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E N E R G Y E F F I C I E N C Y P R O J E C T
C O M M E R C I A L B U I L D I N G S
In the following graph (Fig. 6), three internal fluxes with changes to the glazing area of the
north zone are examined. The solar aperture is the glass area, as a percentage of the wall area,
multiplied by the SHGF. For example, 40% glass area with a SHGF of 0.86 gives a solar
aperture of 0.344.
Fig. 6 - NORTH ZONE COOLING
900.0
800.0
700.0
Energy Use, MJ/m².a
600.0
500.0
400.0
300.0
200.0
100.0
0.0
0.00 0.10 0.20 0.30 0.40 0.50 0.60
Solar aperture
Hobart(19.5)
Hobart(47.5)
Melbourne(19.5)
Melbourne(47.5)
Brisbane(19.5)
Brisbane(47.5)
Darwin(19.5)
Darwin(47.5)
The graph shows that that the variation of cooling energy use with solar aperture for a specific
internal flux level (19.5 or 47.5W/m 2 ) can be approximated by a linear relationship.
• For example, based on the earlier zone graphs, the solar aperture was 40% x 0.86 =
.344, and the energy use varied linearly with changes in load. For Darwin with an
internal flux level of 19.5W/m 2 the cooling energy use is approximately
510MJ/m 2 .annum. If the glazing area is increased to 50%, a solar aperture of 0.43, the
cooling energy use increases to approximately 580MJ/m 2 .annum. This linear
relationship allows the cooling energy use to be estimated for different apertures if the
internal energy use is either 19.5W/m 2 or 47.5W/m 2 .
However, as the 19.5 and 47.5W/m 2 lines are approximately parallel, the energy use for
internal loads between 19.5 and 47.5W/m 2 would also be expected to vary linearly
across varying solar apertures. The result would be a suite of parallel lines for varying
internal fluxes.
When the internal fluxes are modelled for the Form E building as a whole, the cooling energy
use also demonstrates a linear variation. This is shown in Fig. 7 below.
Accordingly, the linear relationship for the variation in internal flux levels for a particular
zone/building geometry and orientation can be used to estimate the effects of other flux levels
on that same geometry and orientation. This has particular advantages in that it can reduce
the amount of modelling required to examine the effect of internal flux levels on the fabric
energy saving measures.
18 April 2002 Page 8 of 13