Vapor Compression Cycle Research Articles

Examining the feasibility of a bi-evaporator cooling/electricity cycle: A comprehensive analysis of thermodynamic, economic, and environmental aspects, and bi-objective optimization

Although geothermal energy is generally considered benign, it still has its share of problems, including the emission of greenhouse gases that harm the environment. To make informed decisions about geothermal systems, it is imperative to study their environmental impacts. This study uses six approaches to propose and analyze an innovative geothermal-driven bi-evaporator cooling/electricity plan. The proposed efficient design is made of a single-flash cycle and the integration of a modified vapor compression cycle and ejector cooling system assisted by a thermoelectric power generator device. Exergoenvironmental and extended-environmental assessments are performed to examine the environmental impacts of the current devised scheme, including calculating CO2 emissions rate and sustainability index. The suggested plan's performance in the basic design mode using 14 various working fluids showed that R143m had the highest exergetic efficiency, lowest exergoenvironmental index, and lowest cost of production at 35.9%, 0.6002, and 24.67$/GJ, respectively. This working fluid was used for parametric study and bi-objective optimization, which revealed that the vapor generator destroys 157.7 kW of exergy at the optimal point. Additionally, the vapor turbine is the most expensive component at 14.44$/h. Pareto frontier also indicates that the final chosen optimal mode (scenario C) has 27.02% energetic efficiency and 21.33$/GJ production cost, which are higher than the base scenario by 12.55% and 15.66%, respectively. In addition, the optimal scenario reduces the payback period to 8.64 years from 15.68 years in the base scenario.

Performance of Low Power Electric Energy Clothes Dryers for Households

One of the problems faced by middle to lower economic class people in big cities is drying clothes, both in the dry season and in the rainy season. Artificial clothes drying equipment is needed that can replace the role of solar energy. The purpose of this study was to determine the performance of electric energy clothes dryers and the length of time needed to dry clothes on a household scale. The clothes dryer works by using a heat-pump based on the vapor-compression cycle. The total power of the heat pump is 200 watt. The working fluid of the heat-pump is R134a. The working fluid used to dry clothes is air, using a closed airflow system. The research was carried out experimentally by varying the amount of clothes in the drying chamber. The clothes dryer performance (COP) of the heat pump is 7.94. Drying time for 15, 25 and 40 clothes respectively for 210 minutes, 330 minutes and 450 minutes.

Techno-economic-environmental performance of multi-stage evaporation based poly-generation system under multiple energy supply scenarios

To fulfil the seasonal energy demand in buildings, a novel thermally-driven poly-generation system is proposed based on organic Rankine cycle (ORC) and two-stage vapor compression cycle (TSVCC). The thermodynamic model of the combined cooling, heating and power (CCHP) system was constructed based on the laws of thermodynamics and energy-supply scenarios were also analyzed. Techno-economic-environmental performance of CCHP system was analyzed and compared with the traditional standalone energy-supply modes. Results show that the heating capacity of novel poly-generation system is at least 11% higher than single heating system. For the power generation performance, the novel poly-generation system is almost the same with the traditional ORC. The cooling capacity of poly-generation system is 8% worse than absorption refrigeration system due to the relatively low efficiency of ORC. The poly-generation system can meet the seasonal demand in buildings, the overall performance becomes more attractive with a rising heat source temperature, optimal operating parameters and proper working fluid. The net power output is 3199.37 kW and payback period will lower than 3 years if the heat source temperature is 473.15 K and R1233zd as the working fluid. Therefore, the proposed poly-generation system is excellent and should be employed in engineering applications.

