Good morning,
we are still in the early stages of our new build project and have not yet consulted an energy advisor, but we are interested to know whether our current planning status allows any conclusions about the primary energy demand or the achievement of various KfW standards. If possible, we would appreciate an expert estimate.
The building will be constructed in the greater Hamburg area. It is a timber prefabricated house (10 m x 12 m) with two full floors and approximately 204 m² (heated) living area. It features a pitched roof with a 30° slope. Whether the attic will be converted for living space is currently undecided; the assumption is that the attic is unheated. Below are some details about the building envelope, varying in detail and technical information (partly from the supplier’s construction specification).
Base slab
Currently, the occupants would be two adults and a small child; in the long term, the plan is for two adults and three children.
Questions: Would the presumably better insulation already count as a sufficient compensatory measure according to the Renewable Energies Heat Act? Would a gas condensing boiler be sufficient to heat the outlined building to at least the minimum Energy Saving Ordinance (EnEV) standard? Can the primary energy demand already be estimated based on the information given, perhaps by experience with similar buildings?
The current building services plan is as follows: primary heating with a gas condensing boiler connected to a sufficiently sized buffer/storage tank (uncertain about stratified or mixed storage and sizing). A fuel cell system is also planned, specifically the BlueGEN from SolidPower (electrical output W_el = 1.5 kW, thermal output W_th = 0.6 kW) with an appropriate battery (sizing unknown). The fuel cell is mainly intended to cover the electricity demand (this decision is firm, so please no discussions about feasibility, payback, etc.). It should also at least cover the heat demand (hot water) during the northern German summer months and possibly also in transitional seasons. Finally, a controlled mechanical ventilation system with heat recovery will be installed.
Question: Since our goal is the KfW 40 standard, we would like to know if the planned setup as described is achievable. We understand that for a precise assessment many parameters are missing, but perhaps experts among you can provide a “gut feeling” based on experience. We are aware that the fuel cell does not contribute much heat energy, so we are hoping even more that the insulation will have a positive effect on the balance.
Because we are not completely convinced by various heat pump systems, we definitely want a gas condensing boiler as the primary heat source, and the mentioned low-temperature radiators in the bedrooms will remain. What other alternatives would there be to achieve the KfW 40 standard with these boundary conditions?
Thank you very much for reading this rather long text. We look forward to your answers. We will try to provide further details as best as we can if you have any specific questions.
Best regards
Hans
we are still in the early stages of our new build project and have not yet consulted an energy advisor, but we are interested to know whether our current planning status allows any conclusions about the primary energy demand or the achievement of various KfW standards. If possible, we would appreciate an expert estimate.
The building will be constructed in the greater Hamburg area. It is a timber prefabricated house (10 m x 12 m) with two full floors and approximately 204 m² (heated) living area. It features a pitched roof with a 30° slope. Whether the attic will be converted for living space is currently undecided; the assumption is that the attic is unheated. Below are some details about the building envelope, varying in detail and technical information (partly from the supplier’s construction specification).
Base slab
- top layer of floating concrete screed with 100 mm (4 inches) insulation
- 200 mm (8 inches) insulation under the base slab
- 60 mm (2.4 inches) wood fiberboard
- Load-bearing structure = 240 mm (9.5 inches) KVH (timber beam) with infill = 240 mm (9.5 inches) cellulose insulation
- 12 mm (0.5 inches) OSB boards
- 12.5 mm (0.5 inches) Fermacell boards
- in the finished area with 300 mm (12 inches) cellulose insulation
- Ug = 0.5
- Uw = 0.74
- “warm edge” spacers
Currently, the occupants would be two adults and a small child; in the long term, the plan is for two adults and three children.
Questions: Would the presumably better insulation already count as a sufficient compensatory measure according to the Renewable Energies Heat Act? Would a gas condensing boiler be sufficient to heat the outlined building to at least the minimum Energy Saving Ordinance (EnEV) standard? Can the primary energy demand already be estimated based on the information given, perhaps by experience with similar buildings?
