types of fridges compared for efficiency?

Hi,

It depends on the ambient temperature to some extent. I 'played' with my kill-o-watt unit when it arrived and found my home fridge was a duty cycle of 1:6. The fridge was brand new and it was April.

40% might be a 'safer' number to use.

JaxDad wrote:

pianotuna wrote:
A 120 volt modern fridge draws about 160 watts, other than the start up surge. Duty cycle is 1:6

MrWizard wrote:
A compressor fridge will use less electric energy than an evaporation fridge, 7.5 CuFt residential fridge draws 9~10 battery amps about 100w compared to 300+ for a RV fridge
Duty cycle around 40%

I'm a little confused, 1:6 is ~17%, that's a big spread to 40%. Where's the difference from? High efficiency vs standard efficiency?

pianotuna wrote:
A 120 volt modern fridge draws about 160 watts, other than the start up surge. Duty cycle is 1:6

MrWizard wrote:
A compressor fridge will use less electric energy than an evaporation fridge, 7.5 CuFt residential fridge draws 9~10 battery amps about 100w compared to 300+ for a RV fridge
Duty cycle around 40%

I'm a little confused, 1:6 is ~17%, that's a big spread to 40%. Where's the difference from? High efficiency vs standard efficiency?

2oldman wrote:

bandit86 wrote:
From what I learned in college airplane alternators are more efficient at higher rpm like 400 hz, the house being 60 hz as it is below what humans can hear.

You learned that in college?

In a previous job I designed military radar equipment. Most military aircraft use 400Hz, while shipboard units used 60Hz. The reason they use 400Hz is that inductive devices (motors, transformers, inductors, coils, filters, etc.) at 400Hz use less iron in the cores than at 60Hz. This means less weight, which is a big factor for aircraft, which have to get airborne. You wouldn't want a 400Hz motor anywhere you want quiet, because they let out a shrill screech that is VERY annoying.

Steve

bandit86 wrote:
From what I learned in college airplane alternators are more efficient at higher rpm like 400 hz, the house being 60 hz as it is below what humans can hear.

You learned that in college?

I have an Engel 45 with a Sawafuji swing motor compressor, and an Edgestar 86 quart with a Danfoss type compressor. They are both DC 12 and 24v and accept 115 which is converted internally.

The advantages are:
12v, 24v, 110v
Low amp draw, Engel 45 is about 38 watts and Edgestar 86 is about 80 watts.
They can handle being off level.
They are adjustable from 50F to -15F.
They are a chest type, so when you open them they don't spill all the cold air out.
They are portable.
They chill down in about 45 min.

I would love to have both installed where the current fridge is, with both stacked and on pull out drawers.
I have to admit though, my Amish fridge works excellent on propane and it can run for weeks with little propane, DC power, or fan noise.

Hi,

We can hear to 20 hertz.

We can see about 20 to 25 hertz as a flicker. That is why 60 hertz was chosen. That way we can't see lights flickering. Ontario used to use 50 hertz. All the electric motors had to be changed or modified when they dumped 50 and went to the 60 hertz standard.

bandit86 wrote:
the house being 60 hz as it is below what humans can hear.

The most efficient compressors are inverter driven, multiphase, so no capacitors, easy starting, and easily variable speed. The motors have position sensing, so the inverter knows where it is. The side benefit is DC operation- even AC is rectified first.
Most DC models have jumpers to match the compressor speed to the load.

I've long wanted to put together a system using one of the compressors from http://www.aspencompressor.com/.

I wrote a webpage a long time ago here that explains how absorption refrigeration works- their best advantage is being multi-fuel, and you can store a lot of refrigeration capacity in a single LP cylinder.

bandit86 wrote:
I understand how a compressor type fridge works, it was the evaporation type that is giving me trouble.

Interesting idea; a compressor type fridge powered by a variable frequency drive to ramp operation of the motor up to 80 hz. Faster compression should create more heat. If I wasn't 1200 mile from home I'd try it. From what I learned in college airplane alternators are more efficient at higher rpm like 400 hz, the house being 60 hz as it is below what humans can hear.

I think this is how the 12V fridges like Engel, ARB, and similar brands work. They are very efficient, from what I have read about them. That's what I will install if I modify a van myself for RV use.

I understand how a compressor type fridge works, it was the evaporation type that is giving me trouble.

Interesting idea; a compressor type fridge powered by a variable frequency drive to ramp operation of the motor up to 80 hz. Faster compression should create more heat. If I wasn't 1200 mile from home I'd try it. From what I learned in college airplane alternators are more efficient at higher rpm like 400 hz, the house being 60 hz as it is below what humans can hear.

No timer is involved. The working 'fluid' circulates because heat. The duty cycle on mine does not seem to vary much from 2:3 other than the initial cool down. Time to first cycle at an ambient of 20 c (68 f) is around 6 hours.

bandit86 wrote:
If a 2 way fridge has a 2:3 duty cycle is it run off a timer, or temperature setting? Like does the gas flame actually turn off at all?