A solar powered off-grid air conditioning system with natural refrigerant for residential buildings: A theoretical and experimental evaluation

Residential air-conditioning units are essential for providing suitable interior comfort in regions experiencing hot climates. Nonetheless, these units contribute significantly to CO2 emissions in these countries due to their reliance on non-renewable energy sources and the use of environmentally unfriendly working fluids. This research aims to evaluate the feasibility of operating an off-grid solar-powered air-conditioning bed unit using low-GWP refrigerants that can efficiently replace conventional refrigerants. A model was developed to evaluate the vapour compression cycle's energetic and exergetic performance. Various refrigerants were employed as feeds to the mathematical model in order to simulate the unit's performance if environmentally friendly refrigerants supersede the conventional substances. An assembled prototype air-conditioning unit was built to provide cold air to a connected canopy. Two 400 W photovoltaic panels power this system, with battery storage providing electricity to the unit at night. TRNSYS was used to evaluate the batteries' energy storage capability, whilst Integrated Environmental Solutions Virtual Environment (IESVE) was used to estimate the amount of solar energy required to power the unit. On the basis of the energetic and exergetic findings, R290 and R600a have demonstrated their suitability as replacements for conventional refrigerants. In comparison to R134a, the system showed a 2.42% improvement in COP when using R290. This improvement was accompanied by a reduction in input work by 2.31% and an increase in exergetic efficiency by 2.37%. This paper provides a guideline for analytical design, combined with a coherent process system. This offers an excellent solution to the very real problems of major energy consumption in warm countries, combining a renewable energy source with an eco-friendly air-conditioning cycle.

Assessment of control strategies for energy management in vapor compression cycles

Assessment of control strategies for energy management in vapor compression cycles

Ejector and Vapor Injection Enhanced Novel Compression-Absorption Cascade Refrigeration Systems: A Thermodynamic Parametric and Refrigerant Analysis

This study investigates the performance of two novel compression absorption cascade refrigeration systems, the Ejector Compression Absorption Cycle (ECAC) and Ejector Injection Compression Absorption Cycle (EICAC), in comparison to traditional system. In these cascaded systems, the absorption cycle (top cycle) is modified by adding a refrigerant hear exchanger (RHX) which provides higher mass flow of refrigerant to increase the COP. The simple vapor compression cycle (bottom cycle) performance is enhanced by incorporating the ejector and Vapor Injection technologies. A systematic analysis is accomplished to establish the optimal operating conditions for performance enhancement, taking into account of ejector parameters and the effect of different environmentally friendly refrigerants by the energy and exergy method. The findings demonstrate that both ECAC and EICAC systems can achieve near 15 % and 6 % higher COP, respectively, compared to conventional cascade system when using the R41-LiBr/H2O refrigerant pair under different working conditions. Maximum exergy efficiency is found to be achieved at around 73 °C, with ECAC and EICAC showing higher exergy efficiency of near 20 % and 10 %, respectively than the conventional system. The analysis also reveals that while the COP of all layouts augments linearly with increasing evaporator temperature, the exergy efficiency decreases at different rates, making the cascade systems more efficient for low-temperature applications. The LiBr/H2O refrigerant pair demonstrates superior COP and exergy efficiency as HTC refrigerant, while R161, R290, and R1270 perform better as low-temperature refrigerants for both ECAC and EICAC from both energetic and exergetic perspectives. The results of this detailed theoretical thermodynamic analysis provide a comprehensive understanding of the performance of ECAC and EICAC systems and offer valuable insights for further improvement and optimization.

Applying position and time dependent nusselt number and friction factor into 1D model to improve regenerator design for solid-state caloric cooling cycles

