Design and Transient Simulation of Vehicle Air Conditioning Systems

Abstract

This paper describes the need for dynamic (transient) simulation of automotive air conditioning systems, the reasons why such simulations are challenging, and the applicability of a general purpose off-the-shelf thermohydraulic analyzer to answer such challenges. An overview of modeling methods for the basic components are presented, along with relevant approximations and their effect on speed and accuracy of the results. THE MOTIVATION: THE NEED FOR DYNAMIC MODELING Major Department of Energy (DoE) objectives include developing innovative transportation technologies and systems that decrease vehicle fuel consumption and emissions across the nation, thereby reducing the nation's reliance on foreign oil consumption. Recent changes to the Federal Test Procedure have added SC03 and US06 drive cycles to form the Supplemental Federal Test Procedure (STFP), with corresponding requirements for evaluating vehicle emissions during additional driving conditions. In particular, the SC03 drive cycle is specifically intended to evaluate vehicle emissions while the air conditioning (A/C) system is operating in typical high-temperature, high solar load conditions. The US06 drive cycle is intended to evaluate vehicle emissions during more high speed, high acceleration conditions. The addition of the SC03 drive cycle creates a significant need for better understanding the impact of dynamic conditions (i.e., vehicle external environments, passenger compartment environments, etc.) on the vehicle A/C systems and their dynamic response to these conditions. Since vehicle A/C systems represent the major auxiliary load on the engine of light-duty passenger vehicles, sport-utility vehicles (SUV), and heavy-duty vehicles, the A/C system performance has a dramatic effect on fuel consumption and exhaust emissions. Recent studies (Ref 1) have shown that, during the SC03 drive cycle, the average impact of the A/C system over a range of light-duty vehicles was to increase 1) fuel consumption by 28%, 2) carbon monoxide emissions by 71%, 3) nitrogen oxide emissions by 81%, and 4) non-methane hydrocarbons by 30%.

An advanced nonlinear switched heat exchanger model for vapor compression cycles using the moving-boundary method

“…hardware-in-the-loop/ software-in-the-loop simulation, embedded system emulators) require that the code run in real-time. While finite volume or finite difference models are fully capable of predicting system transients (Cullimore and Hendricks, 2001;MacArthur and Grald, 1989;Eborn et al, 2005;Limperich et al, 2005), Grald and MacArthur (1992) showed that the ''lumped parameter'' or ''moving-boundary'' method is much faster. Even though real-time capability using a finite volume technique has been demonstrated by Rossi and Braun (1999), the faster speed of the moving-boundary method has caused it to become the method of choice for controls' purposes (Rasmussen, 2006;Willatzen et al, 1998;He et al, 1995;Leducq et al, 2003;Cheng and Asada, 2006;Jensen and Tummescheit, 2002) The primary reason for the speed difference is that the moving-boundary method divides the heat exchanger into a minimum number of zones (at most three), representing regions where refrigerant is in the superheated vapor, saturated mixture, and sub-cooled liquid phases.…”

A New Automotive Air Conditioning System Simulation Tool Developed in MATLAB/Simulink

“…Some examples of previously developed non-commercial full system-level simulation include [6,7,8]. However, to the best of our knowledge, none of them is both developed in the widely used dynamic system simulation platform MATLAB/ Simulink (which is helpful for controls engineers) and available to the public at the same time.…”

Coupling Between an Accumulator and a Loop in a Mechanically Pumped Carbon Dioxide Two-Phase Loop

“…SINDA/FLUINT is a comprehensive software package used by over 400 sites in the aerospace, energy, electronics, automotive, aircraft, HVAC, and petrochemical industries for design, simulation, and optimization of systems involving heat transfer and fluid flow. It is the NASA-standard analyzer for thermal control systems (Baumann et al 2000;Cullimore et al 2004a, b, Cullimore 2001Cullimore and Hendricks 2001;Hendricks 2001;Panczak et al 1998).…”