Some field inspectors like to instructs us on installing solenoid valves at the liquid inlets of two-stage DX cooling coils. The reason for this and they really required or just optional?
LLSVs are installed for three reasons:
1. Pump down sequence – see previous posts on pump down,Other pumps use and operation.
2. Charge migration control – during the off sequence, refrigerant will move to the coldest part of the system. The LLSV minimizes the refrigerant moving and potentially moving to the suction of the compressor. The combination of crankcase heaters and a LLSV keeps most systems out of problems.
3. Evaporator capacity control – you can decrease the evaporator surface area by isolating a coil / TXV. When a compressor is unloaded or common compressor(s) is turned off, you need to match the evaporator area to the compressor capacity. The LLSV will remove a section of an active coil / TXV. Most TXV are only good to 50% of the nominal tonnage.

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