A section through a triple-glazed, high performance wooden window is shown at A - Leaving Cert Construction Studies - Question 5 - 2013

To calculate the U-value for the triple glazed argon-filled unit, we follow a similar approach:

1. Glass (Single Pane):

   • Conductivity (k) = 1.050 W/m·°C
   • Thickness (T) = 0.004 m
   • Resistance (R) = T/k = 0.004 / 1.050 = 0.00381 m²·°C/W

2. Argon Gas:

   • Conductivity (k) = 0.160 W/m·°C
   • Thickness (T) = 0.040 m
   • Resistance (R) = T/k = 0.040 / 0.160 = 0.25 m²·°C/W

3. External Surface:

   • Resistance = 0.075 m²·°C/W

4. Internal Surface:

   • Resistance = 0.110 m²·°C/W

5. Low-e Glass (for each pane):

   • Conductivity (k) = 3.400 W/m·°C
   • Assuming 3 panes:
   • Resistance for the low-e glass layer = 3/3.400 = 0.294 m²·°C/W

6. Total Resistance (R_total): $R_{total} = R_{glass} + R_{argon} + R_{ext} + R_{int} + R_{low-e} = 0.00381 + 0.25 + 0.075 + 0.110 + 0.294 = 0.73381 \, m^2 \, °C/W$

7. U-value (U): $U = \frac{1}{R_{total}} = \frac{1}{0.73381} = 1.363 W/m²·°C$

The U-value of the traditional single-glazed wooden frame can be calculated using the following:

1. Wood Conductivity: 0.150 W/m·°C.
2. Thickness (T): 0.040 m
3. Resistance (R): $R = T / k = 0.040 / 0.150 = 0.267 m²·°C/W$
4. U-value (U): $U = \frac{1}{R} = \frac{1}{0.267} = 3.745 W/m²·°C$.

The U-value of the traditional single glazing:

1. Conductivity (k): 5.300 W/m·°C.
2. Thickness (T): 0.004 m
3. Resistance (R): $R = T / k = 0.004 / 5.300 = 0.000755 m²·°C/W$
4. U-value (U): $U = \frac{1}{R} = \frac{1}{0.000755} = 1324.67 W/m²·°C$.

The thermally broken wooden frame provides efficient insulation compared to the traditional single-glazed windows. The U-values calculated show that the thermally broken wooden frame has a significantly lower U-value (0.113 W/m²·°C) compared to the traditional wooden frame's U-value (0.317 W/m²·°C).

The triple-glazed unit further reduces heat loss due to its lower U-value, thereby enhancing overall thermal performance, which is crucial in energy-efficient design. The traditional single-glazed wooden window has a high U-value, leading to increased heat losses.

Using materials with a lower embodied energy and better insulation (like the wooden frame and argon gas) contributes to reduced carbon emissions and a lower environmental impact. The thermally broken wooden frame is made from sustainable wood, which helps preserve natural resources.

In contrast, traditional single glazing leads to high energy consumption for heating, thereby increasing the environmental footprint. Enhancing the thermal efficiency of windows through improved design yields lower energy consumption, contributing positively to climate change mitigation.

To design a window detail:

• Frame Material: Use thermally broken wooden frame.
• Cavity Insulation: Include high-density insulation (50mm or proprietary cavity insulation) around the frame.
• Absence of Thermal Bridge: Ensure design avoids cold bridging.
• Sealing: Use rigid insulation (minimum 100mm) to seal against the inner leaf and provide full-fill cavity insulation.

The window head should integrate flashings with thermal breaks to minimize heat loss and include adequate drainage to avoid moisture infiltration.