Pump Down Question

[Stewie007]

Still engineering here. It was a while ago that it was suggested so I went with the idea of a Pump down. I have one question before I complete the design.

When the compressor evacuates the low side need I worry about the pressure in the condenser? At operation I am going to shoot for somewhere in the neighborhood of 30-40C condensing temperature. So we're talking from 200-260PSIG. Should I worry about considerable pressure increase? In other words, should I be installing a pressure relief device?

[DetroitAC]

Why a pump down cycle? I didn't read the old discussion...

[Stewie007]

Hehe, old discussion is right with a stress on the OLD part. Xeon the MG Pony recommended the pump down along with the CPR valve. Probably 3 years ago. Lol, amazing how priorities change.... I swear its like I'll never finish the dang thing......

Anyways, he was concerned that my low temperature compressor was going to have trouble with start up load. So he told me to use a pump down cycle with a CPR to protect the compressor from overpressure and liquid slugging. Since the compressor is not exactly a chiller compressor, the way I am using it seems to make such equipment mandatory. I'm going to run at hopefully between -15C to -23.3C (0F to -10F).

So this will give me 20 - 40PSI. So will there be enough volume to increase the pressure in the condenser greatly enough that I should worry about reaching 450 PSI? I would think not, but without knowing the volume of refrigerant that will exist on the low side I am not sure.

Edit: I'm never sure about anything. My right side says that it will be no problem. My left side says that it will. Hehe, inner conflict....... its a beeotch.

[Xeon th MG Pony]

Best thing to do is use a slightly over sized condenser this allows for good system efficiency and lower head pressures, if not, simply use a liquid receiver befor the metering device, in this event it is all win win! cap tube or txv

Condenser > Receiver > Solenoid for pump down > Metering device

[Stewie007]

I once thought of using such a thing but wasn't sure how it would affect the system. I'll add it to my design.

[Xeon th MG Pony]

It ensures the metering device a constent suply of liquid only, and can assist in subcooling in some cases, it all so makes the systems volume apear larger as far as charge goes, they are sort of mode operandie for TXV systems.

[Stewie007]

Now I just need to find a place to get large copper tubing and fittings on the cheap..... this design is getting 'spensive...... Thats it below......

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