Solar radiation through glasses and the overall thermal transfer value of building envelopes

Many modern buildings with high window-to-wall ratio (e.g. curtain-walled) are constructed in Hong Kong in this ten years. In addition to other technical problems such as visual comfort and fire safety, building energy is now of great concern. The government is considering to set up some regulation on controlling the cooling load in those air-conditioned buildings. The concept of Overall Thermal Transfer Value (OTTV) of is proposed to be used as a guideline for designing building envelopes. There are three components in the OTTV equation but the part related to solar radiation through glasses is believed to be very important for this kind of curtain-walled buildings. Its magnitude might be much greater than the other two parts, i.e. conduction through walls and fenestration. This paper aims at investigating the amount of thermal radiation through glasses and its effect on the OTTV equation under local weather condition. Thermal radiation transferred through the glass is calculated using the DOE-2 program developed at the U.S. Department of Energy on a centrally air-conditioned building. The window-to-wall ratio for this example building is varied to compute the important parameters involved.