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HansHirse30 Aug 2018 09:23Good 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
The 2016 Energy Saving Ordinance should not be a problem at all.
KfW40 is always cutting it close and is ultimately decided by minor details, with the building services systems usually being the decisive factor.
Using only a gas boiler without any renewable energy – no way!
With a fuel cell of this size, the balance calculation will also be tight; perhaps with controlled mechanical ventilation it might work. Instead of the fuel cell, maybe 10m² (108 sq ft) of solar thermal plus 3–5 kWp photovoltaic?
As you can see, whether KfW40 is achievable is hard to say in general terms; it must be calculated first to see what contributes how much. The building envelope should be sufficient.
The 0.6 kW thermal fuel cell produces about 12 kWh of heat per day for domestic hot water, which is enough for 240 liters (63 gallons) at 50°C (122°F), or 300 liters (79 gallons) at 40°C (104°F). That should be enough for 95% of the days.
KfW40 is always cutting it close and is ultimately decided by minor details, with the building services systems usually being the decisive factor.
Using only a gas boiler without any renewable energy – no way!
With a fuel cell of this size, the balance calculation will also be tight; perhaps with controlled mechanical ventilation it might work. Instead of the fuel cell, maybe 10m² (108 sq ft) of solar thermal plus 3–5 kWp photovoltaic?
As you can see, whether KfW40 is achievable is hard to say in general terms; it must be calculated first to see what contributes how much. The building envelope should be sufficient.
The 0.6 kW thermal fuel cell produces about 12 kWh of heat per day for domestic hot water, which is enough for 240 liters (63 gallons) at 50°C (122°F), or 300 liters (79 gallons) at 40°C (104°F). That should be enough for 95% of the days.
You may not want to discuss it, but low-temperature radiators are now only installed in basement rooms (storage areas) and no longer in living spaces. We built to KfW55 standard using gas and solar thermal energy (heating + hot water) along with a controlled ventilation system. Additionally, we have a 9.92kW photovoltaic system on the roof. KfW40 would have been possible with even better insulation, but the savings are not significant anymore, and eventually, there is a limit to costs, users, and effort.
Regarding fuel cells: A colleague of mine also has a fuel cell installed in his basement, but the manufacturer has since gone bankrupt, leaving him without service or warranty.
Regarding fuel cells: A colleague of mine also has a fuel cell installed in his basement, but the manufacturer has since gone bankrupt, leaving him without service or warranty.
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Schnurrbart30 Aug 2018 19:59Honestly, I wouldn’t dogmatically pursue KFW40... it’s unreasonable and uneconomical.
Radiators with a concrete screed – why not underfloor heating?
Radiators with a concrete screed – why not underfloor heating?
What is your goal here?
The house already has more than adequate insulation and very good windows. That’s almost passive house standard in my opinion.
Then you want to install a fuel cell and an energy storage system. A five-figure investment with no chance of payback. Idealism?
But then no underfloor heating and a gas boiler as well? What?!
I find it very difficult to see a clear strategy behind this.
The house already has more than adequate insulation and very good windows. That’s almost passive house standard in my opinion.
Then you want to install a fuel cell and an energy storage system. A five-figure investment with no chance of payback. Idealism?
But then no underfloor heating and a gas boiler as well? What?!
I find it very difficult to see a clear strategy behind this.
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