INDOOR AIR QUALITY

By Gary Luepke

e ost people involved in the business of indoor air quality (lAO) will agree that it's a com­

plex, multifaceted issue. No "silver bullets" exist to remedy every problem. There are simply too many potential contaminants and sources. Not only do the contami­nants that originate inside a build­ing threaten the quality of its envi­ronment, but those brought in from the outside through the ventilation system and infiltration must be con­sidered as well.

The most common indoor con­taminants are volatile organic compounds (VOCs). A common source of contaminants is out­gassing from interior building mate­rials and furnishings.

Microbiological contaminants, namely bacteria, mold, mildew and fungi, run a close second. Though ventilation provides a means of com­bating contaminants through dilu­tion, the fundamental long-term lAO strategy for any building must be contaminant source control.

Today, we have a good under­standing of the sources and causes of microbiological contamination within a building. These microbes are living organisms and need four basic ingredients to thrive: organic

24 RSES Journal - February 1998

nutrients, moisture in the form of liquid water or high humidity in the air, a surface on which to grow and a lack of light.

Therefore, by keeping the air con­veyance system

inside or outside the building) that distributes a mixture of ventilation and recirculated air through ducts to control terminals located in the indi­vidual zones.

- the air han­dler, ductwork and terminal devices - clean

Typical Terminal System

and dry, you can significantly reduce the poten­tial for microbial contamination within a build­ing. How you accomplish this objective some-what depends on the type of air system in the building.

Air handling systems can be divided into two general cate­gories: central systems and ter­minal systems. A central hvac sys-tem includes a central air han-dling unit (installed either

Outdoor Air---.

VAV Box

/ Supply Air

~ Terminal Unit

~ Return Air

Typical Central System

Rooftop Unit or Air Handler

Return Air

_____ ., _ YAY Box

Return Air

Figure 1. The illustrations depict the two general categories of air-handling systems.

1

Figure 2. A double-sloped condensate drain pan Is recommended for

effective drainage.

EHective hvac equipment and component

design can make maintenance easier and

help ensure proper IAQ. Here are some key

characteristics to look for in equipment and

some basic maintenance tips

By contrast, a terminal hvac sys­tem has a dedicated fan-coil unit, unit ventilator or heat pump in each zone that handles the ventilation, fil­tration and comfort conditioning duties for that specific space. (Figure 1 depicts these two system types.)

ASHRAE Standard 62-1989, Ven­tilation for Acceptable Indoor Air Ouality, defines the present "stan­dard of care" for the design of venti­lation systems used in commercial buildings. Standard 62 not only pro­vides guidance for determining the required amount of ventilation air, but also cites three specific equip­ment design characteristics that can reduce the hvac system's potential for becoming a source of microbial contamination.

These basic characteristics -sloped drain pans, cleanable sur­faces and accessibility - apply to equipment in both system types and can be considered the "lAO equip­ment basics." Before we look at each characteristic in detail, let's briefly review the fundamentals involved with system contaminants.

Malicious microbes In the normal process of dehumidi­fying a building, outdoor ventilation air and recirculated air pass through a cooling coil that lowers the mixed

air temperature below its dew point. This causes some of the water vapor in the air to condense on the cold coil and be removed from the air stream.

The condensate collects in a drain pan beneath the coil (see Fig­ure 2) and eventually flows to the building drain. In this process, some of the particulate matter (dirt) from the passing air stream is washed into the drain pan with the water. This dirt contains organic matter that microbes can use for food.

This food source, coupled with the wet, dark, temperature-con­trolled environment, creates an excellent habitat for mold and fun­gal growth. The mold releases spores into the hvac system then circulates throughout the building. These bioaerosols can have serious health effects on some people.

Until recently, air handlers and terminal units were equipped with flat condensate drain pans. This design allowed water to collect in stagnant pools, fostering the growth of mold and slime and increasing the likelihood of air stream contami­nation.

