Hey Bob,
I started with counter flow, but am now running inline, in order to have lower suction side vapor temperatures, which are needed for compressor cooling. It dd not measurably change water cooling. My 40 plate BHPE is a bit larger than I needed.
I've been doing some reading on the influence of higher temperatures on air cooling performance. I didn't realize how huge the COP/EER losses were as outside temperature climbs.
From this paper with some R410a testing data, page 6:
file:///C:/Users/Bruce/Downloads/A_Comparison_Of_An_R22_And_An_R410A_Air_Conditione.pdf
"If we evaluate the combined data obtained with both compressors, the air-side capacity decreased in a nearly linear manner as the outdoor temperature increased from 27.7 °C (82.0 °F) to 68.3 °C (155.0 °F). Over this temperature
range, air-side capacity decreased from 11.8 kW (40345 Btu/h) to 6.7 kW (22699 Btu/h); a decrease of 43.7 %. The COP (EER) also decreased linearly by 80.3 % as it dropped from 5.36(18.3 Btu/Wh) to 1.06 (3.6 Btu/Wh). "
This performance affect of ambient temperature is much, much higher than I expected. With the ground heating effect, my air inlet is 10F over ambient. My worst case ambient is 103F. So a condenser inlet of 113F. That will give me a COP reduction of 33%, (in my case from 3.5 to 2.35). This has a huge effect on my BTUs, since I don't have enough head room at the compressor for increasing watts much. I should have started with a larger compressor, and limited it's BTU's and watts at the evaporator valve. Then power could climb as temperatures rise to keep the output closer to 10K BTUs.
Evap cooling will buy me 20F in June with single digit humidity in the mid day, so I'd be OK at 103F ambient. I don't like it because of the maintenance with my hard water, but it would be a huge energy leveler/reducer that could make my current condenser unit viable. One thought that comes to mind is since my run hours per June and July are low, if I could find a descale chemical spray to use that wouldn't wreck the fine aluminum fins, maybe I could just use the fan rim system with my well water. That's super simple; I just add a tray and float valve, fed by 1/4 drip tube, controlled by a solenoid triggered by ambient air temperature. I'd just have to blow out the water line in the fall.
I'll probably have to add a water bypass at the BPHE, also, to allow the TXV suction line bulb to in effect, limit the outgoing water temperature. This lets the water (and suction vapor) temperature in the BPHE to be lower than the re-combined combined water temperature, by diverting some water directly from inlet to outlet pipes, not going through the BPHE. I tried to get the 1" Pex crimp tees I needed for this yesterday but ACE didn't have them.
I've read some papers about R290 performing well for higher temperatures, and will follow up on that reading to try and look at their data to see if it's significantly better. It requires a larger volume capacity compressor compared to R410a; R22 compressors are a better match.
More research required, while I wait on the TXV.