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Sillmarillion31 Jan 2020 12:51Hello everyone,
I have just spent a long time browsing this forum because I am planning to build a house this year and was looking for tips to find answers to my questions. Some things have become clear to me already, but others are still not, so I decided to write a post. Our plan is a single-family house (detached house) for five people (parents + 3 children) with about 150-170 m2 (1,615-1,830 sq ft). I have renovated several houses before, but never built one.
Basically, we would like to avoid gas and coal (for cost reasons as well as environmental protection), but we are not sure if that is also practical. We live in the north, where it often gets colder (though not this winter).
I would appreciate any answers and tips.
Best regards
I have just spent a long time browsing this forum because I am planning to build a house this year and was looking for tips to find answers to my questions. Some things have become clear to me already, but others are still not, so I decided to write a post. Our plan is a single-family house (detached house) for five people (parents + 3 children) with about 150-170 m2 (1,615-1,830 sq ft). I have renovated several houses before, but never built one.
- We definitely want to build a low-energy house, and the reason is clear – we want to save on heating and energy costs. At the beginning of our planning, a passive house seemed like the ideal solution, but after more research we concluded that might be overdoing it – maybe a “regular” low-energy house with good insulation is enough? Do you have any experience with this? What I also wonder is – don’t these passive houses with their large south-facing glass walls turn into greenhouses in summer?
- We would also like to install photovoltaic systems on the roof, but we found two different options: for the hot water heater or for electricity generation. The latter would of course be ideal, but I would appreciate practical feedback here – is it worth it, and can photovoltaic systems produce enough electricity (also for winter)?
- Following that – are heat pumps recommended, and do they work everywhere or do they require certain geothermal conditions?
- Can ventilation systems with heat recovery also be installed in regular low-energy houses, and is it worthwhile?
- I have read in some places that it is cheaper (both when building and later for living costs) to do without basements and multiple floors, and instead plan a sprawling single-story design if the plot allows it. Would you agree with that?
Basically, we would like to avoid gas and coal (for cost reasons as well as environmental protection), but we are not sure if that is also practical. We live in the north, where it often gets colder (though not this winter).
I would appreciate any answers and tips.
Best regards
1. You need to balance things out; every additional centimeter of insulation and other measures cost money that may never actually be saved. In other words, you have to find the right balance for yourself.
2. Solar thermal systems are only worthwhile if you can install them cheaply on the roof. So, in principle, this is rather rare. Photovoltaic systems are more common, but of course, you will have little to no output in winter. There are experts in this forum who can definitely help you with that.
3. Depending on what energy source you use for your heat pump—such as air, water, or ground—you need to check with your local authority whether it is permitted. Air is obviously possible everywhere but usually has the lowest efficiency.
4. Controlled residential ventilation systems can be installed in any type of house and provide constant fresh air. Ideally, you should actually install one. In terms of energy savings or financial benefits, it’s not really worthwhile. However, a controlled ventilation system significantly increases comfort and saves you time that you can use elsewhere.
5. A basement is always more expensive than an upper floor, and expanding horizontally is also costly. So basically, a simple one-and-a-half-story house on a concrete slab is the cheapest option if you want a bit more space.
2. Solar thermal systems are only worthwhile if you can install them cheaply on the roof. So, in principle, this is rather rare. Photovoltaic systems are more common, but of course, you will have little to no output in winter. There are experts in this forum who can definitely help you with that.
3. Depending on what energy source you use for your heat pump—such as air, water, or ground—you need to check with your local authority whether it is permitted. Air is obviously possible everywhere but usually has the lowest efficiency.
4. Controlled residential ventilation systems can be installed in any type of house and provide constant fresh air. Ideally, you should actually install one. In terms of energy savings or financial benefits, it’s not really worthwhile. However, a controlled ventilation system significantly increases comfort and saves you time that you can use elsewhere.
5. A basement is always more expensive than an upper floor, and expanding horizontally is also costly. So basically, a simple one-and-a-half-story house on a concrete slab is the cheapest option if you want a bit more space.
Solar Energy for Hot Water = Solar Thermal — Not Worth It.
Solar Energy for Electricity = Photovoltaics — Still Worth It.
However, in winter you will struggle to meet even the basic electricity demand. Storage systems are not worthwhile — they are too small in summer and too large in winter.
Solar Energy for Electricity = Photovoltaics — Still Worth It.
However, in winter you will struggle to meet even the basic electricity demand. Storage systems are not worthwhile — they are too small in summer and too large in winter.
You still lack a lot of basic knowledge, which is noticeable. Take some time to read up more. I think a KfW40 or KfW40 Plus standard would probably be a good choice for you.
Forget about solar thermal systems. They don’t make much sense. Plan for a photovoltaic system to generate electricity, and if possible, try to orient your house to optimize this—so roof slopes facing east and west. No fireplace (you won’t need one in a low-energy house with a heat pump anyway). Ideally, avoid skylights. Use the entire roof surface. That way, you can install a system that reaches around 20 kWp. Then you’ll get a good amount of energy even in winter. For example, my 24.5 kWp system produced 678 kWh just in January. If you design and adjust your heat pump properly, you can generate a significant portion of the electricity it needs yourself. And this is true even in one of the worst months of the year.
