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 1.5 bar (R22,R407C),
2.5 bar (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:
Defr
ost star
t. S
top all c
ompr
essors
4 W
ay
Valv
e (4W
V) sta
ys in hea
ting
mode
.
EX
V opened t
o tr
ansf
er liquid fr
om
out
door t
o indoor e
xchanger thanks
to pr
essur
e diff
er
enc
e
W
hen pr
essur
es ar
e almost balanc
ed*,
change 4W
V t
o c
ooling mode
.
W
hen pr
essur
es ar
e almost balanc
ed*,
change 4W
V t
o hea
ting mode
.
Star
t C
p1 and C
p 2 with 0.5 sec
onds
dela
y bet
ween 2 suc
cessiv
e star
ts
Star
t C
p1 and C
p 2 with 0.5 sec
onds
dela
y bet
ween 2 suc
cessiv
e star
ts
Defr
ost end
. S
top all c
ompr
essors
4 W
ay
Valv
e (4W
V) sta
ys in hea
ting
mode
.
EX
V opened t
o tr
ansf
er liquid fr
om
indoor t
o out
door e
xchanger thanks
to pr
essur
e diff
er
enc
e
Defr
ost
* 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%
37
FRCC.PC.012.A7.02
GENER
AL INFORM
ATION
PR
ODUC
T INFORM
ATION
INTEGR
ATION INT
O SY
STEM
ORDERING INFORM
ATION
SY
STEM DESIGN
Содержание Danfoss Maneurop MT
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