**8. Conclusions**

This study provided a comparative assessment of metrics of energy consumption and CO2 emission for various PDSs with a rated power in the range of 2.2–200 kW. The converter-fed PDSs with the IE3 IM, IE4 IM, and SynRM are considered. The analysis was based on extensive data from the technical specifications of the PDS [43–45] and pump manufacturers [27–30]. These data were processed using mathematical methods of polynomial and bilinear interpolation, regression, and a semianalytical model of a variable-speed pump unit. As a result of the analysis, the interpolating polynomials were constructed to evaluate the metrics of interest for any PDS from the entire considered power range.

This study showed that to achieve the goals of reducing greenhouse gas emissions, it is extremely important to use electric motors of higher energy-efficiency classes. The state of the art (IMs and SynRMs of the IE4 class) already allows effectively implementing the requirements of the European Commission [10], prescribing the mandatory use of IE4 class motors in the rated power range of 75–200 kW from 1 July 2023. The results showed that when replacing IE3 motors with IE4 motors, the largest reduction in CO2 emissions was shown by the low-power motors, which make up the vast majority of electric motors in service [54]. This justifies the mandatory use of IE4 motors for lower power ratings.

In addition, it was shown that the SynRMs of the IE4 class demonstrated significantly better indicators of reduction of CO2 emissions and energy savings than the IMs of the same energy-efficiency class. Moreover, SynRMs have several operational advantages, such as their simpler design and manufacturing technology, at a price comparable to the price of the IE3 IMs. As a result, when replacing an IE IM, the energy savings of an IE4 SynRM will be approximately 2 times higher, and the payback period will be approximately half that of the IE4 IM for the entire considered power range. At the same time, the influence of the SynRM's lower power factor compared to IMs and the associated need for frequency converters with a higher power rating does not significantly affect the payback period.

According to the results of this study, in order to achieve the goals of the European Green Deal [1,2], it is recommended to legislatively expand the mandatory power range of electric motors of IE4 class from 75–200 kW to at least 7.5–200 kW.

In future work, the potential for significant reductions in greenhouse gas emissions in other mass applications of electric machines will be investigated. For example, fans and compressors are in principle similar to pumps, but have different typical operating conditions. The subject of future work may be an assessment of the energy-saving potential, payback periods, and CO2 emissions for various typical operating profiles of such equipment. Moreover, a fast-growing quantity of electric vehicles also consumes an increasing share of electricity, which makes analysis in this area relevant.

In addition, on the basis of the developed model, it is possible to optimize the operating points of multipump units, which include pumps operating in parallel on the same pipeline.

**Author Contributions:** Conceptual approach, V.D. and V.P.; data curation V.D. and V.G.; calculations and modeling, V.G. and V.K.; writing of original draft, V.D., V.G., V.K. and V.P.; visualization, V.G. and V.K.; review and editing, V.D., V.G., V.K. and V.P. All authors have read and agreed to the published version of the manuscript.

**Funding:** The work was partially supported by the Ministry of Science and Higher Education of the Russian Federation (through the basic part of the governmen<sup>t</sup> mandate, Project No. FEUZ 2020-0060).

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** In this article, for the analysis, the technical specifications of the manufacturers of electric motors and pumps were used [27–30,43–45].

**Conflicts of Interest:** The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.
