AHU – Relief Openings

Relief openings in large buildings should be constructed similarly to outdoor air intakes, but they may require motorized or selfacting backdraft dampers to prevent high wind pressure or stack action from causing the airflow to reverse when the automatic dampers are open. The pressure loss through relief openings should be 25 Pa or less. Low-leakage dampers, such as those for outdoor intakes, prevent rattling and minimize leakage. Relief dampers sized for the same air velocity as the maximum outdoor air dampers facilitate control when an air economizer cycle is used. The relief air opening should be located so that the exhaust air does not short-circuit to the outdoor air intake.

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