Single stage from 14" of vacuum

[Iceman717]

I came across a plant where they run their blast freezer at -35 F with one screw. I'd probably want my evaporator temp at -45 to -50 for that temp. That's implying about 14"hg suction. One compressor pushing it all the way to head pressure.

Has anyone seen it done this way? I was talking to an engineer who told me that lately, if the target temp is above -40 that they find it's cheaper to single stage than to deal with a booster compressor and intercooler.

Seems like a bit of a stretch to me. Ending up with compression ratios well over 14:1.

Kids these days, I swear... :D

[RANGER1]

Iceman, It it done often these days as cheaper to install. The screw compressor has to have economizer to get any efficiency.
Compressors are much more efficient these days to with very small clearances achieved consistently.
Air cooler design is also high tech to get most out of it.

I'm sure Magoo will comment on this one.

[iBigChill]

I know of facilities in my company that do it. Also, Ranger1 is correct in that it's the construction costs are cheaper. You can't use the word cheaper and say anymore than 5:1 compression ratio....

[Segei]

Single stage compressor with economizer can give us efficiency close to two stage compression. Definitely, construction of two stage compression is more expensive. In real life it has pressure drop between first and second stage and this issue reduce efficiency of this approach. Actual compression ratio is greater than 20:1 because this is ratio of absolute pressures.