COP Improvement Research Articles

Refined one-dimensional modeling and experimental validation of scroll compressor with vapor injection for electric vehicles

Vapor injection technology represents a highly promising avenue for enhancing the efficiency of heat pump systems within electric vehicles, especially in challenging cold ambient conditions. Although a simplified isentropic process is commonly employed to assess the thermodynamic functioning of scroll compressors with vapor injection (SCVI), it diverges significantly from actual operational dynamics. This study introduces a sophisticated 1D mathematical model that incorporates key factors such as internal leakage and thermal losses, thereby providing a more accurate representation of SCVI's operational realities. The research includes comprehensive performance evaluations of a short wrap profile SCVI, with a specific focus on low-temperature ambient conditions, supported by rigorous experimental validation. Comparative analyses against non-injection scenarios reveal notable enhancements, including a maximum 17.2 % increase in mass flow, a 10.5 % rise in heating capacity, and a 2.15 % improvement in heating COP. Both the simplified isentropic process calculation model and the enhanced 1D mathematical model are utilized to analyze compressor operations. The integration of internal leakage and heat loss considerations significantly narrows the gap between calculated and experimental results for heating capacity and discharge temperature, reducing discrepancies from nearly 20 % to a mere 4 %. This refined mathematical model demonstrates a high level of alignment with experimental data, achieving an accuracy within 5 % when assessing the compressor's real-world operational dynamics.

Energy and exergy analysis of a novel two-stage ejector refrigeration cycle using binary zeotropic mixtures

To improve the ejector refrigeration cycle performance, this paper presents a theoretical thermodynamic analysis of a novel two-stage ejector refrigeration cycle (TSERC) with a gas-liquid separator using R134a/R32 and R600a/R290 as refrigerant. By separating the relatively low-boiling-point and high-boiling-point refrigerants, the cycle compression ratio decreases, the cycle performance increases, and the energy utilization efficiency can be improved. Energy and exergy analysis were conducted for the traditional single-stage ejector refrigeration cycle (SSERC) and TSERC. The effect of the mixture mass fraction on cycle performance under a fixed external heat source operating condition was studied, and the cycle performance comparisons between TSERC and SSERC at different evaporation temperature, condensation temperature and generation temperature were conducted. Results show that for TSERC, the maximum COP values 0.126 and 0.11, the maximum exergy efficiency 4.51 % and 4 % are obtained as the low-boiling-point mass fraction equals 0.6 and 0.4 respectively for R134a/R32 and R600a/R290. It is found that exergy destruction mainly occurs in the low-pressure sub-cycle of TSERC, the top three largest exergy destruction components are ejector 1, condenser 1 and generator 1, while the smallest exergy destruction occurs in pump 2. In addition, cycle performance comparison between SSERC and TSERC shows that the maximum COP improvement increased by 41.6 % and 89.6 % for 134a/R32 and R600a/R290 for TSERC, while the maximum entrainment ratio improvement increased by 32.4 % and 87.6 %. Moreover, it is concluded that the cycle performance improvement of TSERC is more significant at lower evaporation temperature, higher condensation temperature, and lower generation temperature compared to SSERC.

Performance Evaluation of Novel Advanced Recompression Absorption Refrigeration Systems Equipped with Ejector and Vapor Injection Technology

