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Figure 12. Discharge temperatures of the heat pump with (ON) and without (OFF) IHX.

Figure 12 Discharge temperatures of the heat pump with (ON) and without (OFF) IHX.

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Figure 1. Heat pump system (a) without IHX; (b) with IHX.
Figure 1. Heat pump system (a) without IHX; (b) with IHX.
Figure 2 shows the thermodynamic cycle of the heat pump in the p-h diagram. Figure 2. p-h diagram of heat pump system.
Figure 2 shows the thermodynamic cycle of the heat pump in the p-h diagram. Figure 2. p-h diagram of heat pump system.
The evaporator shell and tube heat exchanger is shown in Figure 3. Figure 3. Sketch of the shell and tube heat exchanger.
The evaporator shell and tube heat exchanger is shown in Figure 3. Figure 3. Sketch of the shell and tube heat exchanger.
The evaporator consists of two zones, namely: section I—evaporation; and section Il—superheating (see Figure 4).
The evaporator consists of two zones, namely: section I—evaporation; and section Il—superheating (see Figure 4).
Figure 5. Photo (a) and scheme (b) of the experimental set-up. Figure 5 shows a schematic diagram and photograph of the experimental test facility Table 1 shows the main components of the heat pump system and their characteristics. Thermocouples and transducers were used to measure the temperature and pressure of the refrigerants and the cooling water (brine) and hot water. The mass flow rate of the refrigerants was measured with a Coriolis mass flow meter. Water flow sensors and turbine flow meters were used to measure the volumetric flow of the cooling and heating water. The thermocouple was immersed in the refrigerant through a drilled }-inch hole in the tube. The welding socket was welded to the pipe over the hole. The welding socket has a 5-inch NPT thread in the center. Teflon tape was applied to the 5-inch NPT thread of the thermowell. The thermowell was then inserted into the welding socket. The power requirements of the compressor were measured using a digital wattmeter. The list of measuring points with the corresponding measuring devices can be found in Table 2.
Figure 5. Photo (a) and scheme (b) of the experimental set-up. Figure 5 shows a schematic diagram and photograph of the experimental test facility Table 1 shows the main components of the heat pump system and their characteristics. Thermocouples and transducers were used to measure the temperature and pressure of the refrigerants and the cooling water (brine) and hot water. The mass flow rate of the refrigerants was measured with a Coriolis mass flow meter. Water flow sensors and turbine flow meters were used to measure the volumetric flow of the cooling and heating water. The thermocouple was immersed in the refrigerant through a drilled }-inch hole in the tube. The welding socket was welded to the pipe over the hole. The welding socket has a 5-inch NPT thread in the center. Teflon tape was applied to the 5-inch NPT thread of the thermowell. The thermowell was then inserted into the welding socket. The power requirements of the compressor were measured using a digital wattmeter. The list of measuring points with the corresponding measuring devices can be found in Table 2.
Table 1. Main characteristics of the experimental set-up components. Table 2. Main characteristics of the measurement instrumentation.
Table 1. Main characteristics of the experimental set-up components. Table 2. Main characteristics of the measurement instrumentation.
4.2. Boundary and Initial Condition
4.2. Boundary and Initial Condition
Table 3. Boundary and initial conditions. 4.3. Testing Procedure
Table 3. Boundary and initial conditions. 4.3. Testing Procedure
Table 4. Main properties of the considered refrigerants. At the beginning of the test, the temperature of the inlet water in the evaporator was Tog = 3.94 °C, and the mass flow rate was 1-¢ = 0.28 kg/s, while the evaporating temperature of the refrigerant was Teva = —6.1 °C, and the pressure was Peva = 178 kPa. On the other side of the heat pump system, the water outlet temperature in the condenser was Ty¢ = 35.1 °C, while the condensing temperature was Ton = 48.7 °C, and the pressure was Peva = 966 kPa. The mass flow rate of the refrigerant was m, = 9.7 g/s.
