Compressor Discharge Research Articles

Thermal design and optimization of high-temperature heat pump integrated with district heating benchmarked in Denmark for process heat supply

This work aims to assess and optimize the performance of cascade high-temperature heat pump (HTHP) integrated with district heating (DH) to produce 1 MW steam at 160 °C for the industrial processes. The heat available in the primary loop of the DH network at 80 °C is considered as the heat source; which is cooled down 70 °C through the HTHP evaporator, before supplying the DH secondary loop. The use of alternative hydrocarbons in the low-temperature loop are examined; and considering the gas compressor limitation, the HTHP performance of using each refrigerant is optimized and compared to each other.The optimization results reveal that pentane- hydrocarbon with the highest critical temperature- is the most promising refrigerant to be paired with steam in the high-temperature loop, reaching the highest COP of 2.66. However, concerning safety and compressor sizing issues, butane is an excellent candidate; with volumetric heating capacity (VHC) of about two times more than that of pentane, in the expense of just about 4 % reduction in the HTHP COP. In addition, water injection theoretically controls the steam compressor discharge temperature successfully, with just 0.9 K superheating at the compressor outlet; and reduces its power consumption and the HTHP COP up to 4.3 % and 1.7 %, respectively. Moreover, techno-economic analysis demonstrates that the HTHP technology shows a better business case compared to the conventional natural gas and electric boilers.

Numerical Prediction of Refrigerant Oil Two-Phase Flow from Scroll Compressor Discharge to the Suction Side via Back Pressure Chamber

Oil lubricates the contact between the orbiting and stationary scroll in the refrigerant scroll compressor, while the sealing between the scrolls is achieved through the refrigerant vapour pressure in the sealed back pressure chamber. The back pressure should be adjusted using the refrigerant oil two-phase flow from the oil separator at the compressor discharge to the back pressure chamber and the refrigerant oil flow from the back pressure chamber to the compressor suction side. Both of the flows are conducted through connecting tubes with corresponding high-pressure and low-pressure nozzles with small diameters. Models for predicting the refrigerant oil critical and subcritical flows through the nozzles were developed and applied in enable the prediction of the back pressure. The models are original, because the slip between the oil and the refrigerant as well as the refrigerant solubility in the oil are taken into account. The critical flow model is validated against the experimental data that are available in the literature. The back pressure is predicted by equating the mass flow rates of refrigerant and oil two-phase mixtures through the high- and low-pressure nozzles. The results show that the critical flow takes place through the high-pressure nozzle, while the subcritical flow through the low-pressure nozzle can also exist in cases with a small pressure difference between the back pressure chamber and the compressor suction side. The refrigerant solubility in the oil has a small influence on the critical and subcritical refrigerant oil mixture mass flow rates, while the influence on the back pressure is more pronounced.

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.

A hybrid control strategy for frequency regulation with variable refrigerant flow air conditioning system

Heating, ventilation and air conditioning (HVAC) systems of buildings are abundant sources for the Frequency Regulation (FR) ancillary service, whose actuating devices are controlled to follow the real-time power reference signals with the contractual capacity. For HVAC practice, model-based FR controls are hindered by expensive model acquisition. This paper presents a two-layer control strategy for HVAC systems to perform energy efficient FR service, with a rather low model requirement. At the lower level, the FR operation with a selected actuator is realized with a sliding mode control which is robust to power map variation. At the higher level, system efficiency is optimized in real time via a model-free constrained extremum seeking control (CESC). A conceptual variable refrigerant flow (VRF) system is used as the illustrative application, for which the outdoor unit fan offers the FR power reference tracking with SMC. At the outer loop, the compressor discharge pressure is adjusted by a CESC to minimize the total power consumption while the zonal temperature regulation is reinforced as equality constraint. The proposed strategy is evaluated with simulations on a Modelica simulation, and the results validate its effectiveness. The Net Energy Cost can reduce by 15% to 23% under different load levels.

