Hello everyone
We are currently taking the next steps toward building our own home. We have looked at several prefabricated houses and spoken with sales consultants from various providers. Based on this, we have created a top 5 list. Now I want to contact these 5 companies with our floor plan and the standards we want. This way, I hope the list will be reduced by 2-3 providers after receiving the first offers.
In my inquiry, I want to roughly outline what we have in mind. KFW55, KFW40, or KFW40+ is not yet very important—it will be one of these standards. Our floor plan does not differ much from the standard layouts offered by prefab house suppliers. Something like a simple 8x10 meter (26x33 feet) rectangular shape... To be able to compare the 5 offers reasonably, I want them all to be as similar as possible. Therefore, I would like to specify the heating system.
Now the question is, what is the right choice… I assume this is partly a matter of philosophy? The options are an air-to-water heat pump, an air-to-air heat pump, or a ground-source (geothermal) heat pump. I assume most have one of these three systems combined with solar panels on the roof.
My first thought was this: an air-to-air heat pump, since we would also have an automatic ventilation system in the house, making manual airing less or unnecessary. However, I have learned that all KFW-certified houses are so well insulated that they almost always have automatic ventilation. So this argument is no longer valid. Nevertheless, I still find the air-to-air heat pump interesting. We also want to install a wood stove in the living room. With an air-to-air heat pump, the indoor air is circulated throughout the house, so I could benefit from the wood stove’s heat everywhere, right? Perhaps even with heat recovery, which is usually included.
Another advantage of the air-to-air heat pump would be that if it ever gets too warm, we could install a fixed air conditioning unit somewhere in the house, and the whole house would benefit. The built-in cooling systems in these heat pumps usually aren’t as effective as promised.
Is it true that an air-to-air heat pump cannot provide domestic hot water? Then a second system would be needed just for hot water, which means more costs, two systems to maintain, and more space taken up. In the forum, I mostly see air-to-water heat pumps mentioned, probably combined with underfloor heating. That seems to be the most popular system. Is there a particular reason for this?
Geothermal heating combined with a heat pump seems to be the most efficient. But then I would also have underfloor heating, right? We actually didn’t want underfloor heating, but as I’m writing this, I’m starting to convince myself toward geothermal or air-to-water heat pumps…
How did you make your decision and why? Somehow, I don’t fully trust the salespeople, since they want to sell what makes more money, right? And since I’m not very technical in this area, I’m hoping to benefit from your experience.
Best regards Andreas_79
We are currently taking the next steps toward building our own home. We have looked at several prefabricated houses and spoken with sales consultants from various providers. Based on this, we have created a top 5 list. Now I want to contact these 5 companies with our floor plan and the standards we want. This way, I hope the list will be reduced by 2-3 providers after receiving the first offers.
In my inquiry, I want to roughly outline what we have in mind. KFW55, KFW40, or KFW40+ is not yet very important—it will be one of these standards. Our floor plan does not differ much from the standard layouts offered by prefab house suppliers. Something like a simple 8x10 meter (26x33 feet) rectangular shape... To be able to compare the 5 offers reasonably, I want them all to be as similar as possible. Therefore, I would like to specify the heating system.
Now the question is, what is the right choice… I assume this is partly a matter of philosophy? The options are an air-to-water heat pump, an air-to-air heat pump, or a ground-source (geothermal) heat pump. I assume most have one of these three systems combined with solar panels on the roof.
My first thought was this: an air-to-air heat pump, since we would also have an automatic ventilation system in the house, making manual airing less or unnecessary. However, I have learned that all KFW-certified houses are so well insulated that they almost always have automatic ventilation. So this argument is no longer valid. Nevertheless, I still find the air-to-air heat pump interesting. We also want to install a wood stove in the living room. With an air-to-air heat pump, the indoor air is circulated throughout the house, so I could benefit from the wood stove’s heat everywhere, right? Perhaps even with heat recovery, which is usually included.
