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Old 04-06-10, 02:18 PM   #1
Piwoslaw
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Default Small heat pump with automotive A/C compressor?

How would one go about using an automotive A/C compressor as a small heat pump?
Just attach a motor and spin it at the right rpm?
How efficient would that setup be?
How much heat could it transfer?
Has it been done?

Since the driver usually notices when the A/C kicks in, it robs the engine of a good amount of power. 2kW? 10kW? Does this mean that if I couple it to a 2kW electric motor I can move 5kW of heat? I think that replacing the heat exchangers with larger ones should raise the efficiency (no space restrictions).

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Old 04-06-10, 03:40 PM   #2
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Interesting idea. Your numbers sound at least somewhat accurate to me (which doesn't mean much haha).

I fear that route is a much more difficult one though. Over here in the US we seem to have an abundance of window air conditioners to be had for cheap. They already have a motor and AC plug on them ready for hacking. It doesn't get too much better than that. Perhaps you don't have these available?
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Old 04-06-10, 05:19 PM   #3
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Quote:
Originally Posted by Daox View Post
Interesting idea. Your numbers sound at least somewhat accurate to me (which doesn't mean much haha).
Just guesstimating, actually. I think that the A/C systems in cars have lots of inefficiencies, mostly from compromises that had to be made (large temperature swings, highly variable input rpms, durability in harsh environment, size restrictions, etc.). So a compressor sucking 2kW from the engine may only be pumping 2kW of heat or less. Though maybe in more ideal conditions (steady rpms, large heat exchangers) the system would work much better.

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Over here in the US we seem to have an abundance of window air conditioners to be had for cheap. They already have a motor and AC plug on them ready for hacking. It doesn't get too much better than that. Perhaps you don't have these available?
Air conditioning was a very luxurious item until only 10-15 years ago, and for economic and political reasons the only buildings that had it before the 1990's were hotels for foreigners. Plus the climate here is nowhere near, say, the American Southeast. There are lots of new, high tech A/C and split units for sale, but almost nothing at the scrap yard. So if I want to recycle a compressor, it'll either come from a fridge or a car.

The car option differs from the refrigerator option since it is not integrated with the motor, so I can use whatever I need, not necessarily AC power.

Anyway, I'm at least 1-2 years from actually doing anything with this idea, but it's nice to know what to look for.
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Old 04-06-10, 06:03 PM   #4
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Too bad they weigh so much. I'd ship you one that I have. I have a couple just laying around.
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Old 04-06-10, 10:17 PM   #5
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Has anyone used a A/C compressor from a car? - XtremeSystems Forums
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I'm an automotive refrigeration engineer, and that is a Sanden 508. The power they draw...sounds simple, but depends on the LOAD! It's crazy to say they draw a fixed amount of power! Depends on the pressure ratio and RPM that it's working against. You could hook this up to an 1/10hp motor, with the appropriate pulley ratio to work against a given pressure ratio, it would be turning very slowly, and have small refrigerating capacity. You could hook this up to a 10hp motor and spin it at 7000 RPM against a very high pressure ratio, and a have high refrigerating capacity perhaps as high as 8kW.
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Old 04-07-10, 01:39 AM   #6
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Thanks Mike
So it's really not worth it. I'll look around for fridges. European environmental law forbids disassembling refrigerators, and the ones I see tossed into the woods are without compressors and heat exchangers, so I'll probably have to look for a repair shop when this project gets going.
Thanks again guys
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Old 04-07-10, 09:27 AM   #7
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If I were trying to use an old car AC compressor, I would study the design of the newer
Inverter type mini-split ASHP units, and maybe think about using PV to power the motor..

My guess is, a medium sized car would need between 12,000 & 18,000 BTUh..
So, that could be the approximate top limit of your compressor's range.

Here's an 18,000 BTU Solar Powered Direct Current Air-Conditioner / Heat Pump
that most likely will need about 2kw of PV, depending on your night cooling needs.

DC Air Conditioner: 12 Volt 24 volt 48 Volt DC Air Conditioners DC Solar Air Conditioning




A Bushless EV motor might do the trick.. I'll bet this one could kick out some HP..
Electric Motorsport EV Parts :: PMAC Motor
But, you would need some major PV to run it..

They make smaller EV bushless motors for bikes and scooters that might work.
Even a large RC bushless motors might work for a low BTU output..

Robot MarketPlace - Power 90 Brushless Outrunner Motor 325 kV

Last edited by Xringer; 04-08-10 at 08:38 AM.. Reason: URL
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Old 04-09-10, 03:00 AM   #8
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Default Hang on a second

"So it's really not worth it. I'll look around for fridges. European environmental law forbids disassembling refrigerators, and the ones I see tossed into the woods are without compressors and heat exchangers"

This is what made me think of "auto" A/C---or heat pumps. The new stuff is 134a, anyone can purchase. It is fairly cheap, lots of parts to hack from(USA)
All of the older A/C's, fridges, etc. are R22, pricey and you need documentation to purchase. Not hacker/DIY friendly.

The thread Mike linked was more about cooling, I see why they weren't to excited about it. Just mod an A/C unit.

Here's what I've found.

A 2004 F-150 puts out 32f off the evap, 160-180f off the condenser at 30f ambient, at 700rpm. Less?? at the compressor. It did start cycling pretty quickly as it didn't take long to drop the temp inside the truck. Seems like the right hack/combo might put out some decent heat.

Most of the evaps on home heatpumps are not over 120f, are they???

They are power hungry, 3-5hp(2-4kw) but I was thinking of using wind power with a hydraulic pump/motor combo. I get a lot of wind, and thought of "free" heat for my shop/basement. Maybe when I get retired.

For now, the 410A is not regulated, and probably just as easy/cost effective to hack/modify/experiment with, for me anyway.

Xringer has more knowledge of electric motors/apps than I do. I does seem to me there is a lot of "room" for ideas, with variable speeds, d/c, p/v, etc.

Depending on a specific situation, it could very well be "worth it". And much easier/simpler than the heavy electronics needed to "get it done" with the current available designs.
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Old 04-10-10, 06:36 PM   #9
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Quote:
Originally Posted by AirSepTech View Post
This is what made me think of "auto" A/C---or heat pumps. The new stuff is 134a, anyone can purchase. It is fairly cheap, lots of parts to hack from(USA)
All of the older A/C's, fridges, etc. are R22, pricey and you need documentation to purchase. Not hacker/DIY friendly.
22a Refrigerant Details and Online Ordering at Enviro-Safe, Inc
There's a HFC mixture that replaces R22. No EPA certification needed.
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Old 09-06-13, 11:55 PM   #10
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Built a heat pump with an old chrysler 2 piston compressor and parts from cars 30 years ago. Welded the magnetic clutch closed, belt driven with 5 HP 184T frame motor.

Worked well for a while, I did not pay enough attention to suction line slopes and ran a rod thru the piston head one day due to an oil slug; so, not a simple as just hooking it up. Pay attention to suction line slopes. The car has a huge condensor fan an relatively small condensor, and even smaller evaporator compared to same BTU rating mini-split, so you should double up on evap and condensor - I used 2 evaporators in parallel with 2 TXV, one feeding each evap. Did a GSHP from a pond and used car evap for one and 30 feet of pipe inside poly pipe for tube in tube diy evaporator, series condensors. Assy advantage was that the 1960s/70s cars used all flare fittings so easy to assemble.

Next try used scroll compressor, much lower noise level, works much better, etc. .

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