Capacity vs Temperature and The True Cooling Capacity of Fridge Compressors

[Kompulsa]

Hello.

I always thought that refrigerator compressors were far more expensive per BTU than the air conditioner compressors because an 820 BTU is almost as expensive as a 9,000 BTU air conditioner compressor. When I looked at Embraco's R-134a fridge compressor datasheet, I realized that that 820 BTU rating was at a temperature of -23.3 C, which is much colder than the temperatures at which the air conditioner compressors operate, and cooling capacity drops.

The same datasheet showed that the cooling capacity of the R-134a compressor is 1,768 BTU at -10 C, which is still far colder than an air conditioning unit. -10 C is the highest temperature the datasheet provides performance details on.

The EER is also 8 at -10 C and 4 at -23 C. Maybe the cooling capacity of this compressor could be much higher than 1,768 BTU if operated at a temperature of 10 C above 0? Does anyone know how much I can expect from it at temperatures above 0? That would be helpful.

I guess the main concern is whether or not these compressors are capable of reliably operating at higher evaporator temperatures since they are designed for refrigerators which operate below 0?

Or is it the other way around...I was told that my R22 air conditioner compressor would overheat too much at temperatures below 7 C, so maybe it is the other way around? I would love some insight into this...

Thank you.

[NH3LVR]

This is a question that I had many years ago. The answers are quite simple.

The total refrigeration effect of a system is determined by the amount of refrigerant being circulated through it. (Among other factors) As the suction pressure drops the suction gas becomes less dense. (Fewer molecules of gas being pumped per piston stroke)
So in order to produce the same refrigeration effect at a lower suction you need a bigger bore piston or a longer stroke. The Horsepower needed will go down as well. (Lower suction at the same head pressure equals lower power draw)

You would not want to use a high pressure compressor for a low pressure application as the motor would be larger than needed and waste energy.

Conversely if you use a compressor designed for low pressure on a high pressure application the motor will be too small and overheat.

The compressors motors used in Industrial applications are selected according to the conditions where they will be run. Start up may require high pressure unloading switches in some applications.

[Kompulsa]

This is a question that I had many years ago. The answers are quite simple.

The total refrigeration effect of a system is determined by the amount of refrigerant being circulated through it. (Among other factors) As the suction pressure drops the suction gas becomes less dense. (Fewer molecules of gas being pumped per piston stroke)
So in order to produce the same refrigeration effect at a lower suction you need a bigger bore piston or a longer stroke. The Horsepower needed will go down as well. (Lower suction at the same head pressure equals lower power draw)

You would not want to use a high pressure compressor for a low pressure application as the motor would be larger than needed and waste energy.

Conversely if you use a compressor designed for low pressure on a high pressure application the motor will be too small and overheat.

The compressors motors used in Industrial applications are selected according to the conditions where they will be run. Start up may require high pressure unloading switches in some applications.

The compressor I want to use at those high air conditioner-like temperatures is an Embraco FGS 80HAW 1/4 HP. Is the compressor designed for low pressure you referred to a refrigerator compressor?

[mikeref]

Low temperature compressors are for freezer applications. Whether it be a domestic, commercial or industrial.
Your 1/4 hp compressor will be for small space cooling such as an all fridge or a fridge/ freezer combo or just a freezer on it's own. 1/4 horse power will run a 500 litre chest freezer at -20c