An Introduction to UVC Surface Disinfection and Evaluation of its Use in California K-12 School Air Conditioning Systems Stacia Okura RLW Analytics, Inc.

An Introduction to UVC Surface Disinfection and Evaluation of its Use in California K-12 School Air

Conditioning Systems

Stacia Okura

RLW Analytics, Inc.

Presentation Outline (Page 1)

The Situation• Opportunity for Coil Disinfection

UVC System Attributes • IEQ, Maintenance and Energy Benefits• Types of UVC Systems• Sizing and Location of UVC Systems• Safety Issues• Field Experience• Ownership Costs

Presentation Outline (Page 2)

Study Methodology & Goals UVC System InstallationMicrobial Sampling and ImpactsAC Efficiency ImpactsOther Environmental IssuesFuture Research Needed

The Situation

Poor Indoor Environments Exist in Many Schools

High Concentrations of Indoor Pollutants are Linked to Reduced School Performance and Attendance• Dirty coils, drain pans and plenums may have

been fouled by growth of microorganisms• Air passing over these components can be

contaminated and contribute to poor indoor air quality in the teaching environment

The Situation

Microorganism Growth Can also Reduce Cooling System Performance

Cleaning of the Coils and Other Surfaces Could Enhance System Performance and Indoor Air Quality• What are the options?

• Do nothing• Manually clean the coils and other surfaces• Use ultraviolet light to clean the coils and other

surfaces

How Important is Coil Fouling and Resulting Performance Degradation?

Coil fouling is defined as an increase of pressure drop of greater than 100%

Efficiency degradation with 100% increase in pressure drop can cause efficiency degradation of only about 5% or less

Significant degradation of coil performance due to microbial growth is most likely to occur in warm, humid conditions that have gone untreated for some time

How Does UVC Operate?

UVC is ultraviolet radiation in the “C” range of 200 to 280 nanometers (nm)

UVC lamps are designed to emit radiation strongly at the wavelength of 253.7 nm that produces the greatest disinfection ability

This radiation is absorbed by the DNA of the microorganism, producing mutation, inability to reproduce and subsequent deactivation

UVC or Traditional Coil Cleaning?

UVC Pros- surface cleaning quick and effective, continuous cleanliness maintained, maintenance(lamp cleaning and replacement) quick and simpleTraditional Coil Cleaning Pros- Coil is fully cleaned after initial treatment, HVAC technicians familiar with this technology, existing infrastructure in place for its use

UVC or Traditional Coil Cleaning?

UVC cons- unclear how well and how fast light penetrates below the surface envelope of the coil, only addresses biofouling, timing issues in coordinating the cleaning with building occupancy

Traditional Coil Cleaning cons- pressure washing could drive contaminants deeper into the coil, chemicals and biocides need to be removed from the coils, shut down of the building and disassembly of the equipment may be required, cleanliness degrades steadily immediately after treatment

What are the Possible Benefits of UVC?

Indoor Air Quality- cleaner air is delivered to the classroom

Maintenance- coils kept continuously clean, avoiding laborious traditional coil cleaning actions

Energy- savings from reduced pressure drop and enhanced heat transfer resulting from clean coils

How Important is Indoor Air Quality?

Microbiological pollutants are associated with increases in asthma effects and respiratory infections; both of which are related to the health, performance and attendance of students and teachers

What are the Maintenance Issues?

UVC can replace a traditional coil cleaning program that needs to be done 3 or 4 times per year

UVC lamps need to be replaced regularly (normally annually)

UVC lamps need to be inspected (often quarterly) and cleaned (with simple procedures) if dirty

How Does UVC Save Energy?

UVC can reduce air side pressure drop and improve heat transfer and system capacity, reducing cooling system energy use

UVC lamps are generally operated continuously

The energy savings due to reduced pressure drop and improved heat transfer needs to be greater than the lamp energy use for net savings to accrue

Types of UVC Systems

In-duct-kills microorganisms in the air flowing past the lamps

Upper room- installed near the ceiling in occupied rooms, relying upon personnel movement and heat sources to create currents that move the air

Air handler unit (AHU)- lamps placed near the coil and drain pan in the delivery plenum to clean the surfaces of the AHU

UVC for Cleaning Air Handling Units (AHUs)

