indoor air quality - hvac systems

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16HVACSystems

Overlooked and underappreciated, the heating, ventilation, and air condi-tioning (HVAC) system is the heart and blood of a building. It is the centralconveyance of all indoor air contaminants. It may capture and entrain out-door pollutants. It may be the source of poor indoor air quality, or it mayprovide the means for improving indoor air quality.

HVAC systems are designed to provide air exchange, air cooling/heating,and air distribution throughout a building. Sometimes indoor air qualityand HVAC design and maintenance are in conflict. The purpose of this chap-ter is to present the basic concepts, describe inspection abnormalities, pro-vide a means for HVAC system sampling, and afford a means whereby thisinformation can be assimilated for use in an action plan.

The Basic Design1, 2, 3

A basic HVAC system consists of temperature controls, a fan to move theconditioned air, air filtration media, heating/cooling coils and condensatedrip pan, a heat exchange condenser, and a distribution system (e.g., ducting,air supply louvers, and return air grills). The simplest of these is the residen-tial HVAC system.

A typical residential HVAC consists of a return air damper, a filter, cool-ing/heating coils, condensate drain pan, and fanall of which are housedin an HVAC closet. The condenser, generally located outdoors, circulates aheat exchange fluid (e.g., refrigerant) to and from the cooling/heating coils.Most residential units do not provide for outdoor air. Thus contaminated airis returned back into the conditioned spaces of a home. In these cases, theonly means of diluting the indoor air where there is no outdoor air intakeis through doors, windows, and structural leaks. The tighter the building,the less air exchange is likely to occur. Also of note, residential units haveremote heat exchange condensers with insulated condenser-to-unit convey-ance line.

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Commercial, institutional, and some larger home systems are either similarto that of a typical residence yet housed in a mechanical room, or the HVACunit is unitized as an all-in-one package. Mechanical rooms often serveas a return air plenum (i.e., mixing box or chamber), and, once again, com-ponents are separateparticularly the heat exchange condenser. Separationof components may result in heating/cooling losses when conveyed to theconditioning coils at a remote location.

Unitized units are typically rooftop units (some enclosed within a rooftoppenthouse). See Figure16.1. The unitized units are all in one with the excep-tion of the distribution system. They are more efficient than the units withthe separate heat exchange condensers.

In large volume air spaces, HVAC units may be centralized (e.g., a singleunit) or decentralized (e.g., multiple units). While decentralized multipleunits require less ducting and are less expense initially, the centralized sin-gle units require a more complex means of air distribution, but less mainte-nance is required. Each type of unit has its own problems.

Decentralized multiple units require multiple unit maintenance checks,multiple filter changes, and multiple repairs. Temperature controls are, how-ever, more manageable. An office building with different occupants willgenerally have a separate unit for each office space. Wherein office space isrented, each office is generally responsible for its own HVAC energy costs andmaintenance/upkeep. A maintenance provision is generally in most officespace contracts. This is typically overlooked by the occupant and comes as asurprise to the renter when a problem arises.

Condenser HousingCooling Coils

Heating CoilsFilter(s)

Outside Air Damper

Return Air DuctSupply Air Duct

Blower Fan

FIGURE 16.1Basic design schematic of rooftop air handling unit.

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Centralized single unit distribution systems are zoned. Each zone willgenerally have its own temperature controls. Yet if not properly designed,zones can be problematic, especially as conditions change within each zone.Inconsistencies may result as:

Temperature requirements vary, within a zone, due to increased/decreased occupancy in some areas or introduction of heat-producingequipment (e.g., computers).

Radiant heat gains and losses create uneven distribution of hot andcold as the sun shifts during the day. This is a common cause of com-plaints in office building. On the west side, occupants complain itstoo cold in the morning and too hot in the afternoon.

To further complicate and confuse, some level of awareness and knowledgeis prudent when assessing an HVAC system. A single HVAC system mayhave one or several zones, each of which has its own temperature control(e.g., thermostat), and each zone will have its own dedicated air distributionbox. The distribution boxes are sites where dust, air contaminants, and mois-ture can and do collect. Distribution boxes are briefly described as follows:

Constant Air Volume (CAV)varies temperature of the air deliv-ered to the occupied spaces; temperature is regulated by control-ling delivery of heated and cooled air to a mixing box for each zoneaccording to their requirements; and mixing box may collect, retain,and distribute air contaminants.

