Error Analysis of In-Situ Field Tests of Fenestration Performance

The need for information about fenestration net energy performance under realistic conditions is discussed and the method of measuring it in a field test on a complete building is reviewed. A detailed consideration of the energy flows entering the energy balance on a building space adjacent to a fenestration system and the effect of random measurement errors on the determination of fenestration performance is presented. Estimates of the error magnitudes are made for prototypical field tests utilizing a residential and a moderate-sized commercial building. In both cases, it is shown that these errors make it difficult to isolate the fenestration performance even for relatively low-performance windows (1-2 times the resistance of single glazing). It is concluded that whole-building measurements are not well adapted to measuring the performance of advanced fenestration system (thermal resistance 2-10 times that of single glazing or shading coefficient less than 0.7).