Effect of Sky Clearness Index on Transmission of Evacuated (Vacuum) Glazing
Glazing transmittance variation with clearness index has higher influence than incident angle for soar energy application. This work presents variation of vacuum glazing transmittance with clearness index. Clearness index and transmittance was calculated from measured one year (2014) solar radiation and glazing transmittance data in Dublin, Ireland. Clearness index below 0.5 offer single value of transmittance whereas above 0.5 clearness index glazing transmittance varies with clearness index. For different azimuthal orientation, clearness index associated with vertical plane glazing transmittance has been proposed. In Dublin for south facing vertical plane, vacuum glazing has 35% transmittance below 0.5 clearness index. Yearly usable single transmitted solar energy and solar heat gain coefficient for vertical plane south facing vacuum glazing are 87 W/m2 and 0.22 respectively.