Ok, what I am going to do first is run the outdoor unit like a big heat pump water heater to measure its baseline performance. I have a water heater gleaned from the rental trailer that is still water tight. It was getting clogged with lime, and tenant tried to flush it. Doing so, the drain spout got gunked up and clogged. My dad figured it was old enough to change, so we stuck a new one in the trailer.
30 gallon
I blew some compressed air into the drain spout, then muriatic acid, to get the gunk out. I haven't looked inside the tank yet, but both heating elements still work. Usually when the tank gets thick deposits inside, the calcium builds up around the bottom element and it burns out.
I have a question about this plan: what size and length of copper tubing is enough to make the thing operate at high efficiency? I am planning on taking the bottom element out and running a pipe and Union into the heating element bung like Memphis did with his. That way, I can log temperature and flow of water and refrigerant to tell how much heat is being produced in various configurations, as well as overall cycle times and such.
I already have a couple of 2 ton TXV's I can use with this rig, as well as an A-coil from a 2.5 ton unit, among other components, laying around. After a decent operating profile is charted from the stock outdoor unit, I will change the cap tube metering device with a TXV and chart the new operation profile.
For practical purposes, let's say I can heat the greenhouse or barn with this unit. I won't be installing the rig where I live, because I rent. The town house I'm renting has its own (undersized) central heat pump, and I have a mini window shaker heat pump (perpetually set at 70 degF) hung in an upstairs bedroom already. All of the stuff at home works well down to around -10 degF, which never happens here for long, if ever. If I were to venture a guess, I could probably count the number of days that bottomed out that low on one hand in the last 2 decades.
Another idea: my parents have a pond about 15 yards away from their house. The same pond is about 20 yards from the barn. I could possibly rig something to use the pond as a heat dump or source in place of the stock outdoor HX to do some testing with. The only problem with that idea: the pond is part of the front yard, surrounded with lawn. Digging up the front lawn would definitely be frowned upon.
I'll be going over there soon, and will edit some pics and commentary into this post.