Exergy analysis of cooling towers for optimization of HVAC systems

Abstract

Exergy analysis is a useful thermodynamic technique for assessing and improving the efficiency of processes and systems. By examining the exergy destruction properties, it is possible to optimize the environmental and economic performance of the systems. This research applies exergy analysis technique to investigate and optimize the performance of evaporative cooling towers in HVAC (heating, ventilating and air conditioning) systems. The analysis is carried out in two steps. The first step considers the physical exergy of each component and process within a whole HVAC system for a typical office building. The building’s cooling load and cooling energy requirements are determined by building energy simulation software. Exergy destruction and exergy efficiency of the system are calculated from theoretical models. The result indicates that the exergy loss of cooling tower is quite significant, and the loss is affected by outdoor environment and condensing water temperature. The second step considers the chemical exergy of condensing water and outdoor air. A counter-flow wet cooling tower is investigated by experiments and theoretical models. The dry-bulb temperature and relative humidity of outdoor air are studied by an exergy approach in order to maximize the cooling tower performance. The distribution of exergy loss within the system has been shown and information to minimize exergy destruction and optimize the system efficiency can be determined.