ᐅ Combination of air-to-air heat pump, air-to-water heat pump, solar thermal system, and photovoltaic system with storage
Created on: 29 Sep 2020 14:57
K
KevinHoehne
Hello everyone,
I hope I’m in the right subforum.
About my project:
My wife and I plan to build a new house (expected start spring 2021) with a KfW55 energy standard. The usable floor area will be approximately 209m² (2250 sq ft) plus a basement.
Our builder includes heating and domestic hot water via an air-to-water heat pump and an air-to-air heat pump, both with a fresh air system including a heat exchanger. Additionally, we decided on a 6 kWp photovoltaic system with a 6.5 kWh battery storage (available as a "spring offer" for about €10,000).
Since I’m generally someone who tries to avoid unnecessary costs (in this case electricity costs for hot water), I’ve been considering having a solar thermal system installed as well. Without the photovoltaic system, I expect savings of around €200 per year (about 800 kWh/year for hot water). If our household grows in the future, the savings would naturally increase.
In our last conversation with the architect, he was convinced that it would make more financial sense to increase the photovoltaic system to 8 kWp (additional cost approximately €5,000) instead of installing the solar thermal system. He couldn’t provide a price for the solar thermal system because it’s not listed in the price catalog, but I assume it would be a similar amount.
Now to my questions:
a) Does anyone have experience with similar energy system combinations?
b) Are there resources or services where one can have such calculations done?
Thank you in advance and best regards,
Kevin
I hope I’m in the right subforum.
About my project:
My wife and I plan to build a new house (expected start spring 2021) with a KfW55 energy standard. The usable floor area will be approximately 209m² (2250 sq ft) plus a basement.
Our builder includes heating and domestic hot water via an air-to-water heat pump and an air-to-air heat pump, both with a fresh air system including a heat exchanger. Additionally, we decided on a 6 kWp photovoltaic system with a 6.5 kWh battery storage (available as a "spring offer" for about €10,000).
Since I’m generally someone who tries to avoid unnecessary costs (in this case electricity costs for hot water), I’ve been considering having a solar thermal system installed as well. Without the photovoltaic system, I expect savings of around €200 per year (about 800 kWh/year for hot water). If our household grows in the future, the savings would naturally increase.
In our last conversation with the architect, he was convinced that it would make more financial sense to increase the photovoltaic system to 8 kWp (additional cost approximately €5,000) instead of installing the solar thermal system. He couldn’t provide a price for the solar thermal system because it’s not listed in the price catalog, but I assume it would be a similar amount.
Now to my questions:
a) Does anyone have experience with similar energy system combinations?
b) Are there resources or services where one can have such calculations done?
Thank you in advance and best regards,
Kevin
KevinHoehne schrieb:
Yes, of course, a mechanical ventilation with heat recovery system is installed. This system includes an integrated air-to-air heat pump for heating or reheating the air (in addition to the heat exchanger). The exhaust air from this is then also used to generate domestic hot water via an air-to-water heat pump.Oh, I’ve never considered it that way before. Why do you do it like this? What do you use to heat the house? Only the air-to-air heat pump for space heating, and the air-to-water heat pump just for domestic hot water?
Does it really make sense to risk the air-to-water heat pump freezing due to the very cold exhaust air from the air-to-air heat pump? The outside temperature must always be higher than the exhaust air, no matter the type of heat pump, right?
To me, it sounds like a very complex system that definitely needs to be questioned! In my opinion, straightforward solutions are best when building. Especially if you’re building to KfW55 standard, you should seriously reconsider using an air-to-air heat pump for heating the living spaces.
Mechanical ventilation systems with heat recovery usually have a heating element to prevent freezing. Is that what you mean?
K
KevinHoehne7 Dec 2020 13:17The roof faces south with a pitch of 25° – I know it’s not ideal, but the gable height is limited by building regulations. With a steeper roof, fitting two full stories would be difficult.
The system will have 24 modules at 340 watts heat pump each. The next "upgrade" from the home builder is 10 kWp, but apparently those won’t fit on the roof anymore (~12 m (39 ft) ridge length x 5 m (16 ft) rafter length).
The system will have 24 modules at 340 watts heat pump each. The next "upgrade" from the home builder is 10 kWp, but apparently those won’t fit on the roof anymore (~12 m (39 ft) ridge length x 5 m (16 ft) rafter length).
K
KevinHoehne7 Dec 2020 13:19OWLer schrieb:
Oh, I’ve never seen it that way before. Why is it done like that? What do you use to heat the house? Only the air-to-air heat pump, and is the air-to-water heat pump solely for hot water?
Does it make sense to cool the air-to-water heat pump with the freezing exhaust air from the air-to-air heat pump? The outside temperature must always be higher than the exhaust air, no matter which heat pump it is?
To me, this seems like a very complex system that definitely needs to be questioned! In my opinion, keeping it simple is best when building. Especially if you’re building a KfW55 standard house, you should strongly reconsider using an air-to-air heat pump to heat the living spaces.
There is a heating coil in the controlled ventilation system to prevent freezing. Is that what you mean?So, originally it should be that only the air-to-air heat pump handles heating, right? We also have a wood stove planned with 8kW heating output, which in the best case will more or less make the air-to-air heat pump unnecessary.
The heating coil is included as well.
I’m not sure to what extent mentioning companies or products is allowed here, otherwise I could show the corresponding system.
Regards
My urgent advice: skip the air-to-air heat pump and use an air-to-water heat pump combined with underfloor heating for both heating and cooling! Air is a very inefficient energy carrier.
If you go on a ski trip or long-distance travel in winter and can’t heat your home daily, you will end up heating almost entirely with direct electric power in cold conditions.
Try searching for "Proxon heat pump high electricity consumption."
If you go on a ski trip or long-distance travel in winter and can’t heat your home daily, you will end up heating almost entirely with direct electric power in cold conditions.
Try searching for "Proxon heat pump high electricity consumption."
K
KevinHoehne7 Dec 2020 14:58I’m afraid it’s already too late for a change.
According to the 2014 Energy Savings Ordinance calculation and the energy performance certificate, the house should have a primary energy demand of 14.9 kWh/m²/year, which, for approximately 209 m² (2250 ft²) plus 100 m² (1075 ft²) of basement area—of which only about 35% is actually heated—amounts to roughly 4500 kWh. This is before deducting the heat generated by the wood stove.
I’ll have to wait and see if it really turns out that bad—I hope not. In spring and autumn, the photovoltaic system should ideally provide a significant amount of energy for heating. For winter, of course, that’s uncertain.
According to the 2014 Energy Savings Ordinance calculation and the energy performance certificate, the house should have a primary energy demand of 14.9 kWh/m²/year, which, for approximately 209 m² (2250 ft²) plus 100 m² (1075 ft²) of basement area—of which only about 35% is actually heated—amounts to roughly 4500 kWh. This is before deducting the heat generated by the wood stove.
I’ll have to wait and see if it really turns out that bad—I hope not. In spring and autumn, the photovoltaic system should ideally provide a significant amount of energy for heating. For winter, of course, that’s uncertain.
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