# Feasibility Analysis of Industrial High-Temperature Heat Pumps in Greece
## 3 Results and Discussion
### Sustainability Analysis  
The last part of the present investigation is devoted to the economic and environmental assessment of HTHPs. The results are compared with a baseline scenario of producing the process heat demand with a natural gas boiler. Comparative studies are carried out for the case of 300 kW process heat production. Three-dimensional plots are included in the present work with the aim of presenting the results briefly. Firstly, the COP is depicted in Figure 15 for different combinations of process heat temperature and WHS temperatures. It is clear that the COP takes higher values as the WHS temperature increases and the process heat temperature decreases, as stated in the previous subsections. Figure 16 illustrates the life cycle cost (LCC) of the unit for the different design scenarios of the WHS-driven HTHP. The maximum LCC was found for T\({}_{\text{win}}\) = 50 \({}^{\circ}\)C and T\({}_{\text{process}}\) = 180 \({}^{\circ}\)C. Moreover, Figure 17 depicts the results for the levelized cost of energy (LCOE), which is also maximized at T\({}_{\text{win}}\) = 50 \({}^{\circ}\)C and T\({}_{\text{process}}\) = 180 \({}^{\circ}\)C. However, the optimal scenario from an economic point of view is the one with the minimum economic indexes, which are observed for T\({}_{\text{win}}\) = 100 \({}^{\circ}\)C and T\({}_{\text{process}}\) = 100 \({}^{\circ}\)C. At this point, it is valuable to comment that this design scenario requires HTHP because the WHS of 100 \({}^{\circ}\)C is a stream of finite mass flow rate and it cannot provide a process heat at a constant temperature of 100 \({}^{\circ}\)C. Moreover, it is worth stating that the LCC was found to vary from 1.448 MEUR to 6.728 MEUR, while the LCOE varied from 0.0220 EUR/kWh to 0.1024 EUR/kWh. The LCC of the natural gas boiler was found to be 3.954 MEUR and the LCOE was 0.0602 EUR/kWh. Therefore, it is obvious that there are scenarios in which WHS-HTHP is beneficial economically, but in other cases, it is not the optimal choice. For the process heat production temperatures of 100, 110 and 120 \({}^{\circ}\)C, all the scenarios with WHS-based HTHP are economically viable. For T\({}_{\text{process}}\) = 130 \({}^{\circ}\)C, the economically viable designs require T\({}_{\text{win}}\)\(\geq\) 55 \({}^{\circ}\)C; for T\({}_{\text{process}}\) = 140 \({}^{\circ}\)C, the economically viable designs need T\({}_{\text{win}}\)\(\geq\) 65 \({}^{\circ}\)C; for T\({}_{\text{process}}\) = 150 \({}^{\circ}\)C, the economically viable designs need T\({}_{\text{win}}\)\(\geq\) 80 \({}^{\circ}\)C; and for T\({}_{\text{process}}\) = 160 \({}^{\circ}\)C, the economically viable designs need T\({}_{\text{win}}\)\(\geq\) 90 \({}^{\circ}\)C. On the other hand, all the scenarios with T\({}_{\text{process}}\) = 170 and 180 \({}^{\circ}\)C are not economically feasible solutions. Figure 15: COP variation for different combinations of WHS inlet temperature and process temperature. The environmental impact of HTTP use is evaluated through the CO\({}_{2}\) emissions, which are compared to the respective natural gas boiler scenario. Figure 18 shows that the annual CO\({}_{2}\) emissions are higher when the WHS temperature decreases and the process heat temperature increases. The maximum calculated value is 637.4 tn\({}_{\text{CO2}}\)/year for T\({}_{\text{win}}\) = 50 \({}^{\circ}\)C and T\({}_{\text{process}}\) = 180 \({}^{\circ}\)C. This value is lower than the value for the natural gas boiler scenario, which is 735.8 tn\({}_{\text{CO2}}\)/year. Therefore, in all the scenarios involving WHS exploitation, CO\({}_{2}\) emissions are avoided. Figure 19 depicts the CO\({}_{2}\) emission reduc  
Figure 16: LCC variation for different combinations of WHS inlet temperature and process temperature. Figure 17: LCOE variation for different combinations of WHS inlet temperature and process temperature. tions compared to the natural gas boiler scenario. Specifically, the reduction ranges from 13.38% to 82.61%.