SOLAR PASSIVE ARCHITECTURE - Military Engineer …mes.gov.in/imgtis/TI 01 of 2011.pdf · 2.6 Passive cooling 2.6.1 Exterior colours reflecting - absorbing 2.6.2 Landscaping and gardens

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SOLAR PASSIVE ARCHITECTURE BY

DTE OF WORKS

ENGINEER-IN-CHIEF’S BRANCH MILITARY ENGINEER SERVICES

INTEGRATED HQ OF MoD (ARMY)

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CONTENTS

TITLES

1. INTRODUCTION

1.1 Passive solar Architecture.

1.2 As a science

1.3 Passive Solar thermodynamic principles

1.4 Convective heat transfer

1.4.1 Radiative heat transfer

1.4.2 Conductive heat transfer

1.5 Summary of considerations for Solar passive design

2. KEY PASSIVE SOLAR CONCEPTS.

2.1 Direct solar gain

2.2 Indirect solar gain

2.3 Isolated solar gain

2.4 Heat storage

2.5 Insulation and glazing

2.5.1 Special glazing systems and window coverings

2.5.2 Equator-facing glass

2.5.3 Roof-angle glass / Skylights

2.5.4 Angle of incident radiation

2.5.5 Operable shading and insulation devices

2.6 Passive cooling

2.6.1 Exterior colours reflecting - absorbing

2.6.2 Landscaping and gardens

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7. EFFICIENCY AND ECONOMICS OF PASSIVE SOLAR HEATING

8. CONSIDERATIONS

9. PASSIVE SOLAR SYSTEMS RULES OF THUMB

10. Zero Energy Building.

11. Adoption in MES.

12.References.

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1. INTRODUCTION

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1. INTRODUCTION

1.1 Passive Solar Architecture.

Heavy energy demand for heating, cooling, ventilation and lighting of the buildings is

leading to depletion of precious environmental resources. These resources can be

conserved by designing and developing future buildings utilizing renewable energy sources.

Solar energy is one such resource.

There are two approaches for application of solar energy to buildings, namely active

systems and passive systems. In an active system, solar collecting panels, the storage unit

and the energy distribution system are installed with one or more working fluids. Energy is

distributed by the circulation of working fluids using electrically-operated pumps and fans.

In a passive system all the functions of collection, storage and distribution are carried out by

the building materials themselves. The term ‘passive’ refers to the solar-related architectural

concept which describes the methods to utilize solar heat that is available to buildings by

natural means. Generally, no electrical, mechanical or power electronic controls are used.

Passive solar applications, when included in initial building design, add little or nothing to

the cost of the building, yet has the effect of realizing a reduction in operational cost and

reduced equipment demand. It is reliable, mechanically simple, and is a viable asset to a

building.

In passive solar building architecture, windows, walls, and floors are made to collect, store, and distribute solar energy in the form of heat in the winter and reject solar heat in the summer. This is called passive solar design or climatic design because, unlike active solar heating systems, it doesn't involve the use of mechanical and electrical devices.

The key to designing a passive solar building is to best take advantage of the local climate. Elements to be considered include window placement and glazing type, thermal insulation, thermal mass, and shading. Passive solar design techniques can be applied most easily to new buildings, but existing buildings can be adapted or "retrofitted".

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India is divided into six climatic zones. For a given location, the knowledge of climate

can help evolve better design of solar passive buildings. Various climatic factors that

affect the solar passive design are: wind velocity, ambient temperature, relative

humidity and solar radiation. For a particular climate suitable combination of solar

passive techniques are required to be selected to obtain the highest possible comfort

at the lowest possible expenditure for material and energy.

