Estimating Power from MelCloud data

Hardware Heatpump
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Hi,

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?

Many Thanks,

Chris

2

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:

FlowTemperature - ReturnTemperature × WaterPump1Status × WperK → heat and heat_kwh

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As this uses Log and Power to kWh processes, so can’t be done with virtual feeds.

I also have a method to estimate electrical consumption from MelCloud, but you don’t need that if you have power from emonTX.

2 Likes
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@Timbones - Thank you so much for the detailed response.

Do you use a similar calculation for the hot water?

And will the MyHeatPump app then sort out COP, etc?

4

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:

Screenshot_20240925_185129_com_android_chrome_ChromeTabbedActivity
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Use WaterPump2Status for central heating signal.

1 Like
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Thank you. Really appreciate your help.

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Hi @Timbones,
I was wondering about the input and output power from MELCloud as at the CN105, Input power seems to be:

0 if between 0 and 1kW,
1 if between 1 and 2kW,
Etc.

I would be interested to see your formula for input power estimation

Output power seems to be rounded to the nearest kW, but both in & out reported on the CN105 to 0d.p.

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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.

Screenshot_20240926_074900_com_android_chrome_ChromeTabbedActivity
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For anyone who needs to know: Flow rate can be read from Running Information on the FTC unit, code 540. It’s not available from MelCloud.

Beware that glycol systems will show a slightly lower flow rate by a couple l/min, so will need to adjust for that.

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@Timbones - So what is available in FTC may not be accurate? What sort of magnitude of adjustment are we talking?

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Two points of clarification please -

The MELCloud value is not in Hz when this is the units presented by the CN105?

How do you account for frequency limiting in Eco hot water (60 or 64Hz maximum)?

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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.

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  • 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?

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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.

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Based on my rating sticker:

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Is maximum 2668W or 2093W?

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

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Looking at the manufacturer’s spec sheet [PDF], maximum input is 3.27 kW.

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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).

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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.

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This is based on equations for mass flow rate heat transfer.

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.

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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:

# Carnot heat calculation
condensing = flowT + 2 + 273
evaporating = outdoorT - 6 + 273
carnot_cop = condensing / (condensing - evaporating) * 0.5

if electric < 100: # ignore standby power
    carnot_heat = 0

carnot_heat = electric * carnot_cop

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.

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This is how i was thinking of doing it -

or, trying to determine based on onboard monitoring where it might be: