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Home , Air conditioning, Boiler, Cooling tower, Refrigerant, Thermal comfort, Water quality

Appendix B: HVAC Systems and

This appendix provides information ■ age of the design about specific HVAC system designs and ■ climate components in relation to indoor air ■ building codes in effect at the time of quality. It also serves as introductory the design for building owners and managers ■ budget that was available for the project who may be unfamiliar with the terminol- ■ planned use of the building ogy and concepts associated with HVAC ■ owners’ and designers’ individual (heating, ventilating, and ) preferences system design. Further detailed informa- ■ subsequent modifications tion can be found in ASHRAE manuals HVAC systems range in complexity and guides and in some of the guidance from stand-alone units that serve developed by other trade and professional individual rooms to large, centrally associations. (See Guidelines of Care controlled systems serving multiple zones Developed by Trade Associations in in a building. In large modern office Section 5.) Additional information can be buildings with gains from lighting, obtained using Appendix G or through people, and equipment, interior spaces discussion with your facility engineer. often require year-round . Rooms at the perimeter of the same building (i.e., BACKGROUND rooms with exterior walls, , or roof All occupied buildings require a supply of surfaces) may need to be heated and/or Working with the electrical components of an HVAC outdoor air. Depending on outdoor cooled as hourly or daily outdoor weather system involves the risk of conditions, the air may need to be heated conditions change. In buildings over one electrocution and fire. A or cooled before it is distributed into the story in height, perimeter areas at the lower knowledgeable member of the building staff should occupied space. As outdoor air is drawn levels also tend to experience the greatest oversee the inspection of the into the building, indoor air is exhausted or uncontrolled air . HVAC controls. allowed to escape (passive relief), thus removing air contaminants. The term “HVAC system” is used to refer to the equipment that can provide heating, cooling, filtered outdoor air, and control to maintain conditions in a building. Not all HVAC systems are designed to accomplish all of these functions. Some buildings rely on only natural ventilation. Others lack mechanical cooling equipment (AC), and many function with little or no humidity control. The features of the HVAC system in a given building will depend on several variables, including:

HVAC Systems and Indoor Air Quality 121 Some buildings use only natural complains that it is too cold or too hot and ventilation or exhaust fans to remove the observed (measured) conditions are and contaminants. In these buildings, outside of the ASHRAE comfort zone, thermal discomfort and unacceptable then the HVAC system needs to be indoor air quality are particularly likely evaluated. Sometimes the problem can be when occupants keep the windows closed relieved by fine tuning or repairing the because of extreme hot or cold tempera- HVAC system, but in some cases the tures. Problems related to underventilation system cannot perform as expected, and a are also likely when infiltration forces are long-term must be investigated. weakest (i.e., during the “swing seasons” and summer months). TYPES OF HVAC SYSTEMS Modern public and commercial build- Single Zone ings generally use mechanical ventilation systems to introduce outdoor air during the A single air handling unit can only serve occupied mode. is more than one building area if the areas commonly maintained by mechanically served have similar heating, cooling, and distributing conditioned (heated or cooled) ventilation requirements, or if the control air throughout the building. In some system compensates for differences in designs, air systems are supplemented by heating, cooling, and ventilation needs systems that carry or to among the spaces served. Areas regulated the building perimeter zones. As this by a common control (e.g., a single document is concerned with HVAC ) are referred to as zones. systems in relation to indoor air quality, Thermal comfort problems can result if the the remainder of this discussion will focus design does not adequately account for on systems that distribute conditioned air differences in heating and cooling loads to maintain occupant comfort. between rooms that are in the same zone. This can easily occur if: Roles of the HVAC System Operator ■ The cooling load in some area(s) with- and Facility Manager in a zone changes due to an increased The system operator(s) and facility occupant population, increased lighting, manager(s) (or IAQ manager) are among or the introduction of new heat-produc- the most significant factors in determining ing equipment (e.g., , copiers). whether IAQ problems will occur in a ■ Areas within a zone have different solar properly designed, constructed, and exposures. This can produce radiant heat commissioned HVAC system. HVAC gains and losses that, in turn, create systems require preventive maintenance and unevenly distributed heating or cooling prompt repairs if they are to operate needs (e.g., as the sun angle changes correctly and provide comfortable condi- daily and seasonally). tions. The operator(s) must have an adequate understanding of the overall Multiple Zone system design and its limitations. The Multiple zone systems can provide each HVAC system capacity and distribution zone with air at a different by characteristics should be evaluated before heating or cooling the airstream in each renovations to the building, changes in its zone. Alternative design strategies involve occupancy, or changes in the use of an area. delivering air at a constant temperature System operators must be able to while varying the volume of airflow, or respond appropriately to occupant com- modulating with a plaints. For example, if an occupant

