The following sequence of operation from the Laboratory Control and Safety Solutions Applications Guide (1994), is provided as an example that could be included in the construction bid set:
Each exhaust stack outlet shall be sized to produce an upward airflow velocity of approximately 3,000 feet per minute while exhausting 50% of the minimum facility exhaust airflow rate and with the outside air bypass damper at 50% open. As the facility exhaust airflow rate increases beyond the minimum, the outside air bypass damper shall be modulated toward the closed position as necessary to maintain the required exhaust system static pressure. This shall decrease the amount of outside bypass air and partially compensate for the increased facility exhaust airflow thus limiting the increase in stack discharge velocity.
The two primary (and an optional standby) exhaust fans shall all be identical, and each shall be sized to provide 60% of the required maximum facility exhaust airflow at the exhaust system design static pressure and with the outside air bypass damper at 50% open.
The three primary (and an optional standby) Exhaust Fans shall be identical, and each shall be sized to provide 40% of the required maximum facility-exhaust airflow at the exhaust system design static pressure and with the outside air bypass damper at 50% open.
Each exhaust fan's minimum operating speed shall be sufficient to maintain a minimum of 3,000 feet per minute exhaust stack exit velocity at the required static pressure and with theOutside Air Bypass Damper 50% open.
Static pressure shall be sensed at two locations. One static pressure sensor shall be in the exhaust plenum just after the entry of the main exhaust inlet duct. The other sensor shall be in one of the exhaust system duct branches at the location where the static pressure is anticipated to be at the lowest value (least negative value). Typically, this will be in the longest exhaust system branch duct, at the farthest end from the exhaust plenum.
