Question-and-Answer Resource for the Building Energy Modeling Community
 | 1 | initial version |
To model a two-speed fan, you need the two-speed coil object (Coil:Cooling:DX:TwoSpeed) with a VAV fan (Fan:VariableVolume), and VAV No Reheat terminal units at the zone (AirTerminal:SingleDuct:VAV:NoReheat). The minimum air flow fraction on the terminal unit should match the Fan Power Minimum Flow Fraction on your fan, the coil's Rated Low Speed Air Flow Rate, and the Central Heating Maximum System Air Flow Ratio in the System:Sizing object (so your heating coil is sized to meet load at low speed). The best example of two speed fans are in the CBECC-Com prototype models (see Retail-Med).
Plot below is Fan Flow (blue) and OA flow (orange) from the Retail-Med CBECC-Com prototype model.
