Tata Motors and MAHLE partner to develop a prototype Secondary Loop Mobile Air Conditioning System on a vehicle
Tata Motors Limited and MAHLE have signed a joint development agreement for designing and developing a Secondary Loop Mobile Air Conditioning System (SL-MAC), under the aegis of United Nations Environment.
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. This process allows the safe use of slightly flammable refrigerants that have a low GWP and in turn achieves high cooling capacity, minimizing the losses and achieving an optimized overall thermodynamic efficiency in the process. This is in contrast to the conventional mobile AC system, where the cabin air is directly cooled by the refrigerant HFC-134a, which is ozone safe but has a high GWP.
The new SL-MAC system, which is testing the low-GWP refrigerants, is expected to increase vehicle energy efficiency. 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.
MAHLE and Tata Motors, along with the Institute for Governance and Sustainable Development (IGSD), which is coordinating the project, received funding for developing the SL-MAC system from the Climate and Clean Air Coalition to Reduce Short-Lived Climate Pollutants (CCAC), a global initiative to support fast action and make a difference in the areas of climate, public health, and food and energy security. This project envisages use and trial of environment friendly, low global warming potential (GWP) refrigerants HF01234yf (ASHRAE A2L) and HFC-152a (ASHRAE A2).
ASHRAE is the American Society of Heating, Refrigerating and Air-Conditioning Engineers. A2L and A2 are safety classifications.
A team comprising representatives of the California Air Resources Board (CARB), the Mobile Air Conditioning Society Worldwide (MACS), the National Renewable Energy Lab (NREL), MAHLE, Tata Motors, and IGSD reviewed the newly constructed SL-MAC system and the prototype at the MAHLE Behr facility in Lockport, New York in April.
A Tata vehicle based on a new generation platform for utility vehicles, consisting of a more complex architecture with front and rear air conditioning system, has been selected for this joint development program.
The SL-MAC system will first be installed in the Tata utility vehicle as a prototype.
The Secondary Loop System will permit the use of alternative refrigerants like HFC-152a (GWP of 138) and HFO-1234yf (GWP<1) which have much lower GWPs than the current most-commonly used refrigerant, HFC-134a (GWP of 1300). We will be comparing the life-cycle carbon footprint of HFC-152a—with a higher GWP offset by higher energy efficiency—to the carbon footprint of HFO-1234yf, and we will be estimating the cost of manufacture and ownership for each system.— Dr. Stephen O. Andersen, Director of Research for IGSD
The SL-MAC project is on schedule, as expected, with anticipated environmental and cost advantages to be determined in the next stages. The prototype will be tested on the Indian roads later in the third quarter of 2017, where long seasons of hot and humid weather and stop-start driving conditions make a secondary loop air conditioning system highly advantageous.
Andersen, S., Chowdhury, S., Craig, T., Kapoor, S. et al. (2017) “Comparative Manufacturing and Ownership Cost Estimates for Secondary Loop Mobile Air Conditioning Systems (SL-MACs),” SAE Technical Paper 2017-01-0173 doi: 10.4271/2017-01-0173