ᐅ Planning Heating and Ventilation Systems for a KfW 40 Plus Single-Family Home

Sure, no problem. And wood is a renewable resource, so it cannot be compared to oil.

Hello everyone,

Here is a brief summary of the conversation with the heating engineer. First of all: Our general contractor (GC) works almost exclusively with this heating engineer. Accordingly, it would be quite difficult to hire someone else—unless the building services are completely excluded from the GC’s scope.

Overall, the heating engineer was very likeable and patiently answered all of our questions. He comes across as competent, although somewhat old-fashioned. Examples include:

- He was not familiar with the term "smart grid."
- Installation spacing is done "based on experience" and "feeling." It is not always possible to maintain pipe spacing of a maximum of 10cm (4 inches). He usually installs at 15cm (6 inches) spacing (tighter in bathrooms).
- The length of heating circuits is also “felt out,” but never exceeds 120m (394 feet) in his opinion.
- He would not perform heat load calculations for each room. For sizing the system, he relies on his experience.

Occasionally, he mentioned something along the lines of: "That’s rarely asked about..." which surprised me. Apparently, many homeowners do not engage in the details of their building services, which I find quite unfortunate.

Regarding air conditioning, he quickly dismissed the topic. He said it wouldn’t fit with an ecologically designed 40Plus house, and basically expressed no interest in the subject. I suspect he doesn’t want to install air conditioning because—if I read between the lines correctly—he is not authorized to install such systems. You need some kind of refrigerant certification for that, don’t you?

About mechanical ventilation with heat recovery, he made the following proposal, which I personally find quite interesting, although I can’t judge whether it’s technically feasible:

- Pipes would be installed underground during earthworks and connected to the ventilation system, so the incoming fresh air passes through the pipes underground and is cooled accordingly (temperature in the soil approx. 8°C (46°F)). Additionally, a cooling coil is installed before the ventilation unit to further cool the air. A second path (for winter) would deliver fresh air directly to the mechanical ventilation without going through the underground pipes and cooling coil. This way, you can switch between “winter” and “summer” modes.
- For additional summer cooling, the supply temperature of the air-to-water heat pump would be set to 20°C (68°F).

For the mechanical ventilation system, he recommends the manufacturer WOLF. He still wants to look up the exact model/type.

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

In winter, he estimates that the air-to-water heat pump will operate with a supply temperature between 25 and 28°C (77 and 82°F) to achieve the desired room temperatures of 22-23°C (72-73°F) or 23-24°C (73-75°F) in the bathroom. An additional wall heating system in the bathroom wouldn’t be necessary. However, we should plan for an electric towel warmer to dry or warm the towels.

The air-to-water heat pump is supposed to be from Vaillant. Either the FlexoTHERM exclusive (with aroCOLLECT) or the Arotherm plus or split. In his view, the advantage of the FlexoTHERM is that it is very robust, reliable, and low-maintenance. The downside is that the FlexoTHERM may not be eligible for BAFA incentives. The aroTHERM is relatively new on the market and, according to him, still has some teething problems and is more maintenance-demanding compared to the FlexoTHERM. However, the aroTHERM is eligible for BAFA funding.

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

I already like Vaillant as a manufacturer. Ideally, I would also like the mechanical ventilation system from the same manufacturer. That would be the recoVAIR system from Vaillant, which seems to make a good impression. Or from your point of view, would it be okay to combine the Vaillant air-to-water heat pump with a mechanical ventilation system from WOLF?

It definitely sounds like a case of "we've always done it this way." That can be either good or bad.

DaSch17 schrieb:

Wouldn’t fit with an ecologically designed 40Plus house, etc.

Well, you have to sit in the heat during summer, not him. Experience aside... once the heat is inside, it doesn’t leave quickly because the houses are primarily built to retain heat.

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

DaSch17 schrieb:

Ideally, I would want the controlled ventilation system from the same manufacturer as well.

