Plus energy house with hydronic pellet stove + WWWP for cooling?

That is a misconception. The house heats up just as much as an old property. It just takes longer for the heat to get into the house and then also longer for you to get it outside again.

Subjectively, our house (if it is not shaded) heats up extremely quickly – but it also cools down extremely quickly again – whenever the envelope is opened. In other words, when the blinds are up in summer, it gets very warm very quickly. But if I open the doors/windows at night in summer, it really cools down quickly again. Timber frame construction – there is hardly any storage mass for the energy there.

Hello Wastl, first of all thank you for your detailed post.

My opinion: a water-bearing fireplace is unnecessary, too expensive and you bring way too much technology into your house unnecessarily. A wood-burning stove, especially from a "coziness" perspective and not really counted in the house concept, can still be installed. Of course, you then overheat your place – so what? Then you just open the windows while the stove is running – it’s not efficient – but cozy.

You are right that coziness is the main focus. But the idea of opening windows in winter to avoid overheating seems a bit ridiculous to me. However, it should be possible to design the stove so that it doesn’t overheat: water-bearing, not dimensioned too large, no direct exhaust, stone slab, as high a proportion of heat output via water as possible. And as I said: shouldn’t the central ventilation distribute the heat throughout the house?

Cooling with the heat pump: You don’t cool the air with the heat pump, but the floor, meaning you send cold water through the underfloor heating, so the room cools down. Many commercial units have "cooling ceilings" installed where exactly this is done. Cold air sinks, which is why this works quite well, but does it cool upwards from a cold floor? Better a decentralized air conditioning or a proper one via controlled residential ventilation, then just be careful with condensate.

I understand the principle of cooling with a heat pump. The performance is naturally limited. Perhaps a decentralized solution for bedroom and living room is better after all. I have only heard that cooling with controlled residential ventilation can only deliver limited capacity due to condensate.

Does fully automated garden irrigation make sense? That depends on the garden, the location, and the rainfall where you are. For me it makes no sense... I can water 10 times in summer if I want,... Whether a garden well pays off has already been hotly debated here, a garden well in the intake shaft of the heat pump? I am curious whether that is technically possible and sensible, you don’t want to suck your heat pump water through the garden pump and then end up without a heat pump?

Well, the idea would be to simply use some of the water that comes out of the heat pump for garden irrigation instead of sending it all back into the ground via the soakaway well. The water would already be up and have been used by the heat pump, so it could then also water the garden.

Regarding the Plus-energy house, I am missing your concept regarding photovoltaics, storage, power management, etc. Do you only want to generate more on paper or actually be independent (including household electricity)?

Well, there is no final concept yet anyway. There are so many unknowns. For example, I am not sure whether a battery is already worthwhile. But the heating system should already be integrated into comprehensive management so that, for example, hot water is prepared when electricity is available. Some devices can then also run when power is available.

True independence seems far from economical at present. In winter you will always depend on external power supply. We are generally still unsure whether a Plus-energy house is even the best idea. Reliable calculations are rare and the future development of electricity prices is difficult to predict.

But it should be possible to design the stove so that it does not overheat: water-carrying, not dimensioned too large, no direct exhaust

A stove heats! Additionally! Overheating occurs!

Stone slab

Stone slabs store the heat

And as I said: Shouldn't the central ventilation distribute the heat throughout the whole house?

The heat distributes actively.

I am not an expert in heating matters, but we have a stove for coziness. The underfloor heating cannot lower as quickly as the heat comes from the fireplace. After a few hours, you no longer want the few degrees increase due to the stove and you throw it out the window.

Whether you passively heat your water with the energy or not – the feeling in the room remains the same.

Cost for the coziness: about 10,000 for a gable roof house all in – certainly a few thousand more if you want to heat your water with the stove. Whether that brings the necessary savings is questionable.

Hello,

It is supposed to be a prefabricated house.

Prefabricated house in the sense of "all services from one source" or an actual prefabricated house?

We have basically made two considerations: We would like to have a wood-burning stove for coziness.

In a current new building, even 4 burning Advent candles already count as a small wood stove.

An energy consultant told us that it is almost impossible to operate a water-bearing pellet stove sensibly in such a well-insulated house because the direct heat output is already significantly too high. Is that correct?

Yes, so why do you doubt the statement of a professional?

After some research, we found out that a heat pump can also cool.

At most by about 2°; you must not forget that this will cause condensation on tiles, which is like a free slipping hazard.

.... with a (preferably) water-water heat pump

Why?

Is such a variant more economical than conventional air conditioning? Or would another heat pump technology be worth considering? Does anyone here cool with a heat pump? What are the experiences?

You "seem" to have not had a proper consultation yet; otherwise, you would already know that your planning so far overshoots the goal of "sensible" by far. "Much" was never good; compressing technologies as well. 'Wastl' has left some very good approaches for you here.

We are really grateful for any tips or suggestions as well as further information. If more information is needed, please just post.

Have consultation talks; by talking to an energy consultant, you have already taken a first good step.

In my opinion, you should not focus solely on KFW 55 funding; €100,000 sounds nice at first, no question. However, if I keep in mind that the savings in energy costs from the Energy Saving Ordinance (or old KFW 70) to KFW 55 are marginal, I consider the required expenditure borderline, certainly uneconomical.

True independence currently seems far from economical to me. In winter, you will always rely on external electricity supply. We are generally still not quite sure whether a plus-energy house is the best idea at all. Reliable calculations are rare, and the future development of electricity prices is hard to predict.

Complete autarky is not possible in our latitudes in NRW; 70% is—aided by storage—a realistic number. But you don’t need the detour via KFW 40 Plus for that. One of our builders—we handed over his house in 2014—recently proudly told me that his energy costs have settled at €10.00/month. He achieves this through a new building according to KFW 70 plus photovoltaic on the roof. I will meet him next week and have him give me a copy of the annual statements.

In short—you should ask yourself: "What do I want?" If it is about claiming subsidies—you have to reach KFW 55; if it is about the best possible reduction of energy costs, very different routes lead to Rome. If the thought of a possible resale of the property plays into your considerations, remember that potential buyers are not interested in which standard your single-family house was built. They are only interested in the condition of the property and ongoing consumption costs.

Best regards from the Rhineland

As an alternative to air conditioning, a system with evaporative cooling might also be interesting.

How does something like that work? What are the advantages or disadvantages?

That is a misconception. The house heats up just as much as an old property. It just takes longer for the heat to get inside the house and then even longer for you to get it out again.

Interesting. I thought they would heat up less strongly. But good to know.

A stove heats! Additionally! It creates overheating!

On the other hand, the underfloor heating would of course have to be turned down. But I already notice that a stove is probably not a good idea in a plus-energy house.

Stone slabs store heat
The heat is distributed actively.

Yes, because the stone slab stores heat, it releases it more slowly. What do you mean by the heat being distributed actively?

I am not an expert in heating matters, but we have a stove for coziness reasons. The underfloor heating cannot be turned down as fast as the heat from the stove comes in. After a few hours, you no longer want the few degrees increase caused by the stove and throw it out the window.

Well, but I don’t really find that sensible. And if it is not possible to size the stove accordingly or to find a corresponding working variant, then I guess it’s not right for us after all.

But thank you anyway for your opinions. Do you all, who have a wood stove here, open the windows wide to get rid of the heat again?

The heat of the oven spreads directly into the room - that is what is meant. We have a fireplace for comfort - if it should get too warm, we ventilate, yes. Not everything in life has to make sense. Even underfloor heating cannot react to that.