Effective U-values and Shading Coefficients of Preheat/Supply Air Glazing Systems

Abstract

Research is documented which makes use of a computer program called VISION, This computer program was developed specifically to provide a detailed analysis of heat transfer occurring in glazing systems. VISION was modified to perform an analysis of the energy flows in supply air windows. A model used to quantify heat transfer in the supply air flow is described. Ventilation air is brought in through supply air windows and the energy recovered by the preheat of the air flow is credited to the thermal performance of the window itself, Thus, the net energy flow between the conditioned space and the window was used to calculate an effective U-value and shading coefficient, The use of these "effective" window performance parameters permits the subsequent quantification of energy flows to or from the supply air glazing system without the necessity of modelling the detailed mechanisms of energy transport within the glazing system itself. A variety of glazing system designs are simulated. Indoor glazing temperature is reported for each system. In all cases the presence of preheat ventilation improved the effective shading coefficient moderately and increased the effective thermal resistance appreciably.