• Energy Research

Range reduction caused by climate control is a barrier to widespread adoption of electric vehicles (EV). Higher efficiency and lower energy consumption by the air conditioning system will mitigate this disadvantage, as power consumption inside electric vehicles is a very relevant issue. Moreover, several European Union directives prohibit the use of HFC 134a or any other fluorinated greenhouse gas with a Global Warming Potential (GWP) higher than 150 in new mobile air conditioning systems by January 2017. The Adoption of environmentally friendly refrigerants and minimizing the charge of refrigerant gas would be a viable option to endorse the EU directives. In this lecture, alternative climate control systems which profit from the advantages of thermochemical energy storage will be presented. In order to investigate the suitability of these systems for the high temperature fuel cell range extender vehicle (HTFCREX) developed by the DLR Institute of Vehicle Concepts, suitable climate control systems based on the use of hydrogen are developed, modeled and designed using the simulation environment Modelica/Dymola and the Air Conditioning Library. Based on simulation results, the alternative climate control systems are compared with regard to their efficiency, weight, volume and performance. These systems exhibit a reduction of 5 % to 22 % of electrical energy consumption depending on the system design in comparison to the reference HVAC.

In this work, an innovative vehicle air-conditioning unit that provides heat, cold and electric power is presesented. The environmentally friendly unit is based on the integration of two alternately working compact metal hydride reactors between a hydrogen pressure tank and a fuel cell. At the component-level the design and testing of two small lab-scale reactors is explained. At the vehicle-level it is shown that it is possible with this hydrogen-based unit to reutilise up to 75% of the compression work in the tank to increase the range of fuel cell cars by up to 8% in hot weather conditions.

In comparison with common combustion motor driven vehicles future electric driven vehicles vary more in their reachable range because of the high drive train efficiency and the different energy demand requirements in different drive conditions. One of the main issues to improve the overall range is the minimization of energy consumption. On the one hand an adapted energy management strategy is needed to achieve a more comfortable and acceptable equalization in the range. On the other hand it is important to recuperate mechanical, electrical and thermal energy, both inside and from the vehicles wherever possible. For example, it is thinkable to use the kinetic energy of braking vehicles outside the vehicle to power traffic lights. If a combustion process is used, a lot of waste thermal energy can be reused from the tailpipe. Or solar energy may be used. If a vehicle has a varying duty-cycle it makes sense to adapt the powertrain to suit the power need. Whatever the available energy, it has to go hand in hand with minimizing the energy consumption. This paper is based on the knowledge and combination of future technologies [2], which are useful to collect and convert energy coming from different sources within a vehicle.

Abstract High pressure storage of hydrogen is the established storage technology for automotive systems. However, around 15% of the lower heating value of hydrogen is spent to compress hydrogen up to the pressure of 700 bar. Since this energy is available on board but so far wasted, an open air-conditioning system based on metal hydrides is promising to reutilize this compression work. Here we present the experimental demonstration of a first of its kind system. The setup consists of two alternately operating plate reactors, each filled with around 1.5 kg of Hydralloy C2 ( T i 0.98 Z r 0.02 V 0.41 F e 0.09 C r 0.05 M n 1.46 ), coupled to a polymer electrolyte membrane fuel cell. The demonstration at an electrical power of 5 kW shows that the fuel cell operation is not affected by the alternately H2 desorbing reactors (half-cycle duration of 150 s). The system’s average cooling power was 662 W for an ambient temperature of 30 °C and a cooling temperature of 20 °C, reaching of specific cooling power of 227 W k g M H - 1 . Related to the maximum obtainable cooling power of 18.3% of the electrical fuel cell power, the cooling efficiency corresponds to 75%. As an innovative hydrogen pressure transducer the presented system can be transferred to all applications where an unused hydrogen pressure difference is available.

