Sensitivity of the Solar Heat Gain Coefficient of Complex Fenestration Systems to the Indoor Convection Coefficient

Abstract

Accurate estimation of the solar gain of a fenestration system is important in analyzing the energy performance of buildings. Recently, models were developed for complex fenestration systems – glazing systems with attachments such as venetian blinds and insect screens. These models use a three-node network for modeling heat transfer at the indoor-side of a glazing system. Empirical expressions based on observation and known limits were originally proposed for the corresponding convection coefficients. To address any ambiguity or error associated with these expressions, a research project is underway to develop techniques for evaluating these convection coefficients more accurately. The purpose of the current paper is to quantify the sensitivity of the U-value and solar heat gain coefficient of complex fenestration systems to the indoor-side convection coefficients. Configurations comprised of low-e glazings, roller blinds, venetian blinds, drapes and insect screens are examined in design summer and winter conditions using the window analysis software VISION5. Results show that the presence of an indoor-mounted attachment can significantly change the solar heat gain coefficient of a fenestration system. Nevertheless, the solar heat gain coefficient and the overall heat transfer coefficient are not sensitive to the indoor convection coefficient.