November 2009

Volume 18, Number 11

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ASHRAE Requires Mechanical Ventilation in Naturally Ventilated Commercial Buildings

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A common design solution for green buildings, at least in temperate climates, will now get more complicated. The American Society of Heating, Air-Conditioning, and Refrigerating Engineers (ASHRAE) has decided that natural ventilation alone cannot meet indoor air quality needs in most commercial and high-rise residential buildings. The organization has amended its Standard 62.1-2007 (Ventilation for Acceptable Indoor Air Quality) to require backup mechanical ventilation systems for naturally ventilated buildings. Addendum N has been approved after a public comment period and will be incorporated into the 2010 version of Standard 62.1.

According to Roger Hedrick, chair of the committee that oversees the standard, the addendum is based on the same logic used to require mechanical ventilation for low-rise residential buildings in Standard 62.2. “Residential buildings have traditionally relied on windows for ventilation,” he said, with leakage in the building envelope adding to the flow of air when windows were closed. As buildings became tighter, ventilation came only through the windows, which weren’t always opened by occupants because of weather conditions or air quality concerns. ASHRAE 62.2 now requires mechanical ventilation in low-rise residential buildings for that reason, says Hedrick. “We feel like the same reasoning applies [to commercial buildings],” he told EBN.

The new requirements “will certainly have a cost impact,” said Hedrick. And it is not yet clear how the new requirements will affect other standards and rating systems, such as LEED, that refer to ASHRAE 62.1. According to Brendan Owens, vice president of LEED technical development at the U.S. Green Building Council, the changes will influence how the rating system treats natural ventilation, but it is unclear what any changes will be. He’s also not sure the addendum is the best answer to what he acknowledges is a problem. “Characterizing all naturally ventilated buildings as risks in need of standards action seems like a pretty broad brush for such a complex topic,” he told EBN.

– Allyson Wendt

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Comments (1)

1 Curious Quote posted by Chris Dixon on 12/09/2009 at 08:44 am

The quote attributed to Mr. Owens is a little curious because, according to a telephone conversation I had with the 62.1 committee Chair, Roger Hedrick, it was at Mr. Owens urging that the committee consider adding a requirement in the Standard for mechanical ventilation for "naturally" ventilated buildings. If the USGBC weren't concerned about the risks associated with buildings that are only ventilated "naturally" urging ASHRAE to add the mechanical ventilation requirement to the Standard makes no sense.

I think readers should know that the USGBC is driving this change.

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October 30, 2009