Hydrometeorological determinants of green roof performance via a vertically-resolved model for heat and water transport

In this study, the Princeton ROof Model (PROM) is developed, validated and used to simulate the hygrothermal dynamics of green roof systems. PROM is embedded within the framework of the Princeton Urban Canopy Model, with a multi-layer spatially-analytical heat transfer scheme and an improved hydrological module. The model is validated by comparing simulated surface temperature and soil moisture to the measurements at two experimental sites, one in Beijing, China and the other in New Jersey, USA. The results demonstrate that PROM is able to capture the diurnal cycle of roof temperatures and the soil moisture dynamics of green roofs with high accuracy. Driven by a 30-day summertime meteorological forcing from July 2001, PROM is used to investigate the green roof thermal improvement to the urban indoor and outdoor environments, compared to conventional roofs. The impact of green roofs is significant in reducing surface temperatures, and outdoor and indoor heat fluxes during this summer period. To quantify this thermal improvement, three indices related to surface temperature, outdoor heat flux and indoor heat flux, are introduced; and the dependence of these indices on hydrological and meteorological conditions is investigated. The results indicate that incoming solar radiation and medium layer moisture are the main determinants of the green roof performance.

► A new vertically-resolved green roof water and heat transfer model is developed.
► Validation with two different forcing datasets shows the model is highly accurate.
► Simulation results confirm green roofs improve thermal environment.
► New indices are proposed to quantify the thermal performance of green roofs.
► Solar radiation and soil moisture are the main governing hydrometeorological factors.