Memphis
I encourage the DIY side when it makes sense. But as you can see, the cost of the parts are beginning to add up. Getting the parts to play together well can be a bit of a struggle as you have seen.
The build of a ground source or even an air source water heater is another story. The parts are cheap and sometimes free. The effort is low. The return on investment is beyond huge. So I would support this all day.
Now, I'm not going to leave you high and dry because I think the value in the DIYing this heat-pump doesn't make financial sense. I've made you aware and the rest is up to you.
Again with the VFD driving a 3ph compressor with 1ph power maybe a little trouble. I had tried driving a 3ph motor with a VFD and one brand of drive worked and the other faulted out. But that was a number of years ago so I can't offer any empirical knowledge.
Oh yes the link.
Climate Master Tranquility 20 Geothermal Heat Pump | eBay
Now the ad wasn't specific to the power requirement. It says 3ph. but that could be 460volt and that's no good to you. I've seen other HPs 1ph and less money. As I had mentioned its high season for procuring a heat-pump now.
What about seeing if you can get a scrap outside unit around 2- 3 ton 240v 1ph even if its a recip. I was able to keep a large not so air-tight shop fairly comfortable with it. 1600 square feet. With better HXs I bet it would have done a lot better. For the weeks where the temp dropped to -20 Deg. plus huge wind it wouldn't keep the shop comfortable.
Randen