**5. Conclusions**

In this study, the energy savings and economic performances of the EGH recovery system from ICE was analyzed and evaluated for supplying hot water to the resort. The new heat exchanger system to recover exhaust gas heat from ICE and utilize to heat the water was proposed considering the dew point temperature and back pressure of exhaust gas system. The heat recovery and economic efficiency were calculated and evaluated. The regular hot water demand for the resort is ranging from 2–6 m3/h which could be fully satisfied by the proposed system which supplies the hot water with the flow rate of 14 m3/h at 25% ICE load and the hot water flow rate of 26 m3/h at 80% load. These flow rates have sufficient and excess capacity to satisfy the current hot water demand of 6 m3/h at temperature of 55 ◦C to the resort. In case the demand of hot water supply increases in future due to higher number of tourists then it could be achievable by the proposed system up to maximum 29 m3/h with increasing ICE load. Despite of increasing hot water demand and recovering larger amount of waste heat from the exhaust gas using the proposed system but still the exhaust gas temperature is lower than the dew point temperature which depicts the safe operation without condensation and corrosion in the exhaust system. At the hot water flow rate demand of 6 m3/h, the proposed system achieves the heat recovery power of 155 kW and heat recovery efficiency of 23%. And the heat recovery power and efficiency are achieved maximum up to 645 kW and 97%, respectively at the maximum hot water flow rate demand of 25 m3/h. The proposed system reduces the daily fuel consumption of DO up to 400 L/day which results into the annual saving of 110,880 \$/year and the calculated payback time for the proposed system is 9 months. Apart from excellent performance and economics, the proposed system could reduce the CO<sup>2</sup> emission by saving fuel consumption which results into reduced global warming and environmental degradation. The results indicate that the potential energy savings of recovered EGH system from ICE is significantly large. The proposed system has effectively utilized the energy economically and the generated scientific data could be used in the construction of new heat recovery system. In the proposed system still larger amount of waste heat is remained un-utilized therefore, as the future direction, the designed new heat exchanger could be optimized based on heat transfer performances to make the efficiency utilization of remaining waste heat which could improve the economics of the proposed heat recovery system. In addition, various statistical approaches such as, Taguchi analysis, grey relational analysis and analysis of variance could be employed to evaluate the most influencing factors to the performances of designed waste heat recovery heat exchanger in the future works.

**Author Contributions:** Conceptualization, N.-H.N. and D.-Y.L.; methodology, N.-H.N. and D.-Y.L.; formal analysis, N.-H.N. and D.-Y.L.; investigation, N.-H.N. and D.-Y.L.; resources, N.-H.N. and D.-Y.L.; data curation, N.-H.N. and D.-Y.L.; writing—original draft preparation, N.-H.N., D.-Y.L., K.S.G. and M.-Y.L.; writing—review and editing, N.-H.N., D.-Y.L., K.S.G. and M.-Y.L.; visualization, N.-H.N. and D.-Y.L.; supervision, M.-Y.L. and D.-Y.L.; project administration, M.-Y.L. and D.-Y.L.; funding acquisition, M.-Y.L. and D.-Y.L. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

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

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** The data presented in this study will be available on request to the corresponding author.

**Acknowledgments:** This work was supported by the Dong-A University research fund.

**Conflicts of Interest:** The authors declare no conflict of interest.
