Hello everyone,
We are currently planning a single-family house with approximately 160m² (1,722 sq ft) of living space based on the KFW55 standard. Since we are still at the beginning of the planning phase, many details are not yet finalized.
From the start, we have focused on the heating system. Our current favorite is an air-to-water heat pump. The main reason for this choice was especially the aspect of “underfloor heating,” which is supposed to provide a certain level of comfort. Many consultations we had confirmed this point.
However, we were recently advised to consider an air-to-air heat pump instead. The reasoning was that the underfloor heating would be installed under a roughly 15cm (6 inch) thick screed layer anyway, so an air-to-air heat pump would be preferable because it heats more directly. It was also said that the comfort without underfloor heating would be comparable.
Now our question is which argumentation we should trust.
Is underfloor heating preferable to a radiator-based heating system?
Which heating concept provides more comfort to the house?
And do the additional costs of underfloor heating justify the added value?
What are your opinions on these points? Which concept would you choose, and why?
We would greatly appreciate your feedback.
Thank you & best regards,
matze007
We are currently planning a single-family house with approximately 160m² (1,722 sq ft) of living space based on the KFW55 standard. Since we are still at the beginning of the planning phase, many details are not yet finalized.
From the start, we have focused on the heating system. Our current favorite is an air-to-water heat pump. The main reason for this choice was especially the aspect of “underfloor heating,” which is supposed to provide a certain level of comfort. Many consultations we had confirmed this point.
However, we were recently advised to consider an air-to-air heat pump instead. The reasoning was that the underfloor heating would be installed under a roughly 15cm (6 inch) thick screed layer anyway, so an air-to-air heat pump would be preferable because it heats more directly. It was also said that the comfort without underfloor heating would be comparable.
Now our question is which argumentation we should trust.
Is underfloor heating preferable to a radiator-based heating system?
Which heating concept provides more comfort to the house?
And do the additional costs of underfloor heating justify the added value?
What are your opinions on these points? Which concept would you choose, and why?
We would greatly appreciate your feedback.
Thank you & best regards,
matze007
Nobody should be prevented from routing the exhaust air through a heat exchanger. These are usually combined devices that already integrate the mechanical ventilation with heat recovery system.
Unlike a pure exhaust air heat pump, outside air is used as the heat source, with an outdoor unit, etc., instead of just extracting the thermal energy from the exhaust air.
Unlike a pure exhaust air heat pump, outside air is used as the heat source, with an outdoor unit, etc., instead of just extracting the thermal energy from the exhaust air.
Alex85 schrieb:
No one prevents you from routing the exhaust air through a heat exchanger. These are usually combined units that integrate the controlled mechanical ventilation system. Unlike a pure exhaust air heat pump, outdoor air is used as the heat source, with an external unit, etc., instead of just extracting heat energy from the exhaust air.No one is stopped from doing so, but it reduces efficiency. Standard systems implement the controlled mechanical ventilation function by using the extracted exhaust air for the exhaust air heat pump. Unfortunately, commercially available devices usually don’t include a heat exchanger beforehand, even though it would make sense. However, it is still better to use the exhaust air with a heat exchanger during the heating season because it is always warmer than the outside air. Taking the exhaust air at 10cm (5 inches) instead of outside air at -5°C (23°F) after the heat exchanger would result in higher efficiency. Neither approach solves the dry air issue, nor the fact that fairly warm supply air is needed at low outdoor temperatures. This might be feasible with a true passive house having approximately 1–2 kW heating demand during the coldest winter period. Ideally, a combination system would allow the heat pump to freely mix supply air from exhaust air and outdoor air to achieve the highest possible inlet temperature, without drawing too much indoor air.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 of the exhaust air to warm up the supply air.
If I understand you correctly, the “heat exchanger” aspect logically only relates to efficiency. It probably doesn’t improve comfort much, does it?
Can one generally say…
- that the air-to-water heat pump with underfloor heating provides a more comfortable indoor climate because it doesn’t use dry air for heating?
- that you should always choose an air-to-air heat pump with a heat exchanger?
How about 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 be expected for installing an air-to-water heat pump in a single-family house of about 160m² (1,722 ft²)?
One more question: In my original post, I referred to a single-family house built to KFW55 standards. Would the answer be clearer in favor of an air-to-air or air-to-water heat pump for a KFW40 house? Is the situation different there, or is it always more a matter of preference when deciding between the two heating technologies?
Thanks a lot for your feedback!
Best regards,
matze007
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 of the exhaust air to warm up the supply air.
If I understand you correctly, the “heat exchanger” aspect logically only relates to efficiency. It probably doesn’t improve comfort much, does it?
