Error analysis of in situ field tests of fenestration net energy 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 fesestration system (thermal resistance 2 – 10 times that of single glazing or shading coefficient less than 0.7).