ASHRAE Journal - November 2010 - 60

iaq applications
below the 62.1 body odor guideline, and a risk of infectious disease that is not significantly higher than that for continuous ventilation. While the higher ventilation rates specified for intermittent systems in Standard 62.2, provide for rates that result in corresponding time averaged 24-hour indoor air concentrations that are approximately equivalent to those of continuous systems, the peak concentrations are substantially higher during the off periods. We conclude that new homes are being built more airtight for energy conservation purposes, and this combined with the fact that many people never open windows for ventilation, results in very low outdoor air exchange rates and elevated indoor concentration of air contaminants with indoor sources. We note that the Standard 62.2 ventilation rates are insufficient to control formaldehyde concentrations below the eight hour and chronic OEHHA guidelines of 9 µg/m3 and a reduction of the emission rates of formaldehyde from indoor building materials and furnishings, in combination with ventilation, will be required to reduce concentrations below this level. Therefore, it is important that airtight energy-efficient homes be provided with mechanical outdoor ventilation that is at least that prescribed by Standard 62.2. For a 1,764 ft2 (164 m2) home with an 8 ft (2 m) ceiling and three bedrooms, this translates into just 48 cfm (23 L/s), which depending on climate and utility rates, costs between $100 to $300/year for the fan power and energy to heat/cool/dehumidify the outdoor air. Residential intermittent ventilation systems, as operated according to Standard 62.2 recommendations, allow for periods where indoor air contaminant concentrations can increase and exceed short-term exposure guidelines, causing odors, irritation, and increased exposure to airborne infectious disease organisms. This is especially true for intermittent ventilation systems with long cycle times (e.g., greater than two hours). To minimize periods of poor indoor air quality, intermittent ventilation systems should be operated with cycle times no greater than two hours. What we must always remember is that buildings are for people, and thus health must trump energy. When concerns for energy costs exist because of cold or hot climatic conditions, the response should not be to reduce the outdoor air ventilation, but rather to pursue energy conservation measures. Similarly, when concerns are present for high outdoor air contaminant concentrations, then air cleaning measures should be pursued. The home ventilation mantra remains; build tight, but ventilate right.

References
1. Offermann, F.J. 2009. “Ventilation and Indoor Air Quality in New Homes.” California Air Resources Board and California Energy Commission, PIER Energy-Related Environmental Research Program. 2. Offermann, F.J. 2010. “Standard 62.2 Intermittent Residential Ventilation: What’s It Good For, Intermittently Poor IAQ?” Ventilation and Indoor Air Quality and Energy Conservation Conference.

Francis (Bud) J. Offermann, P.E., is president of Indoor Environmental Engineering in San Francisco.

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ASHRAE Journal

November 2010

ASHRAE Journal - November 2010

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