ASHRAE 62.1, Section A1.2.2 states:
Er is less than 1.0 for plenum return systems with secondary recirculation (e.g. fan-powered VAV with plenum return)
Er is 0 for ducted return systems with secondary recirculation (e.g. fan-powered VAV with ducted return)
Er is 1.0 for systems with system-level recirculation (e.g. dual-fan dual duct systems with ducted return)
Other system types = 0.75.
Our system is NOT dual-fan or dual-duct and our VAV boxes do NOT have fans and do NOT have secondary recirculation so I would assume this system would be defined as 'other types' and the Er would be 0.75.
GBCI review comment:
The Ventilation Rate Procedure (VRP) calculations have utilized a Zone Secondary Recirculation Fraction, Er, of 0.75. This value is typically used for fan-powered terminal units. Based on the mechanical schedules provided in PI Project Information, the terminal units are shut-off VAV boxes (non-fan-powered); therefore, the Er value should be zero or left blank.
So I guess Er is zero for non-fan powered boxes. But do not understand the logic.
