air heat pump in combination with solar, optional gas connection

Hello everyone,

we want to build a city villa with two full floors without a basement. A air-to-water heat pump was recommended to us. However, we want to support it with a solar system for an additional cost of 7,500 euros, if it is to be used for heating.
Our neighbors are having a gas boiler installed.

Now we thought that a gas connection should be available, just in case.
But having all connections installed also costs money.

We are two adults with two children, the floor area is 9.5 m x 8 m. With a classic underfloor heating system without a ventilation system for the rooms, the basis is set for new buildings.

What makes sense now?

Opinions: In winter there is little sun anyway, and the air heat pump hardly works in summer, so high electricity costs are not to be expected. And solar energy would not be very helpful in winter.

Gas is cheap, but what is the relation if the connection is only optional and may not be used.

I hope it was understandable. I look forward to experiences, opinions and the exchange of knowledge. Thank you.

Take the 7500€ and invest it in a photovoltaic system, you will benefit much more from that than investing in solar. Solar is usually mandatory to comply with the Energy Saving Ordinance with a gas connection, but it hardly ever pays off. There is no need for solar with a heat pump. The be-all and end-all with the heat pump is the proper planning and dimensioning of the system. Your attention should be focused here. PS: I would also reconsider the ventilation system carefully.

. With a classic underfloor heating system without a ventilation system for the rooms, the basis is created for new buildings.

I don't understand this sentence, what does "basis created" mean? I consider the combinations heat pump + photovoltaic or gas + solar to be sensible, but not heat pump + solar. I would prefer gas, but that's probably a matter of belief. I would also take the ventilation system. I would probably not have the gas connection installed now and then not use it.

Then, after reading along in the forum for a while, I would also like to contribute something.

The problem with the air heat pump is that it delivers the lowest COP value exactly at the times when it is supposed to operate. In winter, room heating is needed in addition to hot water. However, in winter the outside air is cold and the temperature lift the heat pump has to perform is higher, which negatively affects the coefficient of performance. At this time, the solar thermal system will also not contribute much to the required heat. So at this time, you have an "inefficient" heat pump and a solar thermal system that is barely active.

In summer, you have the solar thermal system, which depending on the design can cover a large part of the hot water demand, and a heat pump that operates in the optimal range for the conditions. So for the summer case, there is rather an oversupply.

Whether a photovoltaic system can be used efficiently in combination with a heat pump would have to be examined in great detail. It involves similar factors as the interaction between the heat pump and solar. For the photovoltaic system, further measures would probably be necessary to increase the self-consumption rate.

Since noise emissions play a major role with the air heat pump and you have that possibility, I would rather go for gas condensing boiler + solar thermal. Alternatively, the ground source heat pump, which, however, is correspondingly more expensive.

Thank you very much for the informative lines.

I think we are heading in the right direction if we imagine the heat pump unit in a hybrid setup in combination with gas. This way, we would get the optimum in terms of heat and costs in both warm and cold seasons, provided the control system works intelligently.

I don’t know how high the costs are for servicing such gas systems. And whether they pay off over the years when looking at the connection as well as the purchase costs of these hybrid systems.

Either or, everything else is economically quite nonsense. An air-to-water heat pump also operates in winter with about the same efficiency that the costs are approximately those of gas, otherwise the technology wouldn’t even exist here. Geothermal energy would then be cheaper and more efficient than gas, but again more expensive. If you have an older house with high consumption and a gas heating system, you can consider supplementing it with an air-to-water heat pump as a bivalent system in combination with [Photovoltaik] for the transitional months – but not with a new building. Air-to-water heat pump and a large [Photovoltaik Anlage] and you have neither electricity nor heating costs. Whether this makes sense for the specific construction project, or gas or geothermal energy is cheaper, must be examined very carefully, unless it is written in the stars.