94 the HVAC module is measured in detail in test bench setups. This task is performed by an experienced cooperation partner, IPETRONIK GmbH & Co. KG, with whom ARRK Engineering has been working closely on thermal management for 10 years. In addition to the HVAC module, the measurement of all other relevant components, such as those of the refrigeration circuit, can also be carried out by IPETRONIK GmbH & Co. KG. In order to transfer the hardware measurements to the simulation, a detailed model of the vehicle cabin and occupant is also required, which is created using ARRK‘s proprietary simulation software THESEUS-FE. To represent the occupants, the tool includes a complex human model based on the Fiala occupant model. It imitates the human body functions relevant for air and heat exchange such as breathing, blood circulation, sweating as well as cold shivering and considers different clothing situations. In order to provide detailed boundary conditions on all parts of the body for thermal comfort statements with the human model, the tool enables a very fine and automated discretization of the total air volume into individual air zones with the newly developed “pseudo-3D approach”. Furthermore, the simulation speed is enormously increased by the “pseudo-3D approach”, which is essential for the highly dynamic transient simulations. Within the air zones, detailed statements can be made in each case about the air velocity, temperature and humidity as well as about the long-wave and shortwave radiation. Of course, in summer load cases, the position of the sun and the areas illuminated or shaded by it are automatically determined as a function of the vehicle and window geometry as well as the vehicle orientation. Since the air and surface temperatures influence each other, THESEUS-FE considers radiation, flow and heat conduction processes on a defined component as a coupled system. Finally, the comfort index according to ISO 14505-2, which describes the thermal sensation in vehicle cabins on the basis of the equivalent temperature and is implemented in THESEUS-FE, represents the basis for the evaluation of the measured and modeled thermal comfort. With the help of this index, objective statements about the influence of different dynamic factors on the climate comfort in the vehicle interior shall be made. Finally, these should be available for the definition of general comfort and air conditioning targets – and consequently for the creation of universal specifications. Development of a comfort use case for transient climate load cases Once the individual models have been correlated, the resulting simulations will have to be compared with real driving data in the coming months and any sources of error and inaccuracies in the calculations identified and compensated for. To this end, test drives have already been carried out with the ARRK dummy developed in-house. This is equipped with 31 sensors evenly distributed over the body for measuring air temperature and humidity, long and short wave radiation and wind speed. A revised version of the dummy is currently under development. In the future, it will not only have around three times the number of sensors, but will also be able to record additional values such as contact heat flows. The effects that interact during such journeys are caused on the one hand by the external climate, the course of the road intraurban or out of town, and changing direct and indirect solar radiation from different angles and directions. In addition to these external factors, which affect the occupants and the thermal comfort they perceive depending on their age, physical condition and body mass, the respective number of people in the passenger compartment also plays a role. Once the simulations have been verified, the focus shifts to the final project: the numerous factors influencing the vehicle interior climate and thus the comfort value are to be evaluated and objectified in all their facets. The future of thermal comfort assessment and application As soon as ARRK Engineering can simulate these dynamic journeys with sufficient precision and speed, the last major step in the development process for air conditioning and climate comfort will be tackled. After all, when all the pieces of the puzzle necessary for calculating the transient load cases can be reproduced virtually, this puts the specialists in the promising position of being able to derive concrete effects on the climate-related well-being of the occupants from these values. Accordingly, objectified action instructions for the thermal management system with integrated control of the HVAC system can follow. Once these dynamic processes are recorded in a comfort specification, the actual application work in the test vehicle can be reduced to a minimum, namely only the fine-tuning on the final vehicle. In this way, the use of the virtual application, which can be used to address changed load cases and boundary conditions early, quickly and easily, will result in significantly reduced development time compared to manual application. This will fundamentally change the future approach to thermal comfort assessment and application in automotive development. ARRK Engineering www.arrk-engineering.com Share Due to increasing competition in the industry, thermal comfort in the vehicle cabin is increasingly coming into focus as a differentiating feature. Image: © hiphotos35/iStock Engineering expertise – Two strong partners. A well-rehearsed team. ARRK – IPETRONIK is a cooperation based on partnership to implement development scopes of thermal management constructively, simulatively, functionally as well as in testing and trials. IPETRONIK as a measurement technology manufacturer with individual test bench solutions and engineering is the ideal complement for ARRK as a strong engineering service provider with knowhow in the entire vehicle development. For years, the partners have been working together with OEMs and Tier1s on components and systems from the early development phases to series production. As a result, ARRK and IPETRONIK can draw on in-depth know-how and are very familiar with all the processes and specializations of a wide range of manufacturers. A successful cooperation that stands for component and system development in the field of thermal systems for the future.
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