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This study presents a review of advances made in evaporative cooling technologies, emphasizing their application in indoor thermal comfort. It highlights that the rising demand for cooling has primarily been met by conventional mechanical vapor compression systems. However, these systems face two significant issues: high electrical energy requirements and the use of refrigerants like chlorofluorocarbons (CFCs) and hydrofluorocarbons (HFCs), which contribute to ozone layer depletion and global warming. The findings indicate that evaporative cooling technology is a promising alternative due to its low energy demand and potential to integrate renewable energy, therefore enhancing its environmental benefits. The study also details various evaporative cooling technologies, recent improvements in their performance, practical applications, challenges, and opportunities for providing indoor thermal comfort. [ABSTRACT FROM AUTHOR]

In this work, a new solar cooling system that is powered by a concentrated photovoltaic thermal module is presented. Given the intermittent nature of solar energy, the essence of this system lies in its capability to offer continuous cooling. Furthermore, the proposed cooling system is versatile in operation, with three alternative modes available depending on the user's demands. Two operating scenarios of the system are presented. In the first scenario, thermal energy is utilized for cooling during the daytime, while electric energy is stored as compressed air for nighttime use. In the second scenario, both thermal and electric energies are employed for cooling during periods of high demand. The system is studied under different evaporator temperatures, various ambient temperatures, and different solar intensities. The results show that at an evaporation temperature of 4 °C, the system can provide continuous cooling, generating up to 10.24 kW of cooling power during the daytime and up to 7.66 kW during the nighttime, with an overall coefficient of performance of 0.612. [ABSTRACT FROM AUTHOR]

Atmospheric water harvesting (AWH) devices represent a fruitful hope to cope with water shortage problem throughout the world. The vast development in AWH technology and the wide spread of the various AWH techniques will largely contribute in the implementation of AWH machines in different household, agricultural and industrial applications. In the last decades a huge amount of research has been done on AWH methods with amazing differences in results that miss lead the readers and even researchers. In this study the AWH theoretical technology developments, various AWH methods and the various AWH machines in the market are reviewed. A comparison between the different theoretical methods is presented, concentration on unifying results based on area and energy consumption per harvested amount is performed for clear judgment on the different published data. Gaps between theory and market available devices are stated with recommendations for further development in AWH technology.

In the medical field, refrigeration systems are used to store and transport vaccines, blood, and other medical supplies that require specific temperature ranges to remain effective. As technology continues to advance, the demand for more efficient and sustainable refrigeration systems is also increasing. The freezer compartment is typically designed to maintain a temperature of −18°C to −23°C for storing frozen items. Consequently, this work aims to develop a hybrid refrigeration system that combines a thermoelectric cooler system (TEC) and a vapor compression refrigeration cycle (VCC) system to achieve lower temperatures than conventional refrigerators. Also, the performance of the proposed hybrid refrigeration system is experimentally assessed with various operating conditions, including varying the voltage delivered to the system. The experimental results exhibited that the temperature inside the freezer room reached −33°C, while the cold side temperature is −47°C. Also, the maximum coefficient of performance of the VCC system, TEC, and hybrid system is 2.07, 1.06, and 0.37, respectively, at a DC voltage applied of 6 V. Moreover, the results revealed that the hybrid system combining a TEC and a VCC system can be a valuable technology for specific applications with low temperatures and limited capacity requirements. [ABSTRACT FROM AUTHOR]

The study and development of miniature refrigeration and climate conditioning systems based on vapor compression for small-scale applications have received wide interest in recent years due to their advantages compared with other available technologies, both active and passive. This paper identifies different applications and areas of opportunity, including electronic components and personal cooling, where small-scale vapor compression refrigeration systems are anticipated to play a key role in technological development. This paper presents the current state of the art, including applications, component designs, operating conditions, experiments, published results, etc. to describe the current status of small-scale vapor compression refrigeration and illustrate a perspective for the future of this technology. [ABSTRACT FROM AUTHOR]

Atmospheric water harvesting (AWH) devices represent a fruitful hope to cope with the water shortage problem throughout the world. The vast development in AWH technology and the wide spread of various AWH techniques will largely contribute to the implementation of AWH machines in different household, agricultural and industrial applications. In the last decades, a huge amount of research has been done on AWH methods with amazing differences in results that mislead readers and even researchers. In this study, the AWH theoretical technology developments, various AWH methods and various AWH machines in the market were reviewed. A comparison between the different theoretical methods was presented, concentration on unifying results based on area and energy consumption per harvested amount was performed for clear judgment on the different published data. The gaps between theory and market available devices were stated with recommendations for further development in AWH technology. [ABSTRACT FROM AUTHOR]

