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First plot done. Initially I missed the discrete minus sign before the 100 that changes the sign of the percentage differences, but it is inluded in this plot:
In fact, some of the differences are negative, at and above around 14.5°C OAT. Methinks that is because that is around about the heat loss break even point (no heating actually needed at and above this OAT).
Midea 14kW (for now...) ASHP heating both building and DHW
Meanwhile, I have done the residual plots for the analysis. These are somewhat technical, but in general terms, these plots indicate whether it is reasonable to use an analysis method that has been used. Here they are, for the two data sets, Setback and No Setback:
The left clustering in the Residuals vs Fitted plots is because there are more data points at higher OATs and so lower energy use. Otherwise, the plots are OK, there is reasonably equal spread about the Residual zero line. The Normal Q-Q plots are also OK, points are on or close to the diagonal dotted line. Conclusion: this suggests the method used was reasonable.
Midea 14kW (for now...) ASHP heating both building and DHW
And finally, the mean daily IAT against mean daily OAT plots. I have broken my 'Y axis must start at zero' rule because on this occasion is may make sense to do so.
Midea 14kW (for now...) ASHP heating both building and DHW
And finally, the mean daily IAT against mean daily OAT plots. I have broken my 'Y axis must start at zero' rule because on this occasion is may make sense to do so.
Thanks for the analysis! This last graph possibly shows the reason for the reduced energy usage at lower OATs. The no setback IAT is broadly flat as OAT drops below 10C, although IAT actually rises below 5C. While the setback IAT diverges noticeably downward, at OATs from 10C to 5C the difference (to the no setback IAT) approximately doubles to over 2C.
You have shown a 10% consumption difference at both 5C and 10C OAT, yet the mean IATs are different (and difference to the no setback IAT), this suggests that to achieve the 10% difference at lower OATs the mean IAT will need to be progressively lower.
The mean IAT with setback is only ~18.5C at 5C OAT and from the no setback values you seem to like an IAT of about 20.5C. If the lines are extrapolated to sub-zero OATs then the setback mean IAT will be 3-4C below the no setback IAT, how low does the IAT get during the setback period at these low OATs?
Also, can I ask how you derived the 1.18 correction factor to the energy consumption? Your independent electricity meter monitors the largest and most variable source of consumption, the other sources of electricity consumption, like water pump and electronics, will essentially be constant and not proportional to heat pump (mainly compressor) consumption.
@hcas thanks for your message saying that from a pure energy consumption (kWh) perspective, a setback makes sense and that you see the same in Havenwise data... could you please expand?
