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Abstract The performance of an ejector-assisted condenser outlet split dual-evaporator cycle is compared with a conventional dual-evaporator cycle albeit consisting a pressure reducing valve. The cycles do not employ any separator due to its inability to efficiently separate the liquid and the vapor phases. The comparison of both the cycles has been made for the same cooling capacity in low-temperature evaporator and unit flow rate of R134a and R1234yf as refrigerants. The impacts of changing the operating temperatures of evaporator and condenser have been examined in the current investigation. The study reveals that with the increase in temperature of the high-temperature evaporator, the cooling capacity of the high-temperature evaporator yields, while that of the low-temperature evaporator plummets in both the cycles. Further, the compressor work is allayed in the ejector-assisted cycle; thus, the COP is enhanced considerably. The percentage COP improvement over the basic cycle is obtained from 14.7 to 17.53% for the refrigerant R1234yf and from 14.45 to 17.32% for R134a; however, the COP of both the cycles with R12134yf is slightly lower than with R134a. The ejector has been modeled assuming a constant pressure theory. The observed trend indicates that the entrainment ratio is improved with the rise in the temperature of low-temperature evaporator, whereas it is decreased with the rise in the temperature of high-temperature evaporator.

Abstract Magnetic refrigeration utilizes the magnetocaloric effect of a magnetic material, whose temperature changes according to the change of magnetic field strength. It is regarded as an eco-friendly refrigeration technology in that it uses magnetic materials as refrigerants instead of CFC, HCFC, and HFC refrigerants used in vapor compression refrigeration. It is also regarded as an energy-efficient refrigeration technology in that it does not use noisy and power-consuming compressors. This paper presents thermodynamic analysis on a magnetic refrigeration system using experimental results obtained from a magnetic refrigeration apparatus. The magnetic refrigeration apparatus was built using two sets of concentric Halbach cylinders consisting of permanent magnet segments. Specifically the coefficient of performance (COP) of the magnetic refrigeration system was calculated using the energy removed from the working fluid across an AMR bed and the work input to run electric motors.

To examine the influence of different parameters of a 10 kW refrigeration unit on the performance of a refrigerated vehicle, the capacity, coefficient of performance (COP), and pressure performance of the circulation system of a refrigeration unit were tested using experimental and simulation methods. Additionally, changes were made to the refrigerant charge, degree of superheating, and refrigerant type to conduct experimental and simulation studies. The results showed that the capacity and COP of the refrigeration unit exhibited different trends with changes in the refrigerant charge and superheat. The cooling capacity and COP errors between simulation and experiment were 6.4% and 8.5%, respectively, and the error of all results was within 10%. It was confirmed that the performance variation in the refrigeration unit was more sensitive to the variation in the degree of superheating than to the refrigerant charge. The best capacity and COP were achieved when the degree of superheat was 4 ℃ and the refrigerant charge was 7.4 kg. Furthermore, through numerical simulation, it was determined that the COP performance of the refrigerant R449A, used in the refrigeration cycle system, was approximately 4% higher than that of R404A. It was confirmed that the refrigerant R449A can be used instead of R404A.

In terms of the performance characteristics of a centrifugal chiller, a performance simulation algorithm was proposed using the iterative calculation of compressor power and condenser heat transfer in the range between the maximum capacity based on the maximum current and the minimum capacity with respect to surge. Thus, a performance simulation software for the centrifugal chiller integrating the heat transfer calculation of the shell and tube heat exchanger, performance calculation of the centrifugal compressor, and surge prediction was developed. The accuracy of the simulation model was verified using the prototype test results. The results indicate that within the entire load range, the maximum error of the COP is 6.43%; the maximum error of the chilled water pressure drop is 7.28%; the maximum error of the cooling water pressure drop is 4.45%; the maximum error of the power input is 6.87%; the maximum error of the evaporator saturation temperature is 3.83%, and the maximum error of the condenser saturation temperature is 1.24%. The simulation software successfully predicts various parameters, such as chilled water temperatures, cooling water temperatures, and flow rates of the centrifugal chiller under different loads.

A transcritical CO2 system combined with an ejector and dedicated mechanical subcooling (EJ-DMS) was developed to improve the performance of the CO2 system in the space heating and cooling of buildings throughout the year. A thermodynamic model of the system was devised. Then, the discharge pressure and subcooling degree were optimized using a genetic algorithm by considering the coefficient of performance (COP) as the objective function. Using five typical cities as application scenarios, the energy consumption and annual performance factor (COPann) of the system were analyzed. The results show that, compared with a conventional mechanical subcooling system and the conventional ejector system, the heating COP of EJ-DMS is enhanced by 10.90% and 5.58%, respectively, and the cooling COP is increased by 8.99% and 18.12%, respectively. The COPann values are improved by 7.95% and 5.98%, respectively. Compared with the conventional ejector system, the discharge pressure of EJ-DMS is reduced by 0.47 MPa and 0.77 MPa in the heating and cooling modes, respectively. In addition, the COPann improvement ratio of the EJ-DMS system is the highest when operating in Guangzhou and Harbin, indicating that the EJ-DMS system is more suitable for regions with relatively high or low ambient temperatures, such as hot summer and warm winter or severely cold regions. This study provides a theoretical reference for the development and optimization of a combined cooling and heating CO2 system.

