Vehicle climate control

 

Energy Efficient HVAC and Thermal Comfort in Automobile Cabins

 

Heat Transfer Measurement of Automobile Structural Components

Copyright: EBC Fig. 1: Thermographic photography of a test car with inner heat

For numerical simulation and benchmark of total energetic performance of vehicles the knowledge of specific values regarding to the behavior of heat transfer is required. This is particularly of interest if energetic simulation models are employed, to evaluate the performance of automotive heating, ventilation and air conditioning systems. A solution is measuring the heat transfer coefficients of the automobile structural components. Creating a test bench, there is the problem how to place the components to reproduce the influence of the thermal bridge of the adjacent parts respectively to achieve a generally adiabatic case. Therefore, it was developed a simple and practically orientated proceeding for an integral measurement and estimation of the heat transfer for automobile components.

 
 

Measurement of Air Change Efficiency in Car Cabins

Copyright: EBC Fig. 2: CO2 concentration at different positions in the cabin

Heating and cooling of the inlet air cause an energy demand with a direct effect on the range of electrical vehicles. With the aid of a CO2 measuring system the air change efficiency in car cabins can be determined. Hence an evaluation of different variations in terms of the air flow can be enforced. The best cases defined by the lowest required air flow and avoiding of short circuits can be identified as a result of these investigations. Therefore, reducing the air change rate under compliance with a maximum value for carbon dioxide fraction in the air leads to minimized energy demand in regard to the air conditioning system.

 

Subject Group Experiments for Thermal Comfort

Copyright: EBC Fig. 3: Test persons evaluate different air conditioning scenarios

In addition to numerical simulation subject group experiments are used for evaluation of different climate control setups, concerning the optimization of energy efficiency and thermal comfort. Therefore, the indoor air conditions are evaluated by a panel of test persons. These test persons are questioned in regard to the thermal comfort and the thermal sensation for different ventilation scenarios. For simple handling the questionnaire is completed on an IPadŽ. Attendant to this, the thermal boundary conditions are measured and the flow field within the cabin is visualized for selected scenarios.

 

Coarse Grid Simulation of Air Flow in Car Cabins

Copyright: EBC Fig. 4: Simulated and measured air temperature inside the car cabin

The flow field inside of a car cabin is very important to ensure high air exchange efficiencies and good thermal comfort for the occupants. The usual way to simulate the air flows are CFD simulations with very fine grids. These grids lead on the one hand to high accuracies. On the other hand, they take very long to create results. Because of this, coarse grid simulation methods with a real-time functionality are used to simulate a 3-dimensional result of velocity, temperature and humidity. A comparison between a measurement and a simulation result at a given setting is represented in figure 4.

 

Innovative Concepts for Conditioning of Car Cabins

Copyright: EBC Fig. 5: Simulated heat demand (l) and relative humidity close to window (r) or different AC setups

Holistic car models were developed, which allow a detailed comparison of different innovative car cabin conditioning concepts. These models contain different methods of heat generation and contribution and are coupled with the 3-dimensional coarse grid air flow model. Furthermore, a combination with a complex comfort model is possible. This set of models makes it possible to compare different systems like window-heating, surface-heating, heat recovery etc. and combinations of those. The air flow model can provide important information like the prognostic relative humidity close to the windows to avoid safety related condensation.