Variable Air Volume (VAV)varies air volume delivered to theoccupied spaces as demand needs vary by zone; possible failure toreceive adequate makeup air as required by the American Society ofHeating, Refrigerating and Air Conditioning Engineers (ASHRAE)Standard for Ventilation for Acceptable Indoor Air Quality.

Hybrid Systemsthe best and the worst of both CAV and VAV.

Last, but not least, air distribution is generally, not always, through air duct-ing. The duct may be insulated on the interior or exterior. It may be exter-nally insulated flex or metal ducting. It may be fiberglass board that is itselfinsulated. And the air supply duct in commercial units is often insulatedinternally. Should there be leaks in the duct, air movement can draw outsideair (e.g., hot, dusty, insulated attic) into the air conveyance, delivering con-taminants picked up along the way.

The complexity of HVAC systems is much greater than the simple descrip-tion provided herein. The intent has been merely to cover the basics so theinvestigator can visualize and conceptualize the possible impact a poorlymaintained HVAC system may have on indoor air quality. Should you wishto become more enlightened, books on HVAC systems abound everywhere.


HVAC Visual Inspection

The complexity of an HVAC system is such that there are multiple things thatcan go wrong, multiple things that could contribute or add to building-relatedhealth complaints. From stem to stern, inside the units and outside, the pos-sibilities are endless. Herein is a discussion of a few of the possibilities.They are only a start. Understand the system(s) and do not ignore oddities.Investigate and consider all out-of-place items as part of the puzzle. The devilis in the details!

Outdoor Air Intake

The outdoor air intake louvers should be checked. Some are manuallyadjusted and most are computer-operated. It is not unheard of that the com-puter shows the louvers are open wherein upon inspection they are actuallyclosed. If not closed, the intake may be clogged. See Figure16.2. Do not beoverly surprised to find a cardboard cut-out covering the air intake!

The air intake should ideally have an air filter that filters out the outdoorair that mixes with the air returnafter the return air has been filtered. Inother words, if the intake air is not filtered or minimally filtered (e.g., MERV 4disposable fiberglass filter), most of the outdoor dust and debris will becomeentrained in the HVAC system. As the U.S. Environmental Protection Agency(EPA) National Primary Ambient Air Quality Standard for outdoor total

FIGURE 16.2Rooftop air intake louveropen 100 percent with some collection of debris. (Courtesy ofOmega Southwest Consulting, Canyon Lake, Texas.)

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particles (75 g/m3) exceeds the Leadership in Energy and EnvironmentalDesign (LEED) acceptable limit for indoor total particles (50g/m3), clearlyunfiltered outdoor air can contribute to or be the source of poor indoor airquality.

In commercial and high-rise office buildings, measure and calculate theamount of outside air intake in terms of cubic feet per minute (CFM) perperson. The CFM per occupant should comply with the latest ASHRAEStandard for Ventilation for Acceptable Indoor Air Quality.

Outdoor Air in the Vicinity of Air Intake

Investigate the area(s) around the HVAC air intake for bird (e.g., pigeon) and batdroppings, garbage, leaves, and puddles of water. Locate sewer vents, kitchenexhausts, chimneys, and cooling towers within the vicinity of the air intake.There is no magic number to define vicinity. Use good judgment based onwind patterns and suspect potential source of complaints and how they mightrelate to times when the louvers are most likely to have been open.

Indoor HVAC Equipment Rooms

Many commercial HVAC units are located indoors in a room that also servesas a return air plenum. It is astonishing how often one will find the samerooms being used as storage for wet, dirty mops, paints, solvents, cleaningfluids, oils, and other delightful surprises. Sometimes the investigator willsee something that just doesnt look right. If it looks out of place, it probablyis! For example, a black stain was observed on top of and at the return entry.It was directly under a fluorescent light fixture that was found to have burned,emptying its product on the air handler. The light ballast contained PCBtransformer fluid that burned and blew the by-products onto surfaces withinthe room that served as a return air plenum. See Figure16.3. The by-productsof PCB combustion are among the most toxic chemicals known to man (e.g.,polychlorinated dibenzofurans and polychlorinated dibenzodioxins).

