ᐅ Combination of split air conditioning, gas heating, and solar energy
Created on: 22 May 2022 20:10
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Nutshell
Hello fellow home builders,
We have been living since 2014 at an altitude of about 300 meters (1000 feet), in a solidly built house. The house has a rather simple shape. A standard gable roof without dormers or skylights (one gable-side window per room on the upper floor).
Styrofoam was not an option for various reasons, so we chose the more expensive monolithic lightweight concrete blocks with a thermal conductivity of 0.08 W/m·K (lambda).
Size: 111 sqm (1200 sq ft) of living space.
Exterior wall: 36.5 cm (14.4 inches) Ytong blocks // thermal conductivity 0.2 W/m²K
Floor slab insulated with XPS // thermal conductivity 0.21 W/m²K
Upper floor sloped ceiling with 24 cm (9.4 inches) depth, ceiling insulated with 34 cm (13.4 inches) of mineral wool // thermal conductivity 0.12 W/m²K
Doors and windows are triple-glazed and gas-filled // overall including frame 1.05 W/m²K
Heating system:
Gas condensing boiler: Viessmann Vitodens 300
System control: Vitotronic 200
Solar collector 5 sqm (54 sq ft): Vitosol 200-F
Solar storage tank: Vitocell 100-W 300 liters (79 gallons)
The solar system is used only for domestic hot water (no heating support).
Our gas boiler is switched off for heating from May to September and consumes about 100 kWh over the summer.
In winter, the solar system barely manages to heat the domestic hot water (for two people), so it mostly runs on gas.
Ventilation is decentralized with Lunos e² units, featuring 90% heat recovery.
On average, our annual gas consumption is 8000 kWh.
During cold spells in February, daily consumption is about 45–75 kWh, depending on the outside temperature.
The attic often becomes uncomfortably warm, so we plan to air condition the master bedroom, children’s room, and office with split system air conditioners. We also want to install an indoor unit in the open-plan living room/kitchen on the ground floor.
Outdoor unit:
CU-4Z68TBE
Master bedroom (12 sqm (130 sq ft), east-south facing)
CS-Z20XKEW
Children's room (12 sqm (130 sq ft), west-north facing)
CS-Z25XKEW
Office (12 sqm (130 sq ft), south-west facing)
CS-Z35XKEW
Living room (35 sqm (377 sq ft) + 15 sqm (162 sq ft) kitchen)
CS-Z35XKEW
I would also like to use these for heating, not just cooling. Now that gas prices are very high, this should definitely pay off with such a high-quality, modern air conditioning system. Of course, it’s impractical when it’s minus 10°C (14°F) outside. But if, as private individuals, our gas supply were suddenly cut off, I would have a working fallback solution—even if the usual 23°C (73°F) indoor temperature can’t be maintained everywhere with only one unit on the ground floor. At least it should be suitable as an emergency operation.
What do you think of these expansion plans?
We have been living since 2014 at an altitude of about 300 meters (1000 feet), in a solidly built house. The house has a rather simple shape. A standard gable roof without dormers or skylights (one gable-side window per room on the upper floor).
Styrofoam was not an option for various reasons, so we chose the more expensive monolithic lightweight concrete blocks with a thermal conductivity of 0.08 W/m·K (lambda).
Size: 111 sqm (1200 sq ft) of living space.
Exterior wall: 36.5 cm (14.4 inches) Ytong blocks // thermal conductivity 0.2 W/m²K
Floor slab insulated with XPS // thermal conductivity 0.21 W/m²K
Upper floor sloped ceiling with 24 cm (9.4 inches) depth, ceiling insulated with 34 cm (13.4 inches) of mineral wool // thermal conductivity 0.12 W/m²K
Doors and windows are triple-glazed and gas-filled // overall including frame 1.05 W/m²K
Heating system:
Gas condensing boiler: Viessmann Vitodens 300
System control: Vitotronic 200
Solar collector 5 sqm (54 sq ft): Vitosol 200-F
Solar storage tank: Vitocell 100-W 300 liters (79 gallons)
The solar system is used only for domestic hot water (no heating support).
