Defrost Operation - Nu-Air NU0103 Operating, Maintaining & Installing

9 Defrost Operation

Proportional Defrost Cycles
Your unit will adjust defrost frequency and duration, based on outdoor temperature: -5º C (23º F)
-15º C (5º F), -20º C (-4º F) and -27º C (-17º F).
Circulation Defrost:
When outdoor temperature is below -5º C (23º F), a defrost cycle is initiated for a fixed duration.
The fresh air motor will run and the exhaust air motor will shut down. A damper will shut off the
cold supply port, directing ambient air through the core for defrosting. The unit will resume
normal operation for a fixed duration, then the processor will read outdoor temperature and
initiate defrost as necessary. Defrost times and intervals will vary according to temperature
below -5º C (23º F).
Timed Fan Shut-Down Defrost:
The outside air before the core is monitored. When below freezing, a timed defrost cycle is
activated. The supply fan shuts down while the exhaust fan continues to move warm air through
the core. After a predefined temperature based time cycle, the HRV reverts to exchange mode.
NOTE: In circulation defrost mode, this unit will not induce indoor negative pressure nor recycle
exhaust air; rather it will redistribute ambient room air.
Rev 2.3 July 17, 2017 18