# Feasibility Analysis of Industrial High-Temperature Heat Pumps in Greece
## 3 Results and Discussion  
### Parametric Analysis of the Waste Heat Source-Driven System  
The parametric investigation of the WHS-driven HTTP is presented in this section and also useful relative results are included in tables in Appendix A. The influence of the WHS temperature and the process heat capacity are studied, as well as the process heat temperature level. Figures 3-5 show the impact of the WHS temperature on the COP (Figures 3a, 4a and 5a) and on the exergy efficiency (subfigures (Figures 3b, 4b and 5b). In these figures, different curves correspond to different process heat capacities, specifically to 100, 200, 300, 400 and 500 kW. The process heat temperature is 100 \({}^{\circ}\)C in Figure 3, 140 \({}^{\circ}\)C in Figure 4, and 180 \({}^{\circ}\)C in Figure 5.  
The results of these figures indicate that increases in the WHS temperature lead to higher COP values as the heat pump is supplied with a higher exergy input. Conversely, increases in the process heat temperature lead to smaller COP values because there is greater difficulty in producing useful heat at higher temperatures. Additionally, an increase in the process heat capacity leads to a decrease in COP, which is a reasonable outcome, since higher heat production requires HTTP to operate in more difficult conditions, and therefore, the performance is reduced. The mass flow rate of the WHS is the same in all \begin{table}
\begin{tabular}{c c} \hline
**Parameter** & **Value** \\ \hline Gas boiler efficiency & 70\% \\ \hline Natural gas cost & 0.06 EUR/kWh\({}_{\text{th}}\) \\ \hline CO\({}_{2}\) specific emissions factor for the natural gas & 0.196 kgC\({}_{\text{O}2}\)/kWh \\ \hline CO\({}_{2}\) specific emissions factor for the electricity & 0.252 kgC\({}_{\text{O}2}\)/kWh \\ \hline HTTP cost & 300 EUR/kWh \\ \hline Electricity cost & 0.15 EUR/kWh \\ \hline Maintenance cost & 2\% of the capital cost \\ \hline Lifetime period of the investment & 25 years \\ \hline Discount factor & 3\% \\ \hline Operation time per year & 8760 h \\ \hline \end{tabular}
\end{table} 
Table 3: Parameters for economic and environmental analysis. cases. This assumption limits HTTP's ability to produce higher heating product, leading to a lower COP. Practically, in cases of higher capacity, the WHS must be cooled further, which lowers the evaporation temperature and consequently reduces the COP. For the nominal capacity of 300 kW, the COP ranges from 2.388 to 5.175 for T\({}_{\text{process}}\) = 100 \({}^{\circ}\)C, while for T\({}_{\text{process}}\) = 140 \({}^{\circ}\)C, it ranges from 1.607 to 2.669, and for T\({}_{\text{process}}\) = 180 \({}^{\circ}\)C, it ranges from 1.039 to 1.526. These results indicate that there is a significant reduction in the COP as the process temperature increases. Also, for the case with T\({}_{\text{process}}\) = 180 \({}^{\circ}\)C, a high WHS temperature is required to achieve an acceptable COP. Figure 3: System performance. (**a**) COP, and (**b**) exergy efficiency for process heat temperature at 100 \({}^{\circ}\)C and variable combinations of WHS temperature and process heat capacities. Regarding the exergy efficiency, the curves are close to each other for the different capacities, while only the curve of 100 kW corresponds to significantly lower exergy efficiency, specifically for high WHS temperatures. Moreover, for the process heat temperatures of 100 \({}^{\circ}\)C and 140 \({}^{\circ}\)C, the efficiency curves are close to 45%, while for 180 \({}^{\circ}\)C, they drop down to 35%. These results indicate that the system can efficiently exploit the WHS and convert it into process heat; however, in high-temperature applications, HTHPs become less favorable due to reduced exergy efficiency. Furthermore, for the majority of the exergetic efficiency curves, the exergy efficiency is maximized for an intermediate WHS temperature. This is a reasonable result because while the WHS increases, there is higher exergy input  
Figure 4: System performance.