A2A Can I measure COP for heat-pump that doesn't use water? How do I configure it?

I have: A self-hosted EmonCMS server, an IoTaWatt sending data to it, and a newly installed Bosch air-source heat pump.

I want: COP data in the My Heatpump app on EmonCMS.

I’ve been reading a lot from this forum and from the docs and from what I gather people are measuring the heat of water from their heat pump, but for my system, except when the temperature gets low and the gas boiler turns on to make up the heat difference I don’t think there’s any water involved. I’m fairly confident that the lines between the condenser and the air handler are filled with coolant fluid, not water, so the pictures in the docs don’t apply to me.

Question I have is: is it possible to gather enough metrics from just the air temperatures to figure out the COP with EmonCMS?

I can easily get: 1. The return air temperature (usually 20-24° C), 2. The leaving air temperature (usually 12° C when actively cooling), 3. The indoor temperature, 4. The outdoor temperature.

So assuming I can use this data, how to do configure the app with it?

  • I understand heatpump_elec and heatpump_elec_kwh, I’ve got that.
  • I have no idea how to measure heatpump_heat in kwh, how do I measure this?
  • Is heatpump_flowT the air temperature leaving the unit after it’s been conditioned?
  • I understand heatpump_returnT, I assume it’s fine to use the return air temperature instead of the return water temperature, yes?
  • I undertsand heatpump_outsideT, I can provide this
  • I understand heatpump_roomT, I can provide this
  • I have no idea what heatpump_flowrate is, would this be the air pressure difference measured with a manometer?
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Hello @guidoism

There are a couple of similar threads that might be useful:

I did try to estimate heat output on a Midea split air to air heat pump a few years ago, but have not revisited in detail. These were the notes I took down at the time:

Test results:

  • Average power consumed by the heatpump in test: 670W
  • Average air out: 40.3C
  • Average air in: 22.7C
  • Delta T: 17.6K
  • Outside temperature: 17.3C

Air to air calcs:

heat_output_factor (W/K) = (fan_air_rate (m3/h)/3600) x air_density (kg/m3) x specific_heat (J/kgK)

deltaT = air out - air in

heat_output = heat_output_factor x deltaT

3 air rates in the datasheet: 600 m3/h, 500m3/h, 360 m3/h

heat_output_factor (W/K) @ 600 m3/h = (600÷3600)×1.204×1012 = 203 W/K

heat_output_factor (W/K) @ 500 m3/h = (500÷3600)×1.204×1012 = 169 W/K

heat_output_factor (W/K) @ 360 m3/h = (360÷3600)×1.204×1012 = 122 W/K

Running on full fan power ~600m3/h suggests heat output factor of~203W/K

Lets say ± 50m3/h so 550-650 m3/h fan speed to give us an error range

So heat output ~ 17.6K x 203 W/K (186-220) = 3573 W (±300W)

COP = 5.33 (4.9 - 5.8)

The problem with this is knowing the fan air rate accurately, especially on variable speed blower units…

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These are notoriously difficult to instrument

Short of setting up a cowling to (a) even out and (b) measure the air velocity accurately you’re scuppered on mini splits

If it’s a centralised, ducted, setup with more even duct velocities you might have more luck. I would be researching how to measure duct velocities in air handling systems - north america should have better resources for this and it would be a great product / solution to develop given the energy use of some homes.

Note @TrystanLea you ALSO need to take into account condensation when cooling. A lot of your cooling energy in the “sticky season” is going into dropping water out of the air; not just cooling the air. This could probably be measured volumetrically if it syphon-emptied through some clockwater water meter.

Heating is easier to measure.

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Thank you for all of this information. I had missed the assumption that heat pumps in the UK tend to be air-to-water. All of the documentation here makes a lot more sense now.

It really is unfortunate that these metrics are difficult to capture. Here in the US, HVAC has an aura of mysticism and ignorance surrounding it and when working on my new system I had trouble finding a contractor that was even aware that modern heat pumps work below 5° C or that someone would even want that.

I had my fingers crossed for a nice plug-and-play solution but I’m happy to deep dive into this world and see what sort of data we can uncover. As stated in another thread, calibrating the measurements is going to be the problem.

I’ve wired up some BME-680 sensors to some Pi Picos to get temperature, humidity, and air pressure measurements from the input and output of the air handler.

At least that’s some data to start with. Maybe won’t be able to get some single number that I can compare with others but it’s something to watch during different seasons.

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Hello @guidoism, sorry to highjack this thread but I’m really interested in your calculation of the COP of your Midea AC.

I have a Faikin installed on my Daikin split unit and it provides a lot of data to play with. I have radiator (liquid) temperature, some information on airflow (fan rpm to calculate cfm), room temperature at the unit and outside temperature.

Do you think this would be enough to calculate the energy output and therefore the unit COP?

@adude0 what is the radiator temperature on A2A split? is that the temperature of the condenser? do you have outside temperature? and electricity consumption?

It is the temperature of the condenser/evaporator (depending which mode you’re using) inside the split.

I have outside temperature and electricity consumption. Also room temperature at the split itself.

Would this be enough to calculate energy production therefore COP?

No answers I’m afraid but I’m following this discussion with interest since I will need to heat a not-yet-constructed building that won’t have any stored hot water and I’m currently favouring a multi-split Air-to-Air system from Daikin - and I very much like the look of the Faikin boards for doing the monitoring.

(That screenshot looks like it’s from openHAB, is that right?)

You can infer heat/cool delivery if you know about the compressor and the temperatures on the refrigeration side in addition to the leccy power. I suspect some OEMs will offer estiamted heat/cool delivery based on this.

You could measure heat/cool delivery if you knew the inlet/outlet temperature/humidity and the mass airflow.

You don’t have either of those unfortunately.

What are these ‘Faikin’ boards/tools? Looking at a Daikin A2A myself.

I could measure temperature and humidity of the inlet and outlet side with two am2301 but I won’t have a mass airflow sensor.

So it’s a no then :confused:

Faikins are small esp32 boards with an open source firmware. There is a port for esp2866 too. You can get them on amazon for around 40€/$40 or build them yourself.

The firmware interprets a daikin serial protocol and they connect to almost every daikin split unit, sometimes it’s a direct connection sometimes you need to connect a couple pins here and a couple pins there :slight_smile:

Unfortunately apparenty they do not provide enough information to calculate heat/cool delivery, even tough they do provide a lot more info than the cloud-only app.

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Apropos to the conversation: https://www.youtube.com/watch?v=Hv6urCTRV70 This guy straps temperature sensors to the vapor and the liquid lines.