This paper presents a comparison of the thermodynamic performances of magnetocaloric and vapor compression cooling technologies when operating the same wine cooler cabinet. The vapor compression system used is a commercially available 31-bottle domestic wine cooler, while the magnetocaloric cooling device is a state-of-the-art (TRL-5) prototype connected to the retrofitted wine cooler cabinet. The test procedures involved characterizing the unsteady and steady-state behavior of both technologies. Detailed instrumentation of both systems allowed for a unique low-level performance comparison, considering first- and second-law-based parameters, which has not been explored in the literature. Overall, the wine cooler was found to be more efficient when operated by the vapor compression system. For an ambient temperature of 25 °C and a cabinet temperature of approximately 12 °C, the coefficient of performance (COP) and second-law efficiency of the wine cooler were 0.7 and 3.6% respectively when using the vapor compression system, whereas they were 0.49 and 2.0% respectively when using the magnetocaloric refrigerator system. However, despite the contrast between the internally ideal coefficient of performance of the magnetocaloric wine cooler and the vapor compression wine cooler, significant but realistic design improvements were suggested. These suggestions were evaluated and quantified using a system-level magnetocaloric refrigerator model. The numerical results indicate that with changes in the current pumping system and magnetocaloric materials, an improved version of the magnetocaloric wine cooler could surpass the COP of its original version by 88% and the vapor compression system by 31%. • Magnetic (MR) and vapor compression (VC) coolers are compared on the same basis. • The MR device is a TRL-5 prototype connected to a retrofitted wine cooler cabinet. • For a 12 °C/25 °C span, the VC and MR systems' COPs were 0.7 and 0.49, respectively. • Design improvements were suggested for the MR system using a validated model. • An improved MR cooler could surpass the COP of its original version by 88%. [ABSTRACT FROM AUTHOR]

This study adopts a numerical thermo-economic investigation of a novel desalination system. In this system, a vapor compression (VC) heat pump is used to drive a balanced humidification-dehumidification (HDH) desalination unit with multiple extractions. The mathematical model of the proposed VC-HDH system is validated experimentally. The system is examined for water production under a condenser temperature of 45 °C, evaporator temperature of −5°C, feed saline water temperature of 30 °C, feed saline water flow rate of 1 kg/s, and an energy effectiveness value of 0.85 for the HDH unit’s components. The results show that without air extraction, the system can produce 6.62 kg/h of desalinated water for 0.011 $/l with a gained-output-ratio (GOR) value of 9.1. On the other hand, when a single air extraction is applied, about 20 kg/h of desalination water is produced by the system for 0.0042 $/l and 29 GOR. Increasing the number of air extractions to two yields a freshwater production rate of approximately 40 kg/h for 0.0026 $/l and a GOR value of 57. A considerable positive effect of the HDH unit’s performance is found on the system’s performance on both thermodynamic and economic scales. For better desalination performance, it is found that the feed water temperature should be maintained between 25 °C and 30 °C. Finally, the theoretical ceiling of the proposed system’s GOR is estimated.

The study and development of miniature refrigeration and climate conditioning systems based on vapor compression for small-scale applications have received wide interest in recent years due to their advantages compared with other available technologies, both active and passive. This paper identifies different applications and areas of opportunity, including electronic components and personal cooling, where small-scale vapor compression refrigeration systems are anticipated to play a key role in technological development. This paper presents the current state of the art, including applications, component designs, operating conditions, experiments, published results, etc. to describe the current status of small-scale vapor compression refrigeration and illustrate a perspective for the future of this technology.

