McQuay UV News Letter

8/3/2019 McQuay UV News Letter

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UV Lights And AirHandling EquipmentAs the building design and constructionindustry has evolved over the past 30years, so too has the HVAC industry,

keeping pace with the ever-increasingdemands placed on the products andservices that we supply. Some times, thejob requirements have forced tradeoffs toachieve better indoor air quality orenergy efficiency. Its not often that atechnology comes along that is a win,win. That technology is UV lights.

BackgroundThe use of Ultraviolet (UV) lamps fordestruction of harmful microorganismsdates back to the late 1800s. Throughout

this article, we will refer to all such effortsand effects as disinfection, although,without more detail, no claim can bemade for the complete eradication of100% of all microorganisms that couldcause some illness in humans. UV lightfor disinfection was first usedcommercially in the late 1930s, and hasbeen used widely in water and airapplications.

Ultraviolet Germicidal Irradiation(UVGI) utilizes the light energy in theUVC bandwidth (UVA is used for

tanning lamps and black lights, UVB fordermatology and tanning) whichproduces germicidal effects on pathogens,scrambling their DNA, thus killingthem and reducing the number of viablebacteria and colony forming units ofmold. It has been scientifically proveneffective, and thousands of drinkingwater plants in Europe and waste waterplants in the United States use UV asone of their primary disinfectants.

The primary difference in using UV inair treatment and surface irradiation isresidence time (i.e. the amount of UVenergy a given microorganism is exposedto). With surface irradiation, there is anunlimited amount of residence time.The UV is irradiating the surfaceconstantly and therefore less UV energyis necessary to kill and maintain thesurface at the desired level of disinfection.In a moving air stream, pathogens are

ENGINEERING

In this issue, we make a case forthe expanded use of UltravioletGermicidal Irradiation (UVGI)

in air handling applications. The useof Ultraviolet (UV) lamps for destruc-tion of harmful microorganisms datesback over 100 years. Now, thetechnology and its application have

advanced to the point where it canmake economic sense and improveindoor air quality (IAQ) in nearlyany air handling unit application. Infact, the most recent GSA FacilitiesStandard for federal facilities calls forultraviolet lights to be incorporateddownstream of all cooling coils andabove all drain pans to controlairborne and surface microbial growthand transfer.

In recent times, the threat ofbioterrorism has been prevalent innews stories. In this article, however,we focus on the constant control thatcan be provided by UVGI, instead ofsuch actions that represent singleevents.

UV lights supplied by UltravioletDevices, Inc. (UVDI) are nowavailable as a factory-installed optionon McQuayVision air handlers.The combination of Vision airhandlers and UVDI lights representthe only UL and ETL agency-

approved application of the devices inthe industry.

For more information on UV lightsand Vision air handlers, contact yourlocal McQuay Representative or visitwww.mcquay.com.

Hugh CrowtherDirector of ApplicationsMcQuay North America

S Y S T E M S O L U T I O N S

Edition No. 15 February 2003

CosmicRays GammaRays X-Rays Untraviolet Infrared RadioWavesMicroWaves

Long Wave UV(UV-A)

Middle Wave UV(UV-B)

Short Wave UV(UV-C)

VacuumUV

10-1m10-7m10-9m

100 185 254 300 315 400200 280

10-13m

(nm)

Violet Visible RedUltraviolet light spectrum


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traveling at a high rate of speed andtherefore may be exposed for only afraction of a second. Because of this, itbecomes important to apply more UVenergy (lamps) to get the level ofdisinfection desired.

The dose delivered to disinfect is a product

of UV energy and time using the followingequation:

N(t) = e-kIt

N(0)

Where:N = number of microbesk = rate constantI = UV intensityt = time

Bugs Are Everywhere!Microbiologists will tell you that mold and

bacteria are everywhere (ubiquitous). Theymay be compared to dormant weed seedsthat become active and reproduce with thefirst appearance of activity-conducivemoisture. Control of these microorganismscan be likened to controlling mosquitoes:no matter how much we spray and/oreliminate standing rainwater from ourproperty, the mosquitoes come back in fullforce with warm temperatures and highdew points (or at least they do in myneighborhood). And, as the recent spread ofthe West Nile Virus has made so apparent,

microorganisms can spread as far as anyplane, train, automobile or person cancarry them.

Unlike mosquitoes, the majority of moldsand bacteria are not sources of irritation inthe concentrations we encounter in oureveryday lives. However, given the rightconditions warm, humid ambientconditions and/or standing water theirability to multiply exponentially canquickly raise concentrations tounacceptable levels, creating a biological

soup that eventually can contribute toSick Building Syndrome.

