Experimental Study Of Solar Chimney For Natural Ventilation In Buildings～2

In the recently years, more emphasis is given to energy conservation and passive system in order to maintain a clean environment. Natural ventilation is thought of as a low energy cooling strategy which can provide healthy and comfortable interior environment, with flexible user control, at a low capital and maintenance cost. Ventilation is generally defined as a supply of outside air to the interior for air motion and replacement of stagnant air by fresh outside air for healthy and comfortable interior environment. For natural ventilation, there are two causes of air motion through the building, namely, (i) wind force.(ii)thermal or temperature force or stack effect. A solar chimney generates air movement by buoyancy forces, in which hot air rises and exit from the top of the chimney, drawing cooler air through the building core in a continuous cycle.The solar chimney system is a natural draft device,which integrates the two organically.It uses solar radiation to provide upward momentum to a mass of air,thereby converting the thermal energy into kinetic energy.A vertical roof solar chimney model for natural ventilation in buildings were experimentally studied.A theoretically and experimentally study has been carried out to predict airflow rate, temperature field and velocity field for different chimney gap and heat flux.The experimental solar chimney has internal dimensions of 2.0m high, 1.0m length and a variable chimney gap from 400 to 1200mm. Results showed that, for veritical roof solar chimney,there is an optimum ratio of chimney gap-to height to achieve a maximum airflow rate. The optimumratio of chimney gap-to height is about 1/2. The airflow rate increases with solar radiation.Meanwhile,temperature field and velocity field of solar chimney were analyzed. Air velocity inside solar chimney decreases with the increase of chimney gap and increases with theincrease of solar radiation. Air temperature inside solar chimney increases with the increase of solar radiation and solar chimney height. It is seen that the air temperature distributions across the chimney gap are not uniform, with higher air temperatures near the heated surface, the temperature rose when approaching the opposite surface of the heated shims. This temperature rise is caused by the radiation from the heated shims.Satisfactory correlation was abtained with numerical data from other investigations.