The Homemade Heat Pump Manifesto

[AC_Hacker]

Originally Posted by Thepprof

Actually I'm just trying to understand more regarding HVAC...

I hope you read the signature block of my posts... it's no joke, I really am not an HVAC tech.

However, your reply gives me a better idea of what you are trying to do.

I think you are correct to be concerned with liability and the use of R290 in a rental, etc.

That being said, and since this is for educational and experimental purposes...

I would say that charging by weight is the best way to go if you are using the original refrigerant on a piece of unmodified equipment and have a good scale. There are some loose estimates of refrigerant weight correction factors when changing to a different refrigerant. But if you do change refrigerants, all of the careful design considerations that went into your unit, all go out the window, and you really are flying by the seat of your pants.

Method #1:

My limited experience is with R22 and R290, and in this case, I found that for R290, the pressures, both high pressure and low pressure, were about half of what was specified for R22. I did some adjusting of the pressure levels until I got a visual indicator (frost) that everything was working properly. I also put some measuring instruments on the machine, and logged data, and put the data into a spreadsheet that had formulas that would calculate efficiency over a 5 minute time period. I used the efficiency numbers to 'tweak' pressure until I reached maximum efficiency.

Method #2

randen used a much smarter way than my method... he measured temperature output and also amps. He had a heat pump, and looked for the coldest output from the output of his evaporator HX (as I recall). He attempted to reach the coldest temperature possible, and also, the minimum current used. So there was a bit of a balancing act there.

Method #3

This would go for the optimum super/sub heat values. Be aware that these will not be the same values as for R22 or R410a. There was a good discussion previously on the Manifesto thread that addressed the optimum super/sub heat values when using R290. There are also 'smart' field pieces that have those values built in, and show super/sub heat... with everything calculated automatically. I suspect my life would be much improved if I had one of these things.

Method #4

This would be your method, wherein you use an IR thermometer and look for a full and even cooling (or was it heating) of your coil area. Personally, I thought that this was pretty darn smart, if you have an air cooled or heated coil. It might not work so well with a brazed plate HX, or a tube-in-tube HX.

So, to my knowledge, these are the approaches to use, in order to get an optimum charge for your machine.

Since most of us here are hacking existing systems, and changing them in ways that are not in keeping with how they were originally designed... and also that we are doing things that would make any properly schooled, god-fearing HVAC tech have uncontrollable conniptions, we have to develope and use experimental methods. And the method you have devised is now part of our possible approaches, our way of working. Thank you for your input.

I would like to hear more from you about what you are learning here... and I would also like to hear from other experimenters as to their ideas and ways of approaching the problem you have brought up.

Best,

-AC_Hacker