technology,in particular with regard to small residential coolers and some agricultural applications..Support possibilities. EAC has substantial applicability as a demand-side management tool, in gov-ernment offices and schools. Technical assistance to developing countries, pilot programs, anddemonstrations all may provide further opportunities for EAC.

Introduction 7

Figure 1.3. Direct Evaporative Air-Conditionerfor Transport Use

Note he EAC unit(onthe forklift at right) wasbut by imatran andisbeinginstalledontoatytransitbusinDenverColorado.More than 400 buses in the United States and more than 1,200 in Australia use evaporative air-conditioning.Source: R. Foster.

Opportunities and Constraints

Climatological Factors

Unlike vapor-compression air-conditioning, which can work under virtually any climatic conditions,evaporative air-conditioning varies in applicability and efficiency with the relative humidity of the out-side air: that is, the drier the air, the more suitable EAC is and the better it cools. The general climaticparameters for applying EAC for comfort cooling can be superimposed on the world map in terms ofthree types of climatic zones that are, respectively, highly, moderately, and marginally suitable for EAC(Annex 2 contains maps showing these zones of applicability of EAC for each continent). The climatetypes are listed in Table 2.1, and for each type the effectiveness of EAC is indicated. This effectiveness israther constant for desert climates, but for both the steppe and savanna climates, a generalization aboutapplicability masks what may be significant month-to-month variations in the actual comfort derivedfrom EAC. It should be emphasized, moreover, that this sort of zoning provides only a rough indicationof suitability; each zone may contain areas that are better or worse suited for EAC than their assignmentto the zone would suggest. Moreover, some specialized EAC applications (e.g., in greenhouses or poultryhouses) are effective and commonly used in even the most humid of climates outside of these zones.

EAC is already popular in the desert climate zones such as the arid southwestern United States,Mexico, Australia, Iran, Iraq, Jordan, Libya, Spain, Sudan, Egypt, India, Pakistan, and South Africa. These

Table 2.1. Effectiveness of Evaporative Cooling by Climate Type

Climate type General effectiveness of EAC

Desert Real comfort during the whole cooling season (e.g., offices, homes, libraries, restaurants)Steppe Real comfort during the dry period of the hot season and moderate relief cooling during

more humid periodsSavanna Only can provide relief cooling during the hot season (e.g., warehouses, greenhouses,

poultry houses).

Source: Authors.

9


Box 2.1. Relative Humidity and Wet-Bulb Temperature

Apart from using the rough measure of climate zones or the level of humidity, one can predict the effectiveness of EAC for aparticular location fairly accurately using the locally prevailing wet-bulb temperatures (WB). Table 2.2 shows how these aremeasured. In brief, by adding about 5-C (9°F) to the WB, one knows the effective room temperature that can be reached withEAC. Because the WB varies over seasons and during the course of the day, it does not suffice to use average WB. Rather, oneshould consider the WB at the time when cooling is most important-for example, around noon.

areas have in common high summer temperatures coinciding with low humidity-that is, high ambienttemperatures combined with low wet-bulb temperatures. This combination means that EACs can bevery efficient and can provide real indoor comfort (see Table 2.2 and Box 2.1 for a range of benefits). Atotal of about 20 million EAC units are presently in use worldwide.

EAC is largely unknown, however, in many areas with steppe or savanna climates, even though itcould constitute a real alternative to VAC.

Comfort Issues

"Human comfort" depends on a range of factors ranging from temperature, humidity, and air movementto clothing and culture. What is comfortable for one person in one society may be entirely uncomfortablefor another. Someone who has long lived without VAC may find an artificially air-conditioned environ-ment uncomfortable, whereas people who take VAC for granted in their homes and workplaces mayavoid being outside during hot weather all together.

Standards

Comfort zones are often shown on standard psychrometric charts and have been developed to indicateregions where a person is "comfortable." In the United States, the American Society of Heating, Refriger-ating and Air-conditioning Engineers (ASHRAE) has developed comfort zones based on psychrometriccharts. However, these standard types of comfort charts have more limited relevance related to evapora-tive air-conditioning. First, standard comfort zones are based on air velocities typical of vapor-compres-sion air-conditioning systems, not the higher air velocities used with evaporative air-conditioners. Sec-ond, the traditional comfort zones used today (unlike those of the past) have horizontal, constant humid-ity-ratio (constant dew point) lines supposedly aimed to minimize respiratory diseases, mold growth,and similar problems. Relative humidity boundary lines are just as effective (and were previously used)and would distort comfort analysis less. Tests have shown that human comfort is a continuum, not con-fined between dewpoint lines. Consequently, the standard comfort zones commonly used face shortcom-ings relative to EAC.

Table 2.2. Relation between Wet-Bulb Temperatures and Effectiveness of Evaporative Air-Conditioning

Wet-bulb Typical supply air temps

temperature Type of EAC Unit (Dry-bulb) Cooling effectiveness

15-210C Direct 17-230C Real comfort21-230C Direct 23-250C Moderate relief

Indirect / direct 22-230C Real comfort23-270C Direct 25-300C Some relief

Indirect / direct 23-260C Moderate relief

Source: ECI.

Opportunities and Constraints 11

The Modified Comfort Standard for Evaporative Air-Conditioning

The effect of a given air stream on a person can be determined by an effective temperature chart, as iscommonly used when calculating wind chill. By increasing the velocity of movement, air feels cooler. Forevaporative air-conditioning, it is more reliable to consider a comfort zone bounded by relative humidityand extended to take into account the cooling effect of increased airflow, as shown in Figure 2.1.

Figure 2.1. Modified Evaporative Air-Conditioning Comfort Zone Taking into Account Increased AirflowCompared with ASHRAE Comfort Zone Based on Vapor Compression Air-Conditioning

23.9

Wet-BulbTemperature (°C) 18.3 90_L_g

Modified Comlbrt Zone

< 2i AtArddt ioning 70

7.2 12.7 18.3 23.9 29.4 35.0 40.6Dry-Bulb Temperature (0C)

Source: ECI.

Actual Comfort

The actual comfort derived from EAC for a given dry and wet-bulb temperature depends on the follow-ing factors:

* Saturation effectiveness of the evaporative air-conditioner. Only if the saturation effectiveness is 100percent can the temperature of the air leaving the air-conditioner be equivalent to the wet-bulbtemperature. This depends on the condition and quality of the medium, heat losses from the mo-tor, fan, and pump, and heat absorption through exposure of the air-conditioner cabinet to directsolar gain. Typical saturation efficiencies are between 60 and 90 percent for commercially availablemedia.

* Heat absorption of the space to be cooled. This depends on exposure of walls and roof to solar gain,shading, number, size, and location of windows and construction materials.

* Heat generation in the space. Number of people present in the room, their activity and the presenceof heat generating equipment such as copy machines, stoves, television, and computers.

* Sizing of the EAC unit.* Proper installation and airflows. Cooled air should be properly divided and directed so as to most

effectively "wash" the space and occupants to be cooled.* Activity of the occupants. Sedentary people require less cooling than physically active persons.

EAC may only be the only realistic way to provide a high level of comfort for every day of the year inmany desert climates. In some locations, EAC maybe acceptable for users willing to experience less thanfull comfort from the EAC for a few hours on the hottest days of the year because the slight discomfortdoes not outweigh the extra costs associated with VAC.


Expected Performance of Evaporative Air-Conditioning

The expected performance for both direct and indirect/direct EAC units commonly found in the marketfor selected locations worldwide is given in Table 2.3.

Table 2.3. Evaporative Air-Conditioning Perfornance in Selected Locations at 1 Percent Cooling DesignConditions

1% design conditions Direct supply Indirect/DirectLocation DB/WBa Air DBb Supply Air DBC

Asia/PacificAlice Springs, Australia 39.4/20.0 22.9 17.6Beijing, China 35.0/23.31 25.1 22.1Bangalore, India 35.5/23.3 25.2 22.2Christchurch, New Zealand 27.8/17.8 19.3 16.4Melbourne, Australia 34.4/20.6 22.6 18.9Kabul, Afghanistan 36.7/17.8' 20.6 15.6Singapore, Singapore 32.2/26.1 27.0 25.6

Middle EastRiyadh, Saudi Arabia 43.9/20.0 23.6 17.1Ankara, Turkey 36.1/18.3 21.0 16.1Jerusalem, Israel 33.3/17.2 19.6 15.0Tehran, Iran 38.3/16.7 19.9 13.7

AfricaCairo, Egypt 38.9/23.3la 25.6 22.1Casablanca, Morocco 34.4/21.1la 23.1 19.0

EuropeMadrid, Spain 35.6/20.0 22.3 18.2

South/Central AmericaCali, Colombia 28.9/20.0 21.3 19.0Santiago, Chile 32.2/19.4 21.4 17.9Caracas, Venezuela 28.9/20.6 21.8 19.7San Jose, Costa Rica 29.4/20.6 21.9 19.7

North AmericaLos Angeles, California, USA 35.6/20.0 22.3 18.2Denver, Colorado, USA 33.9/15.0 17.8 12.2Albuquerque, New Mexico, USA 35.6/16.1 18.1 13.3Las Vegas, Nevada, USA 42.2/18.9 22.4 16.1Dallas, Texas, USA 38.9/23.9 26.1 22.2Guadalajara, Mexico 33.9/18.9 21.1 17.2Mexico City, Mexico 28.9/15.6 17.6 13.9Ciudad Juarez, Mexico 37.8/17.8' 20.8 15.2

a. Temperatures in °C, 1% Dry-bulb/Mean Coincident Wet-bulb design conditions (ASHRAE).1. 1% design dry bulb condition and 5% design wet-bulb condition (U.S. Army).la. (ASHRAE).

b. Direct saturation effectiveness of 85% is assumed; dry-bulb supply temperature °C.c. All cases assume an overaU performance factor of 65% for the indirect process and asaturation effectiveness of 85% for the

direct process; dry-bulb supply temperature 'C.Source: ECI.

Opportunities and Constraints 13

Power Supply

The power requirements for EAC units can range from 100W for the smallest units to more than 1,000Wfor the larger packaged sizes. Because a packaged EAC unit has a low-mass fan and a centrifugal waterpump, it creates little demand for extra current during start-up. This means that if the unit requires acurrent of 1 amp for operation, a power supply of 1 amp is also sufficient for starting. In contrast, a VACof, say, 1,200W and 5 amps would require a starting current of at least 10 amps.

In developing countries where power demand often exceeds the supply, voltage drops are not un-common. This is detrimental to VAC units because the compressor motor has to supply a constant torqueand may draw too much current and burn its windings. EAC units on the other hand are much moretolerant of voltage fluctuations because both the fan and the centrifugal pump draw less current at lowervoltage and thus simply run at a lower speed without overheating.

Water Supply

The water consumption of most packaged EAC units varies from 5 to more than 100 liters per day dependingon cooler size, ambient temperature, relative humidity, and operating hours. The units can be directly con-nected to the main water line, controlling the water feed through a float valve, or they can be manually filledfor smaller indoor units. Access to a water supply is a prerequisite for EAC. The units with automatic waterfeed can make do with a relatively small reservoir, but the manually filled units use a larger reservoir capacitycommensurate with the water consumption so as not to require refilling more than once or twice a day.

Advantages of Evaporative Versus Vapor-Compression Air-Conditioning

EAC has several significant benefits over VAC (Table 2.4 summarizes the comparative benefits). For onething, EAC consumes significantly less energy than VAC. The only power-consuming components of adirect evaporative cooler are fans and small water pumps; in contrast, VACs and heat pumps are morecomplex, having more fans and a compressor (see Figure 2.2 for a summary of use by VACs). Peopleliving in dry regions that require cooling thus can realize large energy (and cost) savings by using EACinstead of VAC systems. As noted, the energy savings of EACs vary with humidity levels and tempera-tures. Direct systems in low humidity regions typically yield energy savings of 60 to 80 percent over VACsystems. Indirect/direct systems yield 40 to 50 percent energy savings in moderate humidity zones (Fig-ure 2.3). Indirect systems with vapor-compression second stages can provide adequate comfort coolingin high-humidity zones with savings of up to 25 percent.

Table 2.4. Benefits of Evaporative Air-Conditioning Versus Vapor Compression Air-Conditioning

Item EAC VAC

Power consumption 50 to 70% Lower than AC HighIndoor air quality Much better using 100% outside air Poor with 20% outside airRefrigerants Water CFCs, HFCs, HCFCsMaintenance Annual pad change for aspen, Bi-annual filter change

five year pad change for celluloseFabrication Simple Moderately complicatedPollution emissions No CFC emissions CFC, HFC, HCFC emissions

lower power plant emissions high power plant emissionsWater consumption High (evaporation and Moderate (water needed at the

bleed-off) power plant)Local employment High for fabrication, distribution, Moderate for fabrication,

installation, and maintenance high for distribution, installation,and maintenance

Source: Authors.


Figure 2.2. Annual Energy Use Summary: Vapor Compression Air-Conditioning (SEER = 9.5for Phoenix,Arizona, USA)

12,000 -

s 10,000

E 8,000

2 6,000

>, 4,000NbO

2,000

0

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Month

Natural gas * Electricity

Source: ECI.

Figure 2.3. Annual Energy Use Summary: Indirect/Direct Evaporative Air-Conditioning (2,000 scfn,forPhoenix, Arizona, USA)

12,000

,_ 10,000

8,000

> 6,000

b 4,000

2,000

0

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Month

Natural gas * Electricity

Source: ECI.

