[jeff5may]

Thanks for the rundown on your data logging process. What equipment are you using between the wiring and your eyeballs? What level of accuracy does this mysterious device provide? Is it some obscure, laboratory grade instrument, or a Chinese hobbyist contraption? Or something in between?

Being a captube driven rig, the flow rate is mainly determined by the difference in pressure the compressor can force. When the tank is cool, the delta T between tank temp and ambient air is small, so the compressor will be moving the most volume possible due to the low compression ratio. As tank temp rises to your target temp, discharge pressure will follow. This rise in compression ratio has a double effect: on the one hand, there is a larger delta P across the cap tube, so it will pass more liquid. OTOH, the compressor needs to do more work on every stroke.

What this says simply is that as tank temp rises, mass flow will generally rise, due to the increased delta P across the cap tube. At high tank temps, you can flood your evaporator if it cannot boil off all of the refrigerant. With what you have logged, this will not happen unless the suction saturation (pt chart) temperature rises close to ambient. This condition can occur regardless of fan speed if you add too much charge. This is why you want to set your system charge above your max tank temp during normal operation. Let's say above 130 degF, since you are going to be popping your thermostat around 110 degF.

If you slow your evap fan down, this potential for flooding will increase, due to its reduced effectiveness. The refrigerant will travel further through the evaporator before it's fully boiled off. This condition is desirable, since more working surface area generally equals more heat transfer. With the high superheat values exhibited, you are not fully loading your evaporator, due to the massive airflow in relation to the compressor capacity. In simple terms, the surface area in your evap coil is being wasted.

Matching airflow to compressor flow can be done either way. You can add charge, moving more energy faster at higher power draw, or you can slow the fan speed, slowing heat flow over more surface area at lower power draw. There is no way to know where your optimum design conditions will lie until you define what you strive to accomplish with this rig. If you want max power savings, everything will end up different than if you want maximum recovery rate. In a way, me and rb are both correct in our recommended courses of action.

Keep running trials, what you just posted for numbers is better performance than some store-bought units. How much ROI you get out of the unit depends on longevity as well as COP, so if you run close to the edge of your operation envelope it may not live a long time. Either way, this is an excellent rig to learn about the factors at play. Since you aren't dealing with thousands of watts of energy, it is much more forgiving than a larger system. It ain't gonna run away on you and blow something up in a hurry.

I hope this helps and doesn't confuse you too much.