Active caloric regenerative cycles have recently attracted much attention as a promising cooling technology that can potentially replace the vapor compression cycle based on its high efficiency and eco-friendly characteristics. The use of modeling is necessary in optimizing the active caloric regenerative cycle due to the system’s complex structure and numerous parameters that need to be taken into account. The cycle uses oscillatory flow to efficiently exchange heat between the caloric material and the heat transfer fluid and to generate a desired temperature gradient in the regenerator. When the oscillatory flow is used, hydrodynamically and thermally developing regions occur all over the regenerator when the direction of the fluid flow changes.To the best of the authors’ knowledge, no previous research has considered the oscillatory developing regions in a 1D model. Therefore, this study incorporated the developing regions generated by the oscillatory flow as well as the entrance developing regions into a regenerator model for the first time. Based on the modeling results, the influence of the oscillatory developing regions and the average Nusselt number increase with higher cycle frequency. Additionally, the new 1D model produces average Nusselt number similar to the 2D model with a maximum error of 4 %. Considering that the 2D model requires very high computational cost to solve the transient condition of the caloric cycle, the advanced 1D model can accurately assess the performance of the caloric cycle and provide a detailed analysis of heat transfer phenomena and fluid dynamics in the regenerator at modest computational cost.The parallel plate type, optimized using the new model, has a hydraulic diameter of 0.1 mm. However, maintaining such a small space between the plates can be challenging from an application standpoint. Therefore, this study proposes the use of a wide rectangular microchannel matrix as the regenerator. The rectangular microchannel matrix, with an aspect ratio of 30, produces a coefficient of performance of 5.65, which is comparable to the parallel plate matrix. Consequently, the wide rectangular microchannel matrix can achieve both high Nusselt number and structural stability simultaneously.

Assessing the Potential of Heat Pumps to Reduce the Radiator Size on Small Satellites

Future small satellites will demand high-performance on-board electronics, requiring sophisticated approaches to heat rejection beyond simply increasing the radiator surface area. An interesting alternative approach is to increase the surface temperature of the radiator, using a heat pump. In this study, calculations were carried out to compute the theoretical radiator size reduction potential enacted by having a heat pump as part of a satellite’s thermal management system. The practical likelihood of a ‘typical’ vapor compression cycle (VCC) heat pump satisfying theoretical requirements was considered. In agreement with theoretical calculations, employing a ‘typical’ VCC heat pump could either increase or decrease the required radiator surface area. The choice of heat pump and its design is therefore crucial. A heat pump with a large temperature lift is essential for satellite radiator cooling applications, with the coefficient of performance (COP) being less important. Even with a low COP, such as 2.4, a ‘typical’ heat pump providing a large temperature lift, close to 60 °C, could reduce the satellite’s radiator surface area by a factor close to 1.4. This is a significant potential reduction. The decision on whether to pursue this approach compared to alternatives, such as deployable radiators, should consider the relative complexity, cost, weight, size, reliability, etc., of the two options. The focus of this study is VCC heat pumps; however, the results provide performance targets for less mature heat pump technologies, e.g., caloric devices, which could ultimately be applied in space.

Vapor Compression Cycle: A State-of-the-Art Review on Cycle Improvements, Water and Other Natural Refrigerants

Air conditioning and refrigeration have become necessary in modern life, accounting for more than 7.8% of greenhouse gases (GHG) emitted globally. Reducing the environmental impact of these systems is crucial for meeting the global GHG emission targets. Two principal directions must be considered to reduce the environmental impact of air conditioning systems. Firstly, reducing the direct effect by looking at less harmful refrigerants and secondly, reducing the indirect effect by searching for options to improve the system efficiency. This study presents the latest developments in the vapor compression cycle and natural refrigerants, focusing on water as a refrigerant. Natural refrigerants, and especially water, could be the ultimate solution for the environmental problems associated with the operation of vapor compression cycle (VCC) cooling systems, including ozone depletion (OD) and global warming (GW). Reducing the environmental impact of building cooling systems is essential, and the recent system improvements made to enhance the system coefficient of performance (COP) are thoroughly discussed in this paper. Though the cycle improvements discussed in this work are essential and could increase the system efficiency, they still need to solve the direct environmental impact of refrigerants. Accordingly, this paper suggests that natural refrigerants, including water, are the most suitable strategic choice to replace the current refrigerants in the refrigeration and air conditioning industry. Finally, this study reviews the latest VCC system improvements and natural refrigerants in order to guide interested researchers with solutions that may reduce the environmental impact of VCC systems and suggest future research areas.

