Improvimg the energy efficiency in hvac systems through evaporative cooling

Abstract

The national and European legislative framework has, among its objectives, the improvement of energy efficiency of air conditioning equipment. Hence, the need to explore alternative air conditioning systems aimed at reducing energy consumption compared to existing systems. In this regard, systems capitalizing on the benefits of evaporative cooling represent one of the most effective solutions. This thesis aims to investigate two approaches to achieve this goal. The first involves the use of cooling towers, which are based on this principle but have the drawback of causing significant environmental impact due to the water droplets emitted during the process. The other method involves precooling the incoming air of conventional air conditioning equipment using ultrasonic atomisers, a technique that lacks references in the literature.This thesis addresses the experimental characterization of the thermal performance and emission levels of a novel cooling tower prototype that has been designed and patented to prevent the release of suspended particles into the atmosphere. The aim is to reduce the environmental and health impact typically associated with such evaporative cooling systems. The experiments were conducted in a pilot plant built ad hoc for this purpose.In the environmental impact assessment (drift emissions), the sensitive paper method was used. A comparison between the obtained results and those found in the literature for similar cooling towers indicates that performance of the inverted cooling tower in terms of emissions is remarkable, with a drift rate of 1.47 ⋅ 10 −6 kg/s (0.00015% of circulating water). This value is up to 130 times lower than the limits imposed by several international standards and involves a reduction in terms of emissions ranging from 40.21% to 82.54% compared to commercial towers. Regarding the size of the droplets escaping from the tower, the results were also promising, with a maximum diameter of 50 μm and a Sauter Mean Diameter of the ensemble of droplets of 31.42 μm.Concerning thermal performance evaluation, the studied tower is classified as a mechanical forced draft, counterflow-parallel flow cooling tower. For this reason, the influence of the analysis method (Merkel and Poppe) and the arrangement of flow between the water and air streams (counterflow, parallel flow, and counterflow/parallel flow) on the tower's performance under specific operating conditions has been discussed. The main novelty lies in the use of the Poppe model combining two different flow arrangements: parallel flow and counterflow. Additionally, the adaptation of the Poppe model for parallel flow, which is an approach not commonly found in the literature. From this analysis, it is concluded that the most appropriate method for assessing the thermal performance of this innovative prototype is one that uses the Poppe theory and combines counterflow and parallel flow arrangements to evaluate thermal performance. This approach not only it provides the best predictions for the outlet water and air temperatu...