Thermal comfort at pedestrian levels in a large multi-storey development in maritime tropical climate

While a lot of attention has been given in the study of indoor air distribution and its thermal performance, buildings clustered together in a development modify the outdoor environment to a great extent and the outdoor thermal performance of such a development is a critical factor for its success as to its acceptance by the tenants and visitors and their enjoyment of the outdoor activities. In such a development, careless design may lead to areas of stagnant or little air movements, which may lead to a very uncomfortable condition for even a few minutes of walk in a tropical maritime climate which has a predominantly humid and hot weather.  A  study was carried out to assess and predict the outdoor environment at a proposed development to contain seven multi-storied buildings in Singapore. The pedestrian level airflows were determined using a Computational Fluid Dynamics  software  for various predominant wind velocities  and directions. At certain locations in the developments, outdoor sedentary activities, such as outdoor restaurants were considered. For such places, the local air velocities can  be  combined with the relative humidities and dry bulb air temperatures to calculate the Predicted Mean Vote (PMV) to predict the thermal comfort levels, assuming that the space is shaded from the direct sun. The other physical parameter in the comfort equation is the mean radiant temperatures. While it is possible to simulate the surface temperatures by considering the solar geometry and a database of solar radiations, the present study concentrated on the CFD simulations and the mean radiant temperatures were assumed to be 2 degrees above the dry bulb air temperatures. This assumption is based on a thermogarpic study of building surfaces under shades, in which the surface temperatures were found to be about 2 degrees above the air temperatures for over a large percent of time. In warm and humid climatic areas, air movements are very welcome as it can remove the sweatings by convection and evaporation. The original development plan showed pockets of stagnated air, which are very uncomfortable. With help of CFD simulations, modifications were suggested for the building designs to offer more airy environments around the buildings. The solution opened up the possibilities of enjoying the outdoor green environment and leisurely pastimes by the owners, tenants and visiting public to the development.