Proceedings of the
5th International Seminar on
ORC Power Systems
9 - 11 September 2019, Athens Greece
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Exhaust Waste Heat Recovery for Intercity Bus Climatisation Using Rankine Technology with Focus on Topology Design

Go-down orc2019 Tracking Number 35

Session: Session 4C: Waste heat (2)
Room: Templar's
Session start: 14:00 Tue 10 Sep 2019

Maximilian Hebeler
Affifliation: TU Braunschweig / Institut für Thermodynamik

Philipp Ebeling
Affifliation: TLK Thermo GmbH

Wilhelm Tegethoff
Affifliation: TLK Thermo GmbH

Jürgen Köhler
Affifliation: TU Braunschweig / Institut für Thermodynamik

Topics: - System Design and Optimization (Topics), - Simulation and Design Tools (Topics), - Waste heat recovery (Topics), - Oral Presentation (Preferred Presentation type)


In times of increasing energy prices and decreasing CO2-emission limits it becomes compulsive to improve energy efficiency. This does not only account for the sector of passenger cars but also for public and commercial passenger transportation, like intercity busses, which transport often more than 30 passengers. For short distance intercity busses one way of achieving this goal is to electrify the powertrain, since the needed range can be covered with current battery technologies. For long-range intercity busses with travel distances up to 1000 km or even further it is still more feasible to use an internal combustion engine (ICE). However, as a rule of thumb one third of the supplied chemical energy is converted into mechanical work, one third is rejected via the cooling system and one third is rejected as hot exhaust gas into the environment. That last portion of energy still comprises an unused exergetic potential. In order to use that exergetic potential a Waste Heat Recovery (WHR) system can be applied, e.g. an Organic Rankine Cycle. This system can be used for either reducing the engine load mechanically or by driving auxiliary loads e.g. the alternator or the refrigerant compressor, and thereby reduce fuel consumption. The compressor of the Air-Conditioning (AC) System of an intercity bus uses up to 15 kW of additional mechanical power from the engine, which reduces the effective work output for vehicle traction. For the period of a long haul journey that power input accounts for around 8 % of the overall diesel fuel consumption. Therefore, combining the waste heat recovery and air-conditioning system is a promising method for reducing primary energy usage. Still, it is a challenge to combine these two systems efficiently, since there are many possible topologies to consider. In this work, three topologies for air-conditioning using exhaust waste heat are presented. The first topology uses direct mechanical coupling between WHR system, ICE and AC system. The second topology uses an indirect thermal coupling, where the AC condenser is used as a preheater for the WHR system. The third topology is based on a combined Organic Rankine Cycle and Vapor Compression Cycle (ORVC), where AC and WHR are using the same working fluid and share the condenser. The focus of this work is on simulating the presented three topologies with respect to transient exergetic potential as well as optimal operating strategies. The goal of that topology comparison is to preevaluate, respectively analyze benefits and drawbacks of those configurations for further research. In addition, it is discussed if hybridization of components or subsystems can enhance system performance. The simulations are based on real life driving cycles such as journeys from Hannover to Munich and real life weather data.