High Temperature Heat Pump System Research Articles

Performance simulation study of multi-stage compression-throttle water working medium high-temperature heat pump system

In order to meet the demands of industrial high temperature heat and waste heat recovery in an economical and low-carbon manner, there has been a growing interest in the high-temperature heat pump using water as working medium. The study aims to address the issue of higher exhaust temperature in water working medium heat pumps resulting from a substantial increase in temperature, especially for the large temperature difference system which needs to adopt multi-stage compression. This will be accomplished by proposing a new and energy-efficient high-temperature heat pump system that utilizes water as the working medium. The optimized system combining with self-circulating water spraying and multi-stage compression, which can significantly reduce exhaust superheat and steadily improve system performance. A thermodynamic analysis was conducted on both two-stage and three-stage high-temperature heat pumps, taking into account the improved structure. The results indicate that the three-stage compression-throttle type can achieve the highest maximum water spraying ratio and the lowest exergy loss. This can effectively decrease the superheat of the compressor exhaust and enhance the overall system performance. Furthermore, in the three-stage compression-throttle system, when the evaporation temperature is set at 100 °C with a temperature increase of 40 °C, a mere 0.01 % augmentation in the water spraying ratio results in approximately a 0.0776 uplift in the COP of the water working medium system. This notable observation suggests that the implementation of self-circulating water spraying considerably enhances the system’s overall performance. Subsequently, an analysis of the corresponding design and operating parameters was conducted. It is important to note that the temperature of the waste heat source and the rotational speed of the compressor are the two key parameters that significantly impact the operation of the system. By this study, it provides some theoretical guidance for practical engineering applications.

Advanced Exergy and Exergoeconomic Analysis of Cascade High-Temperature Heat Pump System for Recovery of Low-Temperature Waste Heat

Cascade high-temperature heat pumps (CHTHPs) are often applied to recover low-temperature industrial waste heat owing to their large temperature lift. Through a comprehensive consideration of thermodynamic and economic performance, conventional and advanced exergy and exergoeconomic analyses are employed in this study to evaluate the potential for the improvement in CHTHP systems. The results show that the avoidable endogenous exergy destruction in a CHTHP system accounts for 62.26% of its total exergy destruction, indicating that most of the exergy destruction comes from the components. This suggests that CHTHP systems still have significant potential for improvement. The very low exergoeconomic factor of the total system (only 0.75%) implies that the exergy destruction cost has a great influence on the economic performance of a CHTHP system. The high- and low-temperature compressors are the two components with the highest exergy destruction, accounting for 34.14% and 26.79% of the total exergy destruction in the system, respectively. Moreover, their exergy destruction cost is much larger than that of the other components. Thus, the priorities for improvement should be the high- and low-temperature compressors. The decrease in exergy destruction in compressors produces a reduction in carbon emissions. This comprehensive analysis of thermodynamic and economic performance supplies guidance for the engineering application of CHTHPs in low-temperature waste heat recovery.

Analysis and optimization of injection characteristics and comprehensive performance of low GWP refrigerant HP-1 in high temperature heat pump systems

In the context of low-GWP refrigerants becoming a research hotspot, the environmentally friendly refrigerant HP-1 with independent intellectual property rights in China has demonstrated significant advantages in fields such as data centers and 5G base stations. However, there are few applied studies in the field of high-temperature heat pumps (HTHPs), therefore, in this study, HP-1 was utilized in HTHP system and this process was combined with the injection technology. It has been proven to be an effective approach for performance improvement. The injection characteristics of HP-1-based HTHP were analyzed and optimized with a focus on safety, stability, and efficient operation. The application advantages of HP-1 were compared and analyzed in terms of thermodynamic performance and Total Equivalent Warming Impact. The results indicated that there were three types of characteristic injection pressures based on system performance, corresponding to the maximum coefficient of performance (COP), the lowest electronic expansion valve inlet refrigerant temperature, and the lowest exhaust temperature of the compressor. Further, the corresponding control equations for injection pressure were obtained. Based on the safety injection pressure, the optimal COP under injection pressure could effectively improve the COP of the system by 2.1–5.2 %, and the exhaust temperature also increased by 6.1–10.1 %. When the temperature of the heat source was 50 °C and the target heating temperature was 120 °C, the heating capacity of HP-1 increased by 10.8 % compared with that of R245fa, the COP of the system increased by 2.7 %, and the volume heating capacity increased by 10.3 %. Moreover, the emission reduction effect of HP-1 was significant, and the carbon dioxide emissions were reduced by 15.4–39.1 %. The analysis shows that HP-1 exhibits better performance and environmental characteristics than HFC-245fa. This study is of guiding significance to improve the thermodynamic performance of HTHP, for the safe and efficient operation and energy saving and emission reduction in the industrial field.