1.2 As a science

The scientific basis for passive solar building design has been developed from a combination of climatology, thermodynamics (particularly heat transfer), and human thermal comfort (for buildings to be inhabited by humans and animals). Specific attention is dissected to the site and location of the dwelling, the prevailing level of rain, design and construction, solar orientation, placement of walls, and incorporation of biomass. While these considerations may be directed to any building, achieving an ideal solution requires careful integration of these principles. Modern refinements through computer modelling and application of other technology can achieve significant energy savings without necessarily sacrificing functionality or aesthetics. Architecture thus meets science in Solar Passive Architecture.

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This occurs as a result of the inclination of the Earth's axis of rotation in relation to its orbit. The sun path is unique for any given latitude.

In Northern Hemisphere non-tropical latitudes farther than 23.5 degrees from the equator:

• The sun will reach its highest point toward the South (in the direction of the equator)

• As winter solstice approaches, the angle at which the sun rises and sets progressively moves further toward the South and the daylight hours will become shorter.

• The opposite is noted in summer where the sun will rise and set further toward the North and the daylight hours will lengthen.

The converse is observed in the Southern Hemisphere, but the sun rises to the east and sets toward the west regardless of which hemisphere you are in.

In equatorial regions at less than 23.5 degrees, the position of the sun at solar noon will oscillate from north to south and back again during the year.

In regions closer than 23.5 degrees from either north-or-south pole, during summer the sun will trace a complete circle in the sky without setting whilst it will never appear above the horizon six months later, during the height of winter.

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The 47-degree difference in the altitude of the sun at solar noon between winter and summer forms the basis of passive solar design. This information is combined with local climatic data (degree day) heating and cooling requirements to determine at what time of the year solar gain will be beneficial for thermal comfort, and when it should be blocked with shading. By strategic placement of items such as glazing and shading devices, the percent of solar gain entering a building can be controlled throughout the year.

Although the sun is in the same relative position six weeks before, and six weeks after, the solstice, due to "thermal lag" from the thermal mass of the Earth, the temperature and solar gain requirements are quite different before and after the summer or winter solstice. Movable shutters, shades, shade screens, or window quilts can accommodate day-to-day and hour-to-hour solar gain and insulation requirements.

Careful arrangement of rooms completes the passive solar design. A common recommendation for residential dwellings is to place living areas facing solar noon and sleeping quarters on the opposite side. A heliodon is a traditional movable light device used by architects and designers to help model sun path effects. In modern times, 3D computer graphics can visually simulate this data, and calculate performance predictions.

1.3 Passive Solar thermodynamic principles

Personal thermal comfort is a function of personal health factors (medical, psychological, sociological and situational),ambient air temperature, mean radiant temperature, air movement (wind chill, turbulence) and relative humidity (affecting human evaporative cooling). Heat transfer in buildings occurs through convection, conduction, and thermal radiation through roof, walls, floor and windows.

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1.4.1 Convective heat transfer

Convective heat transfer can be beneficial or detrimental. Uncontrolled air infiltration from poor weatherization / weatherstripping / draft-proofing can contribute up to 40% of heat loss during winter, however strategic placement of operable windows or vents can enhance convection, cross-ventilation, and summer cooling when the outside air is of a comfortable temperature and relative humidity. Filtered energy recovery ventilation systems may be useful to eliminate undesirable humidity, dust, pollen, and microorganisms in unfiltered ventilation air.

Natural convection causing rising warm air and falling cooler air can result in an uneven stratification of heat. This causes variations in temperature in the upper and lower conditioned space, and can serve as a method of venting hot air, or be designed in as a natural-convection air-flow loop for passive solar heat distribution and temperature equalization. Natural human cooling by perspiration and evaporation may be facilitated through natural or forced convective air movement by fans, but ceiling fans can disturb the stratified insulating air layers at the top of a room, and accelerate heat transfer. In addition, high relative humidity inhibits evaporative cooling by humans.

1.4.2 Radioactive heat transfer

The main source of heat transfer is radiant energy, and the primary source is the sun. Solar radiation occurs predominantly through the roof and windows (as also through walls). Thermal radiation moves from a warmer surface to a cooler one. Roofs receive the majority of the solar radiation delivered to a building. A cool roof, or green roof in addition to a radiant barrier can help prevent the top floor/ ceiling from becoming hotter than the peak summer outdoor air temperature.

