KfW55: Gas or air-water heat pump with/without photovoltaics

Hello,

I myself am overwhelmed by all the abbreviations in the subject line. I asked a similar question elsewhere, which was apparently wrong since I did not get good answers.

We want to build in NRW (Dortmund) and have not yet decided on the heating technology (single-family house, 150 sqm, solid construction, underfloor heating). According to Kfw55, these two approaches are possible for us:

[*]Condensing boiler, solar domestic hot water preparation (standard values according to DIN V 4701-10), central ventilation system with heat recovery (heat provision efficiency > 80%)

[*]Air-water heat pump with surface heating system for heat transfer, central ventilation system with heat recovery (heat provision efficiency > 80%)

Acquisition costs: Option 1 is cheaper, although with option 2 we can do without the gas connection
Operating costs: can they be considered equal?

Option 1 and 2: I have to drill holes in the wall to get fresh air, for both options. When does an ugly box (fan) have to be placed in front of the house

Option 2: THZ304 (integral system) was recommended to us. Is that suitable for our house and normal consumption? There is also a THZ304 SOL version of the system.

Option 2: would it be worth installing photovoltaics additionally so that there are no too high electricity costs in the cold months (heating rod)? But in winter there is little sun anyway, then photovoltaics won’t help much.

We simply have to decide on either 1 or 2 and I am grateful for any competent answer. The main thing is no fan box on the house

Best regards
Marko

[*]Condensing boiler, solar domestic hot water preparation (standard values according to DIN V 4701-10), central ventilation system with heat recovery (heat supply efficiency > 80%)

[*]Air-water heat pump with surface heating system for heat transfer, central ventilation system with heat recovery (heat supply efficiency > 80%)

Acquisition costs: Variant 1 is cheaper, although with Variant 2 we can do without the gas connection
Operating costs: can we say the same?

Variant 1 and 2: I have to drill holes in the wall to get fresh air, for both variants. When does such an ugly box have to stand in front of the house (fan)?

If I were you, with a KFW 55 standard and underfloor heating, I would choose the air-water heat pump + controlled residential ventilation/heat recovery.

Operating costs: Definitely comparable, not much difference. +/- 10 euros per month more or less. Thermal solar is not economically viable.

The box: is the heat exchanger of the air-water heat pump, which with a split system has to stand in front of the house or in the garden. There are also integrated systems where the heat exchanger is inside the house. Let your heating installer advise you on what makes sense in your specific case (preferences, structural conditions, heating load, domestic hot water storage, noise levels, ...).

The controlled residential ventilation / heat recovery requires one or two core drillings, depending on the design and model. You do not have a box with a fan on the house with this. Mostly there are two ventilation openings in a selectable form and design at different heights.

A photovoltaic system also produces some electricity in winter, but the rule of thumb is: 3 months per year little to almost none. Installing photovoltaics only to support the heat pump in winter is not practical, although I think it makes more sense than a thermal solar system, which does nothing in winter.
Photovoltaics, especially with a small storage battery, help you reduce your electricity costs and pay off - properly dimensioned - within reasonable periods. You should decouple the issues. And in the case of pro-photovoltaics, you should be glad that you will have a certain usable share even in winter. In transitional periods anyway. From March to October, most of the load runs through such a system.

Best regards
Thorsten

We were faced with a similar decision and chose 2.

We face the same choice and tend towards option 2. Also because you have a much tidier utility room without a controlled residential ventilation system on the wall, the large buffer plus three expansion vessels and the boiler itself. Instead, you have this massive cabinet. However, for us it was also said that with option 1, a bit more insulation still needs to be installed and overall it is somewhat more expensive.

The Tecalor that was offered to you is a system without the box in front of the house. But I’m not quite sure whether at around 150 or 160 sqm it doesn’t reach the limit for the stronger 404. Because you don’t have the noise box in front of the house, you do, however, have some action in the utility room.

We faced a similar decision and chose option 2.

And did you regret the decision? I don't think so, right? Which air-to-water heat pump system did you install, also THZ304?

We are facing the same choice and are leaning towards option 2. Also because you have a much tidier utility room without the controlled residential ventilation system on the wall, the large buffer tank plus three expansion vessels, and the boiler itself. Instead, there is just this massive cabinet. However, we were also told that with option 1 a bit more insulation would have to be installed and that it would be somewhat more expensive overall.

The Tecalor offered to you is a system without the box in front of the house. I’m not quite sure whether for around 150 or 160 sqm that’s not the limit before moving up to the stronger 404. Since you don’t have the noise box in front of the house, you do get some action in the utility room.

So up to 150 sqm the THZ304 should be sufficient.
Regarding noise, we were told that with an air-water heat pump, the utility room is additionally insulated.

For the THZ304, a sound power level of 56dB is specified. No idea whether that is a lot or not.