The system I would like to monitor is an ASHP. Currently I am monitoring the HP’s power use with a CT sensor as well as the heat output using a heat meter and the outside air temperature. Using these feeds I have set up the my heatpump app. However, I saw on the learn guide a section on how to set up a simple heat pump model (Learn | OpenEnergyMonitor) and was trying to get it to work to compare the approximate value I get here to the one on the app. However, I am getting VERY different values hopefully someone can point me in the right direction!
Here is what I did:
First I wasn’t very sure whether the T_flow was the HP’s supply to the radiators (hot) temperature or return (cold) temperature. So I created two feeds to see which one got me closer to the COP that i was getting on the app (spoiler…none).
In the website it says the following:
Since the temperatures from my sensors are in Celsius I converted to Kelvin before adding the 4K. Here is how my process list looks like with the two T_flow I mentioned above:
Next I did I similar conversion of units for the T_evaporating feed using the input equivalent to that of the outside air temperature:
Lastly I calculated the COP (using the temperatures already in Kelvin) and then the practical COP.
This is what the full input process list looks like when I used return flow temperature as T_flow:
This is what the full input process list looks like when I used supply flow temperature as T_flow:
Finally here is how the approximated COP look like vs the COP using the app:
ps. A_COP corresponds to that obtained from supply temperature and Approx_COP from return temperature.
Any idea as to which one would be the correct temperature to use and why the COPs are so different? Thank you!!