ᐅ Heating System Choice: Air-to-Air or Air-to-Water Heat Pump

Created on: 19 Jun 2023 11:18

Hello everyone,
we are just at the very beginning of our home building journey – specifically in choosing the construction company. Neither of us are experts, and we are currently educating ourselves a lot -> please excuse us if some technical terms are unfamiliar or used incorrectly 😉
Among many other questions, we are uncertain about the heating system.

Construction Company A strongly recommends an air-to-air heat pump – meaning a central ventilation system with 'heating through the air flow.'
Company B suggests an air-to-water heat pump – combined with underfloor heating + still a central ventilation system.

And now about our lack of knowledge…
The air-to-air solution seems initially cheaper – but according to the advisor from Company B, there are disadvantages:
- Every room is the same temperature -> so having a cold bedroom and warm living room wouldn’t be possible?
- Warm air always rises -> so the floor would feel cold.

Neither of these issues would occur with underfloor heating since it can be controlled separately, and of course, your feet would be warm.
I don’t want to start a (new) fundamental debate – just wondering if you see it the same way? Unfortunately, we don’t know anyone who heats ‘with air’ 😉

HeimatBauer20 Jun 2023 16:49

#19

RotorMotor schrieb:

Where does a full roof not make sense?

The price usually decreases with larger systems.
You only need one scaffold, (usually) one inverter, one installation team, etc.
That’s why it is very rare to stop at half the capacity!

1. There used to be limits that significantly affected the yield, causing a sharp jump in the business case at, for example, 10kWp.
2. There were also subsidies with caps. Here too: it’s important to carefully consider whether to install 10kWp or go directly for 30, as there was nothing viable in between.
3. If the budget runs out at 10kWp, then it runs out—and it isn’t always reasonable to take out a loan just to achieve “full roof” capacity.
4. It depends heavily on the goal. If the goal is return on investment, a full roof is sensible. If the goal is meaningful self-consumption or energy independence, the benefit of an additional 20kWp is rather marginal. You can’t be more than 100% energy independent. Exporting power to the grid is another matter, but people have different objectives.
5. I simply ran the simulations. My east-west system provides excellent self-consumption for eight or nine months because it starts early in the morning and runs late into the evening. But in winter, the panel angle becomes a serious disadvantage, and here, south-facing panels optimized for winter perform much better. Again, this approach may not satisfy investors focused solely on returns but is ideal for those who appreciate significantly improved energy independence during winter.

RotorMotor20 Jun 2023 17:18

#20

HeimatBauer schrieb:

1. There used to be limits that significantly impacted the yield, causing a sharp jump in the business case at around 10kWP.
2. There were subsidies with caps as well. Here too: you needed to carefully consider whether to go for 10kWP or straight to 30kWP, as there was nothing in between.
3. Once the funding for 10kWP is exhausted, it’s gone—and it’s not always sensible to take out a loan just to fully cover the roof.
4. It really depends on your goal. If the goal is return on investment, maximizing rooftop capacity makes sense. If the goal is meaningful self-sufficiency, it’s different. The additional 20kWP offers only a marginal increase in self-sufficiency. You can’t be more than 100% self-sufficient, of course. Exporting to the grid is an option, but people have different priorities.
5. I simply ran simulations. My east-west system provides excellent self-consumption for eight or nine months because it starts early in the morning and ends late in the evening. But in winter, the tilt angle works against it, and winter-optimized south-facing panels are a much smarter choice. Again, this is probably not for those focused solely on returns but for people who value significantly improved self-sufficiency in winter.

1. and 2. are not relevant anymore, as they refer to the past.
3. Loans can easily solve that.
4. What exactly is meant by “meaningful self-sufficiency”? That doesn’t sound very clear. The goal is either return on investment → maximize rooftop capacity or environmental protection → also maximize rooftop capacity.
5. Either it’s worth it or it’s not; it has nothing to do with “meaningful or pointless summer and winter self-sufficiency.”

However, running simulations and calculations always makes sense!

HeimatBauer20 Jun 2023 17:24

#21

RotorMotor schrieb:

1. 2. not relevant, as they refer to the past.
3. Can be easily solved with loans.
4. What exactly is a "meaningful self-sufficiency"? That doesn’t sound reasonable. The goal is either return on investment -> full roof
or environmental protection -> also full roof
5. Either it’s worth it or it’s not; this has nothing to do with "meaningful or pointless summer and winter self-sufficiency."

Simulating and calculating always makes sense though!

Points 1 and 2 are absolutely relevant for an existing system.
Point 3 is easier said than done—I recall the huge stress I had with my government-subsidized loan. My wife was close to giving up on the entire photovoltaic project. So: loan yes/no is not a simple decision.
Point 4 What is so hard to understand about the term self-sufficiency? It works easily in summer; in spring and autumn it depends on weather and yield. The days when a 10 kW system is no longer enough but a 30 kW system is, are few. That is a goal you simply don’t consider, but it exists.
Point 5 See point 4, for you it’s only about return on investment. No problem, that is a valid goal and for that, as I wrote, a fully utilized roof is absolutely reasonable. Different people, different goals, different solutions.

mayglow20 Jun 2023 20:18

#22

RotorMotor schrieb:

Where does a full roof not make sense?

We have a 40° (40°) roof pitch and an almost exact north-south orientation. I’m not completely sure yet, but from everything I’ve been told, covering the north side would probably just be for enthusiasts. :/

RotorMotor20 Jun 2023 20:20

#23

mayglow schrieb:

We have a 40° roof pitch with a fairly exact north and south orientation. I'm not entirely sure yet, but from everything I've been told, installing on the north side is probably more of a preference. :/

Yes, it’s clear that some roof sides don’t make sense, and areas can be excluded due to trees or other shading.

But something like "reasonable self-sufficiency" without money because loans are too complicated, and therefore the wife stops the project, is more "interesting" than sensible.

HeimatBauer21 Jun 2023 08:26

#24

RotorMotor schrieb:

But something like "reasonable self-sufficiency" and no money because loans are too complicated, leading the wife to stop the project, is more "interesting" than practical.

That is what you would call the reality of other people.

ᐅ Heating System Choice: Air-to-Air or Air-to-Water Heat Pump

Reaktionen