ᐅ Plus-energy house with a hydronic pellet stove and a ground source heat pump for cooling?
Created on: 29 Feb 2016 23:55
D
Ddorfer
Hello everyone,
I have been following this forum with interest for some time now. I would like to start a topic myself and hope for lots of good ideas, suggestions, and tips.
We have been considering building a house for a while, but we are still in the research and planning phase. According to our current ideas, it should be a Plus Energy House, although I am still not entirely sure if it will be cost-effective (I plan to start a separate discussion on that). It will be a prefabricated house. The providers’ plans generally include a central ventilation system with heat recovery and photovoltaic panels.
We have mainly two points to consider: We would like to have a wood-burning stove for coziness. Economic efficiency plays only a minor role here. From our research, we found stoves that are hydronic, releasing only 15-20% of the heat directly into the room air, meaning at least 80-85% can be used for heating and hot water production. We thought an automatic pellet stove would be well suited to support or even fully cover heating and hot water needs during winter when there is little sun. This would be a nice bonus. However, an energy consultant told us that it is almost impossible to operate a hydronic pellet stove efficiently in such a well-insulated house because the direct heat output is already too high. Is that true? Does anyone have experience with this? Shouldn’t the central ventilation system distribute the heat effectively throughout the house? Do we possibly have to give up our dream of a wood-burning stove because it doesn’t work well in combination with a Plus Energy House?
The second point is cooling. Since moving out of my parents’ house, I have always lived in rented apartments that became far too warm in summer, sometimes 26-28°C (79-82°F) or even higher, despite shading and night ventilation. I definitely don’t want to experience that anymore. Who can sleep properly under such conditions? In addition to automatic shading (roller shutters on all windows), we have therefore been thinking about a central air conditioning system. After some research, we found out that a heat pump can also provide cooling. Of course, a heat pump also offers benefits during the rest of the year. Therefore, our idea is to combine the system with a (preferably) water-to-water heat pump. In summer, it could cool our house, especially the bedrooms, to comfortable temperatures (max. 22°C (72°F) in the bedrooms at night and 24°C (75°F) in the main living areas during the day) and otherwise support heating and hot water production. Additionally, the wells for the water-to-water heat pump could be used for automatic garden irrigation, which makes sense anyway. Is such a solution more cost-effective than conventional air conditioning? Or would another heat pump technology be worth considering? Does anyone here cool their home with a heat pump? What are your experiences?
We are truly grateful for any tips, suggestions, or further information. If more details are needed, just ask.
Thanks in advance for your replies.
Best regards,
Ddorfer
I have been following this forum with interest for some time now. I would like to start a topic myself and hope for lots of good ideas, suggestions, and tips.
We have been considering building a house for a while, but we are still in the research and planning phase. According to our current ideas, it should be a Plus Energy House, although I am still not entirely sure if it will be cost-effective (I plan to start a separate discussion on that). It will be a prefabricated house. The providers’ plans generally include a central ventilation system with heat recovery and photovoltaic panels.
We have mainly two points to consider: We would like to have a wood-burning stove for coziness. Economic efficiency plays only a minor role here. From our research, we found stoves that are hydronic, releasing only 15-20% of the heat directly into the room air, meaning at least 80-85% can be used for heating and hot water production. We thought an automatic pellet stove would be well suited to support or even fully cover heating and hot water needs during winter when there is little sun. This would be a nice bonus. However, an energy consultant told us that it is almost impossible to operate a hydronic pellet stove efficiently in such a well-insulated house because the direct heat output is already too high. Is that true? Does anyone have experience with this? Shouldn’t the central ventilation system distribute the heat effectively throughout the house? Do we possibly have to give up our dream of a wood-burning stove because it doesn’t work well in combination with a Plus Energy House?
The second point is cooling. Since moving out of my parents’ house, I have always lived in rented apartments that became far too warm in summer, sometimes 26-28°C (79-82°F) or even higher, despite shading and night ventilation. I definitely don’t want to experience that anymore. Who can sleep properly under such conditions? In addition to automatic shading (roller shutters on all windows), we have therefore been thinking about a central air conditioning system. After some research, we found out that a heat pump can also provide cooling. Of course, a heat pump also offers benefits during the rest of the year. Therefore, our idea is to combine the system with a (preferably) water-to-water heat pump. In summer, it could cool our house, especially the bedrooms, to comfortable temperatures (max. 22°C (72°F) in the bedrooms at night and 24°C (75°F) in the main living areas during the day) and otherwise support heating and hot water production. Additionally, the wells for the water-to-water heat pump could be used for automatic garden irrigation, which makes sense anyway. Is such a solution more cost-effective than conventional air conditioning? Or would another heat pump technology be worth considering? Does anyone here cool their home with a heat pump? What are your experiences?
