ORLANDO, Fla. - "Addenda" is not a word that fires the imagination. Nevertheless, the addenda to ASHRAE Standard 62-2001, "Ventilation for Acceptable Indoor Air Quality," will have a major impact on HVAC contractors, especially those who work in commercial system design.

The standard is a living, working document, and the review process has sometimes been grueling. According to Dennis Stanke, a staff applications engineer with Trane, La Crosse, Wis., "Each addendum was drafted, discussed and refined by a balanced committee of industry experts and practitioners. Each addendum was issued for public review - sometimes repeatedly if needed - and revised in response to public comments."

Key changes to the standard reflect advanced understanding of air quality, moisture, air distribution, and the building as a system. Its purpose remains the same: "to specify minimum ventilation rates and indoor air quality that will be acceptable to human occupants and are intended to minimize the potential for adverse health effects." The means of reaching this goal have evolved.

Stanke, who also is vice chair of SSPC 62.1, offered his view of the impact of these addenda on design engineers and contractors, service and installation contractors, and manufacturers.

Filtration And Moisture

Condensate management (addendum 62t):New requirements ensure proper management of condensate produced by dehumidifying coils, for instance, to reduce the likelihood of consistently wet surfaces and the resulting potential for microbial growth in air distribution systems. These are critical in efforts to improve indoor air quality (IAQ).

"Drain pans must drain, drain lines must seal, finned-tube coils must be reasonably easy to clean, and access for inspection and cleaning must be provided for devices that create turbulence in the supply airstream," he said.

System designers may need to add details to drawings, for example, instructing contractors on how to properly install drain seals.

"Installing contractors may need to take extra care to ensure that drain lines are sized properly and that drain seals are both designed and installed properly, to reduce the likelihood of drain pan overflow or (perhaps worse) ingestion of air through the drain line in draw-through coil configurations," Stanke said.

Manufacturers are likely to choose to provide air-handling equipment with properly sloped drain pans, properly sized and placed drain openings, and instructions on proper drain seal design.

Indoor relative humidity and the building envelope (addendum 62x): Other new requirements limit indoor air humidity and specify building envelope design elements, to reduce potential IAQ problems related to microbial growth.

"The mechanical cooling system must be designed so that space relative humidity does not exceed 65 percent at design dew point conditions," Stanke pointed out. "It also must be designed so that mechanical intake airflow exceeds mechanical relief airflow when dehumidifying, to reduce negative building pressure and the resulting infiltration of moisture."

This requirement may add analysis and design work for many engineers and contractors. "Simple HVAC configurations with sensible-only control are unlikely to result in space relative humidity below 65 percent when analyzed psychrometrically at dew point design conditions, especially in humid climates," he said.

"Contractors may notice an increase in the number of systems that use 100 percent outdoor air units, systems that use enhanced unit configurations such as return air bypass, as well as those that require installation of humidity sensors." Manufacturers may offer more sophisticated equipment to ensure direct or indirect control of space humidity at part sensible load conditions.

Particle filtration (addendum 62r): Outdoor air filtration is now mandatory for systems located in areas with high outdoor particle concentrations. The requirement for filters rated at MERV 6 or higher, however, only applies when the designer is using the Ventilation Rate Procedure (VRP). (See page 10.)

"These requirements are expected to have little impact on engineers, contractors, or manufacturers," he said.

Although MERV-6 outdoor air filters may be required, most installations (in fact, all installations with mechanical cooling or other wet devices in the airstream) must include at least a MERV-6 filter upstream of any wet-surface devices, such as dehumidifying coils, to meet other requirements in the standard, Stanke said.

Smoking Distinctions

Minimum ventilation rates (addendum 62o):The minimum rates listed in the standard's Table 6-1, which is used for VRP calculations, now apply only to spaces where smoking is not allowed, Stanke stated.

"Smoking-permitted occupancy categories, such as smoking lounges, are no longer listed and the minimum rates for some occupancy categories, such as bars and cocktail lounges, are reduced to reflect ‘absence of smoking.'

"For smoking-permitted spaces," he continued, "ventilation rates must be increased by an unspecified amount, and/or air cleaning must be increased for higher contaminant-removal rates over that required for no-smoking spaces with the same occupancy category."

In addition, air from smoking-permitted spaces must be exhausted outdoors. It can't be recirculated or transferred to no-smoking areas.

"Engineers must use judgment, based on their knowledge and experience, to determine specific ventilation rates and/or air cleaning efficiencies for smoking-permitted spaces," Stanke said. "Contractors are unlikely to notice any significant impact," he stated.

"Manufacturers of air cleaning equipment may notice an increase in the use of air cleaning devices in some applications," Stanke said. "In general, regulatory agencies may choose to restrict smoking in a broader range of venues, even though such restrictions are not necessary for compliance with Standard 62.1 requirements."

Contaminant containment (addendum 62y): Limiting the transfer or recirculation of contaminants from zone to zone within a system affects smoking-permitted areas, but it's not limited to containing tobacco smoke.

The air in each occupancy category must be classified according to its typical expected contaminant level and/or odor intensity, Stanke said. In general, systems must be designed so that air with a higher classification (that is, more contaminated air) does not transfer or recirculate to zones with air of a lower classification.

In some applications, such as restaurants and some retail stores, designers must recognize the difference in air classifications and create air distribution systems that comply with the air-transfer limitations. "This is new, and perhaps more, work for many engineers," said Stanke.

