Homemade Heat Pump Water Heater (R290)

[AC_Hacker]

Originally Posted by Ron342

So I will put a receiver before the cap tube (and a filter/dryer too ? and where?)

In my opinion, you should just try it out as is. I recently had lunch with a retired refrigeration tech, with 40 years experience on all systems including cascade systems for cryogenic applications, who told me that a receiver was not required on a cap tube system. I think you should keep it as simple as possible, try to get it working and introduce improvements as you go.

Originally Posted by Ron342

Use R290 instead of R22 when I charge it up. Do I do anything about oil?

R290 is not exactly the same, but very similar to R22 in terms of output and in terms of the metering device and in terms of oil.

Originally Posted by Ron342

And I charge slowly looking for frost at where the cap tube enters the evap (will the frost remain as it reaches full charge?)

You should look for frost to form right at the end of the cap tube, where it enters the evaporator. For now, the point at which frost is forming is full charge.

Originally Posted by Ron342

...and for the right temp pressure (120 - 140f) at the high side just before entering the condenser?

Since this is a hack-job (in the most favorable sence of the word), and not a rigorously designed system, you'll just have to see what you get.

For now, let frost be your guide.

Originally Posted by Ron342

Thanks so much guys - I hope each of you realizes that this is akin to voodoo to the rest of us!

Well, it may be voodoo to you, but remember that you are messing with dangerous extremely flammable gas, and if you introduce R290 into a system that contains air, you have a bomb, so vacuum well before gassing. Also remember that R290 is heavier than air, and will collect in low places. Only work outside or in an open garage with forced fresh air circulating.

May the blessed saint of refrigeration, Saint Frosty, be there to guide you to success.

-AC