ᐅ KfW55: Gas or Air-to-Water Heat Pump with or without Photovoltaic System

Hello,

I’m overwhelmed by all the acronyms in the subject line. I asked a similar question elsewhere, but it seems I wasn’t in the right place, as I didn’t receive good answers.

We plan to build in NRW (Dortmund) and have not yet decided on the heating technology (single-family house, 150sqm (1615 sq ft), solid construction, underfloor heating). According to KfW55 standards, these two options are suitable for us:

• Condensing boiler, solar domestic hot water system (standard values according to DIN V 4701-10), centralized ventilation system with heat recovery (heat delivery rate > 80%)
• Air-to-water heat pump with surface heating system for heat distribution, centralized ventilation system with heat recovery (heat delivery rate > 80%)

Initial costs: Option 1 is cheaper, even though with Option 2 we can avoid a gas connection.
Operating costs: can we consider them about the same?

Options 1 and 2: I have to drill holes in the wall to get fresh air for both options. When is it necessary to have an unsightly box (fan) placed outside the house?

Option 2: We were recommended the THZ304 (integrated system). Is this suitable for our house and average consumption? There is also a THZ304 SOL version of the system.

Option 2: Would it be worthwhile to install photovoltaic panels as well, to avoid high electricity costs during the cold months (for the electric heating element)? But in winter there is little sun anyway, so photovoltaics might not be very effective.

We simply need to decide between Option 1 or 2, and I would appreciate any competent advice. Above all, no ventilation box on the house, please.

Best regards,
Marko

bvlgari schrieb:

• Condensing boiler, solar domestic hot water system (standard values according to DIN V 4701-10), central ventilation system with heat recovery (heat supply efficiency > 80%)
• Air-to-water heat pump with underfloor heating system for heat delivery, central ventilation system with heat recovery (heat supply efficiency > 80%)

Initial costs: option 1 is cheaper, although with option 2 we can avoid the gas connection
Operating costs: can we say they are about the same?

Option 1 and 2: I need to drill holes in the wall to access fresh air for both options. When does such an ugly box (fan) have to be installed outside the house?

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

Operating costs: Quite comparable, not much difference. Plus or minus about 10 Euros per month. Thermal solar does not pay off economically.

The box: is the heat exchanger of the air-to-water heat pump, which, in a split system, must be placed outside the house or in the garden. There are also integrated systems where the heat exchanger is installed indoors. Have your heating engineer advise you on what makes sense for your specific situation (preferences, building conditions, heating load, domestic hot water storage, noise, etc.).

The controlled residential ventilation / heat recovery system requires one or two core drillings, depending on the design and model. You won’t have a box with a fan outside the house. Usually, there are two ventilation openings, which can be designed and positioned at different heights.

A photovoltaic system usually produces some electricity even in winter, but as a rule of thumb: for about three months a year, production is low to almost none. Installing photovoltaics just to support the heat pump in winter is not really useful, although I think it makes more sense than a thermal solar system, which basically does nothing in winter.
Photovoltaics, especially when combined with a small battery storage, help reduce your electricity costs and—if properly sized—pay off within reasonable time frames. You should separate these issues. And if you decide on photovoltaics, you can be happy to have some usable output even in winter, and definitely during the transition periods. From March to October, such a system performs quite well.

Best regards,
Thorsten

We faced a similar decision and chose option 2.

We are facing the same choice and are leaning towards option 2. Also because you get a much tidier utility room without the mechanical ventilation unit on the wall, the large buffer tank plus three expansion vessels, and the boiler itself. Instead, there is this massive cabinet. However, we were also told that option 1 requires a bit more insulation to be installed and is generally slightly more expensive.

The Tecalor system offered to you is one without the outdoor unit box. But I’m not sure whether for around 150 or 160 sqm (1,615 or 1,722 sq ft) you’re not close to the limit where the stronger 404 model would be needed. Since you won’t have the noise box outside the house, however, you will have some noise inside the utility room.

MarcWen schrieb:
We faced a similar decision and chose option 2.

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

ares83 schrieb:
We are facing the same choice and are leaning towards option 2. Mainly because it results in a much tidier utility room without the mechanical ventilation system mounted on the wall, the large buffer tank plus three expansion vessels, and the boiler itself. Instead, you just have this large cabinet. However, we were also told that option 1 requires a bit more insulation and is overall somewhat more expensive.

The Tecalor unit offered to you is a system without the outdoor box. I’m not sure if, for around 150 or 160sqm (1,615 or 1,722 sq ft), you don’t reach the limit where the more powerful 404 model would be needed. Since you don’t have the noise enclosure outside the house, you will have some noise inside the utility room.

So, up to 150sqm (1,615 sq ft) the THZ304 should be sufficient.
Regarding noise, we were told that with an air-to-water heat pump, the utility room is additionally insulated.

For the THZ304, a sound power level of 56dB is specified. I have no idea if that is a lot or not.