Transcritical-transcritical cascade CO2 heat pump cycles for high-temperature heating: A numerical evaluation

Industrial heat pumps are becoming increasingly popular as a low-emissions technology due to the ability to leverage renewable electricity at high efficiencies. While heat pumps are already well-established for process temperatures below 100 °C, high-temperature heat pumps that can produce greater temperatures are limited by high pressure and temperature requirements that surpass the performance of conventional heat pump compressor technologies. Alongside this, new heat pump cycles which are being developed need to be compatible with low GWP and low ODP refrigerants. This paper presents a numerical evaluation on the thermodynamic performance of high-temperature heat pumps for supplying 200 °C sink temperatures with large temperature glides. Four new transcritical–transcritical cascade CO2 heat pump systems are modelled in this study which aim to limit the pressure requirements required to achieve high sink temperatures. An air heating case study for milk powder spray drying is presented. To achieve a COP of 3, all cycles had a similar maximum air outlet temperature between 110 °C and 113 °C. The transcritical-transcritical cascade cycle with internal heat exchangers on both the top and the bottom cycles achieved the lowest compressor discharge pressure (13.47 MPa maximum) for this case. The same cycle also achieved the highest COP of 2.22 when air outlet temperature was fixed at 200 °C (i.e., complete replacement of external heating). For such a heat pump to be economically feasible for heating air to 200 °C, an electricity-to-reference price ratio equal to or below 2.06 is required.

Effect of drying air supply temperature and internal heat exchanger on performance of a novel closed-loop transcritical CO2 air source heat pump drying system

A novel closed-loop transcritical CO2 air-source heat pump drying (HPD) system with a relatively simple structure, higher drying temperature, and internal heat exchanger (IHX) for the drying of medical equipment was proposed and built. With or without the IHX in the system, the effects of different drying air supply temperatures on the performance of transcritical CO2 HPD system were studied experimentally. The results showed that the maximum drying air supply temperature (DAST) in the designed system could reach 72.9 °C. As the DAST raised, whether with or without the IHX in the system, the coefficient of heating performance (COPh), coefficient of system performance (COPsys), and specific moisture extraction rate (SMER) decreased gradually and moisture extraction rate (MER) increased continuously. When the DAST was 70 °C, COPh, COPsys, MER and SMER were respectively 3.68, 6.07, 3.27 kg/h and 1.68 kg/(kW·h) in the HPD system without the IHX, and were respectively 4.00, 6.89, 3.67 kg/h and 1.97 kg/(kW·h) in the HPD system with the IHX. In contrast, the compressor discharge pressure decreased 4.26 %–5.99 %, COPh increased 1.39 %–8.65 %, COPsys increased 1.89 %–13.57 %, MER increased 4.68 %–14.01 %, SMER increased 6.93 %–17.18 % in the HPD system with the IHX.

Accelerated Degradation Test on Electric Scroll Compressor Using Controlled Continuous Liquid Slugging

Refrigerant-based electric scroll compressors are known for their reliability, efficiency, and quiet operation. They are often used in heat pump systems due to their ability to efficiently handle varying levels of load conditions, both for heating and cooling modes of operation. As electric compressors are considered the heart of the heat pump system, being able to determine degradation of compressors prior to failure is of paramount importance for the health of this system. Typical failures for electric scroll compressors range from electrical faults, refrigerant leaks, to mechanical failures and overheating. Specifically, one of the primary failure modes for an electric scroll compressor is mechanical damage due to the high stress effects of refrigerant liquid slugging. These stresses are due to excessively high internal pressures exhibited on the compressor scrolls, which are generated by compressing liquid refrigerant at the suction side of the compressor. This paper provides a new testing methodology that introduces liquid slugging at various degrees of refrigerant quality to degrade a compressor to near the end of useful life. Furthermore, this test aims to determine specific operating conditions and signals that can indicate early compressor degradation. This fault injection configuration consists of a modified heat pump system with the addition of two low pressure heat exchangers added in parallel (with respective electronically controlled expansion valve for each heat exchanger) used to control the refrigerant quality during compressor operations. For a given refrigerant quality, the heat pump system was operated at a fixed compressor performance conditions to sustain liquid slugging for a fixed duration. Afterwards, refrigerant was controlled to be pure vapor at the compressor suction side and the compressor was controlled at several different performance conditions (i.e., fixed compressor suction superheat temperature and compressor pressure ratios, at various compressor speeds), so as to duplicate conditions known to us from the compressor component data sheet for an ideal electric scroll compressor. Through these tests, the results show that the severity of scroll failures depend heavily on the refrigerant quality and the amount of liquid slugging exposure time. Furthermore, symptoms of compressor degradation are detected using the following signals: i) temperature and pressure at the compressor suction side, ii) temperature and pressure at the compressor discharge side, and iii) electric compressor speed and power consumption. To further aid in determining the compressor degradation ground truth, complete compressor teardown was performed to identify sections within the compressor that exhibited significant amounts of wear as compared to a stock compressor.