The absorption refrigeration cycle (ARC) faces challenges considering its decreased working pressure and COP. By integrating Recompression technology (RAC) into ARC, these issues are partly addressed. To address these inefficiencies, in this study, ejector and vapor injection techniques are incorporated into refrigerant side of the RAC cycle, resulting in the development of advanced systems: Refrigerant ejector enhanced recompression absorption cycle (RE-RAC) and Vapor injection enhanced recompression absorption cycle (VI-RAC). Key metrics assessed are 1st and 2nd law efficiency, system exergy destruction rate, compressor load, and generator heat requirements. Conclusively, under analogous operating conditions, RE-RAC and VI-RAC demonstrate a substantial improvement in COP, achieving 76 % and 63 % enhancements, respectively, over the standard RAC system. Compared to the conventional solution ejector-based SE-RAC, these systems show performance increases of 28 % and 19 %, respectively. The findings also highlight the sensitivity of these systems to parameters such as generator temperature and pressure, evaporator temperature, absorber temperature, evaporator recovery and normal pressure ratio. At higher evaporator temperature and lower generator temperature, the performance of these systems as well as enhancement of RE-RAC over VI-RAC is higher observed. The optimal value of generator pressure and recovery pressure ratio for maximum efficiency and minimum total exergy destruction rate is also dependent upon these. At a generator temperature of 67 °C and an evaporator temperature of 8 °C, RE-RAC exhibits a 35 % higher COP compared to VI-RAC. However, at −10 °C evaporator temperature, changes in external generator heat input and compressor work reduce the COP enhancement to 5 %.

Experimental investigation of a transcritical CO2 refrigeration system incorporating rotary gas pressure exchanger and low lift ejectors

Natural refrigerants like CO2 are playing a significant role in making refrigeration and heat pump systems climate-friendly by slowly phasing out the high global warming refrigerants like hydrofluorocarbons (HFCs). However, the efficiency of a transcritical CO2 refrigeration system declines significantly when the ambient temperature increases, primarily attributed to the high-pressure lift and the losses incurred during expansion. To remedy this issue, this paper presents a novel rotary gas pressure exchanger (PXG) device, which simultaneously achieves high differential pressure expansion work recovery and the “free compression” of the portion of the flash gas in a compact, rotary machine. For this, a PXG device is designed, fabricated, and tested to achieve free compression of CO2 over the entire differential pressure of approximately 70 bar between a receiver and a gas cooler. This is one of the highest free-pressure lift provided by any device to date in CO2 refrigeration. However, there is a small pressure loss of approximately 1–2 bar in the system due to viscous and inertia losses in the piping and in the PXG itself, which needs to be overcome by an external booster device. Results on a baseline PXG integrated system with two low lift booster compressors are presented, which show up to 60 bar free pressure lift and up to 18.2 % COP improvement provided by PXG. Additionally, key performance characteristics of the PXG, like the expansion work recovery, the mass boost ratio, direct fluid-to-fluid contact, and no pass-through operation are experimentally quantified. This work also presents a novel method to integrate two low lift ejectors with PXG to eliminate the need for separate low lift compressors. The low lift ejectors are designed, fabricated, and tested in-house, followed by their integration with the PXG device. A new type of transcritical CO2 refrigeration system is designed to integrate these low lift ejectors with PXG, and experiments are conducted at various evaporator thermal duties and gas cooler exit temperatures, simulating varying ambient temperature conditions. A novel control system to control the gas cooler pressure to optimal thermodynamic levels using PXG rotational speed is demonstrated experimentally. Further, automated control of high-pressure low lift ejector mass flow using an in-built needle design has been successfully demonstrated to optimise PXG mass boost performance. The LP low lift ejector achieved a successful pressure lift of 3.8 bar, and the HP low lift ejector showed a lift of 5.7 bar on the top of 42 bar free pressure lift provided by PXG for up to 5.8 kg/min mass flow delivered by free PXG compression. The results from this study demonstrate that the PXG device provides a significant energy efficiency improvement to the transcritical CO2 refrigeration system, and the novel low lift ejectors, when integrated with PXG, provide a successful method to maximise PXG’s thermodynamic potential.