Another less obvious problem is that the slime can clog the drain line forcing the condensate water to overflow into the bottom of the air

handler or the build­

ing. This can result in more wet

interior surfaces and thus more potential

mold growth, not to mention the more obvi­

ous equipment and building damage that can

result. ASHRAE Standard 62-

1989 states that" ... conden­sate drain pans shall be designed for self-drainage to preclude the buildup of microbial slime." The version of the standard currently under revi­sion (1989R) further defines self­drainage by requiring all drain pans to pass an operational drainage test.

To comply with this requirement, condensate drain pans on all new equipment with cooling coils should be sloped, preferably in two direc­tions, to assure positive drainage. The pans should also be constructed of stainless steel or polymer to resist corrosion and pooling of water.

Proper trapping of all drain con­nections is equally important to reduce the risk of drawing sewer gases into the air handler and dis­tributing them throughout the build­ing. The equipment manufacturer's trapping instructions must be care

February 1998 - RSES Journal 25

INDOOR AIR QUALITY

By Gary Luepke

e ost people involved in the business of indoor air quality (lAO) will agree that it's a com­

plex, multifaceted issue. No "silver bullets" exist to remedy every problem. There are simply too many potential contaminants and sources. Not only do the contami­nants that originate inside a build­ing threaten the quality of its envi­ronment, but those brought in from the outside through the ventilation system and infiltration must be con­sidered as well.

The most common indoor con­taminants are volatile organic compounds (VOCs). A common source of contaminants is out­gassing from interior building mate­rials and furnishings.

Microbiological contaminants, namely bacteria, mold, mildew and fungi, run a close second. Though ventilation provides a means of com­bating contaminants through dilu­tion, the fundamental long-term lAO strategy for any building must be contaminant source control.

Today, we have a good under­standing of the sources and causes of microbiological contamination within a building. These microbes are living organisms and need four basic ingredients to thrive: organic

24 RSES Journal - February 1998

nutrients, moisture in the form of liquid water or high humidity in the air, a surface on which to grow and a lack of light.

Therefore, by keeping the air con­veyance system

inside or outside the building) that distributes a mixture of ventilation and recirculated air through ducts to control terminals located in the indi­vidual zones.

- the air han­dler, ductwork and terminal devices - clean

Typical Terminal System

and dry, you can significantly reduce the poten­tial for microbial contamination within a build­ing. How you accomplish this objective some-what depends on the type of air system in the building.

Air handling systems can be divided into two general cate­gories: central systems and ter­minal systems. A central hvac sys-tem includes a central air han-dling unit (installed either

Outdoor Air---.

VAV Box

/ Supply Air

~ Terminal Unit

~ Return Air

Typical Central System

Rooftop Unit or Air Handler

Return Air

_____ ., _ YAY Box

Return Air

Figure 1. The illustrations depict the two general categories of air-handling systems.

1

Figure 2. A double-sloped condensate drain pan Is recommended for

effective drainage.

EHective hvac equipment and component

design can make maintenance easier and

help ensure proper IAQ. Here are some key

characteristics to look for in equipment and

some basic maintenance tips

By contrast, a terminal hvac sys­tem has a dedicated fan-coil unit, unit ventilator or heat pump in each zone that handles the ventilation, fil­tration and comfort conditioning duties for that specific space. (Figure 1 depicts these two system types.)

ASHRAE Standard 62-1989, Ven­tilation for Acceptable Indoor Air Ouality, defines the present "stan­dard of care" for the design of venti­lation systems used in commercial buildings. Standard 62 not only pro­vides guidance for determining the required amount of ventilation air, but also cites three specific equip­ment design characteristics that can reduce the hvac system's potential for becoming a source of microbial contamination.

These basic characteristics -sloped drain pans, cleanable sur­faces and accessibility - apply to equipment in both system types and can be considered the "lAO equip­ment basics." Before we look at each characteristic in detail, let's briefly review the fundamentals involved with system contaminants.