Typical UVC Lamp Installation in AHUSchematic courtesy of UVDI

UVC for Cleaning AHUs

Device components and operation that are similar in principal to a fluorescent fixture: Quartz or soda barium glass lamps that

transmit UVC Low-pressure mercury vapor

– No phosphors Pin-Based Socket Ballast Weather Proof Electrical Enclosure

UVC System Operation

Lamps most effective in still air at 25CLamps most effective when new and cleanHumidity has little effect on lamp output but

germicidal efficacy appears to decrease with increasing relative humidity

Lamps should be operated continuously to prevent microorganism growth

UVC Lamp Location

Need to be as close to the irradiated surfaces as possible while maintaining good coverage of the coil face and drain pan and other air handler unit surfaces of interest

UV rays should have a travel path directly between the coil fins

UVC System Sizing

Many approaches are possible:CatalogsTablesAnalytical MethodsRules of Thumb

UVC Safety Issues

Excessive exposure can cause skin redness and conjunctivitis

View ports to monitor system operation should be constructed of glass or Lexan

Avoid exposure to plastic-coated wire and glues that hold filters together

Do not exceed recommended human exposure limits

UVC Safety Issues

The Illuminating Engineering Society of North America (IESNA) has cited the following exposure limits set by the American Medical Association:

UVC Human Exposure Limits

Exposure Duration Exposure Limit

Continuous 0.1 μW/cm2

7 hours/day 0.5 μW/cm2

10 minutes 22 μW/cm2

2.5 minutes 90 μW/cm2

Has UVC Been Used Before?

Installations in SchoolsCapistrano Unified School District, California-

reduction of indoor air contaminantsLaPorte Independent School District, Texas-

10% reduction in energy use, improved indoor air quality

Stepping Stones Center, Ohio- removed mold from an otherwise unusable building

Has UVC Been Used Before?

Installations in a Hospital and Office BuildingFlorida Hospital Orlando, Florida- reduced

HVAC systems pressure drop by over 60% and energy use by more than 15%

Office Building, Montreal, Canada- reduced AHU surface microorganisms by 99%, airborne bacteria by 25 to 30%, worker absenteeism by 20% and respiratory problems by 40%

Has UVC Been Used Before?

Office Building Installation Central and Southwest

Corporation (now American Electric Power), Dallas, TX- removed mold and organic buildup from the coils and reduced HVAC system energy use by 28%

(Photo courtesy of Steril- Aire)

What are the Ownership Costs?

Capital Costs- Lamps and InstallationOperating Costs- Lamp Energy Use and

Incremental HVAC Energy SavingsMaintenance Costs- Lamp Replacement and

CleaningProductivity and Health- extra revenue from

increased school attendance, more productive teachers and better educated students, higher neighborhood property values

Background Summary

Coil cleaning procedures can be beneficial in situations where dirty coils degrade HVAC system performance

UVC may save energy by reducing coil pressure drop and improving heat transfer

UVC is simple to maintain UVC may improve indoor air quality Safety considerations are important but straight

forward Information on sizing, locating and operating is readily

available Benefits of UVC have been documented for cleaning of

air handler surfaces in facilities around the U.S

Genesis of the Study

One of two K-12 IEQ projects Funded and approved as statistical study

Occupant surveys, billing analysis and ADA

Study goals were altered to include technology field study assessment

Study Goals & Methodology

The hypotheses that were tested for the study, UVC reduces surface microbial growth UVC assists the AC units to run more efficiently Decrease in microbial levels affect average daily

attendance (ADA) – not complete

Side by side, pre vs.. post installation measurements on similar AC units (same model number, size, and grade level in classroom)

Two treated groups and a control group

Study Design

3 year-round school districts across California 54 air conditioning units in study

36 treated units and 18 control units Each unit served single classroom Rooftop and wall mount units Manufacturers installed systems to ensure proper

configuration

3 air conditioning units per group, 18 groups total 6 week study period commencing in August 2005

District Locations

District 1

District 2

District 3

System Installation Issues

Physical constraints Compact units Air filter location Fan location

Lamp orientation to coil finsUpstream versus downstream locationsApproximate equipment cost $300-600Safety options

Installation Challenges

Microbiological Sampling

Pre and post tests on all 54 unitsSwabbed one square inch of coilCultured by independent laboratorySwab difficult to get between coil fins

Microbiological Sampling

Supply Fan

Cooling Coil

UVC Lamp

Typical Sample Location

Gram Positive Bacteria Pre and Post UVC Contamination Levels

Unit ID Pre CFU Post CFU Reduction

1 80 - 80 2 - - - 3 20 - 20 4 - - - 5 - - - 6 - - - 7 - 20 (20) 8 - - - 9 208,000 - 208,000

10 3,400,000 - 3,400,000 11 - - - 12 - 2,260 (2,260) 13 20 - 20 14 6,000,000 - 6,000,000 15 6,000,000 6,000,000 - 16 - 200 (200) 17 19,200 - 19,200 18 - - -