122 Appendix B supplementary system (e.g., perimeter hot water piping). TESTING AND BALANCING Constant Volume Modern HVAC systems typically use sophisticated, automatic controls to Constant volume systems, as their name supply the proper amounts of air for heating, cooling, and ventilation in commercial buildings. Problems during installation, operation, mainte- suggests, generally deliver a constant nance, and servicing the HVAC system could prevent it from operating as airflow to each space. Changes in space designed. Each system should be tested to ensure its initial and contin- are made by heating or ued . In addition to providing acceptable thermal conditions cooling the air or switching the air han- and ventilation air, a properly adjusted and balanced system can also reduce operating costs and increase equipment . dling unit on and off, not by modulating Testing and balancing involves the testing, adjusting, and balancing of the volume of air supplied. These systems HVAC system components so that the entire system provides airflows that often operate with a fixed minimum are in accordance with the design specifications. Typical components and system parameters tested include: percentage of outdoor air or with an “air ” feature (described in the ■ all supply, return, exhaust, and outdoor airflow rates ■ Outdoor Air Control discussion that control settings and operation ■ air temperatures follows). ■ speeds and power consumption ■ filter or collector resistance Variable air volume systems maintain The typical test and balance agency or contractor coordinates with the thermal comfort by varying the amount of control contractor to accomplish three goals: verify and ensure the most heated or cooled air delivered to each effective system operation within the design specifications, identify and correct any problems, and ensure the safety of the system. space, rather than by changing the air A test and balance report should provide a complete record of the temperature. (However, many VAV design, preliminary measurements, and final test data. The report should systems also have provisions for resetting include any discrepancies between the test data and the design specifica- tions, along with reasons for those discrepancies. To facilitate future the temperature of the delivery air on a performance checks and adjustments, appropriate records should be kept seasonal basis, depending on the severity on all positions, equipment capacities, control types and loca- of the weather). Overcooling or tions, control settings and operating logic, airflow rates, static , fan speeds, and horsepowers. overheating can occur within a given zone Testing and balancing of existing building systems should be per- if the system is not adjusted to respond to formed whenever there is reason to believe the system is not functioning the load. Underventilation frequently as designed or when current records do not accurately reflect the actual occurs if the system is not arranged to operation of the system. The Associated Air Balance Council recom- mends the following guidelines in determining whether testing and introduce at least a minimum quantity (as balancing is required: opposed to percentage) of outdoor air as ■ When space has been renovated or changed to provide for new occu- the VAV system throttles back from full pancy. airflow, or if the system supply air ■ When HVAC equipment has been replaced or modified. temperature is set too low for the loads ■ When control settings have been readjusted by maintenance or other present in the zone. personnel. ■ After the air conveyance system has been cleaned. BASIC COMPONENTS OF AN HVAC ■ When accurate records are required to conduct an IAQ investigation. ■ When the building owner is unable to obtain design documents or SYSTEM appropriate air exchange rates for compliance with IAQ standards or guidelines. The basic components of an HVAC system Because of the diversity of system types and the interrelationship of that delivers conditioned air to maintain system components, effective balancing requires a skilled technician with thermal comfort and indoor air quality are: the proper experience and instruments. Due to the nature of the work, which involves the detection and remediation of problems, it is recom- ■ outdoor air intake mended that an independent test and balance contractor be used and ■ mixed-air plenum and outdoor air control that this contractor report directly to the building owner, facility manager, or IAQ manager. ■ ■ heating and cooling coils ■ humidification and/or de-humidification equipment

HVAC Systems and Indoor Air Quality 123 FIGURE B-1: Typical HVAC System Components

Courtesy Terry Brennan ■ supply fan The illustration above shows the Camroden Associates ■ ducts general relationship between many of Oriskny, N.Y. ■ terminal device these components; however, many ■ return air system variations are possible. ■ exhaust or relief fans and air outlet ■ self-contained heating or cooling unit Outdoor Air Intake ■ control Building codes require the introduction of ■ outdoor air for ventilation in most build- ■ ings. Most non-residential air handlers are ■ water designed with an outdoor air intake on the The following discussion of these return side of the ductwork. Outdoor air components (each of which may occur introduced through the can be more than once in any total HVAC system) filtered and conditioned (heated or cooled) emphasizes features that affect indoor air before distribution. Other designs may quality. It may be helpful to refer to this introduce outdoor air through air-to-air section when using the HVAC Checklists. heat exchangers and operable windows.

124 Appendix B Indoor air quality problems can be produced when contaminants enter a building with the outdoor air. Rooftop or wall-mounted air intakes are sometimes located adjacent to or downwind of building exhaust outlets or other contami- nant sources. Problems can also result if debris (e.g., bird droppings) accumulates at the intake, obstructing airflow and poten- tially introducing microbiological contami- nants. If more air is exhausted than is introduced through the outdoor air intake, then outdoor air will enter the building at any leakage sites in the shell. Indoor air quality problems can occur if the leakage site is a door to a loading dock, parking garage, or some other area associated with .

Mixed-Air Plenum and Outdoor Air Controls Outdoor air is mixed with return air (air that has already circulated through the HVAC system) in the mixed-air plenum of an air handling unit. Indoor air quality problems frequently result if the outdoor air damper is not operating properly (e.g., if the system is not designed or adjusted to allow the introduction of sufficient outdoor air for the current use of the building. The amount of outdoor air introduced in the occupied mode should be sufficient to meet needs for ventilation and exhaust make-up. It may be fixed at a constant volume or may vary with the outdoor temperature. When dampers that regulate the flow of outdoor air are arranged to modulate, they are usually designed to bring in a mini- Above: The air intake in the background is mum amount of outdoor air (in the located too close to the sanitary vents (the occupied mode) under extreme outdoor straight pipes to the left and in the center temperature conditions and to open as foreground) and the exhaust vent (next to the sanitary vent on outdoor temperatures approach the desired the right side). Below: The return air indoor temperature. Systems that use dampers in this mixed-air plenum are open outdoor air for cooling are called “air (top), but the outdoor air damper (left) is al- most completely closed. Complaints in the economizer cooling” systems. Air building indicate that economizer systems have a mixed air under-ventilation is a problem.

