Planning of heating and ventilation technology for KfW 40-Plus single-family house

Sure, no problem. And wood is renewable, so not comparable to [ÖL].

Hello everyone,

below is a brief summary of the conversation with the heating installer. In advance: our general contractor (GU) works almost exclusively with this heating installer. Accordingly, it would be very difficult to commission another one - unless the building services are completely removed from the GU's offer.

Basically, the heating installer is very likeable and patiently answered all our questions. Overall, he gives a competent impression, although a bit old-fashioned. Examples:

- the term "Smart-Grid" was not known to him
- pipe spacing is laid "by experience" and "feeling." It is not always possible to maintain the maximum spacing of 10cm. He would usually lay 15cm (tighter in the bathrooms).
- the length of the heating circuits is also "by feel," but for him never longer than 120m
- he would not perform heating load calculations for each room. For the dimensioning of the system, he would rely on his experience.

Here and there, a phrase like, "That is really very rarely asked..." came up. That surprised me a lot. But apparently many building owners don't deal with their building services in detail, which I find very sad.

Regarding the air conditioning topic, he quickly dismissed it. It would not fit an ecologically designed 40Plus house, etc. In short: not his topic and he doesn’t feel like doing it. I suspect he doesn’t want to install an air conditioner because - if I understood between the lines correctly - he has no authorization to install such systems. One needs some kind of refrigerant certification for this, right?

On the topic of controlled residential ventilation, he made the following suggestion that I personally find pretty cool, although I can’t assess whether it is technically feasible:

- Pipes are laid into the ground during excavation work, which are then connected to the ventilation system so that the fresh air sucked in must first pass through the pipes in the ground and is thus cooled accordingly (temperature in the ground approx. 8 degrees). Additionally, a cooling coil is placed in front of the ventilation system to cool the air further. A second path (for winter) leads the fresh air directly to the controlled residential ventilation without the detour through the ground and cooling coil. Accordingly, you can switch back and forth between "winter" and "summer mode."
- For additional cooling in summer, a supply temperature of 20° from the air-water heat pump would be provided.

For the controlled residential ventilation, he foresees the manufacturer WOLF. He still wants to look up the exact designation of the system (model/type).

Is something like this possible? Does anyone have experience with this?

In winter, according to his assessment, the air-water heat pump will be operated with a supply temperature between 25 and 28 degrees to achieve the desired temperatures of 22-23 degrees or 23-24 degrees (bathroom). An additional wall heating in the bathroom would not be necessary for this. However, we should plan an electric towel radiator to dry or warm the towels.

The air-water heat pump should come from Vaillant. Either the FlexoTHERM exclusive (with aroCOLLECT) or the Arotherm plus or split. The advantage of the FlexoTHERM is, in his view, that it runs very robustly and without faults and is very low-maintenance. The disadvantage of the FlexoTHERM: it apparently is not eligible for BAFA funding. The aroTHERM has not been on the market for that long and, in his opinion, still has teething problems and is more maintenance-prone compared to the FlexoTHERM. However, it is BAFA-eligible.

What do you think of these two air-water heat pumps?

I find Vaillant as a manufacturer very good. Ideally, I would also want the controlled residential ventilation from the same manufacturer. That would be the recoVAIR system from Vaillant, which also makes a good impression in my opinion. Or would it be okay from your point of view to take the air-water heat pump from Vaillant and the controlled residential ventilation from WOLF?

It already sounds very much like "we've always done it this way." That can be good but also bad.

Would not fit an ecologically designed 40Plus house, etc.

Well, then you have to sit in the heat in summer, not him. Experience or not... if the heat is inside, it won’t come out quickly because that’s basically what these houses are built for. To keep the heat inside.

I would definitely at least air-condition the bedrooms or have refrigerant lines, etc. installed during construction. For that, he wouldn’t need a refrigeration certificate either.

Ideally, I would also want the controlled residential ventilation system from the same manufacturer.

It has no special advantages. If the Wolf is cheaper for that, take it. It’s the same thing inside everywhere anyway. The difference in controlled residential ventilation systems is marginal. The controlled residential ventilation works perfectly standalone no matter who it comes from.

- Pipes are laid into the ground during earthworks, which are then connected to the ventilation system so that the drawn-in fresh air must first pass through the pipes in the ground and accordingly cools down (temperature in the ground approx. 8 degrees). In addition, a cooling coil is connected in front of the ventilation system to cool the air additionally. A second path (for winter) leads the fresh air directly to the controlled residential ventilation without the detour through the ground and cooling coil. Accordingly, you can switch back and forth between "winter" and "summer" modes.

You have to be very careful here. This is a ground heat exchanger for the controlled residential ventilation, and if it is not executed meticulously, you will end up with more worries than benefits.

- For additional cooling in summer, a supply temperature of 20° from the air-water heat pump would provide.

Yes, that then cools the floor. But it hardly affects the air temperature and humidity in the house. This has been discussed often enough here and everywhere. Yes, it is a quasi free cooling, but it does not cool what should be cooled to have a noticeable effect.

An air conditioning system costs about the same investment and then produces around 200 euros operating costs per year. But then you have the desired temperatures where you want them.

- Laying distances are installed "based on experience" and "feeling." It would not always be possible to maintain laying distances of max. 10cm. He usually lays 15cm (tighter in bathrooms accordingly).
- Length of heating circuits is also based on his "feeling," but for him they are never longer than 120m.
- He would not do heating load calculations per room. For the dimensioning of the system, he relies on his experience.

Here and there the phrase was loosely said: "This is really rarely asked....". That surprised me a lot. But apparently many builders do not deal with their building technology in detail, which I find very sad.

Ah, they all seem cut from the same cloth. Our heating engineer basically said exactly the same thing on the phone. But after I met him in person, I realized he knows a lot more. I believe he only gets paid for the standard ("We've always done it this way - it usually works") from our general contractor. Ours can and does more - but only if you explicitly ask.

In any case, I had a proper argument with the general contractor about what I believe I contractually agreed with him. The result was that I had the heating load calculation created and also had the floor heating layout planning done. It cost me just under 300€, and the heating engineer is now supposed to execute it exactly that way.

How it will turn out now, we shall see. So far, we are still at least a month away from roofing, so it’s not that urgent yet. I can only recommend this approach as well – but without the argument. The 300€ don't break the bank, but you get an independent opinion on the whole thing and can get better involved in the discussions. Especially when it comes to laying distances and, for example, wall heating.

They are right. It will be warm and affordable. And that’s exactly what you commission and pay for as a standard builder. Those who want more take care of it beforehand. Unfortunately, there is a thread here where with several hundred posts people fight either to get the house warm or to save electricity. For your and my luck, we read up beforehand and not only after the child has fallen into the well.

Has no special advantages. If Wolf is cheaper for that, take it. It’s basically the same inside everywhere. The difference in controlled residential ventilation units is marginal. Controlled residential ventilation works wonderfully standalone no matter who it comes from.

My heating engineer, however, would like to install "state-of-the-art" rotary heat exchangers from ZEWO. Apparently, there are still small catches to the matter that you have to watch out for. But we are getting Wolf now, too.

... You have to be very careful here. This is a ground heat exchanger for the controlled residential ventilation, and if it is not executed meticulously, you will have more problems than benefits afterward. ...

I assume you mean condensation in the pipe and then eventually mold?

Exactly this risk prevented us from implementing it, also the "allegedly" low efficiency despite still manageable costs (I think it was about 1.5 - 2K since we would have needed an inspection shaft outside due to no basement...)

If you have heat recovery in the controlled residential ventilation, the geothermal exchanger is counterproductive anyway.