ᐅ Ventilation System: Concept for a KfW55 Solid Construction House

Hello everyone,

We are planning to build a single-family house soon, with two full floors, 150sqm (1,615 sq ft), a shed roof, solid construction, underfloor heating, and aiming for KfW55 standard. We have already gathered some initial offers, but we are particularly uncertain about one aspect: the ventilation concept and heating system.

What could such a concept look like in order to meet the KfW55 requirements in the end?

• Gas condensing boiler and solar system for domestic hot water heating and heating support and/or central ventilation system with heat recovery
• Combination unit consisting of a central ventilation system with heat recovery and an air-source heat pump, allowing the gas connection to be eliminated.

I am especially unsure about option 2 and how it would work. This combination unit is supposed to cost around 10,000€ and makes it possible to completely forgo the gas connection. But how would heating work in winter then? Only with heat recovery and some electricity, or how should I imagine it?

Sorry for asking such beginner questions.

Best regards,
Marko

As mentioned elsewhere, your KFW advisor will be the best person to provide information on this. You will most likely need to install a ventilation system with heat recovery.

MarcWen schrieb:
As mentioned elsewhere, the best source of information for this will likely be your KfW advisor. You will probably not be able to avoid installing a ventilation system with heat recovery.

That is clear to me—I won’t manage without a ventilation system with heat recovery—but one option is gas with solar, and the other is entirely without gas and without a solar panel. I am skeptical about the electricity costs because we would completely give up gas.

bvlgari schrieb:


What might such a concept look like in order to ultimately meet the KfW55 standards?

• Gas condensing boiler and solar system for domestic hot water heating and heating support and/or central ventilation system with heat recovery
• Combination unit of central ventilation system with heat recovery and air-source heat pump, eliminating the gas connection.

Are these two proposals from the construction company in consultation with the KfW expert, or did you come up with them yourself? I assume we will also receive such options to decide on. I also see either gas or air-to-water heat pump for our project. I’m also a fan of photovoltaic systems, which definitely make sense especially when paired with a heat pump.

bvlgari schrieb:

I am particularly unsure about how position 2 is supposed to work.

Air-source heat pumps can still extract heat from the air at temperatures below 0°C (32°F). The lowest temperature at which the heat pump operates depends, among other things, on the model. Fundamentally, you are right that when the temperature gets very cold, the water is eventually heated electronically via an electric heating element. If the heating system is poorly planned, this can lead to very high heating costs. With proper planning, this is less of an issue.

DragonyxXL schrieb:
Air-source heat pumps can still extract heat from the air at temperatures below 0°C (32°F). The lowest temperature at which the heat pump operates depends partly on the model. Generally, you are right that when it gets very cold, the water is electronically heated by an electric heating element. If the heating system is poorly designed, this can result in very high heating costs. With proper planning, this is less of an issue.

The model is Tecalor THZ 304.
Who can say whether the heating system design is correct or not? My building surveyor?
If the house is built according to Kfw55 standards, then I should have even fewer worries when it is -10°C (14°F) outside or