Thermodynamic Analysis of Modelled and Simulated Heat Pump Drying System Using Azeotropic Mixture of Organic Working Fluids

It is well-known that the choice of working fluid significantly impacts the performance, cost estimation, and environmental effect of a heat pump. In this study, the performance of pure working fluids (dimethyl ether and ethanol) was compared with that of azeotropic mixture working fluids used in vapor compression heat pumps. The study also examined the effect of compression ratio and different compressor models on the performance of a vapor compression heat pump for heating processes and drying tomato slices at an air temperature of 40 °C and an air flow rate of 200 kg/hr. Using ethanol as the working fluid at evaporating and condensing temperatures of 10 °C and 15 °C, respectively, the specific moisture extraction rate was 0.2112 kg/kWh, and the Carnot coefficient of performance was 57.60. The study demonstrated a COP improvement of more than 15% for azeotropic mixtures compared to a pure working fluid. The maximum overall energy efficiency and exergy efficiency, achieved with Mixture II, were 5.68% and 27.32%, respectively. As suction pressure increased while maintaining constant discharge pressure, the compression ratio and work done by the compressor decreased, while the system's overall energy efficiency, and overall exergy efficiency improved under the given conditions.

Innovative heat management method and metaheuristic algorithm optimized power supply-demand balance for PEMFC-ASHP-CHP system

The evolution of distributed building energy systems fuels the growing demand for sustainable energy solutions. In this paper, Proton Exchange Membrane Fuel Cell (PEMFC) and Air Source Heat Pump (ASHP) were integrated to form PEMFC-ASHP-CHP systems in three combination methods, i.e., Direct Combination (DC), Parallel Combination (PC), Series Combination (SC). And compared the energy management strategies and power balance of the system. To further improve reliability and flexibility, a diversion PEMFC-ASHP-CHP system was proposed by combining PC and SC's system advantages. Additionally, an iterative algorithm addressed the mismatch between power supply and demand. An empirical formula was proposed to improve iterative convergence speed for practical control situations. The coefficients were optimized using six metaheuristic algorithms, and the outcomes were summarized into an optimized operational plane to enhance the system control response speed further. The results show that the PC method performs better than DC and SC. It achieves a power consumption reduction of 52.8% and a COP improvement of 111.4% compared with the ASHP system. Meanwhile, the diversion system can more effectively utilize waste heat from the PEMFC and further improve the system's performance. The Queuing Search Algorithm (QSA) demonstrates superior accuracy for coefficient optimization. By using the established empirical formula, the convergence speeds of global and local iterative methods are improved by 26.10% and 41.78%, respectively, compared to the direct iterative algorithm. Ultimately, the optimized operational plane can achieve a maximum 37.16% hydrogen consumption reduction compared to the unoptimized system.

Comprehensive performance evaluation on a transcritical CO2 ejector-expansion heat pump system

In order to reduce irreversible loss and recover expansion work for improving automotive thermal system performance, this study experimentally evaluated the performances and characteristics of a CO2 ejector-expansion (EJE) heat pump system for electric vehicles under typical cooling and heating operating modes, examined the adaptability of the EJE system with a fixed-dimension ejector, and compared the EJE system with the basic-regenerative (REG) and vapor-injection (INJ) systems in the − 30 °C to 50 °C range. The results show that the increasing electronic expansion valve (EXV) opening leads to an increasing entrainment ratio and a decreasing lift ratio in both two modes. The maximum COP is 2.00 at 35 °C/27 °C (out-cabin/in-cabin air temperature) and 1.85 at 0 °C/20 °C. The COP improvement reaches a maximum of 21.6 % and 31.0 % at the ejector design temperature of 45 °C, compared to the REG and INJ systems, respectively. However, the heating performance of the ejector designed at a high temperature significantly decreases as the ambient temperature goes down. At − 30 °C/20 °C, the EJE system performs worse with a COP degradation of 6.1 % compared to the REG system.

