ᐅ Air-to-water heat pump combined with solar thermal and a wood-burning stove: costs, benefits, and practicality
Created on: 1 Feb 2015 15:57
M
M.Mustermann
Hello everyone,
Here are a few key points upfront:
We plan to build a single-family house with 121sqm (1300 sq ft) of living space this summer. Ground floor and upper floor, for 2 adults and 2 children.
The roof will face south.
We will use Ytong (30cm (12 inches)) blocks, with triple-glazed windows. Underfloor heating will be installed.
We live in Hesse, Rhine-Main area.
A air-to-water heat pump will be installed since we do not have gas and do not want to have any tanks for gas, oil, or pellets either inside the house or buried in the garden.
We would also like a fireplace for coziness and because we have almost free access to firewood. Solar thermal is also being considered; the question is whether it is worthwhile and if it should be used just for hot water or also for heating.
The following offer has already been presented to us:
A Nibe air-to-water heat pump split system with building heat load up to 7 kW, a buffer storage tank of 270l (71 gallons) with an additional 100l (26 gallons) buffer tank including Pedotherm underfloor heating.
For solar, 4sqm (43 sq ft) – 2 collectors and a 230l (61 gallons) buffer tank would be added.
The extra cost for solar is about 4000,- €.
For connecting a hydronic fireplace, including piping, pump, return lifting, and drainage protection, nearly 3000,- € is charged.
I am calculating about 3500,- € for a fireplace with an external chimney.
So, including the air-to-water heat pump, it would be over 10,000,- € for the fireplace and solar combined.
Regarding the questions:
The buffer storage tank seems very small for this project—is that accurate?
What makes sense for the heating system, considering it should pay off as much as possible? Because of the fireplace desire, it might not be possible, but well, the fireplace is a luxury and would be accepted even if it is not cost-effective.
I am concerned about only having an air-to-water heat pump in the cold season, due to electricity costs, and 7 kW building heat load seems low (though I have no expertise). A friend has an air-to-air heat pump and currently the electricity costs are extremely high.
What makes sense? What else should I include in the calculation, what might I have overlooked or should consider?
What do you think about Nibe?
Regards,
Max
Here are a few key points upfront:
We plan to build a single-family house with 121sqm (1300 sq ft) of living space this summer. Ground floor and upper floor, for 2 adults and 2 children.
The roof will face south.
We will use Ytong (30cm (12 inches)) blocks, with triple-glazed windows. Underfloor heating will be installed.
We live in Hesse, Rhine-Main area.
A air-to-water heat pump will be installed since we do not have gas and do not want to have any tanks for gas, oil, or pellets either inside the house or buried in the garden.
We would also like a fireplace for coziness and because we have almost free access to firewood. Solar thermal is also being considered; the question is whether it is worthwhile and if it should be used just for hot water or also for heating.
The following offer has already been presented to us:
A Nibe air-to-water heat pump split system with building heat load up to 7 kW, a buffer storage tank of 270l (71 gallons) with an additional 100l (26 gallons) buffer tank including Pedotherm underfloor heating.
For solar, 4sqm (43 sq ft) – 2 collectors and a 230l (61 gallons) buffer tank would be added.
The extra cost for solar is about 4000,- €.
For connecting a hydronic fireplace, including piping, pump, return lifting, and drainage protection, nearly 3000,- € is charged.
I am calculating about 3500,- € for a fireplace with an external chimney.
So, including the air-to-water heat pump, it would be over 10,000,- € for the fireplace and solar combined.
Regarding the questions:
The buffer storage tank seems very small for this project—is that accurate?
What makes sense for the heating system, considering it should pay off as much as possible? Because of the fireplace desire, it might not be possible, but well, the fireplace is a luxury and would be accepted even if it is not cost-effective.
I am concerned about only having an air-to-water heat pump in the cold season, due to electricity costs, and 7 kW building heat load seems low (though I have no expertise). A friend has an air-to-air heat pump and currently the electricity costs are extremely high.
