Negative pressures

[Acrisoft]

Hi

The chart below shows what seems to be negative pressure (inHG) on top in red and their
evaporation temperature.

http://www.toughtank.com/fyi/289/advantageFYI289.php

I wonder if my thought is correct and if theses negative pressures can be used (in low side) to generated such lower temperatures or is it only a concept.

Moises

[NH3LVR]

You can. However any leaks will draw air and moisture into the system.
It is very common to run negative pressure in a NH3 system. Uncommon in ***** systems.
You also can have discharge temperature issues if the compression ratios are too high, even in a positive pressure system.

[Tayters]

Hi Moises,

You certainly can! Normally you don't though.

If there is a leak in the low side then there is a chance of sucking in air and moisture. I don't think it will make it the most efficient system either as at such a low pressure less mass of refrigerant will be drawn into the compressor.
That said, I've seen a few freezers on R12 and R134a which run borderline 0psig. Sure there are more about, maybe on some crazy cascade system.

Remember it's only negative with respect to our atmospheric pressure - gauge pressure. They will work down to a pressure of 0psia - absolute pressure. This is referenced from a perfect vacuum.

Hope that helps,

Cheers,
Andy.

Edit: Beat me to it NH3LVR. Must learn to get thoughts onto screen quicker...