3Economics

In general, evaporative air-conditioners are much less expensive to purchase and operate than vapor-compression air-conditioners. It must be noted, however, that these two cooling technologies must becompared with care because VAC can always provide full comfort (provided the unit is adequately sizedfor the load and the owner is willing to pay the electric bill), but EAC cooling depends on local climato-logical conditions. Thus it is only in settings where both EAC and VAC can provide comfort cooling thata true comparison can be made. Before delving into the economics of EAC and VAC, it is worth enumer-ating several elements that play a role in the economics of both types of cooling:

* Cost of the cooler* Cost of installation• Length of the cooling season* Cost of electricity* Cost of water* Interest rate.

Economics of Residential Coolers

Worldwide, the most widespread EAC applications are small- and medium-sized packaged residentialcoolers. More than 20 million residential units are installed around the globe. They are produced in dif-ferent ways. In India, small enterprises use a labor-intensive production process (1 million units a yearare manufactured by some 300 to 400 enterprises in New Delhi alone). These "desert coolers," made ofsheet metal, wood fiber pads, and a simple pump, find their way onto the market either as finishedproducts or as kits and are transported and installed all over India. The other fabrication techniques aremore sophisticated. For example indirect-direct EAC production in Australia and the United States usecoated sheet metal, plastics or fiberglass, efficient cellulose paper pads, computerized thermostats, andbleed-offs. These units are marketed with glossy brochures and exported to a number of countries. Pricesvary as much as production. In India, the smallest coolers are about US$35 and the largest US$150 ormore. In Australia and the United States, direct EAC outdoor units sell for US$300 to US$700, and simple

15


indoor units are available for US$40 and up; however, the largest and most expensive units sell for morethan US$1,200.

The investment cost for a direct-indirect system is roughly double that for a direct EAC unit (and infact approaches the level as VAC). However, the direct-indirect EAC's power consumption is only about25 percent higher than direct EAC on an annual basis, and the total cost of electricity and maintenance forindirect-direct EAC systems amounts to only about 50 percent of that of conventional VACs of compa-rable performance.

Investment Costs

Figure 3.1 compares typical total investment costs of EAC and VAC systems for different room sizes (20,60 and lOOm2 ) for the United States. In all cases EAC is the cheaper option.

Figure 3.1. Typical Investment Costsfor Evaporative Air-Conditioning in the United States

2,500 -

, 2,000-

- 1,500 _

E 1,000 ,

500-

20 EAC 20 AC 60 EAC 60 AC 100 EAC 100 AC

Room size in sq m for EAC and AC

ES Installation cost Cost cooler

Source: R. Foster.

It is striking that although the cost of EAC coolers in the United States is low, the cost of installationis relatively high, because of the labor involved in placing the cooler, connecting it to water and electricpower sources, and providing a drain for the flush water.

The same has been done for India in Figure 3.2. Here the difference between EAC and VAC is muchmore pronounced because EAC units are made by small wayside industries at very low cost, whereasVAC units are either imported or made by large, inefficient industries at much higher cost.

The cost of installation in India is low because labor is cheap. These typical investment costs for Indiaand the United States illustrate that the relative economic merits of EAC are more pronounced in devel-oping countries than in the industrialized world.

Life-Cycle Costs

The life-cycle and operational costs have also been analyzed for these two countries, as depicted in Fig-ures 3.3 and Figure 3.4.

Economics 17

Figure 3.2. Typical Investment Costs for Evaporative Air-Conditioning in India

1,000-

Cei- 800

600 -

i 400 -

200-

0

20 EAC 20 AC 60 EAC 60 AC 100 EAC 100AC


Installation cost Cost cooler

Source: R. Foster.

Figure 3.3. Typical Life-Cycle Costs: Evaporative Air-Conditioning versus Air-Conditioningfor the United

States

6,000 -

,5,000

m) 4,000

8 3,000

2,000

1,000

0



* Depreciation 2 Energy n Water

D Interest Maintenance

Source: R. Foster.


Figure 3.4. Typical Life-Cycle Costs: Evaporative Air-Conditioning versus Air-Conditioningfor India

6,000 - -_

rA 5,000-

4,000

8 3,000

2,000 -

1,000

0- , ,



* Depreciation E Energy n Water

D: Interest Maintenance

Source: R. Foster.

For the calculation of the operational costs it was assumed in all cases that the maintenance is done bya hired professional, which explains the rather high annual maintenance cost for EAC in the United States.In reality, however, many EAC owners do their own maintenance because it is easy and saves money. Indeveloping countries where labor is cheap, maintenance is generally done by professionals. In India, forexample, it is common for owners of EAC units to have a maintenance contract with an EAC dealer.

Market Situation

At least 20 million residential EAC units are in operation worldwide. Of these, some 8 to 10 million are inIndia, and more than 4 million are in the United States. Other significant markets also exist in Australia,South Africa, Pakistan, and Saudi Arabia. EAC also has significant market potential in many other areasof the world (e.g., in the Sahel); yet in most of these areas, EAC technology is unknown.

A significant reason why EAC units are not in operation in more areas around the world is that halfor more of the world's population lives in coastal regions, or within 100 kilometers of coasts, and theseareas are typically humid and hence generally not the most favorable sites for EAC units. In contrast, themost favorable climatic conditions for using EAC are in dry and hot desert regions, and these are com-paratively sparsely populated.

Population differences notwithstanding, sufficient populations live in dry and hot regions to consti-tute meaningful markets for EACs. In the United States, for example the current sales of direct EACs aremore than US$150 million per year. Moreover, the recent growth of the U.S. EAC market has been signifi-cant, with annual increases of 10 percent reported by manufacturers.

California, which traditionally has used VAC, represents one of the world's fastest-growing EACmarkets. The California Energy Commission (CEC), noting the 50 to 80 percent energy savings pos-sible with EAC (as opposed to VAC) technologies statewide, adopted energy credits for EAC as part ofthe Title 24 code compliance program in January 1993. Inclusion of EAC in the Title 24 program facili-tates significant prospective growth of the industry in California. The CEC is also promoting an EAC

Economics 19

commercialization program that seeks to accelerate adoption of EAC to maximize its energy saving,environmental, and economic development potentials.

Several California utilities are promoting EAC for commercial and residential applications as well.Pacific Gas and Electric (PG&E) offers rebates for commercial use of evaporative cooling equipment.Under the utility's customized program, hybrid and two-stage EACs can receive a US$200/kW reduc-tion as replacements for VAC technologies. PG&E also offers a line-item rebate for the installation ofcommercial evaporative cooling equipment at US$80 per ton displaced of VAC for new construction aspart of a "Retrofit Express" program.

Locally in California, the Sacramento Municipal Utility District (SMUD) has a new construction rebateprogram that provides rebates to EAC in the commercial sector based on calculated energy savings com-pared with conventional cooling. In late 1992 Southern California Edison began offering US$100 rebatesfor installation of residential EAC (direct and indirect-direct) in their service territory. The company haspromoted these rebates actively in desert locations, offering an incentive of US$125 for replacement ofresidential VAC units with EAC equipment. Southern California Edison also provides and maintains EACsat no cost to qualifying low-income residents in their service area. On the commercial front, the companyis interested in energy conservation in the retrofit market and offers rebates at US$75 per ton for directEAC and US$100 per ton for indirect-direct EAC for displaced tonnage of VAC (they use 1,250 cfm = 1 toncooling). About 30 to 50 commercial installations are taking advantage of this program each year.

The State of New Mexico is requiring the use of EAC (mainly indirect-direct systems) instead ofVAC systems in new public schools and additions. New Mexico places about 100 new EAC applica-tions per year in schools.

The Stratospheric Ozone Protection Division of the U.S. Environmental Protection Agency (EPA) hasincluded EAC as an acceptable technology in the EPA's Significant New Alternatives Policy (SNAP)rulings on alternative refrigerants and technologies. This should further encourage the adoption of EACtechnologies in the United States.

Greenpeace and other environmental organizations are advocating EAC as an environmentally re-sponsible technology worldwide. This type of interest from environmental organizations should alsofurther global market development.

The greatest market development problem facing the EAC industry currently is the lack of a normal-ized test standard for performance ratings. Saudi Arabia and Australia have some limited general teststandards. However, the American Society of Heating, Refrigerating and Air-Conditioning Engineers(ASHRAE) standards committees on EAC have submitted a proposed test standard for testing indirectevaporative air conditioning equipment adopted by ASHRAE in 1996. Similarly, a proposed ASHRAEtest standard for direct EAC units should be adopted in 1998. When these standards are adopted, theindustry worldwide will benefit from a proposed certification program for rating EACs based on theASHRAE test standards by the Evaporative Cooling Institute. This certification program will providedesign engineers worldwide with an independent performance-based test standard for rating EAC units.

The EAC market should continue to grow worldwide as interest from utilities and countries in-creases in applying the technology as an energy conservation tool. Given advances with indirect andhybrid systems that widen the climatic range of application, the potential market penetration of thistechnology is large. Indeed, when coupled with desiccant technologies, EAC could displace VAC tech-nologies in many applications in the coming century.

4Technology

Direct Evaporative Air-Conditioning

A residential evaporative air-conditioner consists of a cubical box with large, vertical filter-like "pads," asump at the bottom, an electric-motor-driven fan, a water pump, and a water distribution system (seeFigure 4.1). The fan draws in warm outside air through the wet pads, cooling the air. The water pumplifts the water from the sump through the distribution system on top of the pads from where it tricklesdown by gravity back to the sump. The cooled air is then delivered either directly through a grill into asingle room or into a duct system to cool more than one room.

This is a "direct" evaporative air-conditioner in which the cooled and humidified outside air flows tothe room and removes the heat. An efficient wetted pad can reduce the air temperature by as much as 95percent of the wet-bulb depression (ambient dry-bulb temperature less wet-bulb temperature), while aninefficient and poorly designed pad may only reduce this by 50 percent, or worse. A simplified processdiagram for direct evaporative air-conditioning is shown below. There is actually very little change inenergy state of the air (i.e. there is no sensible cooling) other than energy inputs from the fan and make-up water. Direct EAC is simple and cheap but it has the disadvantage that if the ambient wet-bulb tem-perature is higher than 21°C (69.8°F), the cooling effect is not sufficient for indoor comfort cooling.

The saturation effectiveness of a direct evaporative air-conditioner best describes the performance ofthe unit. Saturation effectiveness is defined as the difference between the entering and exit dry-bulb (DB)temperatures over the wet-bulb (WB) depression and can be defined as follows:

Saturation effectiveness = DBI - DB2

DB, -WB1

whereDB1 = Entering (typically ambient) dry-bulb temperatureDB2= Exiting dry-bulb temperatureWB1= Entering (typically ambient) wet-bulb temperature

21


Figure 4.1. Simplified Evaporative Air-Conditioning Process

Dry air Water Moist air

Latentenergy

35 0C e.. Latent.DB energy

:::. Heat neededto evaporatewater

DirectSensibl evaporative

heat ~~~cooler 210Cenergy D

Water ha

You feel 35°C Sensible and You feel 21°Clatent heat energy

Sensible heat in the air is used to evaporate water(transfered to latent energy in the moist air)

Source: Authors.

A psychrometric chart, which shows moist air properties, more clearly demonstrates the evaporativecooling process. The initial dry-bulb and wet-bulb temperatures are shown at the start of the process, andthe endpoint of the evaporative cooling process is found to the left at the end of the arrow along the lineof constant wet-bulb temperature. For example, taking 1 percent design conditions for Ciudad Juarez,Mexico, of 37.7°C (99.9°F) dry-bulb temperature at a mean coincident wet-bulb temperature of 17.7°C(63.9°F), and using evaporative media that has a saturation effectiveness of 85 percent, we find that theevaporative media will change the state of the airstream to a dry-bulb temperature (supply air) of 20.7TC(69.3°F). This process is shown in Figure 4.2 for Ciudad Juarez.

Figure 4.2. Psychrometric Processfor Direct Evaporative Cooling, Mexico

20.70CDB forS.E.=85%

a / / \ ~~~Direct Evaporative oa

/4/ / \ti~~Coling Process +;o0

Cd. Jukrez, Mexico i

37.7 DBJ17.7°C WB 2

Dry-Bulb Tempearture °C

Source: ECI.

Technology 23

Direct evaporative coolers do not recirculate air in applications. Instead, air is passed only once throughthe system and then exhausted. This leads to superior indoor air quality. Evaporative cooling media alsoact as a wetted filter that scrubs out many contaminants (see also Figure 1.1).

Pads

The pad-or medium, as it is often called-serves to bring the water and air into contact so that the aircan absorb moisture and lower the dry-bulb temperature (cooling effect). An ideal pad should have thefollowing characteristics:

* Minimum resistance to airflow* Maximum air-water contact for vaporization* Equal distribution of airflow resistance, air-water contact, and water flow* Resistance to chemical or biological degradation* Ability to self-clean airborne matter* Durability and consistent performance over life-cycle* Low cost.

In reality, all pads fall short of this ideal and thus require some trade-offs among advantages. Thereare at present three major types of pads: aspen (or other similar type) wood, rigid pads, and syntheticpads. Each has its own advantages and disadvantages.