Filters

Check the filter bank(s) for effectiveness. What does this mean? Look for gapsbetween filters and around them. Air will follow the path of least resistance.If it can, it will! Air will go around, not through the filter(s). In a filter bank(e.g., multiple filters), the gaps/openings between the filters should be sealed(e.g., aluminum or duct tape). Sometimes filters are installed improperly orare not sturdy enough to withstand the air movement over the filter surface.The result may be a deformed filter. See Figure16.4. with a large volume ofunfiltered air!

Air filters should be inspected for cleanliness the have been recentlyreplaced, filters are not expected to be squeaky clean, but they should not

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immediately after the filter. The residence had recently been crop dustedwith a powderlike pesticide that showed evidence that it had passed throughthe HEPA filter and returned into the breathing zone of the residents. This isan example of a filter not performing as intended.

The perceived efficiency of air filters does not always withstand a real-ity check. When asked about the efficiency of a filter in a commercial unit,maintenance personnel will generally look up the efficiency that may saythe filter is 95 percent efficient, but looking further, the efficiency on the specsheet is based on a wide range of particle sizes. In reality, maybe the boulders(greater than 10 microns in diameter) are captured, but the fine particles findeasy passage. The Minimum Efficiency Reporting Value (MERV) rating isthe most commonly accepted system and should be sought wherever pos-sible. See Table16.1. Not all filter manufacturers volunteer the MERV ratingwithin their specification sheets.

FIGURE 16.4Multiple filters in large commercial HVACdeformed filter allowing unfiltered air to passthrough.


Condensate Drain Pan

Inspect the condensate drain pan. It should be free of standing water, or atleast it should be in the process of draining as the chilled water condensates.If the air conditioning unit is not operating or there is standing water thatdoes not appear to be draining, either the drain is plugged or the drain panis not leveled to allow for drainage. See Figure16.6. Standing water is a safehaven for mold and bacterial growth.

In colder months when the heater is operating, evidence of poor waterdrainage during the summer months is a rusted, dirty drip pan. Observethe pattern of the rust. If drip pan level is a problem the rust stain will serveas an indicator of that which was and that which will be again. Where therust is even, all the way to the top of the pan, there is or was likely a cloggeddrain. Where the rust is uneven, away from the drain line, the pan is likelynot properly leveled.

In commercial units, maintenance often places biocide tablets in the drippan to minimize microbial growth. These are often dropped into the drippan and forgotten. Biocide tablets come with instructions. These instruc-tions generally include a refresh/change schedule (e.g., monthly). They arerarely read or followed. The presence of an empty container or deteriorated

FIGURE 16.5Hospital bag filtercaked on dust/debris at upwind side with evidence of damage, moldgrowth, and debris on the downwind side of the filter.

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TABLE16.1

MERV Rating Summary

Residential Filters (MERV 1 to 4)MERV 1 (e.g., self-charging woven panel filter)

Arrestance: 65%Spot efficiency: 90Controls: welding fumes and auto emissions

MERV 12 (e.g., nonsupported microfine fiberglass or synthetic media)Arrestance: 7075%Spot efficiency: >95%Controls: 1.03.0 microns

Superior Commercial Buildings and General Surgery (MERV 1316)MERV 13 (e.g., rigid cartridge filters 6 to 12 inches deep)

Arrestance: 8990%Spot efficiency: >98Controls: fine aersols such as sneezes

MERV 16 (e.g., nonsupported microfine fiberglass or synthetic media)Arrestance: NASpot efficiency: NAControls: 0.31.0 microns

Carcinogenic, Pharmaceutical, Radioactive Materials, and Cleanrooms (MERV 17 to 20)

Note: Partial list, shows range of MERV ratings in each functional filter types.


canister is an indication of acknowledged water excesses in the drip pan andan easy fix in place of leveling the pan.

Fan Housing

The fan blades within the fan housing move the air. Subsequently, whatever airpasses through the HVAC will leave a forensic trace of all substanceslargeand small. The fan belt deteriorates with time, and rubber particles are likelyto be a portion of the dirt and dust found on the fan blades and on the outsideof the housing. See Figure16.7. The fan blades are a great collector of materialthat can later be analyzed as if it were a crime scene. Follow the evidence!

