Comfort: Air/Water Heat Pump vs. Air/Air Heat Pump

Don't stop anyone from sending the exhaust air through a heat exchanger. These are usually combined units anyway, which have the controlled residential ventilation integrated. In contrast to the pure exhaust air heat pump, outside air is used as a heat source, with an outdoor unit etc., instead of just trying to extract the heat energy from the exhaust air.

No one is stopping anyone from sending the exhaust air through a heat exchanger. These are mostly combined units anyway that have controlled residential ventilation integrated. Unlike pure exhaust air heat pumps, outdoor air is used as a heat source, with an outdoor unit, etc., instead of just trying to extract the heat energy from the exhaust air.

No one is stopping anyone, but it reduces efficiency. The normal systems realize the controlled residential ventilation part by using the extracted air for the exhaust air pump. Unfortunately, the commercially available devices usually do not have a heat exchanger beforehand, which would make sense. But the exhaust air should be used even with a heat exchanger, because it is always warmer than the outside air during the heating period, and that would result in higher efficiency; better to take the 10-degree cold exhaust air after the heat exchanger than the -5-degree outside air. Neither solves the dry air problem, nor that with proper cold weather you need pretty warm blower air. It might work if you have a real passive house with maybe 1-2 kW heating demand in the coldest winter. The best would be a combination, where the heat pump can freely combine the supply air from exhaust air and outside air so that it is as warm as possible without having to draw too much air from inside.

Hello everyone,

first of all, thank you very much for the numerous responses!

The recommended air-to-air heat pump would be a model with a heat exchanger that uses the residual heat from the exhaust air to heat the supply air.

If I understand you correctly, the point "heat exchanger" is (logically) only related to the aspect of "efficiency". It hardly improves comfort, does it?

Can one generally say...
- that the air-to-water heat pump with underfloor heating provides the more comfortable room climate because it does not use dry air for heating?
- that one should always use a model with a heat exchanger for an air-to-air heat pump?

How does it actually behave with regard to efficiency? Are the operating costs of an air-to-water heat pump with underfloor heating lower or higher than those of an air-to-air heat pump with a heat exchanger?

In your opinion, what additional costs should one expect for the installation of an air-to-water heat pump in a single-family house of about 160m²?

One more question: In my original post I mentioned a single-family house with KFW55. Would the answer be more clearly "for AA heat pump" or "for AW heat pump" with a KFW40 house? Is the factual situation different there, or is it always more a matter of belief which of the two heating technologies one chooses?

Thank you for your feedback!

Regards,
matze007

- that one should always use only one model with a heat exchanger for an air-to-air heat pump?

No, the important thing is not to use an exhaust air heat pump, unless it is a passive house, because otherwise it turns into electric heating. The concept only works if more energy is supplied to the house through waste heat from the occupants, electrical appliances, and solar gains through windows than escapes through the building envelope, ventilation, etc.
The system is completely unrealistic if the exhaust air-to-air heat pump is also supposed to provide hot water.
To compensate for this drawback, an electric heating element is then switched on, which wastes electricity.
The advantage of the whole idea: the investment is cheap and you usually also have the function of controlled residential ventilation included. The disadvantage is the extreme electricity bills that result in the end (but the general contractor is no longer interested in these).

An exhaust air heat pump does not have to be air-to-air! We have a Nibe F750 air-to-water exhaust air heat pump. I find an outdoor unit annoying for the neighbors and geothermal energy too expensive.

I wouldn’t want air-to-air in any house.

Although underfloor heating in a low-energy house is not that warm on the feet. With a flow temperature of 35°C, the floor is cooler than body temperature. Still, this creates a cozy climate. It just feels different than with classic radiators.

*-Water is always more pleasant than air as a heat carrier and a water heat pump is actually never less efficient, the only disadvantage is that installing underfloor heating is a bit more expensive than just air ducts (which you already have anyway because of controlled residential ventilation). So rather an idea of the developers to reduce costs than something to increase comfort. Another advantage of underfloor heating is that you can basically switch the heating more easily - that is, install/add a completely different heating system that then simply heats the water.

Apart from that, separating heating and ventilation also has the advantage of separating the devices (failure, configuration, for example).
If you have a party and need more ventilation, with separated devices you do not affect the heating system, for example.

Otherwise, I would only use an exhaust air heat pump for additional hot water supply, never for heating. Because a heat exchanger (enthalpy heat exchanger) can recover a real majority of the heat energy and moisture, and that without significant costs.
The missing energy can then never be obtained from the heat pump or the exhaust air in too cold weather.

I have, with controlled residential ventilation + enthalpy heat exchanger and water heat pump, currently about 190 sqm of heated space and ~60 sqm of unheated basement rooms (but within the insulated envelope, so it never gets really cold there through heat transmission, minimum 17-18°C), an annual energy consumption of ~1600 kWh for heating AND hot water. Energy standard according to the current energy regulation is, by the way, probably the minimum (formerly KfW 70 according to the 2009 Energy Saving Ordinance).