Daylight availability, building orientations and ground factors in urban areas: a case in Sweden

Daylight availability is a crucial environmental indicator of sustainable urban areas,
especially in terms of human well being, health and energy savings. This study
analysed the impact of building orientations and ground surface reflectances
on the potential of indoor daylight utilization in the Swedish urban context.
Two fundamental building layouts in Swedish cities were investigated: linear
model and square model. For the ground between buildings, six various
surface reflectances have also been studied: 0.2 (a common ground
reflectance); 0.07 (soil), 0.3 (grass), 0.4 (concrete), 0.55 (old snow) and 0.8
(fresh snow). They could represent the typical photometric properties of the
ground materials found in the Swedish cities. The linear model has north and
south building facades to be studied, while the façades with four different
cardinal orientations were assessed in buildings of the square model.
DAYSIM, a CBDM package, was adopted to simulate the annual profile of
vertical illuminance at the façade position with a height of 2 metres above the
ground. It has been found that under Swedish climate conditions, orientations
take little effect on the daylight availability of the bottom facades, especially
during the heating seasons (Nov 1 – March 31). The increasing ground
surface reflectances significantly increase the vertical daylight levels at the
studied façade position. Taking the basic reflectance (0.2) as a reference, the
percentage differences of average illuminace of various ground materials are:
-10% (soil), 16% (concrete), 28% (old snow) and 50% (fresh snow).