Table 4. Main properties of the considered refrigerants. At the beginning of the test, the temperature of the inlet water in the evaporator was Tog = 3.94 °C, and the mass flow rate was 1-¢ = 0.28 kg/s, while the evaporating temperature of the refrigerant was Teva = —6.1 °C, and the pressure was Peva = 178 kPa. On the other side of the heat pump system, the water outlet temperature in the condenser was Ty¢ = 35.1 °C, while the condensing temperature was Ton = 48.7 °C, and the pressure was Peva = 966 kPa. The mass flow rate of the refrigerant was m, = 9.7 g/s.
Figure 6. Comparison of the experimental and predicted cooling capacity. Figure 6 shows the predicted and measured values for cooling capacity for the case of cooling with IHX and without applying IHX. The predicted values are within the margin of error of 7.4%.
Figure 6. Comparison of the experimental and predicted cooling capacity. Figure 6 shows the predicted and measured values for cooling capacity for the case of cooling with IHX and without applying IHX. The predicted values are within the margin of error of 7.4%.
Figure 7. Comparison of the experimental and predicted power consumption of the compressor To validate the mathematical method, the results of the experimental tests were compared with the results of the numerical simulation. Figures 7-10 show the measured and numerical simulation predicted results of the heat pump with and without the application of IHX. Both cases include the refrigerants R1234yf and R1234ze(E). The figures show the maximum deviation (max) between the measured and predicted values.
Figure 7. Comparison of the experimental and predicted power consumption of the compressor To validate the mathematical method, the results of the experimental tests were compared with the results of the numerical simulation. Figures 7-10 show the measured and numerical simulation predicted results of the heat pump with and without the application of IHX. Both cases include the refrigerants R1234yf and R1234ze(E). The figures show the maximum deviation (max) between the measured and predicted values.
Figure 8. Comparison of the experimental and predicted condenser capacity.
Figure 8. Comparison of the experimental and predicted condenser capacity.
Figure 9. Comparison of the experimental and predicted coefficient of performance.
Figure 9. Comparison of the experimental and predicted coefficient of performance.
Table 5. Contribution of uncertainty of independent parameters. From the data for water (heating fluid), the gradient for specific heat between 35 and 50 °C is nearly zero. Therefore, the first term in Equation (68) can be neglected. The same reasoning applies to the density of water; thus, the second term in Equation (68) can be neglected. The absolute systematic uncertainty of the temperature is 0.2 °C according to Table 2 and 0.3 °C considering the influencing parameters described in 4.5.1 (cumulatively 0.5 °C). The random uncertainty of the temperature is assumed to be 0.2 °C based on previous measurements. According to Equation (68) and Table 5, the calculated standard uncertainty of COP is from 3.55% to 3.89%.
Table 5. Contribution of uncertainty of independent parameters. From the data for water (heating fluid), the gradient for specific heat between 35 and 50 °C is nearly zero. Therefore, the first term in Equation (68) can be neglected. The same reasoning applies to the density of water; thus, the second term in Equation (68) can be neglected. The absolute systematic uncertainty of the temperature is 0.2 °C according to Table 2 and 0.3 °C considering the influencing parameters described in 4.5.1 (cumulatively 0.5 °C). The random uncertainty of the temperature is assumed to be 0.2 °C based on previous measurements. According to Equation (68) and Table 5, the calculated standard uncertainty of COP is from 3.55% to 3.89%.
from 1.79% to 4.76% higher for the R1234yf refrigerant than without IHX, while it increased from 1.15% to 3.11% for the R1234ze(E) refrigerant. Similar results were obtained by Cho et al. [13]. The relative differences in power consumption of the compressors with (ON) IHX obtained with R1234yf refrigerant ranged from 29.86% to 36.79% higher than those with the R1234ze(E) refrigerant, while the relative differences without (OFF) IHX with the refrigerant R1234yf were higher, from 27.91% to 35.74% than those with the refrigerant R1234ze(E). Figure 10. The compressor power consumptions of the heat pump with (ON) and without (OFF) THX.
from 1.79% to 4.76% higher for the R1234yf refrigerant than without IHX, while it increased from 1.15% to 3.11% for the R1234ze(E) refrigerant. Similar results were obtained by Cho et al. [13]. The relative differences in power consumption of the compressors with (ON) IHX obtained with R1234yf refrigerant ranged from 29.86% to 36.79% higher than those with the R1234ze(E) refrigerant, while the relative differences without (OFF) IHX with the refrigerant R1234yf were higher, from 27.91% to 35.74% than those with the refrigerant R1234ze(E). Figure 10. The compressor power consumptions of the heat pump with (ON) and without (OFF) THX.
