Heat Pump Water Heater - Coil in Tube

[jeff5may]

The best way to plumbing the hx is a trade off. It depends upon your priorities. Is low cost more important than durability? If so use cast iron or PVC.

How permanent or removable should the hx be? SweAt fittings are cheap and durable but permanent, especially if brazed.

There are many ways around the barn and more traps than that. Just keep the number of separate parts at the bare minimum no matter what you design. So what if a 2 x 3/4 x 1/4 tee fitting costs 12 dollars? It's guaranteed to be watertight. Adapter and reducer and sex change fittings are bad karma, don't do it.

When in doubt, look up how the big dogs do it. In this realm, it is boiler room and distillery and refinery equipment. From homebrew and distilling moonshine all the way to bulk petrochemical companies, the road to safety and success has already been paved and signs have been installed for ease of use.

[vwhead77]

I was taught that one can never have too many unions and ball valves. All of my components are interchangeable. I am gaining ground - yes, I'm trying to develop a simple design using readily available components. if you see my previous post, I've added the new design - all copper inside an insulated PVC jacket. 20 degrees delta-T is pretty impressive - big dog or not

[vwhead77]

This latest model I've made is actually producing results with no leakage- 4.5 amps of power / 115V @ 20 degree delta-T. Just need to add the insulation to the pipes and I'll have a real Water Heater from scratch. Trying to use R209 refrig. but thinking that R22 or equivelant would add better cooling affect to the compressor. Project costed me about 60.00. Sometimes it never hurts to try to re-invent the wheel eh?

[NiHaoMike]

R290 heats less on compression and would be a better choice for that application.

[Mikesolar]

What model of tank is that? Are the ports all at the top?

[Ron342]

Great work!
I'm having trouble seeing how it thermosyphons the hot water from the water heater tank tho - like others have mentioned.
Looks like it would quickly (thats a big ac unit!) reach steady state hot water temp in your heat exchanger because of low flow of the water then the delta T would drop, pressure would go up along with current draw??? But that would only need a little pump or some rearranging the loop? I hate the pump option because it has to run under dhw pressure unless there are simple magnetic coupled pumps available cheap?

And how did you do such really nice coil winding???

[vwhead77]

Tank is a Weil-McLain - indirect fired. Little background; The house used to have radiant heat but it wasn't installed correctly -burned 100gal. fuel oil/mo. I installed our Wood Stove and dismantled the radiant heat. Unfortunately, the HW tank was still dependant on the boiler for hot water production @ about 165.00/mo.(still can be used if necessary). As it is now, I have installed an On-Demand 208V Rheem electric water heater (@ about 115.00/mo.) When the T-stat on tank calls for the circ pump. - everything is activated. I installed BVs to allow just enough flow to gain heat through either the coil under the woodstove or the HP coil (which ever is in place) As the water heats up, the delta-T actually stays pretty much the same - suction and discharge raise (HS about 300 lbs/R290 @130 deg.) and the Amps go to about 4.5 - the Rheem uses about 12 Amps. The coil under the woodstove has a little 12V pump that helps to keep the loop warm. The entire system at this point is redundant but each part helps the whole.

PS- I wrapped the coil tightly by hand - just rolled it under the 2" Copperand kept it close.

[NiHaoMike]

Here's a pump that should work fine for this application:
http://www.amazon.com/Brushless-Sola...rds=solar+pump
It will run off a common 12V wall wart. Connect it using those short flex lines often used to connect faucets.

You'll get better results having the refrigerant entering the condenser at the top and exiting the bottom.

[jeff5may]

V2 heat exchanger looks 100 times better than V1. Well done!

If this one doesn't transfer enough heat for you as-is, you can improve on it the way it is.
You can either paint it or solder it. If you paint it, use cold galvanize paint:it's loaded with zinc. If you solder it, use the tinning flux. Both methods fill in the gap between the coil and pipe and dramatically increase heat transfer efficiency. If it still isn't good enough, it never will be.

[vwhead77]

excellent Idea! (s) As -is I'm getting 20 - 30 degrees rise in HW temp. Going to flip it over so the high side runs in top and out the bottom, solder copper to copper, insulate my pipes, and wire my 24V contact to bring on the 115V HP along with the circ pump. I may have a bit too much compressor though. I haven't checked super heat yet (maybe today) but I dont' seem to be getting very cool gas back to the compressor windings a bit worried that it's running too hot. Highside goes up to about 300 psi (135deg) low side up to about 50 lbs (20 deg) - Suction line feels cool but compressor is a little hotter than I'd like. I may reduce levels but thinking I might be better off using a different refrigerant or smaller compressor.