How to model ASHRAE 90.1 App.G Fan System Operation

Modified on Mon, 2 Dec at 4:27 PM

This article explains how to model the supply and return fan according to ASHRAE 90.1 App.G Fan System Operation.

App.G Fan System Operation

Supply and return fans shall operate continuously whenever spaces are occupied and shall be cycled to meet heating and cooling loads during unoccupied hours. Supply, return, and/or exhaust fans will remain on during occupied and unoccupied hours in spaces that have health and safety mandated minimum ventilation requirements during unoccupied hours.

Night Cycle

The Night Cycle (See: generic Air Handling Unit or Unitary Generic AHU) can be used to enable cycling of an air system to comply with App.G Fan System Operation.

This mechanism offers flexibility in determining how the nighttime on/off decision will be made. The temperature in one specific zone may be used or the temperatures in all the zones connected to the AHU may be sampled. You can specify a temperature tolerance and a run time for the system once it switches on. There is also an applicability schedule for scheduling when this mechanism may be applied.

Cycling fan operation mode

The Cycling fan operation mode (see: Fan on/off) can be also used to model fans according to App.G Fan System Operation.

For example, in System 1 and System 2 packaged terminal fans can be set to operate continuously during occupied hours and to cycle during unoccupied hours by setting the appropriate "Supply air fan operating mode schedule".