Aspen Wood Pads. These pads are composed of thin shredded wood slivers, packed loosely to athickness of 3 to 5 cm. This material is spread equally over the pad-holder surface and held in place by aflexible steel or plastic grid. The thin wood strands absorb water and ensure good diffusion of the waterover the surface of the pad, which gives it sufficient cooling characteristics. This good cooling, combinedwith the very low cost (US075 per replacement pad) has made aspen wood the most popularly used padmaterial worldwide. Aspen pads have some serious deficiencies in performance and durability, however.First, because wood is an organic material, it degrades fairly quickly in humid conditions. In application,this means that the strands decrease in strength and sag under the weight of the water they have absorbed.T'he sagging means that some areas of the pad become more compact, blocking the airflow, while otherareas become more open, increasing airflow at the cost of reduced saturation efficiency. This combinationleads to reduced cooling. Moreover, dust, pollen, and other airborne organic or inorganic matter are trappedbetween the strands of the pad, increasing resistance to airflow and imparting unpleasant odors to thecooling air if the pad is not properly dried during daily use. Similarly, when the EAC is turned off and theremaining water in the pad evaporates, it leaves behind a deposit of minerals, called scale. This scale is notcompletely dissolved when the unit is restarted and it impairs the airflow and blocks the pad.

Depending on the intensity of usage, the level at which mineral concentrations are controlled (ad-equate bleed-off), and the outside air quality (quantity of dust in the air) aspen pads may be replacedonce a cooling season or sometimes after two cooling seasons. Even so, optimum performance of theEAC may only be achieved in the first weeks after installation of pads. A properly packed pad may startwith 70 percent saturation efficiency but may decline to 50 percent efficiency after only a few weeks,operating at that level or less until it is replaced.

Another problem with aspen wood pads is their sensitivity to installation technique. That is, the padsmust be installed so as to ensure that the woody material is spread in equal density across the pad's totalarea. If this is not done, the saturation efficiency will be reduced from the start. Because replacement ofpads is needed regularly and appears to be a relatively simple task, many EAC owners will do it-withvarying results in terms of efficiency-themselves.

Rigid Pads. Rigid pads became available in the early 1980's. They are made of a specially impreg-nated type of paper or glass fiber and typically use a honeycomb type structure. They are made of stripsof corrugated paper alternative with upward and downward slopes, cemented together where the corru-gations touch (Figures 4.3 and 4.4). This arrangement eliminates most of the problems associated withaspen wood because rigid pads have the following advantages:


Figure 4.3. Commonly Available Rigid Cellulose Pads Provide Superior Saturation and Cooling Comparedwith Ordinary Aspen Pads

Source: Munters Corporation.

Figure 4.4. Close-up of Rigid Cellulose Pad Made of Corrugated Paper

Source: Munters Corporation.

* Long and fairly constant service life between three and seven years, depending on maintenance* Largely self-cleaning (i.e., dust washes off)* No biological deterioration of the pad material* More consistent saturation efficiency of about 75 to 90 percent* Low pressure drop across the pad.

The disadvantage is that rigid media are more costly (about US$100 more on an EAC that would costUS$300 if using aspen wood pads). They are also bulkier, which makes them difficult to use in smallerunits. At present, about 25 percent of the EACs sold in the United States are fitted with rigid pads, a share

Technology 25

that is growing. In fact, some U.S. manufacturers expect that eventually most EACs will be fitted withrigid pads because of their performance advantages over aspen pads.

Other Pad Materials. In a bid to improve on aspen wood, some manufacturers are supplying padsmade of woven plastic. The plastic pads avoid many of the disadvantages of aspen wood but have thedisadvantage of poor cooling efficiency because of the poor wetting characteristics (low saturation effec-tiveness) of the plastic material. Other substances have been tried as pad materials such as woven ex-panded paper, fabrics, wood wool made of pine, fir, cottonwood, cedar, redwood, spruce, plain andetched glass fibers, copper, bronze and galvanized screening, but none of these are extensively used.

Country-Specific Pad Materials. In each country where evaporative air-conditioners are used or areintended to be used it may be advisable to look for an inexpensive and easily available indigenous padmaterial-such as Khus-khus grass in India-or a long-lasting alternative such as a rigid pad. The objec-tive, of course, is to avoid the need for continuous large-scale shipment of pad materials such as aspenwood from the United States or Australia or if corrugated paper from Europe.

Cabinet

The cabinet of the air-conditioner is usually made of hot dip galvanized steel, coated with baked on highquality paints (see Figure 4.5). Corrosion can be a problem with drip air-conditioners because most partscome into contact with highly oxygenated water and concentrated solutions of waterbome or airbornechemicals. To eliminate corrosion problems some manufacturers supply stainless steel air-conditionersand some others air-conditioners made entirely of polypropylene, polyurethane, or glass fiber. In Austra-lia at least one manufacturer brings an aluminum air-conditioner on the market. Stainless steel air-condi-tioners are expensive and very sensitive to electrolytic corrosion (one screw of the wrong material maycause corrosion of the whole air-conditioner) and glass fiber or plastic models are subject to deteriorationdue to ultraviolet radiation. If galvanized steel cabinets are cleaned and repainted inside after every sea-son, they should last 10 years or more.

Fan and Motor

Small air-conditioners (up to 55m3/min of washed air), serving only one or two rooms are often fittedwith an axial propeller type fan. These fans, with 2 to 4 blades, operating at 900 to 1,400 rpm are noisierthan centrifugal types but are about twice as efficient. For higher airflow resistance, as is usually the casefor larger air-conditioners delivering air to a duct system, centrifugal fans are more suitable. They arevery quiet in operation but the efficiency is only half of that of an axial fan.

Axial fans are usually fitted directly on the motor shaft but centrifugal fans are belt driven and geareddown to roughly 1/3 of the motor speed. In general it can be said that the larger the fan and the lower thespeed the more quiet it is.

The motors for most residential air-conditioners are two-speed, single-phase, shaded-pole and four-pole types in the range of 200 to 1000W. They should have a drip proof construction and a 50°C allowabletemperate rise, certified by some recognized authority. More advanced designs are beginning to incorpo-rate variable speed motors.

Recirculation Pump

The most popular pump is a small submerged centrifugal pump driven through a vertical shaft from anair-cooled motor mounted dry above the waterlevel in the sump. These pumps are inexpensively made(US$15 retail price) and may last no more than three to five seasons. They require no maintenance but canbe vulnerable to dry running. The capacity is generally not more than 20 1/min against a head of aboutlm. In many cases there is a small outlet besides the pump discharge for the purpose of continuously


Figure 4.5. Common Cabinetsfor Residential Coolers in India

Photo: R. Foster.

bleeding off some of the water circulated to prevent an excess concentration of minerals in the water. Tocombine this bleeding off with operation of the pump limits the loss of water during operation only.

Controls

Direct-drip air-conditioners can generally be run on two speeds, with or without the pump. Operatingthe air-conditioner without the pump can be desirable when the outside humidity is too high for effectivecooling but ventilation still provides some comfort. In the United States and Australia many EACs arenow also supplied with an indoor thermostatic control to stop the unit when it gets too cold and start itwhen it gets too hot.

The air outlet of either the air-conditioner or the duct is usually fitted with a bidirectional set oflouvers to control the direction of the airflow.

Indirect-Direct Evaporative Air-Conditioning

A two stage air-conditioner combining indirect and direct processes is gaining popularity in the UnitedStates in places where the higher wet-bulb temperatures (i.e., higher ambient humidity) does not permitsufficiently low indoor temperatures from a simple direct air-conditioner. In this system the outside air isprecooled in an indirect stage and then further cooled in a subsequent direct stage. The first stage coolsthe air without adding moisture and in the second stage moisture is added. The result is that the final airtemperature leaving the air-conditioner is generally 3.5 °C lower than what could be achieved with adirect air-conditioner only. This expands the application of evaporative air-conditioning considerably toareas with slightly higher wet-bulb temperatures. Commonly 65 percent indirect stage efficiency (perfor-mance factor) is reached which allows an ambient wet-bulb temperature of up to 25°C to provide lowenough room temperature for real comfort (see Figures 4.6 and 4.7 for pictures of direct and indirect-direct evapoative air-conditioning).

The investment cost is however roughly double that of a direct air-conditioner (nearly the same levelas for refrigerative air-conditioning) but the power consumption is only about 25% higher on an annualbasis than for direct air-conditioners. The total cost of electricity and maintenance for indirect/directsystems amounts to roughly 50 percent of that of vapor-compression for the same performance.

Technology 27

Figure 4.6. Cutaway of a Direct Evaporative Air-Conditioning

Key 1: galvanized and painted steel (or sometimew plastic) housing, 2: louvered pad frame for air-inlet, 3: blower wheel and shaft4: water distribution system (header), 4: motor with belt driven centrifugal fan, 5: thermally protected water pump with bleed-off,6: extra finish is good against rust, and 7: float valve, also overflow and bottom drain are located in the water sump.Source: ECI.

Figure 4.7. Plate-Type Indirect-Direct Evaporative Air-Conditioning

Conditioned Secondary Outside AirSupply Air Pad

uts Air

Secondary OutsideAir Exhaust

Source: ECI.


Many buildings in drier regions that use vapor-compression air-conditioning can replace it with indi-rect/direct evaporative air-conditioning systems to provide comfort cooling. Residences can also benefit inthese regions by employing indirect/direct evaporative cooling as well. One potential problem for retrofitsituations is that existing building or residential ducts may be inadequately sized for the increased airflowdelivery required by indirect/direct evaporative coolers over vapor-compression systems.

For indirect systems, typically a secondary (or scavenger) airstream is used in which the evaporativecooling takes place. One method of doing this is based on using coils with water that has been evapora-tively cooled. Water evaporatively cooled through a cooling tower is circulated through a heat exchanger.The supply air to the space is passed over the other side of the heat exchanger. If the evaporatively cooledwater is colder than the supply air passing over the heat exchanger fin, than the supply air will be cooledwithout the addition of moisture to the airstream. The heat removed from the airstream raises the tem-perature of the water which is returned to the evaporative cooling process to be cooled again throughevaporation of some of the water. Obviously, by adding the heated water to the evaporative cycle from anexternal source this is no longer an adiabatic process.

Another common method used employs air-to-air heat exchange, one side of which is wetted. Theevaporative cooling occurs on the wet-side and heat is transferred from the conditioned airstream on thedry-side. Figure 4.8 shows a typical type of indirect/direct evaporative air-conditioning system using aplate heat exchanger. The first stage (indirect) sensibly cools the air, which is then passed through thesecond stage (direct) which evaporatively cools the air.

Figure 4.8. Indirect-Direct Evaporative Air-Conditioners on a Public School Rooftop, Colorado Springs, USA

Source: Norsaire Systems, Inc.

Performance of indirect evaporative cooling is measured by the performance factor which is the ratioof the reduction of the dry-bulb temperature of the dry-side airstream to the initial difference betweendry-side dry-bulb and wet-side wet-bulb temperature. The performance factor is affected by equipmentsize and effectiveness, as well as overall air and water quantities. Industry ratings are normally based ona specific ratio between dry-side and wet-side air quantities.

Performance factor = DB, - DB2 (dry-side)

DB1 (dry-side) - WB1 (wet-side)

The indirect process is shown as a sensible cooling process on the psychrometric chart (the identicalprocess for vapor-compression refrigeration). This process follows a line along a constant humidity ratiosince no moisture is introduced in the indirect stage. Often a direct stage is introduced after the indirect

Technology 29

stage, and sometimes several indirect stages can be used to further enhance the sensible cooling effect.Some larger commercial units are designed to use the building exhaust air coupled with evaporativecooling on the heat exchanger to provide even better performance. Figure 4.9 shows an indirect/directevaporative cooling process for Ciudad Juarez, Mexico for 1 percent design conditions of 37.7°C(DB)/17.7°C(WB). Whereas when only a direct stage a supply air temperature of 20.7°C was possible, addingan indirect stage with a performance factor of 65 percent followed by an 85 percent effective direct stageyields a final supply air temperature of 15°C(DB), which is 5.7°C less than a direct stage alone.

Figure 4.9. Indirect-Direct Evaporative Air-Conditioning Process

// ~~~~~~~al

{ //

0< ~~~~~~~~~~~E

~~ ~ 151C DB for

/ IdDirect Process Pj~~~~~~~~~lndrc 4 , Process r

Cd. Juirez, Mexico .

37.7 DB/17.7°C WB E

Dry-Bulb Temperature 'C

Source: ECI.

Desiccant Cooling

Evaporative air-conditioning can be coupled with desiccant technologies to expand the range for comfortcooling applications. A desiccant assisted evaporative cooling system is used to dehumidify the ventila-tion air first with the desiccant to a desired state, and then to use evaporative cooling (either direct orindirect or a combination thereof) to cool the air to the desired supply temperature.

Processes developed use either liquid (e.g., trimethylene glycol) or solid (e.g., silica gel) desiccants.Desiccants do not have the environmental problems associated with CFCs. The desiccant must be reacti-vated with a low grade and inexpensive thermal heat source such as natural gas, solar, geothermal, orwaste heat. A desiccant combined with an evaporative air-conditioner provides sensible cooling that canmeet cooling comfort needs even in the most humid environments without use of CFCs. A typical desic-cant assisted evaporative cooling cycle is shown in figure 4.10. Thermal COPs of 2.0 or higher, with an EERof 35 or better for electric parasitic power (fans, pumps, wheel motors) are possible for desiccant-assistedevaporative air-conditioners. Desiccant-assisted evaporative air-conditioners have recently become com-mercially available in the last couple years, although no residential models exist yet. Size and costs ofdesiccant equipment are gradually decreasing, which should lead to general acceptance by the market-place over time, and greater use of evaporative cooling to more humid regions for comfort cooling.


Figure 4.10. Ventilation Cycle Desiccant Cooling System

Outside cooler ~~~~~~~~~~~~~Supply

Air dry air ~~~~~~~~~ooer~ Air

OUA E ~~~~~~~~~hot-dry airm

houtsidUe air cR°BdIEva?|Rtay moister

Exhau sHeat

RetuAir

Source. ECI.

