Randen, when you were stating your temps for HX's, did you say that the outgoing refrigerant and the outgoing radiant water temps were within two degrees of each other, or did I read that wrong? If that's correct, then your radiant water is entering at 72*F, leaving at 82*F and your refrigerant is entering at 179*F and leaving at 85*F(is that correct?). That water temp seems low compared to AC Hacker's or anyone else's hot water side temps. Does this suggest something not efficient with the HX(does not appear to be likely) or does it simply mean that your floor able to transfer out every bit of heat this HP is putting into it with a floor to air Delta T as small as 4*F, or 13*F(66*F or 75*F to 62*F)? Have you tried shutting off the flow to the air handler and seeing how well it's able to heat just the radiant floor in the office space, or vice versa and run just the air handler? That might tell you more about your heating and sizing needs.
I myself am severely pained that I can't work on my heat pump project. I'm currently away at college so I don't have the space or tools and an air conditioner to tinker with. My project is an air source to water heat pump which I plan to use as the main heat source for my hot tub. I know a 1375w(approx 4800 BTU) heating element is enough to maintain the temp if it runs constantly, but that literally doubled our power bill last winter the one month it was running. The A/c should put out a little more then that, or hopefully at least that many BTU's, but using half the power. I don't have much time to hack, but I've already got a window A/C lined up(early Christmas present to myself) to use when I go home for winter break.
Due to break only being a month long, and me not having the gauges vac pump or any other equipment(or the budget, poor college kid here) to hook up a real heat exchanger, I'm going to keep the circuit intact. My plan is to bend the tubes(very carefully) and simply lower the condenser coil into the tub in front of a jet for circulation. I know it's not the most efficient but it will work for my temporary trials. Past tests have shown that the small coil used on the evap side of window a/c's can make frosting a problem due to how low the coil temps can get when it's cold outside. My plan to help combat this is to use a more powerful fan like this(
FlowPro High Velocity Floor Fan — 18in., 4550 CFM, 1/8 HP, Model# 10180 | Floor Fans | Northern Tool + Equipment ) which I already own, to force much more air through the coil and hopefully keep the coil temp from dropping as low thus slowing the forming of frost, which should also increase heat output a little.
I've even thought about the defrost issue which I'm sure will arise and my plan is simple. Turn off the unit and fan, and place a propane Mr. Buddy heater directly in front of the evap coil to quickly melt the ice. This can also be left there with the unit running to significantly increase heat output if I need the BTU boost to keep up with the heat loss while we use the hot tub.
If the hot air coming off the tub wasn't so humid reusing it would make for a very efficient system, but I'm afraid the speed it would cause frost to form would make it not worth doing.
Any huge holes in my plan I need to address?
By the way, this thread has done a lot in the way of inspiring me to plan projects for my home in the future. I'm already dreaming of and have drawn up plans for a very efficient(somewhat complicated system) using a fresh air economizer(if temp and humidity are optimal) and a Heatpump, maybe a (hacked inverter minisplit running water-water?) with multiple sources, ground, air, and solar water inputs which it senses and automatically picks the best that I have dreams of designing and building one day. Reading more of this thread made me remember I also want to include the three buffer tank system for DHW, in floor radiant, and cold water preheat or snow melt. Of course, taking one last tip I learned here, I will insulate and seal my house as much as possible so my demand loads shouldn't be to big to begin with.
Thanks,
Adam