Windows are a ready and predictable site for thermal radiation. Energy from radiation can move into a window in the day time, and out of the same window at night. Solar heat gain through windows can be reduced by insulated glazing, shading, and orientation. Windows are particularly difficult to insulate compared to roof and walls. When shading windows, external shading is more effective at reducing heat gain than internal window coverings.

Western and eastern sun can provide warmth and lighting, but are vulnerable to overheating in summer if not shaded. In contrast, the low midday sun readily admits light and warmth during the winter, but can be easily shaded with appropriate length overhangs or angled louvres during summer. The amount of radiant heat received is related to the location latitude, altitude, cloud cover, and seasonal / hourly angle of incidence.

Another passive solar design principle is that thermal energy can be stored in certain building materials and released again when heat gain eases to stabilize diurnal (day/night) temperature variations, what is called ’ thermal lag ’.incidence

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1.5 Summary of considerations for Solar passive design

The following site specific considerations are significant-

• Latitude and sun path • Seasonal variations in solar gain e.g. cooling or heating degree days, solar

insolation, humidity. • Diurnal variations in temperature • Micro-climate details related to breezes, humidity, vegetation and land contour • Obstructions / Over-shadowing - to solar gain or local cross-winds

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2. KEY PASSIVE SOLAR CONCEPTS.

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2. KEY PASSIVE SOLAR CONCEPTS.

There are six primary passive solar energy configurations:

• Direct solar gain • Indirect solar gain • Isolated solar gain • Heat storage • Insulation and glazing • Passive cooling

2.1 Direct solar gain

Direct gain attempts to control the amount of direct solar radiation reaching the living space. This direct solar gain is a critical part of passive solar house design as it imparts to a direct gain.

2.2 Indirect solar gain

Indirect gain attempts to control solar radiation reaching an area adjacent but not part of the living space. Heat enters the building through windows and is captured and stored in thermal mass (e.g. water tank, masonry wall) and slowly transmitted indirectly to the building through conduction and convection. Efficiency can suffer from slow response (thermal lag) and heat losses at night. Other issues include the cost of insulated glazing and developing effective systems to redistribute heat throughout the living area.

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Figure 1

2.3 Isolated solar gain

Isolated gain involves utilizing solar energy to passively move heat from or to the living space using a fluid, such as water or air by natural convection or forced convection. Heat gain can occur through a sunspace, solarium or solar closet. These areas may also be employed usefully as a greenhouse or drying cabinet. Glass placement and overhangs prevent solar gain during the summer. Earth cooling tubes or other passive cooling techniques can keep a solarium cool in the summer.

Measures should be taken to reduce heat loss at night by providing window coverings or movable window insulation.

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2.4 Heat Storage

The sun does not shine all the time. Heat storage, or thermal mass keeps the building warm when the sun cannot heat it.

In buildings in sunny regions, the storage is designed for one or a few days. The usual method is a custom-constructed thermal mass. These include a Trombe wall, a ventilated concrete floor, a cistern, water wall or roof pond.

In subarctic areas, or areas that have long terms without solar gain (e.g. weeks of freezing fog), the ground is used as thermal mass large enough for annualised heat storage by running an isolated thermosiphon under the building.

2.5 Insulation and glazing

Thermal insulation or super insulation (type, placement and amount) reduces unwanted leakage of heat. Some passive buildings are actually constructed of insulation.

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2.5.1 Special glazing systems and window coverings

The effectiveness of direct solar gain systems is significantly enhanced by insulative (e.g. double glazing), spectrally selective glazing (low-e), or movable window insulation (window quilts, interior insulation shutters, shades, etc.).

Generally, Equator-facing windows should not employ glazing coatings that inhibit solar gain.