What makes sense? What else should I include in the calculation, what might I have overlooked or should consider?
What do you think about Nibe?
Regards,
Max
Heimat201518 Feb 2015 00:52By now, this is the 1001st post on the topic of air-to-water heat pumps combined with water-bearing wood-burning stoves. Unfortunately, I still haven’t reached a clear conclusion! Not even the heating engineers can give a precise answer on whether it really makes sense and how complex the control system would be, so that I don’t end up damaging the efficiency of the air-to-water heat pump when the stove isn’t burning.
Here are the facts I’ve gathered so far (please feel free to correct me):
– If I plan a wood stove with water integration, I need a buffer storage tank.
– An air-to-water heat pump does not require this buffer tank because it directly supplies the underfloor heating, and it would be a waste of energy to heat a buffer of about 500 liters (130 gallons).
– When I look at a system where solar thermal is combined with an air-to-water heat pump, it also requires a buffer tank! How does that work in winter then? Do I just save extra energy in summer and waste it in winter?
Solar and air-to-water heat pump systems seem very inefficient to me. In summer, when the air-to-water heat pump works efficiently, I support it, but in winter, I receive no backup.
Which system or manufacturer covers everything? The complete control system from a single manufacturer? And efficient like the Vaillant geoTHERM?
Without the stove, I only see one option for myself: the Vaillant geoTHERM Plus.
We are building with 36.5 cm (14 inches) solid Poroton bricks without mechanical ventilation (for me, that’s the worst invention ever—I would never want that in my house. I have two healthy hands to open windows, but that’s another story).
The house is 160 m² (1720 sq ft) over two floors.
Here are the facts I’ve gathered so far (please feel free to correct me):
– If I plan a wood stove with water integration, I need a buffer storage tank.
– An air-to-water heat pump does not require this buffer tank because it directly supplies the underfloor heating, and it would be a waste of energy to heat a buffer of about 500 liters (130 gallons).
– When I look at a system where solar thermal is combined with an air-to-water heat pump, it also requires a buffer tank! How does that work in winter then? Do I just save extra energy in summer and waste it in winter?
Solar and air-to-water heat pump systems seem very inefficient to me. In summer, when the air-to-water heat pump works efficiently, I support it, but in winter, I receive no backup.
Which system or manufacturer covers everything? The complete control system from a single manufacturer? And efficient like the Vaillant geoTHERM?
Without the stove, I only see one option for myself: the Vaillant geoTHERM Plus.
We are building with 36.5 cm (14 inches) solid Poroton bricks without mechanical ventilation (for me, that’s the worst invention ever—I would never want that in my house. I have two healthy hands to open windows, but that’s another story).
The house is 160 m² (1720 sq ft) over two floors.
Häuslebau3r18 Feb 2015 07:39Good morning everyone,
@f-pNo Regarding your calculation, you really have to question what ultimately pays off. I received information from an acquaintance who, at the time of building his house, had a combination of a photovoltaic system with east/west orientation and an air-to-water heat pump calculated, and this option turned out to be more efficient than a purely south-facing photovoltaic system. Additionally, he was told that, due to the garage’s orientation, it might still be possible to install a small south-facing photovoltaic system there.
Until now, I also believed that an east/west orientation of the photovoltaic system combined with an air-to-water heat pump was the best solution. Especially considering, as you already mentioned, that in about 5-10 years battery storage should become economically viable and profitable.
@Heimat2015 I recently attended a lecture where ovens with heat-retention features were also discussed. It was mentioned that a photovoltaic system combined with such an oven is probably the best combination. I have also read that a photovoltaic system combined with an air-to-water heat pump is another option. In this setup, the excess electricity generated by the photovoltaic system is stored in a water tank for domestic hot water (not for underfloor heating, which is supplied by the air-to-water heat pump) and used together with an electric heating element. Of course, it is said that the electricity is actually too valuable for this purpose, but the 12 cents for feeding electricity back into the grid don’t make you wealthy either. I don’t have precise details, it was just an idea or a contribution I came across somewhere.