Energy and exergo-environmental performance analysis of a Stirling micro-fridge with imperfect regenerator

In search of very small and ecological refrigeration machines, Stirling chillers are studied on a micro-scale. This article analyzes the performance of a Stirling microcooler using a new modeling approach. This micro-cooler consists of a pillar network as regenerator, a compression and expansion chamber suitable for batch manufacturing, Alpha configuration with helium as working fluid. The Schmidt model with imperfect regeneration is used with consideration of work losses due to gas spring hysteresis. The equations solved analytically using the laws of thermodynamics are used to evaluate the energy and exergy performance of the microcooler. The parameters like height and internal width of the regenerator, phase angle, temperature ratio, swept volume ratio, cooling pressure, dead volume ratio are studied. A numerical code is developed in Matlab. Results show that optimal parameters develop a cooling capacity of 18.99 mW at a phase angle of 45°, a coefficient of performance of 1.104 at an internal height of the regenerator of 0.85 mm, an ecological coefficient of performance of 10.9 mW, an exergy yield of 6.13%, a destroyed exergy of 0.66 mW. The comparison between the present work and those in the literature shows that the current micro-cooler explores a COP improvement of 35%.

High-glide refrigerant blends in high-temperature heat pumps: Part 1 – Coefficient of performance

Climate change necessitates the reduction of primary energy consumption. Industrial heat pumps can contribute by replacing oil and gas fired boilers in various applications. To cater the application, heat pumps must often impose temperature differences of 25 K or more to the heat source and heat sink, causing great irreversibility if evaporation and condensation occur at constant temperatures. Many theoretical studies suggest that high-glide refrigerant mixtures designed to match the temperature differences have a superior COP for such applications. In contrast to the numerous theoretical studies, systematic experimental studies are missing. This study tests high-glide mixtures at varying compositions at constant operating conditions. COP improvements of 16 % are shown comparing the best mixture against the best pure fluid. The improvement was established despite a significant degradation in the heat transfer coefficient, which could presumably be alleviated with larger heat exchangers. Additional parametric studies are conducted on the temperature differences of heat sink and source as well as the temperature level. The results show that mixtures not only outperform pure fluids at certain operating conditions but can maintain a higher COP across varying operating conditions. The binary and ternary mixtures in this study have glides between 10 and 40 K and consist of R1336mzz(Z), R1233zd(E), R1224yd(Z), R1234yf and R32.

Experimental investigation into the influence of different system configurations on charge optimization in an R410A chiller with a dedicated subcooler

The current study addresses the important issue of reducing the amount of refrigerant used in HVAC&R systems due to new regulations and the phase-down of high Global Warming Potential (GWP) refrigerants. Specifically, this research compares the optimal refrigerant charge for two distinct scroll compressors: a variable speed compressor and a single speed compressor, both operating within the same R410A chiller equipped with a condenser, receiver and dedicated subcooler. The nominal cooling capacity of this chiller is 8 kW. One novelty of this study lies in assessing the charge optimization not only at full load but also at part load conditions to determine if there is any effect of using continuous capacity modulation like a variable speed compressor on the optimum charge. The results reveal that the COP maximizing charge corresponds to when some part of the two-phase heat transfer happens in the dedicated subcooler and not when the receiver is partially filled with liquid refrigerant as expected. Interestingly, at part load conditions, the compressor lacking continuous capacity modulation demonstrates higher optimum subcooling and COP improvement potential compared to full load conditions. Moreover, the study also analyzes the impact of operating at peak COP charge on seasonal performance using a variable speed compressor. This seasonal performance investigation reveals that although cooling capacity obtained when the system is operating with COP maximizing charge is 6 % lower, the seasonal performance is 11 % higher when compared to typical operating charge. Notably, for the first time, charge optimization is conducted in the same experimental with different configurations of the condenser with/without receiver and with/without subcooler to understand the contribution of these components. This systematic comparison revealed the absence of abnormal COP peak in configurations without a dedicated subcooler.

