Climate control: Pleasantly climatised interior from the start

Sep 4, 2018

Cars with combustion engines use their waste heat to warm the interior. Electric vehicles are more efficient – which means lower energy losses but also less waste heat to warm the interior. In other words, the engineers needed new, intelligent concepts.

A sophisticated system with a heat pump and electric heater boosters pre-climatises the interior, ideally when charging. This increases range, as the energy requirement from the high-voltage battery can be greatly reduced. The EQC (combined power consumption: 22.2 kWh/100 km; combined CO2 emissions: 0 g/km, provisional data)1 also uses the waste heat from the battery as an energy source. The integrated overall cooling concept, which cools both the power electronics and the rotors of the electric motors, is also designed for efficiency.

Thanks to pre-entry climate control, EQC drivers neither need to scrape windows nor get into ice-cold cars. And even in hot summer temperatures, the interior is cooled to a pleasant level before starting a journey. Pre-entry climate control can be controlled via the multimedia system MBUX – Mercedes-Benz User Experience – or conveniently from the home or office using the Mercedes me App.

Pre-entry climate control uses target values as a basis. In other words, when the driver inputs a departure time, the EQC is climatised to the set temperature by that time. The driver can do this either individually for each journey and every stretch of the journey, or with the help of a weekly profile. Pre-entry climate control is also activated automatically for five minutes as soon as the vehicle is unlocked using the key. When the maximum one-hour pre-entry climate control pre-programmed via the Mercedes me App or MBUX is started or ended, the driver receives a push notification and is always fully informed.

In addition to automatic air conditioning, pre-entry climate control includes heating of the exterior mirrors and rear window, as well as the seat heating for the driver and front passenger.

[1] Figures for power consumption and CO2 emissions are provisional and were determined by the German Technical Service corporation. The range figures are also provisional. EC type approval and conformity certification with official figures are not yet available. There may be differences between the stated figures and the official figures.

Sophisticated control technology: how climatic comfort comes about

In the winter, many electric vehicles either fail to achieve the climatic comfort of conventional cars or their range is significantly reduced because the battery power is also used to heat the interior. Furthermore, the operating temperature of the high-battery should be kept within a certain range in the interests of battery operating life, which means that it must be cooled or heated as necessary.

In the EQC Mercedes-Benz uses a sophisticated system with a heat pump function and two electric PTC (Positive Temperature Coefficient Thermistor) heater boosters. A heat pump – also familiar from domestic appliances – operates on the same principle as a refrigerator, transporting heat from a lower to a higher temperature level. This means that “cold thermal energy” [1], which occurs particularly frequently in electric vehicles, can be used to heat the interior.

The PTC heater boosters are in principle immersion heaters whose performance is however dependent on the inflow temperature of the coolant. The advantage is that the component itself prevents overheating, making additional protection unnecessary. This is because at low temperatures, the ceramic PTC components have a very low electrical resistance and allow a high flow of current for a good heating output. The effect is reversed if the temperature rises, however: The electric current is reduced by the increasing resistance of the ceramic blocks, therefore the system releases less heat. The two PTC heater boosters in the EQC are located in the right and left wheel arches.

For the best possible climate control compromise between efficiency and comfort (both in terms of interior temperature and air humidity), the influencing factors of battery temperature, outside temperature, humidity and dewpoint are registered and evaluated. Operation of the heat pump improves efficiency over a wide outside temperature range.

Other new features in the EQC are the water-cooled condenser and regulation of the chiller (evaporator) by an electric expansion valve. This allows more usable performance, and this can be better managed. As a result the temperature at the evaporator does not suddenly change when the chiller is required to increase its performance.

The water-cooled condenser feeds the heat from the refrigeration circuit into the heating circuit. It also ensures that the heat from the supply air and recirculated air, the waste heat of the compressor and the waste heat of the battery are available to heat the interior. In the ideal case these heat sources are sufficient to heat the interior energy-efficiently with the heat pump down to outside temperatures below 0°C without having to activate the PTC heater booster.

[1] Temperatures just a few degrees above zero which are not perceived as warm.