The application performance of a type of thermochromic double glazing is first demonstrated in a full-scale room. The experimental results show that the low-mass room with a VO2 double window consumes approximately 11.1% less cooling energy than that with an ordinary double window. Three types of windows, a VO2 double window, an ordinary double window and a VO2 single window, are then analyzed as improvements for an ordinary single window. The analysis indicates that in hot climate conditions, the application of the VO2 single window uses less energy than that of the ordinary double one but uses more energy than that of the VO2 double window. Two widely investigated methods to enhance the energy performance of a window, optimizing the capacity for the regulation of solar radiation and improving the thermal insulation performance, are embodied in applications of two hypothetical windows and then further discussed. The results indicate that, in a hot climate, whether a window with an extremely low U-value is favorable for energy efficiency will depend on the set point of the indoor temperature: an indoor temperature lower than 23 degrees C makes the window more efficient than an ordinary single window. However, the low U-value window still has worse energy performance than a window with an appropriate solar heat gain coefficient, which highlights the effect of regulating the solar radiation. (C) 2015 Elsevier Ltd. All rights reserved.