Airflow And Distribution

Minimum airflow under any load (addendum 62u):"Seemingly innocuous, this brief but important addendum requires that the ventilation system be designed ‘to maintain the minimum outdoor airflow as required by Section 6 under any load condition,'" Stanke explained. "VAV systems must be designed to deliver proper ventilation to the occupied zones regardless of the primary airflow rate."

System designers may need to design VAV systems that modulate the outdoor air intake damper based on primary fan airflow; in response to sensed outdoor airflow; or in response to systems that include injection fans for outdoor air. "Balancing contractors may be responsible for making sure that intake airflow matches the required airflow rate at various primary airflow conditions," Stanke said.

Manufacturers of air-handling equipment may need to include controls to maintain proper intake flow. Manufacturers of airflow-sensing devices may see increased demand for their products.

Air distribution and balancing requirements (addendum 62v): New requirements will ensure that air distribution systems can deliver outdoor air to the occupied spaces. Means for air balancing must be provided and, for systems that mix recirculated air and outdoor air in a supply plenum, the system must be designed to ensure that each zone receives adequate ventilation air.

Designers may spend more time planning some systems, particularly those with plenum mixing, to make sure ventilation air can be properly distributed, Stanke said.

"Contractors may see more installations that require air balancing before startup." Manufacturers of ceiling-mounted terminal equipment, such as water-source heat pumps, may see an increase in the use of terminal-mounted mixing boxes, he said.

Outdoor Air Concerns

Outdoor ozone removal (addendum 62z):What's the point of bringing in more outdoor air if it's more polluted than the indoor air? This addendum is intended for systems in areas with very high levels of outdoor ozone. Gaseous air cleaning devices must be used to remove ozone from intake air with at least 40 percent volumetric efficiency, when using the VRP to determine ventilation rates, Stanke said.

The impact will be limited geographically to a few counties in California and in Texas, he added. "Contractors may be installing more gaseous air cleaners in some locations." Manufacturers of air cleaning devices may see an increased demand for some products. Manufacturers of HVAC equipment may notice specifications that require more space for air cleaners and more fan static pressure capacity.

Outdoor air intake location and protection (addendum 62aa): Protection from rain entrainment, for instance, can help reduce the likelihood of contaminants entering the air supply from known outdoor sources. A table prescribes intake separation distance from various outdoor sources, such as the cooling tower. An appendix offers a performance-based method for calculating separation distances.

"Engineers are likely to work more closely with architects when locating equipment, both indoors and outdoors, and intakes," Stanke said. "Contractors and manufacturers are unlikely to notice significant impact."

Because the standard changes as new addenda are published, he summarized, contractors and others who need to remain up to date "are encouraged to sign up for the free Internet list server for this standard, which provides notice of all public reviews and approved and published addenda and errata."

For more information, visit www.ashrae.org.

Sidebar: The IAQ Procedure And Ventilation Rate Procedure

Two new rates and procedures may have a big impact on some design contractors: the IAQ Procedure and the Ventilation Rate Procedure (VRP).

"Those who have been accustomed to providing ventilation capacity based only on a cfm per person rate, without regard to zone-level or system-level ventilation efficiencies, may find the new procedures more complex," said Trane's Dennis Stanke.

"Although Standard 62-2001 and earlier versions required - albeit somewhat cryptically - that intake airflow for multiple-zone systems be based on worst-case system ventilation efficiency, many engineers ignored this requirement," he said. "Now written in mandatory language, these calculations can no longer be easily ignored."

The actual required outdoor air intake flow, he continued, may actually be less than what was required by Standard 62-2001.

"So perhaps the perceived increase in calculation complexity will be offset in many designs by a reduction in intake airflow and the associated outdoor air preconditioning costs."

IAQ Procedure (addendum 62h and 62i): This alternative to the prescriptive Ventilation Rate Procedure "now requires, in mandatory language, that minimum ventilation rates be determined based on target contaminant concentrations and specified occupant satisfaction levels," he explained.

The committee hopes this requirement will result in more design firms applying the IAQ Procedure more consistently, especially when the design requires specific contaminant levels or specific levels of occupant satisfaction. It also allows for ventilation credit in cases where contaminants are removed by air cleaning devices.

The requirements may be clearer, said Stanke, but design professionals may find that they need to make a lot more judgments and calculations in order to comply. Installation contractors probably won't see a significant impact, "although the materials and processes used during construction may be limited by source-conscious specifications."

"Manufacturers of various products may choose to alter their offering," he said. For instance, air cleaner manufacturers may choose to develop products to remove some contaminants more efficiently.

The Ventilation Rate Procedure (VRP; addendum 62n): This method is used to determine outdoor air rates for the entire system as well as for individual zones. It requires minimum "breathing-zone" outdoor airflow - the minimum amount of outdoor airflow for areas where occupants are. This is based on both a per-person rate and a per-unit-area rate, and it has been prescribed for 63 occupancy categories.

"In general, the new rates and calculation procedure result in slightly lower breathing-zone outdoor air rates compared with Standard 62-2001 in some occupancy categories," said Stanke.

The system outdoor air intake flow is based on the ventilation system type instead of breathing zones. "This quantity is more readily measured than breathing-zone outdoor airflow," he explained.

Finally, the VRP requires minimum exhaust rates from 19 specific occupancy categories, "a substantial increase in the number of spaces with prescribed exhaust requirements."

HVAC equipment manufacturers may notice a change in equipment selection due to changes in outdoor air load, "and perhaps a trend toward 100 percent outdoor air systems to reduce system-level calculation complexity," Stanke said. Manufacturers of outdoor air preconditioning equipment (such as 100 percent outdoor air units and energy recovery devices) may see a change in demand for some products.

- B. Checket-Hanks

Publication date: 03/21/2005