Malicious microbes In the normal process of dehumidi­fying a building, outdoor ventilation air and recirculated air pass through a cooling coil that lowers the mixed

air temperature below its dew point. This causes some of the water vapor in the air to condense on the cold coil and be removed from the air stream.

The condensate collects in a drain pan beneath the coil (see Fig­ure 2) and eventually flows to the building drain. In this process, some of the particulate matter (dirt) from the passing air stream is washed into the drain pan with the water. This dirt contains organic matter that microbes can use for food.

This food source, coupled with the wet, dark, temperature-con­trolled environment, creates an excellent habitat for mold and fun­gal growth. The mold releases spores into the hvac system then circulates throughout the building. These bioaerosols can have serious health effects on some people.

Until recently, air handlers and terminal units were equipped with flat condensate drain pans. This design allowed water to collect in stagnant pools, fostering the growth of mold and slime and increasing the likelihood of air stream contami­nation.

Another less obvious problem is that the slime can clog the drain line forcing the condensate water to overflow into the bottom of the air

handler or the build­

ing. This can result in more wet

interior surfaces and thus more potential

mold growth, not to mention the more obvi­

ous equipment and building damage that can

result. ASHRAE Standard 62-

1989 states that" ... conden­sate drain pans shall be designed for self-drainage to preclude the buildup of microbial slime." The version of the standard currently under revi­sion (1989R) further defines self­drainage by requiring all drain pans to pass an operational drainage test.

To comply with this requirement, condensate drain pans on all new equipment with cooling coils should be sloped, preferably in two direc­tions, to assure positive drainage. The pans should also be constructed of stainless steel or polymer to resist corrosion and pooling of water.

Proper trapping of all drain con­nections is equally important to reduce the risk of drawing sewer gases into the air handler and dis­tributing them throughout the build­ing. The equipment manufacturer's trapping instructions must be care

February 1998 - RSES Journal 25

III

fully followed to assure correct drainage under all operating condi­tions.

More lAO basics Even with proper equipment de­sign, operation and maintenance, unexpected events such as equip­ment malfunctions, power outages or drainage problems may occur. These can result in wet surfaces, or excessively high humidity levels inside the building. Relative humidi­ty over 60 percent within a building can support microbiological growth on building surfaces.

Therefore, it's important to regularly inspect the entire air han­dler and duct system for signs of contamination as a part of normal hvac system maintenance. If any growth is found, it must be removed immediately.

ASHRAE Standard 62-1989R prohibits the use of exposed insul­ation in wet areas of air handlers. Specifically, ASHRAE states: "Ex­posed internal insulation shall not be used ... from the exit ofthe coil to the end of the drain pan ... unless the insulation is impermeable to water."

The type of materials used on the interior of the hvac equipment and air delivery systems can significantly impact its ability to be cleaned. It has been customary to line the inte­rior surfaces of equipment and duct­work with matte-faced insulation for thermal and acoustical attenuation purposes. However, this porous liner can hold dirt and moisture and is almost impossible to clean, short of removing it altogether, which can be extremely disruptive and costly.

Today, the preferred practice is to use double-wall construction on all larger air handling equipment and to insulate the exterior surfaces of the ductwork. Double-wall construc­tion sandwiches the insulation between an inner and outer metal layer that meets the thermal insula­tion requirements, while providing a cleanable surface.

26 RSES Journal - February 1998

It should be easy to see that pro­viding smooth, nonporous surfaces inside ducts and equipment greatly simplifies inspection and cleaning. The type of equipment involved, however, will determine how this can be accomplished.

For example, terminal equipment such as fan coils and V A V terminals can be lined with either closed-cell foam or foil faced insulation. Both materials provide surfaces that are washable. Central air handlers de­mand a more durable liner like sheet metal (see Figure 3) because of their physical size and maintenance requirements.

The need for smooth, nonporous surfaces that permit thorough clean­ing also applies to drain pans. Only noncorrosive materials should be used to avoid the pitting that ac­companies corrosion. Likewise, the sprayed foam commonly used on

drain pans and other interior sur­faces in the past is no longer accept­able because of its ability to harbor microbial growth and its inability to be thoroughly cleaned.