Regarding solid construction, do you mean a ventilation system when you say “air atomizer”? At first, I also thought natural ventilation would be easy, but in a solid build or one close to KfW 70 / 55 standards and beyond, I would now lean toward a central or decentralized ventilation system. Considering both people could be working full-time, I don’t believe that ventilation requirements could be consistently met. If mold appears later on, it just causes frustration. But that’s my personal view.
@f-pNo Regarding your calculation, you really have to question what ultimately pays off. I received information from an acquaintance who, at the time of building his house, had a combination of a photovoltaic system with east/west orientation and an air-to-water heat pump calculated, and this option turned out to be more efficient than a purely south-facing photovoltaic system. Additionally, he was told that, due to the garage’s orientation, it might still be possible to install a small south-facing photovoltaic system there.
Until now, I also believed that an east/west orientation of the photovoltaic system combined with an air-to-water heat pump was the best solution. Especially considering, as you already mentioned, that in about 5-10 years battery storage should become economically viable and profitable.
@Heimat2015 I recently attended a lecture where ovens with heat-retention features were also discussed. It was mentioned that a photovoltaic system combined with such an oven is probably the best combination. I have also read that a photovoltaic system combined with an air-to-water heat pump is another option. In this setup, the excess electricity generated by the photovoltaic system is stored in a water tank for domestic hot water (not for underfloor heating, which is supplied by the air-to-water heat pump) and used together with an electric heating element. Of course, it is said that the electricity is actually too valuable for this purpose, but the 12 cents for feeding electricity back into the grid don’t make you wealthy either. I don’t have precise details, it was just an idea or a contribution I came across somewhere.
Regarding solid construction, do you mean a ventilation system when you say “air atomizer”? At first, I also thought natural ventilation would be easy, but in a solid build or one close to KfW 70 / 55 standards and beyond, I would now lean toward a central or decentralized ventilation system. Considering both people could be working full-time, I don’t believe that ventilation requirements could be consistently met. If mold appears later on, it just causes frustration. But that’s my personal view.
Heimat201518 Feb 2015 08:21@hauslebau3r....
Thank you for your post... I’m now starting to share your view on photovoltaic systems as well...
Does it all work automatically? That is, as soon as enough energy is generated from the roof, do I use it myself? If not, do I have to buy electricity?
In that case, I would need to heat everything during the day, so a thermal storage system might be an option again.
Oh man, it’s not that simple...
Regarding the ventilation system, I agree with you, but we have two small children, so the house will always be occupied. When no one is home, it is something to consider.
Still, I’m a bit skeptical about it because if you have such a system, you really need to keep up with maintenance and not just change a small filter now and then. But that’s not the topic here.
That’s why I’m building without additional insulation and think that using Poroton blocks will work well for us...
Thank you for your post... I’m now starting to share your view on photovoltaic systems as well...
Does it all work automatically? That is, as soon as enough energy is generated from the roof, do I use it myself? If not, do I have to buy electricity?
In that case, I would need to heat everything during the day, so a thermal storage system might be an option again.
Oh man, it’s not that simple...
Regarding the ventilation system, I agree with you, but we have two small children, so the house will always be occupied. When no one is home, it is something to consider.
Still, I’m a bit skeptical about it because if you have such a system, you really need to keep up with maintenance and not just change a small filter now and then. But that’s not the topic here.
That’s why I’m building without additional insulation and think that using Poroton blocks will work well for us...
Heimat201518 Feb 2015 09:03It's about life in the house. My children are not home alone... I also have a wife, but that’s not the point...
This is where the keyword "regularly" comes in – 70% of ventilation system owners will not do this, and then it will quickly become unpleasant when the dirt spreads around the home.
This is where the keyword "regularly" comes in – 70% of ventilation system owners will not do this, and then it will quickly become unpleasant when the dirt spreads around the home.
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