ᐅ Energy Saving Regulation 2016 or KfW 55 Standard for a Bungalow with Air-to-Water Heat Pump and Controlled Mechanical Ventilation, Optional Photovoltaic System

nichts zu schwör schrieb:

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

So far, I haven’t seen much useful input from planners, neither for my house nor others, which also has to do with the fact that good building planners usually do not design single-family homes (SFHs). It’s also quite rare for a layperson to successfully hold a planner liable, since the layperson usually signed something they didn’t fully understand when relying solely on the planner.
It’s better to take care of it yourself if possible. General contractors (GCs) often limit your options, so you end up having to choose between gas and an expensive, poorly planned air-to-water heat pump.

Especially with the heating system, you can save significant amounts over decades. Of course, it requires some upfront time investment before construction to get informed and select the right contractors.

Depreciation: The key factor is choosing an affordable and low-maintenance heat pump, suitable subsidies, and/or a cost-effective heat source installation. The standard offer from a GC or builder for a heat pump upgrade costing more than 10,000€ (about $11,000) is usually not economical compared to gas. A layperson financing a house can judge this themselves, as long as they are willing to do so.

nichts zu schwör schrieb:

A heat pump currently only performs well because the primary energy factor was raised by policymakers. This doesn’t change the actual cost per kWh.

I am also very critical of political favoritism because the scales in energy performance certificates and minimum requirements create misleading impressions. “Poor” houses can appear much more efficient on paper and receive disproportionate subsidies.

nichts zu schwör schrieb:

Better insulation does not increase the efficiency of a heat pump, which is generally equally poor for air source heat pumps.
A seasonal performance factor (SPF) of at least 4.0 is an illusion.
[..]
In addition to higher operating costs, air source heat pumps have a shorter service life, and necessary reinvestments directly affect the return on investment (ROI).
(Assuming normal hot gas temperatures.)

From my experience, installing a heat pump was less expensive than installing gas with solar thermal, and replacing the system will also be cheaper. The annual performance factor is close to 5 because we planned the heating surfaces, hydraulics, and the building accordingly.

Insulation in new builds probably has the least influence on the seasonal performance factor; its effect is mainly due to the lower required flow temperature.

In my opinion, for new builds, air-to-water heat pumps or heat pumps with horizontal trench collectors (ring trench collector) are the most sensible heating options, assuming the conditions are suitable.

For us, the air-to-water heat pump was also more affordable than all the alternatives, and the annual performance factor including domestic hot water is 4.5.

Although I’m still waiting for my thermal insulation certificate, we are considering the same questions.

We are building a prefabricated wooden house, specifically a bungalow of about 105 m² (1130 sq ft) with controlled ventilation and a split air-source heat pump.

The house has been ordered to meet KFW 55 standards, as we now consider this our baseline, but we currently do not want/need to apply for KFW 55 subsidies.

For our 120 m² (1292 sq ft) slab foundation, 10 cm (4 inches) of Styrodur perimeter insulation was included as an option during the offer phase.

Depending on the thermal insulation verification (WSNW) that we hope to receive in the next few days, we will decide whether to use the insulation or not. The heating load I roughly calculated beforehand with MH software and the U-values provided by the builder showed about 2.8 kW for the insulated slab and 3.4 kW without insulation below the slab (excluding hot water) at -14°C (7°F).

This is not a detailed calculation by an HVAC professional but provides an idea of the potential energy savings. Over 10 days at -14°C (7°F), that is 240 heating hours; 240 hours × 600 watts (difference between insulated and uninsulated slab) = 144,000 watt-hours = 144 kWh × 30 cents (for simplicity) equals €43.20.

This calculation can be adjusted accurately in any direction with changes in electricity prices or milder winters due to global warming.

By the way, the price for the Styrodur insulation, including installation and VAT, is about €2200.

€2200 ÷ €43.20 = 50.92 years for the insulation to pay off at current electricity prices without any increase.

If I skip the insulation and on paper end up with KFW 56.5 instead of 55, that’s fine with me.

The calculation really doesn’t work at all; it’s better to avoid made-up numbers and just estimate based on experience. For example, you overlook that the heat pump only uses about one-third of the electricity you assumed and draws the rest from the environment. On the other hand, heating typically lasts a bit longer than 10 days per year.

It will probably pay off in about half that time, which is still quite long. It’s an option, but not a necessity. You will likely have some form of insulation under the concrete slab as well.

The heating load is reduced by 600 watts if the calculation is correct, which is quite significant. This might allow for a smaller and more affordable heat pump.

We also decided against obtaining the KfW certification, despite having the corresponding insulation.

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

Even if the calculation is far-fetched, and yes, there is probably an error because I used a delta T of 34K, which doesn’t make sense since the ground temperature in winter is not -14°C (7°F).

But if it’s only the mentioned 200 watts of savings from the insulation, that makes the purchase of the insulation even less justifiable compared to a 600-watt heat loss.