More than a load of hot air

A simulation system based on technology originally designed to help keep NASA astronauts cool will make next-generation cars more comfortable and efficient, its developer has claimed.

Virtual Thermal Comfort Engineering (VTCE), developed by Delphi, is a computer-based simulation technique that predicts car occupants’ ‘thermal’ comfort using a large number of variables, from trouser thickness to air velocity.

The importance of modelling thermal behaviour early in the car design process has recently increased. The tendency to use more and more glass in vehicle styling, leading to warmer interiors, tightening fuel-economy constraints and mounting environmental concern over the use of refrigerants mean that manufacturers cannot just keep increasing air-conditioners’ size.

Dr. Stefan Glober, director of engineering at Delphi Harrison Thermal Systems, said traditional approaches take no account of factors such as cabin humidity, outlet air velocity, solar radiation or the way air flows over each occupant. They also treat each person as a uniform mass that is the same temperature all over.

‘We’ve all been in cars where however fast the fans are running, some part of our body is still too hot,’ explained 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’s system links the CFD calculations on air flow and temperature distribution with a computer model of the thermo-regulation of the human body.

This complicated physiological technique divides a simulated human model into 16 segments, with each segment modelled as four body layers (core, muscle, fat and skin tissues), and a clothing layer. The system can then predict thermal comfort based on external factors (such as solar loading, humidity and ambient air temperature) and individual characteristics (body size, clothing, activity and perspiration).

This enables designers to complement and scale down the air-conditioning by improving air distribution and flow in the car. This would typically be achieved by changing the position of air-vents, or altering the shape and size of windows. ‘VTCE gives us the ability to solve problems on existing vehicles or to provide a noticeably superior level of comfort in a new design,’ he said.

VTCE has been installed at Delphi’s Technical Centre in Luxembourg where it is being used to help car makers meet tough European Automobile Manufacturers’ Association fuel consumption targets. The first vehicle to benefit from the system is likely for launch in 2006.

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