5Choosing and Maintaining Equipment

Available Equipment

EAC units for residential cooling are available in different configurations, sizes, and ratings. Table 5.1gives an overview.

Cooler Selection

Portable Coolers. For cooling needs either inside a building or on the porch, spot cooling can be pro-vided by a portable or trolley mounted small capacity air-conditioner. If these air-conditioners are usedinside there should be sufficient ventilation to prevent recirculation of air through the air-conditionerotherwise humidity will build up and eventually nullify the cooling effect. Preferably the unit should beplaced just inside an open window so that it will mostly draw in outside air, and other windows shouldbe open to allow washed air to escape and not be recirculated. Such portable air-conditioners are some-times sold without proper instruction and by either expecting too much or operating units incorrectly,customers may be dissatisfied. It is often common for persons whose only prior experience is with vapor-compression air-conditioning to try and incorrectly operate evaporative air-conditioners similarly.

Table 5.1. Available Residential Evaporative Air-Conditioning Equipment

Type Space to be cooled Installation Capacities

Portable Single room Window 15-40 m3/minIn room 15-40 m3/min

Fixed Single room Window 20-100 m3/minTwo rooms Window 40-160 m3/min

Home (whole house) Rooftop or 80-300 m3/minThrough-the-wall

Source: Authors.

31


Window Units. If a whole room and possibly a second room needs to be cooled, a window EACunit is often used, blowing the cold air directly into the room without any ducting. Although calledwindow units, sometimes an aperture is made in the wall of the house and the air-conditioner is fittedoutside on brackets. For the same purpose an air-conditioner can be fitted on the roof and have a singlestraight vertical duct into the living room whence the cool air can be directed to another room by theopening and closing of doors and windows. Roof mounting is often preferred because it is generallyconsidered more attractive than wall mounting.

Home Coolers. For cooling more than two rooms with a single air-conditioner and to cool alternatenot adjoining rooms, a ducting may be required and is usually placed between the ceiling and the roof.Thus, it is logical to mount the air-conditioner on the roof.

A disadvantage of roof mounting is the more difficult access to the air-conditioners for maintenance.For roof mounting one should also try to avoid running water lines in the attic as to avoid potentialfreezing of the water lines in winter.

Sizing

Rough Sizing. The capacity of air-conditioners is given in m3/min air displacement. As a rule of thumb anair-conditioner size is chosen which provides an air change in the room between once and four times everyfour minutes, depending on prevailing wet-bulb temperatures (higher means more airchange required),saturation efficiency of the particular cooler (higher efficiency means reduced airchange requirement) andthe features of the building (more heat input means more airchange required). See Box 5.1 for an example.

Take for example a room with a volume of 46m3 with large window area, high sun exposure, littleshading, and poor insulation. The outside air wet-bulb temperature during the hottest time of the day is26'C. It is not possible to cool this room to full comfort because that would require a wet-bulb tempera-ture of less than 23TC, so only relief cooling can be achieved. The highly unfavorable building featuresrequire a maximum airchange and the unfavorable high wet-bulb temperature requires the same. Con-sequently the air-conditioner for this room should be sized for 1 airchange per minute or an air dis-placement of 46m3/min.

In a different situation where for the same room volume there would only be a single window, nodirect sunlight on the walls through shading and trees, good attic ventilation, and an outside wet-bulbtemperature 229C, full comfort can be had if the air-conditioner displaces the room air only once every 3minutes and should thus have a capacity of 12m3/min.

Box 5.1. A Simple Sizing Example

Building Size = 20 x 30 x 3 m = 1,800 m3 for 1% Design Conditions of 37'C (DB)/18°C (WB)This would imply an air change based on 18'C WB of every 4.25 to 2 minutes. A more conservative design would use an airchange every 2 minutes, while the air change every 4.25 minutes would probably be sufficient for most comfort applications.1,800 m3 /4.25 = 423 m3 /min

Recalling that the saturation effectiveness is defined as the difference between the entering and exiting dry-bulb (DB) tem-peratures over the wet-bulb (WB) depression, as given in the equation:Saturation Effectiveness = DB, - DB2

DB1 - WE3where,DB, = Entering (typically amnbient) dry-bulb temperatureDB2 = Exiting dry-bulb temperatureWBI = Entering (typically ambient) wet-bulb temperature

Assuming a unit with an 85% saturation effectiveness, the supply air temperature DB2 for this unit will be:DB2 = 37°C - (.85(37-18'C))

= 20.9'C

Choosing and Maintaining Equipment 33

Other cases are obviously in between those extremes. A room change of once per minute has beentaken as the maximum because higher values will cause unacceptable drafty conditions. The bottomvalue of one room change per four or five minutes is because with a lower value there would be insuf-ficient mixing of the air causing uneven cooling (i.e., cold and warm places).

Using the rough method for sizing inevitably results in some cases of overcooling (need to switch offthe unit earlier) and undercooling in which case (if possible) a higher capacity unit must be bought. Somemanufacturers provide easy to use paperboard slide rules to aid in these estimations. Following is arecommended air change rate for differing design wet-bulb conditions:

Direct Evaporative Air-Conditioning Recommended Air Change Rate for Design Wet-Bulb(WB) Conditions

For Comfort Cooling:

15.5°C WB = One air change every 5 to 2 minutes17°C WB = One air change every 4.5 to 2 minutes18°C WB = One air change every 4.25 to 2 minutes19°C WB = One air change every 4 to 2 minutes20°C WB = One air change every 3.75 to 2 minutes21°C WB = One air change every 3.5 to 2 minutes

For Relief Cooling

220C WB = One air change every 3.25 to 2 minutes23°C WB = One air change every 3 to 2 minutes24°C WB = One air change every 2.5 to 2 minutes

Note that these are general air change volumes used. It is not recommended to use less than one airchange every 5 minutes for most applications. An accurate method is to calculate the heat load of thestructure by the same engineering principles used for refrigerated cooling. With heat loads determined,the cooling system is designed to remove them. To do this the probable washed-air temperature deliverytemperature is computed from the outdoor wet-bulb depression and estimated air-conditioner saturat-ing efficiency. If for instance the outside DB is 35°C, the saturating efficiency is assumed to be 80% and theWB 22°C, than the DB of the washed air is 35-0.8(35-22)=23.6°C.

With a desired indoor design temperature of 27°C, there is a heat gain of 27-23.6=3.4°C. From Table5.2, it is shown that the heat gain falls within the recommended operating zone and that the useful sen-sible room cooling is then about 65 percent. Subsequently the volumetric flow of washed-air needed tomaintain 27°C indoor design temperature is calculated based on the previously established heat load i.e.amount of heat to be removed from the room per unit of time and the specific heat of the washed air.

For larger structures, building computer simulation models such as DOE2.1E are sometimes usedwhich contain algorithms for EAC for more precise sizing and an evaluation of overall system perfor-mance based on TMY or TRY climatological data.

Maintenance

As with any mechanical equipment, EAC units need to be maintained regularly if they are to performwell and last a long time. However the maintenance work is easy and the necessary spare parts andmaterials are usually readily available. This means that the owner can do the job and so avoids the cost ofcalling a professional. The majority of the owners in the USA do the maintenance themselves. In Indiathough, where labor is cheap, it is mostly done by professionals and often they have a maintenance


Table 5.2. Useful Cooling Chart: Percentage of Useful Coolingfor Direct Evaporative Air-ConditioningOutput

Washed air temperature gain in rooms(Room discharge temperature minus room entrance temperature), OC

Temperature gain ICair entering cooler 1.7 2.2 2.8 3.3 3.9 4.4 5.0 5.6 6.1 6.7 7.2 7.8 8.3 8.9(WB depression 'C) (%) (%) (%) (%) (%) (%) (%) (%) (%) (%) (%) t%) (%) (%)

6.7 31 42 52 63 73 84 94

7.8 27 54 63 71 80 89 98

8.9 23 31 39 47 55 62 70 78 86 94

10.0 21 28 34 42 49 56 63 69 76 84 90 97

11.1 19 25 31 37 44 50 56 62 69 75 81 88 94 100

12.2 17 23 28 34 40 45 51 57 62 68 74 80 85 91

13.3 16 21 26 31 36 42 47 52 57 63 68 73 78 83

14.4 14 19 24 29 34 38 43 48 53 58 63 67 72 77

15.6 13 18 22 27 31 36 40 45 49 54 58 63 67 71

16.7 13 17 21 25 29 33 37 4 46 50 54 58 62 67

17.8 12 16 20 23 27 31 35 39 43 47 51 55 59 62

18.9 11 15 18 22 26 29 33 37 40 44 48 51 55 59

20.0 10 14 17 21 24 28 31 35 38 42 45 49 52 56

21.1 13 17 20 23 26 30 33 36 40 43 46 49 53

22.2 13 16 19 22 25 29 31 34 38 41 44 47 50

23.3 12 15 18 21 24 27 30 33 36 39 42 45 48

Drafty zone Recommended operating zone Uneven cooling zone

Source: Adapted from Watt (1986).

contract. The regular maintenance consists of preparing the unit at the beginning of the cooling season byfitting new pads and lubricating the bearings. At the end of the season, the sump should be cleaned outby removing the scaling and repainting the inside.

The following paragraphs set out the maintenance requirements for each component and type ofproblem affecting EACs:

Maintenance of Pads

Pads typically require regular maintenance or replacement, the frequency depending on the materials,construction, and conditions of use of the unit.

* Replacing aspen wood pads. These generally need to be replaced every 6 months of usage depend-ing on factors such as dust in the air, adequate water flow, water hardness and adequate bleed-off. In very dusty conditions filters can be used as well. These filters can be deaned and pad lifeextended. If the water flow is not enough or not equally distributed, dry areas can occur on thepads, accelerating the deposit of scale which can cause localized clogging and increased air ve-locities in other pad areas, which may lead to water being carried over with air and reaching thefan and motor, causing corrosion.

* Regular cleaning of rigid pads. Rigid and some synthetic pads can be cleaned by soaking in a slightlyacid solution that effectively dissolves scale deposits. If this is done every few years, such pads

Choosing and Maintaining Equipment 35

can last 7 years or more. If they are not cleaned regularly they may need to be replaced after threeto five years, depending on water hardness and bleed-off rates.

* Using water bleed-off to control scale deposits. Substantial amounts of water are evaporated in EACunits and because the water contains minerals which are left behind during evaporation, the con-centration of minerals steadily increases. If only new (make-up) water was added, the mineralswould eventually increase to the point that they reached saturation and would begin to crystallizeand be deposited. To avoid this, a small portion of the water is drained from the air-conditionereither constantly or at intervals. The water that is added to the air-conditioner to make up for thewater evaporated is the sum of the evaporated water plus the drained-off water. Generally theamount of bleed-off is roughly equivalent to 2 to 5 percent of the total water flow, which keeps theconcentration of minerals at an acceptable level. It is difficult however to give rules of thumb herebecause the content of minerals in the tap water varies widely from place to place. In New Delhi,India, for example, where about four million units are operational during the summer months, noprovision is made for bleed-off, and reportedly a once-a-year cleaning of the sump and removal ofscale is deemed "sufficient." However, pad life clearly would be increased even in New Delhi withsome small amount of bleed-off.

* Scale control using chemical water treatment. Chemical treatment is not recommended for pads, as itmay shorten the life of the pads and may cause manufacturers to void pad warranties. In particu-lar chemical water treatment should not be used if the chemicals could get into the supply air-stream (e.g., in a direct evaporative air-conditioner). Ideally, scale control can be optimized withmiiimal water consumption. However, some type of scale-management system, preferably a bleed-off, is essential for better performance and lifetime of evaporative air-conditioners media.

Maintenance of Fan Motor and Pump

The motor sometimes has bearings that need lubricating once a year, or comes with prelubricated andsealed bearings that require no attention. The life of the motor is generally between 3 and 6 years, de-pending largely on whether spray water is carried from the pad or not. Because rigid pads are less likelyto clog, there is less chance of water carry over and motors last longer.

Pumps are typically small centrifugal recirculating pumps that have no maintenance requirements.The most commonly used pumps are cheaply mass produced and should last several seasons, however insome countries they don't last more than one season. Replacement pumps should be thermally protectedto prevent the pump from dry-running (which is a fire hazard if the pump dry runs, overheats, and catcheson fire).

Corrosion Prevention for Cabinets

The majority of the evaporative air-conditioners are still made of coated galvanized steel. Because of theextremely corrosive properties of both the air and the water inside these air-conditioners, if left unat-tended, they may become extremely corroded after several years. To prevent this from happening, a oncea year (end of season) clean up and inside repainting should be done. If maintained in this manner thecabinet of a well made air-conditioner can last 10 to 15 years. Plastic or glass fiber cabinets need noregular repainting but given the deterioration of these materials when exposed to UV radiation, theymay not last as long as well-maintained steel ones.

6Solar Evaporative Air-Conditioning

Because evaporative air-conditioners require relatively little energy, and because the presence of strongsunshine often coincides with the need for cooling, a link between EAC and solar energy appears attrac-tive (see Figures 6.1 and 6.2 for a schematic diagram and a picture). Only a few suppliers offer solar-powered air-conditioners, however, even in the southwestern United States, the heart of the EAC indus-try. Companies supplying these devices apparently aim for other markets, such as developing countrieswhere grid electricity is not yet common.

The Market

It is apparent from Table 6.1 that only a very few sources are suppliers of solar EAC. Moreover, inquir-

Figure 6.1. A Solar-Powered Evaporative Air-Conditioner

Solar (PV) panel array

Evaporating pad media

Air distribution baffleAmbient air in

Water storage withrecirculating pump

Axial fan t Supply air out

Source: ECI.

