Electric vehicle
Design of Ancillary Systems10.1
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| 10 Design of Ancillary Systems 10.1 Introduction While the design of major components as discussed in the previous chapter is critical, the design and choice of ancillaries such as the heating and cooling system are also very important. An important issue in ordinary IC engine vehicles is the ever-rising amount of electrical power required to drive the auxiliary systems. Indeed, this problem is very likely to cause a gradual moving over from 14 to 42 V electrical systems. The average power taken by the electrical systems on even a very ordinary car can be as much as 2 kW. Clearly, this is particularly important in battery electric vehicles, and most of the problems addressed in this chapter area particular concern to this type of electric vehicle. The aim will always be to use systems of the lowest possible electrical power. The heating or cooling system of a car or bus is obviously a major consumer of energy. However, other systems such as steering, and even the choice of wing mirrors and tyres, are also important. 10.2 Heating and Cooling Systems There is little point in producing the ultimate energy-efficient electric vehicle, light, aerodynamic and with high motor and transmission efficiencies and then waste precious energy bypassing current directly through a resistance to heat the vehicle. With IC engine vehicles, copious waste heat will quickly warm the vehicle, although starting off on a cold morning maybe unpleasant. For fuel cell vehicles or hybrids with IC engines waste heat is also available, but with battery-powered electric vehicles there is little waste heat, and where heating is required this must be supplied from a suitable source. Of course, heating does not need to be supplied for electric vehicles such as bikes and golf buggies. Vehicle cooling is often needed in hot climates and this can also absorb considerable energy. Batteries have a low specific energy and are expensive. It is better to store heat energy by using the specific heat, or latent heat of materials. As an example, 1 kg of water housed in a suitable insulated container and raised through C above ambient contains 293 kJ or 81 Wh of heat. At 81 Wh kg −1 this is a considerably better specific energy than both Electric Vehicle Technology Explained, Second Edition. James Larminie and John Lowry. © 2012 John Wiley & Sons, Ltd. Published 2012 by John Wiley & Sons, Ltd. 240 Electric Vehicle Technology Explained, Second Edition lead acid and NiCAD batteries. 1 Early night storage heaters used the same principle for storing heat, but they used brick rather than water. More modern night storage heaters use the latent heat of fusion of materials such as wax, which gives an even higher specific energy than that obtained by heating water. Basically the wax is melted and kept in an insulated container. The heat can be drawn from the wax when required. A variation on this theme could be successfully used for storing heat in a vehicle. The heater could be recharged at the same time that the batteries were topped up and heat could betaken off as required. This is the basis of the R ξHP 2 climate control system of Groupe Enerstat Inc. of Canada. For commuter vehicles this method of heating using thermal stores does have an advantage. A consequence would be that on cold days the vehicle would be warm as soon as the driver gets in, which would be a boon for short journeys. A similar technique could be used for storing ‘coolth’. For example, ice could be created at night and the latent heat of fusion released when required. The latent heat of fusion of ice/water is 92 .7 Wh kg −1 and a further 17 .3 Wh kg −1 can be obtained from heating the water to C giving a total specific energy of 110 Wh kg −1 Both of these systems are relatively simple and are worth remembering as methods of heating and cooling electric vehicles. Schematics of both systems are shown in Figures 10.1 and Fuel burning heaters can be used to provide warmth. Such heaters have been used in battery vehicles used by the US postal service. It was said that such heaters could only be controlled by opening the doors and letting the heat out – and the result was that the vehicles ended up using almost as much fuel as the diesel-powered vehicles they replaced! Electric current to supply heat Container with heat retentive material, such as molten wax, where the latent heat of fusion is released as the material cools and solidifies. Warmer air out Cold air in Download 3.49 Mb. Share with your friends:
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