Thermodynamics: Calculating total resistance of window

In summary, a triple glazed window with 3 clear glass panes of 3 mm thickness each, separated by 12 mm air cavities, has a total thermal resistance of 1 KW. The thermal conductivity of the glass panes is 0.8 W•m-1•K-1 and the thermal conductivity of the air cavities is 0.028 W•m-1•K-1. The window area is 1.0 m2 and the air gaps can be ignored due to their small size. To calculate the resistance of the air gaps, the correct thickness of 12 mm should be used instead of 1m.
  • #1
DiamondV
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Homework Statement


A triple glazed window consists of 3 clear glass panes of 3 mm thickness each, separated by air cavities of 12 mm each. The window area is 1.0 m2 . If the thermal conductivity of the glass panes is 0.8 W•m-1•K-1 and of the air cavities is 0.028 W•m-1•K-1 what is the total thermal resistance of the window?

Homework Equations

The Attempt at a Solution


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The correct answer is meant to be 1 KW. I was initially going to do something with the internal air and external air but the question says the total thermal resistance of the window. So it should be conduction1 through the first pane of glass, then convection1 through first air gap then conduction2 through second glass pane then convection2 through second air gap then finally conduction3 thorugh third glass pane.
 
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  • #2
I think the air gaps are small enough for convection to be ignored?

In your working, where you calculate the resistance of the air gaps... You appear to have the thickness as 1m rather than 12mm?
 

1. How is total resistance of a window calculated in thermodynamics?

The total resistance of a window is calculated by adding the individual resistances of each component of the window, such as the glass, frame, and any additional layers or coatings. The formula for calculating resistance is R = L / kA, where R is resistance, L is the length of the material, k is the thermal conductivity, and A is the cross-sectional area of the material.

2. What factors affect the total resistance of a window?

The total resistance of a window is affected by the type and thickness of materials used, their thermal conductivity, the size and shape of the window, and any additional layers or coatings. The quality of installation and the environmental conditions also play a role in the overall resistance of a window.

3. How does the total resistance of a window impact energy efficiency?

The higher the total resistance of a window, the more energy efficient it is. This is because a window with high resistance will better prevent heat transfer, keeping the interior of a building warmer in the winter and cooler in the summer. This can lead to cost savings on heating and cooling bills.

4. Can the total resistance of a window be improved?

Yes, the total resistance of a window can be improved by using materials with higher thermal resistance, such as low-emissivity (low-e) coatings or double or triple-pane glass. Proper installation and sealing can also help improve the total resistance of a window.

5. How is the total resistance of a window related to U-value and R-value?

The U-value and R-value are both measurements of thermal resistance, with the main difference being the unit of measurement. U-value is measured in watts per square meter per degree Celsius (W/m²K), while R-value is measured in square meters kelvin per watt (m²K/W). The higher the U-value or R-value, the lower the heat transfer through a window, indicating a higher total resistance.

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