IMI Magazine

IMI Magazine

Vehicle air conditioning

Refining the comfort zone

Since the majority of new cars are now fitted with air conditioning, the almost inevitable demand is for better, more efficient systems. It’s no longer good enough for a climate control system to maintain a pre-selected temperature inside the car regardless of outside temperature.

While that represented a significant improvement over semi-automatic systems, research from engineers at air conditioning systems producer Delphi indicates that the human body’s approach to temperature control demands a significantly more complex approach. The company has developed a new computer-based modelling system, tagged virtual thermal comfort engineering (VTCE), to accurately predict the temperature-related comfort level at critical areas on each occupant’s body.

According to Dr Stefan Glober director of engineering at Delphi Harrison Thermal Systems, Europe: “Traditional modelling techniques allow air flows and cabin temperatures to be analysed, but cannot show how changing factors such as air temperature and vent location actually affects the comfort of the occupants. VTCE gives us this ability and will lead not just to greatly improved comfort, but also to reduced system costs, better refinement, improved fuel consumption and lower emissions.”

According to Delphi, the temperature of a person’s breath has traditionally been the means of indicating thermal comfort. While that is basically a sound technique, it does not take account of other factors such as cabin humidity, outlet air speed, the heat of the sun, and the way air flows over individual occupants. Neither does it allow for temperature variations across the body.

“We’ve all been in cars where, however fast the fans are running, some part of our body is still too hot,” says Dr Glober. “With VTCE we can look at the comfort of an individual’s foot, a person’s back where it rests on the seat, or any other area.”

Delphi has applied techniques devised by NASA to help increase the comfort of astronauts. By dividing the body into 16 relevant areas, the comfort of each area is assessed. Allowance can be made for body size, clothing types, different activity levels and perspiration. Other factors such as sun radiation, humidity and ambient air temperature are also included.

Dr Glober reckons that the power of an air conditioning system is only half the story. “Achieving the other half depends on clever management of air distribution and flows,” he says. Indications are that manufacturers could reduce the capacity of an air conditioning system by 30 per cent and increase comfort levels. At the same time it can cut development costs and reduce development time for new systems.

Visteon is making similar claims for its approach to studying airflow inside a car. The company has adopted advanced laser technology to monitor air movement in a vehicle’s heating and air conditioning system and in the cabin. The results should be faster demisting and reduced development costs for OEMs.

Valeo unveiled its view of future air conditioning developments at the Frankfurt motor show last September. The company shares similar goals to Delphi and Visteon in its approach - reduced fuel consumption and emissions, as well as reduced complexity. Valeo terms its approach “Ultimate Cooling”. Instead of the various individual cooling systems in a car – for engine coolant, oil cooler, turbocharger air cooler, air conditioning and automatic transmission oil, Valeo plans to integrate all the systems in a single system, with one radiator and water as the coolant.

This would eliminate 70 per cent of the high-pressure hoses that are needed in a car at present for such things as oil, air conditioning and turbocharger air, helping to reduce component costs. Since Ultimate Cooling would also take up less space, Valeo believes it would allow car makers to build in better safety for pedestrians involved in impacts with the front of the car.

“In ten years’ time, such systems may well be specified as standard equipment by car makers”, says Thierry Morin, chairman and chief executive officer of Valeo. The concept would be suitable for all fuel types as well as hybrids.

Such a system would eliminate the need for the refrigerants currently used in vehicle air conditioning. Since those in use are greenhouse gases, this has caused legislators to focus on which refrigerants can be used and how they are handled when systems are serviced or scrapped.

Visteon’s research is leading the company to consider air, propane and carbon dioxide as a refrigerant. Like current refrigerants, carbon dioxide is also a greenhouse gas, but offers several advantages over current refrigerants. Firstly, it can produce better cooling from a smaller air conditioning unit, which means that it will consume less power too. And by using a heat pump in the circuit, a carbon dioxide air conditioning system can act in reverse, by helping to heat a car interior more quickly on cold days, through rapidly transferring heat from the car’s cooling system to the interior. This is particularly useful for modern diesels. The superior efficiency of a diesel means it takes longer to warm up than a petrol engine. Honda has already introduced a similar system on its Accord i-CTDI.

Given the environmental sensitivity of current air conditioning refrigerants, there are plans to introduce a mandatory refrigerant handler registration scheme to ensure that all individuals and businesses handling refrigerants are competent to do so and registered within the scheme.

Legislation was proposed by the end of 2003, with implementation phased in over a period of two to three years. At the time of writing, this has not yet happened, but the Air Conditioning and Refrigeration Industry Board (ACRIB), which has drawn up proposals for the administration of the scheme, already operates a voluntary registration programme which has the full backing of both DEFRA and the DTI. Details are available from ACRIB’s website or by post from ACRIB at Kelvin House, 76 Mill Lane, Carshalton, Surrey SM5 2JR. Tel: 0208 647 7033.

Valeo’s troubleshooter

Valeo Service has introduced what it claims to be one of the most advanced diagnostic tools for air conditioning.

The hand-held Clim Test 2 measures both temperature and pressures of the air con loop using test machine probes. The test machine offers two pressure sensors (high and low), three temperature sensors, two air temperature sensors (including ambient and cabin air), and two connectors for R134a and R12 gas, in addition to a built-in humidity sensor.

Readings are shown on an LCD display and can be printed out. Additional features to the unit – which is the size of a small briefcase – include an electronic data acquisition and measurement module.

Further information 01527 510755.