The effect of daylight and sunlight requirements on the energy balance of New Zealand window systems

Abstract

Windows, because of the complex ways in which it affects energy consumption, demands particularly close attention, in the present situation in which the need for energy conservation has become a major design parameter. This project endeavours to estimate the potential contribution of daylight and sunlight towards reducing lighting energy consumption. Using computer simulation methods, two broad estimates were made, one the total amount of light received through vertical unobstructed windows, and the other the total amount of light received on the horizontal working plane through vertical windows. These were then assessed in terms of energy. The results indicate that even on south facing windows in winter months, the total lighting energy gains can exceed those of conduction losses. However if assessments are made considering only light received on the horizontal working plane, the double glazed windows occupying 10% to 30% of the external wall appear to have a favourable balance for low efficacy lighting systems. But clearly if heat gains are added, the gains will be in excess of the conduction losses over a larger window size range. The task lighting gains also appear to be generally independent of window area, over practical window sizes examined; 10% to 70% external wall area