ᐅ Operating a heat pump independently with a photovoltaic system.

Sebastian79 schrieb:
Yeah, sure...

By the way, I’m the last person here who built their house with profit in mind...

And your amazing additional costs: What are you actually saving compared to the effort? 5 euros per month? 10 euros? When do the costs balance out with the effort?

And sure, they offer a different price—but do you really think it’s a better one? Totally fell for that...

By the way, I’d rather deal with stress than live in a timber frame house—but that’s just my personal opinion. That also cancels out the supposed advantage regarding resale value later on...

And I would never want to build stone on stone again. People can be so different so I’m losing interest in continuing this discussion enjoy your stone castle

Inotsara schrieb:
.... this also kills my motivation to continue participating in the discussion

And I am gradually losing the motivation to point out incomplete profiles; please fill in your occupation.

Regards, Bauexperte

Inotsara schrieb:
A matter of perspective. Nowadays, when buying, I definitely want to know how many additional costs I will face. Since there were no used KfW 40 houses available, we are now having one built.

In my opinion, that is also the mistake. Those who built the best and newest standards 30 years ago do not have KfW 40 houses to offer today. The technology becomes outdated.
So anyone who wants to buy a used house in 30 years and cares about energy efficiency will have to calculate renovation costs. It makes no difference to them whether they buy a former KfW40 or KfW70 house. The heating system and so on will have to be replaced anyway.

Inotsara schrieb:
And achieving KfW 40 is best done with a prefab house provider who specializes in and is familiar with this standard. For them, it’s an easy win, and they offer different prices than an individual planner building brick by brick. Also, the wall is almost half a meter thick, and other aspects are simply better solved with timber construction. Sometimes building materials developed together with major manufacturers, like Knauf, are used.

Don’t just claim things and create theoretical calculations. Just go to a prefab house provider out of interest, have them calculate it, and then compare this to your additional costs and especially the steadily rising electricity costs. Then tell me again it wouldn’t be worth it... The eliminated building stress alone is an enormous added value.

We also had a conversation with this provider once, and they were rather in the category of extremely overpriced.

The little bit of insulation and so on do not justify tens of thousands of extra costs.

The technical brochure sounds nice, theoretically, but ALL of that can be done just as well or better with a solid, massive house. Only the wall construction is different. There, xy provides the component value. The overall value is between 0.12 and 0.13. This can also be achieved with 17.5 cm (7 inches) calcium silicate bricks and 24 cm (9.5 inches) EPS 032 insulation. Just over 40 cm (16 inches), and with plaster still far from half a meter. But it is simply very uneconomical.

For fun, I calculated the energy consumption of our planned KfW 55 house: 3,500 kWh for heating plus an estimated 3,500 kWh for hot water. That makes 7,000 kWh. With a ground source heat pump with a seasonal performance factor of 5, that results in 1,400 kWh electrical consumption.

KfW 40 has 21.4% better insulation than KfW 55. That results in 2,750 kWh for heating, and again 3,500 kWh for hot water. Together 6,250 kWh. But now you have an air source heat pump with a seasonal performance factor of 3.8. That means 1,645 kWh electrical consumption.

So a KfW 55 house with ground source heat consumes 15 percent less than a KfW 40 near-passive house with air source heat pump. This KfW label is in the end just meaningless number games.

Now, let’s continue the calculation assuming you have a ground source heat pump. Then you would only use 1,250 kWh electrically. In this case, you would actually save 3.12 EUR per month (25 cents as energy price without heat pump tariff). According to the current plan, you pay around 5.10 EUR more compared to KfW 55 with ground source heat.

KfW 40, if you want it, is best achieved with the appropriate insulation. Period. You don’t need company xy for that. You don’t even need timber construction. 17.5 cm (7 inches) calcium silicate brick and 20 cm (8 inches) EPS 032 insulation are enough for KfW 40. Completely sufficient.

Now the extreme case. We would build a KfW 70 house, basically the minimum standard. 21.4% higher consumption, that is 4,250 kWh plus still 3,500 kWh for hot water, making 7,750 kWh. We install an air-to-water heat pump, which is really poor—seasonal performance factor 3.5. We need 2,214 kWh, and the price rises to 40 cents. Our monthly prepayment of 73.81 EUR will practically ruin us by 2036.

Edit: Of course, I have now recalculated our consumption up and down. Depending on your orientation, house size, etc., different values apply. What I really wanted to highlight: Whether KfW 70 or KfW 40—we’re just talking small amounts back and forth here.

An annual performance factor of 3.5 is not worse at all, but rather a realistic and commonly achieved value for an air-to-water heat pump.

from on the go

In an older building with a high-temperature heating system, yes. In a new building with a flow temperature of 30-35 degrees Celsius (86-95°F) and 45 degrees Celsius (113°F) hot water in the hygiene storage tank, and without a buffer, it is certainly far too inefficient.