An Experimental Study on the Cooling Performance of Refrigerant (R134a/R1234yf) in Automobile HVAC System

The present work deals with the experimental investigation on the performance evaluation of R134a and R1234yf as automotive HVAC refrigerants. As the usage of R134a increases environmental issues due to its higher global warming potential (GWP), it is necessary to find an alternative without compromising the performance of the HVAC system. R1234yf having low GWP is one such drop-in alternative. But the COP of the system using R1234yf is observed to be low. Hence this work investigates on the effects of using an internal heat exchanger (IHX) with the conventional automotive HVAC system in the performance enhancement. The results indicate acceptable range of cooling capacity, COP and compressor discharge temperature for R1234yf when integrated with IHX and a high efficiency evaporator. COP of the R1234yf IHX system is observed to higher than the COP of R134a baseline system. The results of cooling capacity and compression discharge temperature of R1234yf IHX system also shows an enhancement and matches with the corresponding values of R134a baseline system.

Assessment of the impact of shaped nozzles installed inside the pipeline on the energy efficiency of compressed gas systems

Pressure pulsations and vibrations generated in gas discharge pipelines are one of the main causes of failure in a compressed gas system. Installation of shaped nozzles in the compressor discharge manifold is one of the new ideas to minimize this phenomenon. It has been proven that shaped nozzles technology is able to minimize the unfavorable phenomena of pressure pulsation and thus the pipeline vibration. The production of such components using 3D printing techniques is a very good solution, as they have complicated shapes and are individually produced for a specific installation. The world is currently struggling with an excess of waste and a shortage of energy. Therefore, modern technology should be part of the sustainable development strategy, according to which the amount of energy consumed during the processes should be reduced. This article presents the influence of shaped nozzles on the specific compression power mounted in the discharge manifolds of two different compressors: reciprocating and screw. This influence can also be estimated by a conceptual model presented in the article. Based on the values of specific compression power, obtained during carried out research, it can be concluded that 3D printed nozzles may have a minor impact on the energy efficiency of compression depending on their shape complexity.

Energetic and exergetic analysis of a transcritical CO2 air-source heat pump water heating system in the cold region

To analyze the energetic and exergetic performance of the transcritical CO2 air-source heat pump water heating system in the cold region, the numerical model and simulation algorithm are set up and verified with the experiments. Under the low ambient temperature (−15 °C to 0 °C) and water inlet temperature (9 °C), the performance evaluation of the system is investigated using the developed numerical model at different compressor frequency (75, 80 and 85 Hz). The results show that Qgc, COP and ηex decrease by 14.47%, 12.78% and 20.83% respectively as the ambient temperature decreases from 0 °C to −15 °C. The CO2 outlet state of the gas cooler and corresponding slope of isotherms have significant effects on COP and ηex. The COPopt and ηex,opt exist in the system but at different compressor discharge pressures. With the compressor frequency increasing from 75 Hz to 85 Hz, the increase in Qgc is at the cost of a decrease in COP, and COPopt decreases by 5.31%. The effect of the compressor frequency on ηex is different as the compressor discharge pressure elevates. Thus, a suitable operating condition, considering different needs, should be selected in the system operation.

