ᐅ Experience with indoor installation of air-to-water heat pumps?

Hello everyone,

For our new build (125m² (1,345 sq ft) living space over 2 floors, plus a basement), we are planning a ducted air-to-water heat pump system located in the technical room (basement). So, an indoor installation. The thermal calculation is not yet available, so we are not focusing on the perfect unit for the task at this point (reference: wood-frame construction near KfW55 standard, controlled residential ventilation with heat recovery).

Our questions are more about the following: The basement will protrude about 80cm (31.5 inches) above ground level, so there will be some natural daylight. The system is intended to be installed at the northeast corner. Supply and exhaust air would likely need to be routed outside via a light/air shaft, since at least one heat pump manufacturer specifies an air duct cross-section of 85 x 85cm² (33.5 x 33.5 inches) external dimensions. The intake and outlet ducts will most likely not come from the top of the unit near the ceiling. Is such a solution still feasible without issues?

Which side typically tends to cause more noise problems – intake or exhaust?

Which manufacturers offer well-functioning units designed for indoor installation?

And: which manufacturers present their systems in a way that heating engineers can confidently plan with them?

An alternative might be a system with a ground probe, if that would be cost-effective given the expected low heating demand and if it is permitted in the area. Gas is not planned (gas line length > 30m (98 feet)), nor is wood...

Regards,
I.

85cm by 85cm (33 inches by 33 inches) as an air duct. In that case, it probably doesn't make sense to place a light well in front of it that would obstruct the airflow. What does the manufacturer say about this?

Hello,

Irgendwoabaier schrieb:
... we are planning a air-to-water heat pump system in the utility room (basement). So, indoor installation...

What is the actual demand (capacity, energy) for heating and domestic hot water?
Air heat pumps are basically air conditioning units “misused” for heating purposes. The heating output is completely different from the actual demand (building thermal performance).
Therefore, fully modulating split systems have proven necessary. Fully modulating indoor units are not known. How long the compressors will last under forced cycling remains to be seen.

Irgendwoabaier schrieb:
...an alternative might be a system with a ground probe – if it makes economic sense given the expected low heating demand, and if it can be approved in the area.

For moderate or low demand and locations without extreme cold, a brine-to-water heat pump with vertical ground probes is hardly economically viable. With horizontal collectors installed in trenches and a lot of own labor, the situation looks somewhat more favorable.

Best regards

€uro, I keep seeing this term and finally have to ask. What exactly does "fully modular" mean? What does it do, and how is it different from a system that is not fully modular?
What makes these systems better?

A reference or source for further reading would also be fine, if there is something reliable available.

What price range can one expect for such systems in a (just to name something) 150m² (1,615 sq ft) house (even without knowing the exact loads)?
How do they perform at outdoor temperatures below freezing?

Thank you very much

emer schrieb:
€uro, I keep reading about this "full modulation" and I have to ask now. What exactly does it do, and what is the difference compared to a system that is not fully modulating?

Full modulation means that both the evaporator fans (noise) and the compressor can be regulated to match actual demand.

emer schrieb:
...What makes these systems better?

They probably have a longer lifespan because instead of simple on/off operation, the output is modulated according to demand, and their energy efficiency (seasonal performance factor) is significantly better.

The evaporators have to defrost in their main operating range, which is not necessary for, for example, brine heat pumps. This reduces the achievable seasonal performance factor because some of the energy already produced is used for defrosting and therefore not available to the heating surfaces! This share can be reduced by full modulation.
For this reason, I always recommend external heat meters for air-source heat pumps rather than the integrated ones.

emer schrieb:
...What price range do such systems fall into for a (let’s say) 150 m² (1,615 ft²) house (without knowing exact load details)?

Who can really answer that question?

emer schrieb:
...How do these systems perform at outdoor temperatures below zero?

With well-designed systems, they perform very well; with poorly designed ones, performance is inadequate, depending on where the bivalence point has been set!

Hi,

and thanks for the replies.

Shadowblues schrieb:
85cm (33 inches) square for the air duct. Then it probably doesn’t make sense to put a light well in front that obstructs the airflow. What does the manufacturer say about that?

That was the interesting part – the manufacturer does allow it in the installation manual, requiring a clear width of just over 40cm (16 inches) and air deflection (I don’t have the picture, and it would also be subject to their copyright. I can’t make a sketch here due to the available technology).

€uro schrieb:
Hello,
What is the actual demand (capacity, energy) for heating and hot water?
Air source heat pumps are basically air conditioners "misused" for heating purposes. The heating capacity completely contradicts the actual demand (building thermal characteristic).
Therefore, fully modulating split units have proven to be necessary. Fully modulating indoor units are not known. How long the compressors will survive due to the forced cycling remains to be seen.
With moderate or low demand and not extremely cold locations, ground source heat pumps with vertical probes hardly prove to be economical. With trench collectors and high self-labor, it looks somewhat better.

Best regards

Thanks... As I said, the heat calculation is not available yet, and my own estimate is unsuitable for making an accurate selection. So it’s not about choosing a manufacturer or model yet. The demand will probably not be very high (derived from building volume / surface area / wall and ceiling construction), so a ground source heat pump is probably not economical.
The location is in the flat border area between Odenwald and Spessart, so it’s also not extremely cold.
Reasons for preferring indoor installation: noise disturbance in the neighborhood. The distances to neighbors are quite small, and there are already people who had very negative experiences with outdoor units. Unfavorable choice, poor installation, very unfavorable orientation of the units all came together. Hence the question about manufacturers who actually offer suitable systems for these conditions. Whether these systems are suitable for our specific case can be clarified later.

Regarding systems considered by a potential heating installer in our area, there is unfortunately very little information – once “Inverter with 7 or 10 kW (23,900 or 34,100 BTU/h),” once “modulating with 3–9 kW (10,200–30,700 BTU/h),” plus the coefficient of performance for A2W35. That’s too little to even make any comparisons or ask sensible questions. Therefore, a market overview would be helpful – at least then you know where and who to ask and consider.

Best regards
I.