Supplemental Electric Heat During Heating Mode; Dual Fuel Applications - Heating Mode; Demand Defrost - Rheem P17 Series Installation Instructions Manual

the building load until the maximum compressor
speed is reached. Overdrive is disabled above
32°F. Since the noise level of the compressor
increases as speed increases, the maximum
allowable compressor speed in the Overdrive
Mode can be lowered using the EcoNet
Center Service Menu (RPM Blocking) should
the homeowner find the compressor noise
objectionable in the Overdrive Mode. The current
compressor RPM can also be viewed in the
EcoNet Control Center Service Menu. When the
TM
call for heating has ended, the EcoNet
Center will direct the compressor and outdoor fan
motor to shut down and the indoor blower motor
will ramp down to the minimum air-flow level for
30-45 seconds to extract the residual heating from
the warm indoor coil before it stops.
6.5 Supplemental Electric
Heat in Heating Mode
If the building load should exceeds the heating
capacity in extreme outdoor conditions, the
EcoNet Control Center will direct the air-handler
TM
to energize supplemental electric heat as required
to meet the building load. The indoor air-flow
will be forced to operate at the 2nd stage level
for (-)H2T air-handlers or in the case of EcoNet
enabled (-)HMV air-handlers, the selected electric
heat air-flow level. Refer to the (-)HMV air-hander
installation manual for details on setting electric
heat air-flow. For 13kW heaters and higher, the
supplemental electric heat will be energized in two
stages as required. The compressor and outdoor
blower will continue to operate at maximum
capacity while supplemental electric heat is
energized.
6.6 Dual Fuel Applications
– Heating Mode
If the building load should exceed the heat pump
heating capacity in extreme outdoor conditions,
the EcoNet Control Center will direct the outdoor
TM
unit to shut down and heating responsibility
will be transferred to the gas furnace. An
outdoor ambient temperature can be set in the
EcoNet Control Center to direct the system to
TM
automatically switch to gas heat when the outdoor
ambient temperature drops below that set-
point. If the EcoNet Control Center is set to the
TM
EMERGENCY HEAT (Furnace Only) mode, heating
responsibility will be transferred to the gas furnace.

6.7 Demand Defrost

Defrosting of the outdoor coil in the heating mode
6.0 NORMAL SEQUENCE OF OPERATION
Control
TM
Control
TM
TM
is controlled by the Variable Speed Outdoor
Control (VSODC). (-)P17 heat pumps utilizes
"demand defrost" that initiates a defrost cycle
only when frosting is detected on the outdoor
coil during heating operation. The VSODC
continuously monitors the Outdoor Ambient
Temperature Thermistor (OAT) and Outdoor Coil
Temperature Thermistor (EVAPIN) to determine
when a defrost cycle is required. The following
sequence is followed for defrost cycles.
Defrost Initiation: A defrost cycle is initiated
•
when the following conditions are met.
1. The outdoor coil temperature is below 35°F
[1.7°C].
2. The compressor has operated for at least
34 minutes with the outdoor coil
temperature below 35°F [1.7°C].
3. The VSODC determines a defrost cycle
is required based on the OAT and EVAPIN
temperatures.
If the above conditions are met, the following
action will be taken.
1. The compressor speed is ramped to the
predetermined reversing valve switching
speed for 30 seconds before the reversing
valve is de-energized.
2. The reversing valve is de-energized which
will cause it to shift to the cooling position.
3. The outdoor EXV is driven to the 100%
open position.
4. The outdoor fan motor is de-energized.
5. The indoor air-handler or gas furnace
is directed to supply supplemental heat
to prevent cold air from being discharged
from the supply registers during the
defrost cycle.
6. The compressor speed is ramped to the
pre-determined defrost speed for the
duration of the defrost cycle.
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