HVAC Systems and Indoor Air Quality 125 temperature controller and thermostat outdoor air at the intake and the calculation that are used to blend return air (typically of the percentage of outdoor air by a at 74°F) with outdoor air to reach a mixed temperature or CO2 balance. air temperature of 55° to 65°F. (Mixed air dioxide measured in an occupied space is temperature settings above 65°F may also an indicator of ventilation adequacy. to the introduction of insufficient quanti- Some investigators use tracer to ties of outdoor air for office space use.) assess ventilation quantities and airflow The mixed air is then further heated or patterns. There are specific methods for cooled for delivery to the occupied spaces. each of these assessments. See Appendix A Air economizer systems have a sensible for more information. or control that signals the outdoor Many HVAC designs protect the coils air damper to go to the minimum position by closing the outdoor air damper if the when it is too warm or humid outdoors. airstream temperature falls below the Note that economizer cycles which do not setpoint of a freezestat. Inadequate provide dehumidification may produce ventilation can occur if a freezestat trips discomfort even when the indoor tempera- and is not reset, or if the freezestat is set to ture is the same as the thermostat setting. trip at an excessively high temperature. If outdoor air make-up and exhaust are Stratification of the cold outdoor air and balanced, and the zones served by each air warmer return air in the mixing plenums is handler are separated and defined, it is a common situation, causing nuisance possible to estimate the minimum flow of tripping of the freezestat. Unfortunately, outdoor air to each space and compare it to the remedy often employed to prevent this ventilation standards such as ASHRAE 62- problem is to close the outdoor air damper. 1989. Techniques used for this evaluation Obviously, solving the problem in this way include the direct measurement of the can quickly lead to inadequate outdoor air in occupied parts of the building.

Air Filters Filters are primarily used to remove particles from the air. The type and design of filter determine the efficiency at removing particles of a given size and the amount of needed to pull or push air through the filter. Filters are rated by different standards and test methods such as dust spot and arrestance which measure different aspects of performance. See the discussion of ASHRAE Standard 52-76 on page 138 of this appendix. Low efficiency filters (ASHRAE Dust Proper air can play an impor-tant Spot rating of 10% to 20% or less) are role in protecting the rest of the HVAC often used to keep lint and dust from system and in maintaining good indoor air clogging the heating and cooling coils of a quality in occupied spaces. Air filters system. In order to maintain clean air in should be selected and main-tained to provide maximum filtration, while not occupied spaces, filters must also remove overtaxing the supply fan capability or , pollens, insects, , dust, and leading to “blow out” situa-tions with no air dirt with an efficiency suited to the use of filtration. Shown above are roll filter (top) and bag, panel, and the building. Medium efficiency filters pleated filters (below). (ASHRAE Dust Spot rating of 30% to

126 Appendix B 60%) can provide much better filtration than low efficiency filters. To maintain the proper airflow and minimize the amount of additional energy required to move air through these higher efficiency filters, pleated-type extended surface filters are recommended. In buildings that are designed to be exceptionally clean, the designers may specify the equipment to utilize both a medium efficiency pre-filter and a high efficiency extended surface filter (ASHRAE Dust Spot rating of 85% to 95%). Some manufacturers recommend high efficiency extended surface filters (ASHRAE Dust Spot rating of 85%) without pre-filters as the most cost effective approach to minimizing and maximizing air quality in modern HVAC VAV systems that serve office environments. Air filters, whatever their design or efficiency rating, require regular mainte- nance (cleaning for some and replacement Choice of an appropriate filter and Pleated medium efficiency for most). As a filter loads up with proper maintenance are important to filters are often preferred over low efficiency filters because particles, it becomes more efficient at keeping the ductwork clean. If dirt they offer added protection particle removal but increases the accumulates in ductwork and if the relative to both the HVAC equipment drop through the system, therefore humidity reaches the dewpoint (so that and to indoor air quality, yet reducing airflow. Filter manufacturers can occurs), then the nutrients they do not clog as easily as high efficiency filters. provide information on the pressure drop and moisture may support the growth of Medium efficiency filters do through their products under different microbiologicals. Attention to air filters is need routine maintenance, conditions. Low efficiency filters, if particularly important in HVAC systems however, which the filter in this photo did not receive. loaded to excess, will become deformed with acoustical liner, which is and even “blow out” of their filter rack. frequently used in air handler fan housings When filters blow out, bypassing of and supply ducts to reduce sound transmis- unfiltered air can lead to clogged coils and sion and provide . Areas dirty ducts. Filtration efficiency can be of duct lining that have become contami- seriously reduced if the filter cells are not nated with microbiological growth must be properly sealed to prevent air from replaced. (See later discussion of ducts bypassing. and duct cleaning .) Sound reduction can Filters should be selected for their also be accomplished with the use of ability to protect both the HVAC system special duct-mounted devices such as components and general indoor air quality. attenuators or with active electronic noise In many buildings, the best choice is a control. medium efficiency, pleated filter because Air handlers that are located in difficult- these filters have a higher removal to-access places (e.g., in places which efficiency than low efficiency filters, yet require ladders for access, have inconve- they will last without clogging for longer nient access doors to unbolt, or are located than high efficiency filters. on roofs with no roof hatch access) will be