Highlights: Comparative study of energy performance for a vapor compression chilled water using a new low GWP refrigerant (R1234ze), HFC refrigerants (R134a, R407C, and R410A), and the conventional HCFC22 refrigerant. Analyze the environmental impact of the different tested refrigerants and select the one with the lowest annual TEWI among them. The global concern regarding the environmental repercussions of refrigerants has escalated due to their adverse effects. These substances deplete the ozone layer and intensify the greenhouse effect. International agreements such as the Montreal and Kyoto Protocols and COP21 have imposed restrictions on refrigerants with high global warming potential (GWP) to address these issues. This study aims to explore the feasibility, energy efficiency, and environmental impact of utilizing the HFO (hydrofluoric-olefin) refrigerant R1234ze as a substitute for HFCs (hydrofluoric-carbon) (R134a, R407C, and R410A) and HCFCs (R22) in air-cooled vapor compression refrigeration and air conditioning systems. To determine their effectiveness, we evaluate the energy performance of various refrigerant operating cycles across a wide range of ambient and evaporating temperatures. Additionally, we conduct environmental impact analyses based on the total equivalent warming impact (TEWI) parameter calculated for commercially available chillers that utilize the fluids mentioned above. Our findings indicate that vapor compression chilled water systems employing R1234ze exhibit the highest performance coefficient and the lowest annual TEWI. [ABSTRACT FROM AUTHOR]

• Combination of the absorption and vapor compression heat pump. • Maximum performance enhancements for heating is 45.8%. • Maximum performance enhancements for cooling is 18.9%. • Power savings for heating and cooling are 16.0% and 31.4%, respectively. • Lower the heat-driven temperature for absorption to 60 °C. Decarbonizing the energy sector becomes a key topic to solving man-made climate change. For achieving indoor thermal comfort conditions, conventional heating, ventilating, and air-conditioning systems consume so much energy in both residential and public buildings. In this paper, a novel solar-assisted absorption-compression system for both heating and cooling is proposed to utilize solar thermal energy throughout the year for the heating/cooling supply. The experimental prototype was built and operational modes including solar-assisted heating/cooling mode and vapor compression individual heating/cooling mode. The performance enhanced by assisted heat input of the proposed system is evaluated by comparing it with air-source heat pumps operated under the same ambient conditions. Performance indices consisting of COP ele increment, power-saving ratio (PSR) and energy-saving ratio (ESR) are presented. The results indicate that the combination of the absorption heat pump subsystem and the vapor compression subsystem lowers the heat-driven temperature to 60 °C and thus makes higher solar collection efficiency possible. The maximum of the COP ele increment and the PSR under solar-assisted heating mode are achieved at conditions with 80 °C hot water temperature, of 45.8% and 31.4%, respectively, and the corresponding value for solar-assisted cooling mode are 18.9% and 16.0%. The speed of compressor as well as fan frequency of terminal has a greater influence on heating performance that on cooling performance due to the different coupling mechanisms. [ABSTRACT FROM AUTHOR]

Post-combustion CO 2 capture plants include high costs that are associated with intense energy consumption. Heat pumps can recover heat from the flue gas and other sources in the CO 2 emitting plant and upgrade it to reduce the use of fossil-based steam. The few studies regarding heat pumps in CO 2 capture systems include arbitrary selection among limited working fluids, without optimizing the underlying cycle. This work implements a multi-criteria investigation of the performance of 20 working fluids for vapor compression heat pumps (VCHP) and 21 refrigerant/absorber pairs for absorption heat transformers (AHT), considering the operating optimization of each cycle for each fluid. A cascade cycle combining the two configurations (AHT-VCHP) is proposed, using the optimum fluids cyclopentane and water/potassium nitrate identified for the VCHP and the AHT. The annual operating costs are higher than the annualized capital expenditures. The proposed fluids outperform the conventional options. The VCHP with cyclopentane covers 58 % (2.68 GJ/t CO 2) of the reboiler duty with recovered heat and exhibits the lowest cost of $33.8/tCO 2. This is $18.7/tCO 2 lower than the cost of the conventional direct contact cooling unit that is used in capture plants. The VCHP remains competitive for up to 57 % increase in the electricity price. [Display omitted] • Evaluation of 41 known and novel working fluids through heat pump optimization. • Multi-criteria selection and technoeconomic analysis. • Vapor compression heat pump with cyclopentane covers 58 % of reboiler duty with recovered heat. • Its cost is $18.7/tCO 2 lower than that of a conventional flue gas cooling unit. • Vapor compression heat pump is competitive for up to 57 % higher electricity price. [ABSTRACT FROM AUTHOR]

