I’m looking to take my heat pump monitoring a step further and have been playing with the MyHeatPump app.

My current set up involves feeds of data from emonTx4 (power only), MelCloud, and Octopus.

This gets me pretty close to everything I need to feed into the app. I’m hoping to be able to fill in the blanks - the most prominent of which is heat output.

I fully understand that this figure is not going to be 100% accurate due to MelCloud but want to get as close as I can without adding to the setup. *

MelCloud provides Flow and Return.
I know the flow rate to be 24l/min.

I have been looking at the calculations and believe this should get me to a power figure which I can accumulate to kWh.

Is this a reasonable approach?
Is processing the inputs the easiest way to achieve this? Or can I do anything with virtual feeds?
Do I need to take anything else into account? Pumps, OperationMode, etc?

I have been doing something similar to estimate heat from Melcloud for a handful of systems.

I’ve pre-calculated the heat output for different flow rates. 24 l/min equates to 1672 W per K of dT, where dT is the difference between flow and return. If 20% glycol then this drops to 1572.

The feeds you need to pull from MelCloud are:

FlowTemperature

ReturnTemperature

WaterPump1Status - primary pump

ValveStatus3Way - 0 = heating, 1 = dhw

Then use input processing to compute the following:

Hot water may have a different flow rate, but I’ve not tried to compensate for that. Difficult to fiddle with using input steps, but could be calculated separately and then combined.

Yes, these will plot nicely in My Heatpump app.

Here an example compared against carnot factor 0.5:

When fitted with meters*, Melcloud reports watt-hours for the past minute. Multiply by 60 to get current power in watts.

*CanMeasureEnergyConsumed value will be true.

When there’s no meter, input power can be estimated using HeatPumpFrequency, which is compressor percentage. Divide by a hundred and multiply by the maximum electric input for that model in watts. I.e. 3,270 for 8 kW model, 3,730 for the 11.2 kW model. I also add in the pumps to give something a little more realistic, but it’s very crude. Oh, plus 20W for standby.

I dunno, maybe. For the systems I’ve looked at this happens to map to 100 Hz = full power, and matches the readings I get from my electric meter. Lucky coincidence I guess.

Measured vs. Estimated electricity on left-hand axis up to max input watts for my unit.

HeatPumpFrequency (red) on right-hand axis up to 100 Hz.

I have struggled to sensible numbers from larger units, so maybe they go higher than 100 Hz? So knowing that maximum would allow converting Hz to %. I’ll dig into the history for those units to see if there’s a correlation…

I don’t see why this would matter. This is just equates to less power use, right?

Umm… may need to add 15-25%? FTC claims 12 or 13 l/min for my system, yet calculating the flow from the measured heat & dT comes closer to 15. I presume because the Sika is not calibrated for glycol.

I’ve not tried reading the actual flow rate from the heat meter as it’s hard to get to.

Yeah and this is where i would differ, frequency at Eco cap of 64Hz and consumption continues up to 2670W.
Then swap to heating, frequency up to 78Hz and input power down to ~2000W

I guess this is due to the compressor having to work harder as the refrigerant gets hotter, and so pulls more power for the same frequency. I see the same during the hot water cycle.
(34 Hz, not Eco, but Quiet Mode 1).

So, this estimation of electrical consumption isn’t great and will produce optimistic COP during DHW runs. Could maybe include an extra fiddle factor for flow temperature, I guess. It does seem to be good enough for diagnosing; a couple users have been able to improve performance of their systems based on this data.

An alternative approach uses Carnot COP equation, which might work better where an electric meter is installed. Multiply measured electrical power by Carnot COP to get an estimate of heating power.

Can view this directly in the My Heatpump app, using a typical factor around 0.4 - 0.5. Useful for sanity checking the other estimation method.

Or calculate it programmatically. I use this for a Vaillant system that comes with MID approved electric meter, but doesn’t report flow rate or return temperature so can’t use mass flow equations:

Note the 100W threshold for ignoring standby + pump power; this may need to be higher for larger systems (also a setting in MyHP app). It would be more accurate to subtract the standby + pump power rather than cutting off at the threshold. Or have separate meters for compressor, pumps and controller.