In classical engineering thermodynamics, the irreversibility of heat transfer processes in cycles is taken into account not by studying the kinetics of the process, but as a result of introducing the efficiency of the process into the thermodynamic model of the thermotransformer. This makes it impossible to take into account the scale factor of the installation (design cooling capacity) when assessing the efficiency of thermal transformers, which is unrealistic when using the theoretical Carnot relations. Therefore, the actual applied task is to determine the limiting possibilities of real cycles of vapor-compressor thermotransformers taking into account the average given heat transfer rate, which gives a more realistic estimate of the energy conversion coefficient. A thermodynamic model of a thermal transformer based on the use of generalized statistical information on the integral thermal characteristics of modern chillers and heat pumps has been developed. The model makes it possible to predict the change in the operating characteristics of thermal transformers, including evaporation and condensation temperatures as the installation load changes, as well as the input parameters of heat transfer media. A method for determining elemental exergy losses in chillers and heat pumps by using parameters that are directly measured by technical devices is proposed. This approach is especially in demand in the energy efficiency monitoring systems of thermal transformers in real time, because it does not require information on the values of entropy and enthalpies at characteristic points of the cycle, which are traditionally determined using the database of refrigerant properties. Based on the numerical implementation of the proposed method, conditions have been identified that allow for reducing the energy consumption of chillers and heat pumps when operating in partial load mode by choosing a rational ratio between the water flow in the evaporator and the condenser. In particular, it was found that in order to increase the energy efficiency of the chiller in the partial load mode, the ratio of water flow through the condenser to water flow through the evaporator should be at least two, and the efficiency increases by 5%.