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

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3 System description 34<br />

3.3.1 <strong>Energy</strong> efficiency<br />

Because <strong>of</strong> the heat tr<strong>an</strong>sport a heat pump c<strong>an</strong> “produce” more heat energy th<strong>an</strong> it<br />

consumes through the compressor in the <strong>for</strong>m <strong>of</strong> electricity. The efficiency is there<strong>for</strong>e<br />

indicated by the so-called coefficient <strong>of</strong> per<strong>for</strong>m<strong>an</strong>ce (COP) [20]. It is defined as the<br />

energy delivered (in the heating case) divided by the electric energy<br />

consumed by the compression. A physical upper limit is given by the ideal (lossless) COP<br />

<strong>of</strong> a Carnot process.<br />

℃<br />

(3.38)<br />

For the cooling case the extracted heat is compared to the compressor energy. An<br />

upper limit c<strong>an</strong> be given by the ideal process.<br />

This me<strong>an</strong>s the closer both temperature levels <strong>of</strong> the heat sink <strong>an</strong>d its source<br />

are, the better the COP c<strong>an</strong> be.<br />

Figure 3.11: Comparison <strong>of</strong> refriger<strong>an</strong>ts <strong>for</strong> the cooling case. [19]<br />

℃<br />

(3.39)<br />

The efficiency also depends on the refriger<strong>an</strong>t <strong>an</strong>d the compressor. They give<br />

the limits <strong>for</strong> <strong>an</strong>d <strong>an</strong>d <strong>an</strong> optimal working point. Examples <strong>of</strong> coefficients

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