Motor cooling is key to the reliable operation of centrifugal refrigeration compressors with gas bearings. A mathematical model of a centrifugal refrigeration compressor with gas bearings was devised, and the influences of different refrigerants on the motor cooling process and refrigeration system performance were analyzed. The results show that the internal temperature of the motor reaches the highest when R1234ze (E) is used, and the maximum temperature of the permanent magnet of the motor is 60–90 °C higher than that with R134a and R1234yf. When using the three refrigerants, the average winding temperature of the motor decreases with an increase in the cooling inlet temperature. When R134a and R1234yf are used, the maximum temperature of the permanent magnet decreases with an increase in the cooling inlet temperature. When R1234ze (E) is used, the maximum temperature of the permanent magnet first increases and then decreases with the increase in cooling inlet temperature. The maximum temperature is reached when the cooling inlet temperature is approximately 25 ℃. The outlet vapor quality of the motor cooling circuit decreases by approximately 3%–5% when the cooling inlet temperature increases by 4.5 °C. Compared with traditional systems, systems with motor cooling branches can control the motor temperature within a safer operating range. However, systems using R134a, R1234yf, and R1234ze (E) have COPs reduced by 1.23%–1.82%, 1.23%–1.65%, and 1.14%–1.17%, respectively.

This paper proposes a ''zero-carbon heating'' model that uses the technology of an electric-driven vapor compression heat pump unit with a large temperature difference that can be used for long-distance delivery of heating. The model adapts to the operational characteristics of the power grid and the heating network, which facilitates 'power supply using 'green electricity'' and heat supply mainly with zero-carbon industrial waste heat. Hence, it is the key equipment that features the synergy of heat and power. The studied system was equally cost-effective to the conventional cogeneration system since it can significantly reduce the backwater temperature of the long-distance transmission network and increase the transmission capacity of the heat network; the return water temperature can be very low. The model has a compact structure; therefore, it can adapt to complex working conditions and land requirements. To verify the feasibility of this technical approach, the operating performance of 0.5 MW units used in Yuncheng in two heating seasons from 2020–2022 was measured and analyzed. The test results showed that the unit can operate stably and efficiently within a range of 0–100% operating load. When only the performance of the electric-driven vapor compression heat pump was calculated, the minimum and maximum heating COP were 6.5 and 13.1, respectively, while the annual average heating COP was 8.3. The minimum return water temperature of the primary network can be 33 K lower than that of the secondary network, reaching 15 ℃. When compared with gas-boilers as the baseline, the payback period was four years.

Carbon dioxide (CO2) air-source heat pumps have broad application prospects because of their excellent environmental protection potential and thermal performance. In this study, the CO2 cascade air-source heat pump was implemented in distributed central heating systems in a public building in Qinhuangdao City and a residential building in Shijiazhuang City. Both cases were tested and analyzed to explore the uncertainty of measurements and the operation performance in extremely cold conditions as per the Standard for Energy Efficiency Test of Public Buildings JGJ/T 177—2009 and the Standard for Energy Efficiency Test of Residential Buildings JGJ/T 132—2009. Based on the uncertainty analysis, the relative combined standard uncertainty ranges of COP (coefficient of performance) of #2 units operating at various ambient temperatures in Qinhuangdao and Shijiazhuang were found to be 4.27%–5.87% and 1.90%–4.36%, respectively. These ranges reveal that the measurements have high reliability. The measured daily heating COP of #1 and #2 units in Qinhuangdao are 2.75–3.09 and 2.76–3.15, respectively, when the outdoor daily temperature range is -10.9–2.5 °C. Even in the lowest outdoor temperature (-18 °C), the heating COP of #1 and #2 unitscan still reach 2.19 and 2.88, respectively. When #1 and #2 units operate in Shijiazhuang with the outdoor daily temperature being -6.6–12.5 °C, the measured daily heating COP are 2.32–3.38 and 2.21–3.06, respectively. The analysis of these two projects shows that the heating COP of the CO2 cascade air-source heat pump is not sensitive to the ambient temperature in extremely cold conditions.