Unit and Duct Liner

Chilled water blow-over to the downwind side of the HVAC unit is commoneven in the best of units. A dust covered liner generally contains organic matter(e.g., skin cells)a meal for the molds; the liner gets wetwater for the molds.The outcome is a feltlike carpet of growing mold. There have been report casesof the happy meal deal wherein an investigator did not look at the HVACsystem. He/she found water penetration into the wall cavities of a buildingwith moisture and mold growth in the wall cavity, and stopped the search formold. Having found one source of mold growth, the environmental profes-sional didnt go any further. The investigator felt they had found the cause

FIGURE 16.6Residential HVACwater staining around the base of the unit caused by overflow of drippan.

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of the elevated mold spores, ignoring the possibility that there may be multiplesources, multiple causes, and the HVAC system is ignored.

A tragic example of an ignored HVAC is a 20-story office building wherethe occupants were complaining of severe allergies. An environmental con-sultant investigated and found high mold counts in the occupied spaces andmoisture in the wall cavities associated with leaks in the caulking aroundthe marble exterior of the building. Remediation cost around $750 million,and still complaints persisted. The consultant figured that the cause wasmold in the wall cavity that was escaping from around the wall sockets. So,they persisted in monitoring the wall cavities with no definitive findings.The mold counts still remained high. Another consulting firm investigatedthe HVAC system and found a carpet of mold growth in the HVAC liner.Corrective action was taken, and the indoor air mold counts dropped from2000 counts/m3 to 200 counts/m3. Although there had been no remediation

FIGURE 16.7Fan housingcollection of dust and dirt from air.


on the monitored wall cavity, the fix on the HVAC liner was the silver bullet.The complaints subsided!

Lets go one step further. High humidity can wreak havoc on an entireHVAC system. This occurs where there are no humidity controls or poorlydesigned humidity management systems in a high humidity environment.The evidence is different and distinct from chilled ware blow-over which isgenerally limited to the water impacted areas of the liner. When high humid-ity is the culprit, all liner surfaces (e.g., bottom, sides, and top of the unit andduct) will have a merry display of mold growth. See Figures16.8 and 16.9.Caution! Do not make the assumption that all ducting is affected. Whereasthe supply air duct is covered with mold growth, the air return may not be.Inspect them separately!

Supply Registers and Return Air Grills

Supply registers are generally the telltale sign of problems from within or con-veyance of contaminants through the HVAC system. Return air grills will usu-ally have less of the same as that which is supplied and will be diluted downas the air returns to the air handler. This scenario, however, is not an absolute.Wherein it is drawing in contaminated air directly from the source (e.g., copymachines), the air return grill may display more dirt than the air supply regis-ters. The registers and grill are only signs. A deeper investigation is indicated!

In one instance, there was a disconnect, hole in the air duct through whichmineral wool insulation was drawn into the air stream, conveyed to the air

FIGURE 16.8Residential HVAC systemhigh humidity causing mold growth on unit liner and air supplyducts.

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supply register. The appearance was that of gray dust monsters, swaying over-head from the registers. Black powderlike deposits are often interpreted byoccupants as the black mold wherein it may be shredded fan belt pieces.

Dirt around registers and grills are symptoms. See Figure 16.10. Thesource(s) must be investigated. Contaminants are the clue, and sampling isa must.

FIGURE 16.10Dirty air supply registerwater stain around edge.

FIGURE 16.9Commercial HVAC systemhigh humidity causing mold growth on unit liner.


Level of Maintenance

Evidence of poor HVAC maintenance should set off alarm bells. Some of thesigns include, but are not limited to:

Reduction in energy efficiency Rips and tears in the liners Dirty, clogged cooling coils Frozen chilled water line (see Figure16.11) Used HVAC supplies (e.g., fan belts) left inside air handler Dirty-and-beyond filters (see Figure16.12) Tools and equipment stored in an air handler Rust, dirt, and debris buildup inside the units

FIGURE 16.11Mobile home HVAC unitfrozen chilled water line and condensate water draining throughthe floor in the bottom of the unit.

