All-electric heat pumps

Suppose you want an all-electric heat pump system with a 200-liter built-in boiler and can't put any other money into insulating your home or the delivery system. Then you need to set the central heating temperature to 55℃ for at least one winter to make sure your radiators can keep the house warm at that temperature, too. When that succeeds, your home is suitable. This system is then called a bivalent solution where you supplement the heat pump's shortage of required heat energy (every heat pump has a harder time delivering the required capacity in cold weather) with an electric element. The point at which the heat pump no longer saves it on its own is also called the "bivalent point."

The advice is, of course, to choose the most suitable machine; for the example below, we will use the HMA 100-S from Mitsubishi Heavy Industries. This is due to the fact that the heat pump must be able to make 55℃ of water. The bivalent point of this system is -6 ℃. The rest of the energy must be generated by the built-in electrical element. Based on these data, we can calculate the savings per year. This calculation tells us that you will save only €113 per year with the above example. But of course you don't do it for that, that's not the way to get the purchase of your heat pump out of it!

If you did manage to insulate and have a low temperature delivery system installed, such as underfloor heating (most newly built homes are currently made this way), then the savings would be about €700,- per year. This is because less heat is lost, but also because the heat pump runs more efficiently with a water temperature of 35 ℃. In this case, we would advise against the type 100, mainly because of the higher purchase cost but also because the unit no longer fits the house. A type 71 fits better now, with a bivalent point of -12 ℃ and a savings of €645 over a boiler. The difference of €55,- per year is not made up by the higher investment of about €600,- to €1000,-. An HMA 60-S is the cheapest model and also saves, its bivalent point is around -7 ℃ and the saving is still about €430,- per year. Now it's starting to look like something and you can now also clearly see why insulation and a proper delivery system are so important for heat pumps.

The best choice

With a hybrid system, I would actually always recommend a combi boiler and in the example home choose only the smallest heat pump. After all, the boiler catches the deficits and so the investment remains as low as possible. The use of the combi boiler has everything to do with limiting the installation space, for this reason we also remove the domestic hot water consumption from the calculation. Of course, a hybrid system can also be set up as a bivalent system, in this case, by eliminating the tap water and lowering the water temperature, the bivalent point is 3 ℃ and also the savings are €370 per year. This is already interesting but it can be better. When the machine is used as a hybrid variant and thus turned off at +/-5 ℃ outside temperature the savings grows to about €920,- on an annual basis compared to a boiler alone. With an energy price increase of 3.5% per year, that comes out to almost €17,715 after 15 years.  If in this case the type 100 would be used, the savings are only €35,- more per year and that is not worth it because of the higher investment!