**5. Conclusions**

Several main types of HPs have been critically analysed for obtaining rules and criteria on appropriate HP selection for various process configurations. In addition to the relatively recent JCHP, other HP types are in use and have been industrialised, including the VCHP and TCHP types. This paper performs a comparative evaluation of the performance of the Heat Integration scenarios of different HP types (VCHP, TCHP and JCHP) and processes, by applying the Petro-SIM process simulator and Pinch Analysis.

An answer is provided to the question of which type of HP is most suitable for a specific process. The results show that for processes with larger source and sink slopes on the T–H plot, the COP of JCHP is higher, and JCHP is more suitable. For processes with a relatively smaller and medium slope of the source and sink T–H profiles, the COP of VCHP is relatively large, and VCHP is more suitable. The scope of application of TCHP is small.

For processes with a relatively low source T-H slope and a relatively large sink T-H slope, the COP of TCHP is more substantial, and it is appropriate to select it. Because the critical temperature of CO2 is 31.26 ◦C, the added constraint in this context is a process for which the source inlet temperature is lower than 20 ◦C, the sink temperature requires more than 40 ◦C, and the ΔTin between the source and the sink is less than 10 ◦C.

By improving the waste heat quality of the process, the HPs can save 15 to 78% of the hot utility. The smaller the ΔTin between source and sink is, the larger is the COP of the VCHP. The ΔTin increased from 1.5 ◦C to 11.84 ◦C, and the COP of the VCHP decreased from 13.07 to 4.44. The COP of the VCHP decreased rapidly with the increase of ΔTin between source and sink. However, the COP of JCHP decreased less with the increase of ΔTin between source and sink.

It is shown that if an inappropriate HP is selected to integrate with the process, the COP of the HP would decline, which may lead to an increase in investment and a decrease in the economy of the HP. In the extreme cases, the differences between the most and the least suitable integration mappings can be of the order of 100% and up to tenfold. This shows the importance of performing such an analysis and making the correct choice of a HP.

For the different scenarios of Heat Integration with HPs, this study can provide guidance and suggestions for the selection of HPs, enabling a quick selection of the appropriate HPs. A simplifying assumption for the current work is the use of the COP of the HP—process combinations as the performance criterion, land considering the investment cost of HPs only qualitatively. The full analysis, relaxing this assumption and considering the investment and analysis of the economy is planned for future work. The future research will be targeted to find the balance between the COP and the economy of the HP application.

**Author Contributions:** L.G. has written the draft performing the complete study at the previously published idea of T.G.W. to extend the comparison of heat pump suitability to several applications. P.S.V. has consulted L.G. on the steps of the investigation and the formulation of the concepts and the procedure. P.S.V. has made a thorough refinement of the whole manuscript. J.J.K. has supervised and managed the research actions and the manuscript preparation and finalising, provided consultation to L.G. and P.S.V. on the presentation of the key concepts. T.G.W. has also provided proofreading feedback. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the EU project "Sustainable Process Integration Laboratory—SPIL", project No. CZ.02.1.01/0.0/0.0/15\_003/0000456 funded by EU "CZ Operational Programme Research, Development and Education", Priority 1: Strengthening capacity for quality research under the collaboration agreement with The University of Waikato, New Zealand.

**Conflicts of Interest:** The authors declare no conflicts 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.