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Appearance of a slime or fuzzy growth Dirt, damage, and moisture buildup Condition of the fan belt and motor Debris, dirt, and damage to the fan blades (e.g., broken fan blades) Air deodorants in air supply systems (e.g., disguise odors)

Most residential and some commercial HVAC systems have filter(s) inthe return air grill. There is rarely a problem associated with the returnsunless they are forgotten and ignored. In an office building with strangeisolated niche areas of building-related health complaints, an enclosedoffice where the occupant had severe health complaints was found tohave a return air filter that appeared never to have been changed. The fil-ter was so old it had deteriorated to nothing more than a skeleton, a merethread of its original existence. Dust, dirt, and debris collected aroundthe old filter, and droppings were recycled, becoming part of the officeair quality.

Air Duct

Air duct conveys all that precedes it. If there is a problem upstream, it islikely to be downstream.

There may be damaged, leaking air duct that could result in collection.Leaking duct systems pick up contaminants along the way.

FIGURE 16.12Wet, dirty filtercaked with dirt, debris, and mold growth.


The air duct to supply register connection may be loose or completelydetached. Air blowing in the space around the supply register could result incondensation around the register or elevated dust levels from within the attic.

Sometimes the air duct is not just a conveyance for air but for varmints.Rodents and rodent dropping have been found in air ducts. There was even onereport where an inspector went face-to-face with a snakeinside the air duct.A homeowner saw a paw reaching down from one of the air supply registers.Fearing the worst, brave soul that he was, he let it stay there until he could berescued by the professionals. They found a very hungry, very angry raccoon.Dont be surprised at what might be lurking in them there air ducts!

Strategy and Sampling

Most environmental professionals who investigate HVAC systems are search-ing for mold growth. Yet while mold growth is the most commonly encoun-tered assailant in HVAC systems, there may be a worm or two in the pile.

Investigation is first and foremost. Seek and ye shall find. If somethinglooks strange and it can be sampledsample it. If something looks out ofplace and it can be sampledsample it. If you think you know what it is andit can be sampledsample it.

Surfaces within and around the HVAC system may harbor suspect mate-rial. Whereas contaminants may be distributed into occupied air spaces, mostdistribution substances will be growing on, deposited, and retained on thesurfaces. Thus forensic surface sampling, the simplest approach, is in order.

The most direct, easiest form of surface sampling is the clear tape method.This approach involves the following:

Dispense a 2- to 3-inch-long strip of clear tape (e.g., Moore CrystalClear).

Loosely hold the ends of sticky side between your thumb and fore-finger with sticky side facing out, away from your hand.

Lightly touch, only once, the surface you want to sample. As somesamples are fragileDONT PRESS THE TAPE TO THE SURFACE.Just touch the surface!

Lift the tape and stick it to a surface for transport to a laboratory (e.g.,thick plastic zip-lock baggie or microscope slide).

Label the transport surface with an alpha/numeric identifier. Log sample location, identifier, sample date, and other pertinent

information (e.g., appearance, conditions, photo number, etc.). Fill out chain of custody information, and ship to a mold or foren-

sic laboratory.

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A single lift represents quantifiable material (e.g., mold spores) per surfacearea (e.g., square inch). Multiple lifts from several areas are used for identifi-cation only, but too much sample may obscure, obstruct analysis. So whereina larger sample size is required and the surface dust cannot be scooped up,micro-vacuuming is another option.

Micro-vacuuming requires the use of an air sampling pump and filter. Thesampling pump acts as a miniature vacuum. The attached filter serves as thevessel. This method is as follows:

Using plastic tubing, connect a filter (e.g., polycarbonate, glass fiber,or mixed-cellulose ester membrane filter) cassette to either a low-volume or high-volume air sampling pump. FLOW RATE IS NOTIMPORTANT. However, the higher the air flow, the better will bethe collection.

Decide on the area you wish to sample, and create a template thatcan be clean or discarded between samples. The most common tem-plate size is 4 inches by 4 inches (or 10 cm by 10 cm).

Lay down the template and vacuum the area within. Label the cassette with an alpha/numeric identifier. Log sample location, area sampled (e.g., 100 cm2), identifier, sample

date, and other pertinent information (e.g., appearance, conditions,photo number, etc.).

Fill out chain of custody with the sample info and area information,and ship to a mold or forensic laboratory.