Our gas boiler is switched off for heating from May to September and consumes about 100 kWh over the summer.
In winter, the solar system barely manages to heat the domestic hot water (for two people), so it mostly runs on gas.
Ventilation is decentralized with Lunos e² units, featuring 90% heat recovery.
On average, our annual gas consumption is 8000 kWh.
During cold spells in February, daily consumption is about 45–75 kWh, depending on the outside temperature.
The attic often becomes uncomfortably warm, so we plan to air condition the master bedroom, children’s room, and office with split system air conditioners. We also want to install an indoor unit in the open-plan living room/kitchen on the ground floor.
Outdoor unit:
CU-4Z68TBE
Master bedroom (12 sqm (130 sq ft), east-south facing)
CS-Z20XKEW
Children's room (12 sqm (130 sq ft), west-north facing)
CS-Z25XKEW
Office (12 sqm (130 sq ft), south-west facing)
CS-Z35XKEW
Living room (35 sqm (377 sq ft) + 15 sqm (162 sq ft) kitchen)
CS-Z35XKEW
I would also like to use these for heating, not just cooling. Now that gas prices are very high, this should definitely pay off with such a high-quality, modern air conditioning system. Of course, it’s impractical when it’s minus 10°C (14°F) outside. But if, as private individuals, our gas supply were suddenly cut off, I would have a working fallback solution—even if the usual 23°C (73°F) indoor temperature can’t be maintained everywhere with only one unit on the ground floor. At least it should be suitable as an emergency operation.
What do you think of these expansion plans?
D
Deliverer26 May 2022 14:57That's quite something. The subsidy almost exactly offsets the price increase that has occurred since the subsidy started...
Deliverer schrieb:
That's quite something. The subsidy almost exactly offsets the price increase that has occurred since the subsidy started...Is that really so? I'm not sure... the equipment itself only costs 4000€ purchase price, everything else goes towards labor.D
Deliverer26 May 2022 21:58Until 2020, a rough rule of thumb was 1000 €/kW. This estimate worked well for all projects I was familiar with.
Okay, I could have gotten an 8.0 for a minimal extra cost, but I think 6.8 is more than enough.
In the worst case, I expect 80 kW consumption per 24 hours in winter for heating and hot water.
If there is no Russian gas, I simply won’t have hot water. The system needs to provide an average heating output of 3.33 kWh per hour to cover those 80 kW over 24 hours.
The system should easily manage that. Even if it only converts 1 kW into 1.5 kW of heating power at very low outdoor temperatures, that’s 3.6 kWh. So, the maximum load of the 6.8 unit is sufficient to keep things comfortably warm in the worst case.
In the worst case, I expect 80 kW consumption per 24 hours in winter for heating and hot water.
If there is no Russian gas, I simply won’t have hot water. The system needs to provide an average heating output of 3.33 kWh per hour to cover those 80 kW over 24 hours.
The system should easily manage that. Even if it only converts 1 kW into 1.5 kW of heating power at very low outdoor temperatures, that’s 3.6 kWh. So, the maximum load of the 6.8 unit is sufficient to keep things comfortably warm in the worst case.
D
Deliverer26 May 2022 23:53Generally, smaller is better, especially if you have a backup. The size 8 unit would have been overworked at 30°C (86°F) outdoor temperature in cooling mode. In that case, the size 7 is still too large. For heating, it should fit better (without knowing your house).
Deliverer schrieb:
Generally, smaller is better, especially if you have a backup. The size 8 unit would have been overworked at 30°C (86°F) outdoor temperature in cooling mode. So the size 7 unit is still way too large. It should be a better fit for heating (without knowing your house specifically). Yes, exactly, but there isn’t anything smaller :/
Its power consumption ranges from 0.34 kW to 2.47 kW depending on the load. I think that’s a decent range; it gets more efficient at full load, but well, tough luck if your insulation is that good 😀
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