We are truly grateful for any tips, suggestions, or further information. If more details are needed, just ask.
Thanks in advance for your replies.
Best regards,
Ddorfer
Hello Bauexperte, thank you very much for your detailed post.
At the moment, we are indeed leaning toward a prefab house. However, the decision is not yet final. Based on the information we have so far, this option seems the most attractive to us.
Quite simply, because I’m not sure if he understood that it doesn't necessarily have to be an open fireplace with wooden logs, but we are also considering options that emit less direct heat into the room. And apparently, there seem to be quite a few options here. So far, I just lack the technical knowledge to judge this. For example, how much heating energy is actually released? And how much heating energy is even required in a passive house?
So far, I understood that this could be avoided through appropriate regulation. The 2 degrees might actually be enough. It depends on how much the house heats up. But I am increasingly under the impression that maybe a conventional split air conditioning system would be better after all.
Because, based on what we’ve read so far, this is the most efficient solution. But I’m open to being corrected. However, if in the end a standard air conditioner proves more practical, then the heat pump is probably off the table anyway.
Well, I have talked to a few people in model home parks. But I always had the impression they mainly try to sell me what they offer. Which is logical and not to be criticized. One young guy who tried to rush me because of current interest rates really took it too far. Well, he was probably new.
That’s exactly the question: Is it financially worth it? I would like to calculate this myself. However, I’m missing some important variables, such as the actual savings for different options and the additional costs involved. I feel confident considering the differences in subsidies and making some assumptions about the cost development of electricity, gas, pellets, etc. I found some calculations on the websites of prefab house providers, but of course, they want to sell their houses and don’t disclose all assumptions.
May I ask about the details of the house? Square meters, roof type, size of the solar system, storage, etc.? €10 is an impressive figure. So it seems that the savings potential of KfW 40 compared to KfW 70 may not be that large anymore.
I only want to claim subsidies if it makes sense financially overall. So I can take the repayment grants, the savings from lower interest rates, and energy cost savings and compare them to the additional costs. But as I mentioned earlier, I currently lack the knowledge to estimate energy savings and extra expenses.
If you are an expert, maybe you can shed some light on this?
Oh, and regards back to Bauexperte.
Bauexperte schrieb:
Prefab house in the sense of "all services from one source" or actually a prefab house?
At the moment, we are indeed leaning toward a prefab house. However, the decision is not yet final. Based on the information we have so far, this option seems the most attractive to us.
Bauexperte schrieb:
Yes, why do you doubt the statement of an expert?
Quite simply, because I’m not sure if he understood that it doesn't necessarily have to be an open fireplace with wooden logs, but we are also considering options that emit less direct heat into the room. And apparently, there seem to be quite a few options here. So far, I just lack the technical knowledge to judge this. For example, how much heating energy is actually released? And how much heating energy is even required in a passive house?
Bauexperte schrieb:
At most about 2°; but don’t forget that this will cause condensation on tiles. It’s like a free slip-and-fall hazard.
So far, I understood that this could be avoided through appropriate regulation. The 2 degrees might actually be enough. It depends on how much the house heats up. But I am increasingly under the impression that maybe a conventional split air conditioning system would be better after all.
Bauexperte schrieb:
WWHP preferred: Why?
Because, based on what we’ve read so far, this is the most efficient solution. But I’m open to being corrected. However, if in the end a standard air conditioner proves more practical, then the heat pump is probably off the table anyway.
Bauexperte schrieb:
You “seem” not to have had a proper consultation yet, otherwise you would know by now that your current plan overshoots the target of being “reasonable.” “More” was never better; compressing technologies too much isn’t good either. ‘Wastl’ has left some very good suggestions for you here.
Well, I have talked to a few people in model home parks. But I always had the impression they mainly try to sell me what they offer. Which is logical and not to be criticized. One young guy who tried to rush me because of current interest rates really took it too far. Well, he was probably new.
Bauexperte schrieb:
In my opinion, you shouldn’t focus solely on funding for KfW 55; €100,000 sounds nice at first, no question. But if you consider that energy cost savings going from the Energy Saving Ordinance (or old KfW 70) to KfW 55 are marginal, I find the required investment borderline; definitely uneconomical.
