A study of the U-factor of a window with a cloth curtain

Heating and cooling energy calculations and building energy simulations need the overall heat-transfer coefficient (U-factor) of windows. This study focuses on the U-factor of a window with a cloth curtain indoors. Two side-by-side hot boxes are built in a laboratory for testing the window U-factors. The tested window systems are 100% glass area without frames which are equivalent to the center of glass of practical windows. The two types of tested window systems are the single glazing and the double glazing with a cloth curtain, respectively. The effect of curtain edge sealing conditions on U-factors is also studied. The empirical equations of the center-of-glass U-factors are derived from the experimental data. The corrections for the effects of window frames and outdoor wind velocity are made thereafter. The corrected empirical equations can be easily used to estimate the U-factor of a practical window with a cloth curtain.