Solar heat gains through train windows: a non-negligible contribution to the energy balance
The sector of transportation accounts for about one third of the total energy consumption in Switzerland. A monitoring campaign of the energy consumption of a regional train revealed the critical energy-consuming systems. Heating, cooling and ventilation were identified as major consumers. Windows are a source of non-controlled heat transfer. In summer, it may result in overheating leading to larger cooling loads while in winter, it is an important source of thermal losses. Selective double glazing and solar protection coatings can reduce these effects. Angular-dependent optical properties of a selective double glazing have been measured, and the solar heat gain coefficient (g value) was determined. An estimation of the solar gains received by a panoramic waggon was performed using the monitored solar irradiation and the measured properties of the glazing. These data were compared to the heating and cooling energy consumption monitored in this waggon. Solar gains were found to be in the same order of magnitude that the heating energy during some sunny days. They were also compared to the estimated thermal losses through the glazing and the entire envelope. These results show that the solar gains play a non-negligible role in the energy balance of the waggon. Furthermore, thermal simulations were performed to evaluate the solar gains in different conditions. It showed that 7 to 13% of energy can be saved using the glazing adapted to the climatic conditions. In addition, improving the thermal insulation of the train envelope or equipping the train with an efficient heat recovery system can lead to significant energy savings.
KeywordsEnergy efficiency Public transportation Railway Solar heat gains Energy consumption HVAC Heating Cooling Selective glazing Solar protection Solar irradiation
We gratefully acknowledge Swisselectric Research SER for funding the project “Energy Efficiency of Heating, Ventilation and Cooling in Public Transport” with financial support from the Swiss Federal Office of Energy SFOE and the Federal Office of Transport FOT. We are grateful to our railway company partners BLS and RhB for their help and made the measurement campaign possible. We thank our industrial partner AGC for providing us with glass samples. We are also thankful to all the academic partners involved in this project: University of Basel, Lucerne University of Applied Sciences an Arts and EMPA Dübendorf and SUPSI. We thank Samson Taylor for proof-reading. Moreover, we acknowledge the valuable contributions of Christoph Isenschmid (BLS AG), Hans Burkard (Opit Solutions AG) and Roland Steiner (Uni Basel) for technical support and providing the drawing of the window test bench and Leo Fäh (Rhätische Bahn AG) for providing the photograph of the GEX train.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
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