HVAC Systems and Indoor Air Quality 127 Heating and Cooling Coils Heating and cooling coils are placed in the airstream to regulate the temperature of the air delivered to the space. Malfunctions of the coil controls can result in thermal discomfort. Condensation on under- insulated pipes and leakage in piped systems will often create moist conditions conducive to the growth of , fungus, and bacteria. During the cooling mode (air condition- ing), the cooling coil provides dehumidifi- cation as water condenses from the air- stream. Dehumidification can only take place if the chilled fluid is maintained at a cold enough temperature (generally below 45°F for water). Condensate collects in the drain pan under the cooling coil and exits via a deep seal trap. Standing water will accumulate if the drain pan system has not been designed to drain completely under all operating conditions (sloped toward the drain and properly trapped). Under these conditions, molds and bacteria will proliferate unless the pan is cleaned frequently. It is important to verify that condensate Without proper installation more likely to suffer from poor air filter lines have been properly trapped and are and maintenance, rust and maintenance and overall poor mainte- charged with . An improperly corrosion may accumulate in condensate pans under nance. Quick release and hinged access trapped line can be a source of contamina- heating and cooling coils. doors for maintenance are more desirable tion, depending on where the line termi- The rust in the pan indi-cates than bolted access panels. nates. A properly installed trap could also that it was installed without a Filters are available to remove gases be a source, if the water in the trap pitch or was pitched in the wrong direction, so that water and volatile organic contaminants from evaporates and allows air to flow through did not drain out properly. ventilation air; however, these systems are the trap into the conditioned air. not generally used in normal occupancy During the heating mode, problems can buildings. In specially designed HVAC occur if the hot water temperature in the systems, permanganate oxidizers and heating coil has been set too low in an activated charcoal may be used for gaseous attempt to reduce energy consumption. If removal filters. Some manufacturers offer enough outdoor air to provide sufficient “partial bypass” carbon filters and carbon ventilation is brought in, that air may not impregnated filters to reduce volatile be heated sufficiently to maintain thermal organics in the ventilation air of office comfort or, in order to adequately condi- environments. Gaseous filters must be tion the outdoor air, the amount of outdoor regularly maintained (replaced or regener- air may be reduced so that there is insuffi- ated) in order for the system to continue to cient outdoor air to meet ventilation needs. operate effectively.

128 Appendix B Humidification and Dehumidification Equipment In some buildings (or zones within buildings), there are special needs that warrant the strict control of humidity (e.g., operating rooms, rooms). This control is most often accomplished by adding humidification or dehumidification equipment and controls. In office facili- ties, it is generally preferable to keep relative above 20% or 30% during the heating season and below 60% during the cooling season. ASHRAE Standard 55-1981 provides guidance on acceptable temperature and humidity conditions. (See also the discussion of humidity levels in Section 6.) The use of a properly designed and operated air conditioning system will generally keep relative humidities below 60% RH during the cooling season, in office facilities with normal densities and loads. (See the previous discussion of the cooling coil.) Office buildings in cool climates that have high interior heat gains, thermally efficient envelopes (e.g., insulation), and economizer cooling may require humidi- fication to maintain relative humidity within the comfort zone. When humidi- fication is needed, it must be added in a manner that prevents the growth of micro- biologicals within the ductwork and air handlers. Steam should utilize clean steam, rather than treated , so Above: Occupants of this building complained of an inter-mittant fish tank . that occupants will not be exposed to An investigation showed that this water spray chemicals. Systems using media other humidifi-cation system is regularly than clean steam must be rigorously maintained. The coils are washed roughly every two weeks using fresh , maintained in accordance with the eliminating the need for any use of algacides. manufacturer’s recommended procedures Below: Further investigation identified the to reduce the likelihood of microbiological fact that the maintenance practice was growth. causing the odor problem. This picture of the downstream side of the coils was taken growth problems are more likely one day after the washing. A high pressure if the setpoint located in the stream of water caused algae in the water occupied space is above 45%. The high to foam and float for several days, coinciding with the occupant complaints. limit humidistat, typically located in the ductwork downstream of the point at

HVAC Systems and Indoor Air Quality 129 Fan performance is expressed as the DUCT LEAKAGE ability to move a given quantity of air (cubic feet per minute or cfm) at a given Leakage of air from ducts can cause or exacerbate air quality problems, in addition to wasting energy. In general, sealed duct systems specified with resistance or static pressure (measured in a leakage rate of less than 3% will have a superior life cycle cost analysis inches of water column). Airflow in and reduce the likelihood of problems associated with leaky ductwork. ductwork is determined by the size of the Examples of excessive duct leakage leading to problems include: duct opening, the resistance of the duct ■ leakage of light troffer-type diffusers at the diffuser/light fixture interface configuration, and the velocity of the air when they are installed in a return plenum. Such leakage has been known to cause gross short-circuiting between supply and return, through the duct. The static pressure in a wasting much of the conditioned air. If the “room” thermostat is system is calculated using factors for duct located in the return plenum, the room can be very uncomfortable while length, speed of air movement and changes the temperature in the plenum is operating at the control setpoint. in the direction of air movement. ■ leakage of supply ductwork due to loose-fitting joints and connections It is common to find some differences or “blow outs” of improperly fabricated seams between the original design and the final ■ leakage of return ducts located in crawl spaces or below slabs, allowing installation, as ductwork must share gases and molds to enter the ductwork limited space with structural members and other “hidden” elements of the building system (e.g., electrical conduit, plumbing which is added, is generally pipes). Air distribution problems can set at 70% to avoid condensation (with a occur, particularly at the end of duct runs, potential for subsequent mold growth) in if departures from the original design the ductwork. Adding water vapor to a increase the friction in the system to a building that was not designed for point that approaches the limit of fan humidification can have a negative impact performance. Inappropriate use of long on the building structure and the runs of flexible ducts with sharp bends also occupants’ health, if condensation occurs causes excessive friction. Poor system on cold surfaces or in wall or roof cavities. balancing (adjustment) is another common cause of air distribution problems. Supply Fans Dampers are used as controls to restrict airflow. Damper positions may be After passing through the coil section relatively fixed (e.g., set manually during where heat is either added or extracted, air system testing and balancing) or may moves through the supply fan chamber and change in response to signals from the the distribution system. Air distribution control system. Fire and smoke dampers systems commonly use ducts that are can be triggered to respond to indicators constructed to be relatively airtight. such as high temperatures or signals from Elements of the building can smoke detectors. If a damper is designed also serve as part of the air distribution to modulate, it should be checked during system (e.g., pressurized supply plenums inspections to see that it is at the proper or return air plenums located in the cavity setting. ASHRAE and the Associated Air space above the ceiling tiles and below the Balance Council both provide guidance on deck of the above). Proper coordina- proper intervals for testing and balancing. tion of fan selection and duct layout during the and construction Ducts and ongoing maintenance of mechanical components, filters, and controls are all The same HVAC system that distributes necessary for effective air delivery. conditioned air throughout a building air can distribute dust and other pollutants, including biological contaminants. Dirt or