37


Table 6.1. Available Packaged Solar Evaporative Air-Conditioning Equipment

Required solar Approximate costSupplier Type Rated capacity capacity including PV modules

Jade Mountain Window 25 m3/mnin 60 Wp US$1,400Jade Mountain Home 75 m3/min 300 Wp US$4,500Solar Energie Technik Portable 10 m3/min 110 Wp US$2,500

Source: Authors.

ies of suppliers indicate that only a few units have been sold so far (probably only a few hundred,worldwide, to date). The attractiveness of solar EAC depends largely on the availability and cost ofelectric power. Because photovoltaic (PV) power may cost US$0.25/kWh or more, compared withUS$0.10/kWh for power from the grid, PVs are most likely to be cost effective where grid power doesnot yet reach. Nevertheless, solar evaporative air-conditioning is a proven technology that can be veryuseful and efficient in such circumstances.

Optimizing Evaporative Air-Conditioning Design for Solar Operation

Because of the high investment cost of solar panels (90 percent of the cost of solar EAC is the cost of thesolar array), it is important that the energy requirement of the air-conditioner be as low as possible.Ordinary evaporative air-conditioners are not really designed for minimizing energy need as electricpower from the grid is inexpensive. This means that for evaporative air-conditioners to be suitable forsolar operation, they should really be redesigned to minimize power consumption.

Important points will be the efficiency of the fan (axial rather than centrifugal), motor efficiency,reduced pad resistance (larger area) and a high-efficiency circulation pump. At present, it seems thatmanufacturers simply replace the AC motors with DC motors or add an inverter to make conventionalair-conditioners suitable for solar power.

Such measures will make the cooler more expensive but sharply reduce the investment in the solararray and thus the total system cost. Obvious areas for improving the energy efficiency of EAC for solarpower are presented in Table 6.2.

Table 6.2. Design Measures to Optimize Evaporative Air-Conditioningfor Solar Power

Average Possible Potential ComponentComponent efficiency improvement efficiency efficiency gain

Motor 50% Select optimal DC permanent 70% 40%magnet motor

Fan 25% Replace by axial type 50% 100%radial type

Pump 1% Drive from fan motor 4% 400%Pad n.a. Optimize medium and 25%

reduce air velocityOverall potential reduction

in power requirements: 60%

Source: Authors.

Solar Evaporative Air-Conditioning 39

Figure 6.2. Evaporative Cooler Coupled with Solar Power (System installed by a homeowner in Chaparral,New Mexico, USA)

Source: ECI.

7Introduction and Local Manufacture

in Developing Countries

Maintenance

Unlike conventional air-conditioners and fans, evaporative air-conditioners require simple but relativelyfrequent maintenance and replacement of parts. Some parts, such as the aspenwood pads, need to bereplaced after 6 to 12 months, depending on the local water quality. This means that EAC marketing mustbe accompanied by an after-sale service network and that where sales are just being established, thisafter-sale network will need to be set up as well.

Installation and Sizing

Another important difference between EAC as compared with fans and vapor-compression air-condi-tioners is that EAC requires some knowledge about airflow direction, distribution, and evacuation forthe cooling to be effective. In some cases (e.g., Tunisia, Bangladesh) EACs of the spot-cooling (trolley)type were introduced, but because of lack of proper instruction they were used in closed rooms as if theywere vapor-compression air-conditioners. Since EACs require outside air flow, the units did not functionproperly, causing general disillusionment and failure in the marketplace. The lesson is clearly that EACmust be introduced with adequate and honest information to the users, and replacement materials andtrained service personnel should be ensured.

Manufacturing Requirements

EAC is essentially a low technology and can be wholly or partially produced in developing countries,depending on the existing industrial base. In India and Pakistan, for example, large numbers of units arebeing produced entirely locally (see Figure 7.1).

41


Table 7.1. Work Involved in Manufacturing Evaporative Air-Conditioning

Component Type of work Done where

Cabinet Sheet metal working In houseLouvers Sheet metal working In houseGrill Sheet metal or wood In house or purchasedMotor Motor manufacturing Buy from local supplier or

import directlyFan Metal stamping, aluminum Buy from local supplier

casting or plastic molding or import directlyPad:Rigid pad Highly specialized Buy from local supplier

or import directlyWood wool or other locally Cottage industry Buy from local supplier

available pad material

Source: Authors.