Thermodynamic analysis of high temperature cascade heat pump with R718 (high stage) and six different low-GWP refrigerants (low stage)

Decarbonizing industrial heating globally is a significant challenge, driving the integration of high-temperature heat pumps for heat recovery and electrification in the industrial sector. However, current high-temperature heat pumps with low global warming potential refrigerants face limitations in delivering high-temperature heat due to their restricted compressor discharge temperature or require several compressors/intercoolers. To address these issues, a novel high-temperature cascade heat pump system is proposed, utilizing water (R718) in the high stage, while selecting one among six low GWP refrigerants (R1234ze(Z), R1233zd(E), R1336mzz(Z), R600, R600a, R601) in the low stage, with single compressor at each stage. To manage high discharge temperatures of high stage, liquid water injection is applied during high stage compression, modeled for both wet and dry steam. The model is validated against available experimental data with maximum error less than 5 %. Further, the effectiveness of the internal heat exchanger in low stage cycle is assessed for all investigated low stage refrigerants. Results reveal that R718 + R600 offers the optimal refrigerant working pair, achieving a maximum COP × VHC of 2895.1 kJ m−3 for delivering high temperature heat at water condensation temperature of 190 °C and recovering heat from low temperature waste energy of 50 °C.

Significant thermal upgrade via cascade high temperature heat pump with low GWP working fluids

High temperature heat pump is a promising solution for efficient high temperature heat supply. However, the poor performance when it operates in large temperature lift hinders it from utilizing low temperature waste heat. To solve this problem, a cascade high temperature heat pump with economized vapor injection was established and a simulation model was developed accordingly. The tests were conducted using R134a/R245fa and R1234ze(E)/HP-1 at heat source temperature from 5 to 30 °C and heat sink temperature from 90 to 120 °C, with the coefficient of performance (COP) varying in the range of 1.72–2.73 and 1.77–2.75, respectively. The COP about 2.20 was achieved with R1234ze(E)/HP-1 at optimal intermediate temperature and optimal economized vapor injection pressure when the temperature lift is 100 °C. In the simulated case study, the heat pump water boiler based on the experimental prototype decreases CO2 emission by 62.8 % compared to electric boiler. Moreover, using low GWP working fluids reduces 1.32 × 104 kg direct CO2 emission in TEWI. Under the current technological, pricing, and operational condition, it takes 16 years for heat pump to have economic benefit over electric boiler, but this duration can be shortened with reduced initial cost, improved COP, and increased operating hours and electricity price. In summary, this work presented a high-efficient, environmentally friendly, and economically viable cascade high temperature heat pump system which has potential to utilize the abundant environmental heat source and deliver high temperature heat, being an alternative to the conventional heat generation equipment such as boilers.

Innovative process integrating high temperature heat pump and direct air capture

Direct air capture (DAC) technology plays a crucial role in mitigating the effects of global warming by capturing carbon dioxide (CO2) directly from the atmosphere. A significant technical challenge for DAC is its high thermal energy consumption, which results in an unacceptable overall cost (600$tCO2–1). The combination of a high-temperature heat pump (HTHP) and DAC system offers a substantial reduction in thermal energy consumption, decreased reliance on renewable energy sources, and enhanced DAC system flexibility. This study presents three distinct thermal integration strategies that combine an HTHP with solid adsorbent-based DAC and verifies their effectiveness in reducing energy consumption and CO2 emissions compared to a traditional DAC system. Among them, the deeply integrated DAC-HTHP system (I-DAC) exploits low-grade adsorption heat and waste heat, providing direct heating and cooling energy to the DAC system via refrigerant condensation and evaporation processes. Simulation results indicate that the I-DAC system achieves an extremely low operating energy consumption of 2.77 GJtCO2–1, representing a 69.5% reduction than traditional DAC under the same conditions. Consequently, the I-DAC offers a cost-effective (32.0–46.2 $tCO2–1) negative emission solution. We also demonstrate that the I-DAC is promising for wide application in cities to recycle waste heat and remove CO2 from the air. The comprehensive implementation of the I-DAC in 105 cities could yield a net annual productivity of 980 MtCO2.

