Reduction of glazing transmittance by atmospheric pollutants

Abstract

Glazing transmittance was measured in approximately 500 windows in urban buildings in Sheffield, UK. In addition, laboratory measurements were made of transmittance reduction due to dirt deposited on glass samples on a test rig exposed over a 2-year period. The overall results were that actual glazing transmittances differed significantly from values given in current codes of practice, and that exposure to precipitation, glazing slope and room use are major determinants of glazing transmittance. Where glazing is exposed to rain, deposited dirt on the outside of windows tends to build up in 2-3 months to a level that then remains relatively constant. Typically, the final reduction of transmittance is 4-8% for commercial buildings in clean environments. We suggest values to be used in daylighting calculations.