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The National Renewable Energy Laboratory (NREL) has developed a transient air conditioning (A/C) system model using SINDA/FLUINT analysis software. It captures all the relevant physics of transient A/C system performance, including two-phase flow effects in the evaporator and condenser, system mass effects, air side heat transfer on the condenser/evaporator, vehicle speed effects, temperature-dependent properties, and integration with a simplified cabin thermal model. It has demonstrated robust and powerful system design optimization capabilities. Single-variable and multiple variable design optimizations have been performed and are presented. Various system performance parameters can be optimized, including system COP, cabin cool-down time, and system heat load capacity. This work presents this new transient A/C system analysis and optimization tool and shows some high-level system design conclusions reached to date.

The National Renewable Energy Laboratory (NREL) has initiated projects to investigate the benefits and design challenges of using heat pipe/two-phase flow technologies to provide sub-system cooling and thermal management in future advanced vehicles, hybrid electric vehicles, and heavy-duty vehicles. Projects initially focused on vehicle instrument panel (IP) heat pipe cooling and passenger seat thermal management, but will also investigate engine cooling, electric motor cooling, and battery cooling in the future. Experimental results have demonstrated IP surface temperature reductions of 20°C-30°C during maximum solar intensity environments of 525-800 W/m2 (typical of Golden, CO from January to April) compared to uncooled conditions. The heat pipe cooling effect in the IP also reduced windshield temperatures by 9°C-12°C compared to the non-cooled configuration in April 2001 testing.

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.