Investigations of thermal- and climate conditions in the Koralm railway tunnel

Research output: ThesisDoctoral Thesis

Abstract

Railways represent an essential part of the European transport system and travel infrastructure. The Trans-European railway network has become even more important in recent years and, respectively, decades. The Trans-European Network Transport (TEN-T) contains several trans-European railway tracks, such as the Scandinavian-Mediterranean railway route and the Baltic-Adriatic axis. Both of these railway tracks are partially located in Austria and are currently in phases of construction. Along these routes, three long railway tunnels encompass core sections of the new Austrian railway tracks. In addition to the Brenner-Basistunnel (BBT - Brenner base tunnel, which will be the longest railway tunnel in the world when operation begins, the Semmering-Basistunnel (27 km) and the Koralmtunnel (33 km) will begin operation in the near future.
Generally, several specific aspects need to be addressed to operate such long high-speed tunnels. This is a new experience for the Austrian Federal Railways (Österreichischen Bundesbahnen, ÖBB), mainly due to the limited accessibility and technical equipment required along a tunnel track, e.g. the power supply, telecommunication, remote control and ventilation systems . This equipment is required for standard railway operation but also improves travel comfort and is necessary if a tunnel incident occurs, such as a fire event. For successful tunnel operation, high track availability must be ensured. For this reason, the technical equipment have to withstand unfavourable conditions, as they are exposed to the atmosphere in the tunnel. One major consideration is the effect of thermal loads on sensitive components. Since these components are usually hosted in separate utility rooms to reduce dust and mechanical loads, thermal loads determine the actual lifetime of the components. Several parameters influence thermal conditions in a tunnel, but their impact varies with time and the position in the tunnel. Austria’s newly built high-speed railway tunnels are constructed as twin-tube, single-track tunnels , which are connected by cross passages positioned at equal distances of 500 m. These cross passages mainly serve as escape routes that can be used in an incident situation, but additionally provide the possibility to host the utility rooms.
In previous investigations, researchers found that utility rooms would require cooling systems to keep the operation temperature below an acceptable level. Because tunnel air is the only available cooling medium inside the tunnel, two different cooling concepts can be applied. One is a simple ventilation system which extracts supply air from the tunnel tubes and directly guides it into the utility rooms. The second involves air conditioning systems that are suitable because they have an enhanced cooling potential and separate technical facilities from the tunnel atmosphere. Both systems have advantages and disadvantages. The main advantage of a ventilation system is its simplicity, robustness and the reduced electromechanical effort needed for operation, but sensitive components cannot be separated from the tunnel atmosphere. For this reason, supply air has to be filtered. In addition, the cooling effect strongly depends on the tunnel climate and is thereby limited. Nevertheless, such a ventilation system can offer economic advantages if thermal requirements can be met. The second option, an air conditioning system, comes along with a significantly higher electromechanical effort leading to higher initial investment costs; and significantly increased operational costs. The advantages of this system is that it enables the separation of utility rooms from the tunnel atmosphere and keeps the room air temperature within a well-defined range, thus extending the lifetime of sensitive components.
This doctoral thesis describes the results of extended investigations that were carried out on the tunnel climate in long railway tunnels. Since the tunnel climate must be treated individually for each tunnel, these investigations were based on characteristics of the Koralmtunnel (KAT). In general, the investigations were carried out to provide decision-making data for the selection of cross-passage cooling systems. The methods chosen to generate such data were numerical simulations and in-situ measurements made in a real tunnel environment. Basic numerical investigations were carried out using a one-dimensional CFD solver, which was especially developed for tunnel applications. A common three-dimensional CFD solver was used to perform a detailed assessment of the three-dimensional effects. While the 1D CFD simulations provided a forecast of the tunnel climate for 50 years of operation, 3D simulations were carried out for optimization purposes. Results from the 1D CFD simulations also served as input data to calculate an energy balance for the cross passages and individual utility rooms. In this context, heat sources known for the technical facilities were used to determine the utility room temperatures. Since strict room air temperature requirements are defined for each individual utility room, the tunnel air cannot exceed a certain temperature level, if a ventilation system will be used to cool the utility room.
