Evaluation of Interaction and Blockage Effects for Multi-fan Units used in Public Transport HVAC Systems

Abstract

A specific type of centrifugal fan named the "squirrel-cage" is broadly used in parallel configurations within an evaporator unit of HVAC systems for public transport. In these units, interaction effects arise, both between fans themselves and between fans and the structural elements. Blockage effects, such as the electrical motor, the evaporator gate and some aesthetic covering may also appear when these external elements are located very close to the fans aspiration nozzles. In this work, an experimental study of different configurations enables the determination of the minimum distances between the elements of the multi-fan unit, in order to minimise these interaction effects and, as a consequence, the problems related to them. Also, the quantitative influence of different motor sizes, covering solutions and the evaporator gate on the fans performance have been determined. Appreciable performance losses were found due to these blockage effects, thus recommendations to avoid the location of any external element close to the fans aspiration nozzles are proposed. The practical conclusions obtained in this work could be of interest to manufactures of HVAC systems subjected to installation size restrictions and where fan performance be optimized with low fabrication costs. This is usually the case for many HVAC systems, not only in the public transport applications considered in this paper.