Energy and Exergy Analysis of a Combined Cooling Heating and Power System with Regeneration

Solar assisted trigeneration system has proved to be a potential method in generating power with net zero carbon emissions. The present work aims to address the potential ways to improve the efficiency of the solar energy-integrated carbon dioxide trigeneration system. A regeneration integrated combined cooling, heating, and power system is proposed. With a comprehensive thermodynamic model, the proposed system is simulated for various operating conditions. A component-level exergy analysis is also conducted to estimate the total irreversibility of the system. As the gas cooler exit temperature increases, the overall system irreversibility also increases. When the bleed mass is 20% of the total mass, the system has the lowest energy destruction rate. The potential component that contributes most to system irreversibility is the gas cooler, followed by the regenerator and expansion valve. The proposed system with regeneration yields 29% more COP than the conventional system when operating at lower compressor discharge pressure and a gas cooler exit temperature of 34 °C. It is inferred from the obtained results that to reduce the total irreversibility of the system, it is advised to operate the system at a lower compressor discharge pressure and gas cooler exit temperature.

Performance study of the supplemental combustion type compressed air energy storage system

Compressed air energy storage technology is considered to be the most promising energy storage technology, but it has not been applied commercially on a large scale, partly because of the low system efficiency, with the existing efficiency being about 70%. To improve the round trip efficiency of the system, this paper proposes a supplementary combustion compressed air energy storage system based on adiabatic compressed air energy storage. The system adds supplementary combustion equipment to increase expansion machines’ inlet air temperature by burning fuels such as syngas, hydrogen, and natural gas to increase the power generation of the system. The thermodynamic performance analysis has been conducted through the thermodynamic model of the system, and the effects of parameters such as compressor discharge temperature, supplementary combustion, and air-fuel ratio on the system performance have been further investigated. The research results show that the efficiency of the system is improved by nearly 6% compared with the conventional adiabatic compressed air energy storage system. Meanwhile, the system’s round-trip efficiency can be further increased by appropriately raising the compressor discharge temperature and supplemental combustion quantity.

Experimental Investigation of the Improvement Potential of a Heat Pump Equipped with a Two-Phase Ejector

In this paper, an experimental investigation of the performance improvement of a heat pump equipped with a two-phase ejector, called an “ejector–expansion heat pump (EEHP)”, is proposed. The system performance of the EEHP is compared with that of a vapor-compression heat pump (VCHP). The improvement potential is determined and discussed. The heat pump test system based on a water-to-water heat pump that can experiment with both the EEHP and the VCHP is constructed. A two-phase ejector with a cooling load of up to 2500 W is installed for the experiment. The results show that the EEHP always produces a higher heating rate and COPHP than the VCHP under the specified working conditions. The heating COPHP is increased by 5.7–11.6% depending on the working conditions. It is also found that, under the same heat sink and heat source temperature, the EEHP can produce a lower compressor discharge temperature and a lower compressor pressure ratio than the VCHP. This is evidence that the two-phase ejector can provide the compressor with better working characteristics, which yields a longer compressor lifetime. It is demonstrated that the expansion pressure ratio is key to the performance of the EEHP. A larger expansion pressure ratio yields greater improvement potential when compared with the VCHP.

Theoretical exploration of low GWP refrigerant mixtures as replacement to HFC-134A in a vapour compression refrigeration system

Hydro-fluorocarbons (HFCs) that are not harmful to ozone layer and are used in many appli-cations, including as refrigerants, aerosols, solvents and blowing agents for insulating foams replace chlorofluorocarbons and hydro chlorofluorocarbons (HCFCs). However, some HFCs have a high GWP, which stands for “Global Warming Potential(GWP).” Because of the grow-ing concern over global climate change, researchers are paying closer attention for alternatives to these HFCs. The main focus of this work was on the theoretical analysis of the refrigerant mixtures namely AC5, R430A, and R440A as direct replacements for HFC-134a in a refriger-ator. The performance of the refrigerator may be enhanced using heat exchanger. The com-pressor discharge temperature, COP, VCC, refrigerant mass flow rate, power consumption of a compressor and pressure ratio were used to measure the performance of a home refrigerator. The typical COP of R440A and R430A was about 2.5% and 1.4% higher than that of HFC-134, while the average COP of AC5 was 6.1% lesser than that of HFC-134a. R430A almost has the same VCC (Volumetric Cooling Capacity) as HFC-134a. The results also show that HFC-134a uses more power than AC5, R440A, and R430A. R440A and AC5 have higher compressor outlet temperatures than HFC-134a, which affects the life span of the compressor. In com-parison with all the above refrigerants, R430A gives the best overall performance and used as replacement to HFC-134a in a VCR.