In terms of contaminants, mold andbacteria are classified as Bioaerosols airborne products that includemicroorganisms, their fragments, toxinsand waste products. In addition to moldand bacteria, this category includes viruses,spores, metabolic gases (e.g., CO2),microbial volatile organic compounds(MVOC), and toxins called endotoxin andmycotoxin. Bioaerosols have been generally

overlooked until recently, as all werethought to be only a very small part of aircontaminants. The most recognizable oftheir effects in enclosed spaces are theairborne transmission of diseases weassociate with the symptoms of colds andflu. However, many IAQ investigatorsimplicate bioaerosol activity as the most

significant contributor to IAQ problems.

Dilution or Removal?A simple method of determining thehypothetical concentration of airbornecontaminate would be to introduce aquantity of aerosol into an unventilatedclean space, then divide the quantity ofaerosol by the volume of the space. So ifthe space were 25 x 40 x 8 (8000 ft3),and we introduced 20,000 particles ofaerosol, it would be 20,000 8000 or 2.5particles per cubic foot. For a ventilated

space, a simple mass balance could beused, where we eliminate the fixedquantity of aerosol and replace it with acontinuous source (generation rate) ofaerosol. The quantity of supply air in theequation relates to the size of the space andthe number of occupants. Theconcentration then equals that quantity ofair times the filter efficiency (removal rate)that opposes the generation rate and lookslike this:

Concentration =generation rate

cfm x filter eff.What becomes evident is that, if thegeneration rate goes up (increased numberof people, activity or machines and spacesize, etc.), the concentration will go up too.Conversely, if the generation rate staysconstant but either the airflow or removalefficiency (or both) goes up (removal rate),the concentration would come down.

Taking this a few steps further allows us toinclude the outdoor air amount (dilutionrate, which also adds to the recirculated air

for cfm), and its contaminant, which isadded to the generation rate and it lookslike this: (ASHRAE Standard 62-89Appendix E)

Cs =N + VoCo(1-Ef)Vo + RVr Ef

Where:Cs = steady state space concentration per

cubic footN = internally generated contaminant

rate

Vo = outdoor flow rate in cfm per personCo = concentration of contaminant in

outdoor airEf = efficiency of removal device in

percentRVr = returned air recirculated in cfm

If we add assumptions from Standard 62-

1989 and then artificially populate thealgorithm, it can help us understand whathappens in a space:

7 people per 1000 ft2 (ASHRAE 62-89)15 CFM per person of ODA (15 x 7 =

105)1 CFM per square foot Total Supply

(105 + 895 = 1000)Outdoor Concentration of 2500/ft3

Generation Rate of 500/ft3

No removal device;

Cs=500 + 105 .1 2500

1513105 + 895 0

90% efficient removal device;

Cs=500 + 105 .10 2500

168105 + 895 .90

The example above could represent anycontaminant, provided that the removalmethod is effective on the contaminant atthe assumed efficiency percentage . Whatcan be seen is that, if an offendingcontaminant were outdoors, minimizingthe outdoor air quantity could be useful.Also, the role of the removal device

becomes quite evident, as the 90%removal efficiency shown provides almost alogarithmic reduction in concentrations.Thus, as apparent from cleanroomtechnology, the removal rate can be farmore important than attempting to dilutea space with outdoor air.

Why UV Lights?The HVAC industry has worked well for100 years with only limited use of UVlights in clean rooms and other sensitiveapplications. However, UV lights are now a

very logical and cost-effective addition toalmost any air handling system in almostany application. This is particularly true inareas where ambient conditions routinelyinvolve high humidity levels.

The obvious benefit of UV lights is thereduction of surface mold, bacteria andassociated toxins to reduce the level ofcontamination on coils and drain pans(generally the most likely accumulators ofmoisture in an air handling system). Thecombination of filtration and UV lights


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has been shown to be very effective inimproving IAQ, even when UV lights wereadded to an existing air handling system.

Bacteria range in size from 0.2 to 5microns, while viruses are between 0.01and 0.3 microns. Viruses need a host topropagate and, depending on humidity,

they are generally in droplet nuclei formand/or attached to another particle. Whenthe relative humidity drops, it is assumedthey become liberated and approachtheir individual size, so they canmore easily get past our nose hairsand cilia to cause infection (e.g., inthe winter time). Conventional 30-35% efficient, 2-inch pleated filterswill not arrest bacteria or viruses.Bag or cartridge filters in the 90 to95% efficient range will arrest largerbacteria, but will be less effective

against smaller pathogens. HEPAfilters are 99.97% efficient atstopping 0.3 micron particles andare more efficient on these smallerparticles.

While high efficiency and HEPAfilters are an excellent and proven responseto IAQ concerns, they can also addsignificant air pressure drop to the airsystem. (Dirty HEPA filters generally havea 2.3 inch Air Pressure Drop.) In addition,they require considerable space in the air

handler cabinet, which can increase itslength and cost. Adding UV lights tostandard 2-inch pleated filters can offerperformance against microbes approaching

a much more elaborate filtration system,but for a lower initial and operating cost.

