Estimating the Effect of Green Roofs on a City's Energy Footprint

The temperature generated (and hence energy stored) in a solid layer subjected to sunshine is examined. Two models are developed which permit the calculation of the temperature from the surface to far into the ground. By varying parameters we can replicate heat flow in soil or concrete, there is also the option to include evaporation and evapotranspiration. The results obtained indicate that significant temperature reductions and energy storage in the solid layer can be achieved by a sensible choice of roof covering and composition. The models are one-dimensional but it is a simple matter to extend the calculations to deal with a patchwork quilt of surfaces as would be present in a city. Recommendations are given to reduce heat storage in a city and also on future model improvements.