This study examines the influence of the physical properties of the secondary refrigerant and cooler combinations on the performance of an indirect refrigeration system used in cold storage. An indirect refrigeration system test-bed was built and the performance of two new secondary refrigerants, LM-4 and LM-8, were compared using different coolers to determine the secondary refrigerant with the best performance and the optimal cooler combination. The results demonstrate that the cooling time of the system was affected by the physical properties of the secondary refrigerant and cooler combination. Under the same conditions, the cooling time of the LM-8 system with a finless wall-mounted cooler and a top-mounted fin-tube cooler was the shortest compared with the standalone top-mounted fin-tube cooler and a finless wall-mounted cooler with a finless top-mounted cooler; the cooling time of the LM-8 system is approximately 30.4% less than that of the LM-4 system. The Reynolds numbers corresponding to the optimal working parameters were derived. The optimal refrigeration coefficient of performance (COPr) and comprehensive coefficient of performance (COPc) of the LM-8 system were higher than those of the LM-4 system by 10.7% and 10.9%, respectively. Among the three types of coolers, the total energy consumption of the LM-8 system was 5.8%–13.6%, 2.2%–9.1%, and 3.3%–7.2% lower than that of the LM-4 system. In conclusion, the LM-8 system with a finless wall-mounted cooler and a top-mounted fin-tube cooler is recommended for indirect refrigeration systems in cold storage applications.

To investigate the effect of supply air temperature on the comprehensive performance of a vehicle transcritical CO2 refrigeration system, a simulation model of a single-stage transcritical CO2 refrigeration system is established using the GT-Suite simulation software. Based on three designed operating conditions, system performances under different supply air temperatures are compared, the upper limit of the air volumetric flow rate is specified, and the concept of the effective coefficient of performance (COPeff) is proposed and analyzed. Under the same conditions, increasing the supply air temperature can improve the system coefficient of performance (COP), COPeff, and the effective COP with fan power consumption. Under low cooling load conditions, the optimal value of COPb is 3.819, implying that the air supply temperature is optimal. However, when the cooling load increases to a certain level, the optimal air supply temperature is no longer valid. The research presented herein guides the selection of the supply air temperature for vehicle transcritical CO2 refrigeration systems.

A curved baffle-type inlet structure was designed for a water storage tank to improve the performance of an air-source heat pump water heater system. A heat pump water heater test bench was set up to compare the extraction efficiency and COP of the curved baffle inlet structure to the direct-entrance and side-entrance inlet structures. The experimental results showed that the thermal stratification of water along the height direction was effectively released by the curved baffle-type inlet structure. Compared to the direct-entrance inlet structure water heater, the extraction efficiency increased from 52.87% to 96.60% with a curved baffle-type inlet heat pump water heater when the inlet flow rate ranged from 5 L/min to 10 L/min, and the COP improved from 7.14% to 7.40%. Contrary to the side-entrance inlet structure water heater, the extraction efficiency increased from 38.37% to 76.99% with a curved baffle-type inlet heat pump water heater when the inlet flow rate ranged from 5 to 10 L/min, and the COP improved from 3.22% to 5.53%. The performance improvement increased as the inlet flow rate increased. The curved baffle-type inlet structure of the heat pump water heater simultaneously increased the extraction efficiency and the system’s COP.

In this study a refrigerant pump-driven heat pipe and vapor compression composite cooling system with an evaporative condenser was proposed to solve the problems of high energy consumption and low cooling efficiency of traditional data center cooling systems. Through experimental research, the operating performance of this system under different outdoor temperatures and air velocities of condenser was analyzed. The results show that in the heat pipe mode, when the outdoor temperature is lower than 0 °C, reducing the air velocity of condenser can increase the system coefficient of performance (COP) and effectively prevent condensation in the evaporator. The evaporation temperature increases by 1.8 ℃ on average for every 1 m/s decrease in the air velocity of condenser. When the outdoor temperature is higher than 0 °C, increasing the air velocity of the outdoor unit can improve the energy-saving performance of the system. Compared with air cooling, when the outdoor temperature is 5–10 °C, the COP is increased by 15.5% on average after the evaporative-cooled mode is turned on. At the same time, evaporative cooling also enhances the cooling capacity of the system, increasing the upper limit of the outdoor temperature in the heat pipe mode from 10 °C to 15 °C. In the vapor compression mode, evaporative cooling can effectively improve the energy efficiency ratio of the system. When the outdoor temperature is 30 ℃, after the system is switched to the evaporative-cooled mode, the COP is increased by 17.5%, 16.2%, and 14.3%, respectively under the three air velocity of low (1.5 m/s), medium (2.5 m/s) and high (3.5 m/s).

A new type of air refrigeration cycle combined with a dew-point indirect evaporative cooler (IEC) is proposed. Corresponding thermodynamic calculations on the new cycle were carried out. A comparative analysis was carried out with the ordinary air refrigeration cycle and NH3 vapor compression cycle. The influences of operation conditions on the performances of the air refrigeration cycle before and after combining the dew-point IEC as well as the COP of the NH3 vapor compression cycle were analyzed. The results showed that the performance of the new air refrigeration cycle combined with the dew-point IEC was greatly improved. The maximum COP can be increased by 37.8% under the design conditions. In addition, compared to the NH3 refrigeration cycle, it can operate with simpler processes and equipment.

