Heat pump water heater reality check
 

Criticize me here. Want to hash out my plan before I'm in too deep. I have a 30 gallon electric water heater that I want to install a heat pump onto. Step one will be to move the cold water intake to a tee located at the drain valve. The old cold water intake at the top will have the drop tube removed and a union fitting installed. This union will contain a plug with 2x 1/4 acr copper lines brazed in, continuing to a 25' coil on the tank. Midway the lines will terminate into a 1/2" copper stub which will be crimped around the lines and brazed to make a 180* turn tight enough to fish down through the 3/4 inlet. The heat pump will be a 5k btu R410a unit with original compressor and evaporator. Cap tube replaced with an R22 1/2 ton TXV and running propane for refrigerant. Heat pump will be controlled by a normal water heater thermostat through a 5 minute industrial power on delay timer to prevent any short cycling. Original elements will remain intact and wired up. Beaker off unless the backup is needed. Solid plan? Flaws?

your idea is nice but id use one of the element holes for the coil instead of the cold inlet.

There are several successful HP hot water heaters.

Search for them here.

Better than reinventing the wheel.

-AC_Hacker

Your 5kbtu compressor is not the best choice for propane. Different compression ratio. More in line with r-134a. Expect only half the btu capacity running r-134a through it.

My advice would be to find a used dehumidifier or window ac unit that has r-22 in it. Reclaim what you can, if you need more refrigerant use propane for the remainder. If the HVAC guy asks, tell him it's an experiment. Tell him it's a secret: you're trying to work an impossible miracle.

Hm, I thought there wasnt much difference in the compression ratio between R22 and R4R410a. Like 3.2:1 vs 3.4:1 or so. Already have the 5k, but I could charge with 134a if it would be better, no issue getting it. I'm not too concerned with recovery time since it's just me and I don't use much hot water, just shower and dishwasher. I'll look at the pressure chart for 134 vs propane. The water heater is more to get my feet wet with some hands on refrigeration experience, gearing up for a GSHP later.

On the condenser, does crimping and brazing the two 1/4 lines into a 1/2 stub sound like a good way to make the 180?

Oh, and I agree that running the condenser into the top isn't best. I'm thinking now to tee the drain valve to the side and run the condenser coil in there. Keep it nice and low in the coolest part of the tank.

AC_Hacker I've been reading about heat pumps and water haters here like crazy. :D Will continue to as well.

Howdy fellow Mississippian!
I happen to have some perfectly sized R22 compressors laying around that I wouldn't mind letting you have. If you are close enough to drive, shoot me a pm with your phone number and we can arrange a meet, I'm 12 miles southeast of OleMiss. I can also show you my DXHPWH.

Also if you do decide to go with R134A, don't forget the cheaper option of R152A or air duster. =D

Though I have used a R410A compressor with propane, I don't recommend it, the rating may not be quite 1/2 but it is a lot more than I wanted.

Well howdy!
I'll have to see what the weekend holds for me work wise before I can give am answer but I'll definitely keep it in mind. Thanks!

This weekend is pretty full for me. But my job has me traveling north MS a lot. Where are you in MS? I might be able to get it closer to you if I have a job near by. I've got a dehumidifier with your name on it.

I'm in the Grenada/Greenwood area. I do come up to Batesville from time to time to slide the old Lowe's card. I'd be happy to take it off your hands if it's in the way. :D Never turn down free materials. I'm working this weekend too, and a mandatory training class Saturday.

One of the A/C guys at work has my 5k right now to suck the 410A out of it. If it doesn't work for the water heater then I'll build a chiller for a shop computer cabinet out of it.