Mobile HVAC-System with CO2 as Refrigerant - Simulations and Measurements

Nowadays automobile air conditioning systems normally use R134a as refrigerant. Due to increasing concerns regarding global warming this hydrofluorocarbon (GWP = 1300) seems not to be a long-term solution. In the field of automotive air conditioning CO₂ (R744, GWP = 1) is a promising alternative. It is a high-pressure working fluid, which demands new designs of the components, but offers many possibilities, e. g. the use of the AC system for supplementary heating.

The importance of simulation tools is increasing in order to reduce time and cost in the developing process. Most of these programs only consider the steady state behavior, but the transient performance is of importance for the simulation of the start-up phase (cool-down or warm-up).

Due to the different physical properties of CO₂ new models have to be developed. One of the main focuses of the current work is to develop component models for transient simulation. To obtain reliable results, experimental investigations are of essential importance.

This paper describes:

• The setup of the test rig which is used to verify the simulation results,
• the basic principles of the simulation models, and
• comparisons of computed results and measured data at different operation conditions.