The current building services plan is as follows: primary heating with a gas condensing boiler connected to a sufficiently sized buffer/storage tank (uncertain about stratified or mixed storage and sizing). A fuel cell system is also planned, specifically the BlueGEN from SolidPower (electrical output W_el = 1.5 kW, thermal output W_th = 0.6 kW) with an appropriate battery (sizing unknown). The fuel cell is mainly intended to cover the electricity demand (this decision is firm, so please no discussions about feasibility, payback, etc.). It should also at least cover the heat demand (hot water) during the northern German summer months and possibly also in transitional seasons. Finally, a controlled mechanical ventilation system with heat recovery will be installed.
Question: Since our goal is the KfW 40 standard, we would like to know if the planned setup as described is achievable. We understand that for a precise assessment many parameters are missing, but perhaps experts among you can provide a “gut feeling” based on experience. We are aware that the fuel cell does not contribute much heat energy, so we are hoping even more that the insulation will have a positive effect on the balance.
Because we are not completely convinced by various heat pump systems, we definitely want a gas condensing boiler as the primary heat source, and the mentioned low-temperature radiators in the bedrooms will remain. What other alternatives would there be to achieve the KfW 40 standard with these boundary conditions?
Thank you very much for reading this rather long text. We look forward to your answers. We will try to provide further details as best as we can if you have any specific questions.
Best regards
Hans
H
HansHirse31 Aug 2018 09:12Good morning,
thank you very much for your responses. I will try to address the points you raised. To reiterate, we are still in the early stages of our planning and are definitely open to advice.
In principle, yes, our house-building project has idealistic goals and aims for a certain level of self-sufficiency, as long as it aligns with our expectations. We are not economically driven, meaning that return on investment (ROI) or payback periods do not concern us as long as our costs over the building’s lifespan are not significantly higher than, for example, the minimum energy savings regulation standard with a basic gas heating system. However, this definitely does not mean we have unlimited financial resources for the new build! Our idea is simple: If it costs about the same over its lifespan but saves fossil fuels and is “good for the environment,” or whatever term you prefer, then we want to do it.
Best regards,
Hans
thank you very much for your responses. I will try to address the points you raised. To reiterate, we are still in the early stages of our planning and are definitely open to advice.
In principle, yes, our house-building project has idealistic goals and aims for a certain level of self-sufficiency, as long as it aligns with our expectations. We are not economically driven, meaning that return on investment (ROI) or payback periods do not concern us as long as our costs over the building’s lifespan are not significantly higher than, for example, the minimum energy savings regulation standard with a basic gas heating system. However, this definitely does not mean we have unlimited financial resources for the new build! Our idea is simple: If it costs about the same over its lifespan but saves fossil fuels and is “good for the environment,” or whatever term you prefer, then we want to do it.
- Meeting the KfW-40 standard is a goal, but not an absolute requirement. If we cannot find a realistic solution within our framework, we will accept the KfW-55 standard. We want to try it, though, also because we want to explore what is possible "beyond the usual practice" (heat pumps) to reach the KfW-40 standard.
- Radiators in the bedrooms(!) – since the other half of the house will be heated with underfloor heating! – are planned so that for example the children’s rooms can be warmed up quickly if needed. Based on our research, underfloor heating of any kind is too slow for this, and wall heating systems are either too expensive or too complex. Aside from electric radiators, we have not come across other alternatives. Ideas and suggestions for other options are very welcome!
- According to our research, low-temperature radiators are well suited for heating rooms in well-insulated new builds. Our idea is to use single-panel convector radiators to maximize radiant heat. The bedrooms measure between 14 and 16 m² (150 to 170 ft²), so the required radiators should not have to be very large.
- We prefer to avoid the topic of solar thermal systems. The relevant roof area (30° pitch) will likely face west-southwest, which is no longer ideal. Additionally, there is the well-known problem of peak efficiency in the summer but very little effect in winter. Last but not least, the building site is in northern Germany. Taken together, we have serious doubts that solar thermal systems provide a meaningful – and here truly economic – benefit for us.
