Abstract
The use of a solar chimney for ventilation has a very significant environmental and economic impact. The aim of this work is to found the optimum ratio between height and base length in trapezoidal prism-shaped solar chimney. The idea is to give more flexibility to the architectural design in buildings and offer the possibility of combination with other passive or active systems. Trapezoidal shape of solar chimney can be interesting not by increasing the efficiency comparing with other shapes like the rectangular. It may be more aesthetically pleasing, easily to be installed and retrofitted on trapezoidal roofs even on existing buildings. For this reason, three differents ratios of height to base length (h/l = 1), (h/l = 1.5) and (h/l = 2) have been experimentally studied. Two correlations to predict solar chimney exit air velocity and efficiency were developed and tested; good agreement with experimental results is proved. Results show that the flow rate increase by increasing (h/l) in a logarithmic tendency. The optimum thermal efficiency is given where h/l = 1.65. An approach using RETScreen4 software was also carried out and showed that 1 m² solar chimney installed in favorable conditions can cover 37 m² of living space in term of ventilation. For a 120 m² house, solar chimney system saves the equivalent of 23.9 liters of gasoline per year.
Highlights
Natural ventilation of buildings is the flow generated by buoyancy driving force and by the wind
The aim of this work is to found the optimum ratio between height and base length in trapezoidal prism-shaped solar chimney
Trapezoidal shape of solar chimney can be interesting not by increasing the efficiency comparing with other shapes like the rectangular
Summary
Natural ventilation of buildings is the flow generated by buoyancy driving force and by the wind. Vertical chimney may be not the good architectural arrangement, e.g. when the roof is designed to be a solar chimney, this is why different geometries are studied to obtain the maximum thermal efficiency and flow rate. I×S where η is the thermal efficiency, ρl is the density of the air at chimney temperature, Cp air specific heat (J/kg °K), Tin and Tout are temperatures at chimney inlet and outlet, I incident solar radiation ( W/m2 ), S is the absorber area. The cylindrical outlet is used to allow the combination with other systems such as Stack height effect improvement and facilitates adding of other systems like heat recovery or heating by means of a fan to direct hot air to the internal space in future studies. (c) Fig. 2 (a) Solar chimneys and weather station installation, (b) Schematic experimental setup, (c) 3D illustration of the solar chimney (trapezoidal prism shape)
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