Passive solar cooling systems in hot-arid climates, The architectural implications of

Abstract

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Architecture, 1988.Includes bibliographical references (leaves 245-250).Residential architectural design should fulfill both the comfort and the social requirements of the occupants. Khartoum, the capital of the Sudan was chosen for this study because of two reasons; The first is its unusually hot-arid climate (thus cooling interior spaces becomes a crucial design consideration). and the second is its multi-dimensional urban identity. The city is a mixture of African, Arab, and European influences and resembles at the same time an oasis in the middle of the desert. The research follows two distinct but closely related paths. The first is the study and analysis of the passive and hybrid cooling systems and strategies under which the climatic conditions of Khartoum determines the type and size of each approach. The second stage of the research will focus on the architectural implications of these systems. Both directions lead to better understanding of the built environment and its interactions with man. Two moves were taken into account, when considering the cooling potentials in this climate. First, the solar control strategies which were found to be most appropriate in Khartoum climatic conditions. These include the use of eggcrate shading devices on all openings except for southern exposures which can be shaded effectively by vertical fins to reduce the solar transmission through glazed surfaces. The study showed also that reducing the glazed area reduces the total heat gain but this affects negatively both daylighting and the freedom of design to incorporate the exterior spaces. This can be solved by using the Low-E glass which has better thermal properties in terms of reducing both solar transmission and heat conduction. The results of the study showed that using single Light-Green Low-E glass allows one and half times larger glass area with the same amount of heat gain. For the same area, the Double Low-E glass can reduce heat gain form these surfaces by a factor of two. Economically, their use is hard to justify because of their projected high prices as compared to the DS single pane clear glass. Another effective way of controlling the heat gain through buildingskin is to use thermal insulation on the walls and roof. Roof insulation which Is commonly specified in Khartoum was found to be thermally satisfactory and additional insulation will not reduce heat gain appreciably since the roof share is already reduced with basic insulation. The wall insulation strategy proved to be economically feasible and does not require skilled labor to install or to maintain since it is protected from the weather. Landscaping is another move that will improve the environmental quality through shading and evaporatively cooling the surrounding spaces and at the same time add to the visual quality of the space, but it is not cost effective. The second move was to promote heat losses through ventilation, convection, radiation, and evaporation. Because of the environmental condition of Khartoum, the first three moves are restricted to certain parts of the day or the year. Nevertheless, combination of either one with evaporative cooling increases the thermal comfort. The desert-type evaporative coolers reduce the indoor temperature and increase the relative humidity which is required in the dry periods of the year. Two-stage coolers which combines both evaporative (adiabatic) and sensible cooling concepts increases the rate of heat removal and thus reduces obtained indoor temperature. The air scoops or wind catchers are convective and evaporative cooling systems that admit high winds at high elevations to be circulated inside living spaces for ventilation. This air can be further cooled be passing the air stream over wet Clay jars or through wetted pads.by Adil M.K. Sharag-Eldin.M.S