Pre-design of an air cooling system used by a solar chimney. Simulation with ANSYS® Fluent

Abstract

Passive ventilation systems are being proposed as an alternative method to mechanical ventilation systems in view of their potential benefits in terms of operational cost, energy requirement and carbon dioxide emission. Solar chimney is a passive ventilation system, which relies on solar energy. A significant amount of research has been done on solar chimney since the 1990s. Solar chimneys are generally tall wide structures constructed facing the sun, with a dark coloured matt surface, designed to absorb solar radiation. As the chimney becomes hot, so it heats the air inside it. The hot air rises up the chimney and is vented out of the top, drawing more air in at the bottom of the chimney. Due to the complexity that presents the design of a solar chimney, the present work focuses on the design of the inlet of the system, where a heat exchanger will be placed so as to refrigerate the air coming from the outside of the building. The heat exchanger components are found in DIY stores. The first stage of this work is focused on the determination using empiric models of the heat exchanger necessary to refrigerate air from the outside of the building using a staggered tube bench filled with water at 18 ºC. The different inlet temperatures tested are 34 ºC, 30 ºC and 26 ºC, reached in summer in the city of Barcelona. With the tube diameters used, 8 mm and 12 mm, the total number of tubes necessary to refrigerate the air is 20 in both cases. Subsequently, the results obtained are compared with a heat exchanger designed using ANSYS®. In a second stage, on the basis of the data obtained from the empiric equations, different heat exchangers are designed and modelled using ANSYS® software, proposing two final designs, which are tested in different initial conditions. All of the designs proposed provide a considerable [increment]T in order to make the temperature inside the building comfortable though some of them has a considerable [increment]P.