User Guide

12
HRV Defrost Strategies (Fan Defrost and Damper Defrost)
Fan Defrost
Models 455FD, 700 FD, 650FD, 1200FD
Fan defrost HRV's are equipped with an electronically
controlled fan defrost system to remove frost that col-
lects on the warm air side of the aluminum heat transfer
surfaces of the heat exchanger core. When the outside
air temperature drops below 27°F (-3°C), defrost is acti-
vated which provides for an automatic defrost cycle.
During the automatic defrost cycle the fresh air supply is
shut off while the exhaust fan continues to operate. This
allows warm inside air to flow through the heat exchang-
er core melting frost accumulation. After the defrost pe-
riod, the fresh air supply fan automatically returns to the
normal speed and fresh outside air continues to be
drawn into the building. Water from the melted frost
collects in the bottom drip pans and drains out through
the bottom drain connections. The defrost cycle repeats
automatically until the air temperature rises above 27°F
(-3°C).
Damper Defrost
Models 455DD, 700DD, 650DD, 1200DD
These damper defrost HRV's have an electronically con-
trolled damper defrost mechanism. If the outside temper-
ature drops below 27°F (-3°C ), the defrost timer is acti-
vated. A motor driven damper door mechanism opens
the defrost port and at the same time closes off the sup-
ply air from outside. After the defrost period, the damper
operates in the opposite direction to close off the defrost
port and reopen the fresh air at the supply port. Defrost
cycle repeats until the temperature again rises above 27°
F (-3°C).
Defrost Time Adjustment
DIP switch #8 will adjust the defrost time. Do not
change any of the other DIP switch settings.
455FD/DD, 700FD/DD, 650FD/DD, 1200FD/DD
Change DIP switch #8 only as illustrated on
this page. Do not adjust any other switches.
ATTENTION
!
Factory Setting (DIP Switch 8 OFF)
The HRV enters defrost mode when outdoor tempera-
tures drop below 27°F (-3°C).
The factory defrost cycle is 4 minutes defrost with a 30
minute run time.
Increased Defrost Time (DIP Switch 8 ON)
Cooler climates may require a more aggressive defrost
cycle.
Positioning DIP switch 8 to ON will initiate a 4 minute
defrost with a 20 minute run time.