Building Services Engineering 5th Edition Handbook

Heat loss calculations 77
Stone
Asphalt
5
4
3
25 mm
19 mm
Concrete
150 mm
Air
void
400 mm
Fibreboard
2
12 mm
1
3.2 Roof construction for Example 3.9.
transmittance of the roof structure. On the day of test, the temperatures t 1 , t 2 and t 5
were 19 ◦ C, 17.6 ◦ C and 5 ◦ C. The temperature at node 4 could not be measured owing
to the roughness of the surface. The temperature at node 3 could be measured but it is
not needed. Describe the features of two methods that could be used to insulate the roof.
Decide which materials would be suitable and find the correct thickness for the insulation.
From Tables 3.2, 3.3 and 3.5, R si = 0.1 m 2 K/W, R so = 0.05 m 2 K/ W (low emissivity),
R a = 0.17 m 2 K/W (high emissivity).
From Table 3.1, the thermal conductivities of the materials are:
cast concrete, lightweight
asphalt
stone chippings
glass fibre quilt
polyurethane board
λ = 0.38 W/mK
λ = 0.5 W/mK
λ = 0.96 W/mK
λ = 0.06 W/mK
λ = 0.025 W/mK
The options to be tried are as follows:
(a)
Remove some ceiling tiles and lay a lightweight blanket, such as glass fibre, on top of the
tiles. This depends on whether the fibreboard tiles, support wires and screws are able to
hold the additional weight. Extra support rods may be needed. There will be considerable
disturbance to the room usage. This may preclude installation work during normal working
hours. Removing the tiles will disturb dust and debris from the void and necessitate a cleaning