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

To find the U-value of the triple-glazed argon-filled unit, we again calculate the R-values for each glass layer and the argon gas:

1. Resistance Calculation:

   • Glass (single pane): Conductivity = 1.050 W/m°C, Thickness = 0.004 m $R = \frac{T}{k} = \frac{0.004}{1.050} = 0.0038095 \, m^2 \, K/W$
   • Argon Gas: Conductivity = 0.160 W/m°C, Thickness = 0.040 m $R = \frac{0.040}{0.160} = 0.25 \, m^2 \, K/W$
   • External Surface: Resistance = 0.075 m²K/W
   • Internal Surface: Resistance = 0.110 m²K/W
   • Low-e Glass: Conductivity = 3.400 W/m°C
   • Total Resistance: $R_{total} = 0.0038095 + 0.25 + 0.075 + 0.110 + 0.2941176 ≈ 3.3888 \, m^2 \, K/W$

2. U-value Calculation: $U = \frac{1}{R_{total}} ≈ \frac{1}{3.3888} ≈ 0.294 \, W/m^2K$

For the traditional single-glazed wooden window frame,:

1. Resistance Calculation:

   • Wood Frame: Conductivity = 0.150 W/m°C, Assume Thickness = 0.4 m (example thickness) $R = \frac{T}{k} = \frac{0.4}{0.150} ≈ 2.67 \, m^2 \, K/W$

2. U-value Calculation: $U = \frac{1}{2.67} ≈ 0.375 \, W/m^2K$

For the single glazing, using data:

1. Resistance Calculation:

   • Single Pane: Conductivity = 1.050 W/m°C, Assume Thickness = 0.004 m $R = \frac{0.004}{1.050} = 0.0038095 \, m^2 \, K/W$
   • Total Resistance includes surfaces: $R_{total} = 0.0038095 + 0.075 + 0.110 = 0.1888 \, m^2 \, K/W$

2. U-value Calculation: $U = \frac{1}{0.1888} ≈ 5.29 \, W/m^2K$

The thermally broken wooden frame has a better thermal performance due to its lower U-value compared to the traditional solid wooden frame. The use of insulation between the two wooden layers in the thermally broken version significantly reduces heat loss.

The triple-glazed unit offers further reduction of heat transfer as it combines low-e glass and argon filling, leading to very efficient insulation properties. This drastically cuts down on heating costs, with estimates suggesting it can halve heat loss compared to traditional glazings.

From an environmental standpoint, the thermally broken frame, with its rigid insulation, helps reduce energy consumption, leading to lower CO2 emissions. Utilization of sustainably sourced materials can also lessen environmental impact.

In contrast, traditional single-glazed windows are less efficient and result in higher energy usage, leading to more waste and environmental degradation. The introduction of the triple-glazed unit improves energy efficiency substantially, enabling reduced reliance on fossil fuels over time.

The design of a window fixed in a 350 mm concrete block wall with an insulated cavity should incorporate a few key elements:

1. Window Frame: Ensure a good fit within the cavity to prevent thermal bridging.
2. Insulation: Detail the insulation snugly against the wall, specifying a high-density material to minimize heat loss.
3. Sealing: Use proper seals around the window frame to eliminate air leakage.

Sketch: A rough sketch showing insulation around the window, with notes for minimum thermal bridging, would clarify placement and materials.