UV lights also have the advantage ofdestroying (as opposed to just arresting)surface mold and bacteria along with theairborne ones mentioned above. They domuch of this while the fan is off, making

UV lights a good addition even when highperformance filtration is used.

External to the air handling unit, UVlights can result in cleaner plenums andductwork by reducing the total number ofmicrobials circulated that can collect inthese areas. Building tenants benefit fromlower microbial counts and the odors and

gasses produced by them, which can helpreduce infectious disease, allergies andallergy-induced asthma. Ultimately,building owners can benefit by virtue of

satisfied tenants that are more likely to rentlonger, and are potentially less likely tobring litigation.

Other benefits of UV lights that are not soobvious can include reduced maintenanceand peak equipment performance. Thecontinuous killing action of UV lights

also serves to continuously clean the coiland drain pan. While regular maintenanceand cleaning is always recommended, the

task should involve much less time,effort and chemicals.

Because coils remain cleaner, coilpressure drops and capacities canremain at near new conditions.Clean coils translate into efficientheat transfer and higher energyefficiency. Some studies show thatas much as 37% additional energyis required in equipment with dirtycoils. In addition, a build-up oforganic material (mold andbacteria) can reduce airflowthrough the coils and require theair handler to work harder andconsume more energy.

UV technology has advanced to the pointwhere it can be easily applied in virtuallyany location within an air handler at avery moderate cost as long as there is apower source. The extremely complicatedmath required to determine kill rates can

now be completed with simple to usesoftware modeling programs. There areeven sizing and return on investment(ROI) versions (based on psychometrics,

UV Lights and Filters Augment Each Other

McQuay Vision air handlers are available with an ultraviolet (UV)light option mounted on the downstream side of all cooling coils and

above the unit drain pan. The lights are supplied by UltraViolet

Devices, Inc (UVDI), whose roots date back 54 years in the use of UV

lights for microbial control purposes in both water and air applications.

All UV lights used in Vision air handlers are pre-engineered and factory

installed for proper placement to provide maximum effectiveness. In

addition, UVDI is the only UV light manufacturer to have their units

UL approved to ULs Category Code ABQK specification, HVAC

Accessories, Air Duct Mounted. The combination of Vision air

handlers and UVDI lights represent the only UL and ETL agency-

approved application of the devices in the industry.

For more information on applying UV lights in your new or existing air

handler applications, contact your local McQuay Representative. To

locate your local McQuay Representative, visit www.mcquay.com. For

more information on UV lights, visit the UVDI website at

www.uvdi.com.

McQuay Vision Air Handlers WithUltraviolet Lights

continued on back page.


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For comments or suggestions, please call or write:

Chris Sackrison, Editor

McQuay International13600 Industrial Park Boulevard

Minneapolis, MN 55441

Phone: (763) 553-5419

E-mail: [email protected]

For more information on McQuay products and services, or to speak with your local representative, call (800) 432-1342, or visit our web page at www.mcquay.com .2003 McQuay In ternational

continued from page 3.

operation and maintenance). Lampmaintenance has been reduced becausenewer lamps can last a year even withcontinual use. The lights do not produceozone or other contaminants, whichmitigates environmental concerns.

UV lights have very modest powerrequirements. At a cost around 12cents/day to operate the UV lights,depending on the local utility rates, theycan be economically operated continuously.Given the potential savings in maintenancecosts alone, the annual energy expense forUV lights can potentially be made up in aslittle as one cleaning.

It is, however, important to prevent humanexposure to a lit UVC lamp. Germicidal UV

(UVC) can harm skin and eyes, causingburning of the skin and conjunctivitis of theeyes. In rare cases, it may even causetemporary blindness. Manufacturers havedeveloped safety features to help preventaccidental exposure. It is also possible toinstall cut-off switches at doors and panelsto help prevent exposure when accessing an

area containing a UVC fixture.

ConclusionUV technology has advanced to the pointwhere a case can be made to apply it invirtually any air handler application. Infact, the most recent GSA FacilitiesStandard for federal facilities calls forultraviolet lights to be incorporateddownstream of all cooling coils and above

all drain pans to control airborne andsurface microbial growth and transfer.Details can be found on the GSA websiteat http://gsa.gov/pbs/pc/facilitiesstandards/under Section Five, Sub-Section 5.4, Page130, and the paragraph titled Drains andDrain Pans.

In addition to the IAQ benefits, thepotential cost savings generated by usingUV lights can more than justify theexpense to install and operate theequipment. While UV lights do not replacetraditional filtration, they can augment itseffectiveness and potentially make any airhandling system more effective atdelivering good IAQ.

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McQuay UV News Letter