Microbial Analysis Results

-50%

-25%

0%

25%

50%

75%

100%

Percent Reduction in Number of CFUs

Control

A

B

Broad Spectrum Bacteria

Gram Positive Bacteria

Total Fungus

Means with 90% Confidence Intervals

Microbial Results – No Outliers

-50%

-25%

0%

25%

50%

75%

100%

Percent Reduction in Number of CFUs

Control

A

B

Broad Spectrum Bacteria

Gram Positive Bacteria

Total Fungus

Means with 90% Confidence Intervals

Field Measurements

Airflow Measurements TrueFlow™ Air Handler Flow Meter Readings taken with new air filter in place

Power Measurements Instantaneous power (kW)

Refrigerant Measurements Service Assistant Tool

Air Temperature Measurements Wet and dry bulb, before and after evaporator coil

TrueFlow™ Air Handler Flow Meter

Honeywell Service Assistant

Airflow Impact

N Test Group % Change Error Bound15 Control Group -0.47% 3.70%16 A 0.92% 2.05%16 B 1.79% 3.28%

-6%

-5%

-4%

-3%

-2%

-1%

0%

1%

2%

3%

4%

5%

6%

Percent Change in Measured Airflow

Control

A

B

Efficiency Assessment

)(

)(

kWConsumedPower

kBtuDeliveredCoolingEERFIELD =

Instantaneous efficiency

Efficiency Normalization

Field operating efficiency normalized to ARI standard conditions, 95 F ambient and 67 F evaporator entering wet bulb

Manufacturer’s performance curves used for normalization

Standard DOE2 Packaged DX curves as alternative

Post tests performed on cool days near limits of performance curves

Efficiency Analysis Results

N % Change Error BoundControl 17 -1.62% 5.56%A 17 -4.16% 4.16%B 16 2.30% 7.80%

-12%

-8%

-4%

0%

4%

8%

12%

Percent Change in Normalized EER

Control

A

B

Efficiency Analysis Results – Condenser Balance Only

N % Change Error BoundControl 11 -3.22% 3.48%A 11 -2.94% 3.27%B 11 -0.29% 3.89%

-12%

-8%

-4%

0%

4%

8%

12%

Percent Change in Normalized EER

Control

A

B

Teacher Survey Results

Pressing Air Quality Concerns PercentageToo Hot or Cold in Classroom 62.8%Stuffy Classroom 60.5%Control of Thermostat Settings 34.9%Allergies 14.0%Air Filtration 14.0%Outside Pollution 9.3%Noxious Odors in Classrooms 9.3%Mold in AC System 9.3%Asthma or Other Respiratory Attacks 9.3%Complaints Regarding Respiratory Irritation 7.0%Complaints of Illness Due to Stale Air 7.0%Outdoor Air Ventilation Rate in Classrooms 4.7%Mold 4.7%Drafty Classroom 4.7%Conflicting Occupant Demands 4.7%Untrained Maintenence Staff 2.3%

Teacher Survey Results

Environmental Issues

Majority carpet in many classroomsNo door mats at entry in some roomsWater pooling near outdoor air intakes Dirty roofsDebris and dirt laden cooling coils

Bypass around air filters Low filtration efficiency air filters

Environmental Observations

Environmental Observations

Environmental Observations

Conditions Near Outside Air Intakes

Environmental Observations

Conditions of Coil and 6 Week Old Filters

Independent Opportunities

Increase air filter efficiency Replace filters at more frequent intervalsReduce filter bypassClean dust and debris from coils Test and add or recover refrigerant chargeRetire oldest unitsVerify / increase outdoor air intakeClean cool roofsRequire door mats in every room

Study Improvement

Greater study populationIncrease cooling coil surface sample quantities

and locations – multiple samplesBack-up instrumentationImmediate data quality control via telephoneTake pre and post measurements at similar

conditions12 month study period, 3 month testing intervals

Future Research

Baseline of coil conditions in relevant market to determine the need for UVC

Understanding of the mechanisms involved in coil fouling

Irradiation efficacy as a function of UVC lamp position UVC output degradation over time Relative contribution of AC system microbial growth to

total indoor contaminant load Time needed for UVC to penetrate through fins entirely Standard labeling and testing procedure for the products

on the market

Conclusions

School districts with pre-existing or potential microbial growth or IAQ problems are the strongest candidates

Most effective in areas with long cooling season and high latent loads

Primary potential benefits are coil disinfection and reduced maintenance for coil cleaning

No conclusive energy benefit from coil disinfection in California