Automotive Climate Systems - Investigation of Current Energy Use and Future Energy Saving Measures

Doctoral thesis, 2016

Automotive climate systems use energy to achieve thermal comfort for the vehicle passengers. This energy use affects vehicle fuel consumption. The objectives of this thesis are to understand the energy use of automotive climate systems and investigate the effect of different energy saving measures. The research was conducted in several steps. First, comprehensive laboratory measurements of a complete vehicle, a Volvo S60. The main focus of the measurement was on heat flows and electrical and mechanical work of the climate system. Second, the most important climate systems were modelled with a one dimensional commercial software. The modelled systems were the passenger compartment, air-handling unit and air conditioning system, although engine, water jacket, cooling circuit, oil circuit and drivetrain were also included. Third, development of a test cycle representative for real-world conditions. The test cycle was based on hourly ambient conditions around the world weighted with sales distribution of Volvo Cars and departure time. In the last step, the model and developed test cycle were used to investigate different energy saving measures. The measurement demonstrated that the energy use can be reported individually for better understanding of the system. That is, the different heat flows from sources to sinks and the electrical and mechanical work can and should be presented separately. Furthermore, the developed test cycle showed that intermediate conditions, ambient temperatures from 5 to 22°C, were by far the most common. Combining the simulation model and test cycle provided an estimation of current energy use of automotive climate systems. In average the system used 180 W of electrical power, 475 W of mechanical power, a total of 1820 W for heating and 1030 W for cooling. The average heat flow into the passenger compartment was 1190 W for heating and 280 W for cooling. 26 energy saving measures were investigated. Few single energy saving measures could decrease the energy use significantly, however, combinations of measures had a large potential. A reduction of the electrical power with 50% and the mechanical power with 44% were possible with realistic measures. Further, the heat flows into the passenger compartment could be reduced with roughly 20% for both heating and cooling. Measures on the source side, how the heating and cooling was generated, showed most potential. The results show that how the system operates in intermediate conditions determines the energy use. The interaction between the automatic climate control system, the air conditioning system and the requirement of de-humidification have a large influence on the operation of the climate system in these conditions.