The effect of increasing surface cover vegetation on urban microclimate and energy demand for building heating and cooling

The study examines the potential effects of adding vegetation to an urban neighborhood in Tel Aviv on the microclimate, and subsequently on the potential for cooling by night ventilation and on energy consumption for heating and air conditioning. Computer simulation was employed to first generate modified weather files that account for urban effects of location, surface cover and density in different building configurations. These files were then used to assess the climatic cooling potential (CCP) by night ventilation and as inputs for detailed computer simulation of building energy performance. The microclimate model simulation indicates that elevated urban night-time temperatures will increase summer cooling loads relative to the reference rural site, but this penalty will be more than offset by reduced winter heating loads, resulting in a net decrease of between 2 and 7% in electricity use for heating and cooling (depending on building characteristics). The main impact of the urban heat island in this case is the reduction in the potential for cooling by night ventilation, which is almost completely absent in the summer months. Consequently, the urban climate of Tel Aviv may increase the prevalence of air conditioning use and will make buildings more vulnerable to potential loss of electric power in case of shortages or blackouts during episodes of extreme heat. Implementing a strategy of extensive planting, so that a green surface fraction of 0.5 is obtained, results in a mean annual temperature reduction of about 0.3 °C and an energy saving relative to the current condition of about 2–3%.