HEAT REFLECTING GLAZING
Predicted performance of VERTICAL and HORIZONTAL ARRAYS in Brisbane buildings. Ian Edmonds
A parallel array of narrow laser cut panels (LCP) forming a horizontal array (as shown) rejects high elevation sunlight while maintaining good viewing and daylight conditions.
A vertical array rejects low elevation off-normal sunlight but allows a good external view normal to the window.
Horizontal arrays are effective in rejecting high elevation sunlight and are used, in Australia, on East, North East, North, North West and West facades.
Vertical arrays are effective in rejecting low elevation sunlight and are used on South East and South West facades in Australia.
The horizontal array shown is a fixed array between double glazing to avoid dust accumulation. However, the arrays may be suspended in the same manner as a horizontal or a vertical Venetian blind. The basic function is as shown below:
The defining parameters are the laser cut spacing, D, and the cut depth, W, of the laser cut panel (as above) and the LCP array separation, S, and the array thickness, T (as below).
With these parameters defining the heat rejecting glazing it is possible to calculate the transmission of sunlight through the glazing as a function of time of day and for specific orientation of fenestration and location of building. Examples of the performance of VERTICAL and HORIZONTAL heat rejecting glazings are given below. (Array parameters have not been optimized to the application).
Performance of VERTICAL ARRAY heat rejecting glazing on a South East facade in Brisbane.
The broken curves show the irradiance incident on the glazing. The full curves show the irradiance passing through the glazing to the interior. Evidently a vertical array glazing on a SE or SW window rejects much summer - equinox sunlight while maintaining good viewing conditions.
For example, at 8:30 am in midsummer the radiant heat through one square metre of glazing is reduced from 500 W to 140 W.
Performance of HORIZONTAL ARRAY heat rejecting glazing on a North East facade in Brisbane.
The broken curves show the irradiance incident on the glazing. The full curves show the irradiance passing through the glazing to the interior.
Evidently the horizontal array glazing on a NE or NW window rejects a high fraction of the high elevation sunlight while maintaining good viewing conditions.
For example at Equinox at 10 am the radiant heat through one square metre of glazing is reduced from 550 W to 110 W.
Reference
Reppel J and Edmonds I R, Angle-selective glazing for radiant heat control in buildings : Theory. Solar Energy 62(3), 245-253 (1998)