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Design of an Automatic Control Algorithm for Energy-Efficient ...

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3 System description 35<br />

<strong>of</strong> per<strong>for</strong>m<strong>an</strong>ce <strong>for</strong> three refriger<strong>an</strong>ts <strong>an</strong>d different ambient temperatures are shown in<br />

Figure 3.11. A typical COP around 2 c<strong>an</strong> be seen.<br />

3.3.2 Heat exch<strong>an</strong>ger icing<br />

One main problem <strong>for</strong> the use <strong>of</strong> a heat pump in cars is the icing <strong>of</strong> the front (ambient<br />

air) heat exch<strong>an</strong>ger. Acting as <strong>an</strong> evaporator when heating the cabin, its temperature has<br />

to be lower th<strong>an</strong> the ambient air in order to extract heat from it. Given a humid autumn<br />

or winter weather this c<strong>an</strong> easily lead to condensation <strong>of</strong> water <strong>an</strong>d - below zero degree<br />

- to the development <strong>of</strong> <strong>an</strong> ice layer. This ice will prevent air flow through the structure<br />

<strong>an</strong>d decrease the heat tr<strong>an</strong>sfer (<strong>an</strong>d with it the COP) dramatically. This is not acceptable<br />

since a car heating system has to be able to provide warm air under all circumst<strong>an</strong>ces to<br />

defog the windscreen - especially when it is cold <strong>an</strong>d humid outside.<br />

Deicing<br />

V1<br />

Compressor<br />

V4<br />

HVAC<br />

EV1<br />

EV3<br />

EV2<br />

EV4<br />

PTC-Heater<br />

Condenser<br />

Evaporator<br />

E-Machine-Chiller<br />

Battery-Chiller<br />

Receiver<br />

V7<br />

IHX<br />

Condenser<br />

Mixed Air<br />

Flap<br />

Figure 3.12: The de-icing mode in the ePer<strong>for</strong>m<strong>an</strong>ce heat pump system. [19]<br />

One solution to this problem taken in the ePer<strong>for</strong>m<strong>an</strong>ce system [21] is to temporar-<br />

V8<br />

V3<br />

V2<br />

V6<br />

V5

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