Experimental Performance Comparison of High-Glide Hydrocarbon and Synthetic Refrigerant Mixtures in a High-Temperature Heat Pump

Several theoretical studies have predicted that refrigerant mixtures with glides of more than 20 K can yield COP improvements in heat pumps for operating conditions where the temperature difference between the heat source and heat sink is large, but experimental validations and quantifications are scarce. The application of high-glide mixtures (>20 K) in industrial heat pumps in the field is, therefore, still hampered by concerns about the behavior and handling of the mixtures. This study experimentally investigates hydrocarbon (HC) mixtures R-290/600 (propane/butane) and R-290/601 (propane/pentane) and compares them to previously tested mixtures of synthetic refrigerants. Comprehensive evaluations are presented regarding COP, compressor performance, pressure drop, heat transfer, and the possibility of inline composition determination. The mixtures were tested over a range of compositions at a source inlet temperature of 60 °C and a sink outlet temperature of 100 °C, with the heat sink and heat source temperature differences controlled to 35 K. R-290/601 at a mass composition of 70%/30% was found as the best mixture with a COP improvement of 19% over R-600 as the best pure fluid. The overall isentropic compressor efficiency was similar for HC and synthetic refrigerants, given equal suction and discharge pressures. Pressure drops in heat exchangers and connecting lines were equal for synthetic and HC mixtures at equal mass flow rates. This allows higher heating capacities of HC mixtures at a given pressure drop (mass flow rate) due to their wider vapor dome. A previously developed evaporator heat transfer correlation for synthetic refrigerant mixtures was applicable to the HC mixtures. A condenser heat transfer correlation previously fitted for synthetic refrigerants performed significantly worse for HC mixtures. Composition determination during operation and without sampling was possible with a deviation of at most 0.05 mass fraction using simple temperature and pressure measurements and REFPROP for thermodynamic property calculations. Overall, high-glide HC mixtures, just like mixtures of synthetic refrigerants, showed significant COP improvements for specific operating conditions despite a decreased heat transfer coefficient. Potential problems like composition shift or poor compressor performance were not encountered. As a next step, testing high-glide mixtures in pilot-plant installations is recommended.

Optimization and performance improvement of ultra-low temperature cascade refrigeration system based on the isentropic efficiency curve of single-screw compressor

In this paper, a cascade refrigeration system equipped with a single-screw compressor (SSC-CRS) is proposed and built in order to achieve the goal of high load cooling capacity under ultra-low temperature conditions. Firstly, the isentropic efficiency curve of the single-screw compressor (SSC) is fitted through experimental method in response to the characteristics of low suction temperature and large pressure ratio of the compressor. In addition, the analysis of SSC-CRS with 28 refrigerant pairs are made to compare the coefficient of refrigeration (COP) and power consumption. On the basis of the cascade system, the paper compares the improvement of performance between two circuits with SSC: vapor injection cascade refrigeration system (SSC-ICRS) and ejector vapor injection cascade refrigeration system (SSC-EICRS). The results indicate the COP improvement rate of SSC-ICRS system is 17.39 %–41.98 % and the COP improvement rate of SSC-EICRS system is 49.46 %–68.37 % compared with SSC-CRS.

Performance analysis of a novel ejector-assisted condenser outlet split dual-evaporator refrigeration system

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.

Thermodynamic analysis of a dual-pressure evaporation high-temperature heat pump with low GWP zeotropic mixtures for steam generation

High-temperature heat pumps (HTHPs) have gained attention due to their economic and environmental benefits in utilizing industrial waste heat for steam generation. This study focuses on improving the HTHPs’ performance by employing two-stage separation and dual-pressure evaporation technology in the auto-cascade heat pump cycle. Additionally, binary zeotropic refrigerant mixtures with low-GWP are selected using the polar perturbed-chain statistical associated fluid theory (PC-SAFT) equation of state. The findings indicate that the R1234ze(E)&R1233zd(E) refrigerant mixture outperforms other potential alternatives, exhibiting a thermodynamic effectiveness 0.85%–1.86% higher than the benchmark mixture, R134a&R245fa. The improved cycle demonstrates significant enhancements, achieving a 45.17% increase in heat source utilization efficiency and a 24.48% improvement in COP compared to the basic auto-cascade cycle. Effective temperature matching between refrigerant mixtures and heat sources/sinks is guaranteed in the improved cycle. Moreover, a parameter analysis reveals that increasing the subcooling degree of the cascaded heat exchanger and the separation dryness fraction at separator 2 enables improvements in both COP and heat source utilization efficiency. These findings provide valuable insights into the design of steam generation heat pumps and the selection of refrigerant mixtures.

