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

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Presentation on theme: "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 transcript:

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

2 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

3 Presentation Outline (Page 2) Study Methodology & Goals UVC System Installation Microbial Sampling and Impacts AC Efficiency Impacts Other Environmental Issues Future Research Needed

4 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

5 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

6 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

7 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

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

9 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

10 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

11 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

12 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

13 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

14 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

15 UVC for Cleaning Air Handling Units (AHUs) Typical UVC Lamp Installation in AHU Schematic courtesy of UVDI

16 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

17 UVC System Operation Lamps most effective in still air at 25 C Lamps most effective when new and clean Humidity 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

18 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

19 UVC System Sizing Many approaches are possible: Catalogs Tables Analytical Methods Rules of Thumb

20 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

21 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 DurationExposure Limit Continuous0.1 μW/cm2 7 hours/day0.5 μW/cm2 10 minutes22 μW/cm2 2.5 minutes90 μW/cm2

22 Has UVC Been Used Before? Installations in Schools Capistrano Unified School District, California- reduction of indoor air contaminants LaPorte Independent School District, Texas- 10% reduction in energy use, improved indoor air quality Stepping Stones Center, Ohio- removed mold from an otherwise unusable building

23 Has UVC Been Used Before? Installations in a Hospital and Office Building Florida 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%

24 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)

25 What are the Ownership Costs? Capital Costs- Lamps and Installation Operating Costs- Lamp Energy Use and Incremental HVAC Energy Savings Maintenance Costs- Lamp Replacement and Cleaning Productivity and Health- extra revenue from increased school attendance, more productive teachers and better educated students, higher neighborhood property values

26 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

27 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

28 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

29 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

30 District Locations District 1 District 2 District 3

31 System Installation Issues Physical constraints Compact units Air filter location Fan location Lamp orientation to coil fins Upstream versus downstream locations Approximate equipment cost $300-600 Safety options

32 Installation Challenges

33 Microbiological Sampling Pre and post tests on all 54 units Swabbed one square inch of coil Cultured by independent laboratory Swab difficult to get between coil fins

34 Microbiological Sampling Supply Fan Cooling Coil UVC Lamp Typical Sample Location

35 Gram Positive Bacteria Pre and Post UVC Contamination Levels

36 Microbial Analysis Results Means with 90% Confidence Intervals

37 Microbial Results – No Outliers Means with 90% Confidence Intervals

38 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

39 TrueFlow Air Handler Flow Meter

40 Honeywell Service Assistant

41 Airflow Impact

42 Efficiency Assessment Instantaneous efficiency

43 Efficiency Normalization Field operating efficiency normalized to ARI standard conditions, 95 F ambient and 67 F evaporator entering wet bulb Manufacturers performance curves used for normalization Standard DOE2 Packaged DX curves as alternative Post tests performed on cool days near limits of performance curves

44 Efficiency Analysis Results

45 Efficiency Analysis Results – Condenser Balance Only

46 Teacher Survey Results


48 Environmental Issues Majority carpet in many classrooms No door mats at entry in some rooms Water pooling near outdoor air intakes Dirty roofs Debris and dirt laden cooling coils Bypass around air filters Low filtration efficiency air filters

49 Environmental Observations


51 Conditions Near Outside Air Intakes

52 Environmental Observations Conditions of Coil and 6 Week Old Filters

53 Independent Opportunities Increase air filter efficiency Replace filters at more frequent intervals Reduce filter bypass Clean dust and debris from coils Test and add or recover refrigerant charge Retire oldest units Verify / increase outdoor air intake Clean cool roofs Require door mats in every room

54 Study Improvement Greater study population Increase cooling coil surface sample quantities and locations – multiple samples Back-up instrumentation Immediate data quality control via telephone Take pre and post measurements at similar conditions 12 month study period, 3 month testing intervals

55 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

56 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

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