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
Häuslebau3r18 Feb 2015 13:39Heimat2015 schrieb:
@hauslebau3r....
Thank you for your contribution... I’m starting to share your view on photovoltaics as well...
Does everything run automatically? As soon as enough energy is generated from the roof, do I use it myself? If not, do I have to buy electricity?
Then I would have to heat everything nicely during the day, so a buffer storage might become relevant 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 is always going to be occupied. If no one is home, then it’s something to consider.
Still, I see this topic critically because if you have such a system, you really need to pay attention to maintenance and not just change a simple “filter” every now and then. But that’s another topic.
That’s why I’m building without additional insulation and with Poroton blocks—I think that will work out quite well...As other users have already mentioned, there is no single best solution. I’m no professional either and, like you, I’m looking for the right technical conditions, so I’m interested in following this topic further. Somehow, it seems to be a matter of setting preferences and maybe building with the future in mind, for example with a photovoltaic system, so that in 10 years it might be possible to use storage devices to store the generated electricity cost-effectively in relation.
Heimat201522 Feb 2015 19:47Cascada schrieb:
How large is the house, which climate zone, how many occupants, energy saving regulation standard?
What does the heating load calculation say? If you have that, then you can start to think about itThe house has exterior dimensions of 10x10m (33x33 ft), usable floor area of 197m² (2,120 ft²), building volume of 616m³ (21,740 ft³), 4 occupants, KfW 70 standard.
The heating load calculation, if you mean the annual heating demand, is 8,280 kWh/year.
Since I am not a professional, I can think about this no more than before. I can only rely on what I learn from "experts"/specialists!
Heimat2015 schrieb:
The house has exterior dimensions of 10x10m (33x33 ft), usable floor area of 197m² (2,120 sq ft), building volume of 616m³ (21,740 cu ft), 4 residents, KfW 70 standard.
If by heating load calculation you mean the annual heat demand, it is 8,280 kWh/a.
Since I am not an expert, I can only consider as much as before. I can only rely on what I hear from "experts" or professionals!If the 8,280 kWh/a refers to the annual external thermal energy demand for heating and hot water, then yes. I do not have access to the documents, though.
Assuming you install a properly sized and commissioned air-to-water heat pump with a seasonal performance factor (SPF) of 3.5, you would realistically need about 2,365 kWh/a plus some additional energy for the circulation pump and controls. The mentioned 8,280 kWh/a likely refers to the "standard DIN" conditions with a 19°C (66°F) room temperature and so forth.
Experts can provide more details on this.
At least you have a figure to work with.
As already mentioned – with this heating load (do you live in a cold or milder climate?), I would rely exclusively on the air-to-water heat pump and omit a fireplace, whether hydronic or not. The reasons have already been explained.
Heimat201523 Feb 2015 14:17According to the documents, an annual performance factor of 4.3 is stated. We are using a Vaillant geoTHERM vwl... Does the unit specify the annual performance factor, or is it determined by several factors?
The region is not really cold but not really warm either, around Heidelberg.
The region is not really cold but not really warm either, around Heidelberg.
Just search for heat pumps and consumption databases. For the systems listed there, the average annual performance factor in 2014 was 3.43 for air-to-water heat pumps and 4.18 for ground-source heat pumps. Personally, I also don’t know of any car that meets the manufacturer’s fuel consumption specifications…
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