Hello everyone!
A quick question:
Why do people actually add solar thermal systems to their gas heating?
Is it because they have to comply with the energy saving regulations?
Wrong, you are allowed to skip solar thermal if other measures reduce energy consumption by at least 15%.
Example:
I’m planning a KfW-55 house with gas heating, solar thermal, controlled ventilation with heat recovery, and excellent insulation.
Now I remove the solar thermal system. What happens?
I lose the KfW-55 status and end up with KfW-70, so I lose a €2,500 subsidy. But I save €6,000 by not installing solar thermal. The operating costs increase by €50 per year due to the missing solar thermal, which adds up to €1,000 over 20 years. So overall, I still save €2,500.
Savings:
€6,000 saved by not installing solar thermal*
- €2,500 lost KfW-55 subsidy
- €1,000 higher operating costs due to no solar thermal*
=======
€2,500
Sounds like an attractive alternative, or is there a major calculation mistake somewhere?
The whole calculation would also apply to a KfW-85 house, which would qualify as a KfW-100 house without the solar thermal.
Best regards
jx7
PS:
Please don’t bring up heat pumps or pellet heating; this is not meant to start a fundamental debate about gas versus heat pumps (with sharp increases in energy prices, heat pumps will eventually become more cost-effective). The initial question is simply: "If using gas, then maybe without solar thermal?"
* Source: xxx-Heizungsvergleich-de "Gas + 5sqm solar thermal"
A quick question:
Why do people actually add solar thermal systems to their gas heating?
Is it because they have to comply with the energy saving regulations?
Wrong, you are allowed to skip solar thermal if other measures reduce energy consumption by at least 15%.
Example:
I’m planning a KfW-55 house with gas heating, solar thermal, controlled ventilation with heat recovery, and excellent insulation.
Now I remove the solar thermal system. What happens?
I lose the KfW-55 status and end up with KfW-70, so I lose a €2,500 subsidy. But I save €6,000 by not installing solar thermal. The operating costs increase by €50 per year due to the missing solar thermal, which adds up to €1,000 over 20 years. So overall, I still save €2,500.
Savings:
€6,000 saved by not installing solar thermal*
- €2,500 lost KfW-55 subsidy
- €1,000 higher operating costs due to no solar thermal*
=======
€2,500
Sounds like an attractive alternative, or is there a major calculation mistake somewhere?
The whole calculation would also apply to a KfW-85 house, which would qualify as a KfW-100 house without the solar thermal.
Best regards
jx7
PS:
Please don’t bring up heat pumps or pellet heating; this is not meant to start a fundamental debate about gas versus heat pumps (with sharp increases in energy prices, heat pumps will eventually become more cost-effective). The initial question is simply: "If using gas, then maybe without solar thermal?"
* Source: xxx-Heizungsvergleich-de "Gas + 5sqm solar thermal"
Are you sure that the 300-liter (79-gallon) tank is for domestic hot water only? That would mean you also have a plate heat exchanger for potable water. However, I believe the business case for the solar thermal system just for hot water doesn’t add up – no matter how you look at it. The consumption is too low and the investment costs are too high.
V
Vespa Fahrer29 Jul 2015 11:45alexm86 schrieb:
You don’t have a mechanical ventilation system with heat recovery? What year was your house built? How about the insulation—under the slab, walls, roof, windows?Sorry, but what exactly is a mechanical ventilation system with heat recovery?
Roof: about 200mm (8 inches) of insulation (Rockwool) plus 50mm (2 inches) of insulation between rafters, U-value 0.032 W/(m·K)
Masonry: double-wall construction with cavity insulation (inner layer of sand-lime brick, outer layer of facing brick)
Basement: waterproof concrete shell (white tank) with external insulation
Windows: triple-glazed; roof windows double-glazed
Construction completed in 2014
D
DerBjoern29 Jul 2015 12:25Vespa Fahrer schrieb:
Hello,
we received a standard KW 70 house. Approximately 220m² (2370 sq ft) total area, including 170m² (1830 sq ft) of living space floor area with sloped ceilings. Heating is gas with a 300-liter (79 gallons) hot water storage tank connected to solar thermal panels on the roof (2 panels).
Since May, I haven’t used any gas. All the domestic hot water is currently supplied by the panels. During the transition period, when the sun was shining, the underfloor heating was also fed by the solar system. We are now at an energy consumption of about 30 kWh/m² (9.3 BTU/sq ft) for gas. I can’t say what the consumption would be without the solar thermal system.
PS (However, I burned about 3 cubic meters of wood in the fireplace during winter; you should add this energy amount on top.)That adds up to another 6000 kWh or 27 kWh/m² (8.5 BTU/sq ft).
Thank you
Controlled residential ventilation with heat recovery
Vespa Fahrer schrieb:
Sorry, but what is controlled residential ventilation?
Controlled residential ventilation with heat recovery
V
Vespa Fahrer29 Jul 2015 13:41No, without controlled residential ventilation.
Yes, I think that roughly matches the additional consumption, although actually about 2 cubic meters (2.6 cubic yards) of solid wood were burned. However, it doesn’t really matter cost-wise since we pay €65 per cubic meter (€65 per 1.3 cubic yards) and only light the stove for comfort (after all, it’s CO2 neutral excluding delivery).
Yes, I think that roughly matches the additional consumption, although actually about 2 cubic meters (2.6 cubic yards) of solid wood were burned. However, it doesn’t really matter cost-wise since we pay €65 per cubic meter (€65 per 1.3 cubic yards) and only light the stove for comfort (after all, it’s CO2 neutral excluding delivery).
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