How do I know if my heat pump is using too much electricity?

[dymonite69]

I suspect my heat pump is needing more electricity to heat our house than necessary.

We have a well insulated house with double glazing.

I made some thermal conductivity calculations and estimate that the entire house should be losing around 5.5 kW. This is based on the R values of the building materials and the indoor-outdoor temperature gradient.

We have a Daikin 15.5 kW inverter system.

My assumption is that the amount of heat lost by the house needs to be equally replaced by the AC.

However, our electricity consumption suggests that the unit is putting out 10-12 kW heating energy * continuously just to maintain our thermostat setting. This is at least double what I would expect. Furthermore we only condition half the house at any point in time.

Is there a way of knowing the true heating output of the unit given its electricity consumption.

I would be grateful for any comments.

* Assumes COP 3 (outdoor 6C indoor 21C)

[RSTC]

Don't forget you have to add on the heat lost through infiltration/ ventilation. That could be as much as 4 or 5 kW (depending).

[Yuri B.]

Not original idea: take the note of how much electricity has been consumed for a week using the heat pump, then turn off the heat pump for another week and heat your house (keeping the same temperature and relative humidity) with electrical heaters, and finally, compare the measurements (taking into consideration what outside mean temperatures there were) - you will see how effective the heat pump is.

[RSTC]

^good suggestion, but a couple of hours on a cold day will give the same result as it's not an exact science.

On top of the compressor power many heat pumps have 'back-up' electrical heaters, make sure these are being controlled correctly, I've seen these on 24/7... same with immersion heaters for DHW.

If it's water to water take a look at pumping power that could be a couple of kW in total (that's over 10,000 Kwhr/yr)