Hello,
Yesterday we had the selection appointment for our KfW 70 house. Dark gray aluminum roller shutters would suit the dark gray windows and are also good for dirt resistance. However, our window installer said they would get too hot. Our large windows face west. I don’t understand this argument since we have triple glazing. What are your experiences? Venetian blinds with a wind sensor are not an option for us.
Thanks for your answers.
Yesterday we had the selection appointment for our KfW 70 house. Dark gray aluminum roller shutters would suit the dark gray windows and are also good for dirt resistance. However, our window installer said they would get too hot. Our large windows face west. I don’t understand this argument since we have triple glazing. What are your experiences? Venetian blinds with a wind sensor are not an option for us.
Thanks for your answers.
(Mythbuster Mode: ON)
To address all the assumptions about thermal expansion, here are some facts, specifically the calculation of length changes due to temperature variations.
I am using extreme values:
Length of the aluminum slat from a roller shutter or venetian blind: 2 m (6.6 ft)
Temperature range: 80°C (from -20°C (−4°F) in winter to +60°C (140°F) in summer on a heated dark surface)
Coefficient of thermal expansion for aluminum: 23×10⁻⁶ m/°C
This results in a length change of 3.7 mm (0.15 inches) over the specified temperature range.
Assuming the slats are at their normal length at 20°C (68°F) and contract when cold and expand when warm,
the length change when warming (from +20°C to +60°C) is 1.8 mm (0.07 inches), and when cooling (from +20°C to -20°C) it is also 1.8 mm (0.07 inches).
All these values are insignificant. Whether roller shutters, venetian blinds, or louvered blinds, the slats have enough clearance to accommodate this thermal expansion. They are quite loosely fitted, just try shaking them.
(Mythbuster Mode: OFF)
To address all the assumptions about thermal expansion, here are some facts, specifically the calculation of length changes due to temperature variations.
I am using extreme values:
Length of the aluminum slat from a roller shutter or venetian blind: 2 m (6.6 ft)
Temperature range: 80°C (from -20°C (−4°F) in winter to +60°C (140°F) in summer on a heated dark surface)
Coefficient of thermal expansion for aluminum: 23×10⁻⁶ m/°C
This results in a length change of 3.7 mm (0.15 inches) over the specified temperature range.
Assuming the slats are at their normal length at 20°C (68°F) and contract when cold and expand when warm,
the length change when warming (from +20°C to +60°C) is 1.8 mm (0.07 inches), and when cooling (from +20°C to -20°C) it is also 1.8 mm (0.07 inches).
All these values are insignificant. Whether roller shutters, venetian blinds, or louvered blinds, the slats have enough clearance to accommodate this thermal expansion. They are quite loosely fitted, just try shaking them.
(Mythbuster Mode: OFF)
No, that’s not correct either. Otherwise, the roller shutters would be completely pointless... they are installed for heat protection. There is an air gap between them, and air can also escape through the gaps, so the heat stays outside regardless of the color of the roller shutters.
No, that is not nonsense. Depending on the color, different amounts of sunlight are reflected, meaning dark roller shutters heat up much more than light or “silver” ones. The warmer the roller shutters get, the warmer the air in the cavity behind them becomes – some of this heat is definitely transferred into the house (though still much less than without roller shutters). Try opening a window behind closed roller shutters in summer, and you’ll immediately notice that the air behind them is much warmer than the outside air.
Additionally, there is a second effect: thermal radiation. Hot roller shutters emit much more heat radiation – also toward the window! The radiated energy increases with the fourth power of the temperature, meaning if the temperature doubles, the radiation becomes 16 times stronger! You probably know that you can feel the warmth from hot radiators (70°C (158°F) and above) even from some distance. Aluminum has high thermal conductivity compared to plastic, so the inside surface is just as warm as the outside. This means that dark roller shutters radiate significant heat inward toward the window as well.
Additionally, there is a second effect: thermal radiation. Hot roller shutters emit much more heat radiation – also toward the window! The radiated energy increases with the fourth power of the temperature, meaning if the temperature doubles, the radiation becomes 16 times stronger! You probably know that you can feel the warmth from hot radiators (70°C (158°F) and above) even from some distance. Aluminum has high thermal conductivity compared to plastic, so the inside surface is just as warm as the outside. This means that dark roller shutters radiate significant heat inward toward the window as well.
Yes, I understand that the air in the air gap gets warmer, but you shouldn’t forget the chimney effect, provided the blinds are not fully closed... this allows the air to circulate, and the windows or the house hardly absorb any of the heat... and that’s how the blinds are usually used. As soon as the sunlight is strong enough, you lower the blind, but not completely, so you don’t have to sit in the dark... the air circulates and the heat stays outside... completely independent of the color of the blinds.
Then, for example, the first pane of glass and the frame might get a bit warmer... but everything else remains at the original temperature...
Then, for example, the first pane of glass and the frame might get a bit warmer... but everything else remains at the original temperature...
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