Interpreting the graphs from the emonPi monitoring my heat pump

Applications
1

I have a 6kw Carrier air to water heat pump connected to a 6-zone underfloor heating system and a mains pressure 200 litre hot tank. The system has only one circulation pump, no buffer vessel and a three-port valve to switch between hot water heating and underfloor heating with the hot water as the priority service. I have fitted a heat pump monitoring system to find out if:- is the heat pump short cycling, is it switching off when few zones are calling for heat and is it working properly. The underfloor pipes are buried in thick screed/concrete so have a high thermal storage of heat and I operate the heat pump with an off-peak electricity supply. For most of the year I only turn the heat pump on during the off-peak hours - midnight to 5am (I have added an extra expensive hour until 6), 1pm to 4 pm and 8pm to 10 pm. This keeps my running costs down.
My emonPi monitoring system has temperature sensors on the top of the tank and the flow and return pipes leading to the hot tank. The electrical sensor measures the total electrical supply to the system including pumps. There is no connected immersion heater.

I attach copies of several graphs
1

This was last night when it was cold (below zero) outside and the heat pump seems to be de-icing regularly. It started at midnight and heated the hot water to 45C until 12:30 and then switched to underfloor heating.

2
This was during the day – it heated the water until 2:20 pm and then switched to underfloor heating – you can see 2 zones turning off completely at 14:30 and 14:40 and the thermostat cycling the heating before turning off and on each zone shown by the closely packed vertical lines.

One further thing I noted from all the graphs over the last month was that at no time did the heat pump turn off as a result of an inadequate load/flow.

I am surprised at the lack of switching off and wonder if my heat pump has a variable output run by an inverter and DC motor as, despite no buffer tank, it seems very tolerant of a completely zoned underfloor heating system. My heat pump is a 30AWH006XB.

I would be most grateful for any comments on my interpretation of these graphs and any further comments on what I can learn from them.

Screenshot 2024-02-12 100251 ice removal
Screenshot 2024-02-12 100251 ice removal1722×1005 205 KB

Screenshot 2024-02-12 100459 - heating zones turn off
Screenshot 2024-02-12 100459 - heating zones turn off1741×999 162 KB

2

Your charts only show temperatures relating to the hot water cylinder. Do you have temperature sensors on the flow and return pipes leading to the heat pump? This would make it easier to see how the heating is performing.

It is odd though to see the flow temperature for the cylinder rising with each heating cycle, but not the return temp. Perhaps it is too close to the diverter valve, and some heat is leaking across from the heating circuit?

Yes, this model does have an inverter compressor, so it is able to reduce power in response to the demands of the property. In the second chart we can see the heat pump power reducing as some zones switch off.

Looking at the heat pump power, if does not appear to be cycling, and the frequency of defrosts looks about what we’d expect.

3

No, as the geography makes it more difficult than monitoring the hot water flow and return pipes.
The flow sensor is located on the pipe about a meter away from the hot tank under the insulation so it reflects the room temperature after a while. The return sensor is located on the pipe much closer to the tank so receives heat/cold from the tank when there is no flow.
" Yes, this model does have an inverter compressor, so it is able to reduce power in response to the demands of the property. In the second chart we can see the heat pump power reducing as some zones switch off.
Looking at the heat pump power, if does not appear to be cycling, and the frequency of defrosts looks about what we’d expect."
Thanks you - that is very helpful to see it all seems to be normal.

One further question - the flow rate for the hot water is 12 liters/min and for the underfloor heating is a max of 10 liters/min with all the zones calling for heat. The heat pump seems to be able to deal with this low flow rate as it doesn’t do short cycling but would the performance be improved by adding an extra pump to increase the flow rate?

Edited post for readability. Moderator - BT