Thermal and visual comfort analysis of an office with thermochromic smart windows applied

Abstract

Although windows are important for providing daylight and solar heat gain control, they are also a direct cause of about 50% energy loss through convection, conduction and radiation through what is typically a heavily insulated envelope within which they sit. Hence improving the performance of windows is critical for saving energy consumption of buildings. Thermochromic (TC) smart windows, which change colour and optical properties in response to temperature variations, are one of the most promising technologies for regulating energy consumption in buildings. In this paper, an office room with two different types of TC smart windows were studied at three different climatic conditions (Harbin, Guangzhou and London) using building simulation software Energyplus. The selected two TC smart windows are Wdoped VO2 film and VO2 nanoparticles coated double glazing with transition temperatures of 20°C and 40°C, respectively. The results show that there is an over 50% reduction in cooling loads of the office building with the W-doped VO2 TC smart window installed, and approximately 15% of annual total energy saving, compared with the office with normal double glazing installed at the same climatic condition - mild and humid climate, however, due to TC windows having a relatively lower visible transmittance (e.g. For the VO2 nanoparticles coated TC glazing, the visible transmittance is 63% below the transition temperature and 60% above the transition temperature), the total annual artificial lighting energy consumption is increased. In hot climates, W-doped VO2 film TC window induces a nearly 9.7 % increase of cumulative thermal comfort hours. In terms of thermal comfort, it is concluded that TC smart windows are suitable to be applied in regions with very hot summer and warm winter. It is also found that TC windows reduce illuminance below a comfortable range, therefore, increase the use of indoor artificial light, however, it reduces the appearance of glare. A comprehensive understanding of TC windows performance at various climatic conditions will benefit their future application on practical buildings.