2.5.2 Equator-facing glass

The requirement for vertical equator-facing glass is different from the other three sides of a building. Reflective window coatings and multiple panes of glass can reduce useful solar gain. However, direct-gain systems are more dependent on double or triple glazing to reduce heat loss. Indirect-gain and isolated-gain configurations may still be able to function effectively with only single-pane glazing. Nevertheless, the optimal cost-effective solution is both location and system dependent.

2.5.3 Roof-angle glass / Skylights

Skylights admit sunlight either horizontally (a flat roof) or pitched at the same angle as the roof slope. In most cases, horizontal skylights are used with reflectors to increase the intensity of solar radiation depending on the angle of incidence. Large skylights should be provided with shading devices to prevent heat loss at night and heat gain during the summer months.

Equatorial-facing skylights provide the greatest potential for desirable winter passive solar heat gain than any other location, but often allow unwanted heat gain in the summer. Unwanted solar heat gain can be prevented by installing the skylight in the shade of deciduous (leaf-shedding) trees or adding a movable window covering on the inside or outside of the skylight.

Special glazing can help control solar heat gain while still allowing high levels of visible light transmittance. Skylights are often the only method to bring passive solar into the core of a commercial or industrial application or workspace.

2.5.4 Angle of incident radiation

The amount of solar gain transmitted through glass is also affected by the angle of the incident solar radiation. Sunlight striking glass within 20 degrees of perpendicular is mostly transmitted through the glass, whereas sunlight at more than 35 degrees from perpendicular is mostly reflected.

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2.5.5 Operable shading and insulation devices

A design with too much equator-facing glass can result in excessive winter, spring, or fall day heating, uncomfortably bright living spaces at certain times of the year, and excessive heat transfer on winter nights and summer days.

Variable cloud cover influences solar gain potential. This means that besides latitude-specific fixed window overhangs, other seasonal solar gain control solutions are required.

Control mechanisms (such as manual-or-motorized interior insulated drapes, shutters, exterior roll-down shade screens, or retractable awnings) can compensate for differences caused by thermal lag or cloud cover, and help control daily / hourly solar gain requirement variations.

2.6 Passive cooling

2.6.1 Exterior colours reflecting - absorbing

Materials and colours can be chosen to reflect or absorb solar thermal energy. The thermal radiation properties of reflection or absorption of a colour can assist the choices of ‘cool colours’.

2.6.2 Landscaping and gardens

Energy-efficient landscaping materials for careful passive solar choices include hardscape building material and "softscape" plants. Trees, hedges, and trellis-pergola features with vines; all can be used to create summer shading. For winter solar gain it is desirable to use deciduous plants that give year round passive solar benefits. Non-deciduous evergreen shrubs and trees can be windbreaks, at variable heights and distances, to create protection and shelter from winter wind chill.

Xeriscaping with 'mature size appropriate' native species of drought tolerant plants, drip irrigation, mulching, and organic gardening practices reduce or eliminate the need for energy-and-water-intensive irrigation, gas powered garden equipment, and reduces the landfill waste footprint.

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Advantage of prevailing breezes

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3. OTHER PASSIVE SOLAR PRINCIPLES

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3. OTHER PASSIVE SOLAR PRINCIPLES

3.1 Passive solar lighting

Passive solar lighting techniques enhance taking advantage of natural illumination for interiors, and so reduce reliance on artificial lighting systems.

This can be achieved by careful building design, orientation, and placement of window sections to collect light. Other creative solutions involve the use of reflecting surfaces to admit daylight into the interior of a building. Window sections should be adequately sized, and to avoid over-illumination can be shielded with a Brisesoleil, awnings, well placed trees, glass coatings, and other passive and active devices.

Another major issue for many window systems is that they can be potentially vulnerable sites of excessive thermal gain or heat loss. Whilst high mounted clerestory window and traditional skylights can introduce daylight in poorly oriented sections of a building, unwanted heat transfer may be hard to control. Thus, energy that is saved by reducing artificial lighting is often more than offset by the energy required for operating HVAC systems to maintain thermal comfort.

