Results are great on the total of 21 inch shortened cap tube (stock 63 inches, dual tube).
My BTU's have gone from 9000 to 13000 at 4.5 amps/1035W total (fan plus compressor). Water in: 69.8 after running for a while, water out 56.8F. My COP has gone from 2.76 to 3.68 ! (3809W/1035W)
What a difference the proper expansion valve flow makes!
My suction side temperature is 54.5F, still closely tied to the water out (I'm using the "wrong" water flow to make it lower.)
This is good because most compressors specify 60F for the minimum suction temperature for compressor cooling. The vapor enters the hollow pump cavity to provide essential cooling.
Ambient Conditions: 80F, morning shade. Measured at fan inlet, also 80F, Fan outlet 94F.
Amps: 4.5A I stopped here as incrementally charging as spec is 4.6 at 230V. I can operate at a lower charge and amps, to allow head room for hot afternoons if not using a TXV.
High pressure: 356 psi, Low 127 psi. (low gauge reads 10 psi low at 200 psi equalized)
Temps near BPHE: liquid line 94F , suction 54.5F (water out 56.8, wrong flow direction used to lower suction temp).
I expect the amps to climb with heat, and I'll check that this afternoon. That would be where the TXV would help, as the increased liquid line pressure will throttle back flow, reducing amps. Even though the superheat bulb won't do much. The unknown is if this Emerson TXV will allow the much higher flow rate I need with air to water cooling, instead of air to air, as it was designed for. A 1.5 ton unit might be needed, if so. First I'll see how much the temperatures affect current draw this afternoon.
I'm relieved that I'm finally getting the BTU's I need, and a decent COP for an 80F morning.
Edit- Addendum of follow on testing with increased outdoor temperature.
While still in shade, and condenser fan inlet now up to 90F, (10F increase), and current climbed 0.4 amps. I reduced the charge until 4.5Amps again, noted the low side pressure just below 100 (indication of too little charge) and got only 8,000 BTU of cooling. So now I see the need for a custom tailored TXV to get an optimal COP, you really need to adjust the expansion valve flow rate to control amps, not starve it for refrigerant charge. This means I'm now too short on the cap tube for inlet air temps over 85F.
Next week I'll try to make it work with the surplus Emerson TXV. Hopefully the Emerson unit will be sufficient; pressures rise with temperature and motor draw, and that should decrease TXV valve flow. Otherwise, I'll have to go with electronic controlled valves. Some are quite cheap, but I've not designed or seriously researched stepper motor drives before. I could control the expansion valve based on motor amp draw and outgoing water temperature. The latter to intentionally limit the low water temperature to avoid condensation at the PEX manifolds.