BUENA VISTA, Fla. - Mechanical system code requirements are often based on standards developed by the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE). Ventilation and indoor air quality (IAQ) systems are no exception. So, when ASHRAE announces changes to its low-rise and high-rise ventilation and IAQ standards, HVAC contractors need to listen up.

Standard 62.2-2004, "Ventilation and Acceptable Indoor Air Quality in Low-Rise Residential Buildings," is the only nationally recognized IAQ standard developed solely for residences.

"The standard is still relatively new when it comes to its impact on the industry and the public at large," said Steven Emmerich, with the National Institute of Standards and Technology (NIST), Gaithersburg, Md. "Once the standard begins to be adopted into code and begins to be used more in the field, we expect to see homes with IAQ and reduced moisture problems that provide better value to owners and occupants."

Emmerich chaired a seminar on the standard at ASHRAE's 2005 Winter Meeting. He also spoke on Guideline 24P, "Ventilation and Indoor Air Quality in Low-Rise Residential Buildings," the standard's companion guideline.

Max Sherman, Ph.D., Lawrence Berkeley Laboratory, Berkeley, Calif., addressed efficacy of intermittent ventilation. "How can one compare a ventilation pattern that changes over time to a constant one?" he asked. "That is an issue of interest.

"Standard 62.2 and other ventilation standards usually specify the constant ventilation rate that is required to meet IAQ concerns," he said. "Residential buildings in particular use a variety of ventilation strategies that are not constant over time and need a way of ‘getting credit' for them in the standard." Sherman has developed a mathematical basis for determining the efficacy of such variable ventilation patterns.

Combustion Backdrafting

The 2004 standard contains changes made via two addenda, which are the first changes resulting from continuing maintenance proposals from the public.

The standard no longer contains combustion appliance backdrafting test requirements. The test included in the 2003 standard was based on the best industry-accepted method found in the National Fuel Gas Code, but questions arose about its application to solid fuel-burning appliances, according to David Grimsrud, chair of the committee that wrote the standard.

There also was concern about not being able to perform the test until a home is completed. In that case, the contractor would need to perform remedial balancing at a difficult stage of construction and sale, he said. Although the test requirements have been eliminated, the standard sets an upper limit of exhaust flow to 15 cfm/100 square feet when natural draft combustion appliances are present.

Finally, the standard's climate definitions are now consistent with proposed revisions to the International Code Council's climate zone definitions. This should help simplify implementation of Standard 62.2 into code, said Grimsrud. ASHRAE has proposed that the standard be included in the 2006 International Residential Code.

On A Larger Scale

The society also made strides to communicate changes to Standard 62.1-2004, "Ventilation for Acceptable Indoor Air Quality," for commercial, institutional, and high-rise residential buildings. A seminar held during the Winter Meeting discussed the entire standard, "one section at a time, to enable users to better understand the changes that have occurred and the rationale behind those changes," said Eli Howard, who chaired the seminar.

There were a lot of changes to review. The 2004 standard contains 17 addenda that were included during continuous maintenance. The methodology for calculating ventilation rates for buildings, for example, is fundamentally changed for the first time in 15 years, said Howard, who is with the Sheet Metal and Air Conditioning Contractors' National Association (SMACNA), Chantilly, Va. The standard also contains new requirements for building components and systems.

Andy Persily, Ph.D., also with NIST, introduced and reviewed the standard. He covered the outdoor air quality assessment, IAQ procedure, and the content of new appendices.

"The new outdoor air quality assessment clarifies what one must do with respect to evaluating outdoor air quality, which is much clearer than in the 2001 standard," Persily said.

"In addition, the new IAQ procedure uses mandatory/enforceable language, making it much clearer on how one can comply with this alternative, performance-based procedure."

Dennis Stanke of Trane, La Crosse, Wis., discussed multiple-zone systems and other adjustments, such as how to calculate the required outdoor air intake flow for constant-volume reheat, single-duct VAV, and fan-powered VAV systems; how to find default system ventilation efficiency; and how to calculate system ventilation efficiency using equations from the appendix.

What It Means To You

"The impact of the standard has been ongoing, but until now, it wasn't necessarily clear what constituted the requirements of the standard on any given date," Stanke told members of the press at ASHRAE's Winter Meeting Press Breakfast. "With this publication, current requirements will be clear."

The impact on engineers may be significant, he said, because ventilation rates and calculation procedures have been changed. "The impact on contractors is expected to be minor." The impact on manufacturers falls somewhere in between.

Perhaps the most important, highest impact change for all parties, he said is that all requirements are now stated in mandatory - enforceable - language.

The standard is a work in progress, and it's up to HVAC contractors to keep up with its revisions. "Using continuous maintenance procedures, the requirements in the standard have evolved through the ongoing approval of focused addenda," said Stanke - addenda which expand or modify existing requirements and add new ones.

"Standard 62.1 is continuously revised, potentially several times a year, by addenda that are publicly reviewed, approved by ASHRAE and ANSI [American National Standards Institute], and published on the ASHRAE Web site."

Answering Critics

"On the positive side," Stanke explained, "mandatory language eliminates many arguments between various stakeholders and increases consistency of ventilation design from one engineer to the next."

Among the standard's benefits, Stanke pointed out that its system-level calculation procedures, which account for system ventilation efficiency, "ensure that intake airflow is sufficient to provide proper ventilation in all zones." Design calculations have been improved for high-occupant-density areas. Moreover, "Relative humidity limitations may help to reduce indoor air quality problems associated with microbial growth in buildings."

One gets the idea that the committee has been dealing with detractors so long, it knows their complaints practically by rote.

"Some argue that the standard contains too many requirements that seem to be only indirectly related to ventilation," Stanke said, "even though the scope of the standard has always included more than just ventilation rates. ... Some argue that the concept of ventilation rate ‘additivity' adds unnecessary complication and may not be scientifically accurate."

However, he pointed out, "No single model is accurate under all conditions, and significant re-search and long-term practice in the field of industrial hygiene supports the general concept of the additive nature of the impact of multiple contaminants on an organ, like the nose."

Some people may also contend that by including zone air change effectiveness and system ventilation efficiency in multiple-zone systems, the 62.1 committee unnecessarily complicated a standard intended to be used for minimum code levels. "But, ventilation systems inherently exhibit these inefficiencies. Good engineering practice must account for them," Stanke replied.

Last but not least, there is the issue of what to do about no-smoking spaces - the section where this committee has long learned the meaning of damned if you do, damned if you don't. "Some argue that the standard inappropriately limits its prescribed ventilation requirements to no-smoking spaces," Stanke said.

"This is inaccurate, since outdoor rates prescribed for no-smoking spaces must be increased and/or air cleaning levels must be increased for smoking-permitted spaces, although the magnitude of the increase cannot be specified until cognizant authorities set limits on smoking-related contaminant concentrations."

With its latest addenda, Standard 62.1 now presents only minimum ventilation-related requirements written in mandatory language. "All ‘good-practice' recommendations and ‘advisory' phrases have been eliminated," he said. What the standard presents should be considered mandatory in order to follow the standard, not optional or recommended.

"Presenting minimum requirements in mandatory language, the standard is expected to be more easily understood and more uniformly applied by ventilation system designers and other users," Stanke said. It should also be more readily adopted by building code authorities, he said.

For more information or to order either standard, contact ASHRAE Customer Service at 800-527-4723 (U.S. and Canada), 404-636-8400 (worldwide); 1791 Tullie Circle N.E., Atlanta, Ga. 30329; www.ashrae.org.

Publication date: 03/07/2005