Besides window coverings, various methods can be employed to address this such as insulated glazing, novel materials such as aerogel semi-transparent insulation, optical fiber embedded in walls or roof and hybrid solar lighting.

3.2 Interior reflecting

Reflecting elements, from active and passive day lighting collectors, such as light shelves, lighter wall and floor colours, mirrored wall sections, interior walls with upper glass panels, and clear or translucent glassed hinged doors and sliding glass doors take the captured light and passively reflect it further inside. The light can be from passive windows or skylights and solar light tubes or from active day lighting sources.

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3.3 Passive solar water heating

There are many ways to use solar thermal energy to heat water for domestic use. Different active-and-passive solar hot water technologies have different location-specific economic cost benefit analysis implications.

Fundamental passive solar hot water heating involves no pumps or anything electrical. It is very cost effective in climates that do not have lengthy sub-freezing, or very-cloudy, weather conditions. Other active solar water heating technologies, etc. may be more appropriate for some locations.

It is possible to have active solar hot water, which is also capable of being "off grid" and qualifies as sustainable. This is done by the use of a photovoltaic cell, which uses energy from the sun to power the pumps.

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4. SOLAR PASSIVE HEATING TECHNIQUES

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4.SOLAR PASSIVE HEATING TECHNIQUES

In solar passive techniques the windows, walls, floors and roof of a building are used

as the heat collecting, storing , releasing and distributing system. These very same

elements are also a major element in passive cooling design but in a very different

manner.

The techniques for solar heating of energy efficient buildings are :-

4.1 Direct System Gain

Direct heat gain technique is generally used in cold climates. A direct gain passive

solar heating system is shown :-

Winter Sun

Summer Sun

Overhang roof

Summer Sun

WinterDoubleglazedwindow

Sun rays

DIRECT HEAT GAIN SOLAR PASSIVE SYSTEM

• Double glazed windows are located facing South to receive maximum sunlight during winter.

• An overhang above the windows or at the roof level is provided to give shade, during summer when the elevation of the sun is high.

• Insulating curtains are provided to cover the windows to reduce heat loss during night.

• Massive flooring and walls are used to increase the thermal mass to store heat during day time; heat is released during the night to warm the interior.

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4.2 Indirect Gain System (Thermal Storage Wall)

In an indirect gain system, thermal mass is located between the sun and the

living space. The thermal mass absorbs the sunlight that strikes it and transfers

it to the living space. The indirect gain system uses 30%-40% of the sun’s

energy striking the glass adjoining the thermal mass. A few commonly used

indirect gain systems are discussed below.

4.2.1 Trombe Wall

In the Trombe wall passive system:

• The entire south-facing wall is double glazed by two sheets of glass or plastic

with an air-gap between the wall and the inner glazing. Hot air flows from

bottom to top through the air gap owing to natural convection.

• A large blackened thermal storage wall is constructed with the outer side facing

the sun. Sunlight after penetration through the glazing is absorbed by the wall

and the wall is thus heated.

Accordingly, the air between the glazing and the wall gets heated and flows into the

room through the top vent. This circulation process continues and the cool air from the

room enters into the gap through the bottom vent. In addition, the room is also heated

by radiation and convection from the inner surface of the wall facing the room. During

night both vents are closed and heat transfer takes place only by radiation.

During summer the vent A at the top of the south-facing wall is kept closed while the

vents B, C and D are opened. The hot air between the glazing and the wall then flows

out through the vent C and the air from room flows in to fill this space. Simultaneously,

the air is pulled into the room through the vent D which is located in the shaded cool

area. The construction of the building is such that the overhanging roof prevents direct

sun rays to heat the glazing during summer.

