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Nowadays, improving the efficiency of power plants by utilizing secondary energy resources is gaining more attention in the energy sector. In this paper, the combined cycle gas turbine (CCGT-420T) was considered, where exhaust heat from the main and auxiliary equipment is utilized, and sent to a water supply system through a closed-circuit heat exchanger, as a result, the heat transferred ( Q 6.4 MW) is rejected into the environment through a cooling tower. Moreover, an effective modelling method for utilizing heat in a closed cycle, using a steam compressing heat pump unit (HPU) is proposed. In addition, a calculation of the effectiveness of utilizing secondary energy resources depending on the number of HPU stages. In addition, the calculation of the effectiveness of the use of secondary energy resources depending on the number of stages of HPU was carried out. Several options of the model were discussed in this work, such as, two-, three-, and four-stage HPU and the coefficient of performance was calculated. Moreover, the work of these compressors for each option of the model was discussed in this work. Finally, the economic benefits of using of a multi-stage HPU instead of a traditional one-stage HPU during the annual operation of the CCGT-420T was discussed.