HVAC systems for trains, metro and tramways: dynamic simulation modelling for an energy efficient design and case study

Nowadays, for modern trains high indoor comfort standards as well as reduced HVAC systems electricity demands are required. Note that, in such trains the energy consumption due to heating and cooling systems can reach 30% of the overall electricity demand. The design of new trains as well as the revamping of the existing ones have to take into account new criteria regarding comfort, energy efficiency needs and avoided CO2 requirements. The dynamic simulation approach can be today considered as a possible effective tool for reaching the above mentioned aims (by simulation results optimal system layouts can be achieved). In this paper the energy, economic, environmental impact and thermal comfort performance analysis obtained through several innovative actions regarding the train envelope -HVAC system are investigated by means of such tool. To this aim, a novel dynamic simulation model was developed and implemented in TRNSYS (version 17). Here, innovative system layouts are compared to traditional system configurations. Note that, all the train components as well as the train trips can be suitably modelled by using TRNSYS environment. In particular, the train envelope geometry and the related energy features are developed by means of the Google SketchUp TRNSYS3d plug-in and TRNBUILD (Type 56), respectively. A suitable simulation case study is also presented. It refers to an existing regional train traveling on a typical daily trip in South-Italy for a whole year. Here, space heating and cooling loads and demands, as well as the related electricity requirements, are dynamically assessed by considering the effective loads profiles and the different occurring train orientations during the whole trip. A number of energy efficiency actions are modelled for the railway coach envelope-HVAC system revamping. Specifically, they refer to diverse refrigerant fluids, different compressors, on-off and inverter technology, free cooling option, CO2 sensors for modulating the outdoor air, heat recovery exchangers and heat pump for the heating season (instead of electric resistances). For the train envelope the considered actions regard the thermal insulation typology, cool paints, selective window glasses. LED lightings are also considered for replacing the conventional devices. The obtained simulation results are compared to those of the traditional system. Significant benefits in terms of energy saving, avoided CO2 emissions and comfort are achieved. Useful design and operating criteria for trains manufacturers and users are also provided