130 Appendix B dust accumulation on any components of increased levels of pollutants and should an air handling system — its cooling coils, be carried out by experienced workers. plenums, ducts, and equipment housing — Correcting theproblems that allowed the may lead to of the air ductwork to become contaminated in the supply. first place is important. Otherwise, the There is widespread agreement that corrective action will only be temporary. building owners and managers should take The porous surface of fibrous glass duct great precautions to prevent dirt, high liner presents more surface area (which humidity, or moisture from entering the can trap dirt and subsequently collect ductwork; there is less agreement at water) than sheet ductwork. It is present about when measures to clean up therefore particularly important to pay are appropriate or how effective cleaning attention to the proper design, installation, techniques are at making long-term filtration, humidity, and maintenance of improvements to the air supply or at ducts that contain porous . In reducing occupant complaints. addition, techniques developed for The presence of dust in ductwork does cleaning unlined metal ducts often are not not necessarily indicate a current microbio- suitable for use with fibrous glass thermal logical problem. A small amount of dust liner or fiberboard. Such ducts may on duct surfaces is normal and to be require a special type of cleaning to expected. Special attention should be maintain the integrity of the duct (i.e., no given to trying to find out if ducts are heavy brushing tools that might fray the contaminated only where specific prob- inner lining) while removing dirt and lems are present, such as: water damage or debris. biological growth observed in ducts, debris More research on both the efficacy and in ducts that restricts airflow, or dust the potential for unintended exposures to discharging from supply diffusers. building occupants from various cleaning Problems with dust and other contami- techniques is needed before firm guidance nation in the ductwork are a function of can be provided regarding duct cleaning. filtration efficiency, regular HVAC system Pay attention to worker safety when maintenance, the rate of airflow, and good working with air handling systems housekeeping practices in the occupied including during duct cleaning. Any space. Problems with biological pollutants worker who may potentially breathe duct can be prevented by minimizing dust and contaminants or biocides should wear dirt build-up, promptly repairing and suitable protective breathing apparatus. water damage, preventing moisture Workers who are doing the duct cleaning accumulation in the components that are should be encouraged to also look for supposed to be dry, and cleaning the other types of problems, such as holes or components such as the drip pans that gaps in the ducts that could allow contami- collect and drain water. nants to enter the ventilation airstream. In cases where sheet metal ductwork Building managers can obtain more has become damaged or water-soaked, information on the issue of HVAC building owners will need to undertake contamination and cleaning from the clean-up or repair procedures. For professional standards developed by some example, in cases where the thermal liner trade associations (See Guidelines of Care or fiberboard has become water-soaked, Developed by Professional and Trade building managers will need to replace the Associations in Section 5 and refer to affected areas. These procedures should Appendix G for a list of organizations be scheduled and performed in a way that with expertise and materials on these does not expose building occupants to issues.)

