New Tool Estimates Climate Impact of MAC Systems

Optimized Thermal Systems (OTS), a Beltsville, Md.-based R&D consultant, has developed a new tool for estimating the life cycle climate performance (LCCP) of a mobile air-conditioning (MAC) system, which calculates the system’s total lifetime CO₂e greenhouse-gas (GHG) emissions.

OTS developed the software – dubbed the Improved Mobile Air Conditioning Green House Gas Life Cycle Climate Performance (IMAC-GHG-LCCP) tool – in concert with the Society of Automotive Engineers (SAE), said Cara Martin, COO of OTS. The new tool builds on a previous model, GREEN-MAC-LCCP, developed by General Motors.

OTS presented a detailed paper on the software, “Development of a Tool for Estimating the Life Cycle Performance of MAC Systems,” at SAE’s WCX  (World Congress Experience) conference, held in Detroit last April. The paper looks at the GHG emissions of MAC systems, including  refrigerants R134a, R152a, CO₂ (R744) and R1234yf. 

“The IMAC-GHG-LCCP) tool is now available for license to the industry," said Martin. "OTS will continue to further develop and support the tool's use,” said Martin.

The LCCP of a system is calculated by adding up its direct and indirect CO₂e emissions. According to the paper, a MAC system’s direct emissions, which are its refrigerant lifetime leakage, include leaks during operation, leaks due to accidents, service-related emissions, end-of-life emissions, leakage during refrigerant production, and atmospheric degradation products. A MAC system’s indirect emissions include those associated with component and refrigerant manufacture, MAC operation, fuel use and equipment.

“With this information, automobile manufacturers are able to make evidence-based design modifications, meet applicable standards, and select the most appropriate refrigerants to reduce the emissions of greenhouse gasses,” said the OTS website.

Several improvements

According to the website, the IMAC-GHG-LCCP tool features several improvements over its predecessor, including a simplified user interface, decreased runtime  and expanded weather-data selection. User input options have been expanded to include the type of refrigerant, leakage rate, vehicle type, vehicle lifespan and climate conditions for more cities.

In addition, the new tool can address the use of electric compressors and water-based systems in MAC systems. “This gives auto manufactures a stronger start in the transition to electric cars on a mass scale,” said the OTS website. “With this new tool, capacity and power consumption inputs for a vehicle using an electric compressor can be entered for each combination of ambient temperature and vehicle speed, instead of ambient and compressor RPM as for a belt-driven compressor. This encourages the evolution of existing technologies and enables the testing of new MAC technologies.”

Also incorporated is support for systems with multiple evaporators, multiple chillers, and additional sources of power consumption beyond the compressor.

The paper suggests that future development of the software may include additional detail for electric cars, including heat pump systems.