An update on this post and test result.
The above test results were based on readings from the internal Daikin temperature sensors and flow meter, read using Arnold-n’s P1P2 MQTT bridge. @ColinS has since fitted a class 2 heat meter in order to verify the readings.
We had been using the Daikin’s own internally calculated heat output, but had also been calculating the heat output separately from the Daikin flow rate and DT between flow and return temperatures. Interestingly the heat meter agrees particularly closely with the latter. E.g in the following example from a few days ago:
- Daikin internal heat calculation: 7218W (9.3% below heat meter)
- External heat calculation based on daikin internal sensors: 7715W (3% below heat meter)
- Heat meter: 7956W
Checking the “external heat calculation based on daikin internal sensors” value for the test above (November 29th 2023), we find that the average output is 9.4 kW rather than 8.7 kW [Dashboard] over the 4 cycles. The 0.6C, 7.8 kW cycle, is now 8.4 kW.
If the heat meter is correct and the actual heat output is 3% higher than the calculation based on the daikin sensors then the average output over the four cycles may have been 9.7 kW and for the last cycle 8.7 kW.
While both of these numbers are closer to the datasheet value of 11 kW, that last cycle at the colder outside temperature still represents a 20% lower than datasheet output.
Test 2
Looking at another test from January 2nd this year
Daikin internal heat calculation 0.7C outside, 7.9 kW output.
External heat calculation based on daikin internal sensors 0.7C outside, 8.4 kW output.
Adding 3% we would have expected the heat meter to record 8.7 kW, Which is a similar result as the previous test.
The datasheet output at a mean water temperature of 40C is a little lower at 10.5 kW and a little lower still at 35C = 10 kW (Daikin Technical Datahub). The test temperatures are somewhere in middle so perhaps 10.25 kW. The test result would therefore represent an output that’s about 15% below the datasheet.
Test 3:
January 11th this year
Daikin internal heat calculation -6.5C outside (metoffice), 7.7 kW output.
External heat calculation based on daikin internal sensors -5C outside (daikin sensor), 8.3 kW output.
Adding 3% we would have expected the heat meter to record 8.5 kW. The datasheet output at -5C @35C is 9.6 kW, @40C it is 10.2 kW (Daikin Technical Datahub). While the average test temperature was 33.5C the peak temperature before the defrost is around 38C so perhaps closer to that 10.2 kW output figure. An overall result that is somewhere between 12% and 17% below the data sheet.
Summary of results
| Outside Temp | Flow temp | Test output | Datasheet | Difference |
|---|---|---|---|---|
| 1.3°C | 44°C | 9.4 kW | 10.95 kW | 14% |
| 0.6°C | 40°C | 8.7 kW | 10.5 kW | 17% |
| 0.7°C | 40°C | 8.7 kW | 10.25 kW | 15% |
| -5°C | 38°C | 8.5 kW | 9.9 kW | 14% |