is known from equation 2 the enthalpy h 3 can be calculated easily from the enthalpy difference h 3 u2212 h 2 for control the refrigerant temperature t 4 at the compressor outlet is calculated from the point of intersection of the line of enthalpy h 3 with the line of the pressure p 2 in the log p h diagram of fig2 subsequently the heat output qh of the refrigeration machine is calculated from the difference of the calculated enthalpies h 3 and h 1 in accordance with the equation the electrical power qe 1 taken up by the compressor 14 was already determined using the compressor model and is preoperational to the difference of the enthalpies h 3 and h 2 in accordance with equation 4 to determine the coefficient of performance cop or the efficiency of the refrigeration machine subsequently only the quotient of the heat output qh and of the electrical power qe 1 still has to be formed in addition the annual performance index of the refrigeration machine can be determined by an integration of the coefficient of performance over time accordingly the heat output qh and the electrical power qe 1 can be integrated over time to indicate the heating energy and the taken up electrical energy the power take up of additional devices such as pumps electronics etc can in this respect be.