Performance investigation and exergoeconomic optimization for a solar-driven direct heating and cooling system

Integrating solar energy with direct heating and cooling (DHC) systems can improve system efficiency and reduce polluting gas emissions. To assist buildings in better selecting a DHC system, an exergoeconomic analysis and optimization model combined with building loads and environmental parameters is proposed. The exergoeconomic optimization model is applied to a novel DHC system based on transcritical carbon dioxide heat pump (TCHP) and solar energy. The sold electricity ratio and operating time ratio are defined to transform the building loads and environmental parameters into specific operating conditions of the system. The compressor discharge pressure is optimized to obtain the lowest total unit exergy cost (UEC) of the DHC system. The exergy, energy, and exergoeconomic performance of the DHC system are analyzed under optimal conditions. The results indicate that when the compressor discharge pressure in the heating mode and cooling mode are 7.31 MPa and 8.93 MPa, respectively, the DHC system has the lowest UEC, 0.629 $/kWh. The total UEC is reduced by 43.56% compared to the reference system. Under optimal configuration, the exergy and energy efficiency of the DHC system are 1.81% and 40.30%, respectively. The sensitivity analysis shows that the exergy and energy efficiency, the total UEC, and the UEC in the heating and cooling modes are positively correlated with the sold electricity ratio. The above results demonstrate that the exergoeconomic optimization methods can provide better assistance in selecting the DHC system.

Applicability evaluation of internal heat exchanger in CO2 transcritical cycle considering compressor operation boundaries

CO2 transcritical cycle has been widely promoted as a green energy utilization technology. Internal heat exchanger (IHX) is under consideration for cycle efficiency improvement. However, the interaction between IHX and compressor in CO2 cycle has not yet been fully explored. In this regard, compressor operating boundaries are introduced as constraints to IHX applicability evaluation in CO2 cycle. It indicates that considering compressor limits, IHX can either benefit or attenuate the CO2 cycle performance, depending on operating conditions. By reducing optimal discharge pressure, IHX helps CO2 cycle avoid the upper pressure limit, further improving performance by 5%. Over a wide range, however, IHX increases compressor discharge temperature, indirectly resulting in up to 50% performance degradation. The major factors affecting the duality of IHX in CO2 cycle are compressor discharge temperature limit, IHX efficiency and motor heat loss. Finally, performance-oriented IHX design guidelines for mainstream single-stage CO2 applications are provided. For automotive air conditioner, optimum IHX efficiency improves cycle performance by up to 30% in cooling mode. By contrast, IHX contribution is negligible in heating mode. For heat pump water heater and refrigeration system, both can benefit from IHX, particularly when compressor discharge temperature tolerance is high.

The thermodynamic potential of high-temperature transcritical heat pump cycles for industrial processes with large temperature glides

Industrial heat pumps up to 200 °C are an emerging technology with the potential to reshape the industrial heating supply. For large heat sink temperature glides, transcritical cycles are able to increase the power-to-heat efficiency. Its potential is however yet to be unlocked. To examine this potential, a thermodynamic optimization model is proposed. The model includes robust cycle optimization, is able to screen a large set of working fluids, and includes proper post-processing. This model is applied to three highly relevant industrial cases, namely thermal oil heating, superheated steam drying and spray drying. The heat sink temperature glides for the respective case studies are 60 K, 81 K and 105 K. The results show that a temperature glide larger than 60 K is desired to achieve a better coefficient of performance (COP) with transcritical cycles compared to the classical subcritical cycles. Moreover, potential working fluids were identified for these high operational temperatures. For the case study with a heat sink temperature glide of 81 K, transcritical cycles allowed for a COP increase of 4.6%, whereas this increased to 7.3% for a heat sink temperature glide of 105 K. Furthermore, transcritical cycles introduce a much larger volumetric heating capacity, a lower compressor discharge temperature and a substantially lower pressure ratio. In addition, the best performing working fluids for subcritical cycles are highly flammable, which is only the case for some transcritical working fluids. Therefore, these cycles can be beneficial for temperature glides below 60 K. The compressor for transcritical cycles should however be able to cope with pressures up to 60 bar. If these compressors are available, transcritical cycles are shown to be superior compared to classical subcritical cycles.

