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Old 02-06-17, 02:30 PM   #1
Zwerius
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Default Heatpump from number of old refrigerators?

I was thinking about building a heatpump consisting of a number of old refrigerators. So actually a number of small heatpumps in parallel. By switching on a larger number by colder weather, you have a kind of modulating system.
If the outside temperature rises again, more compressors can be switched off.
Of course the order in which compressors start, must be random, so that they wear out evenly.
Advantage: Old refrigerators can mostly be had for free...
However I have no idea of the COP when using an old refrigerator as heatpump.
The idea was, to exchange the evaporators for copper pipe coils. Getting the heat from ground water (to be pumped from a well).
Anyone who used refrigerators as heatpumps?
And any idea about the COP's that can be achieved. Probably not so good because there's no control valve, but only the fixed restriction (capilarry pipe)?

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Old 02-06-17, 03:03 PM   #2
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It's probably a matter of time before someone more knowledgeable swings by and explains it more thoroughly, but this sounds like an exercise in futility. Maybe not impossible, but it will most certainly perform poorly and be incredibly complex. Re-reading your post it sounds like you plan on keeping the refrigerant loops separated and running a bunch of refrigerant to water heat exchangers in series? So the water loop would run through each heat exchanger one after another and the compressor for that each exchanger would either be on or off depending on load?
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Old 02-06-17, 03:55 PM   #3
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Yes, the idea was to have a number of separate refrigerant loops.
In the moment I don't know if putting the heat excahngers in series would be the best option. Maybe in parallel, with valves to include/exclude them from the flow.
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Old 02-06-17, 11:52 PM   #4
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Sounds like an ice maker to me. Have you thought about selling ice? Because this machine would do it. Let me elaborate.

Refrigeration compressors are generally built a little heavier than normal a/c compressors. The main reason is simple: they are designed to survive lower evaporator temperatures. In freezer boxes and such, the refrigerant evaporating pressure drops as the heat is extracted from the space inside. As the box temperature normally draws down, the mass flow through the compressor drops with suction pressure. If the compressor could not keep cool during these low flow conditions, it wouldn't survive long.

The drive motors and compression heads, built for low suction pressure and medium to high discharge pressure, are larger and stronger than those found in a/c equipment. When operating in temperature and pressure ranges normally found in HVAC systems, they can (and will) move more than their rated capacity. However, they generally will not use much less electric power than in their original configurations. This is due to the mass of the rotating parts. The compressors end up getting better energy efficiency than they did before, but not quite as much as compressors designed for higher suction pressure operation.

The sweet spot in the capacity vs efficiency curve of most residential refrigeration compressors lies right around or somewhat below the freezing point of water. As you know, it takes a lot more Watts to freeze water than it does to cool it to its freezing point. These little units can be rigged to make ice, and it would drastically reduce the volume of water drawn from your well. You could harvest the heat and have ice as a by-product to sell. More ice equals more money in your pocket.

If you don't want to sell the ice, you could always just shut the compressor off. The well water would melt it pretty darn quick. Then you could start making ice again.
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Old 02-07-17, 08:00 AM   #5
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The forming of ice in the evaporator is mostly determined by the amount (and temperature) of the well water. So if the flow is high enough, no ice formation will occur.

Rotating mass has only little influence on the power used.

But actually I was just wondering if anybody has ever built a heatpump from a small refrigeration system and what the practical results were.
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Old 02-07-17, 08:46 AM   #6
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I use the condensing units from refrigerators for small room heaters. They consume between 150 and 400 Watts while running (depending on size) and move about twice that much heat. Most fullsize American models have about a 1/4 to 1/3 HP compressor in them, and the larger units max out at around 4 thousand BTU with higher evaporator pressures. As the evaporator temp and pressure falls, heat output suffers.

For something free, they put out more heat per watt than an infrared space heater.
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Old 02-07-17, 10:45 PM   #7
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Have you seen this old thread?
Dual compressor heat pump
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Old 02-08-17, 12:10 PM   #8
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Default Zwerius, your idea really Rocks!!

Quote:
Originally Posted by Zwerius View Post
I was thinking about building a heatpump consisting of a number of old refrigerators. So actually a number of small heatpumps in parallel. By switching on a larger number by colder weather, you have a kind of modulating system.

I think you idea is absolutely great!

The two-stage heat pumps are nothing more than that.

To keep inter-action to a minimum, build each small heat pump as a stand-alone unit: compressor, HXs, etc. Maybe call it a uHPU (micro Heat Pump Unit). You have choices in that you could combine them into a single house heating loop, or you could set up several independent units.

You could just switch in extra units as required, if they were combined into one loop.

My previous research indicated that maximum COP for mini-split units was obtained in the 9,000 to 12,000 BTU range. Bigger is not better.

It is easy to get cheap or free small units.

You could deploy these units separately throughout a house, which would give you de facto zoning.

A knock-on advantage is that should a unit fail, it would not take out a home's heating or cooling system... just a smaller % of it. But the real advantage to you is that you would create reliability by using cheap redundant parts (uHPU). This is the same concept that the Internet was based on!!

Zwerius, I think your idea is brilliant, and that you should absolutely do it.

My only advice would be to take loads of photos so we can see what you're doing.

Best of luck on your project, your idea really Rocks!!

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Old 02-09-17, 07:07 AM   #9
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Default Wow!

If you ran a geo water line and return to a refrig unit in each room you'd have potential for a very small very cheap heat pump in each room. More $ in the reversing valves than anything else. Are refriges on r134 commonly now?
Jeff, did you just exchange with outside air?

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