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irishcapa
01-16-2006, 10:30 PM
If I have a conditioned space of 25 degrees F and an outside temp of 30 Degrees F with a 4:1 compression ratio; What would the compression ratio be if outside air temp climbed to 65 degrees? I'm using R-22

Milk man
01-16-2006, 11:38 PM
3.963743918 to 1

25 degrees-10 degrees = 15 degree = 52.405 absolute.

65 degrees + 30 degrees= 95 degrees = 207.72 absolute.

207.72 / 520.405 = 3.963743918 to 1

I guess.

Milk man
01-16-2006, 11:40 PM
But I'm figuring 2.219444709 to one for your example.

I guess.

hvac-prof
01-17-2006, 01:54 PM
Compression ratio is calculated by dividing the high side pressure in psia by the low side pressure in psia. Since you have a box temperature of 25 degrees, assuming a 10 degree delta-t between the box temperature and the evaporator saturation temperature, you have a 15 degree coil, which equates to a 38 psig low side pressure. conveting this to an absolute pressure give you about 53 psia.

Since you said you had a 4:1 compression ratio, your high side pressure in psia is 210.8 psia, or about 196 psig.

Since your outside ambient is 30 degrees, you have some type of head pressure control that is designed to maintain the high side pressure at 196 psig.

So, if the outside ambient temperature rises to 65 degrees, the system will still maintain 196 psig and your compression ratio will remain the same.

Hope this helps.

Milk man
01-17-2006, 06:34 PM