apophis,
Thank you for writing from Finland, a country I hope very much to visit some day.
I will let someone else comment on the theoretical aspects of R290 vs. R407C, other than to say that I know that in terms of performance, they are are very similar, and that R290 is often used as a 'drop-in' replacement for R407C.
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Originally Posted by apophis
Originally the Nibe 410P makes over 50 degrees water from the constant exhaust air of about 22 degrees.
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It sounds like your unit is scavenging heat from house exhaust air and returning it to in-house use, which is a very clever design. I do not know of any designs like that in the US. It sounds like some of our guys could take this as an excellent challenge, to make their own units that operate in this manner. I have heard of industrial units that operate like this, and they are described as 'active heat exchange ventillators'.
Quote:
Originally Posted by apophis
This system can make 47 degrees easily from 10 degrees ambient air. I wonder if I should change the software to make hotter water when ambient temp is higher? How would it affect COP? And what is theoretically possible with R290?
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This is a very good, to be thinking like this...
I would say that if you try to make hotter water from ambient air, that is remaining at the same temperature, your COP will decline, and the hotter you want to go, the more the COP will decline.
On the other hand, the COP, of a fixed-temperature tank will increase as ambient air temp increases.
So, when you try to do both of these things at the same time, you will have a multi-variant relationship. Which is very difficult to predict intuitively. It would be possible to predict the COP vs ambient air vs. tank temp relationship, if more data was available...
If you did actual testing, and had the appropriate data that was of the scenario wherein you had constant tank temp, and varying ambient air, it would be possible to graph a curve that would portray COP vs ambient air. From these data points you could do a regression analysis and determine the mathematical equation that would accurately predict that curve.
In a similar fashion, if you did actual testing, and had the appropriate data that was from the scenario wherein you had no limit on the tank temperature, and let the tank rise to whatever temp it might rise to after runs of the same time duration, with the external difference being only ambient temperature, you could plot this data as tank temp vs. COP. From these data points you could do a regression analysis and determine a second equation, that would accurately predict that curve.
Then you could combine these two equations, and the resulting equation would portray the multi-variant situation that you are concerned by.
This final equation could be predictively incorporated into the software of your Raspberry Pi program.
Or, you could do it by trial-and-error.
Best,
-AC