Another advantage of the air-to-air heat pump would be that if it ever gets too warm, we could install a fixed air conditioning unit somewhere in the house, and the whole house would benefit. The built-in cooling systems in these heat pumps usually aren’t as effective as promised.
Is it true that an air-to-air heat pump cannot provide domestic hot water? Then a second system would be needed just for hot water, which means more costs, two systems to maintain, and more space taken up. In the forum, I mostly see air-to-water heat pumps mentioned, probably combined with underfloor heating. That seems to be the most popular system. Is there a particular reason for this?
Geothermal heating combined with a heat pump seems to be the most efficient. But then I would also have underfloor heating, right? We actually didn’t want underfloor heating, but as I’m writing this, I’m starting to convince myself toward geothermal or air-to-water heat pumps…
How did you make your decision and why? Somehow, I don’t fully trust the salespeople, since they want to sell what makes more money, right? And since I’m not very technical in this area, I’m hoping to benefit from your experience.
Best regards Andreas_79
rdwlnts schrieb:
Well, the house is warm even without a fireplace. The extra heat is actually too much. Or does one want to be cold beforehand? At least the temperature increase is buffered.
But because of this, one has to turn off the underfloor heating and the screed starts to cool down (warm air rises), so the actual heat storage mass of the house makes the heat pump do extra work through a temporarily increased supply temperature.
A highly efficient underfloor heating system is not regulated and runs continuously, day and night. The fireplace slightly reduces the overall heating demand from the heat pump but makes it less efficient over the year. And it still gets too warm when using the fireplace. That’s why partial ventilation is needed and the heat pump’s heating demand increases again.
Nowadays, there are artificial fireplaces that look just like real ones. And they don’t cost 10-15k€.
If the wood is not properly dried, it actually releases more CO2 than coal.
There’s also fine dust released into the living space.
We simply need to stop constantly burning things, and a fireplace cannot be justified reasonably. A well-designed underfloor heating system in such a case uses the self-regulating effect, preventing the heat pump from becoming less efficient.
Yes, the temperature in the house will rise, maybe from around 21 to 24 degrees Celsius (69.8 to 75.2 degrees Fahrenheit), depending on the construction. This is perceived as pleasant radiant heat and does not necessarily have to be ventilated out.
R
RotorMotor4 Aug 2021 13:19rdwlnts schrieb:
If the wood is not dried sufficiently, it releases more CO2 than coal.How could more H2O in the wood lead to more CO2 being produced? The calorific value decreases because the water evaporates and absorbs heat, but producing more CO2 simply doesn't make sense.
Wood always releases the same amount of carbon dioxide that it absorbed during its growth.
However, incomplete combustion can produce toxic carbon monoxide and, of course, fine particulate matter.
RotorMotor schrieb:
Wood releases the amount of CO2 it absorbed during its growth.The same applies to coal as well.See also:
"Does replacing coal with wood lower CO2 emissions? Dynamic lifecycle analysis of wood bioenergy
John D Sterman1,4
, Lori Siegel2 and Juliette N Rooney-Varga3 Published 18 January 2018 • © 2018 The Author(s). Published by IOP Publishing Ltd"
R
RotorMotor4 Aug 2021 15:12@rdwlnts :Yes, of course, but what does this have to do with the moisture content of the wood?
Wood has a lower energy density compared to coal. This is further reduced when the wood contains a high moisture content. During combustion, the energy must first be used to heat the water and provide the heat of vaporization, which does not directly generate heat. This significantly reduces heating efficiency. Extremely wet wood may not burn at all, to illustrate the point with an extreme example. Some claim that wood has 1.4 times the energy content of coal, but I do not see it that negatively.
However, if all coal combustion were immediately replaced by wood, we would face a very large CO2 problem, even greater than what we currently have. This is explained in the paper.
However, if all coal combustion were immediately replaced by wood, we would face a very large CO2 problem, even greater than what we currently have. This is explained in the paper.
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