For a full year I have lived in a house that has one of these.
It’s a hot summer and I’m delighted that it can not only heat but also keep my place cool!
Now I got an email from my electricity provider that during the last weeks (I was at home most of the time) my electricity consumption was roughly twice of what it usually is.
Hence my question: compared to its heating capabilities, does a heat pump use much more electricity for cooling?
I’m not looking for a scientific breakdown.
edit:
Thanks for all replies so far. Cooling seems to be trickier than heating and I should keep my windows closed, which just feels wrong during summer… but apart from that cooling does not use more energy than heating.
Why would they use more energy in one direction versus another? This doesn’t really make sense to me. Heating and cooling is just swapping which element is the condenser and which element is the evaporator.
The line pressures are much higher when heating so the compressors are having to work harder. Plus some units have resistive heaters in the compressors that come on during low temps.
The gradient determines that. Moving heat energy from inside ambient 25°C to outside ambient 30°C is easier than moving heat energy from outside ambient 5°C to inside ambient 20°C, for example.
Heat pumps move heat. In the summer, it’s pulling heat from inside and moving it outside and the opposite of that in the winter.
Basically, the temperature differential is what makes the difference. The larger the differential, the more energy it has to use.
In the winter, when it’s 30 degrees (F) outside, and you want it to be 70 inside, that’s 40 degrees it has to move. In the summer when it’s 90 degrees outside, and you want it at 70 inside, that’s only 20 degrees.
Air source heat pumps, as the name implies, pull heat from (and exhaust heat to) the ambient air. When it’s really cold in the winter, there’s less ambient heat to move inside, so it has to run longer. Some (all?) heat pumps also have an auxiliary resistive heating element to make up the difference which lowers efficiency quite a bit.
Granted, newer heat pumps can work well down to lower temperatures without having to engage the aux heat than the older ones I’m familiar with, but in a nutshell, that’s why they can potentially use less energy in the summer.
If nothing else, the temperature range differential needed is very different from cooling in the summer to heating in the winter. Apologies for my Celsius friends. I think most humans consider 70 degrees to be comfortable. If its 80 degrees outside the differential is only 10 degrees (80-70=10). For most people the hottest outside temperature they may have is 100 to 110 degrees. So we’re looking at a differential of 30 to 40 degrees the heat pump would need to keep.
Now lets look at winter during the coldest months where I am 0 degree days are pretty common and -10 to -30 can happen occasionally. So the normal differential is a 70 degrees! And the uncommon differential can be as bad as 100 degrees! Further, I believe heating/cooling follows the inverse square law which means for each degree of temperature change it doesn’t just increase the effort linearly, but rather exponentially. So the farther away the different the harder it is to reach it, and we’ve just seen that winter is much farther away (larger differential) than summer.
I know for my home’s heat pump I use between 2kW and 4kW running for normal cooling (its a variable speed compression in mine) while in the depths of winter it usually is around 4kW and when really cold outside gets as high as 8kW (in pure heat pump mode). Because the differential is so much larger in the winter, I’m asking it to do much more work.
Besides the temperature differential that everyone else mentioned, there’s also sometimes the need to defrost the outside bits, which means running the heat pump in reverse and undoing a bit of the heating it already did.
Like other commentators have already stated, the conditions (temperature difference) in winter and summer are different.
However, if the temperature differences are the same, only reversed, heating requires less energy than cooling, as the (electric) power is also transformed to heat which in winter, when in heating mode is also usable heat, while in summer, it adds to the heat that needs to be discharged outdoors.
E.g. a heat pump with a electric power consumption of 1 kW and a COP of 5 transfers 5 kW usable heat, but has only a cooling power of 4 kW (and thus, an EER of 4).
There’s the answer I was looking for.
Do you think your example is realistic? That would be 20% - a relevant difference. Not ALL the electrical power consumption will be turned into inside heat I guess?