In this study, a desiccant-based hybrid cooling system supported by a vapor compression system and a heat recovery unit (rotary heat wheel) was analyzed from energetic and exergetic perspectives during the daily working hours of an office building in Istanbul to meet the desired comfort conditions. We focus on the impact of different refrigerants; namely R32, R1234yf, R290, R134a, R600a, R245fa, and R717, on hybrid rotary desiccant-vapor compression systems. While the highest electricity consumption was obtained in the system using R1234yf, the lowest electricity consumption was achieved with R717. However, with the effectiveness of the desiccant wheel, the best results were obtained for R1234yf with those pertinent to R717 at the other extreme. Considering the total electricity consumption of the system, the highest energetic and exergetic performance parameters were achieved with the use of R717 as the refrigerant. Compared to R1234yf, the daily average energetic performance parameters obtained with R717 increased by 22.3 % for COP r , 21.8 % for COP el , and 4.7 % for COP th. Similarly, compared to R1234yf, the daily average exergetic performance parameters in R717 presented increases of 13.6 % for COP x,el , 7.5 % for COP x,th , and 8.1 % for η x. • The effects of different refrigerants on the hybrid cooling system were compared. • Power consumption of compressor can be significantly reduced with the use of R717. • The highest performance parameters in the system belong to the use of R717. • The performance results obtained with R1234yf and R32 in the system are very close. • In the system, R600a exhibits better performance compared to R134a and R32. [ABSTRACT FROM AUTHOR]

Abstract To overcome the problem of walking in the scorching heat and to encourage people to use more public transport (ie, trams and metros), the idea of sustainable climate refuge shelter is highly needed. In this study, the proposed shelter includes semi‐transparent photovoltaic cells located on the roof integrated with batteries to keep the system running at nighttime and in unfavorable irradiation conditions. An atmospheric water generator for freshwater production is employed for drinking and water misting in addition to a vapor compression cooling system with a fan. Freshwater is collected by extracting water from humid air through cooling with dehumidification. The system is analyzed thermodynamically through energy and exergy efficiencies. The overall energy and exergy efficiencies of the system are 19.45% and 9.58%, respectively. The electrical efficiency of the photovoltaic cells decreases from 16.87% to 15.24% with an increase in cell temperature from 309 K to 315 K. Hourly analysis of the proposed system for the whole year is performed to evaluate the energy profile. The proposed system generates electricity in winters that is sufficient to keep the system operational for 2 days (only for drinking water requirement), but in the summers, only 24 h due to extensive cooling load. The effects of several parameters such as irradiance, ambient temperature, relative humidity, transmittance, and occupancy rate are studied.

The global concern regarding the environmental repercussions of refrigerants has escalated due to their adverse effects. These substances deplete the ozone layer and intensify the greenhouse effect. International agreements such as the Montreal and Kyoto Protocols and COP21 have imposed restrictions on refrigerants with high global warming potential (GWP) to address these issues. This study aims to explore the feasibility, energy efficiency, and environmental impact of utilizing the HFO (hydrofluoric-olefin) refrigerant R1234ze as a substitute for HFCs (hydrofluoric-carbon) (R134a, R407C, and R410A) and HCFCs (R22) in air-cooled vapor compression refrigeration and air conditioning systems. To determine their effectiveness, we evaluate the energy performance of various refrigerant operating cycles across a wide range of ambient and evaporating temperatures. Additionally, we conduct environmental impact analyses based on the total equivalent warming impact (TEWI) parameter calculated for commercially available chillers that utilize the fluids mentioned above. Our findings indicate that vapor compression chilled water systems employing R1234ze exhibit the highest performance coefficient and the lowest annual TEWI.

Entropy generation minimization and exergy destruction minimization concepts are applied on various refrigeration systems. For comparative analyses, coefficients of performance, exergy destruction and entropy generation rates are found for refrigeration systems at same atmospheric conditions. They are also calculated for individual components of each refrigeration system and for various other systems. After analyses, 2.27 coefficient of performance is found for vapor compression refrigeration system, which is maximum among such systems. As maximum exergy destruction and entropy generation rates are obtained for compressor, i.e., 386.07 kJ/h and 1.288 kJ/h-K, minimum rates are found for evaporator. Maximum total destruction and generation rates are recorded for water cooling refrigeration system, but minimum total destruction and generation rates are estimated for vapor absorption refrigeration system. A comparison of both systems is done, and it is concluded that absorption system performs better on the basis of entropy generation and exergy destruction minimization theories (i.e., minimum 39.332 kJ/h and 0.131 kJ/h-K). It is also found that maximum destruction ratio (i.e., 0.999) is calculated for compressor, so irreversibilities or losses must be reduced by perfect designing of compressor. [ABSTRACT FROM AUTHOR]

