Thermal Performance Study of Extensive Green Roof in Shanghai District: a Case Study of Lightweight Building in Winter

摘要

This paper aims to investigate the thermal performance of extensive green roof under free-floating and air-conditioned conditions in winter. A field experiment was conducted on two full-scale rooms from 01/12/2014 to 17/12/2014 in Shanghai, one room was covered by green roof while the other was covered by common roof. Temperature distribution along the vertical direction of both roofs was recorded, and so were heat flux through the roofs as well as soil volumetric water ratio of green roof, local weather data was collected simultaneously. The results indicated that cooling effect of green roof was significant when solar radiation was strong, and green roof showed insulation effect only at night when the indoor air temperature was about 3°C higher than that of common roof. Under free floating condition, temperature profile of green roof was like a saddle surface while common roofs profile was like a Mexican hat. And green roofs temperature profile pattern is similar to that of common roof under air-conditioned condition. Energy balance analysis shows that net solar radiation and heat convection is the major heat gain for both roofs in winter, and net long wave radiation and evapotranspiration dissipate most heat gain for green roof while net long wave radiation is the main heat dissipation for common roof.