Experimental and simulation study on R134a/RE170/R152a mixture as R134a replacement in a moderately-high temperature heat pump

A novel ternary mixed refrigerant was proposed in this study, and its optimal ratio was determined. The newly proposed refrigerant was termed RDR-a. Experiments were performed to compare the system performance of RDR-a and R134a for applications in the moderately high-temperature heat pump (MHTHP) system. As indicated by the results of this study, RDR-a achieved a lower cost, and it exhibited the capability of applying to the system of R134a directly. Besides, RDR-a achieved a GWP of 61.79% lower than R134a. Moreover, the coefficient of performance (COP) of RDR-a and R134a was elevated by 0.071/℃ and 0.037/℃, respectively, with the inlet temperature of chilled water. Moreover, the COP of RDR-a and R134a declined by 0.09/℃ and 0.037/℃, respectively, with the outlet temperature of cooling water. The COP of RDR-a and R134a tended to be first increased and then decreased with the rise of the charge amount, and RDR-a achieved an optimal charge amount that only accounted for 80.95% of that of R134a. Furthermore, RDR-a achieved a COP of 4.94%, 10.01% and 20.52% higher than that of R134a, respectively, as the inlet temperature of chilled water, the outlet temperature of cooling water and the charge amount of the refrigerant varied. The heating capacity of RDR-a was examined to be 13.61%, 19.14%, and 29.47% higher than that of R134a, respectively.

Dual pressure condensation heating high temperature heat pump using eco-friendly working fluid mixtures for industrial heating processes: 4E analysis

To make better use of waste energy for the industrial heating processes, dual pressure condensation heating high temperature heat pump system (DPS) is proposed, to achieve the purpose of step heating. Meantime, environmental-friendly working fluid hydrocarbons are selected as the components of the mixtures. The energy, exergy, environmental and economic (4E) analysis models are established, and the system performance is optimized, compared with single-stage (SS) system and fossil fuel-fired boilers. There is an optimal intermediate water temperature corresponding to the highest system energy efficiency. The maximum COP of 5.29 is achieved when R600a/R601a (50/50) is adopted, improved by 18.23% and 24.18% compared with DPS and SS systems using pure working fluid. By using zeotropic working fluid, the irreversible heat transfer loss can be significantly reduced. The overall exergy loss with R600a/R601a (50/50) is 21.68–41.27% and 12.26–16.69% lower than pure SS and pure DPS systems, respectively. In terms of environmental and economic aspects, DPS with zeotropic working fluid shows excellent performance. In comparison with boiler, pure DPS and pure SS system, the reduction of carbon emissions through the whole lifetime is 81.22%, 15.35% and 20.04%, and the life cycle cost is decreased by 93.91%, 9.70–15.05%, and 27.89–38.07%.

Theoretical investigation of a novel high-temperature heat pump exploiting low-temperature waste heat and using two-phase machines with zero electric consumption

A novel high-temperature heat pump (HTHP) exploiting low-temperature waste heat is presented, which is enabled by two-phase compressors and expanders without the need for any requirement of external electric power. The investigation involves a sensitivity analysis at the design point, considering the concurrent variation of five independent variables. The aim is to identify the best-performing conditions for a rubber manufacturer and a canning industry which have different temperatures of waste heat and required heating power. The COP of the overall HTHP system, which is the ratio between the output heating power and the input thermal power (coming from the heat source) is evaluated. The maximum COP values are 0.258 for the rubber manufacturer and 0.452 for the canning industry. The primary energy saving is assessed in terms of equivalent fuel consumption. For the rubber manufacturer, the resulting yearly cost saving is in the range of 129 ÷ 646 €/kWth of HTHP installed capacity, and 140 €/kWth for the canning industry. The economic viability of the HTHP is contingent upon achieving isentropic efficiencies of the expanders and compressors higher than 0.59 and 0.55, respectively, for the rubber manufacturer, and both higher than 0.45 for the canning industry.