Figure 7.1. Evaporative Air-Conditioners in Kamla Market, New Delhi, India

K. 1 ~~~~A-

~~~ , N-

Source;R. . F-

f -._ _ 3

Suc; >R _ .S Foser

Introduction and Local Manufacture in Developing Countries 43

Certain components are easier to make than others. Electric motors, fans, and water circulation pumpscan only be produced in countries with a reasonably large industrial base, such as India, Pakistan, andChina. Yet even where such items cannot yet be made locally, they can be imported, and their sourceshould not be of vital consequence to most manufacturers of coolers because they will be purchasingthem for assembly in any case. Table 7.1 gives an overview of the items that are needed for building andassembling EACs and who makes or supplies the components.

It follows from Table 7.1 that the production of coolers is essentially sheet metal working, while themechanical items are usually purchased. Such sheet-metal work can be done on a small scale and re-quires very little in the way of investments in machines, molds, or accommodation. In short, EACs are agood product for small-scale entrepreneurs as well as for larger industries.

Know-How

Although the production of EACs itself is rather straightforward, a need remains for a good design if thecooler is to work satisfactorily. A "good design" means that motor, fan, pump, and pad should be wellmatched to obtain good performance, energy efficiency, and cost effectiveness. This industry-specificknow-how often falls short of the mark in developing countries where EAC is already popular, and itmay be lacking altogether in countries where local production is yet to be initiated.

Local enterprises that wish to obtain EAC know-how have basically two options:

* Establish a joint venture with an EAC manufacturer in the West.* Secure training from independent experts.

8Commercial Evaporative Air-Conditioning

The principle of evaporative air-conditioning is used not only in residential coolers but also in numerouscommercial installations. Direct EAC is used in commercial and industrial applications such as schools,greenhouses, buses, laundries, warehouses, factories, kitchens, and poultry houses. Direct and indirectEACs are also used to provide comfort cooling in many buildings such as schools, libraries, and offices.

Commercial versus Residential Cooling

Many commercial cooling applications are quite different from comfort cooling. Comfort cooling en-hances the well-being of individuals living in homes, working in offices, and so on, in areas where ambi-ent temperatures are high. The use of EAC for comfort cooling thus depends partly on the type of climateand the time of the year and partly on the needs of people for "comfort."

In many commercial cooling applications a factor additional to the type of climate and the time ofyear may well be present. That is, the presence of an additional heat source in the form of machines,ovens, dryers, animals, and so on. In such applications, cooling systems often must be sized and de-signed to work for the whole year. For example, kitchens often need cooling even during winter. Anotherimportant aspect of commercial EAC, in certain places where a heat source can be cooled directly (e.g.,spot-cooling in a manufacturing plant), is the air stream.

Another difference between commercial cooling and comfort cooling with EAC is that in commer-cial applications EAC can play a significant role that VAC systems can do only with difficulty or greatexpense. The best example is that of cooling towers in power plants. Moreover, in some agriculturalapplications EAC is the only realistic alternative; in greenhouses, for example, VAC would be extremelyexpensive to operate. Similarly, in horticulture and floriculture, EAC is useful precisely because it addsmoisture to the air. Because it is an "air-washer," EAC may have distinctive advantages in other appli-cations as well. Although in some applications-such as in hotels, restaurants, commercial laundries,and kitchens-only the VAC options are typically considered. But managers of such facilities shouldcompare VAC and EAC systems and assess the potential of EAC properly before making decisions oninvestments. EAC's advantages of ventilation and direct cooling may make it the most appropriateand effective solution.

45


Commercial Kitchen Evaporative Air-Conditioning

Makeup air, or exhaust air replacement, is typically needed in food service facilities-by building and healthcodes, if for no other reason-and EAC can be used to good effect in meeting these requirements. Properkitchen ventilation in particular has safety implications and requires a well-designed makeup air system. Inconcert, EAC and makeup air systems can improve the comfort, safety, and efficiency of commercial kitch-ens while affording energy savings, improving worker morale, and providing customers better comfort.

Cooling Comfort

Heating/cooling rooftop makeup air units provide summertime cooling to commercial kitchens throughdirect evaporative air-conditioning. These systems are ideally suited to commercial kitchens becausethey provide 100 percent fresh air ventilation and cooling, requiring exhaust for proper application, ratherthan recirculation of air. With its large summer cooling potential of 15°C or more, this system can increaseemployee comfort substantially. In many areas of the world, direct evaporatively conditioned air can beintroduced through a makeup air unit into the kitchen at between 5 and 10°C below outdoor dry-bulbtemperatures or lower depending on ambient conditions.

Cost Savings

Although VAC in kitchens is relatively common, it is certainly not the most efficient approach to comfort,because most of the air introduced through the VAC system is immediately exhausted by the stove hoodbefore it can recirculate. Thus, constantly running fresh air through a VAC substantially increases theload on the unit and requires purchasing refrigerated air-conditioning capacity well beyond what wouldbe required for the same internal load with a recirculating system. In addition, a typical rooftop refriger-ated-heated makeup air unit would be oversized on the heat mode as well and would increase the initialcapital cost. By contrast, an EAC unit could supply kitchens with makeup air without water circulationthrough the pads when cooling was not needed.

Sizing

Engineers generally size the makeup air unit to match a predetermined amount of air being exhausted bythe hood ventilator selected. Proper selection of a makeup air unit of the correct size (the quantity of airthat can be delivered by a given unit at the necessary introduction temperature) is the key decision pa-rameter. Temperature rise and air delivery performance vary with different units. The amount of permis-sible temperature rise necessary in a given application is determined by the winter design conditions forthe area in question and by the desired indoor temperature level.

Laundry and Dry Cleaning

Evaporative air-conditioning in laundry and dry-cleaning operations cross a variety of ambient air-condi-tions. Evaporative air-conditioning systems perform important cooling and ventilating functions. Evapora-tive air-conditioning may provide features that give the laundry operator greater cost-effective versatilityin the interior environment as compared to vapor compression air-conditioning and ventilation alone.

Extreme Heat Conditions

The heat levels of laundry and dry-cleaning plants are high. ln addition to the solar gain and human heatload occurring in a typical (140 to 900 square meter) facility, the equipment used generates a large amountof heat. Heat levels can become unbearably high for finishing (ironing) personnel in particular. Workers

Commercial Evaporative Air-Conditioning 47

are exposed to heated areas from steam above 80°C. Every plant has a boiler to provide steam for finish-ing textiles. These units in larger plants are rated as high as 5.3 to 10.5 million KJ/hour (5 to 10 millionBTUh). Although boilers are walled off, at least part of their heat is added directly to the heat load of theplant. Other equipment that contributes to the heat environment includes washers and tumblers, and indry cleaning plants some of the solvent reclamation equipment.

EACs can introduce air approximating the ambient wet-bulb temperature for cooling. Some combi-nation of spot and area EACs can reduce heat stress conditions to acceptable levels. Where temperaturesare exceedingly high, such as at workstations near large boilers, shielding can be used in combinationwith spot cooling to reduce radiant heat. Properly directed evaporatively cooled air washing over hotsurfaces can reduce radiant heat as well. The climate will determine whether the heat load or the ventila-tion load will require the larger capability. In moderate climates, the ventilation load may be greater thanthe airflow required for cooling; the opposite may be true in hot climates.

Industrial Applications

Evaporative air-conditioners and packaged heat/cool ventilating makeup air units combine many fea-tures which make them applicable in diverse industrial applications. EAC systems can be the most eco-nomical approach to comfort, increased equipment efficiency, and code compliance under a variety ofconditions. The uses of EACs in heat treating, forging, casting, welding, milling, rolling finishing, clean-ing and assemblies is also due to safety and comfort concerns for employees and government regulationspertaining to employee welfare.

Direct EAC is often used to combat problems such as:

* Intense heat, as in many forging, foundry and casting areas.* Low humidity, as in computer and electronic control rooms.* Airborne contaminants, as in welding, plating and cleaning areas.

The hot, stagnant conditions present in many casting and furnace rooms may reach indoor dry-bulbtemperatures that exceed outdoor temperatures from 100 to 15'C, and may reach nearly 70°C in someextremely hot casting areas. Molten steel at 1,300'C, must be cast by workers. In many basic metal plantswhere casting, annealing, forging, baking, and drying occur, shutdowns and work slowdowns are typi-cal during summer months. In some factories work reductions and shift stoppages are required if tem-peratures climb too high. Some plants curtail operations or even close during the peak summer coolingperiods. The reasons may be union contracts, walk-outs under hot conditions, and so on. Governmentregulations vary in different countries, but many countries have legally enforceable occupational heat/stress standards. Even without government regulations, many industries attempt to relieve the problemof heat in their plants out of basic practicality. Using evaporative air-conditioning in the plant environ-ment can help prevent mandatory and spontaneous work reductions.

Spot or area cooling with EAC systems, combined with other heat-control methods such as radiantheat shielding, can effectively meet government heat/stress standards. EAC can increase summer-time productivity by as much as 40 to 60 percent in plant areas too large to air-condition with vapor-compression systems.

EAC is used in industries including aluminum production and fabrication; electronics assembly; powergeneration; shop work such as welding, plating and milling; metal fabrication and battery manufacturing.The benefits of cooling hot workers remain essentially the same in most applications: increases work effi-ciency, lengthened work seasons, lowered costs, code compliance and increases equipment efficiency.

Factory Air-Conditioning Design Considerations

Spot cooling is used in industrial areas where people are in close proximity to high-heat processes andcooling of the entire installation is either inefficient or extremely expensive. Spot cooling with EAC


provides two principal benefits: evaporatively cooled air and air movement. The effect of air motion,air temperature and humidity must be combined to derive an index to worker comfort (i.e., effectivetemperature). Spot cooling essentially isolates the worker from the immediate hot environment bydisplacing hot air with a stream of cooled air. Thus, the effect on the worker is determined by the outletair temperature and velocity. Calculations for spot cooling are based on the amount of air being deliv-ered, the heat rise and static pressure in the duct, and the size of the outlet. All of these variables willdetermine the amount of comfort or relief felt by the worker.

Ventilation Control

Makeup air systems, in addition to providing space cooling, help in ventilating high-fume areas and inreducing airborne contaminants in accordance with government standards. Makeup air is typically re-quired by regulation in the design of areas containing plating tanks and paint-spray booths, for example,and it is highly recommended in all areas with industrial exhaust. Makeup air is highly recommended in allareas requiring industrial exhaust. "Air starved" buildings may not be able to provide sufficient flow tooperate the hoods, spray booths, and appliances properly. Inadequate makeup air will cause drastic reduc-tions of efficiency that will affect propeller fans and natural drafts; in some instances the flow may bereversed. In addition, some contaminated areas require a large supply-air flow to the dilution of airbornecontaminants with or without associated exhaust-for example, areas using industrial solvents. When year-round air supply is needed, heating-cooling-ventilation makeup air systems or EACs are often specified.

Equipment Protection

To last and run efficiently over their design lifetime, many pieces of equipment require appropriatecooling. Again the use of EAC is a valid option, certainly when the use of vapor-compression cooling istoo expensive, humidity ratio is not the limiting factor, and ventilation alone is not enough. For ex-ample, considerable waste heat is generated in power generation equipment. Whether the power isgenerated by gas or steam turbines (run on fossil fuel, nuclear energy, or even solar power), the tem-peratures of the installations in which the turbines run must be kept under 41°C, which is the maximumoperating condition for the windings in common alternators. EAC may be used to keep room tempera-tures lower than 41°C allow generators to operate at overload outputs; the general rule is that approxi-mately 6 percent overload capacity is available for every 4.5°C below rated ambient temperature (usu-ally 41°C) achieved by cooling. Other types of equipment also operate more efficiently under coolerconditions. Electric motors, particularly high-horsepower units (200 HP and larger), can require directcooling of the windings for proper operation.

Agricultural Applications-Poultry

Indoor confinement of agricultural livestock is a growing trend worldwide because it yields higher qual-ity and improved productivity. The comfort and well-being of indoor livestock is also becoming of para-mount importance from an ethical point of view. Environmental control of livestock housing such aspoultry has become an increasingly critical technology in which EAC plays an important part.

One of the most commnon areas for applying EAC is in poultry houses. Of the farm buildings commonlyfound in the poultry business, evaporative air-conditioning improves conditions in four major types: thebroiler house, the hatchery, the laying house and the processing plant (see Figure 8.1 for an overview).

Better Growth Rates and Feed Conversion. Proper evaporative air-conditioning of broiler housesallows birds to achieve a weight gain of from 5 to 8 percent with a corresponding cut in the growth periodof 2 to 8 percent. Closely related to poultry growth rates is the factor of feed conversion.

Reduced Mortality Rates. Improved Hatch Rates, Increased Egg-Laying Rates and Egg Size. Hightemperatures-37°C and above-will kill poultry. EAC has been found to decrease poultry production


Figure 8.1. Typical Evaporative Air-Conditioning Applicationfor Poultry Houses

_ ~~~~Evaporative' T ~~~~Cooler Evaporative

F G b(7 Cooler,'

Source: ECI.

mortality rates by 35 percent or greater. The use of environmental control with EAC in the hatcheries hasbeen shown to improve hatch rates from 3 to 10 percent. A commercial egg-laying house, or egg ranch,depends in part on lay rate-the number of eggs laid per hen per day-for its profitability. AppropriateEAC systems have reportedly improved overall poultry egg-laying rates by as much as 15 percent in-creased overall quality, and boosted average egg size from 5 to 6 percent.

Improved Conditions for Workers. EAC in poultry houses improves the life and comfort of thebirds, as well as their overall productivity, but it also improves conditions for people working in thesehouses during the summertime heat. In addition, EAC provides ventilation and other benefits of particu-lar value in the poultry environment.

Greenhouses

Excessive summertime temperatures can reduce plant growth and, if high enough, can kill the plants.Temperatures above 29°C constitute a danger to the health and growth of many greenhouse plants, andsustained temperatures above 35°C are a serious threat to most types of plant life. EAC provides signifi-cantly lower indoor air temperatures that enhance plant viability, reduce mortality, improve plant sizeand increase weight.

Fan and Pad versus Evaporative Air-Conditioners

Evaporative air-conditioning is used in horticulture, floriculture and other high-productivity greenhouseagricultural systems, where the environmental conditions are critical for production. Basically two sys-tems, with different areas of application, are used. Fan and pad systems have one air inlet into the green-house, where the wetted medium is installed and ventilating equipment on the far wall of the building(see Figure 8.2). This approach causes a significant temperature gradient from the inlet side to the venti-lation side of the greenhouse because of the heat the air picks up as it travels the length of the greenhouse.

The other system uses external packaged coolers that maintain a positive pressure in the greenhouse.They are installed outside the greenhouse and blow humidified air through many polyethylene ductsinto the greenhouse (see Figure 8.3). The system maintains a constant overpressure inside the green-house, with exhaust air leaving the greenhouse at an exit louver. This approach supplies an even tem-perature gradient in the greenhouse, since the cooled supply air is delivered through the poly ductsthroughout the greenhouse before it picks up additional heat from the greenhouse. This approach createsa more uniform growing environment inside the greenhouse than does the fan and pad system.


Figure 8.2. Evaporative Cooling Pad Section of Rigid Cellulose Pads

11 ~- I-=-

Pads shown are along west wall of New Mexico State University grower greenhouse maintained by SWTDI in Las Cruces, NewMexico.Source; ECIL

Additional Crops

EAC can allow an extra growing season for greenhouse crops where summers normally would be toohot, thus increasing annual yields. Where shading is normally required to lower indoor temperaturesduring summer, it may be reduced or eliminated, depending on the crop, when EAC is used. This can

Figure 8.3. External Evaporative Air-Conditioners on a Research Greenhouse, New Mexico State University,Las Cruces, New Mexico

l _ _11 k .f.

-.

Source: ECI.


further increase plant yields. Increasing the velocity of air movement permits shade requiring plants tobe grown at higher than recommended light levels without reducing plant quality.

Uniformity among individual plants in a crop is enhanced by EAC. Variation among individual plantsin a crop is reduced by lower summer temperatures. This effect benefits commercial growers attempting toincrease control over the produce they sell. Both size and the date of harvesting of a crop are more uniform.The former is a benefit in business planning, simplifying pricing, while the latter affords the grower morecontrol over the seasonality of the crop, allowing better matching of target dates and deadlines.

Within limits, high relative humidity (RH) is good for plants; however, RH decreases as temperaturerises. EAC provides two benefits to plants under these conditions. The cooling reduces heat stress on aplant, thereby reducing the need for its own "evaporative air-conditioning"-that is, transpiration by itsleaves. The increased RH means greater saturation of the air surrounding the leaf, inhibiting the vapor-ization of water from the leaf itself.

Because of the critical nature of temperature in the maintenance of healthy plants, cooling systems thatfail to maintain conditions necessary to the health and development threaten the success of a greenhouse.

Fine Tuning Greenhouse Environments with Evaporative Air-Conditioning

In warm climates, EAC is useful to ensure that heat-sensitive plants are maintained within safe limits.Cooling may be necessary for plant survival. In milder climates, however, EAC may be used for specialgreenhouse applications. If a greenhouse that is oriented to low-temperature-preferring plants is desired,EAC can be an essential component, no matter the outdoor climate. To maintain such planned environ-ments, EACs can be operated at night or on cool days. For example, air that is 27°C and 30 percent RH canbe cooled to 19°C through EAC. Even at night-when cool-house plants require 7° to 13°C tempera-tures-an EAC either with or without the pump operating can help maintain proper conditions.

Annex 1

Introduction to Evaporative Cooling

Let us first look at the principle of evaporative air- In Figures A1.2 and A1.3, the effect of EAC isconditioning, which can be explained by way of psy- explained. In the cases shown the DB temperaturechrometric charts. These charts present the moisture is 40°C, and the air is not saturated with water,ratio versus the temperature, as it is registered by a RH is only some 15 percent. One can add water,normal thermometer (the dry-bulb temperature; and the temperature will drop until it reaches theDB), in a certain situation. The lines in Figure Al.1 saturation line. What happens is that the heat inconnect the points with the same relative humidity the air is "absorbed" by the evaporating water. TheRH. At a given temperature air can contain an sensible heat is transformed into latent heat. The ef-amount of water vapor. When this amount of wa- fect is that the temperature is lowered to 20°C inter vapor reaches its maximum (100 percent RH), this case. The difference between 400 and 20° isthe dew point is reached and the water starts to con- called the wet-bulb depression. The wet-bulb tem-dense. The dew points are connected by the satura- perature, or WB, is registered by a normal ther-tion line. The higher the temperature in a certain mometer that is wrapped in a wet sock or othervolume, the more water it can contain in its gas- piece of textile. The constantly evaporating watereous stage. In a desert this effect can explain why from the sock causes a drop of the temperature.in the morning, when the temperature is still low, The WB temperature is always lower than the DBone sometirnes sees drops of water on the scarce temperature, except when the RH is 100 percent-vegetation. In the afternoon, when the temperature that is, when the air contains the maximum amountreaches its maximum, the air feels very dry and hot. of water it can hold at a given temperature. TheT1he same amount of water is in the air in terms of WB depression line connects the points with thekilograms of water per kilogram of dry air, but the same enthalpy-the same amount of energy-thefeeling it gives is completely different. sum of latent and sensible heat.

Figure Al.l. Psychrometric Chart and Saturation Figure A1.2. Complete Psychrometric ChartLine

Humidity Ratio Humidity Ratiokg water/kg air kg water/kg air

J / .030 3 80% 60/ 4% .030

.025 /- .025

L < :3I' *. gi{ .020 25aDW Point Temperature.020 ~~~~~~~~~~~~~~.020

Rain or Saturation Line .015 2 .015

100% Relative Humidity .010 X 7.010

1 ... ...005 .005 00

5 10 1'5 iO i.005 3'5-- -45005

5 10 15 20 25 30 35 40 45 50 5 10 15 20 25 30 35 40 45 50Dry-Bulb Temperature °C Dry-Bulb Temperature °C

Source: The Munters Corporation. Source: The Munters Corporation.

53


Figure A.3. Wet-Bulb Depression of Ambient Air Figure A1.4. Saturation Effectivenessfor an 80Percent Effective Evaporative Cooling Pad

5 0J 15 25 30X 20d 40 40 5 2 1 3 2 30/ 351 fi,C A /s lc s la t; 23 25~~~~~ 30 3 43 5 5

Dwy-5BdbThTh, C Dl-mmd Tcn~ab sC

Source: The Munters Corporation. Source: The Munters Corporation.

Figure A1.4 explains the cooling effect of an The outgoing air thus has a DB temperature of 40°CEAC. When water and dry air are mixed in an EAC, - 16°C = 24°C.the air will cool down following the WB depres- Figure A1.5 explains what happens in differentsion line. The efficiency of a certain EAC defines situations when an EAC is used. The arrows pointthie degree of cooling. In this case, the dry air of 40°C at certain combinations of DB temperature and RH.is led through a pad of corrugated paper, which is It is clear that not all these situations are "comfort-constantly wetted with water. The appliance has an able." Only certain combinations of DB and RH areefficiency of 80 percent, which means it cools the actually sensed as comfortable by human beings,airwith O.80OXWB depressionof40°C-20°C = 16°C. and this limits the use of the EAC technology for

F'igure A1.5. Saturation Effectiveness of 80 Percent Figure A1.6. Effect of Indirect Evaporative Coolingfor Evaporative Cooling Pads at Different Ambient on Ambient AirstreamConditions

tiuiai;~~~~~~~~~~~~~~~~~~~~~~~.U Lhgig,=. EbcdtRs

_; : ~~~~~~~~25 2w

20 .< 15 20 < 1

S .C 0g = .C

.500 - .010

O 15 15 25 20 30 c 40 1 3 10 IS 20 2Z 30 35 40 45 S0

1),Y-BWb T-M~~~ -C Lty-BWb TDs-Bx bT C

Note: All are 80 percent effective; in drier conditions the Source: The Munters Corporation.cooling effect is more pronounced than in hu ecid regions.Source: The Munters Corporation.

Annex 1: Introduction to Evaporative Cooling 55

Figure A1.7. Effect of Combined Indirect Evapora- Figure A1.8. Energy-Saving Effect of Using ative Cooling Coupled with Direct Section Smaller Coil Coupled with Indirect and Direct

Evaporative Cooling Sections

025' wN- co,, .000

10 no,o,2~3 / .010 C'Il 04a0,

.D05 25/ .025

~~~~~5 ,.020 s %/17

5 10 1S 20 2 30 35 40 45 S0 5 10 15 20 25 30 35 40 45 soDQ-2oOT=00epaoDC y-Bo1bTon-p-:C

Note: This allows evaporative conmfort cooling to be applied in Source: The Munters Corporation.more huumid regions, as compared wit- direct EAC alone.

