Abstract
-
Conventionally in building performance simulations
(BPS), it is assumed that air entering outdoor HVAC
equipment is at the outdoor ‘ambient’ temperature,
obtained from a weather file. However, significant spatial
variations exist in outdoor air temperature fields,
especially within the thermal boundary layers that form
near exposed surfaces like roofs.
Experiments were conducted at three large-footprint
shopping centre buildings, to characterise the above-roof
temperature field. An empirical model was derived from
the experimental data, and applied in BPS of a shopping
centre with rooftop HVAC equipment in seven Australian
climates. In these cases, the electricity savings and gas
‘penalties’ attributable to cool roofs would have been
underestimated by 44–85% (61% on average) if near-roof
air temperature variations had not been modelled
accurately.