Novel configuration of dual-temperature condensation and dual-temperature evaporation high-temperature heat pump system: Carbon footprint, energy consumption, and financial assessment

To achieve the goal of carbon neutrality for the application of industrial heating by recovery waste heat, the concept of dual-temperature condensation and dual-temperature evaporation is proposed for the high-temperature heat pump (HTHP) by introducing the techniques of ejector and two-stage compression. The energy, exergy, emission, and economic models are developed and optimized for the two new proposed systems. Then, the energy consumption, CO2 emissions and cost (LCC) during the whole life cycle are compared with five existing heat pumps and four traditional boilers. The highest coefficient of performance (COP) of heat pump (HP) can be got when intermediate water temperature on the heat sink side is optimum. The new proposed systems have better performances than the other five HTHPs. During the rated working condition, discharge temperature decreases by the use of dual-temperature condensation and dual-temperature evaporation HP with an ejector (Ej-DCDE). The optimal COP of Ej-DCDE-2 is 4.25, which is 11.55% and 1.43% higher than dual-temperature condensation and single-temperature evaporation HP and Ej-DCDE-1, respectively. The exergy destruction of Ej-DCDE-2 is reduced by 27.88% compared with basic heat pump (Base). Moreover, Ej-DCDE-2 has the lowest primary energy consumption of 14.62 ktoe, 22.19% and 25.09% lower than Base and oil-fired boiler during the total working period, respectively. In general, HTHPs have lower carbon dioxide, gaseous and particular pollutant emissions compared with boilers, especially Ej-DCDE-2. Finally, Ej-DCDE-2 has the minimum LCC, which is 14.67% and 11.75% less than Base and coal-fired boiler. Ej-DCDE-2 shows the most potential advantages of all the heating solutions and is recommended to replace traditional boilers for industrial heating.

Extremum seeking control for real-time optimization of high temperature heat pump systems incorporating vapor injection

In order to minimize the power consumption of a vapor-injected high temperature heat pump system with R245fa as refrigerant, a control strategy, namely Extremum seeking control, is proposed. It can implement real-time model-free optimization control of plants with concave and convex properties. Modelica-based dynamic simulation model of the proposed system is developed. The Newton-based Extremum seeking control is used to optimize the intermediate pressure of the proposed system to obtain the minimum power consumption of the compressor at a fixed heating capacity (200 kW). The adopted ESC strategy requires four measured quantities, namely, injection pressure, condenser outlet water temperature, evaporator outlet superheat and compressor power consumption, to achieve optimal control of the system in real time. Two operation scenarios are simulated: stable and freely variable heat source temperature. For both scenarios, the condenser outlet water temperature was set to 140 °C. The simulation results show that at stable heat source temperature, the power consumption is reduced by 5.2% and the COP is increased by 7.7% compared to a fixed initial intermediate pressure. Under the free-variable heat source condition, the power consumption can be reduced by up to 5 kW compared to a constant input. A total of 283 kWh of power was saved during the 48 h simulation. Thus, the Newton-based extremum seeking control strategy can optimize the intermediate pressure to achieve the minimum power consumption while maintaining excellent transient performance, and demonstrate the superiority of the ESC strategy for real-time optimization..

Multi-variable extremum seeking control for high temperature heat pump system incorporating double refrigerant injection

The use of refrigerant injection technology to enhance the heating efficiency of heat pumps with larger temperature lifts is becoming more common. Heat pumps with double refrigerant injection loops have better energy efficiency than traditional ones with single refrigerant injection loops. A multi-variable extremum seeking control (ESC) strategy for a high-temperature heat pump system with double refrigerant injection technology is proposed in this study. A Modelica-based dynamic simulation model of the considering system is established in Dymola, and a co-simulation with the proposed ESC strategy is built to validate the effectiveness of this control strategy to minimize power consumption. The strategy uses compressor power consumption as the feedback. The effective throttling area of the upper and lower EEVs is adjusted by a PI controller to manipulate the low and high-pressure vapor injection pressures. Three scenarios were simulated for control: stable, step curve, and freely variable heat source temperature conditions. The simulation results demonstrate that the multi-variable ESC has excellent convergence performance and confirm its effectiveness in searching for the optimal operating point.

Theoretical study of low-GWP refrigerants in high-temperature heat pump systems

Abstract In this paper, the thermal performance of three low-global warming potential refrigerants R1224yd(Z), R1223zd(E) and R1336mzz(Z) were studied to replace R245fa in the high-temperature heat pump system. The results showed that the heating capacity of R1224yd(Z), R1223zd(E) and R1336mzz(Z) was 6, 12 and 88% less than that of R245fa, respectively. The coefficient of performance (COP) of R1224yd(Z) and R1223zd(E) was 2 and 1% higher than that of R245fa, respectively. However, the COP of R1336mzz(Z) was 5% less than that of R245fa. The difference in compressor discharge temperature between R1224yd(Z), R1223zd (E), R1336mzz(Z) and R245fa was about ±5°C. R1224yd(Z) is the best refrigerant to replace R245fa. R1223zd(E) is the second. R1336mzz(Z) cannot be directly replaced unless the original system is modified.

