Development of a prototype of Secondary loop Mobile Air Conditioning System

Tata Motor, an Indian car manufacturer, recently signed a partnership with the German automotive supplier Mahle to design and develop a Secondary Loop Mobile Air Conditioning System (SL-MAC), under the aegis of the United Nations Environment Program (UNEP), and thanks to a funding from the Climate and Clean Air Coalition (CCAC). The project is also coordinated by the US-based Institute for Governance and Sustainable Development.

 

The project envisages use and trial of two low global warming potential (GWP) refrigerants, R1234yf and R152a. R1234yf is a A2L refrigerant, meaning it is mildly flammable. It is often used to replace R134a in mobile air conditioning systems. Its GWP is around 1. R152a is very efficient but it is flammable and categorized as A2 refrigerant. Its GWP is 124.

 

A Tata vehicle based on a new generation platform for utility vehicles has been selected for this joint development program. The SL-MAC system will first be installed in this vehicle as a prototype. In the SL-MAC system, the alternative refrigerants first cool a secondary fluid/coolant, which in turn cools the air to comfortable temperatures inside the vehicle cabin. According to the developers, this process would “allow the safe use of slightly flammable refrigerants with high cooling capacity, minimizing the losses and achieving an optimized overall thermodynamic efficiency in the process”¹.

 

This system will turn off the compressor during acceleration and will retain coolness when the compressor is inactive or the engine is turned off for a short duration, allowing rapid cool-down at re-start. In addition to the expected energy efficiency benefits (fuel saving of up to 3%), the SL-MAC system allows the use of refrigerants that should avoid flow into the vehicle cabin. The refrigerant never enters the passenger compartment and instead stays in the engine area. Only the coolant circulates through the interior air conditioning unit.

The developers intend to compare the life-cycle carbon footprint of HFC-152a to the carbon footprint of HFO-1234yf, and to estimate the manufacture and ownership cost of each system.

 

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¹ See Reuters brief from July 13, 2017