Cut costs with a hybrid or all-electric heat pump?
Hybrid vs all-electric heat pumps
Perhaps you know it, you would like to become more sustainable with the result, reduce your impact on the environment. What you do it for is something you decide for yourself. Maybe you do it for your children or theirs, to set a good example or secretly just because you want to reduce your monthly costs with the energy supplier! Whatever the reason, sometimes your resources are not always sufficient to make the move to gasless. Sometimes it is better for the environment, but your consumption in hard euros is still lower if you continue to use a little gas.
Heat pumps may be the answer. There are many options and that doesn't make it any easier. In this blog article, we discuss hybrid systems compared to all-electric systems. When is it better to buy a hybrid system and when is it better to save up for an all-electric solution?
Living in the Netherlands
The average single-family house in the Netherlands in 2012 had an average area of about 120 m2 and was built between 1965 and 2005 with an average of two to three residents. Such a house has a heat demand of about 10 kW (including showering) and a high temperature release system where the central heating combi boiler with an efficiency of about 90% is tucked away in a small space.
Of course, the cause of a problem (in this case that your home loses heat in winter) should be addressed first with insulation, for example. Then you start fighting the symptom (in this case, warming the space that is cooling). With good insulation, you can reduce your heat demand by about 4.8 kW! That's a significant amount.
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.
Hybrid heat pumps
And now back to hybrid systems, in a hybrid system we don't look at the bivalent point of the system, but when the boiler is more economical (in Euros) than the heat pump, from then on the heat pump is turned off and only the boiler does the work. We will now also calculate with a heating line (a heating line provides a higher water temperature at lower outdoor temperatures to provide more capacity, at -10℃ is 55℃ in our example and at 0℃ is around 45℃). We are fingering a water temperature at 45 ℃ in the calculation because that is approximately the water temperature in the firing line at which the boiler performs better than the heat pump, and so we want to look for the heat pump's switch-off point at that water temperature. Because the heat pump also runs at a water temperature below that, the numbers given below are on the low side compared to reality, though. This is because the switch-off point of the heat pump at a water temperature of around 40 ℃ is on the heating line. However, manufacturers give their data at 35℃, 45℃ and 55℃ water.
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!
Our conclusion is: When insulation is not an option, but you want to use a more environmentally friendly way of heating your home, choose a hybrid heat pump. When insulation is one of the options, an all-electric heat pump is the best solution! In both cases, make sure you are well informed and choose the right system for your home. A heat loss calculation can help and costs about €500,- from an independent party.
Energy prices used:
Single tariff: €0.26 p/kWh
Gas price: €0.89 p/m3
https://www.greenchoice.nl/tarieven/ (Aug. 9, 2021)
Efficiency of boiler is set at 90%, upper calorific value of gas 35.16Mj/m3