Source: The Munters Corporation.

certain applications. In some cases, hovwever, such the effect that the direct cooling follows anotheras greenhouses or cattle sheds, the RH can be in- (lower) WB depression line. In this way the end ofcreased without any problem. the arrow comes into the "comfortable zone" again.

EAC technicians have succeeded in reducing Figure A1.8 shows the effect of adding a coolingthe amounts of water that are in the air, so as to coil after an indirect evaporative cooling section (us-increase the possibilities for applying EAC in hu- ing the indirect as a precooler). This allows for amid areas also. Figures A1.6 ard Al .7 explain the smnaller-sized coil to be used, thus saving energy overeffect in an indirect-direct air-conditioner. Before conventional systems. A direct section can be addedentering the wetting air stream, the air is first after this as well if needed. Other systems reduce thecooled by a normal heat exchanger, in which wa- amounts of water by using desiccants, chemicals thatter and air are also mixed. In this case, the DB tem- can remove the water from the air stream before itperature of the entering air is reduced from 37.7'C enters the direct cooler. With these types of combinedto 26.1'C by the heat exchanger. After this, the processes, EAC can be made more efficient in more26.1 'C air is cooled in the direct cooler to a DB of humid areas. The price of these coolers increases with19.6 C. The indirect cooler in the beginning has the more complicated technology.

Annex 2

Suitability of EvaporativeAir-Conditioning in Different

Climate Z ones

Figure A2.1. Suitability of Evaporative Air-Conditioning: Africa (Shaded areas indicate suitability)

IE3RD 28834

The400V,S )ow axies,cT _ * d enwnin0f'tiwis

th. ma .. .;n-tinl4. ;n 9h pa of

57


Figure A2.2. Suitability of Evaporative Air-Conditioning: Asia (Shaded areas indicate suitability)

f 4, * 9 IBIRD 2835

; Suitable Areas

-w-

Stigon

desinUnit of Th World Bank., he boustdariea colorade nauonan and anotherinfo=ationshownon this niap do wot kimply. on the part of Th ol az roup. any I tjudgment on th tegsal tus of any teffitory. or any endorsement or a >

| . - | ,, ~~~~~~~~~~~~~~~~~~~~~~~~~J'-NE !997

Annex 2: Suitability of Evaporative Air-Conditioning in Different Climate Zones 59

Figure A2.3. Suitability of Evaporative Air-Conditioning: Australia (Shaded areas indicate suitability)

S~~~~~~~~~~~


Figure A2.4. Suitability of Evaporative Air-Conditioning: Europe (Shaded areas indicate suitability)

- 3 17 /S ,7 IBRD 28837

I ~ i '> / / S\, J

[ ] < Suitable Areas / -

t X A) a W / a / <s-

J/ X 1)/ .

'I~~~~~~~'

Tnis map was produced by the Map Design Unit ofThe World Bank. The boundaries, colors, denominationsand any other information shown on this map do not imply, onthe part of The World Bank Group, any judgment on the egal zstatus of any territory, or any enaorsement or acceptance of such boundaries. JUNE 1997

Annex 2: Suitability of Evaporative Air-Conditioning in Different Climate Zones 61

Figure A2.5. Suitability of Evaporative Air-Conditioning: North America (Shaded areas indicate suitability)

R8

1


Figure A2.6. Suitability of Evaporative Air-Conditioning: South America (Shaded areas indicate suitability)

WIRD 2W89

k~~~~~~~ La Pazt wN _B

Th6 ma y'wM* ' nUttiteci

> n ,f-< ~ ~~~~~~ *Bra ilia

'dto 'ain S table Areas 9anti *gW

. g # v ~~~~~~~~~~~~~Leosie

C olonia Sarrniento

Thima asm~cdb h a p esgnUiiit

9ithis maP dono wo rt ,on ot he WorldVak Grup, aAy jUd to -the legal status offany orny p or a3epahof such bou ndoresJ

Annex 3

List of Manufacturers and Suppliers

Complete Evaporative Air-conditioners Baltimore Aircoil CompanyAmerica: P.O.Box 7322

Baltimore, MD 21227AdobeAir, Inc. 7595 Montevideo Road500 S. 15th Street Jessup, MD 20794, USAPhoenix, Arizona 85034, USA Tel. 410-799-6262, Fax. 410-799-6461Tel. 602-256-4714, Fax. 602-257-1349 Produces a line of indirect evaporative air-conditioners.Leading USA manufacturer of a wide range of di-rect and indirect direct evaporative air-conditioners. Champion Cooler Corporation

5800 Murray StreetAir & Refrigeration Corporation Little Rock, Arkansas 72209, USAP.O. Box 565126 Voice 501-562-1094, Fax. 501-562-9485Dallas, Texas 75653, USA Full line of residential evaporative air-conditioners.Voice 214-747-0214, Fax. 214-747-0812Evaporative air-conditioners and humidification Convair Cooler Corporationequipment for industrial applications. 2007 Texoma Parkway

Suite 114Alton Manufacturing Company Sherman, TX 75090, USA4830 Transport Dr. Voice 903-463-7191, Fax. 903-463-9627Dallas, TX 75247, USA Marketing a range of whole of house evaporativeTel. 214-638-6010, Fax. 214-905-0806 air-conditioners and portable evaporative air-con-Standard indirect-direct evaporative units with a ditioners (by Seeley).choice of drip media in a variety of sheet metal andstainless steel cabinets. Cool Tower Systems, Inc.

8611 N. Polk Canyon, Suite 216Aztec International, LTD Phoenix, AZ 85021, USA2417 Aztec Rd. NE Tel. 02-995-2101, Fax. 602-995-9272Albuquerque, New Mexico 87107, USA Manufacturers of evaporative air-conditionersVoice 800-545-8306, Fax 505-881-5391 equipment.Indirect and direct air-conditioners standard andcustom units and makeup air units. Cool-Fog Systems

26 Pearl St. #Bldg.Bacchus Industries, Inc Norwalk, CT 06850, USAP.O. Box 465, Sunland Park Manufacturers of evaporative sprayers/misters.New Mexico 88063, USATel. 505-589-5431 Engineered Commercial Concepts, Inc.Manufacturer of a range of fiberglass cabinet air- P.O. Box 29734 - 2356 Glenda La.conditioners from 85 to 180m3/min. Dallas, Texas 75229, USA

Voice 214-484-0381, Fax. 214-620-9880

63


Industrial and commercial direct and indirect Manufacturer of industrial and commercial evapo-evaporative air-conditioners equipment. Stainless rative air-conditioners systems across a broadsteel construction with evaporative media, indirect range of applications. Products include: evapora-and direct gas heating. tive air-conditioners, pre-coolers, cell-cool units,

air washers.Essick Air Products and Champion CoolerCorporation Modine Manufacturing Company5800 Murray Street 1500 De Koven Ave.Little Rock, Arkansas 72209, USA Racine, WI 53402, USAVoice 501-562-1094, Fax. 501-562-9485 Voice 414-636-1200, Fax. 414-636-1665Portable, residential and commercial evaporative Indirect-fired and direct-fired heating and ventilat-air-conditioners. ing equipment with optional evaporative air-con-

ditioners sections in capacities.Evapco West, Inc.P.O. Box 959 Norsaire Systems, Inc.Madera, CA 93639, USA 1314 West Evans AvenueTel. 209-673-2207, Fax. 209-673-2378 Denver, CO 80223, USAEvaporative air-conditioners products. Voice 303-937-9595, Fax. 303-937-0774

Description: Indirect/Direct evaporative air-condi-Gustafson E.H. & Company tioners units with a wicked aluminum exchanger5115 Suffield Terr. or a standard efficiency plastic exchanger.Skokie, IL 60077, USAVoice 708-966-6155, Fax. 708-966-5662 Phoenix Manufacturing, Inc.Manufacturer of air washers utilizing spray coils, 3655 E.Roeser Roadevaporative media, and coil sections to provide hu- Phoenix, Arizona 85040, USAmidification and dehumidification for air-condition- Tel. 602-437-1034, Fax. 602-437-4833ing or industrial apparatus. Full line of residential air-conditioners, air-condi-

tioner pumps, air-conditioner parts and the 'PowerHastings IndustriesNVari-Cool cleaning pump system"P.O.Box 548Hastings, Nebraska 68901, USA Pneumafil CorporationTel. 402-463-9821, Fax. 402-462-8041 226 Westinghouse Boulevard, Suite 309Manufactures Vari-Cool, an indirect-direct evapo- P.O. Box 16348 (28297-8804)rative air-conditioner and direct evaporative air- Charlotte, NC 28273, USAconditioners. Direct air-conditioner capacities from Voice 704-399-7441, Fax. 704-588-734660m3/min to 400m3 /min. Sheet metal manufacturer of evaporative air-con-

ditioners/filtration systems for the gas turbine co-ICC Technologies generation industry; automotive humidifiers, i.e.441 North Fifth Street media type, spray coil, and spray air washers (highPhiladelphia, PA 19123, USA and low velocities). Filtration systems consistingTel. 215-625-0700, Fax. 215-592-8299 of static self-cleaning barrier type and cartridgeManufacturer of commercial desiccant assisted pulse type.evaporative air-conditioners equipment.

Rainmaker Cooling, Inc.Janeco Inc. dba International Energy Saver 945 RutlandDoug Howard Houston, TX 77008, USA2017 S. Cutler Tel. 713-869-2894Tempe, AZ 85282, USA Evaporative spray roof cooling manufacturer.Voice 602-968-3066, Fax. 602-968-5788

Annex 3: List of Manufacturers and Suppliers 65

Rey Industries, Inc. Tradewinds218 W. 36th 616 So. 55th Ave.Boise, Idaho 83714, USA Phoernx, AZ 85043, USAVoice 208-336-4821, Fax. 208-343-0433 Tel. 602-278-1957, Fax. 602-272-9544High-velocity spray bank air washers for plant cooling. Residential and small commercial evaporative air-

conditioners units.Reznor EL.McKinley Avenue United Metal Products, Inc.Mercer, PA 16137, USA 127 S 43rd St.Voice 412-662-4400, Fax. 412-662-4412 Phoenix, AZ 85034, USADescription: Manufacturer of commercial/indus- Voice 602-275-7622, Fax. 602-275-2428trial heating equipment including an evaporative Industrial, Commercial evaporative Cooling Equip-air-conditioners section. ment, Direct, Indirect & Heating type units.

Space-Aire Co.158 No. Graham Rd. Tipton Australia:P.O. Box 888, Pixley, CA 93256, USA Bonaire PyroxTel. 209-752-2222 26 Nylex Ave, SalisburyManufactures of a range of fiberglass down draft South Australia, 5108air-conditioners from 80 to 400 m3/min. Tel.61-8-282-3110, Fax. 61-8-283-0401

Manufacturer, importer and wholesaler of evapo-SPEC-AIR rative air-conditioners equipment.7249 Bosque Rd.Canutillo, Texas 79835, USA Celair-MalmetVoice 915-877-3136, Fax. 915-877-1538 P.O.Box 373Indirect/Direct evaporative air-conditioners mod- Leeton NSW 2705ules and packaged air-conditioners; custom air han- Australiadlers for institutions and industries; make-up air Tel. 011-69-532455, Fax. 011-69-532656systems with evaporative air-conditioners; air Manufactures a range of evaporative air-condition-washers utilizing rigid media; packaged air-condi- ers under the trade mark of CELAIR. Product rangetioners with refrigeration and indirect evaporative starts from 40m3/min to 1600m3/min.air-conditioners; pre-coolers.

Seely International-Convair Cooler CorporationSprinkool Systems, Inc. 1-11 Rothesay Ave., P.O. Box 140P.O. Box 326 Saint Marys AdelaideKilleen, AL 35645, USA South Australia, 5042, AustraliaEvaporative spray roof cooling manufacturer. Tel. 011-618-276-2355, Fax. 011-618-374-2315

Manufacturer of a range (410-250m3/min) of poly-Southern Equipment Co. mer cabinet, whole of house evaporative air-condi-4550 Gustine Ave. tioners and portable evaporative air-conditioners.St. Louis, MO 63116, USA Brand names Convair and Breezair.Voice 314-481-0660, Fax. 314-481-8107High efficiency evaporative air-conditioners to be Southernairused as stand alone or package with blowers, and 29 Aldershot Roadfurnaces (unit heaters and duct furnaces). Lonsdale, South Australia 5160, Australia

Tel. 08 326-3551, Fax. 08 326-3552Titon Inc. Manufacturer of a range of axial fan, roof mountedP.O. Box 6164 evaporative air-conditioners with low profile fiber-South Bend, IN 46660, USA glass cabinet.Tel. 219-271-9699, Fax. 219-261-9771


India: Flippen Valve Company

Ambassador Air-conditioners Private Lmtd. 4127 Temple City Blvd.HA6mbassMohadr Ar-copnditonr Arivate LmtdEl Monte, CA 91734, USAH-6 B-I Mohan Co-op nd. Area Voice 818-575-1411, Fax. 818-575-1549

New Delhi Manufactures extensive line of heavy duty evapo-India rative air-conditioner valves for residential andTel. 91-11-683-3258, Fax. 91-11-683-6903 commercial use.Manufacturer of commercial direct evaporative air-conditioners equipment and of evaporative air-con- Cer-Cor

ditioners media. ~~~~1149 Central AvenueUniversity Park, IL 60466, USATel. 708-534-6595 or 800-323-9161, Fax. 708-534-7581

Kobli anda CoManyi PaharganjManufacturer of cellulose evaporative air-condi-

New Delhi 110 055, India tioners pads for agricultural, horticultural, commer-New. De442i 110 055,Indiacial, industrial and residential applications.Tel. 524428Manufacturers of a range of spot air-conditioners Goettl Enterprises Inc, Amoy Industriesand wall mounted evaporative air-conditioners. P.O. box 20246

2301 E. Buckeye Rd, Phoenix AZ 85036, USASolar Air-conditioners: Tel. 602-273-7483, Fax. 602-275-2881

Blower wheels and associated items for the evapo-Jade Mountain Import-Export Company rative air-conditioning industry. New product de-P.O. Box 4616, Boulder CO 80306, USA velopment programs involving cooling and airTel. 303-449-6601, Fax. 303-449-8266Mail order of solar powered direct and indirect-direct movng equipment.evaporative air-conditioners from 20 to 100m3 /rnin. Little Giant Pump Company

Solar Energie Technik P.O.Box 12010Postfach 1180, D 68801 Altluszheim Oklahoma City, OK 73157-2010, USATel. 06205-3525, Fax. 06205-3528, Germnany. Tel. 405-947-2511, Fax. 405-947-8720Mail order of a solar powered evaporative spot air- Line of non-submersible evaporative air-condi-conditioner. tioner pumps.