In order to get better performance of power-assisted heat pipe systems, the performance of three types of compressors was experimentally studied. The results show that: 1) a compressor with gas pump function has the function of a low compression ratio operation, which can switch between different modes, according to different outdoor temperatures and indoor loads, and simplify the system configuration. Additionally, it has good energy-saving benefits. The coefficient of performance (COP) of the inverter rotor compressor can exceed 20, the COP of the inverter scroll compressor is close to 20, which shows that they can be a good alternative to the liquid pump; 2) for the air-conditioning systems in small data rooms, comprehensive utilization of the gas heat pipe and compression refrigeration technology broaden the utilization time of free cooling. The annual energy efficiency ratio (AEER) is considerably higher than that of the conventional computer room air conditioning. The application of regional energy saving methods such as air cooling, water cooling, and evaporative cooling provide a new strategy for energy saving and emission reduction of modern data centers; 3) for air-conditioning in large data centers, the COP of magnetic bearing compressors exceeds 20, and results in higher energy-saving benefits. However, there is still a certain gap as compared with the liquid pump. At the same time, centrifugal compressors used as gas pumps have a shortage of circulation, which requires the liquid pump to compensate the pressure head.

To study the effect of a variable rotation speed compressor on the performance of a cascade heat pump, an experimental platform was constructed. The changes of discharge temperature, intermediate temperature, heating capacity, power consumption, and Coefficient of Performance (COP) with different rotation speeds of a high-temperature compressor were studied experimentally. Experimental results demonstrated that the system operated safely and reliably under the condition of a condensing temperature of 46 °C and an evaporating temperature between -35 and -10 °C. As the high-temperature compressor speed varied from 1200 to 6000 r/min and the condensing temperature was 46 °C and the evaporating temperature -25 °C, the heating capacity increased by 129.7%, and the low-temperature compressor power decreased by 43.4%. In addition, the COP initially increased and then decreased with the increase of high-temperature compressor speed; there was a maximum COP and corresponding optimal high-temperature compressor speed.

Because of the requirement of annual operation, an air source heat pump water heater has complex and variable working conditions. Therefore, there are higher requirements for air source heat pump water heater system control. Based on the flexible adjustment characteristics of the electronic expansion valve, this study proposes a simple control method of the fixed discharge superheated temperature. Meanwhile, the control methods of a fixed valve opening and fixed superheated temperature were used to conduct experimental research and analyze their internal process. When the ambient temperature is 22 ℃，the experimental results show that the discharge temperature dramatically decreased under the control methods of a fixed valve opening; however, its coefficient of performance (COP) is the lowest and its compression risk with liquid is high. Although the COP is the highest under the control method of a fixed superheated temperature, the discharge temperature is also the highest. Under the control method of a fixed discharge superheated temperature, its COP is slightly lower than that of the fixed superheated temperature control method. However, the discharge temperature is effectively reduced by nearly 7 K on average. Meanwhile, compared to the fixed valve opening, its average COP increased 4.9% and the risk of compressor suction with a large amount of liquid refrigerant can be avoided. Therefore, this method effectively combines the advantage of the other two methods.

The constant-frequency double-stage compression refrigeration system fails to run in the best state at the working or load changing conditions. To improve its performance, maintain the maximum performance coefficient, and achieve rapid and accurate cooling, a variable-flow double-stage compression experimental bench was set up. The proposed method was able to control the refrigerant gas flow rate of the low-pressure compressor and change the refrigerant mass flow rate. Therefore, the experimental study of two-stage compression cooling was conducted. Results showed that the refrigeration capacity of the system decreased with an increase in the ratio of input gas of low- and high-pressure compressors (in the range of 1.25 to 3.33) at the condensation temperature of 30 ℃, evaporation temperature of ?35–?20 ℃. The cooling capacity of the system gradually decreased with the increase of the ratio of input gas of low- and high-pressure compressors and the maximum coefficient of performance (COP) is2.37. The ratio of input gas of low- and high-pressure compressor under the optimum COP increased with the decrease of evaporation temperature. Considerably, as the evaporation temperature decreased by 5 ℃ when the evaporation temperature was in ?35–?20 ℃, the ratio of the inputgas of the low- and high-pressure compressors under the optimal COP increased by 22.10%, 12.52%, and 14.29%, respectively. Therefore, for the actual system design, the experimental data can be used to adjust the ratio of input gas of low- and high-pressure compressors according to the different evaporation temperatures and refrigeration demands.

To improve the performance of an air-source heat pump system under large temperature difference conditions, this paper proposed a triple-loop air-source heat pump system scheme. An energy recovery performance test platform was set up according to the exhaust energy recovery in a public building air-conditioning system. The performances of the single- and triple-loop heat-pump systems were tested through experiments under different outdoor-temperature conditions in winter and summer. The results show that the overall performance of the triple-loop system was significantly higher than that of the single-loop system under all operating conditions. With the increase in the indoor and outdoor temperature difference, the triple-loop heat pump system could significantly minimize the problems of excessive compression ratio and system performance degradation of the traditional air-source heat pump. Under winter conditions, the increase rate of the coefficient of performance (COP) of the triple-loop system reached up to 1.88. When the indoor and outdoor temperature difference was 40 ℃, the COP of the triple-loop system was 54.8% higher than that of the single-loop system. Under summer conditions, the increase rate of the COP of the triple-loop system reached 89.8%. When the indoor and outdoor temperature difference was 13 ℃, the COP of the triple-loop system was 74.6% higher than that of the single-loop system.

