Heat pumps can be fairly complex, well out of the normal DIY range, unless you have experience designing and building HVAC systems. Their thermodynamic characteristics must also be considered during the design phase, something that has already been done by HVAC engineers in commercial systems. I would not recommend a DIY heat pump. People rarely design and build air conditionering systems on their own, either. The most common type of heat pump is not unlike a central air conditioning system. Most of these employ pressurized freon, which requires special handling because it is a hazardous material. A heat pump consists of two heat exchangers (one interior, one exterior), pump, fans, and a controller. In winter, the unit transfers heat from the exterior to the interior. The heat exchangers and piping are usually fabricated from copper tubing strong enough to safely withstand the system pressure. In summer, the operation can be reversed on many models, allowing the unit to operate as an air conditoner. In cold climates, heat pumps are inadequate to fully heat a home, so a supplementary heat source, such as a gas or oil furnace or a wood stove, is required. Less common, but rapidly gaining in popularity are geothermal heat exchange systems. Geothermal systems do not use air as the heat source. Instead, they employ the ground, using heat exchangers that are buried in the ground, sometimes several hundred feet deep. The temperature of the ground is relatively constant at depth, which allows for the extraction of heat for winter heating and its use as a sink for summer cooling. They are also used to preheat water for a home's hot water supply system. Heat exchangers are constructed from copper or plastic tubing buried in the ground. The exchangers can be oriented vertically or horizontally, and use several hundred feet of piping. These often use a low-pressure water/glycol refrigerant, such as found in many commercial heat exchange systems. Systems may also use heat exhangers submerged in water (e.g., lake) or deep wells. The interior heat exchanger is similar to those used for air conditioning systems and freon-based heat pumps. The system also requires a pump, fans, and a controller. More information on these systems can be found at the geothermal heat pump consortium (http://www.geoexchange.org/). In short, it is unlikely you could build a "practical heat pump" on your own without the proper training. If you did, it would cost you more than a commercial unit and you would also need to provide all the technical and maintenance support. Installing a home-made heat pump as the primary source of heat in your home would reduce the home's resale value, because of the risks inherent in using a one-off system that could not be maintained by commercial HVAC repair personnel. If you really want to do this, I would strongly recommend taking courses on the design and maintenance of such systems from a university and/or technical college. An understanding of thermodynamics and HVAC system design is needed to design an effective system and practical training on maintenance is required to maintain such a system. Constructing components, such as the heat exchangers, can be a complicated and labour-intensive task. An efficient controller is no trivial matter, either.

Do you think that evrybody is part of the "two-left-hands-club" ??? Did anybody thout of useing simple "fridge" compressors, auto heat excheangers and butane instead of freon or other CFC's ????

Get yourself a few window airconditioners and put them in the windows backwards! COP is 2.5 to 3 DIY take the front control panel off and put on the rear end. They heat my Garage wonderfully for the last 20 years.

I have built a home-made geothermal heat pump system using several hundred feet of copper tubing, some PVC piping, a straight-cooling split HVAC system and my well as the heat-exchange source. My electric bill is currently about 45% lower than the same period last season.

easy e, i am thinking of doing the same thing as you,i have got a very large reverse cycle window mount unit. my question to you is "would you connect the ground loop to the compressor and fill with refrigerant or fit a small pump and fill the ground loop with antifreeze and pump it around the heat exchanger with the refrigerant in it?" i hope this makes sence thanks

Hi, read all your comments and it appears interesting, I dont think it is rocket science to build a GSHP, which is what I am planning but the design and spec is probably more difficult, I have at present come into possession of several APV Hall 6kw freezer units from a cold store. and hope to convet them to a gshp to run u/f heating. They are 3ph units but I am wondering whether I can connect them , geared of course to a windmill/ wind source does anyone know where I can get diagrams/ details of gshp units , any help welcomed cheers Skyman

I have built a simple heat pump using a couple old airconditioners. Covered my basement floor with a couple hundred feet of garden hose covered in insulation. I have a small circulating pump. Removed one exchanger from the malfunctioning air conditioner. Spray faomed face to face the exchangers together enclosed in a box, the control panel still exposed. Thermostat stuck in a cardboard toilet roll with a small appliance light bulb, (set the control of the airconditioner to minimum, power "on") cycling the "on off" of the light bulb (to trigger compressor on/off)with a timer 1/2 hour "on" 5 minutes "off" (to address any frost build up). Take heat from my bsmt. floor dumping the heat to my living room. Ta Da .....37 dergree celcius air blowing. The average temp of water into my system is 14 dergrees c. and output is coming out at about 4 degress celcius. The airconditioner is really just a small 5.5kw window unit.

Hi, I adjusted the thermostat controlled relay on my air conditioner when I used it as a heat pump. The problem (similar to others') was that the ac pump would cycle "off" when it got too cold, and stop pumping heat. Specifically, I removed the thermostat and sensor (carefully, so the sensor tube would not kink or bend too much) and there was an adjustment screw in the thermostat. The on/off temp can be adjusted with that screw. I calibrated it but putting the sensor in cold water with a thermometer, and adjusting the screw until it "clicked" on or off.

I am thinking that a simple test system should be able to be built fairly easy using a fridge or freezer compressor for a starting place. A person would need refrigerant tools and all the parts and pieces to solder together copper tubing and heat exchangers. A heat exchanger could be made simple enough by harvesting parts from old window air conditioners and by possible making one out of copper tubing like a shell and tube style exchanger. I think they are called sidearm exchangers that are used on hot water heaters. You could take the compressor and fabricate up a loop through the exchanger on the cold side and a heat exchanger on the hot side then leak check it and refill the system with refrigerant. Not sure what efficiencies you would gain over purely resistive heat but it would be an interesting shop project I think….