That’s exactly the question: Is it financially worth it? I would like to calculate this myself. However, I’m missing some important variables, such as the actual savings for different options and the additional costs involved. I feel confident considering the differences in subsidies and making some assumptions about the cost development of electricity, gas, pellets, etc. I found some calculations on the websites of prefab house providers, but of course, they want to sell their houses and don’t disclose all assumptions.
Bauexperte schrieb:
Complete self-sufficiency is not possible in our latitude in North Rhine-Westphalia; 70% - with storage - is a realistic figure. But that doesn’t require going through KfW 40 Plus. One of our clients — we handed over the house in 2014 — recently told me proudly that his energy costs have settled at €10.00 per month. He achieved this with a new build at KfW 70 standard plus photovoltaic panels on the roof. I will meet him next week and ask for a copy of the annual bills.
May I ask about the details of the house? Square meters, roof type, size of the solar system, storage, etc.? €10 is an impressive figure. So it seems that the savings potential of KfW 40 compared to KfW 70 may not be that large anymore.
Bauexperte schrieb:
In short — you should ask yourself: “What do I want?” If it’s about accessing subsidies, then KfW 55 must be met; if it’s about minimizing energy costs as much as possible, then other routes lead to Rome. If you consider possible resale of the property, remember that potential buyers don’t care about which standard your single-family home was built to. They only care about the condition of the property and current running costs.
I only want to claim subsidies if it makes sense financially overall. So I can take the repayment grants, the savings from lower interest rates, and energy cost savings and compare them to the additional costs. But as I mentioned earlier, I currently lack the knowledge to estimate energy savings and extra expenses.
If you are an expert, maybe you can shed some light on this?
Oh, and regards back to Bauexperte.
B
Bauexperte5 Mar 2016 09:43Good day,
If you do choose a prefab house in reality, in my opinion, the question of calculating possible additional costs/speculating on energy prices etc. doesn’t really apply to you because reputable providers generally include KfW 55 standard as standard.
Regards, Bauexperte
Ddorfer schrieb:You’re welcome.
Hello Bauexperte, thank you very much for your detailed post.
Ddorfer schrieb:Okay. Then you also know that—if you hopefully choose a reputable provider—you will need an architect. The well-known providers usually have fixed partnerships. Otherwise, I cannot contribute much on the topic of prefab houses, as I belong to the group of conventional masonry builders.
Currently, we are leaning towards a prefabricated house. But the decision is not yet final. Based on the information so far, this option seems the most attractive to us.
Ddorfer schrieb:In a true passive house—not to be confused with a low-energy or plus-energy house—there should be no heating system installed at all!
How much heating energy is actually needed in a passive house?
Ddorfer schrieb:I always recommend keeping trades separated clearly; for example, I would never buy a washing machine with an integrated dryer.
But I increasingly feel that it might be better to opt for a conventional split air conditioning system.
Ddorfer schrieb:Agreed. However, beyond company-biased information, there are also good sources you can rely on—that was the point of my question. There are more and more quality presentations at trade fairs; energy agencies as well as community colleges (adult education centers) offer valuable input. Construction diaries are also a good indicator of how sales strategies from providers play out in real life.
That makes sense and is nothing wrong with it.
Ddorfer schrieb:That is difficult to calculate since you lack your own experience data from the new build (which still has to be constructed). However, if you read the posts on this forum, you will quickly notice that the energy cost savings of a KfW 55 standard compared to KfW 70—and thus roughly comparable to the current energy-saving regulations—are marginal.
That’s exactly the question: Is it worth it? I would also like to calculate that myself. However, I am missing some important variables, for example the actual savings for the different options and the real additional costs involved. I am confident about considering differences in subsidies and making some assumptions regarding the price trends of electricity, gas, pellets, etc.
If you do choose a prefab house in reality, in my opinion, the question of calculating possible additional costs/speculating on energy prices etc. doesn’t really apply to you because reputable providers generally include KfW 55 standard as standard.
Ddorfer schrieb:146.00 square meters (1,576 square feet) of living space on the building plot, gable roof with a 37° pitch, built to KfW 70 standard, photovoltaic system without battery storage—this is currently all I can offer you. With us, both the calculation and the installation of the photovoltaic system are outsourced to a specialist company—everyone does what they do best. We have another meeting scheduled next week; afterwards, I’ll be happy to provide you with the missing information.
May I ask about the house details? Square footage, roof type, size of the solar system, storage, etc. Ten thousand euros (or 10 Euro) is already a significant amount. So the potential savings from KfW 40 compared to KfW 70 apparently isn’t that large anymore.
Regards, Bauexperte
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