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
nordanney schrieb:
This is a misconception. The house heats up just as much as an older building. It just takes longer for the heat to enter the house and then even longer for you to get it out again. Subjectively, our house heats up very quickly (if there is no shading) – but it also cools down very quickly whenever the building envelope is opened. In other words, when the blinds are up in summer, it gets warm very fast. But if I open doors or windows at night during summer, it cools down really quickly.
Timber frame construction – which means there is barely any thermal mass to store the energy.
Hello Wastl, first of all, thank you for your detailed post.
You’re right that coziness is the main focus. But the idea of opening the windows in winter so it doesn’t get too warm seems a bit counterproductive to me. However, it should be possible to design the stove so that it doesn’t overheat: water-carrying, not oversized, no direct exhaust, stone slab, and a high proportion of heat output through the water circuit. And as I said: shouldn’t the central ventilation system distribute the heat throughout the house?
I understand the principle of cooling with the heat pump. The performance is naturally limited. Maybe a decentralized solution for bedrooms and living rooms is better after all. Regarding cooling via the controlled ventilation system, I have only heard it can only deliver limited capacity due to condensation issues.
Well, the idea would be to use part of the water exiting the heat pump for garden irrigation instead of sending it all back down the soakaway. The water is already at the surface and used by the heat pump, so it could also water the garden.
Well, there is no final concept yet. There are still many unknowns. For example, I’m not sure whether a battery storage is currently cost-effective. But the heating system should already be integrated into a comprehensive management system so that, for instance, domestic hot water is prepared when electricity is available. Some devices could then also run when power is available.
True independence seems far from economical at the moment. In winter, you will always rely on external electricity supply. We are generally not yet sure whether a plus-energy house is even the best idea. Reliable calculations are rare, and the future development of electricity prices is difficult to predict.
Wastl schrieb:
My opinion: A water-carrying fireplace is unnecessary, too expensive, and you bring a lot of unnecessary technology into the house. You can still install a stove, especially for the "cozy" aspect and without factoring it into the house concept. Of course, you will overheat your place - so what? Then you just open the windows while the stove is running - it’s not efficient, but it’s cozy.
You’re right that coziness is the main focus. But the idea of opening the windows in winter so it doesn’t get too warm seems a bit counterproductive to me. However, it should be possible to design the stove so that it doesn’t overheat: water-carrying, not oversized, no direct exhaust, stone slab, and a high proportion of heat output through the water circuit. And as I said: shouldn’t the central ventilation system distribute the heat throughout the house?
Wastl schrieb:
Cooling with the heat pump: You don’t cool the air directly with the heat pump, but rather the floor—you send cold water through the underfloor heating to cool down the room. Many commercial buildings have "cooling ceilings" where exactly this is done. Cold air sinks, so that works quite well. But does cooling the floor also cool the air above? Better to have a decentralized air conditioning system or a proper one integrated into the controlled ventilation system, although you have to watch out for condensation.
I understand the principle of cooling with the heat pump. The performance is naturally limited. Maybe a decentralized solution for bedrooms and living rooms is better after all. Regarding cooling via the controlled ventilation system, I have only heard it can only deliver limited capacity due to condensation issues.
Wastl schrieb:
Fully automated garden irrigation – does it make sense? That depends on the garden, the location, and your local rainfall. For me, it doesn’t make sense… I can water 10 times a summer if needed…. Whether a garden well pays off has already been heavily debated here, and how about a garden well in the inlet shaft of the heat pump? I’m curious if that’s technically feasible and sensible – you don’t want to suck your heat pump water through the garden pump and end up without the heat pump running, do you?
Well, the idea would be to use part of the water exiting the heat pump for garden irrigation instead of sending it all back down the soakaway. The water is already at the surface and used by the heat pump, so it could also water the garden.
Wastl schrieb:
Regarding the plus-energy house, I’m missing your concept concerning photovoltaics, storage, energy management, and so on. Do you want to produce more only on paper, or actually be independent (including household electricity)?
Well, there is no final concept yet. There are still many unknowns. For example, I’m not sure whether a battery storage is currently cost-effective. But the heating system should already be integrated into a comprehensive management system so that, for instance, domestic hot water is prepared when electricity is available. Some devices could then also run when power is available.
True independence seems far from economical at the moment. In winter, you will always rely on external electricity supply. We are generally not yet sure whether a plus-energy house is even the best idea. Reliable calculations are rare, and the future development of electricity prices is difficult to predict.
Ddorfer schrieb:
But it should be possible to design the stove so that it doesn’t overheat: water heating, not oversized, no direct exhaustA stove generates heat! In addition! This causes overheating!
Ddorfer schrieb:
Stone slab Stone slabs store heat.
Ddorfer schrieb:
And as I said: shouldn’t the central ventilation distribute the heat throughout the house?The heat is distributed actively.
I’m not an expert in heating systems, but we have a stove for coziness. The underfloor heating can’t lower its temperature as fast as the heat from the stove arrives. After a few hours, you don’t want the slight temperature increase from the stove anymore and end up wasting it.
Whether you passively heat your water with this energy or not—it feels the same in the room.
Cost for the coziness: about 10,000 for a gable roof house all in—certainly a few thousand more if you want to heat your water with the stove. Whether this results in meaningful savings is questionable.
B
Bauexperte3 Mar 2016 10:51Hello,
Prefabricated house in the sense of “all services from a single source” or actually a prefab house?
In a modern new build, even four lit Advent candles are a small wood stove.
Yes, so why do you doubt the statement of a professional?