The preceding sampling methods have been for surface sampling of rela-tively dry areas. For thick, caked-on, wet surfaces and for water samples(e.g., drip pan water), bulk material collection may be collected in a vial. Thisapproach simply involves scooping up a sample into a collection container.Protective latex or vinyl gloves should be used during the collection of anymaterial that you may contact with your hand (e.g., scooping up water).Water samples should fill the container to the top and be sealed to preventleaks. Dont withhold or limit the thick, caked-on samples, and collect at leasta teaspoonful. In a pinch, if you dont have access to laboratory suppliedsampling vials, you may use a film container or unused medicine bottle andseal them with electricians tape. The laboratory will weigh the sample(s) andprovide results in type of material per gram or measure the liquid weight orper volume of liquid with results reported in term of material per ounce. Login the appropriate information, fill out the chain of custody, and ship to thelaboratory.

Last but not least, one may cut out a portion of the air handling unit inte-rior lining or fiberglass duct. Cut it out or tear it out and place in a zip-lockbaggie or vial. Protective gloves should be worn, and all should be properly


documented as in the preceding methods. Analysis will be reported in mate-rial per weight.

Analyzing the Unknown

The environmental professional will have speculated as to the possible com-ponent of material encountered in and sampled from within the HVAC sys-tem. More often than not, speculation will be the infamous mold sporesand mold growth. In this case, samples may be analyzed by one of manymold laboratories. At that time, the samples should be analyzed for moldspores and growth.

If, however, the investigator wants to go a little further, a forensic labora-tory is in order. Many of the mold laboratories are able to identify most pollenand some allergens in a generic sense. But if you want a better breakdown,forensic laboratories can identify not only particles (e.g., fan belt rubber)but sometimes chemicals that are adsorbed onto the surface of the particlesas well as metal deposits (e.g., deteriorating components), fibers (e.g., resincoated fibers), animal urine, plant matter, and minerals. Forensic laborato-ries are a rare breed. So if a mold laboratory says they can perform forensicanalysis, let it be known that they are limited. A true forensic laboratory willparticle pick (or pick through the sample material under a microscope witha very fine probe) and can identify all components. This is a very expensiveproposition and is often the last resort.

Then, too, if the investigator suspects a specific chemical or substance, thesurface sample (excepting the tape sample) can be analyzed by an indus-trial hygiene/environmental laboratory. This analysis is less expensive thanforensic analysis, but it fails to include all possibilities. All possibilitiesmay be an absurd effort in futility, while a narrow focus may be just whatthe doctor ordered.

Interpretation Not So Simple

The mold spore and growth surface analysis is generally reported in termsof amount and type of mold spores (less than 10 percent coverage) in a com-posite as well as amount and type of mold growth (e.g., 80 percent coverageof Cladosporium).

As for other surface materials, the environmental professional may beseeking confirmation or denial of a specific contaminant already identi-fied in the air within the occupied area(s). There may be a witch huntif

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a previously identified contaminant is in the HVAC system, where is it?How bad is it? Is it in the air supply? Is it in the air return? For instance, apesticide was crop dusted by an applicator inside a residence. A remedia-tion firm cleaned all surfaces and furnishings, but they did not clean theHVAC unit. Upon inspection, a fine white powder was found inside the airhandler immediately beyond a high efficiency box air filter. If the filter hadbeen operating as it should have been, the pesticide should not have gottenthrough. There was a possibility that the white powder was sheet rock dustfrom construction that got into the air handler prior to putting the filter inplace. The intent of the surface sampling had been to determine if the whitepowder was a pesticide or sheet rock. The finding was that the powder wasindeed sheet rock dust.

Summary

This chapter speaks to inspections more so than sampling of HVAC systems.Wherein the HVAC system is the single most conveyance of contaminantsin a building, it is all too often ignored or overlooked. Spend the big buckscleaning up visibly contaminated building materials, complaints temporarilydissipate only to return with a vengeance. Why? The conveyor of all thingsairborne has been overlooked. Always consider the HVAC system. A visibleinspection at the least should be conducted in order to identify anything thatjust doesnt look right. It is a terrible thing to boast that you have identifiedand fixed a problemonly to find the problem still persists.

indoor air quality - hvac systems

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air exchange

air coolingheating

theconditioned air

air grills

hvac units

indoor air contaminants

return air plenum

return air damper