Munters CorporationComponent Manufacturers: Evaporative cooling division

Air Moving Market 108 Sixth Street,SEGE Motors Fort Myers, FL 33907, USAP.O. Box 2205 Tel. 813-936-1555, Fax. 813-936-26572000 Taylor Street Leading manufacturer of rigid pads

Fort Wayne, IN 46801, USAVoice 219-428-4685, Fax. 219-428-4660 Scott Motors CompanyFan motors for evaporative air-conditioners Al do NM88310 USA

applications. Tel. 505-434-0633, Fax. 505-434-4895

Dial Manufacturing, Inc. Manufacturer of evaporative air-conditioner motors.

25 South 51st AvenuePhoenix, AZ 85043, USA Manufacturer's RepresentativesTel. 602-278-1100, Fax 602-278-1991 A K S Sales, Inc.Manufacturer of evaporative air-conditioner replace- 606 Northstarment parts such as pumps, motors, float valves etc. San Antonio, Texas 78216, USA

Annex 3: List of Manufacturers and Suppliers 67

Voice 512-344-1845 U.S. Representatives for Southernair evaporativeManufacturer's representative for evaporative air- Air-conditioners. High efficient axial fan residen-conditioners, Sno-Brese for Texas. tial and commercial air-conditioners.

Barnhart-Taylor, Inc. Consulting Engineering:1602 A E. YandellEl Paso, TX 79902, USA Anderson, De Bartolo and PanTel. 915-533-1231, Fax. 915-533-8942 2480 N. Arcadia Ave.Manufacturers representatives for evaporative air- Tucson AZ 85712, USAconditioners equipment sold in the Southwest U.S. Tel. 602-795-4500, Fax. 602-881-0413and northern Mexico. Consulting engineering specializing in evaporative

air-conditioners designEngineered Air Systems720 12th Street McCartney, Jerome J.Richmond, CA 94802, USA Water Treatment ConsultantTel. 510-234-9322 P.O. Box 498874

Cincinnati, Ohio 45249, USAFry Equipment Co., Inc. Voice 513-489-55472600 W. 2nd Ave. Suite 7 Specializing in chemical water treatment for boil-Denver, Colorado 80219, USA ers, cooling towers, evaporative condensers, andVoice 303-922-8442, Fax. 303-922-8445 closed circuit evaporative air-conditioners.Sales and design engineering desiccant cooling, in-direct evaporative air-conditioners systems with hy- Meckler, G. PEbrid desiccant and compressorized components. President

Gershon Meckler Associates, P.C.Lincoln Associates 590 Hemdon Parkway, Suite 100540 Powder Springs St. SW Hemdon, VA 22070, USASuite 29E Voice 703-478-9552, Fax. 703-478-9446Marietta, GA 30064, USA E conservation, utilization, and management. D ofManufacturers Representative for evaporative air- mechanical and electrical systems for buildings, en-conditioners products for Georgia and Alabama. ergy utilization analysis in system design, energy

conserving retrofit design for existing facilities, andMestek Dallas life cycle economnic analysis.4830 Transport DriveDallas, TX 75247, USA Foster, R.

Project Engineer, Southwest Technology Develop-Mountain Air Sales, Inc. ment Institute8282 So. State #28 College of Engineering, New Mexico State UniversityMidvale, UT 84047, USA P.O. Box 30001, Dept. 3SOLARTel. 303-937-9595, Fax. 303-937-0774 Las Cruces, NM 88003-8001, USA

Voice 505-646-1846, Fax. 505-646-2960Robert E. Jones Co. Analysis and design of direct and indirect evapo-P.O. Box 1129 rative air-conditioning systems, performance test-Newcastle, CA 95658, USA ing, building simulation modeling, research and de-

velopment, training and workshops, solar energyWright-Castillo & Associates, Inc. applications.1268-B Auto Parkway #506Escondido, CA 92029, USAVoice 619-743-6128, Fax. 619-738-9045


NM Energy, Minerals and Natural Resources Tecogen, Inc.Department P.O. Box 9046/45 First AvenueHarold Trujillo, Energy Conservation and Manage- Waltham, MA 02254, USAment Division Tel. 617-622-1323, Fax. 617-622-12522040 South Pacheco Street, Santa Fe, NM 87505, USA Desiccant air-conditioning systems.Tel. 505-827-5900, Fax 505-827-5908Educating and assisting organizations on the imple- Services: LegalLicensingmenting of evaporative air-conditioners, cosponsor-ing workshops on theory and design. Ian G. Fierstein

Attorney at LawNoble, John M. PE Miller Faucher Chertow Cafferty & WexlerP.O. Box 2615 30 North LaSalle St.Taos, NM 87571, USA Suite 3630Voice 505-758-2240, Fax. 505-758-2240 Chicago, IL 60602, USADesign and analysis of indirect and direct evapora- Voice 312-332-3400, Fax. 312-782-4485five air-conditioning systems. Representing developer of industrial process for

molding complex and detailed fiberglass parts toproduce evaporative air-conditioners.

Bibliography

Brown, W. K. 1991. "Application of Evaporative Nationwide, Commercial Applications forCooling Concepts to Save Energy while Imnprov- Evaporative Cooling Systems." Washingtoning the Indoor and Outdoor Environment. State Energy Office, ASHRAE Inland EmpireASHRAE Transactions 97(Pt. 2), IN-91-11-1 Chapter, Spokane, Washington, March 21.

Brown, W. K. 1989. "Humidification by Evapora- McClellan, C. H. 1988. "Estimated Temperature Per-tion for Control Simplicity and Energy Savings." formance for Evaporative Cooling Systems inASHRAE Transactions 95(Pt.1), Atlanta, GA. Five Locations in the United States." ASHRAE

Evaporative Cooling Institute. 1992a. "Commercial Transactions. Atlanta, Georgia.Applications for Evaporative Cooling Systems: McClellan, C. H. 1989. "Evaporative Cooling Ap-Workshop Manual." Governors Energy Office, plication Handbook." Sun Manufacturing, ElTexas Energy Extension Service, Energy Center, Paso, Texas.ASHRAE-El Paso, University of Texas at El Muller, M. J., 1987. "Handbuch ausgewalterPaso, El Paso, Texas, June 16. Klimastationen der Erde." University of Trier,

Evaporative Cooling Institute. 1992b. "Sizing and Forschungsstelle Bodenerosion Mertensdorf,Maintaining Evaporative Cooling Systems: Ruwertal, Germany.Workshop Manual." Governors Energy Office, Peterson, J. L. and B. D. Hunn. 1992. "PerformanceTexas Energy Extension Service, Energy Center, Evaluation of an Indirect Evaporative Cooler."Evaporative Cooling Institute, ASHRAE-El Conservation and Solar Research Report No. 11,Paso, University of Texas at El Paso, El Paso, Center for Energy Studies, University of Texas,Texas, June 16. Austin, Texas, January.

Evaporative Cooling hinstitute. 1995. "CommercialApplcations for Evaporative Cooling Systems."I Puckorius, P. R., P. T. Thomas, and R. L. Augspurger.WApplingonstaterEneprgyatffieCoolingSHRAems 1995. "Why Evaporative Coolers Have NotWashington State Energy Offkce, ASHRAE in Caused Legionnaires' Disease." ASHRAE Jour-land Empire Chapter, Spokane, Washington, nall995qanuary): 29-33.March 21.

Foster, R. E. 1991. 'Evaporative Air-Conditionin Supple, R., 1982. "Evaporative Cooling for Com-FostechnoloiE and1. CvapontributiAlrons tioo*g fort." ASHRAE Journal. 1982(August).Technologies and Contributions to ReducingGreenhouse Gases." Proceedings of the Watt, J. R. 1986. Evaporative Air-Conditioning Hand-ASHRAE Asia-Pacific Conference on the CFC book. Second Edition.Issue and Greenhouse Effect, Singapore, May. Wu, H., 1989. "Performance Monitoring of a Two-

Foster, R. E. 1995. "Evaporative Air-Conditioning Stage Evaporative Cooler." ASHRAE Transac-Technologies: Reducing Energy and CFC Usage tions. 95(Pt. 1). Atlanta, Georgia.

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Recent World Bank Technical Papers (continued)

No. 390 Foster, Lawrence, and Morris, Groundwater in Urban Development: Assessing Management Needs andFormulating Policy Strategies

No. 391 Lovei and Weiss, Jr., Environmental Management and Institutions in OECD Countries" LessonsfromExperience

No. 392 Felker, Chaudhuri, Gy6rgy, and Goldman, The Pharmaceutical Industry in India and Hungary: Policies,Institutions, and Technological Development

No. 393 Mohan, ed., Bibliography of Publications: Africa Region, 1990-97

No. 394 Hill and Shields, Incentivesfor Joint Forest Management in India: Analytical Methods and Case Studies

No. 395 Saleth and Dinar, Satisfying Urban Thirst: Water Supply Augmentation and Pricing Policy in Hyderabad City,India

No. 396 Kikeri, Privatization and Labor: What Happens to Workers When Governments Divest?

No. 397 Lovei, Phasing Out Leadfrom Gasoline: Worldwide Experience and Policy Implications

No. 398 Ayres, Anderson, and Hanrahan, Setting Priorities for Environmental MAnagement: An Application to theMining Sector in Bolivia

No. 399 Kerf, Gray, Irwin, L6vesque, Taylor, and Klein, Concessionsfor Infrastructure: A Guide to Their Design andAward

No. 401 Benson and Clay, The Impact of Drought on Sub-Saharan African Economies: A Preliminary Examination

No. 402 Dinar, Mendelsohn, Evenson, Parikh, Sanghi, Kumar, McKinsey, and Lonergan, Measuring the Impact ofClimate Change on Indian Agriculture

No. 403 Welch and Fremond, The Case-by-Case Approach to Privatization: Techniques and Examples

No. 404 Stephenson, Donnay, Frolova, Melnick, and Worzala, Improving Women's Health Services in the RussianFederation: Results of a Pilot Project

No. 405 Onorato, Fox, and Strongman, World Bank Group Assistancefor Minerals Sector Development and Reform inMember Countries

No. 406 Milazzo, Subsidies in World Fisheries: A Reexamination

No. 407 Wiens and Guadagni, Designing Rulesfor Demand-Driven Rural Investment Funds: The Latin AmericanExperience

No. 408 Donovan and Frank, Soil Fertility Management in Sub-Saharan Africa

No. 409 Heggie and Vickers, Commercial Management and Financing of Roads

No. 410 Sayeg, Successful Conversion to Unleaded Gasoline in Thailand

No. 411 Calvo, Options for Managing and Financing Rural Transport Infrastructure

No. 413 Langford, Forster, and Malcolm, Toward a Financially Sustainable Irrigation System: Lessonsfrom the State ofVictoria, Australia, 1984-1994

No. 414 Salman and Boisson de Chazoumes, International Watercourses: Enhancing Cooperation and ManagingConflict, Proceedings of a World Bank Seminar

No. 415 Feitelson and Haddad, Identification of Joint Management Structuresfor Shared Aquifers: A CooperativePalestinian-Israeli Effort

No. 416 Miller and Reidinger, eds., Comprehensive River Basin Development: The Tennessee Valley Authority

No. 417 Rutkowski, Welfare and the Labor Market in Poland: Social Policy during Economic Transition

No. 418 Okidegbe and Associates, Agriculture Sector Programs: Sourcebook

No. 420 Francis and others, Hard Lessons: Primary Schools, Community, and Social Capital in Nigeria

No. 422 Peter Quaak, harrie Knoef, and Huber Stassen, Energyfrom Biomass: A Review of Combusion and GasificationTechnologies

No. 424 Jaffee, ed., Southern African Agribusiness: Gaining through Regional Collaboration

No. 425 Mohan, ed., Bibliography of Publications: Africa Region, 1993-98

No. 426 Rushbrook and Pugh, Solid Waste Landfills in Middle- and Lower-Income Countries: A Technical Guide toPlanning, Design, and Operation

No. 427 Marifio and Kemper, Institutional Frameworks in Successful Water Markets: Brazil, Spain, and Colorado, USA

No. 428 C. Mark Blackden and Chitra Bhanu, Gender, Growth, and Poverty Reduction: Special Program of Assistancefor Africa, 1998 Status Report on Poverty in Sub-Saharan Africa

No. 431 Severin Kodderitzsch, Reforms in Albanian Agriculture: Assessing a Sector in Transition

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