Using R744 (CO2) to Cool an Up-Armored M1114 HMMWV

The US Army uses a light tactical High-Mobility Multi-Purpose Wheeled Vehicle (HMMWV) which, due to the amount of armor added, requires air conditioning to keep its occupants comfortable. The current system uses R134a in a dual evaporator, remote-mounted condenser, engine-driven compressor system. This vehicle has been adapted to use an environmentally friendly refrigerant (carbon dioxide) to provide performance, efficiency, comfort and logistical benefits to the Army. The unusual thermal heat management issues and the fact that the vehicle is required to operate under extreme ambient conditions have made the project extremely challenging.

This paper is a continuation of work presented at the SAE Alternate Refrigerants Symposium held in Phoenix last June [1]. It presents both wind tunnel and on-road field test data taken on the vehicle as well as breadboard data in the laboratory that demonstrate both superior efficiency and capacity of the CO2 system when compared to the R134a system. It has been a huge collaborative project that has included support from a system integrator and component supplier (Modine), a compressor supplier (Obrist Engineering, GmbH), a university (University of Illinois at Champaign, IL) and two groups within the US Army (CERDEC and PEO CS&CSS PM LTV). The excellent results (and significant improvements made since Phoenix) show that CO2 is indeed a viable alternative for the US Army's vehicular cooling needs in terms of logistics, performance, durability and cost.