Working fluid selection for a high efficiency integrated power/cooling system combining an organic Rankine cycle and vapor compression-absorption cycles

This paper presents the performance evaluation of several combinations of working fluids for a new heat recovery cogeneration system which combines an Organic Rankine Cycle (ORC), a Vapor Absorption Cycle (VAC) and a Vapor Compression Cycle (VCC). NH3–NaSCN is chosen as the working fluid in the VAC. Seven different refrigerants in the ORC-VCC were studied to identify the fluid that would allow the overall system to achieve a high efficiency in the tropical region. These fluids were chosen because of their low Global Warming Potential and Ozone Depletion Potential. A thermodynamic simulation allowed to set the appropriate operating conditions of the VAC. Subsequently, energy and exergy analyses showed that R717 is the appropriate working fluid for system operation in the tropical region. For this fluid, the highest values of cooling capacity, net power output, thermal efficiency, exergy efficiency and exergy destruction of the system were respectively 1205 kW, 158.3 kW, 64.32%, 39.39% and 690.4 kW for VCC evaporation temperature of 15 °C, for ORC-VCC condensation temperature of 40 °C and for ORC steam generator outlet temperature of 219.7 °C. The most exergy-destroying components are the steam generator and the ORC/VCC condenser with 57.29% and 22.58%, respectively.

Centrifugal Compressors Gas-Dynamic Characteristics Influence on the Refrigerating Machines Efficiency

The article is devoted to the study R134a refrigerating machine efficiency and consisting of a centrifugal compressor, a condenser, a temperature-regulating valve and an evaporator. The main purpose of the work is to analyze the centrifugal compressor gas dynamic characteristics effect on the refrigeration machine vapor-compression cycle efficiency. This goal is achieved through the study by actual working process numerical experiment in the refrigeration machine centrifugal compressor with an idealized process for other elements. The object of the study are the refrigeration machine characteristics, expressed by the theoretical refrigeration coefficient COPRt. Single-stage centrifugal compressors with the design conditional flow coefficient in the range from 0.035 to 0.12 are considered. The design of centrifugal compressors was carried out according to a new calculation method to the flow part efficiency increase. The method comprehensively combines the inviscid and viscous flow calculations with the use of the single-criteria and multiparametric optimization. Previously, the method was tested and compared with experimental data. The most important result is the results of the refrigeration cycle efficiency evaluating through the centrifugal compressors highly efficient flow parts design methodology application. An increase in COPRt was obtained taking into account the centrifugal compressor actual process in the range from 2.6% to 7.2%. The significance of the results obtained lies in the possibility of using high-efficiency centrifugal compressors gas dynamic characteristics for the chillers refrigeration cycles analysis and calculation. The level of the compressors isentropic efficiency ranges from 0.80 to 0.85, depending on the design conditional flow coefficient.

Analysis of a Phase Change Material-Based Condenser of a Low-Scale Refrigeration System

This study concerns the numerical simulation and the experimental implementation of a low-scale Phase Change Material-based (PCM-based) condenser, to be included in a PCM-based portable cooling systems. In this category of cooling systems, the PCM can be integrated either in the condenser or in the evaporator. In the present study, the PCM is integrated in the condenser of the vapor compression cycle to absorb the heat power released from the refrigerant fluid (R134a) during condensation, thus eliminating the need to transfer heat to the external environment. The main objective of the present study is to realize and validate a numerical model capable of simulating both the refrigerant fluid and the PCM thermofluid dynamics. For this purpose, a commercial solver was used for the implementation of the developed numerical model, and experimental tests were performed to validate the numerical simulations results. The paper reports the details and test results of both the numerical model and the experimental apparatus. The simulation results indicate a good accordance between the numerical and experimental data.