Figure 11 shows the heat pump mass flow rate with (ON) and without (OFF) IHX for R1234yf and R1234ze(E) refrigerants as a function of condensing and evaporating temperatures. Figure 11. Mass flow rates of the heat pump with (ON) and without (OFF) IHX.
Figure 11 shows the heat pump mass flow rate with (ON) and without (OFF) IHX for R1234yf and R1234ze(E) refrigerants as a function of condensing and evaporating temperatures. Figure 11. Mass flow rates of the heat pump with (ON) and without (OFF) IHX.
Figure 13. Volumetric efficiency versus compression ratio Figure 13 shows the volumetric efficiency as a function of the compression ratio for the R1234ze(E) and R1234yf refrigerants. Considering that the molecular weights of the refrigerants R1234yf and R1234ze(E) are the same, the compression ratios are similar; thus, similar volumetric efficiencies can be expected. CU
Figure 13. Volumetric efficiency versus compression ratio Figure 13 shows the volumetric efficiency as a function of the compression ratio for the R1234ze(E) and R1234yf refrigerants. Considering that the molecular weights of the refrigerants R1234yf and R1234ze(E) are the same, the compression ratios are similar; thus, similar volumetric efficiencies can be expected. CU
Figure 14. The cooling capacity of the heat pump with (ON) and without (OFF) IHX.
Figure 14. The cooling capacity of the heat pump with (ON) and without (OFF) IHX.
Figure 15 shows the relative differences in the heat output of the heat pump systems with and without IHX, between the two refrigerants R1234yf and R1234ze(E), as a function of the condensing and evaporating temperatures. The values of the heating capacity were higher in both cases with the refrigerant R1234yf than with R1234ze(E). Figure 15. The heating capacities of the heat pump with (ON) and without (OFF) IHX.
Figure 15 shows the relative differences in the heat output of the heat pump systems with and without IHX, between the two refrigerants R1234yf and R1234ze(E), as a function of the condensing and evaporating temperatures. The values of the heating capacity were higher in both cases with the refrigerant R1234yf than with R1234ze(E). Figure 15. The heating capacities of the heat pump with (ON) and without (OFF) IHX.
Figure 16. The COP values of the heat pump with (ON) and without (OFF) IHX. When IHX is used, the heating capacity for the R1234yf refrigerant is from 7.7% to 26.44% higher than without IHX, while for the R1234ze(E) refrigerant, it ranges from 5.15% 0 17.32%. The heat output of the R1234yf is between 23.54% and 33. creases with an increase in the eva rises, but the power consumed by effect of increasing heating capaci 27% higher t poration tem: han t. HX. the compressor a heat pump with (ON) IHX obtained with the re hat with the refrigerant R1234ze(E). For a heat pump system without (OFF) IHX, the cooling capacity obtained with the re R1234yf was between 16.41% and 28.52% hig R1234ze(E). Figure 16 shows the COP values as a function of condensing and eva emperatures for variants with and without I t can be clearly seen that the emperature. The heating capacity increases significantly as the evaporating tem frigerant frigerant her than that obtained with the refrigerant porating COP in- perature and a decrease in the condensation perature so increases. Looking at the combined y and power consumption, COP increases slightly.
