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Recent developments in glass treatment techniques have made it possible to improve vehicle compartment climate considerably. At the same time, it has become obvious that traditional temperature measurements do not cover the total need for describing climate properties. This is due to the fact that human heat balance, which is the fundamental process behind feeling cold or hot, is a function not only of temperature but also of draft and radiation. Coating glass is one means of preventing solar radiation from coming into the compartment. In doing so, the solar heat load through the glazing can be reduced by some 50 %. This, of course, gives a lower compartment temperature in parking conditions and also a faster cool-down in hot climate. It has two major secondary impacts on the human being: At a given air flow through the compartment, the necessary inlet temperature is increased, thereby causing less draft. Direct radiation on body surfaces is also reduced.

Effective control of the micro-climate in a vehicle has traditionally been regarded as being important for comfort, but in the absence of experimental results showing any measurable negative effects of compartment temperatures in or near the comfort zone on driver performance, it has not been regarded as a factor in road safety. The authors have recently reported new results demonstrating an unexpectedly large negative effect on driver vigilance at 27°C, in comparison with 21 °C, in a moving vehicle: drivers missed 50% more of the signals presented in the first hour at the moderately raised temperature, and response times were 22% slower on average. These results provide powerful arguments for regarding not only air-conditioning, but also automatic temperature control, as safety features. Compartment temperatures in vehicles without these features often exceed 27°C due to solar and engine load, even at ambient temperatures well below 20°C.

The main problem with the car climate while running is thermal asymmetry on the human body. This asymmetry is caused by solar radiation, drafts from cold air and drafts due to radiation from cold surfaces. During winter, the cold surfaces of the side windows are a major source of discomfort, not only because of the above-mentioned cold radiation towards the outer upper body parts, but also as a result of the air stream needed for demisting the windows. This air stream has a very low temperature when reaching the B-pillar, where it easily deflects, hitting the driver's/passenger's shoulder. In order to avoid these problems, tests have been carried out with side-lights consisting of two hermetically sealed panes with a small air space in between. It was found that the surface temperature is significantly raised, by some 15°C, at low ambient temperatures. Not only are the heat losses reduced, but mist formation is also prevented. Negative aspects are weight and cost.

Energy radiation during clear mornings causes a temperature drop on outdoor surfaces. If this drop is big enough, moisture will condense and lead to frost formation during cold weather. This is a nuisance and a safety risk for the driver when it occurs on car windows. If the surface of the glazing is coated so that the emissivity within certain spectral bands is low, frost formation can be prevented in most situations. In the autumn of 1986, Volvo introduced a windshield on these lines. Tests indicate that the number of mornings when scraping is necessary is reduced by more than 80% in the Swedish coastal climate.