GENERAL INFORMATIONPRODUCT INFORMATIONINTEGRATION INTO SYSTEMORDERING INFORMATION SYSTEM DESIGN
Control logic
Safety control logic
requirements
Cycle rate limit
requirements
Oil management logic
recommendations
Defrost logic
recommendations /
Reversible systems
Danfoss requires a minimum compressor running
time of 2 minutes to ensure proper oil return and
sufficient motor cooling.
Additionally, compressor must not exceed 12
starts per hour.
In some cases, oil management can be enhanced
by control logic:
• If oil return test failed, a function can be
integrated in control logic to run all compressors
simultaneously during 2 minutes every hour in
order to boost oil return. Time and delay can
be fine-tuned by oil return test N°1 in section
“Manage oil in the circuit”. During oil boost, pay
special attention to superheat management to
avoid liquid flood back.
• In manifold system, after running long time in
full load, oil unbalance may appears. A function
can be implemented in control logic to stop all
manifold compressors during one minute every
two hours in order to balance oil. Time and delay
can be fine-tuned by Oil balancing test N°2 in
section “Manage oil in the circuit”.
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. Reducing refrigerant flooding to compressor
by transferring liquid refrigerant from one
exchanger to the other before reversing valve
thanks 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 WV stays in cooling 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”.
In reversible systems, to ensure compressor reliability, the 4-way valve must not reverse when the compressor is stopped due to heating or
cooling demand (stop on thermostat).
Compressor 1
Compressor 2
4WV
EXV
ON
ON
Heating
100%
Safeties
Tripping conditions Re-start conditions
Value Time Value Time
HP safety switch
See Pressure settings table
from section “Manage
operating envelope”
Immediate, no delay.
No by-pass
Conditions back to normal.
Switch closed again
Manual reset
LP safety switch
Maximum 5 auto reset during
a period of 12 hours, then
manual reset.
Electronic module (Motor
protection, DGT)*
Contact M1-M2 opened
Maximum 5 auto reset during
a period of 12 hours, then
manual reset.
* only for DSH240 to DSH485.
R
47FRCC.PC.045.A7.02
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