View Full Version : Avoiding excessive pressure

15-04-2013, 07:15 PM
Subcritical setup, R134a/CO2 VIAA BPHE.
At standstill, a CO2 can face excessive high pressure when ambient rises.
Therefore, a separate small cooling unit (power by a small generator) is connected to a coil, submerged in the CO2 liquid receiver. This maintains a safe pressure < 40 bar.

But, I have now the following idea. The CO2 flows out of the BPHE, kept by the 134a at -10C. If we're sure we keep the BPHE always at -10C, even at CO2 standstill, then we have just above the receiver a point which can reduce excessive pressure without a separate unit.

Am I correct?

15-04-2013, 07:21 PM
Yes, in Danmark I've seen frequently liquid receivers/flash tanks and other refr.components inside of the cold rooms

15-04-2013, 07:44 PM
Dont understand some little words like BPHE)

monkey spanners
15-04-2013, 07:55 PM
Dont understand some little words like BPHE)

I believe its brazed plate heat exchanger.

15-04-2013, 08:42 PM
Mmmm, NNN not a bad idea but what about PED at all? Why not install it directly in the freezer itself?
But I was thinking that the R134a always-running-cascadecondensor acts also a safety device to limit pressure in the receiver at 26 bar (-10C) because this will be always the coldest point above the receiver.

I was surprised all the necessary items are cheaper than expected.

Indeed, BPHE a brazed plate heat exchanger.

22-04-2013, 01:31 AM
I was thinking about this also, My concern is would the B.P.H.E. remove enough BTU's to keep the pressure low at a stand still?

23-04-2013, 08:46 PM
I can't see any conflict between PED and installing a liquid receiver in the cold room.
For what concerns R134a high side preventing boiling in the low side, it's not effective in case of power failure. That's the main reason why the low side shall be kept cold at all times.