Ideal climate in the new R-Class, the Grand Sports Tourer from Mercedes-Benz
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Testing across several continents and in the world's la
rgest climatic wind tunnel Choice of two sensor-controlled air conditioning systems Performance figures on a par with a central heating system for a detached family house Multi-zone THERMOTRONIC with optional rear air conditioning system
A wealth of experience and the use of sophisticated technology were absolute necessities when it came to developing an effective climate control system for the spacious interior of the new Mercedes-Benz R-Class. After all, with its 4.5 cubic metres of interior space, a windscreen area of 1.5 square metres and an optional panoramic sunroof with a glass surface measuring 1.2 square metres, the Grand Sports Tourer is anything but a conventional car in terms of its dimensions. The climate control experts at the Mercedes-Benz Technology Center surmounted what proved to be an extremely stiff challenge by drawing on a vast pool of know-how and expertise. As well as road testing in every climate zone, the Grand Sports Tourer also underwent an extensive test programme in the world's largest climatic wind tunnel. This unique installation run by the Vienna-based company RTA Rail Tec Arsenal GmbH enables staff to simulate practically any imaginable weather conditions -- at little more than the push of a button and always under reproducible laboratory conditions. It takes just a few hours to change from season to season in the climatic wind tunnel. By way of example, the test centre can be cooled from 40 degrees Celsius to minus 30 degrees Celsius in just seven hours - an average cooling rate of ten degrees per hour. During the tests, weather phenomena can be reproduced such as hurricane-force storms up to 300 km/h, intense sunlight with a solar load that is not achievable in the open air even in the hottest areas on the planet, tropical rain, or snow with temperatures between minus five and minus 25 degrees Celsius. Thanks to the standard-fit THERMATIC automatic climate control system, the new Mercedes-Benz R-Class offers passengers optimal climate comfort in all weather and temperature conditions.
Optional equipment includes the multi-zone THERMOTRONIC system which allows three different temperatures to be set in three different zones: the driver area, the front passenger area and the rear passenger area (second row of seats). In addition, the multi-zone THERMOTRONIC package can be extended to include a rear air conditioning system for the third row of seats, which is located in the rear compartment behind the left-hand side wall panelling. Both air conditioning systems have been specifically adapted to cover the immensely spacious interior of the new R-Class, meaning that the performance figures are impressive to say the least. In summer the interior is cooled down rapidly, whilst in winter passengers feel comfortable even when the outside temperature reaches Arctic levels. Measurements show that, when the outside air is cooled to minus 20 degrees Celsius and the coolant temperature is 80 degrees Celsius (in accordance with test regulations), the maximum heating capacity is ten kilowatts - equivalent to a typical central heating system for a detached family house. In the R 320 CDI diesel model, an electric PTC (Positive Temperature Coefficient) heating element is also activated when the outside temperature falls below a certain level in order to provide an extra 1.7 kilowatts of heating output to supplement the heater core. The PTC heating element is required because, due to its high thermal efficiency, the six-cylinder CDI engine delivers impressive fuel consumption but gives off much less heat to warm up the coolant than other engines when running under partial load. To cool the spacious interior, the automatic climate control increases the maximum air quantity to 640 kg per hour, operating with a cooling capacity of nine kilowatts.
THERMATIC: effective two-zone climate control
The THERMATIC automatic climate control system is controlled by sensors which monitor the temperature and the degree of sunlight entering the car. A total of nine sensors are used: seven airflow sensors in the ventilation outlets monitor the temperature of the air entering the vehicle, one sensor in the control panel measures the interior temperature and a solar sensor on the dashboard records the intensity and angle of incidence of the sun's rays. In order to ensure a rapid exchange of information between all the system components, THERMATIC has its own databus
which electronically links the sensors with both the air flap control unit and the main climate control computer. This computer is also connected to the interior databus which supplies important additional information such as the battery voltage, coolant temperature, engine revs, road speed and refrigerant pressure. The computer controls the air conditioning system by comparing the settings selected by the passengers with the actual measured values. This means that, in automatic mode, the temperature, blower speed and air distribution are controlled continuously so as to ensure that the temperatures set by the driver and front passenger are always achieved and maintained at a constant level. If it is hot outside, for example, the automatic climate control will vary the amount of recirculated air in order to cool down the interior more quickly on the one hand and minimise the cooling capacity required on the other hand. The air conditioning compressor is continuously adjustable, thus allowing optimal (i.e. economical) operation of the THERMATIC system. This infinitely variable control is provided by a solenoid valve which varies the volumetric displacement of the air conditioning compressor. Both the driver and the front passenger have an elegant rotary switch for selecting the desired temperature. Red LEDs indicate the set temperature. Buttons for rear compartment ventilation and residual heat utilisation are integrated in the right-hand rotary switch. Buttons for manually adjusting the blower speed, for the defrost function, for rear windscreen heating, for recirculated air mode and for air distribution are located in the central area between the rotary switches. The Mercedes-Benz engineers have also developed a control panel for passengers occupying the second row of seats. Located on the rear end of the centre console, the control panel allows the seat occupants to adjust the air distribution as required.
Multi-zone THERMOTRONIC: with booster blower for the rear compartment
The multi-zone THERMOTRONIC system (optional) provides even greater climate comfort, which especially benefits the rear passengers. Mercedes-Benz has perfected the principle of three-zone climate control, enabling the driver, the front passenger and the rear passengers in the second row of seats to set the temperature, air quantity and air distribution individually. The additional booster
blower located in the centre console enables the air quantity in the rear compartment to be controlled independently of the air quantity at the front. The sensor system for the luxury automatic climate control is even more sophisticated. Eleven sensors supply the microcomputer at the heart of the multi-zone THERMOTRONIC system with up-to-date information: as well as relying on the seven airflow temperature sensors in the ventilation outlets, the central temperature sensor in the control panel and the solar sensor, the automatic climate control system also factors in humidity data supplied by a dew-point sensor. This humidity sensor works in conjunction with the continuously adjustable refrigerant compressor to ensure that the automatic climate control system is always operated in accordance with current requirements. The incoming air is first cooled and dried, depending on its humidity content, before being heated to the desired temperature. The advantage of this air conditioning system is that it is much more economical than conventional systems and ensures a higher level of comfort. A total of 13 airflow temperature sensors are needed if a rear air conditioning system is also installed. Furthermore, the multi-zone THERMOTRONIC system for the new R-Class is equipped with a pollutant sensor which measures the amount of carbon monoxide and nitrogen oxide in the outside air. If the pollutant concentration is too high, the air conditioning system automatically switches to recirculated air mode. In fresh air mode, an activated charcoal filter operates at all times, absorbing pollutants and also preventing unpleasant odours from reaching the occupants. LEDs on the elegant, easy-to-reach rotary switches on the multi-zone THERMOTRONIC control panel indicate the temperatures set by the driver and front passenger. The "mono" button in the left-hand rotary switch enables the settings for the driver, front passenger and rear passengers to be synchronised. The interior temperature can then be selected using the left-hand rotary switch. Source: Text & photos courtesy DaimlerChrysler AG