In this paper, the effect of the water supply temperature on the thermal performance of a heat pump is analyzed. The influence of the water supply temperature on the performance of a heat pump system is investigated for an ambient temperature ?12 °C and ?6 °C and an initial water supply temperature of 20 ℃. The experimental results indicate that, under the same initial temperature, the heating capacity of the compressor system first increased and then decreased, with a maximum heating capacity reached for a water supply temperature of 40 ℃. When the ambient temperature was at ?12 ℃, the water was heated by the heat pump from 25 ℃ to 55 ℃. The power consumption of the system increased from 11,905 W to 24,417 W, an increase of 105%, and the system energy efficiency decreased from 4.03 to 2.11, a decrease of 47.6%.

A theoretical model for analysis of single stage LiBr-H2O absorption heat pump was established and computer simulation for its thermodynamic cycle performance was conducted. The effects of varying operation conditions (circulation ratio, inlet temperature of low temperature waste water, inlet temperature of hot water and inlet temperature of high temperature vapor) on the four performance criteria (COP, entransy efficiency, exergy efficiency and entropy generation) are investigated, and the consistency of the four criteria are examined. It is found that the performance was degraded with the increases circulation ratio, inlet temperature of hot water and inlet temperature of high temperature vapor. Only when the inlet temperature of waste water increased, the performance was improved. It is also found that the variation trends of the four criteria with the operation conditions were different, and some were even opposite. To be specific, the increase of hot water inlet temperature worsens the system performance according to COP and entransy efficiency while improves the system performance according to exergy efficiency and entropy generation. However, the results obtained by the COP agree well with those by the entransy efficiency, indicating that the entransy efficiency is feasible for the heat pump performance analysis.

The heating performance of a heat pump can be improved by using a natural cold source. In this study, two types of sub-cooling systems with natural cold source were proposed: main loop and by-pass loop. A theoretical analysis was conducted and an integrated test bench for an R32 vapor compression heat pump was built. Running parameters such as the discharge temperature, heating capacity and heating coefficient of performance (COP) were investigated in the test bench based on three operation modes: main loop sub-cooling, by-pass loop sub-cooling, and a single-stage system. The results showed that for the main loop and by-pass loop sub-cooling systems, when the sub-cooling volume flow rate increased to 0.02 m3/h, the discharge temperature was reduced to 6.8 ℃ and 8.2 ℃, respectively. In addition, the heating capacity was reduced by 6.4% and 10%, and the heating COP was reduced by 2.5% and 5%, respectively.

In this study, to understand the relationship between compressor frequency and the performance of the R410A/R410A cascade refrigeration system, changes in system performance under different frequency of high and low temperature grade compressors are conducted experimentally and analyzed. The results showed that under the same working conditions, a) the intermediate temperature of the system increased by 2.36 ℃, and the difference between the high and low temperature grade compression ratios was reduced by 44.6% when the frequency of a low pressure compressor increased from 50 to 62 Hz; b) the intermediate temperature of the system decreased by 3.7 ℃, and the high and low temperature grade compression ratios increased by 58.5% when the frequency of the high temperature compressor increased from 50 to 62 Hz. The system cascade temperature difference was smaller when the frequency of high temperature compressor changed, and the system coefficient of performance (COP) was higher than that of the system under the frequency change of low-temperature compressor. When the frequency of both the high and low temperature compressors was 53 Hz, the system cascade temperature difference was the least and the system COP was the optimal.

In this study, the working principle of a heat pipe radiation heating device driven by heat pump was proposed. The prototype has been developed for testing based on a 1 HP compressor and the operating characteristics of the prototype under the working conditions of indoor temperature from 18 ℃ to 22 ℃, outdoor temperature from -15 ℃ to 0 ℃ are tested in the air enthalpy room. The experimental results showed that the heat pipe radiator can start rapidly and has a uniform temperature distribution. The optimal charge of heat pipe working fluid ratio is 0.1. The maximum heating coefficient of performance (COP) of the system can reach 4.1 under the condition of 22 ℃ indoors and﹣15-0 ℃ outdoors.

Thermoelectric cooler（TEC）chips do not work in an ideal condition with uniform temperature in engineering applications due to various reasons, which leads to local high-temperature region. A non-uniform temperature distribution was applied to simulate the working condition while a 3D finite element method was used in the numerical analysis of TEC chips in the study. The influences of variations in the working temperature of the hot end（th：20~40 ℃）, maximum temperature difference （θm：5~30 ℃）, and area ratio of hot space （ω：7/16~12/16） on the performance of TEC chips were considered. The results indicate that the relative refrigerating capacity deviation reaches to -8.788%, the relative power deviation reaches to 2.608%, and the relative coefficient of performance (COP) reaches to -10.9%.