The initial results derived from the 1D CFD simulations and the calculated energy balances assumed that a permanently active ventilation system was used for utility room cooling. These results show that the room air temperature could only be kept below the target value in a few utility rooms. Since these simulations were based on an idealized approach (i.e. the temperature distribution was not considered), 3D simulations were performed to obtain more detailed information. These simulations relativized the results from the 1D CFD simulations in some aspects, since a well-defined temperature stratification within the rooms could be determined. Sensitive components are mainly exposed to moderate temperature levels which are approximately the same as the tunnel air temperature levels. Further simulation runs were conducted to focus on the ventilation control, including an on/off regime for the supply air fan. Results show that sensitive components were not exposed to high temperatures for a period of 70 s, even if the maximum temperatures at the ceiling exceeded 60°C.
A research project funded by the Austrian Federal Railway was carried out to verify the results derived from 3D CFD simulations. This project placed a focus on testing power supply facilities in a real tunnel application, exposing them to an unfavourable tunnel atmosphere. In addition, extensive measurements of thermal conditions in the utility rooms, PM monitoring, as well as determinations of the filter service life were performed in a railway tunnel application. Over a test duration of about two years, 14 test scenarios were run to consider various target temperatures, high humidity and high dust loads. The measurements confirmed the results from the 3D numerical simulations: A well-defined temperature stratification was observed independent of the general temperature level in the utility room. Wall surface temperature measurements gave information regarding the probability of condensation in the utility room. Condensation effects could not observed during the entire measurement period. Nevertheless, condensation effects can not be completely prevented, but are unlikely to occur in a utility room, since the heat released by the technical equipment in the utility room increases the temperature.
The comparison of the results of numerical investigations and in-situ measurements supported the technical optimization of the cross-passage cooling systems. To take a holistic approach toward the design process of technical facilities, an assessment of financial aspects is always required. To address these aspects, a lifecycle cost analysis was carried out with project partners from TU Graz, ÖBB and ACTES Bernard. This analysis enabled the identification of an optimum target temperature for the telecommunication room. This, in turn, enabled the categorization of cross passages as either being most suitable for the installation of a ventilation system or an air conditioning system. Several relevant input parameters were varied in the LCC analysis, including a variation of the target temperature. Four target temperature scenarios within a temperature range of 22–35°C were defined. A dynamic approach was applied in the generated economic model. An optimum target temperature of 30°C was ultimately identified at which the LCC are the lowest. To support this statement, the LCC analysis was complemented by a dominance analysis and a sensitivity analysis for selected parameters.
However, when considering both economic and operational aspects, an optimum target room air temperature of 25°C was identified in terms of lifecycle costs and track availability. These results indicate that using a combination of ventilation and air conditioning systems to cool utility rooms provides optimal results.
Independent of the thermal investigations, a second research topic emerged during the intensive study of the topic of the operation of such long railway tunnels. Dust loads in tunnels always present a special challenge, as these affect cooling systems.
For this reason, extensive particulate matter (PM) monitoring was performed in addition to the thermal investigations in an Austrian railway tunnel. PM concentrations in tunnel air as well as the chemical dust composition were analysed. The derived PM concentration curves were used to determine non-exhaust PM emission factors for various train types. Results show that freight trains have PM emissions that are about seven times higher than passenger trains.
The in-situ measurements were supported by the observation of a pressure loss across a single-stage particulate matter filter. This assessment was used to forecast the expected filter lifetime in a real tunnel application, i.e. approximately half a year.
Translated title of the contributionUntersuchungen zu den thermischen und klimatischen Bedingungen im Koralmtunnel
Original languageEnglish
QualificationDoctor of Technology
Awarding Institution
  • Graz University of Technology (90000)
Supervisors/Advisors
  • Sturm, Peter-Johann, Supervisor
  • Borchiellini, Romano, Advisor, External person
Award date16 Dec 2021
Publication statusPublished - 30 Oct 2021

Keywords

  • railway operation
  • tunnel climate
  • particles
  • Cooling

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