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The glycol will be the main influence on energy here Materially lower heat capacity than water.
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The heat meter temperature sensing is not accurate. It is very precise - the probes are a matched pair and the electical measurement technique ensures high repeatablility/precision - but it does not try to be accurate. The reasons for this are (a) it doesn’t matter for the purpose of measuring heat energy and (b) you can do lower power measurements if you care less for accuracy which is important on devices that need to run on a battery for 15 years.
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Are you not on the refrigerant side here rather than the water side; so will also be seeing the approach temperatures across the heat exchangers here?