AAON RSMV-HP, Technical Manual, Page: 11 / 32

RSMV-HP Technical Guide
SEQUENCE OF OPERATIONS
11
Superheat Control and Heat Pump Operation
Heating and Cooling Superheat
Control
When there is a demand for Heating, the reversing valve changes
the direction and operation of the refrigerant system according to its
confi guration. EXV 1 and EXV 2 that are located at the evaporator
coils are bypassed with a mechanical check valve during Heating.
EXV 3 and EXV 4 (optional) that are located at the condenser coils
are modulated to maintain a Superheat Setpoint. The calculated
Superheat is derived from Coil Temperature Sensors 3 & 4 along
with the Suction Pressure (Saturation) Temperature. The refrigerant
system can be confi gured for one or two Condenser EXVs depending
on the mechanical layout. If two Condenser EXVs are confi gured,
both EXVs will be activated to maintain the Superheat Setpoint when
any of the two compressors are activated.
When there is a demand for Cooling, the reversing valve changes
the direction and operation of the refrigerant system according to its
confi guration. EXV 1 and EXV 2 that are located at the evaporator
coils are modulated to maintain a Superheat Setpoint. The calculated
Superheat is derived from Coil Temperature Sensors 1 and 2 along
with the Suction Pressure (Saturation) Temperature. EXV 3 and
EXV 4 (optional), located at the condenser coils, are bypassed with
a mechanical check valve during Cooling. Since the evaporator coils
are piped in parallel, both EXVs will be activated to maintain the
Superheat Setpoint when any of the two compressors are activated.
Heat Pump Standard Defrost
Operation
If using the RSMV-HP with an installed Coil Temperature Switch,
a Defrost Cycle is available.
If the compressor(s) are operating in the Heating Mode and the
Defrost Coil Temperature Switch closes, the unit will enter the
Defrost Mode, provided the user-adjustable Defrost Interval Timer
has elapsed since the last Defrost Cycle.
In the Defrost Cycle, the reversing valve signal is switched to the
opposite operation, and the compressors are brought to maximum
capacity. Auxiliary Heat will be used to attempt to maintain the
Heating SAT Setpoint.
The unit will leave the Defrost Mode after 10 minutes have elapsed
or the Coil Temperature Switch opens.
If the unit leaves the compressor heating mode, the Defrost Interval
will restart once the unit re-enters the compressor heating mode.
Heat Pump Adaptive Defrost
Operation
The Adaptive Defrost operation adjusts the time interval (Adaptive
Defrost Timer) in between Defrost Mode cycles.
As stated above, the unit will leave the Defrost Mode after 10 minutes
have elapsed or the Coil Temperature Switch opens. If the Defrost
Cycle is terminated because the 10 minute timer runs out, this could
be an indicator that the unit may need more defrost time. To address
this issue, the Adaptive Defrost Timer value will be subtracted from
the original Defrost Interval.
If the Defrost Cycle is terminated between the 8
th
and 9
th
minute, the
Defrost Interval will not be changed.
If the Defrost Cycle is terminated before the 8 th minute, this
could be an indicator that the unit may need less defrost time.
To address this issue, the Adaptive Defrost Timer value will be
inversely proportionally added to the original Defrost Interval as the
termination time moves from 8 minutes to 0 minutes.
Adaptive Defrost can be disabled by setting the VCC-X / VCCX2
Controller’s Adaptive Defrost Timer Setpoint to 0.