A flexible design scheme for a direct expansion solar-assisted heat pump system is presented. Based on the flexible theory for the virtual operating point of the basis design, which was stored in the flexible space, all of the operating points within the flexible space could achieve almost the same heat transfer effect. The weights of the environmental factors for the system’s coefficient of performance (COP) were obtained in a simulation and verified in an experiment, including the irradiation intensity (52.2%), temperature (34.7%), and wind speed (13.1%). A total of 25 sets of systems were simulated under typical weather conditions. The purpose was to verify the operating points that fell in the flexible space based on the weights for the optimal combination of virtual operating points obtained. The values of the irradiation intensity (It), ambient temperature (T0), and wind velocity (uw) were 559.97 W/m2, 21.6 ℃, and 2.89 m/s respectively. The simulation results showed that the variance in the system’s COP was 0.156，which was superior to the traditional static design result.

With the deepening of energy conservation and emission reduction, the improvement of energy efficiency, integrated system coupling refrigeration with heating is bound to be further promoted and applied. Compared with traditional refrigeration system and heating system, the integrated system can comprehensively utilize the energy of both cold and heat. Therefore, whether the calculation of the energy efficiency of individual cold and heat is still applicable to the new system. In this paper, two kinds of integrated system coupling refrigeration with heating of integrated system A with cascade unit and heat pump, and integrated system B with conventional refrigeration unit and heat pump are constructed, and three methods of energy efficiency calculation are proposed. Through specific experiments, three coefficients of performance (COP) calculation methods and results are given for discussion and analysis within the industry. Among them, the third calculation method take into account the cooling capacity of the refrigeration system and the heating of the heat pump system, and the shaft power of the whole system is regarded as the compensation energy, it is the most reasonable method.

Fluid flow maldistribution in each tube of a dry-expansion shell and tube evaporator can cause inefficient heat exchange. In this paper, a numerical simulation of flow distribution in a dry-expansion shell and tube evaporator is carried out using CFD commercial software. A new type of dispenser is proposed to balance the flow distribution between different tubes. A numerical simulation and visualization experiment are compared to verify the reliability of the simulation results. An experimental platform was set up, and a conical liquid distributor was designed and manufactured. The liquid distributor was installed in a chiller. The performance of the chiller under different conditions was tested. The results show that the inlet and out?let pressure drops in the evaporator decreased from about 15 kPa to about 3 kPa, and the entire COP increased by about 5%.

In order to improve the stability and coefficient of performance of the air source heat pump, a scroll compressor refrigeration / heat pump system with flash tank was proposed using R134a, and the experiment platform was built. The compressor’s discharge temperature, power input, cooling capacity, heating capacity, coefficient of performances of the refrigeration/heat pump system were studied. Results showed that, under the condition of condensing temperature 45 ℃ and evaporating temperature from ﹣20 ℃ to 0 ℃, the discharge temperature of the vapor injection system was 6.2 ℃ lower than that of the single stage compression system, power input increased only 1.4% to 2.8%, the cooling capacity and cooling COPc are 19.8% and 17.6% higher than that of the single stage system, the heating capacity and heating COPh are 15.3% and 13.2% higher, respectively.

Based on REFPRO 9.0 and KW2 model parameters, the thermophysical properties of mixing refrigerant HFO-1234ze/HFC-32 were calculated in this paper, and the cycle performance of mixed refrigerant in different ratios was figured out according to the heat pump water heater test standard. The results showed that the optimal mixture ratio is 0.3/0.7. With this ratio, the performance of heat pump water heater in different operating conditions were conducted and compared with R410A. The results indicate that the mixed refrigerant’s compressor power consumption and discharge pressure are lower than R410A system, which is conducive to the safe and stable operation of the water heater; under the standard condition, the COP is 4.03 which is higher than R410A’s 3.6; meanwhile the decline rate of COP is lower than R410A when the temperature is higher than the standard condition. Therefore, the mixed refrigerant is feasible to replace R410A.

In order to enhance the operating performance of air source heat pump, the performance of air source heat pump (ASHP) system with the variable inlet water temperature strategy was experimentally studied. As field test shows, the condition of variable outlet water temperature could satisfy the indoor cooling demmand. Compared with traditional ASHP cooling system adopting fixed 12 ℃ inlet water temperature, this kind of system is proved to be with higher COP and lower power consumption, and therefore is an obvious energy saving system. In addition, the Dymola model was established to verify the experimental results, and the simulation of energy consumption of actual air conditioning system was conducted based on the model. The results indicated that COP would improve 10 percent from 3.99 to 4.39.