Experimental evaluation of split air conditioning performance using nanodiamonds particles in compressor polyester lubricant oil

Rationing energy consumption in air conditioning (AC) systems has become increasingly necessary due to the continuous global increase in energy demand and the prevailing sustainability vision worldwide. Therefore, an AC system utilizing nanodiamond/Polyester (ND/POE) lubricant oil, which shows potential to improve the performance and reduce energy consumption, was investigated. Consequently, a 5-ton refrigeration split AC unit was modified with an oil separator to assess the ND/POE nanolubricant in the compressor’s loop, in particularly. The AC unit was examined under various operating conditions up to an extreme high ambient temperature of 52˚C, with an optimal nanolubricant concentration of 0.1% as recommended from the literature, using a fully automated psychrometric testing facility. The results showed that using ND/POE instead of pure POE resulted in a 4.7% and 3% reduction in compressor discharge temperature and pressure, respectively. Furthermore, the overall system's coefficient of performance (COP) improved by up to 8% due to a reduction in power consumption of up to 3% and an increase in cooling capacity of up to 6%. Therefore, it is anticipated that the use of ND/POE will result in improved compressor durability, reliability, and longevity, as well as a significant improvement in the performance of AC systems operating for prolonged periods, such as those operating in extreme high ambient temperature applications.

Experimental Investigation of Gravity Effect on a Vapor Compression Heat Pump System

Vapor compression heat pumps have the potential to meet the future development requirements of thermal management in aerospace due to the ability to achieve high heat flux dissipation, precise temperature control, and a more compact and lightweight structure. In this study, a variable-angle test stand was constructed to investigate the effect of gravity on the performance, temperature distribution, and oil circulation rate of a vapor compression heat pump system in a ground environment. The results showed that the system could operate stably at various inclination angles, with the compressor exhibiting the lowest power consumption at an inclination angle of 90° and the maximum coefficient of performance (COP) of the vapor compression heat pump reaching 5.5. The system flow rate exhibited a sinusoidal curve with a 10.7% variation relative to the initial flow rate as the inclination angle increased. The evaporating temperature, condensing temperature, and compressor discharge temperature of the system were approximately symmetrical relative to the inclination angle of 180°. At inclination angles ranging from 90 to 270°, the oil circulation rate was highly sensitive to gravity changes and remained at a high level. The oil circulation rate agreed well with the change in subcooling/superheating, yet a rise in the oil circulation rate resulted in a decrease in COP.

Thermodynamic analysis of a novel vapor-injection Joule-Thomson refrigeration cycle with a binary hydrocarbon mixture for −86 °C freezer

This paper proposes a novel vapor-injection Joule-Thomson refrigeration cycle with mixed-refrigerant. The introduction of the compressor with vapor-injection can reduce the pressure ratio of each compression stage, thus reducing the compressor power and discharge temperature. The thermodynamic analysis results show that the performance of the novel cycle is better than that of the basic Joule-Thomson cycle. In addition, this paper studies the binary hydrocarbons applied in −86 °C freezers, and find a binary hydrocarbon R601a/R1150 with Superior performance. The mass fractions of R1150 in R601a/R1150 corresponding to the maximum COP of the novel cycle and basic cycle are 0.45 and 0.44, respectively. Moreover, the maximum COP of the novel cycle is 19.25% higher than that of the basic cycle. The comparison results demonstrate that the novel cycle has a great energy-saving potential. In addition, at different condenser outlet temperatures of 16 °C, 25 °C and 32 °C, both cycles have the optimal condensation pressure of 300 kPa, 500 kPa and 650 kPa with respect to COP. For the novel cycle, the compressor injection ratio has little effect on COP. The increase of intermediate pressure can improve cycle performance, but too high intermediate pressure is not conducive to the normal operation of the system. Furthermore, the exergy analysis result shows that the location of the largest exergy destruction rate is in the compressors for both cycles, followed by the recuperators, condensers, evaporators, and capillary tubes.