ᐅ KfW Energy Calculation with a Cooling Heat Pump

Hello everyone,

we are planning to install a Viessmann Vitocal 200 S heat pump. It is also capable of cooling, allowing the room temperature to be lowered via the underfloor heating system. We are building a KfW 40 energy-efficient house.

Is there anything that needs to be considered regarding KfW or BAFA when using this system? Does activating the cooling function have any negative impact on the energy calculation?

Thanks and best regards,
Markus

No, it is exactly the same as a standard heat pump.

According to our heating engineer, that doesn’t make sense.

It’s better to cool using the mechanical ventilation with heat recovery system – but ideally with an air conditioning system.

DaSch17 schrieb:

According to our heating technician, this doesn’t make sense.

It’s better to cool through the controlled mechanical ventilation system – but ideally with an air conditioning unit.

You can cool with a controlled mechanical ventilation system to some extent, but the airflow rate is usually too low for effective cooling. Cooling via underfloor heating systems is possible to a limited degree. I use it occasionally during the peak of summer and can definitely feel some effect. However, the floor does feel cooler. You shouldn’t overdo it, though, because condensation problems can occur. Also, there is no dehumidification, which would be beneficial in summer. There are plenty of discussions on this topic in the forum.

Of course, the best option is a proper air conditioning system. That’s why I wouldn’t pay a significant extra cost for cooling through the underfloor heating and heat pump unless it is already included.

Our heating contractor recommended using the mechanical ventilation system with a pre-cooled coil to provide cooling during the summer.

Additionally, the supply air in summer (before entering the house) is supposed to be routed through an underground pipe system on the property, to take advantage of the lower temperatures below the ground surface for additional cooling of the fresh air.

The pipe system is to be installed by the civil engineer during the earthworks.

How exactly this should be done—I have no idea. I haven’t looked into it yet. I believe @Mycraft is familiar with the system/principle.

In my opinion, the cooling function is not considered in the calculation.

Regarding the underground pipe, you can find information under the term ground heat exchanger. Essentially, it is just a thicker pipe (15-20cm diameter [6-8 inches]) buried underground that slightly cools the air as it is drawn in.
A pre-installed cooling coil is a bit more complex to explain; I suspect it refers to a brine ground heat exchanger, where a brine loop is laid underground and passes through a radiator, which cools the incoming air blown through it.
The effect of both options is not very significant—typically around 0.5-1.5°C (1-3°F)—but they also provide dehumidification, something that the heat pump’s cooling via underfloor heating does not achieve.

However, both options cannot be compared to a proper air conditioning system, which offers much higher cooling capacity with dehumidification and significantly higher air volumes. In air conditioning systems, there are also additional considerations regarding hygiene in the ducts due to the dew point and potentially occurring condensate.