Cold comfort

Delphi Automotive Systems has developed an automotive air conditioning system that lowers vehicle cabin temperature and fuel consumption.

When the mercury rises, the interior of your vehicle can feel like an oven. No wonder, then, that so many people turn on the air conditioning to cool things down.

But that welcome feature has a few drawbacks: It reduces your fuel economy and can increase vehicle emissions. Now Delphi Automotive Systems has developed an automotive air conditioning system that lowers vehicle cabin temperature and fuel consumption.

For years, people have been trying to cool vehicles. In early attempts, drivers even placed buckets of water on the floor. As air flowed across the water, it dropped in temperature and cooled the cabin.

Evaporative cooling systems soon followed. Then, in 1939, Packard produced the first passenger cars with actual refrigeration system air conditioning (A/C). Cadillac followed suit in 1941, and in 1954, Delphi Harrison Thermal Systems engineered an air conditioning system that located all the major components under the car’s hood.

Since then, automotive air conditioning has blown through the industry. Today, A/C is installed on 91 percent of new vehicles in North America and on 70 percent of new vehicles worldwide. What’s more, some of these vehicles now have thermal comfort systems that enable personalised temperature control in multiple zones throughout a vehicle cabin.

This increased comfort has come with a trade-off, though: decreased fuel efficiency. Operating the air conditioning system in a standard six-passenger sedan can reduce fuel efficiency by 10 percent or more.

But, ‘reducing that fuel economy penalty doesn’t have to mean sacrificing passenger comfort,’ said James Giardino, Delphi Harrison Thermal Systems’ chief engineer, advanced thermal systems.

Delphi has responded to appeals – from consumers and vehicle manufacturers – for advanced, intelligent multi-feature thermal comfort systems that consume less power.

In fact, the new energy-efficient A/C system from Delphi Automotive Systems can deliver operational energy savings as high as 3 percent to 6 percent, and it can help decrease vehicle emissions.

Conventional automotive air conditioning systems draw outside air into the heating, ventilation and air conditioning (HVAC) system, cooling and dehumidifying it before releasing it into the cabin. Once that air passes through the passenger compartment, it exits the vehicle through pressure relief vents. This is akin to air conditioning a house with the windows partially open.

Delphi’s energy-efficient A/C system minimises the energy required to condition the vehicle’s interior to the desired temperature, mixing cool, dehumidified air from the cabin with fresh air from outside the vehicle.

‘Developing a system that could determine the ratio of fresh air to recirculated air was key to this technology,’ explained Wayne Forrest, a member of Delphi Thermal’s advanced HVAC Systems team. ‘Too much fresh air increases the power required by the air conditioning compressor. Too much recirculated air causes the cabin air to become stale.’

Delphi’s system can determine the ratio of outside air and recirculated air necessary to maintain a fresh cabin while minimising the power that the compressor draws from the engine.

‘In conventional A/C systems, the compressor is controlled such that the evaporator temperature is slightly above the point where water will freeze on it,’ Forrest said. He added that on mild days, the air exiting the evaporator is too cool for the passengers, so the air is reheated prior to entering the cabin.

‘This reheat process wastes some of the work of the compressor,’ he explained. ‘We’ve developed an externally controlled compact variable compressor that reduces the amount of cooling and subsequent reheating of cabin air in mild ambient conditions.’

This new technology, coupled with sophisticated compressor control algorithms that reduce compressor pumping capacity, has been shown to reduce compressor power consumption by up to 55 percent at road speeds, depending on the environmental conditions and the application.

What does that mean for the average driver? According to Forrest, testing in real-world and test-tunnel conditions showed a general savings of 1.2 miles per gallon (mpg) on a six-cylinder, six-passenger sedan. Savings peaked at 2.2 mpg under certain ambient conditions.

That energy savings helps reduce vehicle emissions, helping manufacturers address global warming issues linked to automotive exhaust emissions.

‘The new system provides the vehicle cabin with adequate amounts of fresh air. Other systems make no adjustments for vehicle speed or blower speed. Thus, they supply inconsistent amounts of fresh air,’ Giardino said. ‘With the new system, vehicle occupants might notice elevated cabin humidity, which will greatly diminish the ‘dry-eye’ conditions often associated with extended A/C operation.’

On the web