System optimization of steam generation in the dual-flash compound circulation system

Concentrating on the problem of massive energy loss in the compressor, expansion valve, and the other components present in the high-temperature heat pump system under extensive temperature lift, the dual-flash compound circulation system is proposed and the thermodynamic model of the dual-flash compound circulation system was established. The article combines the multivariate simulated annealing algorithm, utilizes the system COP as the optimization goal, and completes the calculation of the thermodynamic parameters in the steady-state of the system that is based on satisfying the conditions of the system process. Using R245fa as the refrigerant, the condensation temperature is set within the range of 110°C–140°C for the model calculation. The results show that, compared to the traditional two-stage compression system under the same environment, the COP of the dual-flash compound circulation system can be increased up to 5.71%–12.13%, and the exergy efficiency can be increased by 5.11%–10.71%, respectively. Besides, steam production per unit refrigerant is also increased by 3.79%–5.14%. Finally, the feasibility of the theoretical model is verified by simulation, and it is concluded that the dual-flash compound circulation system has better steam production performance at the extensive temperature lift and the elevated condensation temperature.

Experimental study on high temperature heat pump system with a double heat source cascade

In order to improve the thermal performance of a high temperature heat pump system, to realize the efficient heat recovery of industrial waste heat, and to make the combined utilization of low and medium temperature heat sources, a high temperature heat pump system with a double heat source cascade is proposed, which can absorb heat from industrial waste heat and the system is capable of heating water up to the required high temperature. The performance of the system is tested and analyzed. It is found that the inlet temperature of the medium temperature heat source has a significant impact on the performance of the heat pump system under working mode of the medium and low temperature heat sources. When the inlet temperature of the intermediate temperature heat source rises from 42?C to 53?C, the heating capacity of the cascade heat pump increases by 18.6%, and its performance coefficient increases by 8.9%. This paper provides a reference for the high efficiency of the cascade high temperature heat pump technology.

Comparison study of conventional and advanced exergy analysis on cascade high temperature heat pump system based on experiment

Cascade high temperature heat pump (CHTHP) has shown remarkable application potential for industrial waste heat recovery owing to its superiority of large temperature lift. Great efforts have been made to optimize the performance of CHTHP by means of conventional exergy analysis (CEA), which was not qualified to uncover the thermodynamic interactions among components. Thus, advanced exergy analysis (AEA) has been adopted to comparatively evaluate the relationships of reversibility among the CHTHP components. Herein, both CEA and AEA were based on the experiment results from a prototype which could realize maximum temperature lift of 100 °C.The CEA results show that total exergy efficiency is 43.23%, while AEA results indicate that endogenous part accounts for 98.27% of the total exergy destruction and 67.69% of it is avoidable. The AEA reveals that the highest improvement priority belongs to low temperature compressor (LTCOM), followed by cascade heat exchanger (CHE) and high temperature compressor (HTCOM) and that low temperature expansion valve (LTEV) and high temperature expansion valve (HTEV) has no improvement potential which is different from the results of CEA theory. Conclusively, AEA can give more detailed guidance about the potential for improvement.

Study on the leakage in water-injected twin-screw steam compressor

Steam compressor shows great energy-saving potential in mechanical vapor compression and high-temperature heat pump systems. However, leakage remains a huge problem for compressor performance improvement and design optimization. In this article, a thermodynamic model with detailed leakage flow model was developed for the working process in water-injected twin-screw compressor. Altogether, leakage in different paths and heat and mass transfer between injected liquid and compressed vapor were considered. Compared with experimental results, the accuracy of predicted efficiency is within ± 5% for all tested operating conditions. In the validated model, leakage flow in five leakage paths and their effects on compressor efficiency was investigated. Results indicate that leakage can reduce volumetric efficiency by up to 50.2%, while the injected water liquid vaporization can improve volumetric efficiency by 7.9% at 5000 r·min−1. The leakage through contact line (CL), tip sealing (TS) line, and discharge end face (DE) show the most important impact on compressor efficiency, while the leakage through blow hole (BH) and suction end face (SE) has little impact on compressor efficiency. Compared with zero leakage under certain conditions, the reduction of volumetric efficiency caused by CL, TS line, and DE can reach up to 22.4%, 20.4%, and 12.7%, respectively. Reducing clearances of the above three leakage paths can efficiently improve the performance of steam compressor, especially for CL.