Thermal comfort-conscious eco-climate control for electric vehicles using model predictive control

In the heating, ventilation, and air-conditioning (HVAC) system of electric vehicles (EVs), an electric heater is often used for a reheating process that warms up the chilled evaporator outlet air for thermal comfort before it is supplied to the cabin. The usage of the electric heater can significantly reduce the driving range of an EV. Therefore, optimal control of the HVAC system with consideration of the reheating process becomes essential for an increased driving range. In addition, considering the primary role of cabin climate control, it is desirable to intelligently consider the passengers’ thermal comfort in climate control design. In this paper, thermal comfort-conscious eco-climate control (TCC-ECC) based on model predictive control (MPC) is proposed to enhance the energy efficiency of the HVAC operation while ensuring passengers’ thermal comfort. The MPC design uses a reduced-order HVAC system model based on an ideal vapor-compression cycle. For the integration of thermal comfort into the MPC, a new approach is proposed to obtain an approximate solution of a predictive mean vote (PMV)-based thermal comfort model, which aims to balance computational efficiency and prediction accuracy. With the proposed TCC-ECC, a parametric study is conducted to analyze the impact of weighting factors on energy consumption and thermal comfort under two different thermal load conditions. Then, the performance of the tuned TCC-ECC is evaluated in comparison with a rule-based (RB) controller and the baseline eco-climate control (ECC) without considering thermal comfort. In the performance evaluation, the proposed TCC-ECC demonstrates that with the inclusion of thermal comfort it performs better in terms of energy efficiency and thermal comfort than manually adjusting a target cabin temperature depending on the environmental thermal load. The energy consumption of the proposed TCC-ECC is 22.5% and 35.24% less than that of the RB controller at an ambient temperature of 24 °C and 35 °C, respectively, and 14.5% and 18.5% less than the baseline ECC at the same conditions, respectively.

Thermodynamic assessment of a new PTC operated polygeneration system for fresh water, cooling, electricity and hydrogen production for a residential community

The current study aims to design a new parabolic trough collector (PTC) operated polygeneration system to produce freshwater, hydrogen, cooling, and electricity in a residential society. Dowtherm A (a heat transfer fluid) is used to transfer the heat from PTC to the Organic Rankine Cycle, which is used to produce electrical power. The produced electrical power is utilized in three different ways, namely, to run the home appliances, to produce hydrogen (via water electrolysis), and to produce cooling (through a vapor compression cycle). The cooling produced by the vapor compression system is utilized to preserve the food, milk, and to operate the freezing desalination process. Effects of several factors, such as direct normal irradiance, evaporator temperature, and seawater inlet temperature, have been analyzed on the overall system behavior. Thermodynamic study results show that for a PTC area of 2000 m2, an electrical output obtained is 72 kW, the cooling rate is 112 kW, and the mass flow rate of fresh water produced is 18.4 l/day and 10.8 kg/day of hydrogen for mean solar irradiation of 700 W/m2. The energy efficiency of the system is found to be 17.5%, and the exergy efficiency of the system is around 10.9%.

Understanding airflow pattern and temperature distribution in domestic refrigerators – A review analyzing recent developments and bridging knowledge gaps

Refrigerators have become an essential appliance in every household, and they consume approximately 30% of total electricity among other domestic appliances such as clothes washers, dryers, and air conditioners. With the refrigerator’s comparatively high energy consumption compared with other appliances, existing research has mainly focused on improving the energy efficiency of refrigerators by changing the design of the compressor, heat exchanger, refrigerant, and insulation. However, previous studies have paid very little attention to the research and development of the temperature distribution in the refrigerator, which is a key parameter in determining energy consumption and food safety. Therefore, this review aims to present an overview of recent design developments to improve the temperature distribution and air circulation in domestic refrigerators, including static refrigerators and no-frost refrigerators. This review article discusses the various operation and design factors that can affect the air circulation and temperature uniformity of the refrigerator, including shelf arrangement, the compressor on/off cycle, thermostat settings, evaporator design, ambient conditions, door opening frequency, and product loading temperatures. Additionally, this review provides a summary of the advanced vapor compression cycle based refrigerators that are expected to provide better energy efficiency and independent temperature control in freezer and refrigerator compartments. This review elaborates on the significance of improving the performance of the domestic refrigerator in terms of temperature distribution and air circulation.