HVAC Systems and Indoor Air Quality 131 PRELIMINARY RECOMMENDATIONS ON DUCT CLEANING 1. Any duct cleaning should be vacuum equipment should only be smell, and are not intended to provide scheduled during periods when used with extreme care because high real control of microbiological the building is unoccupied to negative pressure together with limited contaminants. prevent exposure to chemicals airflow can collapse ducts. 7. Use of sealants to cover and loosened particles. 4. Duct cleaning performed with interior ductwork surfaces is not The air handling unit should not be high velocity airflow (i.e., greater recommended. used during the cleaning or as an air than 6,000 cfm) should include No application techniques have been movement device for the cleaning gentle, well-controlled brushing of demonstrated to provide a complete process. The National Air Duct duct surfaces or other methods to or long-term barrier to microbiological Cleaning Association recommends dislodge dust and other particles. growth, nor have such materials been that the system should be run to Duct cleaning that relies only on a high evaluated for their potential health allow at least eight air changes in the velocity airflow through the ducts is not effects on occupants. In addition, occupied space when duct cleaning likely to achieve satisfactory results using sealants alters the surface has been completed. because the flow rate at the duct burning characteristics of the duct 2. Negative air pressure that will surface remains too low to remove material and may void the fire safety draw pollutants to a vacuum many particles. rating of the ductwork. collection system should be 5. Only HEPA filtered (high- 8. Careful cleaning and sanitizing maintained at all times in the efficiency particle arrestor) vacu- of any parts of coils and drip pans duct cleaning area to prevent uming equipment should be used if can reduce microbiological migration of dust dirt, and the vacuum collection unit is inside pollutants. contaminants into occupied the occupied space. areas. Prior to using sanitizers, deodorizers, Conventional vacuuming equipment or any cleansing agents, carefully Where possible, use vacuum may discharge extremely fine particu- read the directions on the product equipment or fans during cleaning late matter back into the atmosphere, label. Once cleaned, these compo- and sanitizing to make sure that rather than collecting it. Duct cleaning nents should be thoroughly rinsed cleaning vapors are exhausted to the equipment that draws the dust and dirt and dried to prevent exposure of outside and do not enter the occu- into a collection unit outside the building occupants to the cleaning pied space. building is also available. People chemicals. 3. If it is determined that the should not be allowed to remain in the 9. Water-damaged or contami- ductwork should be cleaned, immediate vicinity of these collection nated porous materials in the careful attention must be given units. ductwork or other air handling to protecting the ductwork. 6. If biocides are to be used, then system components should be When gaining access to sheet metal select only products registered by removed and replaced. ducts for cleaning purposes, it is EPA for such use, use the products Even when such materials are essential to seal the access hole according to the manufacturer’s thoroughly dried, there is no way to properly in order to maintain the directions, and pay careful atten- guarantee that all microbial growth integrity of the HVAC system. tion to the method of application. has been eliminated. Access doors are recommended if At present, EPA accepts claims and the system is to be cleaned periodi- 10. After the duct system has therefore registers antimicrobials for cally, and all access holes should be been cleaned and restored to use only as sanitizers, not disinfectants identified on the building’s mechani- use, a preventive maintenance or sterilizers in HVAC systems. (See cal plans. program will prevent the recur- Appendix F for definitions of antimicro- Particular attention is warranted rence of problems. bials.) There is some question about when cutting fibrous glass ducts, and whether there are Such a program should include manufacturers’ recommended any application techniques that particular attention to the use and procedures for sealing should be will deposit a sufficient amount of the maintenance of adequate filters, followed stringently. Use existing biocide to kill bacteria, germs, control of moisture in the HVAC duct system openings where or other biologicals that may be system, and periodic inspection and possible because it is difficult to present. Materials such as deodorizers cleaning of HVAC system compo- repair the damage caused by cutting that temporarily eliminate odors caused nents. (See discussion of Preventive new access entries into the by provide only a fresh Maintenance on page 36 in Section ductwork. Large, high volume 5.)

132 Appendix B Terminal Devices Thermal comfort and effective contami- nant removal demand that air delivered into a conditioned space be properly distributed within that space. Terminal devices are the supply diffusers, return and exhaust , and associated dampers and controls that are designed to distribute air within a space and collect it from that space. The number, design, and location (ceiling, wall, floor) of terminal devices are very important. They can cause a HVAC system with adequate capacity to produce unsatisfactory results, such as drafts, odor , stagnant areas, or short-circuiting. Occupants who are uncomfortable because of distribution deficiencies (drafts, odor transport, stagnant air, or uneven temperatures) often try to compensate by Return air is frequently - adjusting or blocking the flow of air from particularly important to maintain the ried through non-ducted ple- supply outlets. Adjusting system flows integrity of the ceiling and adjacent walls nums. It is more difficult to without any knowledge of the proper in areas that are designed to be exhausted, control leakage of pollutants into or out of this type of re- design frequently disrupts the proper such as supply closets, , and turn air system than a ducted supply of air to adjacent areas. Distribu- chemical storage areas. system. tion problems can also be produced if the After return air enters either a ducted arrangement of movable partitions, return air or a ceiling plenum, it is shelving, or other furnishings interferes returned to the air handlers. Some systems with airflow. Such problems often occur if utilize return fans in addition to supply walls are moved or added without evaluat- fans in order to properly control the ing the expected impact on airflows. distribution of air. When a supply and return fan are utilized, especially in a VAV Return Air Systems system, their operation must be coordi- nated in order to prevent under- or over- In many modern buildings the above- pressurization of the occupied space or ceiling space is utilized for the unducted overpressurization of the mixing plenum in passage of return air. This type of system the air handler. approach often reduces initial HVAC system costs, but requires that the designer, Exhausts, Exhaust Fans, and maintenance personnel, and contractors Pressure Relief obey strict guidelines related to life and safety codes (e.g., building codes) that Most buildings are required by law (e.g., must be followed for materials and devices building or plumbing codes) to provide for that are located in the plenum. In addition, exhaust of areas where contaminant if a ceiling plenum is used for the collec- sources are strong, such as facilities, tion of return air, openings into the ceiling janitorial closets, cooking facilities, and plenum created by the removal of ceiling parking garages. Other areas where tiles will disrupt airflow patterns. It is exhaust is frequently recommended but

