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Calculating COP on a mini split?

bfw577 | Posted in General Questions on

Saw on another post Akos mentioned you can calculate a rough COP number on your mini split with the below forumula. I know many people on here have electricity monitors on their splits and with just a thermometer and the fan cfm off your submittal sheet its pretty easy. I have been recording my return and supply temperatures on both my units as well as electricity consumption.

Its currently 50 degrees here and my unit is running at a COP of 8. 

CFM on low 250 off the fan data
Delta t of 20
Drawing 200 watts.

From Akos post

COP=(RatedCFMofHead*deltaT*1.08/3412) / CompressorPower

250×20×1.08/3.412/200= 7.9

Cop 7.9

Does that look correct? Has anyone else calculated their COP.

I attached screenshots of my live data.

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  1. Jon_R | | #1

    I'd make minor changes. Include the indoor unit, so maybe:

    COP=(RatedCFMofHead*deltaT*1.08/3412) / TotalPowerkW

    (250*20*1.08/3412)/.220= 7.2

    A very different method is to alternate 24 hour periods with electric heat, comparing the total electric usage of each. Optionally adjust for outdoor temperature.

    1. bfw577 | | #2

      Thanks. I realized I was using kw and not watts and had to add a decimal point. I was also drawing slightly over 200 watts. It was closer to 220 as you suggest.

      I am going to experiment measuring the actual CFM for a more accurate result with my digital manometer. Though my numbers are pretty spot on to the published numbers including the NEEP cold climate list.

      Its unusually mild here in New England today and it looks like my 12k Gree Sapphire was running close to a COP of almost 10 for awhile this morning. I didnt realize they could get that high. Most of the published data seems to be for when they are running at max capacity.

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