Danfoss DSF090, Инструкция по применению

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Cp 1
Cp 2
ON
H
1
2
3
4
5
6
7
8
9
Compressor 1
Compressor 2
On
Heating
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
(1)
, change 4WV to cooling mode.
Start Cp1 and Cp 2 with 0.5 seconds delay between 2 successive starts
Defrost
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
When pressures are almost balanced
(1)
, change 4WV to heating mode.
Start Cp1 and Cp 2 with 0.5 seconds delay between 2 successive starts
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).
(1) 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 Operating envelope data .
(1) 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 Operating envelope data .
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
(22 psi) below nominal evaporating pressure with minimum of 1.7 bar(g) (25 psig). Even if suction pressure
increases again, the compressor will not restart.
• Continuous pump-down: traditional pump-down, Compressor restarts automatically when suction pressure
increases up to 4 cycles maximum.
Non Return Valve (NRV)
DSF compressors integrate tight internal non return valve (INRV), therefore no external Non Return Valve (NRV) is
needed.
Reduce moisture in the system
Excessive air and moisture
• can increase condensing pressure and cause high discharge temperatures.
• can create acid giving rise to copper platting.
• can destroy the lubricating properties of the oil.
All these phenomena can reduce service life and cause mechanical and electrical compressor failure.
© Danfoss | Climate Solutions | 2023.06 AB309735209512en-000603 | 53
Scroll compressors, DSF090 to DSF530 | Application