John Mardaljevic
De Montfort University
The evaluation of shading devices is generally carried out using a sequence of
shadow pattern images showing the progression of solar penetration for
particular times of the day or year. This approach can reveal when solar
penetration may occur, say at the summer solstice, but it cannot give a
quantitative measure of the degree and likelihood of solar penetration over a
representative period of a full year. This paper describes a new image-based
technique to quantify the effectiveness of shading devices. It is founded on
predictions of direct solar irradiation using hourly meteorological data for a
full year. In addition to numerical output, the technique produces synoptic
images that reveal the spatial and temporal variation of solar irradiation.
There are no practical limits on the scene geometry and buildings with
thousands of individual shading elements can be evaluated. The technique is
designed to be both fast and highly scalable making it suitable for the
evaluation of a large number of design variants. This is demonstrated in the
paper using a parametrically defined model of a complex roof shading system based
on the Changi airport design. The three thousand six hundred fins that comprise
the roof shading system were generated using a parametric scheme where the fin
orientation has a random component. A total of forty-two design variants of the
roof shading system were evaluated using the new technique.
A Radiance
evaluation of parallax errors in sky simulator domes
John Mardaljevic
De Montfort University
Scale model illuminance measurements in sky simulator domes are inherently subject
to parallax errors. The magnitude of these errors under a number of CIE clear
sky configurations is quantified using computer simulation techniques. In
practical operation of a sky simulator dome, a second parallax error in the
normalization measurements for horizontal illuminance is likely to compound the
parallax error in the other illuminance measurements. This additional parallax
error is accounted for in the simulations. The concept of a parallax-bounded
volume is introduced. This is the volume of the dome which, on the basis of
parallax alone, must contain a scale model if it is not to be subject to errors
in the measurement of illuminance beyond a given tolerance. The findings
indicate that, on the basis of a credible design goal for the sky simulator
dome, high accuracy illuminance predictions (+-10%) are practically
unattainable.