In a similar way, the compressor in the prototype engages when the vehicle is decelerating or going downhill and disengages when it is accelerating or climbing, maximising energy efficiency. Saved energy is stored in the anti-freeze coolant. That feature is possible in any vehicle equipped with a secondary loop or other cold storage device, but the specimen produced by the TATA team is the most finely tuned and highly engineered so far. As the test results demonstrate, the energy savings achieved by this feature more than compensate for the weight of extra parts needed under the car bonnet to accommodate the refrigerant and secondary loop.
The savings in service cost and fuel easily pay back the minor extra upfront cost of around $35 for the SL-MAC system. “Our automotive partners estimate that in India, you need to service older HFC-134a mobile air conditioning systems two or three times in the lifetime of a car. In the new SL-MAC, you service it as little as once,” points out Kristen N. Taddonio, Senior Climate and Energy Advisor to IGSD. That means fewer trips to the garage, and less inconvenience when booking an appointment and waiting. For some commercial fleets, it could cut costs significantly.
Then there is the comfort factor. In most vehicles, it takes 60 seconds for the air conditioning to work every time you start the car. In the SL-MAC, cooling starts immediately after short stops subject to the coolant being cold enough. With the reservoir of energy in the cold antifreeze coolant, the car occupants remain comfortable for longer even if they leave the engine switched off.
But let’s keep in mind the whole reason behind the invention in the first place – the climate. If automakers replaced all HFC-134a MACs with HFC-152a SL-MACs in cars worldwide starting in 2020, we would save billions of tonnes of greenhouse gas emissions by 2050.
The amount of refrigerant needed to cool an SL-MAC-equipped vehicle is less than that of conventional MACs. SL-MAC cars also have a lower leakage rate due to fewer joints in the primary refrigerant circuit. That is why the SL-MAC used with HFC-152a achieves extraordinarily low emissions from the refrigerant, as well as from fuel used to power the MAC.
That is a major consideration, given the massive contribution refrigerants currently make to global warming. According to climate scientists, HFCs would account for an increase in global warming amounting to 0.5˚C if no action is taken – a major portion of the maximum 1.5 or 2˚C of further warming that the planet can tolerate. Of that HFC contribution, 25% to 35% comes from automobiles.
The secondary loop does add complexity. With ab initio engineering of the SL-MAC, including architecture, integration with the engine management systems, higher quality heat exchangers and fittings, it is possible to overcome any disadvantage.
“Automotive manufacturers are looking for every competitive advantage in terms of improving fuel efficiency and reducing costs, so the SL-MAC represents an exciting opportunity,” says Dr. Nancy J. Sherman, Director of Technical Assessment, IGSD. Environmental considerations also weigh heavily on automotive manufacturers and branding due to regulations in place or on the horizon. Any major car producer is of course going to consider fitting similar systems to electric vehicles too. Nowadays, any brand that lays claim to advanced, cutting edge design has to include climate-friendly equipment.