To study the effect of variable chilled water flow rates and temperature on double temperature chiller with large temperature glide zeotropic refrigerant, the chiller’s performance under different conditions was investigated experimentally, including mass concentration ratio of R32/R236fa (0.4~0.6, 0.5~0.5, 0.6~0.4), chilled water flow rates change from 0.25 m3/h to 0.45 m3/h and temperature change of the high temperature chilling water. The experimental results show that the maximum and minimum COP of the unit under different flow rates is 4.17 and 3.27 respectively, this moment, the inlet and outlet water temperature of condenser are 32 ℃ and 37℃, the high-low temperature chilling water are 7 ℃ and 16 ℃. In addition, the temperature change of high temperature chilled water have obvious effect on the performance of the unit. At last, the results of this paper provide database for the application of double temperature chiller.

Since the difficulty of building mechanism model and the structure of COP model of chiller is complex, greatly affected by operating parameter, a COP prediction model of chiller is proposed based on Support Vector Regression, and the parameters are optimized by Particle Swarm Optimization algorithm. In this paper, 396 sets of operating data of chiller of a shopping mall are randomly selected to train and test this model. The results shows that the prediction accuracy of SVR model based on PSO optimization algorithm is higher than that of BP neural network and the relative error is within 3%. At last, operating data of two days in summer and transition season are randomly selected to verify the model. The relative error is within 5%. So this model can provide theoretical basis for the chiller energy efficiency analysis, fault detection and diagnosis and optimizing control.

An ideal process model based on real solution for absorption heat pump is obtained in this paper. First, temperature lift factor is derived for real solution with infinite solution flow rate, and a correction factor kr is used to consider the difference with ideal solution, which is mainly dependent on the activity coefficient of solution in the generator and the absorber. For absorption heat pump, kr is higher than 1 and the COP is lower than that with ideal solution; for absorption heat transformer, kr is lower than 1 and the COP is higher than that with ideal solution. Then for real solution with finite flow rate, temperature lifting factor is defined and compared with solution of infinite flow rate. The correction factor kr is lower for real solution with finite flow rate and influenced by the concentration difference of solution, and the higher the concentration difference, the lower the kr. The COP for solution with finite solution flow rate is lower than the COP with infinite solution flow rate. Whatever the flow rate of real solution is infinite or finite, it always meets thatφCOP1

Superheat of evaporator outlet is a symbol of state of air-conditioning, in order to study the effect on the performance of evaporator and system in automotive air-conditioning, a serial experiments have been done. A new kind of valve has been used to control the superheat in the standard automotive air-conditioning bench, and the effect of superheat on the performance has been study. The results show, capacity of evaporator increases with the decreasing of superheat, and it can reach 19.4% in the study’s system. COP increases to a maximum value then decreases with the decreasing of superheat of evaporator outlet，and it can reach 17.8% in the study’s system.

Electric vehicles don’t have enough waste heat for heating in winter, so the introduction of heat pump system to electric vehicles is of great significance. Two kinds of heat pump system with three heat exchangers and four-way valve are researched in the article, and the result shows that: in most conditions, the two systems’ ability are similar, the difference between them is only 10W to 50W, but the COP of four-way valve system is 15% ~ 18% higher than that of three heat exchanger system, and the compressor power of four-way valve system is 50 to 150W lower than that of three heat exchanger system.

An innovative dual-temperature air conditioning system and the corresponding mixed theoretical refrigeration cycle were proposed. The new air-conditioner consists of an air handling unit and a metal radiation panel as its dual-temperature evaporators, a compressor, a condenser, two thermal expansion valves and an ejector. The state properties in the air handling process and the theoretical refrigeration cycle were analyzed and compared with those of the conventional air conditioner with fresh air. Results indicate that the coefficient of performance（COP）of the dual-temperature theoretical refrigeration cycle may be improved by 13.73% to 7.43. But the COP of the dual-temperature refrigeration cycle will drop by somewhat as the amount of fresh air required and indoor moisture increases. However, it is still greater than the COP of the conventional air conditioner by 5.21%.

To solve the problems of complex structure and unsuitable capacity control of present multi-function heat pump system, domestic energy system is introduced. A new system performance indicator is chosen to describe the performance of space cooling & water heating mode. By comparison with space cooling only mode, this mode has been proved with a little less cooling capacity but with higher total system performance. Series of experiments are conducted with different initial water temperature in tank, compressor load and outdoor ambient temperature conditions. By analysis of transient characteristics and system performance, the performance rules are concluded. Furthermore, the control strategy is proposed to insure the safe and efficient operation of space cooling & water heating mode.

A novel VM cycle refrigerator for air-conditioning temperature zone (>16℃) is introduced. It’s driven by pressure wave converted from heat which can be obtained by solar energy, industrial waste heat or fossil fuels. It has the advantages of compactness, low vibration and high reliability. The influences of volume ratio, void volume and phase difference of hot and cold displacers on theoretical cooling capacity had been studied. Also, five kinds of thermal losses were analyzed. Parameters of one VM cycle refrigerator were designed and the influences of charged pressure and frequency on actual cooling capacity and COP had been calculated. Moreover, the prospect of applications was discussed. The results show that a COP of 2.5～3 at 10 Hz can be obtained with a cooling capacity of 2000W. As to thermal losses, the losses in regenerators are dominant.

