ANALYSIS OF SUPPLEMENTARY HEATING SYSTEMS FOR AUTOMOBILES BASED ON A R744 AIR-CONDITIONING SYSTEM

摘要

A fast warm-up of the passenger compartment is a substantial comfort and safety criterion for automobiles. However, modern high-efficient engines often do not provide enough waste heat at low outside temperatures for a fast heating of the interior. Thus the importance of supplementary heating devices rises. In this context an air conditioning system with the refrigerant R744 offers an efficient possibility. The supplementary heating system can be realized as a simple triangle process or a more complex heat pump. As heat source for the heat pump both the ambient air and the engine cooling cycle are applicable. The numerical simulation of steady state and transient operating conditions can be a helpful tool for the design and optimization of the thermal management of an automobile. For the transient behaviour the thermal masses of the material and thus the warm-up of the components play an elementary role. In this case the use of simulation models that consider the thermal capacities is necessary. This paper describes the analysis of different set-ups of a R744 circuit for supplementary heating. Experimental investigations built the framework for the verification of the simulation results and a comparison of an air/air heat pump, a coolant/air heat pump and a hot gas cycle. The systems have been investigated with respect to the system performance, air temperatures and heating capacity. Special attention is drawn to the simulation of the refrigerant cycle at transient operating conditions.