ASHRAE/IES 90.1aj:2016

Relief and return fans are not well addressed by the Standard. It is possible to have fans that have on/off cycling control which results in very poor building pressure control: before the fan comes on, building pressure can be excessive and once it comes on, the building can be pulled negative. This can cause building operators to disable the economizer to avoid these problems. The cost of adding modulating building pressure control is relatively small: the motor can be an ECM or have a VFD and a building pressure sensor is inexpensive