Access to cleanliness Obviously, a cleanable surface is of limited value if it can't be easily reached. ASHRAE 62-1989R says, "Access doors or panels shall be pro­vided ... for inspection and cleaning of heating (and) ... cooling coils .. . air cleaners ... drain pans ... fans .... " This section of the standard clearly requires all areas of the hvac equip­ment and duct system to be totally accessible for inspection, cleaning and maintenance.

It's an established fact that equip­ment that's easy to service gets ser­viced first and most often. In central air handling equipment, the neces­sary access can be provided with

Figure 3. It'll generally preferable to use cleanable, double-wall construction on larger air handling equipment.

hinged doors and/or removable pan­els (see Figure 4).

Areas accessed frequently, such as filter and cooling coil sections, should be equipped with access doors. Areas accessed less frequently need only to have removable panels. At a minimum, access to the duct­work interior should be provided at areas where dirt is likely to accumu­late, including immediately before and after any duct-mounted devices such as humidifiers and fire dampers.

Equipment designs for terminal products should allow easy inspec­tion and maintenance (for example, filter replacement) with minimal disassembly of the unit. Easy access is especially important for fan coils and unit ventilators. These types of systems typically consist of many units, making inspection and main­tenance a time-consuming process.

Although fan-powered VA V ter­minals don't have cooling coils or drain pans, they must still be designed and located for easy filter replacement and must be accessible for inspection and other normal maintenance within the tight con-

Flgu.re 4. In central air handling equipment, necessary accesS can be provided with hinged

~ doors and/or re,movable panels.

fines of a ceiling plenum. Remember, the key to reducing

the potential for microbiological contamination within an hvac sys­tem is to keep it clean and dry. In addition, all hvac equipment must include the IAO equipment basics: sloped drain pans, cleanable sur­faces and accessibility if you are to satisfy the equipment mandates of ASHRAE Standard 62-1989 as well as the expanded requirements of the revised standard.

One final reminder: Consider all aspects of accessibility when selecting and laying out equipment for a project, whether new construc­tion or renovation. Remember that access for inspection and possible cleaning is required in addition to the standard service clearance requirements .•

Gary L. Luepke is a principal market­ing engineer for the North American Commercial Group of The Trane Co. He is responsible for indoor air quali­ty product communication and the system-level marketing efforts of Trane's air-side businesses.

Engrave your chapter's top achievers or officers' names on an official RSffi Plaque to recognize their achievements. Handsome solid walnut plaque with gold foil RSffi logo preserves their name and accomplishments forever! 25 office titles available (call for list); specify along with name to be engraved. $70 includes name engraving and $5 for each engraved title. To order, call 847-297-6464 or fax your order to 847-297-5038. Pay by check, VISA or MasterCard.

February 1998 - RSES Journal 27

III

fully followed to assure correct drainage under all operating condi­tions.

More lAO basics Even with proper equipment de­sign, operation and maintenance, unexpected events such as equip­ment malfunctions, power outages or drainage problems may occur. These can result in wet surfaces, or excessively high humidity levels inside the building. Relative humidi­ty over 60 percent within a building can support microbiological growth on building surfaces.

Therefore, it's important to regularly inspect the entire air han­dler and duct system for signs of contamination as a part of normal hvac system maintenance. If any growth is found, it must be removed immediately.

ASHRAE Standard 62-1989R prohibits the use of exposed insul­ation in wet areas of air handlers. Specifically, ASHRAE states: "Ex­posed internal insulation shall not be used ... from the exit ofthe coil to the end of the drain pan ... unless the insulation is impermeable to water."

The type of materials used on the interior of the hvac equipment and air delivery systems can significantly impact its ability to be cleaned. It has been customary to line the inte­rior surfaces of equipment and duct­work with matte-faced insulation for thermal and acoustical attenuation purposes. However, this porous liner can hold dirt and moisture and is almost impossible to clean, short of removing it altogether, which can be extremely disruptive and costly.

