## 6 Discussion
However, their influence is low, since the efficiency coefficient is quite high and is equal to 0.978. This enterprise works reasonably efficiently, since the technical efficiency for this enterprise is also equal to 1. The most inefficient enterprises from the sample are CHPPs 3 and 6. Moreover, their inefficiency is caused by both the inefficient operation of the enterprise and unfavorable conditions. For all inefficient enterprises, the required input indicators were calculated to achieve an efficiency coefficient equal to 1. Analyzing the type of return on scale according to these experiments, we can say that CHPPs 3 and 6 are at the point of increasing return to scale, while CHPPs 1, 2, and 4 are at the point of decreasing return to scale. Slacks movements are observed for CHPP 3 and 6 for the BCC model. When calculating using the CCR model, slacks movements are not observed. In experiments 2 and 4, the goal was to increase the supply of thermal energy to heat networks. To this end, efficiency calculations were carried out and the following results were obtained. An output-oriented DEA model was set. Under experiments 2 and 4, CHPP 5 is an effective enterprise according to the presented performance indicators: CRSTE, VRSTE, and SE. The same results were obtained for experiments 1 and 3. Identical efficiency coefficients were also obtained for CHPP 2. For the rest of the enterprises in the sample, the CRSTE performance indicators are also identical, while the performance indicators of VRSTE and SE differ. The most inefficient enterprises from the sample, as in the previous experiment, are CHPPs 3 and 6. Their inefficiency is also caused by both inefficient operation of the enterprise and unfavorable conditions. For all inefficient enterprises, the required output indicators were calculated to achieve an efficiency coefficient equal to 1. In the experiment, it is observed that CHPPs 1, 2, and 4 are at the point of decreasing return to scale. CHPP 3 and 6 are at the point of increasing return to scale. Slack movementswere already observed for CHPPs 1, 3, and 4 for the BCC model. For experiments 1 and 3, only CHPPs 3 and 6 presented slack movements, while no slack movements are found in calculations using the CCR model. In experiment 5, another output indicator was added. This was done in order to see the impact of the environmental factor on the efficiency of the CHPP, adjusting the performance of the CHPP plant while reducing emissions into the atmosphere. In this experiment, the goal was to increase the supply of thermal energy to heat networks and reduce the mass of harmful substances released into the atmosphere. In accordance with the goal set, an output-oriented model with two inputs and two outputs was used. As input indicators, the following were used: the available thermal power of the equipment, the consumption of conventional fuel for the released fuel cell. As output indicators, the following were used: the release of thermal energy to heat networks and the emission mass. The efficiency calculations using the DEA method for CCR and BCC models yielded the following data. In this experiment, with the same sample, three enterprises are already effective enterprises according to the performance indicators of CRSTE, VRSTE, and SE, namely CHPPs 2, 3, and 5. They achieve maximum efficiency in their work. CHPP 6 achieves an efficiency factor of 1 only at SE. This means that for this enterprise, unfavorable conditions have no effect on its efficiency. With a constant return on scale and a variable return on scale, the efficiency coefficients are the same and equal to 0.909. Thus, the inefficiency of this enterprise is wholly caused by the inefficient operation of the enterprise. All performance indicators for the remaining CHPPs are below 1. For these, the required output indicators were calculated to achieve an efficiency coefficient equal to 1. In this experiment, we observe changes in the display of the scale effect. Now, only CHPPs 1 and 4 are at the point of decreasing scale effect (decreasing return to scale).