Especially with new builds, you can plan everything properly from the start and orient everything optimally. Then it’s worth it, even though you’ll often hear the opposite claimed. Of course, I won’t be able to cover the heat pump’s entire electricity demand, but in the transitional months, it could work, and even in the really cold months (December, January, February), you can still cover a decent part.
Oh, and about battery storage: it’s generally not economical... BUT, if you receive a €6,000 subsidy through KfW funding, then it becomes worthwhile!
Forget about solar thermal systems. They don’t make much sense. Plan for a photovoltaic system to generate electricity, and if possible, try to orient your house to optimize this—so roof slopes facing east and west. No fireplace (you won’t need one in a low-energy house with a heat pump anyway). Ideally, avoid skylights. Use the entire roof surface. That way, you can install a system that reaches around 20 kWp. Then you’ll get a good amount of energy even in winter. For example, my 24.5 kWp system produced 678 kWh just in January. If you design and adjust your heat pump properly, you can generate a significant portion of the electricity it needs yourself. And this is true even in one of the worst months of the year.
Especially with new builds, you can plan everything properly from the start and orient everything optimally. Then it’s worth it, even though you’ll often hear the opposite claimed. Of course, I won’t be able to cover the heat pump’s entire electricity demand, but in the transitional months, it could work, and even in the really cold months (December, January, February), you can still cover a decent part.
Oh, and about battery storage: it’s generally not economical... BUT, if you receive a €6,000 subsidy through KfW funding, then it becomes worthwhile!
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nordanney1 Feb 2020 11:47Sillmarillion schrieb:
Maybe a "regular" low-energy house with good insulation is enough? Nowadays, that applies to every new build. Whether my heating costs are €20 or €30 per month is basically not relevant.
Sillmarillion schrieb:
Is it worthwhile, and can photovoltaic systems produce enough electricity (also in winter)? They can produce electricity, but not enough in winter. In my opinion, always install photovoltaics; solar thermal systems only if necessary (they provide a lot of hot water in summer—which often isn’t used—and almost none in winter due to lack of sun).
Sillmarillion schrieb:
Are heat pumps recommended, and do they work everywhere, or are certain geothermal conditions required? Yes, they are recommended. Geothermal conditions are only necessary for ground-source heat pump boreholes. There are also air-to-air and air-to-water heat pumps.
Sillmarillion schrieb:
Can ventilation systems with heat recovery also be installed in normal low-energy houses, and is it worthwhile? Not just possible—they should be installed.
Sillmarillion schrieb:
Don’t these passive houses with their large south-facing glass walls turn into greenhouses in summer? That "problem" affects every new build. It’s not only about insulation but also shading, which must be part of the house design.
Sillmarillion schrieb:
Would you agree to avoid basements and multiple floors and instead, if the plot allows, plan a sprawling single-story building? Basements are expensive but make sense on sloped plots or small lots.
A bungalow is costly because it uses a large plot area and has higher building costs per square meter (due to a less favorable building form).
Sillmarillion schrieb:
Basically, we want to avoid gas and coal (for cost reasons and to protect the environment), but we don’t know if that is practical. We live in the north, where it often gets colder (though not this winter). You will always use some coal if you don’t have gas since it is part of the electricity mix. And yes, heat pumps basically work everywhere in Germany.
Keep researching and feel free to ask more questions. You need to build more fundamental knowledge.
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Sillmarillion3 Feb 2020 14:14Thank you for your expert replies! I am well aware that I still have a lot to learn; otherwise, I wouldn’t have needed to post here.
By now, we are quite sure that we want to build a low-energy house (not a passive house) with a maximum energy consumption of 50 kWh/m² (16,000 BTU/ft²). A passive house seems a bit too risky and expensive for us.
Regarding the photovoltaic system, I am still uncertain because I have seen many pros and cons online. Since the house is yet to be built, I can orient it as I like; I thought it would be best to face it south, but here you suggest an east-west orientation?
The more you dig into the topic, the more questions arise – starting with the foundation (slab?), the exterior walls (single-, double- or triple-layered?), their materials (aerated concrete vs. perforated brick), and the type of insulation (polystyrene or mineral wool). There are many questions, so I appreciate any practical experience shared!
By now, we are quite sure that we want to build a low-energy house (not a passive house) with a maximum energy consumption of 50 kWh/m² (16,000 BTU/ft²). A passive house seems a bit too risky and expensive for us.
Regarding the photovoltaic system, I am still uncertain because I have seen many pros and cons online. Since the house is yet to be built, I can orient it as I like; I thought it would be best to face it south, but here you suggest an east-west orientation?
The more you dig into the topic, the more questions arise – starting with the foundation (slab?), the exterior walls (single-, double- or triple-layered?), their materials (aerated concrete vs. perforated brick), and the type of insulation (polystyrene or mineral wool). There are many questions, so I appreciate any practical experience shared!
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