Quote:
Originally Posted by buffalobillpatrick
It's very low humidity here so no dehumidifier needed.
Would R410a or R22 scroll compressor work best with Propane R290 ?
I don't get: "high evaporating and condensing temperatures" why would I have this?
It looks like the TXV needs to be adjusted for 20-35K Superheat ?
what type of HX for IHX or what ever its called ?
I copied this somewhere:
"In other words: R290
profits in capacity and efficiency from useful superheat, the
use of a heat exchanger between the suction and liquid lines
is therefore an advantage."
BBP
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Then stick to a water source unit for the hot water. It's more efficient. You can either use two water/refrigerant heat exchangers or just put some coiled up tubing inside the DHW (Domestic Hot Water) tank as some others have done. The latter saves the cost of a pump, but requires the heat pump to be attached to the hot water tank. That's probably not an issue for your case.
Use a R410a compressor for the DHW heat pump and a R22 compressor for the main heat pump. The reason you use a R410a compressor for the DHW is because it might need to operate with high evaporating and condensing temperatures. Such as the solar tank being at 90F and the DHW at 140F (for washing dishes). A R22 compressor running on R290 would overload under those conditions, but a R410a compressor would run quite well. I named that the "Davuluri Treatment" after a model who recently lost a lot of weight.
http://ecorenovator.org/forum/geothe...ssor-r290.html
The reason the suction pressure matters and not just the pressure difference is because the refrigerant gas becomes more dense at higher pressures, putting more load on the compressor. For the main heat pump, since you put the maximum solar temperature at 80F (above which you bypass the heat pump altogether), a R22 compressor would likely stay well in spec. You might still want to put in a current sensor and dial back the evaporator water flow if it starts going over spec.
The TXV is generally set for 8-15F of superheat. Try to go as low in that range as you can without the valve hunting.
The heat exchangers commonly used are tube in tube ("snake" or "coax coil") and plate. The former is somewhat more resistant to freezing, has a high thermal mass (easier to design the control system), and more internal volume (easier to get the charge correct), while the latter is more compact. Efficiency of the two are similar and the surplus store has deals on the coax coils, so that's what I recommend.
The benefit of a SLHX is much less than you think, especially with low delta T between the condenser and evaporator. Certainly not worth the cost of another heat exchanger assembly. Soldering the liquid line to the suction line is a cheap way to do it.