There aren’t any significant advantages. If Wolf is cheaper for that, go with them. It’s basically the same components everywhere. The difference between controlled ventilation systems is minimal. Controlled ventilation works perfectly standalone, regardless of the brand.

DaSch17 schrieb:

- During the earthworks, pipes are laid underground that connect to the ventilation system so that the incoming fresh air passes through the pipes in the soil first and is correspondingly cooled (temperature in the soil about 8°C (46°F)). Additionally, a cooling coil is placed before the ventilation system to cool the air further. A second route (for winter) leads the fresh air directly to the controlled ventilation without passing through the soil and cooling coil. You can switch between “winter” and “summer” modes accordingly.

You have to be very careful here. This is a geothermal heat exchanger for the controlled ventilation, and if it’s not executed precisely, you will have more problems than benefits later on.

DaSch17 schrieb:

- For additional cooling in summer, a supply temperature of 20°C (68°F) from the air-to-water heat pump would be used.

Yes, that cools the floor. But it has almost no effect on the indoor air temperature or humidity. This has been discussed enough here and elsewhere. Sure, it provides nearly free cooling, but it doesn’t cool the areas that actually need to be cooled to have a noticeable effect.

An air conditioning system costs about the same investment and then produces around 200 euros (about 215 USD) in annual operating costs. With that, you get the desired temperatures exactly where you want them.

DaSch17 schrieb:

- Pipe spacing is installed "based on experience" and "feeling." It is not always possible to keep the maximum spacing of 10cm (4 inches). He usually installs 15cm (6 inches) spacing (tighter in bathrooms accordingly).
- The length of the heating circuits is also based on "feeling," but for him, it is never longer than 120m (394 feet).
- He would not perform a heat load calculation for each room. When sizing the system, he relies on his experience.

Here and there, something like "This is rarely asked about..." was said implicitly. That surprised me a lot. But apparently, many homeowners don’t deal with their building services in detail, which I find quite unfortunate.

They all seem to be cut from the same cloth. Our heating specialist basically said the same thing on the phone. But after meeting him in person, I realized he actually knows a lot more. I think he only gets paid by our general contractor (GC) for the standard approach ("We’ve always done it this way – it usually works"). Ours can and does more – but only if you explicitly ask for it.

I had a proper argument with the GC about what I believe we contractually agreed on. The result was that I had a heat load calculation done and also the floor heating layout planned. This cost me just under 300€ (about 320 USD) and now the heating specialist is supposed to install it exactly as planned.

How it will turn out remains to be seen. So far, we are still at least a month away from installing the roof, so it’s not urgent yet. I can only recommend this approach—without the argument, of course. The 300€ (about 320 USD) are not a big deal, but you get an independent opinion on everything and can engage better in discussions. Especially when it comes to pipe spacing and, for example, wall heating.

They are right. It will be warm and affordable. And that is exactly what standard homeowners order and pay for. Those who want more take care of it upfront. Unfortunately, there is a thread here with several hundred posts where people struggle either to heat their house or save electricity. Luckily for you and me, we researched beforehand and not only after the problems arose.

Mycraft schrieb:

There are no special advantages. If the Wolf system is cheaper, take that. It’s basically the same inside everywhere. The difference is marginal in controlled residential ventilation systems. Controlled ventilation works perfectly standalone regardless of the manufacturer.

My heating specialist, however, would prefer to install the "state-of-the-art" rotary heat exchangers from ZEWO. Apparently, there are still some minor issues to watch out for there. But in the end, we are getting the Wolf system as well.

Mycraft schrieb:

... You have to be very careful here. This is a ground heat exchanger for the controlled ventilation system, and if it’s not executed precisely, you’ll end up with more problems than benefits. ...

I assume you mean condensation inside the pipe and eventually mold growth?

Exactly that risk prevented us from implementing it, along with the "supposedly" low efficiency despite moderate costs (I think it was about 1.5 to 2K since we would have needed an inspection shaft outside due to no basement...)

If you have heat recovery in your mechanical ventilation with heat recovery system, the ground heat exchanger is actually counterproductive.