Energy Saving Ordinance 2016 or KFW 55 for bungalow with air-water heat pump & controlled residential ventilation, optional photovoltaic

Precisely because a layperson cannot assess the depreciation,
a planner can possibly also be held liable.

Unfortunately, I have seen little sensible input from planners so far, neither for my house nor for others, which is partly because good building planners usually do not plan single-family homes. A layperson can also rarely hold a planner liable, because the layperson has signed something they do not understand if they have solely relied on the planner.
It is better advised to take care of things oneself, if possible. General contractors usually impose restrictions, so you often have to choose between gas and an expensive and poorly planned air-water heat pump.

Especially with the heating system, you save considerable amounts over decades. Of course, it costs one’s own time upfront, before construction, to get informed accordingly and to select the right craftsmen.

Depreciation: the decisive factor is the selection of an affordable and low-maintenance heat pump, subsidies and/or a cheaply installed source. The standard offer from the general contractor or craftsman for a heat pump upgrade for >+10k€ is usually not economical compared to gas. A layperson financing a house can assess this themselves, provided they are willing to do so.

A heat pump currently only stands as well because the primary energy factor has been raised accordingly by politics. Which does not change the cost per kWh at all.

I also view the political preference very critically because the scales in the energy certificate and minimum requirements create false impressions. "Bad" houses can be massively upgraded on paper and accordingly compensated.

Better insulation does not increase the efficiency of a heat pump either, it is generally equally poor with air heat pumps.
An annual performance factor value of at least 4.0 is an illusion.
[...]
In addition to higher operating costs, there is the short service life of the air heat pump; the necessary reinvestments go directly into the ROI.
(normal hot gas temperatures assumed)

For my part, I can say that the installation of the heat pump was cheaper than the installation of gas with solar thermal, and the replacement of the system will also be cheaper. The annual performance factor is close to 5 because we planned the heating surfaces, hydraulics, and building accordingly.

Insulation probably has the least influence on the annual performance factor in new builds; its effect exists through the lower required flow temperature.

In my opinion, an air-water heat pump or a heat pump with ring trench collector is the most sensible type of heating in new buildings, provided the prerequisites are met.

For us, the air-to-water heat pump was also cheaper than all alternatives and the annual performance factor is also 4.5 with [ww].

I’m still waiting for my thermal protection certificate, but we have the same considerations.

We are building a prefabricated timber house, specifically a bungalow of about 105 m2 with controlled residential ventilation and a split air heat pump.

The house was ordered as a KFW 55 because we now consider that the standard, but we currently do not want/must not/will not apply for KFW 55 funding.

For our 120 m2 base slab, a 10 cm Styrodur perimeter insulation was preliminarily offered during the quotation phase.

Depending on the WSNW, which hopefully will be available to us in the next few days, we will decide for or against the insulation. The heating load that I preliminarily calculated using MH software and the U-values given to me by the house builder was about 2.8 kW for the base slab with insulation and 3.4 kW without insulation beneath the base slab (without hot water) at -14°C.

This is not a detailed calculation by a building services professional but provides insight into the potential energy savings. 10 days at -14°C x 24h = 240 heating hours 240*600 watts (difference between insulated and non-insulated base slab) = 144,000 watts = 144 kWh x 30 cents (for simplicity) equals €43.20.

You can of course calculate this in any direction with rising electricity prices or global warming and thus milder winters.

Oh, the price for the Styrodur insulation including installation and VAT is supposed to be just under €2200...

€2200 : €43.20 = 50.92 years until the insulation pays off without electricity price increases.

If I now omit the insulation and thereby only have KFW 56.5 on paper instead of 55, that’s fine with me.

The calculation really doesn’t work even remotely like that, better to estimate without pseudo numbers and go with gut feeling. Among other things, you forget that the heat pump only needs about 1/3 of the electricity you assumed and draws the rest from the environment. On the other hand, heating is done a bit longer than 10 days a year.

It presumably pays off in about half the time, which is still a long time, of course. You can do it, but you don’t have to. You will also have some kind of insulation for the floor slab.

However, the heating load is reduced by 600 watts, assuming the calculation is correct, which is not insignificant. Possibly a smaller and cheaper heat pump would fit.

We also waived the KfW seal, despite corresponding insulation.

The calculation is quite far-fetched. 3.4 to 2.8 is also very unrealistic, more like 3.4 to 3.2 for a bungalow, if at all.

Even if the calculation is far-fetched and yes, there is probably a mistake in it because I calculated with a delta T of 34k, which is nonsense since I don’t have -14°C in the ground in winter.

But if it is only the mentioned 200 watts saved through insulation, that justifies the purchase of the insulation even less than with 600 watts heat loss.