Building Services Engineering 5th Edition Handbook

80 Heat loss calculations
2. The following materials are being considered for the internal skin of a cavity wall:
(a)
(b)
(c)
(d)
(e)
(f)
105 mm brickwork;
200 mm heavyweight concrete block;
150 mm lightweight concrete block;
75 mm expanded polystyrene slab;
100 mm mineral fibre slab and 15 mm plasterboard;
40 mm glass fibre slab, 150 mm lightweight concrete block and 15 mm lightweight
plaster.
Compare their thermal resistances and comment upon their suitability for a residence.
3. Calculate the thermal transmittances of the following:
(a)
(b)
(c)
(d)
(e)
(f)
(g)
single-glazed window, severe exposure;
double-glazed window, sheltered exposure;
220 mm brick wall and 13 mm lightweight plaster;
220 mm brick wall, 50 mm glass fibre quilt and 10 mm plasterboard;
105 mm brick wall, 10 mm air space, 40 mm glass fibre slab and 100 mm lightweight
concrete block;
40 ◦ pitched roof, 10 mm tile, roofing felt and 10 mm flat plaster ceiling with 100 mm
glass fibre quilt laid between the joists;
19 mm asphalt flat roof, 13 mm fibreboard, 25 mm air space, 100 mm mineral wool
quilt and 10 mm plasterboard.
All exposures are normal unless otherwise specified.
4. A lounge 7 m long × 4 m wide × 2.8 m high is maintained at a resultant temperature of
21 ◦ C and has 1.5 air changes/h of outside air at −2 ◦ C. There are two double-glazed woodframed
windows of dimensions 2 m × 1.5 m and an aluminium framed double-glazed door
of dimensions 1 m × 2 m. Exposure is normal. One long and one short wall are external
and constructed of 105 mm brick, 10 mm air space, 40 mm polyurethane board,
150 mm lightweight concrete block and 13 mm lightweight plaster. The internal walls are
of 100 mm lightweight concrete block and are plastered. There is a solid ground floor with
edge insulation. The roof has a thermal transmittance of 0.34 W/m 2 K. Adjacent rooms are
at a resultant temperature of 18 ◦ C. Calculate the steady-state heat loss from the room for
a convective heating system.
5. A single-storey community building of dimensions 20 m × 15 m × 3 m high has
low-temperature hot-water radiant panel heaters. There are 10 windows of dimensions
2.5 m × 2 m. Natural infiltration amounts to 1 air change/h. Internal and external design
temperatures are 20 ◦ C and −1 ◦ C. Thermal transmittances are as follows: walls, 0.6 W/m 2 K;
windows, 5.3 W/m 2 K; floor, 0.5 W/m 2 K; roof, 0.4 W/m 2 K. Calculate the steady-state
heat loss.
6. Calculate the environmental temperature produced in an unheated room within an occupied
building, using the following information: room dimensions, 5 m × 4m× 2.6 m high; a
window of dimensions 2.5 m × 1.25 m in one long external wall; 0.5 air changes/h; external
air temperature, 3 ◦ C; solid ground floor; surrounding rooms are all at an environmental
temperature of 20 ◦ C. The thermal transmittances are as follows: external wall, 1 W/m 2 K;
window, 5.3 W/m 2 K; floor, 0.7 W/m 2 K; internal walls, 1.2 W/m 2 K; ceiling, 1 W/m 2 K.
Assume that the room environmental temperature is equal to the air temperature.
7. A single-storey factory is allowed to have 35% of its wall area as single glazing and 20% of its
roof area as single-glazed roof-lights. Wall and roof U values are not to exceed 0.6 W/m 2 K.
An architect proposes a building of dimensions 50 m × 30 m × 4 m high with a wall U value