HVAC Systems and Indoor Air Quality 133 may not be legally required include: achieving a neutral or slightly positive reprographics areas, graphic arts facilities, pressure. beauty salons, smoking lounges, shops, and any area where contaminants are Self-Contained Units known to originate. In some designs, small decentralized units For successful confinement and exhaust are used to provide cooling or heating to of identifiable sources, the exhausted area interior or perimeter zones. With the must be maintained at a lower overall exception of induction units, units of this pressure than surrounding areas. Any area type seldom supply outdoor air. They are that is designed to be exhausted must also typically considered a low priority mainte- be isolated (disconnected) from the return nance item. If self-contained units are air system so that contaminants are not overlooked during maintenance, it is not transported to another area of the building. unusual for them to become a significant In order to exhaust air from the build- source of contaminants, especially for the ing, make-up air from outdoors must be occupants located nearby. brought into the HVAC system to keep the building from being run under negative Controls pressure. This make-up air is typically drawn in at the mixed air plenum as HVAC systems can be controlled manually described earlier and distributed within the or automatically. Most systems are con- building. For exhaust systems to function trolled by some combination of manual and properly, the make-up air must have a clear automatic controls. The control system can path to the area that is being exhausted. be used to fans on and off, regulate It is useful to compare the total cfm of the temperature of air within the conditioned powered exhaust to the minimum quantity space, or modulate airflow and pressures by of mechanically-introduced outdoor air. controlling fan speed and damper settings. To prevent operating the building under Most large buildings use automatic controls, negative pressures (and limit the amount of and many have very complex and sophisti- unconditioned air brought into the building cated systems. Regular maintenance and by infiltration), the amount of make-up air calibration are required to keep controls in drawn in at the air handler should always good operating order. All programmable be slighter greater than the total amount of timers and should have “battery relief air, exhaust air, and air exfiltrating backup” to reset the controls in the event of a through the building shell. Excess make- power failure. up air is generally relieved at an exhaust or Local controls such as room relief outlet in the HVAC system, espe- must be properly located in order to cially in air economizer systems. In maintain thermal comfort. Problems can addition to reducing the effects of un- result from: wanted infiltration, designing and operat- ■ thermostats located outside of the ing a building at slightly positive or neutral occupied space (e.g., in return plenum) pressures will reduce the rate of entry of ■ poorly designed temperature control soil gases when the systems are operating. zones (e.g., single zones that combine For a building to actually operate at a areas with very different heating or slight positive pressure, it must be tightly cooling loads) constructed (e.g., specified at less than ■ thermostat locations subject to drafts or one-half air change per hour at 0.25 to radiant heat gain or loss (e.g., exposed pascals). Otherwise unwanted exfiltration to direct ) will prevent the building from ever

134 Appendix B ■ thermostat locations affected by heat from nearby equipment To test whether or not a thermostat is functioning properly, try setting it to an extreme temperature. This experiment will show whether or not the system is respond- ing to the signal in the thermostat, and also provides information about how the HVAC system may perform under extreme conditions.

Boilers Like any other part of the HVAC system, a boiler must be adequately maintained to operate properly. However, it is particu- larly important that equipment operate properly to avoid hazardous conditions such as explosions or carbon monoxide leaks, as well as to provide good energy efficiency. Codes in most parts of the country require boiler operators to be properly trained and licensed. Modern office buildings tend to have It is important to determine Both ASME and ASHRAE have made much smaller capacity than older periodically whether the recommendations of how much combus- HVAC controls are correctly buildings because of advances in energy tion air is needed for burning appli- calibrated. In addition, time efficiency. In some buildings, the primary clocks must be checked to ances. heat source is recovered from see if they are properly set Elements of boiler operation that are and running. Power failures the chiller (which operates year-round to particularly important to indoor air quality frequently cause time clocks cool the core of the building). and thermal comfort include: to be out of adjustment.

■ Operation of the boiler and distribution Cooling Towers loops at a high enough temperature to Maintenance of a cooling tower ensures supply adequate heat in cold weather. proper operation and keeps the cooling ■ Maintenance of and breeching to tower from becoming a niche for breeding prevent carbon monoxide from escaping , such as into the building. organisms. Cooling tower ■ Maintenance of fuel lines to prevent any must be properly monitored and chemical leaks that could emit odors into the treatments used as necessary to minimize building. conditions that could support the growth of ■ Provision of adequate outdoor air for significant amounts of pathogens. Proper combustion. maintenance may also entail physical ■ Design of the boiler combustion exhaust cleaning (by individuals using proper to prevent re-entrainment, (especially protection) to prevent sediment accumula- from short boiler stacks, or into multi- tion and installing drift eliminators. story buildings that were added after the boiler was installed).

HVAC Systems and Indoor Air Quality 135 FIGURE B-2: Selected Ventilation Recommendations

Occupancy Cfm/person Cfm/ft2 Application (people/1000 ft2)

Food and Beverage Dining rooms 70 20 Service Cafeteria, fast 100 20 Bars, cocktail lounges 100 30 Kitchen (cooking) 20 15

Offices Office space 7 20 Reception areas 60 15 Conference rooms 50 20

Public Spaces Smoking lounge 70 60 1.00

Retail Stores, Sales Floors, and street 30 0.30 Showroom Floors Upper floors 20 0.20 Malls and arcades 20 0.20 Smoking lounge 70 60

Sports and Amusement Spectator areas 150 15 rooms 70 25 Playing floors 30 20 Ballrooms and discos 100 25

Theaters Lobbies 150 20 Auditorium 150 15

Education Classroom 50 15 Music rooms 50 15 Libraries 20 15 Auditoriums 150 15

Hotels, Motels, Resorts, Bedrooms 30 cfm/room Dormitories Living rooms 30 cfm/room Lobbies 30 15 Conference rooms 50 20 Assembly rooms 120 15

