Dynamic Modelling and Performance Prediction of a Multi-unit Baseline Air Conditioning System for a Generic Bus under Part-Load Conditions

A dynamic model of a multi-unit air conditioning system in a generic bus was developed to investigate different control strategies on the system performance and the cabin comfort level. In this study, a part-load condition was considered, where adopting a proper strategy for governing a multi-unit system is important. Simulink and Simscape toolbox from MATLAB (R2019a) were used to build up the real-time model by integrating a cooling system with a cabin sub-model. The cooling system consists of two independently controlled units, based on a Vapour Compression Cycle (VCC). The cabin is modelled using a moisture air network and is coupled with the cooling system to exchange heat with the refrigerant through the evaporators. Moreover, the sensible and latent loads are incorporated into the cabin by a thermal network. Six different strategies were implemented using different criteria, to investigate the average power and COP (Coefficient of Performance) under a part-load condition. The comfort level was obtained in terms of the Predicted Mean Vote (PMV) and Predicted Percentage of Dissatisfied (PPD) indices. Results are suggestive of a link between the implemented control strategy of a multi-unit AC system and its performance. Results showed that five out of the six proposed strategies might be chosen, depending on the adopted trade-off policy between the comfort level and the system energy demand. In this way, the numerical approach introduced here along with the combination of the presented findings, provide a good support for the decision-making on thermal management inside the cabin, based on the energy consumption and the thermal comfort level.