Passive downdraught evaporative cooling wind-towers: A case study using simulation with field-corroborated results

Abstract

Passive downdraught evaporative cooling wind-towers (cool-towers) have received special interests for their energy saving potential. Improving their performance and broadening their use will therefore be environmentally and economically beneficial. This paper presents a case study where cool-towers are designed and constructed to provide cool air to the semi-open courtyards of the Princess Nora University campus located in the hot, arid region of Riyadh, KSA. Each courtyard is served by two cool-towers, each of 30 m2 cross-sectional area, 32.8 m height. A brief on the system design is provided. The cool-towers performance is investigated through computational fluid dynamics simulation. Temperature and velocity profiles indicate an induced, cooler air breeze in the courtyard; outside air is cooled from 46℃ to 34–38℃, while the induced space velocity ranges from 1.5 to 3.5 m/s. A 560 kW cooling capacity is attained per tower. A substantial energy saving of around 3.30E+05 kW-h per courtyard per season is achieved. The expended energy associated with the used water is only 1% of the saved cooling energy. The normalized water consumption is around 0.04 kg/s per 100 kW cooling. The effect of distance between the towers on their performance is examined. The predicted performance is corroborated through field measurements. Practical application: This article looks at a new breed of cooling wind-towers, which artfully blend the traditional principles behind a wind catcher with today’s technological advances. It tackles a study case where cool-towers are designed to cool outdoor courtyards across the Princess Nora Bint Abdul Rahman University (PNU) in Riyadh, Saudi Arabia. Using CFD, we find that the cool-towers are capable of generating a relatively comfortable zone in the courtyard. The result is an effective, power-efficient piece of technology that transforms the campus environment and the outdoor experience for students. The PNU cooling wind-towers are exceptional power savers, and demonstrate the power of tradition working in tandem with engineering ingenuity.