Today, the preferred practice is to use double-wall construction on all larger air handling equipment and to insulate the exterior surfaces of the ductwork. Double-wall construc­tion sandwiches the insulation between an inner and outer metal layer that meets the thermal insula­tion requirements, while providing a cleanable surface.

26 RSES Journal - February 1998

It should be easy to see that pro­viding smooth, nonporous surfaces inside ducts and equipment greatly simplifies inspection and cleaning. The type of equipment involved, however, will determine how this can be accomplished.

For example, terminal equipment such as fan coils and V A V terminals can be lined with either closed-cell foam or foil faced insulation. Both materials provide surfaces that are washable. Central air handlers de­mand a more durable liner like sheet metal (see Figure 3) because of their physical size and maintenance requirements.

The need for smooth, nonporous surfaces that permit thorough clean­ing also applies to drain pans. Only noncorrosive materials should be used to avoid the pitting that ac­companies corrosion. Likewise, the sprayed foam commonly used on

drain pans and other interior sur­faces in the past is no longer accept­able because of its ability to harbor microbial growth and its inability to be thoroughly cleaned.

Access to cleanliness Obviously, a cleanable surface is of limited value if it can't be easily reached. ASHRAE 62-1989R says, "Access doors or panels shall be pro­vided ... for inspection and cleaning of heating (and) ... cooling coils .. . air cleaners ... drain pans ... fans .... " This section of the standard clearly requires all areas of the hvac equip­ment and duct system to be totally accessible for inspection, cleaning and maintenance.

It's an established fact that equip­ment that's easy to service gets ser­viced first and most often. In central air handling equipment, the neces­sary access can be provided with

Figure 3. It'll generally preferable to use cleanable, double-wall construction on larger air handling equipment.

hinged doors and/or removable pan­els (see Figure 4).

Areas accessed frequently, such as filter and cooling coil sections, should be equipped with access doors. Areas accessed less frequently need only to have removable panels. At a minimum, access to the duct­work interior should be provided at areas where dirt is likely to accumu­late, including immediately before and after any duct-mounted devices such as humidifiers and fire dampers.

Equipment designs for terminal products should allow easy inspec­tion and maintenance (for example, filter replacement) with minimal disassembly of the unit. Easy access is especially important for fan coils and unit ventilators. These types of systems typically consist of many units, making inspection and main­tenance a time-consuming process.

Although fan-powered VA V ter­minals don't have cooling coils or drain pans, they must still be designed and located for easy filter replacement and must be accessible for inspection and other normal maintenance within the tight con-

Flgu.re 4. In central air handling equipment, necessary accesS can be provided with hinged

~ doors and/or re,movable panels.

fines of a ceiling plenum. Remember, the key to reducing

the potential for microbiological contamination within an hvac sys­tem is to keep it clean and dry. In addition, all hvac equipment must include the IAO equipment basics: sloped drain pans, cleanable sur­faces and accessibility if you are to satisfy the equipment mandates of ASHRAE Standard 62-1989 as well as the expanded requirements of the revised standard.

One final reminder: Consider all aspects of accessibility when selecting and laying out equipment for a project, whether new construc­tion or renovation. Remember that access for inspection and possible cleaning is required in addition to the standard service clearance requirements .•

Gary L. Luepke is a principal market­ing engineer for the North American Commercial Group of The Trane Co. He is responsible for indoor air quali­ty product communication and the system-level marketing efforts of Trane's air-side businesses.

Engrave your chapter's top achievers or officers' names on an official RSffi Plaque to recognize their achievements. Handsome solid walnut plaque with gold foil RSffi logo preserves their name and accomplishments forever! 25 office titles available (call for list); specify along with name to be engraved. $70 includes name engraving and $5 for each engraved title. To order, call 847-297-6464 or fax your order to 847-297-5038. Pay by check, VISA or MasterCard.

February 1998 - RSES Journal 27