ᐅ Accurate Calculation by the Energy Consultant? Why Choose Solar for Heating?
Created on: 15 Jan 2016 19:26
K
Kerstin2Hello everyone,
We have received our documents for the KfW loan and want to build a KfW-70 house.
Plan bricks T-18 (24 cm (9.5 inches) Poroton blocks) with 16 cm (6.3 inches) insulation. The foundation slab is insulated with 10 cm (3.9 inches) Styrodur insulation.
10% of the value is now supposed to come from solar support for heating! We didn’t want that at all. Solar should only be used for hot water, not for heating. We end up with a value just over 40, while the maximum allowed for the KfW-70 house is 69.xx. I don’t understand why we have to include solar for heating support when it only covers 10% of the heat demand.
What can we do?
We have received our documents for the KfW loan and want to build a KfW-70 house.
Plan bricks T-18 (24 cm (9.5 inches) Poroton blocks) with 16 cm (6.3 inches) insulation. The foundation slab is insulated with 10 cm (3.9 inches) Styrodur insulation.
10% of the value is now supposed to come from solar support for heating! We didn’t want that at all. Solar should only be used for hot water, not for heating. We end up with a value just over 40, while the maximum allowed for the KfW-70 house is 69.xx. I don’t understand why we have to include solar for heating support when it only covers 10% of the heat demand.
What can we do?
Hi Kerstin,
there are definitely some details missing, I assume,
gas heating?
Was the building permit / planning permission not submitted last year? So the new version of the Energy Saving Ordinance?
In that case, you probably won’t be able to avoid the large renewable energy requirement.
There are two values that both need to be below 70%. One is the transmission heat loss. You are doing very well here at just under 40% (which surprises me a lot. We have the same wall construction—24 cm (9.5 inches) T18 Poroton with 16 cm (6 inches) insulation and good windows—and end up at 68%, which is quite different?!).
Then there is the primary energy factor, which also must be under 70%.
For that, if using gas heating, you need solar thermal systems.
Best regards,
Andreas
there are definitely some details missing, I assume,
gas heating?
Was the building permit / planning permission not submitted last year? So the new version of the Energy Saving Ordinance?
In that case, you probably won’t be able to avoid the large renewable energy requirement.
There are two values that both need to be below 70%. One is the transmission heat loss. You are doing very well here at just under 40% (which surprises me a lot. We have the same wall construction—24 cm (9.5 inches) T18 Poroton with 16 cm (6 inches) insulation and good windows—and end up at 68%, which is quite different?!).
Then there is the primary energy factor, which also must be under 70%.
For that, if using gas heating, you need solar thermal systems.
Best regards,
Andreas
Hello Andreas,
Calculated primary energy demand value 46.15 kWh/m² (15.0 kWh/ft²)
Calculated transmission heat loss value 0.24 W/(m²K) (0.15 Btu/(ft²·°F)), maximum allowed value 0.4.
These values are in the documents. Yes, it will be a gas heating system.
The application was submitted at the end of last year.
Calculated primary energy demand value 46.15 kWh/m² (15.0 kWh/ft²)
Calculated transmission heat loss value 0.24 W/(m²K) (0.15 Btu/(ft²·°F)), maximum allowed value 0.4.
These values are in the documents. Yes, it will be a gas heating system.
The application was submitted at the end of last year.
Hi,
For gas heating systems, including a share of "renewable" energy is mandatory for KfW 70 standards.
Honestly: it doesn’t bring any real benefit. But it is a regulation, even if you meet or exceed the required values.
Domestic hot water solar thermal: It never pays off. You get about 30-40 cents of energy savings per day minus the electricity costs for the circulation pump (5-10 cents/day) on at best 170 - 200 days per year. Practically useless.
With heating support: This only makes sense if vacuum flat plate collectors are used (about twice as expensive as standard collectors). Because in summer and large parts of autumn and spring, you don’t need heating in a KfW 70 house. I know this because I have one myself (with Q_p and H_t values closer to KfW 55). In winter (let’s say from October to mid-March) a conventional solar thermal collector does nothing except look good on the roof (and generate capital costs). The vacuum collector delivers significantly more. And as is well known: especially in winter you need heating, and this nonsense with solar thermal and standard collectors simply doesn’t work then. But in the height of summer you do get 74°C (165°F) hot water for showering and nice hot baths.
So go for the most cost-effective solution. You never recover the investment for this nonsense in our climate zone. It’s nothing more than a nice but unnecessary gimmick for the environmental conscience that has been forced on KfW 70 houses with gas heating.
Best regards
Thorsten
For gas heating systems, including a share of "renewable" energy is mandatory for KfW 70 standards.
Honestly: it doesn’t bring any real benefit. But it is a regulation, even if you meet or exceed the required values.
Domestic hot water solar thermal: It never pays off. You get about 30-40 cents of energy savings per day minus the electricity costs for the circulation pump (5-10 cents/day) on at best 170 - 200 days per year. Practically useless.
With heating support: This only makes sense if vacuum flat plate collectors are used (about twice as expensive as standard collectors). Because in summer and large parts of autumn and spring, you don’t need heating in a KfW 70 house. I know this because I have one myself (with Q_p and H_t values closer to KfW 55). In winter (let’s say from October to mid-March) a conventional solar thermal collector does nothing except look good on the roof (and generate capital costs). The vacuum collector delivers significantly more. And as is well known: especially in winter you need heating, and this nonsense with solar thermal and standard collectors simply doesn’t work then. But in the height of summer you do get 74°C (165°F) hot water for showering and nice hot baths.
So go for the most cost-effective solution. You never recover the investment for this nonsense in our climate zone. It’s nothing more than a nice but unnecessary gimmick for the environmental conscience that has been forced on KfW 70 houses with gas heating.
Best regards
Thorsten
PS: Last year, large parts of Germany experienced very hot, good weather. Here in NRW/Velbert, however, this was clearly not the case. Persistent rain and storms. Sun? None. Only a few days at most.
The system barely managed to produce close to 200 kWh in 2015. This corresponds to gas worth about 12 euros (I am neglecting the proportional gas meter fee) and, for mercy’s sake, I am leaving out the electricity consumption for the solar thermal circulation pump.
Every little water wheel with a dynamo in the gutters would have generated more power here, as would every small wind turbine.
Best regards
The system barely managed to produce close to 200 kWh in 2015. This corresponds to gas worth about 12 euros (I am neglecting the proportional gas meter fee) and, for mercy’s sake, I am leaving out the electricity consumption for the solar thermal circulation pump.
Every little water wheel with a dynamo in the gutters would have generated more power here, as would every small wind turbine.
Best regards
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