An unplastered brickwork has a resistivity of 0.83 m degC/W. For a 230...
To calculate the overall U-value of the wall, we need to consider the heat transfer through the different components of the wall, including the brickwork, window assembly, and door assembly.
1. Heat transfer through the brickwork:
The heat transfer through the brickwork can be calculated using the formula:
Rbrick = (Lbrick / kbrick) * Abrick
where Rbrick is the thermal resistance of the brickwork, Lbrick is the thickness of the brick wall, kbrick is the resistivity of the brickwork, and Abrick is the area of the brick wall.
Given:
Lbrick = 230 mm = 0.23 m
kbrick = 0.83 m degC/W
Abrick = 6 m * 3 m = 18 m^2
Using the formula, we can calculate the thermal resistance of the brickwork:
Rbrick = (0.23 / 0.83) * 18 = 4.95 m^2 degC/W
2. Heat transfer through the window assembly:
The heat transfer through the window assembly can be calculated using the formula:
Rwindow = 1 / Uwindow
where Rwindow is the thermal resistance of the window assembly and Uwindow is the U-value of the window assembly.
Given:
Uwindow = 2.5 W/m^2 degC
Using the formula, we can calculate the thermal resistance of the window assembly:
Rwindow = 1 / 2.5 = 0.4 m^2 degC/W
3. Heat transfer through the door assembly:
The heat transfer through the door assembly can be calculated using the formula:
Rdoor = 1 / Udoor
where Rdoor is the thermal resistance of the door assembly and Udoor is the U-value of the door assembly.
Given:
Udoor = 1.25 W/m^2 degC
Using the formula, we can calculate the thermal resistance of the door assembly:
Rdoor = 1 / 1.25 = 0.8 m^2 degC/W
4. Overall U-value of the wall:
The overall U-value of the wall can be calculated using the formula:
UO = 1 / (Rbrick + Rwindow + Rdoor)
where UO is the overall U-value of the wall.
Using the formula, we can calculate the overall U-value of the wall:
UO = 1 / (4.95 + 0.4 + 0.8) = 1 / 6.15 = 0.16 W/m^2 degC
Since the question asks for the overall U-value in W/m^2 degC, the answer is approximately 0.16 W/m^2 degC. However, none of the given options match this answer. Therefore, there may be an error in the question or the options provided.