Can one generally say…
- that the air-to-water heat pump with underfloor heating provides a more comfortable indoor climate because it doesn’t use dry air for heating?
- that you should always choose an air-to-air heat pump with a heat exchanger?
How about 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 be expected for installing an air-to-water heat pump in a single-family house of about 160m² (1,722 ft²)?
One more question: In my original post, I referred to a single-family house built to KFW55 standards. Would the answer be clearer in favor of an air-to-air or air-to-water heat pump for a KFW40 house? Is the situation different there, or is it always more a matter of preference when deciding between the two heating technologies?
Thanks a lot for your feedback!
Best regards,
matze007
matze007 schrieb:
- that you should always use only one model with a heat exchanger for an air-to-air heat pump?No, the important thing is to avoid using an exhaust air heat pump unless it’s a passive house, because otherwise it basically becomes electric heating. The concept only works if the house receives more energy through the waste heat from occupants, electrical appliances, and solar gains through windows than is lost through the building envelope, ventilation, etc.
The system becomes completely unrealistic if the exhaust air-to-air heat pump is also expected to provide domestic hot water.
To compensate for this shortcoming, an electric heating element is switched on, which consumes electricity wastefully.
The advantage of the whole idea is that the initial investment is low and you usually get a mechanical ventilation system with heat recovery included. The downside is the extremely high electricity bills that result in the end (but the general contractor usually doesn’t care about those).
An exhaust air heat pump does not have to be an air-to-air system!
We have a Nibe F750 air-to-water exhaust air heat pump. I don’t like outdoor units for the neighbors, and geothermal energy is too expensive.
I wouldn’t want an air-to-air system in any house.
That said, underfloor heating in a low-energy house isn’t especially warm underfoot. With a flow temperature of 35°C (95°F), the floor surface is cooler than body temperature. Still, it creates a cozy indoor climate. It simply feels different compared to traditional radiators.
We have a Nibe F750 air-to-water exhaust air heat pump. I don’t like outdoor units for the neighbors, and geothermal energy is too expensive.
I wouldn’t want an air-to-air system in any house.
That said, underfloor heating in a low-energy house isn’t especially warm underfoot. With a flow temperature of 35°C (95°F), the floor surface is cooler than body temperature. Still, it creates a cozy indoor climate. It simply feels different compared to traditional radiators.
*Water is always a more comfortable heat carrier than air, and a water-source heat pump is generally never less efficient. The only downside is that installing underfloor heating is somewhat more expensive than just air ducts (which are usually already installed due to the controlled residential ventilation system). So this is more of a cost-saving idea by developers rather than an improvement in comfort. Another advantage of underfloor heating is that it is generally easier to switch the heating system—meaning you can install or add a completely different heating system that heats the water.
Aside from that, separating heating and ventilation also offers the benefit of having separate devices (for example, in case of failure or configuration issues). If you have a party and need more ventilation, having separate devices means your heating system is not affected.
Otherwise, I would only use an exhaust air heat pump for the additional supply of hot water, never for heating. An enthalpy heat exchanger can recover a significant portion of heat energy and moisture without major costs. Any missing energy during very cold weather cannot be recovered by the heat pump from the exhaust air.
In my setup with controlled residential ventilation plus an enthalpy heat exchanger and a water-source heat pump, currently heating about 190 square meters (2050 square feet) of living space and about 60 square meters (650 square feet) of unheated basement areas (but included within the insulated building envelope, so it never gets really cold there—minimum 17-18°C (63-64°F) due to heat transmission), my annual energy consumption for heating and hot water is about 1600 kWh. By the way, the energy standard according to the current energy regulation is the minimum, I believe (previously KfW 70 according to the 2009 Energy Saving Ordinance).
Aside from that, separating heating and ventilation also offers the benefit of having separate devices (for example, in case of failure or configuration issues). If you have a party and need more ventilation, having separate devices means your heating system is not affected.
Otherwise, I would only use an exhaust air heat pump for the additional supply of hot water, never for heating. An enthalpy heat exchanger can recover a significant portion of heat energy and moisture without major costs. Any missing energy during very cold weather cannot be recovered by the heat pump from the exhaust air.
In my setup with controlled residential ventilation plus an enthalpy heat exchanger and a water-source heat pump, currently heating about 190 square meters (2050 square feet) of living space and about 60 square meters (650 square feet) of unheated basement areas (but included within the insulated building envelope, so it never gets really cold there—minimum 17-18°C (63-64°F) due to heat transmission), my annual energy consumption for heating and hot water is about 1600 kWh. By the way, the energy standard according to the current energy regulation is the minimum, I believe (previously KfW 70 according to the 2009 Energy Saving Ordinance).
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