Hello,
We are currently building to KfW 70 standards, and triple-glazed windows with a U-value of 0.9 are standard for us. I have read several times that there are, of course, better windows available, for example with a U-value of 0.6.
We have many windows in our house, especially large façades facing south and west. All windows can be shaded, but that's just a side note.
I am wondering now if this makes a significant difference in terms of energy loss in winter and solar gain in summer when opting for slightly better windows, even if it might mean paying an additional cost.
Is it possible to quantify this? Or is it negligible?
What are your thoughts?
We are currently building to KfW 70 standards, and triple-glazed windows with a U-value of 0.9 are standard for us. I have read several times that there are, of course, better windows available, for example with a U-value of 0.6.
We have many windows in our house, especially large façades facing south and west. All windows can be shaded, but that's just a side note.
I am wondering now if this makes a significant difference in terms of energy loss in winter and solar gain in summer when opting for slightly better windows, even if it might mean paying an additional cost.
Is it possible to quantify this? Or is it negligible?
What are your thoughts?
We have a U-value of approximately 0.75; a frame U-factor of about 1.0, and a U-value of 0.5.
Example: U-value improves from 1.05 to 0.75, 200 heating days, 30 m² (320 ft²) of windows, average temperature difference to room temperature 13°C (55°F) → €39 per year. If the additional cost is less than €1000, it is economically worthwhile in the long term. (100 assumptions)
Example: U-value improves from 1.05 to 0.75, 200 heating days, 30 m² (320 ft²) of windows, average temperature difference to room temperature 13°C (55°F) → €39 per year. If the additional cost is less than €1000, it is economically worthwhile in the long term. (100 assumptions)
What people often interpret as radiant cold from windows is usually just draft... Airtight sealing was probably not done (always) 20 years ago.
In my opinion, you only notice radiant cold if you sit very close to the window – we’re not talking about single glazing versus a passive house here.
In my opinion, you only notice radiant cold if you sit very close to the window – we’re not talking about single glazing versus a passive house here.
BeHaElJa schrieb:
How many square meters is it? You can calculate quite precisely what could theoretically be saved... for example, 0.3 W/m²K (Watt per square meter per Kelvin) for 10 m² (108 sq ft) of window area on a cold winter day at -10°C (14°F) equals 10 m² * 30 K * 0.3 W = 30 W per hour -> 0.660 kWh -> 4.6 cents Could you please explain the conversion from W/m²K and a temperature difference to an energy unit over time (1 hour) in more detail?
In your calculation of 4.6 cents for 10 m² (108 sq ft) per hour (realistically, it would be somewhat more for an entire house), that would mean additional costs of about €33 per month in winter (30 days x 24 hours). I find this highly unlikely. Please provide the correct full formula.
The 4.6 cents referred to a whole day – sorry.
0.3 W/m²K * 10 m² (108 sq ft) * 30 K * 24 h = 2160 Wh → 2.16 kWh → 1 kWh of gas costs about 7 cents → 15.12 cents (I miscalculated by a factor of 3 because I got mixed up) – but that is correct.
10 m² (108 sq ft) of windows is relatively small for a house… so here is the second example → let’s say 30 m² (323 sq ft) → 45.36 cents on this very, very cold winter day (average -10°C (14°F)).
Now, there aren’t many days like this, and the average temperature during the heating months is closer to 6°C (43°F) between October and April. Let’s assume we don’t heat for the full 240 days but rather 200 days and use 7°C (45°F) average instead of 6°C (43°F) (I have to account somehow for solar gains) – then, for example, 200 days with a 13 K temperature difference → 13 K * 0.3 W/m²K * 30 m² (323 sq ft) * 4800 h = 561 kWh → about €39 gas saved per year… which is probably close to reality.
0.3 W/m²K * 10 m² (108 sq ft) * 30 K * 24 h = 2160 Wh → 2.16 kWh → 1 kWh of gas costs about 7 cents → 15.12 cents (I miscalculated by a factor of 3 because I got mixed up) – but that is correct.
10 m² (108 sq ft) of windows is relatively small for a house… so here is the second example → let’s say 30 m² (323 sq ft) → 45.36 cents on this very, very cold winter day (average -10°C (14°F)).
Now, there aren’t many days like this, and the average temperature during the heating months is closer to 6°C (43°F) between October and April. Let’s assume we don’t heat for the full 240 days but rather 200 days and use 7°C (45°F) average instead of 6°C (43°F) (I have to account somehow for solar gains) – then, for example, 200 days with a 13 K temperature difference → 13 K * 0.3 W/m²K * 30 m² (323 sq ft) * 4800 h = 561 kWh → about €39 gas saved per year… which is probably close to reality.
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