At most around 2°C (3.6°F); you should not forget that this will cause condensation on tiles. It’s like a free slipping hazard.
Why?
You “seem” not to have had a proper consultation yet; otherwise, you would already know your current plan goes far beyond the target of being “reasonable.” “More” has never been better; likewise, compressing too many technologies is not beneficial. ‘Wastl’ has left some very good suggestions for you here.
Have consultations; your meeting with an energy consultant was already a good first step.
In my opinion, you should not focus solely on funding aimed at KfW 55 standards; 100,000 euros sounds appealing at first, no question. However, considering the energy cost savings from the Energy Saving Ordinance (or the previous KfW 70) to KfW 55 are marginal, I find the required investment borderline, definitely uneconomical.
Complete autonomy is not achievable in our climate region in North Rhine-Westphalia; 70%—with storage—is a realistic figure. However, you don’t need to go all the way via KfW 40 Plus for that. One of our clients — we delivered his house in 2014 — recently proudly told me that his energy costs have settled around €10.00 (10 euros) per month. He achieves this through a new build to KfW 70 standard plus photovoltaic panels on the roof. I will meet him next week and have him provide me with copies of the annual statements.
In short, you should ask yourself: “What do I want?” If it’s about securing funding, you must reach KfW 55. If it’s about the best possible reduction of energy costs, completely different paths lead to Rome. If the idea of a possible resale plays a role in your plans, keep in mind that potential buyers do not care which standard your single-family home was built to. They only care about the condition of the property and the ongoing utility costs.
Regards,
Bauexperte
Ddorfer schrieb:
It is supposed to be a prefabricated house.
Prefabricated house in the sense of “all services from a single source” or actually a prefab house?
Ddorfer schrieb:
We have basically considered two things so far: We would like to have a wood stove for coziness.
In a modern new build, even four lit Advent candles are a small wood stove.
Ddorfer schrieb:
An energy consultant told us that it is almost impossible to operate a water-bearing pellet stove effectively in such a well-insulated house because the direct heat output would already be significantly too high. Is that true?
Yes, so why do you doubt the statement of a professional?
Ddorfer schrieb:
After some research, we found out that a heat pump can also provide cooling.
At most around 2°C (3.6°F); you should not forget that this will cause condensation on tiles. It’s like a free slipping hazard.
Ddorfer schrieb:
... with a (preferably) water-to-water heat pump.
Why?
Ddorfer schrieb:
Is such a system more cost-effective than conventional air conditioning? Or would another heat pump technology be more suitable? Does anyone here cool with a heat pump? What are the experiences?
You “seem” not to have had a proper consultation yet; otherwise, you would already know your current plan goes far beyond the target of being “reasonable.” “More” has never been better; likewise, compressing too many technologies is not beneficial. ‘Wastl’ has left some very good suggestions for you here.
Ddorfer schrieb:
We are really grateful for any tips or suggestions, as well as further information. If more information is needed, please just ask.
Have consultations; your meeting with an energy consultant was already a good first step.
In my opinion, you should not focus solely on funding aimed at KfW 55 standards; 100,000 euros sounds appealing at first, no question. However, considering the energy cost savings from the Energy Saving Ordinance (or the previous KfW 70) to KfW 55 are marginal, I find the required investment borderline, definitely uneconomical.
Ddorfer schrieb:
True independence currently seems far from economical. In winter, you will always need external electricity supply. We are generally still unsure whether a plus-energy house is the best idea. Reliable calculations are rare and future electricity price developments are hard to predict.
Complete autonomy is not achievable in our climate region in North Rhine-Westphalia; 70%—with storage—is a realistic figure. However, you don’t need to go all the way via KfW 40 Plus for that. One of our clients — we delivered his house in 2014 — recently proudly told me that his energy costs have settled around €10.00 (10 euros) per month. He achieves this through a new build to KfW 70 standard plus photovoltaic panels on the roof. I will meet him next week and have him provide me with copies of the annual statements.
In short, you should ask yourself: “What do I want?” If it’s about securing funding, you must reach KfW 55. If it’s about the best possible reduction of energy costs, completely different paths lead to Rome. If the idea of a possible resale plays a role in your plans, keep in mind that potential buyers do not care which standard your single-family home was built to. They only care about the condition of the property and the ongoing utility costs.
Regards,
Bauexperte
wrobel schrieb:
Perhaps as an alternative to air conditioning, an evaporative cooling system might be interesting.How does that work? What are the advantages and disadvantages?
nordanney schrieb:
That’s a misconception. The house heats up just as much as an old building. It just takes longer for the heat to build up inside, and even longer for you to get rid of it again.Interesting. I thought it would heat up less. Good to know.
ypg schrieb:
A stove heats! Additionally! It creates overheating!On the other hand, the underfloor heating would of course have to be turned down. But I’m already realizing that a stove is probably not a good idea in a plus-energy house.
ypg schrieb:
Stone slabs store heat. The heat is actively distributed.Yes, because the stone slab stores heat, it releases it more slowly. What do you mean by the heat being actively distributed?
ypg schrieb:
I’m not a heating expert, but we have a stove for coziness reasons. The underfloor heating can’t lower itself as quickly as the heat from the fireplace arrives. After a few hours, you don’t want the few degrees increase anymore and you’re basically throwing it out the window.Well, I don’t really find that very practical. And if it’s not possible to properly size the stove or find a suitable working solution, then that probably isn’t right for us after all.
But thank you very much for your opinions. For those of you who have a wood stove here, do you all open the windows to get rid of the heat?
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