SOURCE: ASHRAE Standard 62-1989, Ventilation for Acceptable Air Quality

136 Appendix B Water used because source strength is usually not known. Water chillers are frequently found in large Whichever procedure is utilized in the building air conditioning systems because design, the standard states that the design of the superior performance they offer. A criteria and assumptions shall be docu- water chiller must be maintained in proper mented and made available to those working condition to perform its function responsible for the operation and mainte- of removing the heat from the building. nance of the system. Chilled temperatures should Important features of ASHRAE 62- operate in the range of 45°F or colder in 1989 include: order to provide proper moisture removal during humid weather. Piping should be ■ a definition of acceptable air quality insulated to prevent condensation. ■ a discussion of ventilation effectiveness Other than thermal comfort, IAQ ■ the recommendation of the use of source concerns associated with water chillers control through isolation and local involve potential release of the working exhaust of contaminants fluids from the chiller system. The rupture ■ recommendations for the use of heat disk (safety release) of the system should recovery ventilation be piped to the outdoors, and ■ a guideline for allowable leaks should be located and repaired. levels Waste oils and spent refrigerant should be ■ appendices listing suggested possible disposed of properly. guidelines for common indoor pollutants

ASHRAE STANDARDS AND Standard 55-1981, “Thermal GUIDELINES Environmental Conditions for Occupancy” Standard 62-1989, “Ventilation for Acceptable Air Quality” ASHRAE 55-1981 covers several environ- mental parameters including: temperature, ASHRAE 62-1989 is intended to assist radiation, humidity, and air movement. professionals in the proper design of The standard specifies thermal environ- ventilation systems for buildings. The mental conditions for the comfort of standard presents two procedures for healthy people in normal indoor environ- ventilation design, a “Ventilation Rate” ments for winter and summer conditions. procedure and an “Air Quality” procedure. It also attempts to introduce limits on the With the Ventilation Rate procedure, temperature variations within a space. In acceptable air quality is achieved by addition to specifications for temperature specifying a given quantity and quality of and humidity, guidelines are given for air outdoor air based upon occupant density movement, temperature cycling, tempera- and space usage. Examples of the tables ture drift, vertical temperature difference, listing the prescriptive amounts of outdoor radiant asymmetry, and floor temperatures. air for the Ventilation Rate procedure are Adjustment factors are described for presented at the end of this section. various activity levels of the occupants, The Air Quality procedure is a perfor- and different clothing levels. mance specification that allows acceptable air quality to be achieved within a space by Important features of this standard controlling for known and specifiable include: contaminants. This procedure is seldom ■ a definition of acceptable thermal comfort

HVAC Systems and Indoor Air Quality 137 test and the atmospheric dust spot test. The atmospheric dust spot test is the test used to determine the “efficiency “ of an air cleaner. The values obtained with these two tests are not comparable. For example, a filter with a weight arrestance of 90% may have an efficiency by the atmospheric dust spot test below 40%. The weight arrestance test is generally used to evaluate low efficiency filters designed to remove the largest and heaviest particles; these filters are com- monly used in residential and/or air-conditioning systems or as upstream filters for other air cleaning devices. For the test, a standard synthetic dust is fed into the air cleaner and the proportion (by weight) of the dust trapped on the filter is determined. Because the particles in the standard dust are relatively large, the This air washer is used to ■ a discussion of the additional weight arrestance test is of limited value in remove particles and environmental parameters that must assessing the removal of smaller, respi- water-soluble gaseous contaminants and may also be considered rable-size particles from indoor air. control temperature and ■ recommendations for summer and winter The atmospheric dust spot test is humidity in the airstream. comfort zones for both temperature and usually used to rate medium efficiency air Such systems are subject relative humidity cleaners. The removal rate is based on the to severe bacterial contamination. ■ a guideline for making adjustment for cleaner’s ability to reduce soiling of a activity levels clean paper target, an ability dependent on ■ guidelines for making measurements the cleaner removing very fine particles It should be noted that space tempera- from the air. However, it should be noted tures above 76°F but within the summer that this test addresses the overall effi- comfort envelope have nevertheless been ciency of removal of a complex mixture of associated with IAQ complaints in offices. dust, and that removal efficiencies for Note: As of summer 1991, a revised different size particles may vary widely. Standard 55 was nearly ready. Recent studies by EPA, comparing ASHRAE ratings to filter efficiencies for Standard 52-76, “Method of Testing particles by size, have shown that efficien- Air-Cleaning Devices Used in cies for particles in the size range of 0.1 to General Ventilation for Removing 1 microgram are much lower than the Particulate Matter” ASHRAE rating. This standard is intended to assist profes- Important features of this ASHRAE sionals in the evaluation of air cleaning standard include: systems for particle removal. Two test ■ definitions of arrestance and efficiency methods are described: the weight ■ establishment of a uniform comparative arrestance test and the atmospheric dust testing procedure for evaluating the spot test. The standard discusses differ- performance of air cleaning devices used ences in results from the weight arrestance in ventilation systems

138 Appendix B ■ establishment of a uniform reporting mat for testing the system for acceptance method for performance by the owner. In addition, the guideline ■ methods for evaluating resistance to addresses adjustments of the system to airflow and dust-holding capacity meet actual occupancy needs within the capacity of the system when changes in No comparable guidelines or standards building use are made and are currently available for use in assessing recommissioning is warranted. the ability of air cleaners to remove - eous pollutants or and its progeny. Important features of this guideline include: Guideline 1-1989, “Guideline for the ■ definition of the commissioning process Commissioning of HVAC Systems” ■ discussion of the process involved in a This guideline is intended to assist profes- proper commissioning procedure sionals by providing procedures and meth- ■ sample specification and forms for log- ods for documenting and verifying the ging information performance of HVAC systems so that ■ recommendation for the implementation they operate in conformity with the design of corrective measures as warranted intent. The guideline presents a format for ■ guideline for operator training documenting the occupancy requirements, ■ guidelines for periodic maintenance and design assumptions, and the design intent recommissioning as needed for the HVAC system. It provides a for-

HVAC Systems and Indoor Air Quality 139