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TROMBE WALL PASSIVE SOLAR HEATING SYSTEM

South facing doubleglass wall

Winter Sun

Summer Sun

Warm air

Trombe Wall

Return cold air

Damper

C

B

A

D

Generally, thickness of storage wall is between 200 mm to 450 mm, the air gap

between the wall and glazing is 50-150 mm, and the total area of each row of vent is

about one percent of the storage wall area. The Trombe wall should be adequately

shaded for reducing summer gains.

4.2.2 Water Wall

Water walls are based on the same principle as that for Trombe walls, except that they

employ water as the thermal storage material. A water wall is a thermal storage wall

made up of drums of water stacked up behind glazing. It is usually painted black to

increase heat absorption. It is more effective in reducing temperature swings but the

time lag is less.

Heat transfer through water walls is much faster than that for Trombe walls. Therefore, the distribution of heat needs to be controlled if it is not immediately required for heating the building. Buildings that work during daytime, such as schools and offices, benefit from the heat transfer in the water wall. Overheating during summer may be prevented by using suitable shading devices.

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4.2.3 Roof-based air heating system

In this technique, incident solar radiation is trapped by the roof and is used for heating

interior spaces. In the northern hemisphere, the system usually consists of an inclined

south-facing glazing and a north-sloping insulated surface on the roof. Between the

roof and the insulation , an air pocket is formed , which is heated by solar radiation. A

moveable insulation can be used to reduce heat loss through glazed panes during

nights. There could be variations in detailing of roof air heating systems.

4.2.4 Sunspaces

A sunspace or solarium is the combination of direct and indirect gain systems. Solar radiation heats up the sunspace directly, which, in turn, heats up the living space (separated from the sunspace by a mass wall) by convection and conduction through the mass wall. The basic requirements of buildings heated by sunspace are (1) a glazed-south facing collector space attached yet separated from the building and (2) living space separated from the sunspace by a thermal storage wall. Sunspaces may be used as winter gardens adjacent to the building space.

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. Sunspaces

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4.2.5 Solar Chimney

Solar chimney is an air-heating solar collector attached to the south wall of the

building. As the air in the solar collector is heated, it expands rises and enters the

house. Cooler house air is drawn into the collector to take its place.

Solar chimneys avoid many of the problems of direct gain systems, such as glare and

heat loss000. But the disadvantage is that like direct gain, too large a system may

result in higher than normal temperature within the rooms. Careful construction is

required to ensure proper efficiency and durability.

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Examples of Solar Chimney

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5. ADVANCED PASSIVE COOLING TECHNIQUES

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5. ADVANCED PASSIVE COOLING TECHNIQUES

Passive cooling systems rely on natural heat-sinks to remove heat from the building.

They derive cooling directly from evaporation, convection, and radiation without using

any intermediate electrical devices. All passive cooling strategies rely on daily

changes in temperature and relative humidity. The applicability of each system

depends on the climatic conditions. This is not new, as traditionally buildings were

designed to take advantage of daily temperature variations, convective breeze,

shading, evaporative cooling, and radiation cooling.

5.1 Ventilation

Outdoor breezes create air movement through the house interior by the ‘push-pull’

effect of positive air pressure on the windward side and negative pressure (suction) on

the leeward side. Good natural ventilation requires locating openings in opposite

pressure zones. Also, designers often choose to enhance natural ventilation using tall

spaces called stacks in buildings. With openings near the top of stacks, warm air can

escape whereas cooler air enters the building from openings near the ground.

5.2 Wind Tower

In a wind tower, the hot air enters the tower through the openings in the tower, gets cooled, and thus becomes heavier and sinks down. The inlet and outlet of rooms induce cool air movement. In the presence of wind,

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air is cooled more effectively and flows faster down the tower and into the living area.

After the whole day of air exchanges, the tower becomes warm in the evenings.

During the night, cooled ambient air comes in contact with the bottom of the tower

through the rooms. The tower walls absorb heat during day time and release it at

night, warming the cool night air in the tower. Warm air moves up , creating an upward

draft , and draws cool night air through the doors and windows into the building. The

system works effectively in hot and dry climates where diurnal variations are high.

