ᐅ How to Design an Efficient Heating System for a New Building?

Hello,

we have chosen a monoblock air-to-water heat pump using propane, combined with a 600-liter (160-gallon) buffer tank with domestic hot water treatment.

Here are a few points explaining our decision:
- Monoblock heat pumps are supposed to operate more efficiently than split systems. We have short pipe runs and more space indoors.
- I’ve heard about the buffer tank issues as well. In the end, we just didn’t dare to omit the buffer tank. The concern was ultimately too great.
- With the fresh water station, I believe the risk of Legionella is eliminated, and you don’t have to worry about high electricity costs from excessive electric reheating. For showering and similar uses, 40°C (104°F) is sufficient.
- As far as I know, in new builds, a thermostat must be installed in every room larger than about 4 m² (43 sq ft). In principle, I also find room thermostats somewhat pointless because new buildings are so well insulated that significant temperature differences are hardly achievable.

I also think having two heat pumps is completely unnecessary.
Geothermal heat pumps are interesting but very complex to install. Usually, they are about 1.0 COP more efficient than air-to-water heat pumps. The real question is: how long do you need to heat to recoup the additional installation costs?
Heat pumps also offer a cooling function. However, I find this option quite risky because of the high risk of condensation. Sure, with sensors and so on, it could work, but who can guarantee that these sensors will always function perfectly and not become faulty after a few years?

Unfortunately, I don’t have any practical experience yet. The house is still under construction.

Mahri23 schrieb:

My recommendation leans towards a ground source heat pump. It is likely to be a bit more efficient than an air source heat pump. However, you will need to have ground drilling done.

The question is whether a (rather small) energy saving compared to one in the high single-digit to low double-digit range is worth it. But it definitely looks better aesthetically (no outdoor unit).

Haus Luni schrieb:

- Monoblock heat pumps are supposed to be more efficient than split systems,

Unfortunately, that is a myth.

Haus Luni schrieb:

600-liter buffer tank with domestic hot water preparation.

So, a combination tank?

Haus Luni schrieb:

- Because of the fresh water station, I think the risk of legionella is eliminated, and you don’t have to expect high electricity costs from the huge electric heating. For showering and similar uses, 40°C (104°F) is sufficient.

The risk of legionella in normal use in a single-family home is negligible at a storage temperature of about 50°C (122°F) (and possibly running a legionella program once a week). In Germany, there are actually no reported cases.
However, your electricity demand will likely be higher with this large buffer tank because you always have to maintain 600 liters at temperature. With a 200-liter tank, it is only one-third of that heat quantity.

Haus Luni schrieb:

- As far as I know, in new buildings, a thermostat must be installed in every room over 4 m² (or so).

Yes, BUT it is relatively easy to get an exemption from this requirement.

Haus Luni schrieb:

There is also a cooling function with heat pumps. However, I find this option very risky because the risk of condensate is quite significant. Sure, with sensors and so on it could work, but who guarantees that the sensors will always work properly and won’t fail after a few years.

You can also cool based on experience and estimates. That works well.

Hello,

nordanney schrieb:

So, a combined storage tank?

Yes, with a combined storage tank.

It is quite possible that the electricity consumption will be somewhat higher because of the buffer tank. I'm also not entirely sure if this is the best solution. Since we have a 16 kWp photovoltaic system, I've convinced myself it's acceptable.

The idea of a thermostat exemption is new to me. For me, it's already too late, but out of curiosity, how does that work?

What do you mean by cooling with empirical values?

Haus Luni schrieb:

It is quite possible that the electricity demand will be somewhat higher due to the buffer tank. I am also not entirely sure if this is the best solution. Since we have a 16 kWp photovoltaic system, I convinced myself it would be fine.

With photovoltaic power, it’s definitely more relaxed.

Haus Luni schrieb:

The thermostat exemption is new to me. Although it’s too late for me, I’m curious—how does that work?

The heating system planner writes a corresponding statement, and you apply for an exemption based on that.

Haus Luni schrieb:

What do you mean by cooling experience?

There are online sources sharing their own experiences with the cooling function. These are especially users of the Geishas etc., meaning the Panasonic monobloc units, since the cooling function has always been integrated and therefore does not involve extra cost. Many report no issues up to a flow temperature of about 18°C (64°F), with most settling around 20°C (68°F).
BUT: Please keep in mind that using the cooling function significantly increases indoor humidity. It then feels like a cool sauna. This makes sense because, unlike an air conditioner that not only cools but also dehumidifies directly, floor heating cooling cannot do that.

Is there still room for changes?
Instead of a combined storage tank, I would prefer to use two separate tanks. Combined tanks often cause problems. The separation between domestic hot water and heating water with their different temperature levels does not work as well as manufacturers claim. Additionally, they are often integrated as a hydraulic separator, which creates extra issues.