I spent a good portion of the weekend building a prototype water heater. My main goal here is to build a functional unit so I can measure stuff like how fast heat is transferred from the foundation to the insulated tank and how much electricity the compressor consumes.
Here is a rundown of the materials used for this project:
$40 used window mounted air conditioner: I purchased a unit at the local Habitat For Humanity Rebuild store. Shopping for this item in mid October is highly advisable. They will not, however, give you a partial refund for all the pieces of the unit that you will end up throwing away.
$6 lumber: I consumed about 16 linear feet of two by fours: These are used to build the stand to mount the compressor and heat exchangers.
$10 uninsulated water tank: This can be any water container that has maximum contact with the floor and minimal insulating properties. I’m keeping my eyes open for a small kiddie pool with a flat bottom.
$20 insulated water tank: Lots of choices for this piece. For testing purposes I’m not so concerned about the insulation, but I would like to have a container that is large enough to simulate the volume of a typical residential hot water tank.
$4 nuts, bolts, and miscellaneous parts: This is all stuff that I already have in my basement, so I’m not going to give a ballpark estimate here.
After crunching all the numbers here I spent $80 on all the materials.
So here is how I got it all together:
Prepare the air conditioner: Remove the outer case and fans from the unit. Most of this can be done fairly quickly with a power drill and an adjustable wrench. Remove the wiring for the fan and any controls that are not needed. This image shows functionally how the system works with the uninsulated tank on the left and the hot water tank on the right.
Build a stand: This allows the cold side heat exchanger to be a few inches off the ground and the hot side exchanger to be on the bottom of the insulated tank. The compressor is placed in between the two tanks.
Mount the compressor and exchangers: The best advice is to plan ahead to minimize how much these components are moved around. The tubing will bend a fair amount, but if you pull too hard the refrigerant will start leaking out. Not a good situation.
Place the stand in the uninsulated tank: The lower exchanger should be completely submerged in water.
Place the hot water tank on the top of the stand: The upper exchanger should be placed near the bottom of the tank. This allows the heated water to passively rise up and the cooler water to be heated.
Once I get this version up and running I’ll be able to measure how well this setup performs. Stay tuned.