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
borderpuschl schrieb:
please reconsider and inform yourself again about the topic of fuel cells.And before you spread such panic, why don’t you ask your professor about the different types of fuel cells and their use as heating systems? If they really exploded that often, I’m sure he could show you some news reports where it’s been reported in a panic.
I don’t know what your professor gets up to in his spare time, but fuel cells used for heating connected to the natural gas grid don’t have a storage tank for hydrogen. The hydrogen is produced on demand directly from methane in the reformer and fed into the stack. This happens at atmospheric pressure or without significant pressure. A combustible mixture only forms inside the combustion chamber, not beforehand. These units are no more dangerous than a conventional heating system, and the biggest risk factor is, as always, the person operating the system.
Don’t confuse this with hydrogen tanks at several hundred bar (several thousand psi). However, those also don’t explode dramatically, at least not like you see in Hollywood with huge fireballs.
By the way, genuinely dangerous things are driving a car or indoor airspace in a house, with or without small children. And indoor air doesn’t even warm the house.
Obstlerbaum schrieb:
by using a pellet heating system instead of gas. Regarding solar thermal energy, I agree with you. It’s a misguided energy policy idea, but what can you do.I don’t see how a pellet heating system is any simpler than a gas-powered fuel cell. Ash, pellet storage, delivery trucks, refilling when empty, more frequent chimney sweeper visits – I’ll leave aside reliability, since I don’t know how fuel cells perform.
And solar thermal: Why is it a crazy idea to use the sun as an energy source in the simplest way imaginable: warming a dark surface to heat water and store the hot water cheaply?
With glycol and vacuum tubes, it’s no longer quite that simple, but much more effective. If the roof surfaces are already there and properly oriented, there’s absolutely no reason against it. Misguided energy policy is happening in NRW at the Hambach Forest.
O
Obstlerbaum25 Sep 2018 10:43dertill schrieb:
I don’t see what is simpler about a pellet heating system compared to a gas-powered fuel cell. Ash, pellet storage, delivery trucks, refilling when empty, more frequent chimney sweep visits — I’ll leave reliability aside since I don’t know how fuel cells perform.
And solar thermal energy: Why is it considered a crazy idea to use the sun as an energy source in the simplest way possible — heating a dark surface to warm water and then storing that hot water cheaply? Using glycol and vacuum tubes isn’t quite as simple anymore but much more effective. If the roof areas are already there and properly oriented, there really is no reason against it. Misguided energy policies are playing out in North Rhine-Westphalia around the Hambach Forest. I literally said that it is easier to achieve KfW40 with a pellet heating system than with gas. Please read everything before commenting.
The idea that a solar thermal system automatically saves money unfortunately also belongs to the realm of myths.
Obstlerbaum schrieb:
I literally said that it is easier to meet the KfW40 standard with a pellet heating system than with gas. Please read everything before commenting.I must have misread that or misunderstood the word "easier." Regarding the KfW requirements, you are right. It is indeed easier to install a pellet heating system.
Obstlerbaum schrieb:
The idea that a solar thermal system automatically saves money unfortunately belongs to the realm of myths.You misunderstood me here. I never said or meant that. I only believe that the promotion or forced use of solar thermal systems is a bad idea. Using solar energy means you need less fuel to heat the building. Switching to pellets only changes the fuel type, not the amount of fuel required.
There are other requirements in the Energy Saving Ordinance and the Renewable Energy Sources Act that I view much more critically than the use of solar thermal systems for heating and hot water.
If you want to save money when building a house, simply build a smaller house. That’s really not that complicated.
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