Figure 16. The COP values of the heat pump with (ON) and without (OFF) IHX. When IHX is used, the heating capacity for the R1234yf refrigerant is from 7.7% to 26.44% higher than without IHX, while for the R1234ze(E) refrigerant, it ranges from 5.15% 0 17.32%. The heat output of the R1234yf is between 23.54% and 33. creases with an increase in the eva rises, but the power consumed by effect of increasing heating capaci 27% higher t poration tem: han t. HX. the compressor a heat pump with (ON) IHX obtained with the re hat with the refrigerant R1234ze(E). For a heat pump system without (OFF) IHX, the cooling capacity obtained with the re R1234yf was between 16.41% and 28.52% hig R1234ze(E). Figure 16 shows the COP values as a function of condensing and eva emperatures for variants with and without I t can be clearly seen that the emperature. The heating capacity increases significantly as the evaporating tem frigerant frigerant her than that obtained with the refrigerant porating COP in- perature and a decrease in the condensation perature so increases. Looking at the combined y and power consumption, COP increases slightly.
Figure 17. Pressure drop of the refrigerants in the condenser. The following figures show the pressure drops of the: refrigerants in the heat exchanger. Figure 17 shows the pressure drop of the refrigerants R1234ze(E) and R1234yf in the condenser as a function of mass flow rate and condensing temperature.
Figure 17. Pressure drop of the refrigerants in the condenser. The following figures show the pressure drops of the: refrigerants in the heat exchanger. Figure 17 shows the pressure drop of the refrigerants R1234ze(E) and R1234yf in the condenser as a function of mass flow rate and condensing temperature.
Figure 19. Pressure drop of the vapor phase refrigerants in the IHX. Figure 19 shows the pressure drop of the refrigerants R1234ze(E) and R1234yf in the vapor phase in IHX as a function of temperature and mass flow rate. It can be seen that the pressure drop of the vapor phase refrigerant R1234ze(E) is between 47.5% and 54.48% higher than the pressure drop of the vapor phase refrigerant R1234yf.
Figure 19. Pressure drop of the vapor phase refrigerants in the IHX. Figure 19 shows the pressure drop of the refrigerants R1234ze(E) and R1234yf in the vapor phase in IHX as a function of temperature and mass flow rate. It can be seen that the pressure drop of the vapor phase refrigerant R1234ze(E) is between 47.5% and 54.48% higher than the pressure drop of the vapor phase refrigerant R1234yf.
Figure 18. Pressure drop of the refrigerants in the evaporator. Figure 18 shows the pressure drop of the refrigerants R1234ze(E) and R1234yf in the evaporator tubes as a function of mass flow rate and evaporating temperature. It can be seen that the pressure drop in the evaporator is significantly higher than in the condenser for both refrigerants. At the same time, the pressure drop is from 49.4% to 64.7% higher when using the R1234ze(E) refrigerant than when using R1234yf.
Figure 18. Pressure drop of the refrigerants in the evaporator. Figure 18 shows the pressure drop of the refrigerants R1234ze(E) and R1234yf in the evaporator tubes as a function of mass flow rate and evaporating temperature. It can be seen that the pressure drop in the evaporator is significantly higher than in the condenser for both refrigerants. At the same time, the pressure drop is from 49.4% to 64.7% higher when using the R1234ze(E) refrigerant than when using R1234yf.
Figure 20. Pressure drop of the liquid phase refrigerants in IHX Figure 20 shows the pressure drop in the liquid phase of R1234ze(E) and R1234yf in THX as a function of temperature and mass flow rate. It can be seen that the pressure drop of the two liquid phase refrigerants is very small and almost identical; the pressure drop is almost negligible. The pressure drop of the liquid phase refrigerant R1234yf is from 7.7% to 10.4% higher than the pressure drop of the liquid phase refrigerant R1234ze(E).
Figure 20. Pressure drop of the liquid phase refrigerants in IHX Figure 20 shows the pressure drop in the liquid phase of R1234ze(E) and R1234yf in THX as a function of temperature and mass flow rate. It can be seen that the pressure drop of the two liquid phase refrigerants is very small and almost identical; the pressure drop is almost negligible. The pressure drop of the liquid phase refrigerant R1234yf is from 7.7% to 10.4% higher than the pressure drop of the liquid phase refrigerant R1234ze(E).
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