Solar heat gains through train windows: a non-negligible contribution to the energy balance

Abstract

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 energyconsuming 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 nonnegligible 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.

Heat and Moisture Relevant In Situ Measurements in a Railway Passenger Vehicle Driving through the Swiss Alpine Region

“…A study focused on the transparent portion of the envelope has been reported by Bouvard et al [6], where the impact of the solar gains on the HVAC energy consumption of a panoramic train (large windows) has been investigated. They showed that the incoming energy due to the solar gains is in the same order of magnitude as required for the heating or cooling systems, and that an appropriate choice of the glazing can lead to energy savings of 7 to 13%, depending on the climate.…”

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“…As such they require mechanical cooling (air conditioning) and ventilation. This, however, consumes a considerable amount of energy, [131] with the result that manufacturers and operators tend to recirculate most of the air and minimise the amount of 'fresh' outdoor air that is supplied to the carriages. [132] CO2 concentrations >1 800 ppm [132][133][134] and as high as 5 525 ppm [135] have been recorded on urban railway carriages during peak periods (CO2 concentrations in well-ventilated spaces are generally <1 000 ppm).…”

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“…In 2018, Bouvard [21] from Switzerland estimated the solar heat gains through train windows; the result shows a 7–13% energy savings from using glazing adapted to the climatic conditions. Solar gains play a non‐negligible role in the energy balance of the wagon.…”