Computational analysis of indoor air circulation and heat transfer in a house ventilated by wind-catch

摘要

Considering that natural ventilation is a climatic factor, a renewable alternative, as well as an important source of comfort, it seems to be relevant to consider its great potential when applied to architecture, taking into account economical and environmental gains. It is difficult to think about studying air circulation without mentioning the north Africa vernacular architecture and its ability to create the best solutions to increase the ventilation without any energy consumption, therefore, adopting passive cooling. According to Hassan Fathy (1986) - an Egyptian architect who developed a collection of fruitful works using natural ventilation and local materials - in that region, ventilation, light and view could not be associated at the same time to a single window because each function demands a different window configuration. Criative systems of passive cooling appeared in these areas and among them the wind-catch or malqaf can be distinguished. It was created to improve ventilation requirements catching wind from high above, where the air is cooler, stronger and with less sand and other particles, and channeling it down into the building. In agreement with Fathy. another advantage of the malqaf is the possibility of solving the problem of screening that is the consequence of building settlements in a ordinary town plan. In Egypt the malqaf is very developed and its first usage dates back to ancient historical periods. In this work, based on the writings of Fathy (1986) we analyse numerically one case in which wind-catch is used. It is the Qa'a of Muhib AdDin Ash-Shafi Al-Muwaqqi. known as Othman Katkhuda, in Cairo, dated from the fourteenth century A.D. presented in Fathy's book, (Fathy 1986). The analyses start by solving the air circulation problems to determine the wind fields, using a mixed stabilised finite element method applied to the full Navier-Stokes equations. With these wind fields, the heat transfer problem is solved and analysed. Numerical results are compared with the studies presented by Fathy (1986). The results obtained suggest the capacity of cooling the indoor air by improving the ventilation with a reasonable arrangement of openings only.