The parallel flow microchannel (PFM) heat exchanger is widely used in automotive air conditioning system, but it has the disadvantage of easy-frost and difficult in water-drain in defrost . The traditional tube and fin heat exchanger can overcome the frost and defrost problem but has low efficiency. In this paper a ?5 tube and fin heat exchanger is developed for the automotive heat pump. Performances of small diameter tube-and-fin heat exchanger and PFM heat exchanger are compared based on benchmark test. Results show that the system with small diameter tube-and-fin heat exchanger has 17.4%~23.7% higher COP in air conditioning mode, 12.6%~35.8% higher COP and 15~28℃ lower compressor discharge temperature in heat pump mode, which indicates that small diameter tube-and-fin heat exchanger is a promising solution to the automotive heat pump system of electric vehicle.

The performance of CO2 heat pump water heater was studied experimentally in this paper by comparing a loop heating and a direct heating hot water. In the loop heating mode, with an increase of the water temperature, the compressor inlet and exhaust pressure increased gradually, the power consumption increased and the gas cooler inlet and outlet temperature increased, too. The temperature difference between carbon dioxide and cooling water and heat transfer decreased, the COP of CO2 heat pump system decreased. The operating parameters of the system were stable and the COP remained unchanged in direct heated condition. When the water temperature is 17℃, the COP of the system is about 3.5, much higher than that in loop heating. The results show that the lower inlet temperature can be obtained by modifying the water tank structure and it is a very effective way to improve system performance.

A new transcritical CO2 heat pump systems with dual expansion valve and balance CO2 liquid reservoir adjustment device was introduced. The influence of the internal heat exchanger (IHX) on the system performances was analyzed on the basis of relative COP and compressor power. It is concluded that: the compressor power of system with IHX is relatively low when the high side pressure is over 10MPa, and the evaporating temperature is below 0℃. The COP of the system without IHX is about 3% to 5% higher than the system with IHX when the evaporating temperature is over 5℃. The new devices can control high and low side pressure effectively, and decrease the impact of pressure fluctuations on its COP. The experimental results provide important basis for the development of the transcritical CO2 heat pump systems.

To set up a platform for evaluating energy efficiency of water chiller and water source heat pump systems with EER or COP, the method of the second thermodynamic perfectibility was introduced. The range of thermodynamic perfectibility of room conditioners, water chillers and water-source heat pumps were calculated. The results show that the thermodynamic perfectibility of most water chillers is in the range of 0.3 to 0.5, the efficient products can reach 0.6, but the thermodynamic perfectibility of air to air products is about 0.2, and the thermodynamic perfectibility of air source heat pump water heaters is between water chillers and air to air products. The thermodynamic perfectibility is a useful index for the performance comparison of same or similar production in difference working conditions. The thermodynamic perfectibility analysis indicated that it characterizes the design and manufacturing level of products at present, and can be important foundation for the decision of minimum allowable performance, energy conservation performance and energy efficiency grade of energy efficiency standards for related products.

The effects of fin type of outdoor coil in an air-source heat pump unit on the dynamic frosting characteristics were experimentally investigated. The fins include the flat, wavy and wavy/slit type. The decreasing orders of both the average and maximum values of the heating capacity, COP and input power are flat, wavy and wavy/slit fins under the frosting condition. The average values of heating capacity, COP and input power for the wavy/slit fin are decreased by 14.57%, 8.26% and 7.11% respectively than those for the flat fin. The performance parameters for the wavy/slit fin decrease earliest and most greatly, then for the wavy fin, and finally for the flat fin. The frost has the advantage of enhancing the air-side heat transfer coefficient due to the phase change from vapor to frost. Meanwhile, it has the disadvantage of decreasing the fan airflow rate across the outdoor coil because the frost decreases the fin spacing and increases the air pressure drop. The curves of the performance parameters have the ascending and descending segments during the frosting period, which accords with the microcosmic growth characteristics of the frost. In the early stage of frosting cycle, the frost crystal grows from the grain shape to the column one which does not decrease the fin spacing remarkably, so the advantage of the frosting is greater than its disadvantage, which results in the ascending segment of performance. In the middle and final stages, the frost crystal grows along the radius direction, then stacks up between the frost columns, so the fin spacing is decreased remarkably and the disadvantage of the frosting is greater than its advantage.

This paper analyzed theoretically the change of refrigerant system after replacement of R410 with R32. Such replacement led to the increase of the discharge temperature of the system. The method of gas refrigerant injection was proposed to reduce the discharge temperature. Some experiments were made to investigate the variation of refrigerant system on charging rate, capacity,COP, discharge temperature after the replacement of R410A with R32. The results showed that, comparing with R410a system,the capacity, COP and discharge temperature of R32 were increased, and the R32 system with gas refrigerant injection can reduce effectively the discharge temperature, andincrease the capacity and COP. It can be concluded that R32 is a promising refrigerant candidate, and the limitation brought by high discharge temperature of R32 can be broken with the gas refrigerant injection system.