The Effect of a Trees’ Shadows on the Indoor Heat Stress Probability and Buildings’ Cooling Loads Reduction in Santiago de Chile

Abstract

Heat waves could cause severe damages on population health in cities. Exposition to heat in some cases can lead to death, as experimented in many European countries during the heat waves of 2003, that reported a total of about 70,000 deaths. Heat stress is defined as the ratio of evaporation needed to maintain the thermal balance of the human body respect to the maximum of evaporation that could be achieved in specific environmental conditions. It depends on the air temperature, the relative humidity, the mean radiant temperature and the air speed. In indoor conditions, a severe heat stress is defined as the condition when the evaporation rate needed is in the range 40–60% of the maximum. Starting from these conditions, air-conditioning is required. So, heat stress and energy needs of buildings are strictly related. A Green Infrastructure has many benefits for inhabitants of cities. Among them, the reduction of probability of heat stress in both outdoor and indoor conditions. Recent studies underlined also the possible role of the trees in controlling the solar radiation gains of buildings through windows. In this paper we focus on the evaluation of the indoor heat stress index for the case of Santiago de Chile, and its relation with cooling needs a typical building. Then, the reduction of heat stress index and energy needs provided by a raw of trees on West building’s facade is assessed. We tested the benefit obtained by using different species, characterized by different morphology and solar permeability to solar radiation. Trees’ permeability is obtained by fish-eye image analysis done using the Gap Light Analyser software. Building simulations to obtain heat stress index and energy needs are run out using TRNSYS v. 17 software. Results confirm the capability of a GI to reduce indoor heat stress probability and energy needs in a 20–40%.