Life cycle techno-enviro-economic assessment of dual-temperature evaporation transcritical CO2 high-temperature heat pump systems for industrial waste heat recovery

Replacing fuel-fired boilers by using efficient heat pump plants to recover industrial waste heat is an effective solution to achieve the “dual carbon” target. Three novel transcritical CO2 high-temperature heat pump systems (Ej-Evap2-A, Ej-Evap2-B, and Ej-Evap2-C) are proposed in this study, by introducing the technique of dual-temperature evaporation realized with an ejector for cascade heat absorption from the heat source. Considering the application in the scenario of industry requirement of hot water heating, the life cycle performances of the new proposed heat pump systems and fuel-fired boilers are comprehensively studied from the perspectives of energetic, emissions, and economic. A sensitivity analysis about the new configuration heat pump system is also conducted considering the variation in electricity and coal price. The results demonstrate there exists an optimum discharge pressure that maximizes the coefficient of performance (COP). Ej-Evap2-C shows a maximum COP of 4.85, which is 14.40% higher than the baseline CO2 heat pump system (Base), and the exergy efficiency of Ej-Evap2-C is 7.86–15.19% higher than that of Base. Among the eight heating methods including coal-fired boilers (CFB), gas-fired boilers (GFB), electric heating boiler (EHB) and five kinds of CO2 heat pump systems, Ej-Evap2-C shows the least pollutant emissions and life cycle cost. Furthermore, Ej-Evap2-C has the shortest payback period of fewer than 7 years compared with the CFB. The dual-temperature evaporation CO2 high-temperature heat pump is promising to substitute traditional fuel-fired boilers to generate high-temperature fluid in the future.

Life cycle performance evaluation of cascade-heating high temperature heat pump system for waste heat utilization: Energy consumption, emissions and financial analyses

Inspired by the principle of cascade energy utilization, the concept of cascade-heating is introduced, and five layouts of cascade-heating high temperature heat pump (HTHP) systems are proposed and optimized to utilize the waste heat. The energy consumption, carbon and pollutant emissions, life cycle cost (LCC) and payback period (PBP) models are established. Meanwhile, detailed comparisons are made with conventional HTHPs and boilers. The results indicate it is more positive for cascade-heating HTHPs in terms of energy consumption, carbon and pollutant emissions, LCC and PBP. The primary energy consumption of cascade-heating water cooled saturated suction system (CWSAS) is declined by 1.8–22.8% and 3.4–19.2% in contrast to conventional HTHPs and traditional boilers, respectively. The life cycle carbon emissions of CWSAS are reduced by 1.7–6.1% and 76.5% compared to conventional HTHPs and electric boiler. The pollutant emissions can also be prominently declined by adopting cascade-heating HTHPs. For life cycle economic performance, LCC of cascade-heating flash tank superheated suction system (CFSUS) can be reduced by 4.5–18.3% compared with traditional HTHPs. Furthermore, PBP of CFSUS is the lowest of 3.1 years, and 15.4–65.9% shorter than traditional HTHPs. CWSAS is the most recommended configuration on account of its remarkable overall energy, environment and economic performances.

Theoretical Study of HFO1336mzz(Z)/HFO1224yd(Z) Refrigeran t Mixtures for High-temperature Heat Pump

Background: The global energy consumption problem is becoming more serious, therefore, it is a hot trend to improve energy efficiency and choose environmentally friendly alternative working fluids. Objective: The main thermophysical parameters of the refrigerant mixture, which blended HCFO 1224yd(Z) and HFO1336mzz(Z) in the high-temperature heat pump cycle, were theoretically studied to replace HFC245fa. The theoretical cycle model of refrigerant mixtures of high-temperature heat pumps was established. Methods: In this paper, a theoretical cycle model of the mixed refrigerant high-temperature heat pump is established, and the cycle performance of the mixed refrigerant in the high-temperature heat pump system under different working conditions is compared. Results: It was found that HFO1336mzz(Z) could reduce the exhaust temperature of the compressor and increase the heat pump coefficient COPh, and HCFO1224yd(Z) could improve the problem of excessive suction specific volume in high-temperature heat pump systems. Conclusion: The result shows that the refrigerant mixture with 0.6/0.4 HCFO1224yd(Z)/HFO1336 mzz(Z) has the best cycle performance when the condensing temperature is 150 °C, and the cycle temperature rise ranges from 50 to 70°C.When the cycle temperature rise is 70°C, and the condensing temperature ranges from 110 °C to 150°C, the coefficient of performance value of the refrigerant mixture with 0.2/0.8 HCFO1224yd(Z)/HFO1336mzz(Z) reaches the maximum of 3.11.