A wind tower works well for individual units but not for multi-storeyed apartments. In

dense urban areas, the wind tower has to be long enough to be able to catch enough

air.

A wind tower system

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5.3 Courtyard effect

Due to incident solar radiation in a courtyard, the air gets warmer and rises. Cool air

from the ground level flows through the louvered openings of rooms surrounding a

courtyard, thus producing air flow.

At night, the warm roof surfaces get cooled by convection and radiation. If this heat

exchange reduces roof surface temperature to wet bulb temperature of air,

condensation of atmospheric moisture occurs on the roof and the gain due to

condensation limits further cooling.

If the roof surfaces are sloped towards the internal courtyard, the cooled air sinks into

the court and enters the living space through low-level openings. However, care

should be taken that the courtyard does not receive intense solar radiation, which

would lead to conduction and radiation heat gains into the building. Intensive solar

radiation in the courtyard also produces immense glare.

5.4 Earth air tunnels

Daily and annual temperature fluctuations decrease with the increase in depth below the ground surface. At a depth of about 4m below ground, the temperature inside the earth remains nearly constant round the year and is nearly equal to the annual average temperature of the place. A tunnel in the form of a pipe or otherwise embedded at a depth of about 4 m below the ground will acquire the same temperature as the surrounding earth at its surface and, therefore, the ambient air ventilated though this tunnel will get cooled in summer and warmed in winter and this air can be used for cooling in summer and heating in winter.

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. 5.5 Evaporative cooling

Evaporative cooling lowers indoor air temperature by evaporating water. It is effective

in hot and dry climate where the atmospheric humidity is low. In evaporating cooling,

the sensible heat of air is used to evaporate water, thereby cooling the air, which, in

turn, cools the living space of the building. Increase in contact between water and air

increases the rate of evaporation.

The presence of a water body such as a pond, lake and a sea near the building or a

fountain in a courtyard can provide a cooling effect. The most commonly used system

is a desert cooler, which comprises water, evaporative pads, a fan, and pump.

5.6 Passive downdraught cooling

Evaporative cooling has been used for many centuries in parts of the Middle East, notably Iran and Turkey. In this system, wind catchers guide outside air over water-filled pots, inducing evaporation and causing a significant drop in temperature before the air enters the interior. Such wind catchers become primary elements of the architectural form also. Passive downdraught evaporative cooling is particularly effective in hot and dry climates.

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5.7 Earth Berming.

Since the ground is nearly always cooler than the air, in the month when cooling is

required, the more a house is in contact with the ground, the cooler it will be.

5.8 Roof Ponds

Roof ponds can be used both for heating during the winter months and for cooling

during the summer months. The roof ponds of contained water are the heating (and

cooling) unit. The movable insulation above the ponds is the weather protection ,

winter time heating is comprised of daytime opening the insulating roof layer to allow

solar radiation to heat the water bed; water bed warming heats the supporting

structure which is also the ceiling for spaces below; heated support structure radiates

heat to the space. At night the insulated roof panels close to contain heat gathered by

the ponds to continue heating the spaces below. Cooling strategies are the opposite

operation.

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6. LEVELS OF APPLICATION

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6.LEVELS OF APPLICATION

6.1Pragmatic

Many detached suburban buildings can achieve reductions in heating expense without obvious changes to their appearance, comfort or usability. This is done using good siting and window positioning, small amounts of thermal mass, with good-but-conventional insulation, weatherization, and an occasional supplementary heat source, such as a central radiator connected to a (solar) water heater. Sunrays may fall on a wall during the daytime and raise the temperature of its thermal mass. This will then radiate heat into the building in the evening. This can be a problem in the summer, especially on western walls in areas with high degree day cooling requirements. External shading, or a radiant barrier plus air gap, may be used to reduce undesirable summer solar gain.

