Mathematical modeling of a low temperature low approach direct cooling tower for the provision of high temperature chilled water for conditioning of building spaces

• Article presents a mathematical model of an open direct contact cooling tower.
• The tower optimised for producing low temperature water for building cooling systems.
• The proposed model has ability to integrate to building energy simulation.
• Cooling tower coefficient used in the model is based on an experimental correlation.

Recent interest in cooling towers, as a means of producing chilled water in conjunction with radiant systems for cooling in buildings, has prompted interest in evaporative cooling in temperate maritime climates. For such climates, evaporative cooling has the potential to offer an alternative approach to refrigeration-based air-conditioning systems for producing chilled water, where conventional refrigeration-based systems can, for certain buildings, be considered to be an over engineered solution and where passive cooling is insufficient to offset cooling loads. The thermal efficiency of evaporative cooling systems is a key performance indicator, as a measure of the degree to which the system has succeeded in exploiting the cooling potential of the ambient air. The feasibility of this concept depends largely however, on minimizing the approach water temperatures within an appropriate cooling tower, at acceptable levels of energy performance. Previous experimental work for a full scale evaporative cooling system has shown that it is possible to produce cooling water with low approach temperatures (1–3 K), at the higher temperatures required in radiant and displacement cooling systems (14–18 °C), with varying levels of annual availability for different temperate climate locations. The current paper is concerned with the development of a mathematical model which describes the behavior of such a low temperature low approach direct evaporative cooling tower. The mathematical model is evaluated against experimental data reported for a number of open tower configurations, subject to different water temperature and ambient boundary conditions. It is shown that the discrepancies between the calculated and experimental tower outlet temperatures are to within ±0.29 °C for a low temperature cooling water process (14–18 °C), subject to temperate climate ambient conditions and ±0.57 °C for a high temperature cooling water process (24–30 °C), subject to continental climate ambient conditions. Considering the associated tower cooling loads, predicted results were found to be within a 6.93% root-mean-square difference compared to experimental data. Furthermore, the influence of different cooling tower coefficients on water outlet temperature and heat rejection of tower is investigated.