Brochure

38 AB218186428184en-US1501
GENERAL INFORMATIONPRODUCT INFORMATIONINTEGRATION INTO SYSTEMORDERING INFORMATION SYSTEM DESIGN
Control logic
Pump-down logic
recommendations
Pump down is initiated prior to shutting
down the last compressor on the circuit by
de-energizing a liquid line solenoid valve
or closing electronic expansion valve. When
suction pressure reached the cut-out pressure,
compressor is stopped, and liquid solenoid valve
or electronic expansion valve remains closed.
Two types of pump-down exist:
• One shot pump down (preferred): when
last compressor of the circuit stops, suction
presssure is decreased 22psi (R22,R407C), 36psi
(R410A) below nominal evaporating pressure.
Even if suction pressure increases again, the
compressor will not restart.
• Continuous pump-down: traditional pump-
dow, Compressor restarts automatically when
suction pressure increases. A non-return valve in
the discharge line is recommended.
Defrost logic
recommendations
In reversible systems, the defrost logic can be
worked out to limit liquid flood back effect by:
1. Running full load during defrost to share liquid
refrigerant between all compressors.
2. Transferring liquid refrigerant from one
exchanger to the other one thanks to pressures.
The following defrost logic combines both
advantages:
Defrost start. Stop all compressors
4 Way Valve (4WV) stays in heating
mode.
EXV opened to transfer liquid from
outdoor to indoor exchanger thanks
to pressure difference
When pressures are almost balanced*,
change 4WV to cooling mode.
When pressures are almost balanced*,
change 4WV to heating mode.
Start Cp1 and Cp 2 with 0.5 seconds
delay between 2 successive starts
Start Cp1 and Cp 2 with 0.5 seconds
delay between 2 successive starts
Defrost end. Stop all compressors
4 Way Valve (4WV) stays in heating
mode.
EXV opened to transfer liquid from
indoor to outdoor exchanger thanks
to pressure difference
Defrost
* EXV Opening degree and time have to be set to keep a minimum pressure for 4 way valve moving.
In any case, defrost logics must respect requirements and tests described in sections “Manage
superheat” and “Manage operating envelope”.
Compressor 1
Compressor 2
4WV
EXV
ON
ON
Heating
100%