Fan power and control for systems 6 and 8

ASHRAE 90.1-2019

G3.1.3.14 Fans in parallel VAV fan-powered boxes shall run as the first stage of heating before the reheat coil is energized. Fans in parallel VAV fan-powered boxes shall be sized for 50% of the peak design primary air (from the VAV air-handling unit) flow rate and shall be modeled with 0.35 W/cfm fan power. Minimum volume set points for fan-powered boxes shall be equal to 30% of peak design primary airflow rate or the rate required to meet the minimum outdoor air ventilation requirement, whichever is larger. The supply air temperature set point shall be constant at the design condition.

PRM-RM

Cooling and heating operation: the terminal fan should be off when the primary airflow fraction is greater than the minimum primary air flow. In EnergyPlus, this is dictated by the “Fan On Flow Fraction”. The Fan On Flow Fraction will be set to 0.0 to allow operating of the secondary fan only when reheat is needed and when the primary air flow is at the minimum.

Key Ruby Methods

Exisiting