Thermal performance of a green roof based on CHAMPS model and experimental data during cold climatic weather

Green roofs are increasingly implemented in cities around the world. They have the potential to improve thermal performance of building systems through evapotranspiration, thermal mass, insulation and shading. Several studies have analyzed the heat flow impact of green roofs in hot weather, but few studies have examined the thermal performance during cold conditions. Roof membranes are known to fail in cold climates due to stress caused by large temperature fluctuations. A green roof can reduce the daily membrane temperature fluctuations (Tmax - Tmin) by an average of 7◦C. This study presents an experimental investigation of a large extensive green roof on the Onondaga County Convention Center in Syracuse, NY from November 2017 to March 2018. The model known as CHAMPS has been applied to simulate the temperature profile through the layers of the green roof. In early winter without snow, the temperatures of the growth medium and roof membrane follow the diurnal cycle of ambient air temperatures with smaller amplitude. An average seven hour peak delay is observed. Under extremely cold weather, snow acts as an insulator. The temperature of the growth medium on the Convention Center remains slightly above freezing and is relatively steady when there is significant snow, even during extremely cold temperatures. Heat flux is dominated by the temperature gradient between interior space and the snow layer. On the basis of this work, it is shown that the CHAMPS model can play a valuable role in informing green roof design decisions