Performance improvement of vapor compression heat pump with superhydrophobic finned-tube evaporator

Residential buildings frequently employ vapor compression heat pump for winter heating. Its advantages over electric and coal-fired heating include great energy effectiveness and low emissions. However, the outside evaporator's frosting negatively impacts the performance of heat pump systems in low-temperature and high-humidity environments. To ameliorate the frosting problem, a finned-tube heat exchanger with superhydrophobic surface wettability prepared by the wet chemical etching method was applied to a vapor compression heat pump in this study. The performance of a commercial evaporator unit and the superhydrophobic evaporator unit under five frosting conditions was investigated through experiments. The maximum heat transfer rate of the superhydrophobic heat exchanger unit was increased by 17%–44% compared with that of the commercial unit. The COP improvement of the superhydrophobic unit reached 11.2%, 14.3%, 18.8%, 20.9% and 31.9%, respectively. The total mass of frost formation of the superhydrophobic unit experienced a 59.2%–76.3% decrease. The operation time of the superhydrophobic evaporator unit before defrosting determination was significantly extended, reducing the number of defrosting times during a long-time operation. This study proves the advantages of superhydrophobic finned-tube evaporators used in heat pumps in terms of heat transfer performance and frost suppression performance, promoting the application of superhydrophobic finned-tube evaporators in heat pump air-conditioning systems.

Parametric analysis and potential evaluation of an all-day radiative sky cooling radiator-assisted ground source heat pump system

Practical utilization of radiative sky cooling (RSC) in an active way to produce cold water breaks the cooling limitation of 150 W/m2 for passive RSC but requires thoughtful system design. Therefore, this study proposes a novel radiative sky cooling radiator (RSCR)-assisted ground source heat pump (RGSHP) system to maximize the cooling potential of using RSCR and GSHP. The RGSHP can take full advantage of the ground’s thermostability to improve the cooling performance of the RSCR. Based on this developed hybrid system, the effects of designing parameters, weather conditions, and spectral properties of coatings on the performances of radiative cooling have been comprehensively investigated. The results show that a larger water flow rate is conducive to cooling power production of RSCR, but a smaller flow rate is beneficial to the COP improvement of the whole system. Moreover, compared with the ideal RSCR (iRSCR), the practical RSCR (pRSCR) shows comparable cooling performances due to the higher convective cooling performances, with an considerable annual average COP which is only 0.8 % smaller than the iRSCR-assisted GSHP system. Due to less heat rejected into the ground by RGSHP, the borehole wall temperature shows smaller values than stand-alone GSHP. For a ten-year simulation, the RGSHP system can reduce borehole wall temperature by 10.2 %. Moreover, using the RGSHP can also achieve cooling storage in the ground during the non-cooling seasons, and thus the RGSHP outperforms the GSHP by 13.2 % regarding the cooling season average COP.

Numerical study on the effect of intermediate pressure pulsation on COP in the vapor injection cycle

The vapor injection cycle with flash tank and two stage compressor is known as an efficient cycle. It is known that the intermediate pressure is a key factor for COP improvement and pressure change during the injection process could reduce the COP. However, the effect of the pulsating intermediate pressure of a two-stage compressor on COP is not clear. In a previous study, the authors experimentally showed that COP varied with injection pipe length. There seemed to be a correlation between COP and the resonance phenomenon caused by pressure pulsation in the injection pipe. However, the mechanism of COP improvement is not well understood. In this study, a one-dimensional simulation model was developed to clarify the mechanism and was verified with the experimental results. The simulation results show that resonance in the injection pipe does not increase the injection mass flow rate into the suction pipe. On the contrary, backflow occurs in the injection pipe and the backflow ratio is minimum in the resonant condition. Due to the high temperature of the backflow coming from the discharge pipe, the saturated vapor from the flash tank is easily heated, causing heat loss and lower COP. It was found that COP can be improved by using resonance to suppress the backflow.