- To discuss geothermal systems briefly: on our plot, only a borehole heat exchanger is possible, meaning we would need a deep drilling. This is too expensive for us, coupled with uncertainty about whether the heating output in winter would be sufficient (without gas as backup).
- We want a fuel cell out of conviction and enthusiasm for technology and, as mentioned at the beginning, to have a constant electricity supply over the year (photovoltaics would be an option in principle, absolutely, but do not provide constant power throughout the year). We expect the 0.6 kW heating output to contribute noticeably to hot water preparation (this was also “confirmed” above), but it will be constant across all months and not just in summer. Regarding the system and the company I mentioned, our research indicates that this is not a “one-hit wonder.” If necessary, it would be an expensive learning experience, but we would still have the gas condensing boiler. Avoiding new technology just because it may seem risky (subjectively or objectively) is not a solution from our point of view.
Best regards,
Hans
S
Schnurrbart31 Aug 2018 10:02Nowadays, houses are no longer heated quickly on demand... especially KFW40 means a slow system that retains heat for a long time.
HansHirse schrieb:
Underfloor heating systems of any kind are too slowThere are renovation systems that can react quite quickly (for example, heating pipes embedded directly in the top few centimeters (inches) of Wediplates, which act as screed, with tiles laid directly on top). However, this only works with tiles and I would avoid this in new builds.
You can also install underfloor heating everywhere and additionally hang small radiators under the windows. That way you get the best of both.
With the planned combination of a gas boiler and fuel cell, the supply temperature is not a big issue; the system’s efficiency does not drop significantly if you have 40-45°C (104-113°F) supply temperature. This is much more critical for heat pumps.
With the recently strongly increased subsidies for fuel cells, this setup is no longer only interesting for enthusiasts. However, it is still not cheaper than gas plus a solar thermal system. Orienting the building to the south-southeast, combined with a roof pitch of only 30° (degrees), is really not ideal for solar thermal or photovoltaic systems.
C
Caspar20202 Sep 2018 17:58HansHirse schrieb:
Radiators in the bedrooms(!) – since the other half of the house will be heated with underfloor heating! – we want them so that, if needed, we can quickly(!) warm up the children’s rooms, for example. According to our research, underfloor heating of any type is too slow for this purpose, and wall-mounted heaters are either too expensive or too complicated for us.KfW 40 houses are very slow to respond; there are hardly any major temperature fluctuations anyway.
It’s also not easy to make it cold enough to require reheating afterward.
B
borderpuschl25 Sep 2018 08:24Hi,
please reconsider and inform yourself again about the topic of fuel cells. Our neighbor is a professor of environmental engineering and researches fuel cells. He also has a fuel cell, but it is located far outside the house because these tend to fail more often than you might think. I wouldn’t want something like that inside the house, especially not in the utility room where your gas connection is also located.
please reconsider and inform yourself again about the topic of fuel cells. Our neighbor is a professor of environmental engineering and researches fuel cells. He also has a fuel cell, but it is located far outside the house because these tend to fail more often than you might think. I wouldn’t want something like that inside the house, especially not in the utility room where your gas connection is also located.
O
Obstlerbaum25 Sep 2018 08:57Low-temperature radiators and quickly heating up a room are mutually exclusive. Running a system with two supply temperatures (one for underfloor heating and one for radiators) would be even more pointless. In a building with such good insulation, you would first have to manage to keep one room significantly cooler than the others.
Achieving KfW40 certification purely for sport is easier by using a pellet heating system instead of gas. Regarding solar thermal systems, I agree with you. It’s the misguided idea of an ill-conceived energy policy, but what can you do.
Achieving KfW40 certification purely for sport is easier by using a pellet heating system instead of gas. Regarding solar thermal systems, I agree with you. It’s the misguided idea of an ill-conceived energy policy, but what can you do.
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