Parametric Study on the Effect of a Domestic Wind Catcher-Solar Chimney System for Arid Regions

To reduce dependence on non renewable energy resources for domestic cooling systems, and thereby reducing global warming, one can think of adopting passive cooling systems in combination with one another. Wind towers or wind catchers are stand alone systems widely used in hot, hot dry and (or) hot humid climates. These tall towers installed on the roof-tops capture wind for cooling the interior dwelling spaces. On the other hand, a solar chimney is a natural way of improving ventilation by virtue of thermal buoyancy effects on air. Within the regions of a room where the circulatory wind speed is low, a solar chimney can be installed in combination with a wind catcher in order to improve the efficiency of the system. We have performed various simulations on such a combinatorial windcatcher-solar chimney system for a closed dwelling space (no windows or other infiltration regions), in order to understand the parametric effects (i.e., dependence on incident (solar) heat flux, E on absorber; ambient wind speed, U∞ and width of air gap in chimney, e) of such a system on the convective air current within the dwelling space. It became evident that substantial air motion can be attained within the closed region with such a combination. The solar chimney in such a system is found to be most effective (incremental improvement in air current) for moderate heat flux on the absorber and lower ambient air speeds (almost 60% increase in room inlet air velocity is observed for such a system with E = 500 W/m2, U∞=3m/s), while at higher wind ambient wind velocities (U∞=5m/s), the main contribution for air current within the room is due to the windcatcher (an increase of nearly 5 times when ambient air speed changes from 1m/s to 5m/s with E = 500 W/m2). Also, a change in windcatcher geometry may not always adversely affect the room air entry velocities if proper blending and smoothing of possible corners and edges are provided. However, frictional losses and thus reduction in flow velocity within the windcatcher cannot be completely avoided since the sudden bends are deliberately provided inorder to settle dust and sand particles carried by dry air in arid geographical regions where such systems are in use. A test case of such a combinatorial system applied for specific geographical location (Jaipur, Rajastan) is also presented.