Experimental investigations on the performance of a thermo-mechanical refrigeration system utilizing ultra-low temperature waste heat sources

Experimental studies that investigate the utilization of ultra-low temperature (between 48 °C and 120 °C) waste heat, which forms 25 % of the global unrecovered waste heat, to drive thermal cooling systems are rare. Thus, this study fills a significant gap in the literature by (i) experimentally evaluating the performance of a new full-scale thermo-mechanical refrigeration (TMR) system at ultra-low temperatures ranging from 50 °C to 85 °C, (ii) characterizing its operation with different commercial refrigerants, and (iii) identifying optimal operating conditions and working fluids for the investigated TMR system. An organic Rankine cycle (ORC), vapor compression cycle (VCC), and expander-compressor unit (ECU) make up the TMR system. To ensure its efficient operation, flexibility, and reliability, a full-scale ECU-based TMR system with a design capacity of 1 kW at a heat source temperature of 85 °C is built and put through a series of tests. Furthermore, the TMR system is tested with different commercial refrigerants (R134a, R410A, R407C) over a wide range of operating conditions of the power loop. The results reveal that the ECU-based TMR system can work with ultra-low temperatures of 65 °C with an energy efficiency of 5.92 % and COP of 2.36, for the ORC and VCC, respectively. At a heat source temperature of 85 °C, a condenser water temperature of 15 °C, and an evaporator water temperature of 33 °C, the energy efficiency of the ORC and COP of the VCC are increased to 9.85 % and 3.99, respectively. For the cooling quality, the TMR system shows a minimum evaporator temperature of −10 °C using R134a in both the power and cooling loop, which is improved to lower than −20 °C by using R407C in the cooling loop. The results presented herein will be beneficial to the development, design, and optimization of refrigeration and power systems that utilize low-temperature waste heat.

Thermodynamic analysis of a waste heat utilization based efficient liquefaction and low-temperature adsorption carbon capture hybrid system

Cryogenic CO2 capture can obtain high-pressure and pure CO2, but existing methods are inefficient as they usually discharge the waste heat of refrigeration. Therefore, a new hybrid system is proposed to recycle the waste cooling, heat, and uncondensable CO2 of liquefaction CO2 capture into low-temperature adsorption CO2 capture. This enhances the overall energy efficiency and the CO2 recovery rate over existing cryogenic CO2 capture without external input. Moreover, it enables practical sub-zero temperature CO2 adsorption while lowering the desorption temperature to 70 °C. This system is analyzed by coupling the liquefaction CO2 capture and low-temperature adsorption CO2 capture thermodynamic models, whose heat and cooling needs are compared to that available by a vapor compression cycle. Results show that for 10% mol. CO2 flue gas, the proposed system is optimal at −53 °C and 5 MPa to yield a 2nd law efficiency of 9%, a CO2 recovery rate of 80%, and specific energy consumption of under 1.65 MJ/(kg of CO2). As the cooling demand is typically twice the heat needed for sorbent regeneration, a vapor compression cycle designed to meet the former can naturally meet the latter. Ultimately, the new hybrid system represents a new carbon capture technology with better potential to achieve carbon neutrality via waste heat utilization.