6.2Annualised

An extension of the "passive solar" approach to seasonal solar capture and storage of heat and cooling. These designs attempt to capture warm-season solar heat, and convey it to a seasonal thermal store for use months later during the cold season ("annualised passive solar.") Increased storage is achieved by employing large amounts of thermal mass or earth coupling. Anecdotal reports suggest they can be effective but no formal study has been conducted to demonstrate their superiority. The approach also can move cooling into the warm season.

6.3 Minimum machinery

A "purely passive" solar-heated house would have no mechanical furnace unit, relying instead on energy captured from sunshine, only supplemented by "incidental" heat energy given off by lights, computers, and other task-specific appliances (such as those for cooking, entertainment, etc.), showering, people and pets. The use of natural convection air currents (rather than mechanical devices such as fans) to circulate air is related, though not strictly solar design.

Passive solar building design sometimes uses limited electrical and mechanical controls to operate dampers, insulating shutters, shades, awnings, or reflectors. Some systems enlist small fans or solar-heated chimneys to improve convective air-flow.

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7. EFFICIENCY AND ECONOMICS OF PASSIVE SOLAR HEATING

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7. EFFICIENCY AND ECONOMICS OF PASSIVE SOLAR HEATING

Technically, Passive Solar Heating (PSH) is highly efficient. Direct-gain systems can utilize (i.e. convert into "useful" heat) 65-70% of the energy of solar radiation that strikes the aperture or collector. To put this in perspective relative to another energy conversion process, the photosynthetic efficiency theoretical limit is around 11%.

Passive solar fraction (PSF) is the percentage of the required heat load met by PSH and hence represents potential reduction in heating costs. Within the field of sustainability, PSF even of the order of 15% is considered substantial.

This can be vary from 5% to 75% depending on the degree of optimization of the PSH system.

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8. CONSIDERATIONS

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8.CONSIDERATIONS

Passive design is practiced throughout the world and has been shown to produce buildings with low energy costs, reduced maintenance, and superior comfort. Most of the literature pertaining to passive solar technology addresses heating concerns. This information is useful and relevant in our area; however, cooling issues, which are equally important in Austin, are less well documented. Key aspects of passive design include appropriate solar orientation, the use of thermal mass, and appropriate ventilation and window placement.

As a design approach, passive solar design can take many forms. It can be integrated to greater or lesser degrees in a building. Key considerations regarding passive design are determined by the characteristics of the building site. The most effective designs are based on specific understanding of a building site’s wind patterns, terrain, vegetation, solar exposure and other factors often requiring professional architectural services. However, a basic understanding of these issues can have a significant effect on the energy performance of a building.

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9. PASSIVE SOLAR SYSTEMS - RULES OF THUMB

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9. PASSIVE SOLAR SYSTEMS RULES OF THUMB

• The building should be elongated on an east-west axis. • The building’s south face should receive sunlight between the hours of 9:00

A.M. and 3:00 P.M. (sun time) during the heating season. • Interior spaces requiring the most light and heating and cooling should be along

the south face of the building. Less used spaces should be located on the north.

• An open floor plan optimizes passive system operation. • Use shading to prevent summer sun entering the interior.

10.Zero Energy Building.

Passive solar building design is often a foundational element of a cost-effective zero energy building. Although a ZEB uses multiple passive solar building design concepts, a ZEB is usually not purely passive, having active mechanical renewable energy generation systems such as: wind turbine, photovoltaic’s, micro hydro, geothermal, and other emerging alternative energy sources.

11.Adoption in MES

In MES there is a need to integrate different technologies i.e. energy conservation (by

providing insulation), use of passive solar techniques and active solar components

and develop a building as a whole. To design these buildings a multi-disciplinary

design team is required where architects & engineers work together in tandem.

References -

(i) www.worldgbc.org

(ii) www.wbdg.org

(iii) www.teriin.org

(iv) www.grihaindia.org

(v) www.igbc.in