basic refrigerator properties

[astein@lear.com]

Hello, I am trying to get a basic feel for the power, COP, and cost of traditional refrigerators so that I can compare them to peltier devices. I know that refrigerators are typically much cheaper on large scales, but I am not sure exactly what happens on small scales. I have looked at some refrigerator spec sheets, but so far, they have not said anything about power or heat transfer. They only mention size and temperature. Can someone direct me to a good resource?

Thank you,
Andy

[bersaga]

Dear Andy,

I can't help you with refrigerator specifics because as you correctly put it, they don't reveal much. But the compressor power and refrigerating capacity in W is most of the time given.

Done a comparison some time ago between using thermoelectrics and mechanical refrigeration. Economically, due to high cost of TE modules , the traditional mech. ref. system is less than 1/3 the cost of using TE air-to-air modules. Do you have a cheap source of TE modules ?

Bernard

[superheat]

COP is watts of electricity divided by btus of heat removed. Spec sheets have BTUs and Watts on them. COP is easy to find.
That is just the compressor though. The heat loss on the box detirmines how much compresser capacity you need. There are refrigerators out there the run on 1/3 the electricity of a standard refrigerator. Add a couple of inches of insulation to your frig and you will be able to see this too. Low power semi conductors can do a good job of cooling with lots of insulation.

[astein@lear.com]

Thanks for your replies.

To bersaga: Nope, no cheap source of Peltiers. Sorry. We're just investigating.

To superheat: I have seen the BTUs mentioned with air conditioners, but not refrigerators. So far, I've just been going to GE's, Kenmore's etc. website and snooping around and their spec sheets haven't mentioned BTUs. If you get a chance, can you tell me where you've seen it?

[Prof Sporlan]

Actually, COP is a dimensionless number. Cooling capacity in Btu/hr divided by electrical input in watts gives you an EER value. One can convert EER to COP with the following:

COP = EER / 3.412

BTW, a SEER rating applies only to residential air conditioning equipment, and it involves several tests. So one cannot derive a SEER value simply knowing EER at some given operating condition.

[superheat]

BTUs will be given on the compressor spec sheet. ASk the manufacturer.

You are right Prof. I got those 2 backwards again. I have always wondered if the EER numbers on the compressor sheet really mean anything. Change the coils to a bigger or smaller size and the system has a new eff. with the same compressor. What is the standard they go by?

[Prof Sporlan]

I have always wondered if the EER numbers on the compressor sheet really mean anything. Change the coils to a bigger or smaller size and the system has a new eff.

Absolutely! EER values for a compressor are useful to know, but it is more important to get your coil and refrigerant line sizing correct if you're optimizing system efficiency.

[zolar1]

Without having to get a 37 year college degree in heat transfer/fluid flow, how would you determine line size versus evaporator?

What if you split a system?

[Dan]

I would size the line per the compressor's capacity at design conditions. I would not pay much attention to the evaporator.