## 5 Conclusions and Outlook  
This work presents a techno-economic analysis of the integration of a Refrigerant-PCM-Water heat exchanger (RPW-HEX) in the hot gas section of an R32 air source HP for heating, cooling and DHW  
Figure 6: Daily DHW consumption and provided energy for energy efficient DHW generation by operating mode (c) \(Q_{\text{DHW},c}\) for (**a**) Case #1 and (**b**) Case #3 and variations from Table 3. The different colors mark the contribution from the condenser (“con”, green), from the refrigerant transferred via the RPW-HEX (“RPW-ref”, blue) and from the energy stored in the PCM-material/aluminum (“RPW-PCM”, orange). The dotted line marks the average DHW consumption and the dashed line mark the average contribution of DHW to the DHW consumption by operating mode (c). generation operated in three different building types located in different climatic zones. The analysis was carried out to identify the optimal RPW-HEX storage size considering hourly based operation for a whole year, a rule-based control strategy and different operating modes. The lowest payback time of 12.4 years, the highest energy savings per year of 622 kWhel, and the highest profits after 20 years of 1083 EUR were found for Case #1, a passive house located in Helsinki with 7.75 standard apartments--operation in eco-mode with 8 large (280 L) DHW storage devices. It turns out that for buildings with medium and large DHW storage devices, the selection of the DHW charging mode (eco, standard or comfort) does not produce an as significant difference in the energetic and economic system performance as for buildings with small DHW storage devices. Thus, operation in the eco-(charging) mode is critical for small DHW storage devices. The results indicate further potential for significant improvements through the interaction with PV if feeding generated electric energy to the grid is less beneficial than storing the energy on site. Such systems rely on DHW storage with a comparatively high volume (high investment costs) in order to store PV generated thermal energy during day time in summer. The integration of an RPW-HEX would not only reduce the electric energy needed for DHW generation (and therefore PV size) but would also add an extra benefit to the installed DHW storage, making effective use of this storage in winter, i.e., in times of the year when the available storage capacity is only partially used by PV. The results of this work indicate that, although there is significant potential for energy savings in a refurbishment building in a hot climate, from the economic point of view, the proposed system is better suited for a low-energy building in average- and a passive house in cold climates considering an average European electricity price of 0.22 EUR/kWh at the time of installation and a discount rate of 2%. The first experimental validations of the proposed system with a first RPW-HEX prototype have already successfully been carried out and are presented in [25]. Conceptualization, J.E. ; methodology, J.E. and K.M. ; software, J.E. ; validation, K.M., F.H., W.P. and J.E. ; formal analysis, J.E., K.M., T.B., G.Z., L.F.C. ; investigation, J.E., K.M. and F.H. ; resources, M.W., A.S., B.N., W.P. ; data curation, J.E., K.M. and F.H. ; writing--original draft preparation, J.E. ; writing--review and editing, all authors; visualization, J.E. ; supervision, J.E. ; project administration, J.E. ; funding acquisition, J.E., T.B., L.F.C., A.S., M.W., W.P. All authors have read and agreed to the published version of the manuscript. This project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 768824 (HYBUILD). This work is partially supported by ICREA under the ICREA Academia programme. The authors thank [PERSON], [PERSON], and [PERSON] for critical discussion. Furthermore, we thank [PERSON] and [PERSON] for their assistance in generating the data of the different buildings.