Performance analysis of the refrigeration system for improving energy efficiency

Refrigeration system holds an important role in many industrial processes. The global industrial refrigeration system market is expected to grow from USD 19.3 billion in 2019 to USD 25.7 billion by 2025, at a CAGR of 4.7%. The traditional systems (cascade/multistage) as well as hybrid system with non-zeotrope refrigerant blends are widely used for processes where more than one temperature level is required. The optimal utilization of energy saving technologies in industrial processes is a key issue for the rational use of energy resources in the process industry. Among the various existing energy saving means, the refrigeration system is a technology area that introduces several degrees of freedom. The goal is to identify the optimal refrigerant/refrigerant mixtures, the optimal temperature levels, and the best cycle's configuration to satisfy the refrigeration requirements of a technological process. It is common that hydrocarbons have great thermodynamic properties, making them efficient refrigerants. The problem is that hydrocarbons are highly flammable, it has restricted their wider adoption for some applications in the refrigeration industry, mostly for applications demanding large refrigerant charges. Targeting to reduce safety as well as regulatory problems getting up from the use of hydrocarbons, the performance of hydrocarbons and carbon dioxide mixtures as refrigerants in a standard vapor-compression cycle has studied. To take into account all energy losses in the compressor, a technique was used that allows one to assess the energy perfection of a hermetically sealed compressor during experimental studies. The given method contains indicators that estimate certain types of energy losses of a hermetic compressor using the electrical efficiency of the compressor.

PERFORMANCE ANALYSIS OF THE THERMOELECTRIC TEC 12706-BASED COOLING SYSTEM IN COOLER BOX DESIGN

The most widely used refrigeration machine today is a refrigeration machine that operates with a vapor compression cycle (SKU). To operate a vapor compression machine, refrigerant is needed as a working fluid. The most widely used refrigerants are chlorofluorocarbon (CFC) and hydrochlorofluorocarbon (HCFC) refrigerants. However, their use can damage the ozone layer and has a great potential to increase the effects of global warming. Therefore, a refrigeration system that is environmentally friendly and also has low power is needed, this can be fulfilled by using thermoelectric. This research was conducted to analyze the performance of temperature differences, heat absorbed, cooling capacity and COP in thermoelectric-based cooler boxes, thermoelectric performance with variations in input voltage and with variations in the addition of heatsinks where the method used is experimental by controlling the variable input voltage. From the research results, the calorific value absorbed is proportional to the increase in the applied voltage. Where the greater the voltage applied, the heat absorbed will be higher and the input power that enters the thermoelectric module is directly proportional to the incoming voltage where the greater the voltage. Then the power that goes into the thermoelectric will also be even greater. Whereas the COP value will decrease as the voltage increases and the best thermoelectric performance is with a voltage of 10 V. This can be seen after 60 minutes, the temperature difference value is 6.6 0K, the absorbed calorific value is 19,150 W, and the COP is 0.921. The thermoelectric performance is not only based on the COP value but also based on a review of the electric power consumed and the cooling speed during the 60 minute test. Then for the addition of a copper heatsink the COP value is 0.4832 and the temperature drop in the cooler box is only 3.9 0K, the value is lower than without the additional heatsink due to the gap between the aluminum heatsinks.

Performance analysis of a double-efficient CO2 cooling and heating system using an ejector

This paper presents a double-efficient CO2 cooling and heating system using an ejector, which can operate as modified dual-evaporators ejector expansion cycle (MDEEC) in cooling mode or as conventional heat pump cycle (CHPC) in heating mode through the reasonable arrangement of valves, and countercurrent heat transfer of CO2 with cooled or heated air is achieved in both modes. An ejector is utilized to recover the expansion work and two evaporators provide independent air dry-cooling and dehumidification in cooling mode. Two thermodynamic models are developed to investigate the effects of various parameters on the cycle performance. Comparison of proposed cycles with ejector expansion refrigeration cycle (EERC) and conventional dual-evaporator vapor compression cycle (CDVCC) are conducted based on energy analysis. The results show that coefficient of performance (COP) of this system is improved by more than 25% compared to EERC, and 33.62–56.27% compared to CDVCC. Besides, performance comparison of CHPC using CO2 and R134a is conducted, which reveals that COP of CO2 cycle is consistently higher, maintained above 2.7, and the maximum value is 5.36. The COP improvement is up to 29.74%, and the minimum value is 5.37%. This study provides a solution for efficient cooling and heating applying CO2 as refrigerant.