EVAPORATIVE COOLING OF EXTERNAL WALLS and ITS INFLUENCE ON INDOOR AIR TEMPERATURES IN AN EQUATORIAL CLIMATE Assoc. Prof. S P Rao 1 , Ati Rosemary Ariffin 2 , Nila Inangda Kesuma 3 Dept. of Architecture, Faculty of Built Environment University of Malaya, 50603 Kuala Lumpur, MALAYSIA e-mail : 1 rao@alambina.um.edu.my 2 ati@alambina.um.edu.my 3 nimk@alambina.um.edu.my ABSTRACT Malaysia and Singapore are located close to the equator and hence are subjected to a very harsh, hot and humid climate. The Solar radiation intensities are coupled with high relative humidity values. Due to the increased affluence of the population, air conditioning of buildings (both commercial and residential) has become one of the design necessities. It is thus imperative to determine the optimum design conditions for thermal comfort so that we can utilise the natural energies in achieving thermal comfort or to minimise air-conditioning usage as an energy conservation strategies. This paper reviews the thermal comfort requirements under the equatorial climate. These are based on actual measurements done in Malaysia and in Singapore on a fairly large population sample. Wetting of the external wall is proposed as a strategy to attain the desired room conditions, without resorting to air-conditioning. The wetting of the external wall acts effectively as a shading device as well as to increase the heat transfer rate at the external surface. Some of the test results are presented. The results would be applicable to buildings in an equatorial climate. Using the evaporative cooling for external walls can lead to considerable energy savings in buildings in an equatorial climate. 1.0 INTRODUCTION [1] 1 Mean radiant temperatures are important considerations of thermal comfort. There are different types of equatorial climates varying from the hot dry to the hot humid. It is the hot humid climate that has posed difficulties in achieving a thermally comfortable environment indoors. Sun is the single most important natural element to be considered in building design. It affects virtually every design decision and has a direct impact on the indoor thermal comfort as well as on the energy budget of the building, if it is air-conditioned. The main features of a hot-humid climate, are the relatively uniform temperatures, high relative humidities and abundant rainfall due to its proximity to the equator. There are no large diurnal variations in temperature. Also, throughout the year the temperatures are fairly uniform. The mean monthly temperature does not vary by more than 1.1 °C from the mean annual value of 26.6 °C. The average diurnal variation of temperature is about 7.0 °C. Excessively high or low temperatures are rarely experienced. For the period 1934 to 2000 the 1 Numbers in parentheses indicate references at the end of the text World Renewable Energy Congress VII (WREC 2002) Copyright 2002 Elsevier Science Ltd. All rights reserved. Editor: A.A.M. Sayigh