Performance analysis of a dual-ejector enhanced two-stage auto-cascade refrigeration cycle for ultra-low temperature refrigeration

Auto-cascade refrigeration cycle (ARC) is a cost-effective solution for ultra-low temperature refrigeration. This paper proposes a dual-ejector enhanced two-stage auto-cascade refrigeration cycle (ETARC). In ETARC, two ejectors replace the throttle valves at the liquid phase outlet of the two gas–liquid separators in the conventional two-stage auto-cascade refrigeration cycle (CTARC). They are connected in series to recover partial expansion work in the throttling process, aiming to lift the suction pressure of the compressor. The ternary mixture component is selected and R600a/R41/R1150 is supposed to be the working fluid due to the best performance. The mass fraction ratio of the refrigerant mixture components, the quality at the inlet of two separators and the expansion ratio of the throttle valve (EPR) of the two cycles are optimized using particle swarm optimization (PSO) with respect to the maximum COP. The performances of the two cycles at optimum operating conditions are compared using energetic and exergetic methods, and the effect of the evaporation temperature and the condensation temperature on cycle performances and operating characteristics are discussed in detail. The results show that applying the two ejectors effectively improves the performance of ETARC. Compared with the CTARC at the evaporation temperature of −85℃, and the condensation temperature of 45℃, the ETARC cycle exhibits 16.07% improvement in COP, 29.43% increase in the volumetric refrigeration capacity qv, 17.17% reduction in the total exergy destruction rate. ETARC shows significant performance improvement and has a remarkable energy-saving potential.

Direct-expansion solar-assisted heat pump coupled with crystallisation-controlled supercooled PCM for shifting building electricity demand

This paper proposes a novel approach for improving the performance of a direct-expansion solar-assisted heat pump (DX-SAHP) system by integrating a crystallisation controllable phase change material (PCM) and building energy demand shifting strategy. The proposed system aims to reduce buildings' energy consumption while utilizing solar energy efficiently. Sodium acetate trihydrate (SAT) as the crystallisation controllable supercooled PCM has a promising feature of releasing the stored latent heat when it is externally triggered, allowing the user to control the stored heat whenever needed. In the study, the PCM can store the thermal energy generated by the DX-SAHP during peak solar hours in an efficient way. This stored energy can be released when solar energy is unavailable, but the heating is requested. This approach not only reduces the load on the heat pump system but also makes efficient use of the stored thermal energy by crystallisation controllable PCM. A detailed controlling methodology of the system is given, and heating output is controlled considering the level of solar irradiance. The proposed system was modelled and simulated using MATLAB, and the results show that the integration of crystallisation controllable PCM and building demand shifting strategy can significantly reduce the energy consumption of the buildings. On the low solar radiation day, the COP improvement compared to the air source heat pump system was found 9.4%, this improvement value can reach 77% on high solar radiation days. The system can also effectively utilize solar energy and reduce the overall carbon footprint of buildings.

Experimental Investigation of Coefficient of Performance Enhancement (COP) in Ice Plant Using Brine-Based Metal Oxide Nanofluids

The research investigates brine-based metal oxide nanofluids to improve heat transfer and ice plant COP. The novelty of the study is in the use of stable nanofluids of ZnO, CuO, and Al2O3 prepared using surfactants and ultra-sonication to improve the performance of an ice plant working on the vapor compression refrigeration cycle. The study found that the COP of the ice plant was significantly enhanced using these nanofluids, with the greatest improvement of 27% observed for Al2O3 nanofluids at a particle volume concentration of 0.3%. The experiment also showed a reduction in compressor power consumption by 22% at the same concentration and temperature, indicating the potential use of these nanofluids in ice plant applications. The study further demonstrated that the COP improvement was more significant at a controlled temperature of 20 °C than at 25 °C.