Hiya, having issues with COP when heat pump is not running.
Showing a negative COP when the heat pump is off.
This impacts the SCOP.
Also flow errors when there is none in the flow rate chart, even when looking for missing data.
Must be a way to screen this out.
I’m guessing that this is your system?
This is likely due to an error on the flow temperature sensor, as this should reading the same as the return sensor. This difference is showing as negative heat.
Check that the flow temperature sensor is correctly fitted.
Though it’s curious that the temperatures are going up without any electricity or heating power? What’s going on there?
Images of what I am getting
can the discrepancy be screened out?
The Screenshot you have taken is when my immersion is being fed from the solar.
This would need to be screened out as well.
The problem I am having is not when the immersion is running.
I have such a large UFH area and radiators that are one zone there will always be a diffence between flow and return tempersatures giving me a negative COP as compressor is not running.
The heat pump will always flow a little even when on standby, unless switched off.
i know with other manufatures this will be an issure too, so not giving correct COP or SCOP.
Cheers
Sean
This period here shows flow temperature below the return temperature: Emoncms - app view - hence the recording of negative heat.
Flow and return temps should be identical when the compressor isn’t running, and so this points to an error from the temperature sensors.
Unless there is significant heat loss through the outdoor unit. How far is it from the heat meter to the heat pump?
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It’s 3m and is all insulated.
I have seen it multiple times and will happen when it comes off heating mode as compressor is off but the system flow temperature is higher than the return temperature, skewing the figures.
So is there no way to fix this discrepancy?
If the offset is stable most people just add that or subtract from one of the sensors.
Could you share a photo of the heat meter showing how it’s installed? Are the temperature sensors in direct pockets? Could there by any other heat sources effecting the temperature sensor readings?
This should never be needed with a MID approved heat meter, they are supplied with a calibrated pair of sensors.
If your system is idle then it’ll be consuming but not generating.
That’s part of its overall performance so suck it up or physically switch it off if it worries you so much.
There’s a lot more important things out there than tens of Watts in standby.
That’s not what’s happening here. Standby watts don’t result in negative COP.
Looking at the numbers in that segment: with around 8.8 liters/minute flow rate, the temperature offset between flow & return is around 0.06 K to get to the shown -36 W. Isn’t that within tolerance?
I find it helps me to understand these situations by thinking about how heat meters work:
- The have one temperature sensor on their ‘input’ (i.e. Return side) and another on their ‘output’ (i.e. Flow side) and they subtract the ‘input’ from the ‘output’
- The have a flowrate sensor and they understand the direction of the flow
- They work out the Heat by looking at the temperature difference and integrating that with the flowrate
- They (quite rightly) don’t care what’s happening on the rest of the heating circuit, because they ‘zero that out’ by subtracting their ‘input’ reading
- For example, they don’t record any energy added by circulation pumps - unless those are located between the heat meter’s ‘input’ and ‘output’ sensors
So the heat meter is reporting negative heat because the Flow temperature is lower than the Return temperature, as a result of the flow through the heat pump. If that is an accurate reading, heat is being removed from the house. As Tim noted, it seems most likely to be either a faulty (or poorly installed) sensor or heat loss from the outdoor unit.
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Heat loss from outdoor unit there.
This can even happen with the pump off if systems thermosyphon. (cold water sinking into house and warm water rising into outdoor unit)