Heating garage with regrigerator heat pump

[Marks heater]

Hi, I'm building an extension to a small garage and considering experimenting with underfloor heating using a used fridge or freezer compressor as a heat pump. I want to do this on the cheap.

I'm not a refridgeration expert but have a general engineering back ground.

The building is small and well insulated and will only need about 1kw of heat.

I can't find any information of anyone whose done something like this on the web. Could any one advise of:
1) How do you find the output of a domestic freezer compressor and would one be big enough - i was thinking of getting one from a large chest freezer but can't find any info on output?
2) Should i use a specific refridgerant / compressor with a specific refriderant.
3) What size and length of coils you should use inside / outside the building. I was thinking of about 6mm coil and about 15-20m long.
4) What material the coils should be. I was thinking of using copper inside and out with it possibly PVC coated. The coils inside will be in concrete and the coils outside in sand.

I'm doing this partly out of fun. Any guidance would be greatly appreciated.

Regards Mark

[Peter_1]

Compressor
You can't use a compressor out of a domestic freezer. The motor can't handle the higher evaporating temperatures you need.
You need for 1 kW heating a compressor taking +/- 0.3 kW (assuming a COP of +/- 3)
You should use a compressor which contains a legally allowed refrigerant (R134a, R410a, R407c, R404a, ...). According to EN378, you must be certified to work on these machines.


Inside
If you want to use copper inside concrete, then they must be very well protected because cement is very aggressive to copper.
How long will the circuits be? They must have equal lengths and pressure drop.
Internal diameter of the tubes depends on desired speed and oil carry over in these circuits.

Outside,
You need +/- 3 times the surface of the garage.

Which receiver will you use?
Which expansion device will you use? How will you select it?

[icecube51]

its better to work whit a second circuit on water, heated by a small vessel or heatexanger.then the lines in the floor can be in plastic or something like that.
better to make a study first and a good work-of plan.

Ice

[Peter_1]

Agree with Ice, although, condenser in the floor gives better efficiency. Masser is also is also installing the protected copper direct in the floor.

[Magoo]

Insulate all walls, ceilings. what ever. Reduce heat loses reduces the heat input requirements. Draft stoppers on doors, double or even triple glazing on windows, the reduced heat loses equals reduced heat input for comfortable conditions, use a R410A system to max heat recovery with heat pump.
magoo