Well, I'm a newbe to the forum, and wanted to get a little bit of insight on some design considerations.

This is a "basement" project, so no customers involved (just dear wife). I have built my own heat pump for my house, from a converted 10 ton Trane a/c unit. Now I want to build a heat pump water heater. By the math on paper, it's far, far more efficent than any means to heat water (resistance heating, or other fuels). So here's my question:

I'm building an outdoor unit, out of old 3 ton a/c unit. I found it out back of someone's store. Turns out tech condemned it for a bad run capacitor. So, I want to use this 'freebe' as my h/p.

In my designing, I'm wondering about defrost. I don't think that I really need a reversing valve, but just a silnoid valve to dump hot gas in the evap. I was going to coil copper tubing in the tank for the condensor, and leave plenty of extra to act partially as a receiver, but to give added capacity of refrigerant during defrost. When the h/g valve opens in defrost, hot gas will come off of the discharge line into the side connector of the distributor. When the hot gas is depleting during defrost, the liquid remaining in the condensor coil will begin to flash off and provide warm vapor to assist until defrost is complete.

Any thoughts, or design considerations I'm missing here before imbarking on this project? Thanks!