ASHRAE Requires Mechanical Ventilation in Naturally Ventilated Commercial Buildings

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