Abstract An open cooling system based on metal hydrides is a promising new technology to reutilize the compression work in a hydrogen pressure tank by generating heat or cold. Our first of its kind system consists of two alternately operating plate reactors, which are filled with around 1.5 kg of Hydralloy C2 ( T i 0.98 Z r 0.02 V 0.41 F e 0.09 C r 0.05 M n 1.46 ) and coupled to a polymer electrolyte membrane fuel cell. In the present study, an extensive performance investigation for a variation of the main influencing parameters is performed: The electrical fuel cell power and the operating temperatures. Overall, it can be observed that in the entire range of various operating conditions, the fuel cell operation is not affected by the alternately operating H2 desorbing reactors. The variation of the electrical fuel cell power between 1.8 and 7.9 kW results in a maximum average cooling power of 807 W at an electrical power of 7 kW, reaching a specific cooling power of 276 W k g M H - 1 . The systems performance decreases with rising ambient temperatures (varied in the range: 24.3–42.3 °C) and decreasing cooling temperatures (varied in the range: 13–25.4 °C) due to increased thermal losses and reduced half-cycle times. Concluding the parameter variations, optimization recommendations are given and the expected performance for an improved system design is derived.

In this paper, different waste heat recovery concepts for a high temperature fuel cell range extender vehicle developed by the DLR Institute of Vehicle Concepts will be presented. These concepts use thermochemical heat storages to recover thermal energy from the powertrain waste heat and to re-use it for heating purpose before or during the drive. The focus will be on metal hydride storages, which have a higher specific energy density than the phase change energy storages and will thus be more advantageous for vehicle application. In order to investigate the developed waste heat recovery concepts in the entire vehicle, appropriate simulation models will be created in the simulation environment Modelica/Dymola, then integrated into an overall vehicle simulation model. It is found that the integration of the thermochemical heat storages into the fuel cell thermal management system leads to increase the range by up to 17 %.

A battery electric vehicle equipped with a range extender is a suitable solution for both urban and long-distance traffic. Compared with the internal combustion engine-powered range extender the fuel cell range extender is a zero emission solution and has been investigated for many years. In this work a system for hydrogen storage for the heating and cooling of a high temperature polymer membrane fuel cell range extender itself using a metal-hydride storage tank [1] is investigated. In order to survey the suitability of this system for electric vehicles, an overall vehicle simulation model using the AlternativeVehicles library [2] is developed. Taking into consideration the challenges that are now placed on modern cars, several scenarios such as cold start and normal operation are created. For these scenarios suitable operating strategies are developed and integrated into the overall vehicle model. Based on various driving cycles the thermal and electrical behavior of the thermally coupled high temperature polymer membrane fuel cell and the metal-hydride storage tank is investigated.

Due to the heating and cooling requirement of the passenger compartment and powertrain components such as the fuel cell, battery, electric motor and power electronics, the fuel cell electric vehicles have increased vehicle thermal management complexity compared to the conventional cars with internal combustion engines. The use of different systems for the cooling and heating of the different components results in increased weight and higher costs. Additionally, the required energy for the thermal management system is provided by the fuel cell and the battery, which is critical to fuel cell vehicle performance and causes reduction in the electric range. The DLR Institute of Vehicle Concepts examine an optimized thermal management system for the fuel cell electric vehicles, which uses thermochemical heat storages in order to minimize the electrical energy required by the thermal management system compared to current solutions. Current work details various thermal management concepts based on thermochemical heat storages, which are able to store the waste heat and generate not only heating but also cooling. In order to survey the suitability of these thermal management concepts for the fuel cell electric vehicles, an overall vehicle simulation model using the AlternativeVehicles library is developed. According to the data of a fuel cell range extender vehicle, which is based on the Smart Fortwo vehicle and uses a high temperature polymer electrolyte membrane fuel cell as a range extender unit, the overall vehicle simulation model has been parameterized and validated with experimental data. Based on various driving cycles and thermal boundary conditions the reduction in the energy consumption using the different thermal management systems is demonstrated. It is shown that the operating range of the fuel cell electric vehicle can be extended by up to 17 per cent.