Vapor compression cycles are not an established technology for microgravity applications yet. One reason for the low technology readiness level in microgravity is the concern of liquid flooding from the evaporator, which could reduce the lifetime of the compressor. Liquid refrigerant can accumulate in the evaporator while the cycle is turned off and slug into the suction line upon the next compressor start-up. This paper describes experiments on parabolic flights, which investigated this issue. A test stand was designed to observe liquid flooding from the evaporator upon compressor start-up. The time from compressor start-up until flooding first occurred and the duration of flooding were recorded and used as quantifiers. They showed that the occurrence of liquid flooding is mainly a function of the refrigerant mass in the evaporator before start-up and that there is a mass threshold below which flooding does not occur. Test were conducted with an off the shelf and one similarly sized transparent evaporator. The hypothesis that the threshold would be significantly smaller in microgravity was not confirmed with the data collected on the parabolic flights. Instead, flooding typically occurred at the same charge level for both evaporators and both testing environments. Flow visualizations showed that mostly stratified flow during start-up in ground testing became mostly annular flow in microgravity. Both flow regimes keep liquid close to the wall so that vapor generated during the start-up process can escape through a void tunnel. [ABSTRACT FROM AUTHOR]

• First vapor compression refrigeration cycle experiment on parabolic flights. • Simple stability indicators show on average less than 15% changes for different measurements across range of operating conditions. • Loss of superheat due to parabolas observed for initial condition of less than 3 Kelvin superheat at onset of parabola maneuvers. • Comparison of operational changes due to parabolas with effects of varying inclination angle in a laboratory. Long duration manned space travel is projected to bring a need for large cooling capacities in microgravity for typical freezing and refrigeration temperatures. Among possible cooling technology alternatives, the vapor compression cycle has the highest coefficient of performance but the confidence for microgravity applications is very low. This research effort experimentally investigated the effects of hyper and microgravity on a vapor compression cycle during parabolic flights. A total of 122 parabolas were flown over four days with a repeating pattern of 5 sequential parabolas. Transient data of the evaporation temperature and cooling capacity for selected parabolas are presented as the test stand experienced alternating hyper and microgravity levels. Most measurements and performance indicators showed mild effects on the cycle operation during the varying g-forces. For example, the refrigerant side cooling capacity fluctuated on average within a band of 15% (+/-7.5%) through all sets of parabolas. A loss of superheat due to gravity changes was observed for one set of parabolas but the set was started with an unusually low superheat of only 3 K. For all other sets of parabolas, superheat and subcooling were maintained. Flight results were compared with inclination testing in a laboratory using the same test stand. Inclination changes from -90° to + 90° impacted both the liquid and suction line mass flow rate while varying the gravity level between 0 and 1.8 g affected the suction line mass flow rate but not the liquid line mass flow rate. [ABSTRACT FROM AUTHOR]

To overcome the problem of walking in the scorching heat and to encourage people to use more public transport (ie, trams and metros), the idea of sustainable climate refuge shelter is highly needed. In this study, the proposed shelter includes semi‐transparent photovoltaic cells located on the roof integrated with batteries to keep the system running at nighttime and in unfavorable irradiation conditions. An atmospheric water generator for freshwater production is employed for drinking and water misting in addition to a vapor compression cooling system with a fan. Freshwater is collected by extracting water from humid air through cooling with dehumidification. The system is analyzed thermodynamically through energy and exergy efficiencies. The overall energy and exergy efficiencies of the system are 19.45% and 9.58%, respectively. The electrical efficiency of the photovoltaic cells decreases from 16.87% to 15.24% with an increase in cell temperature from 309 K to 315 K. Hourly analysis of the proposed system for the whole year is performed to evaluate the energy profile. The proposed system generates electricity in winters that is sufficient to keep the system operational for 2 days (only for drinking water requirement), but in the summers, only 24 h due to extensive cooling load. The effects of several parameters such as irradiance, ambient temperature, relative humidity, transmittance, and occupancy rate are studied. [ABSTRACT FROM AUTHOR]

A newly designed freezing desalination system was constructed. The system operates on the principle of reversed vapor compression. It is equipped with two identical heat exchangers, one of them works as an evaporator and the other as a condenser. A three-way valve was used to reverse the operation of heat exchangers, causing the ice in the evaporator to melt. The performance of the newly designed system was evaluated in both the forward and the reversed cycles. Electric current, power consumption, pressure drop, water productivity, and specific consumption were all investigated. The experiments were conducted with ice ratios of 0.27, 0.39, 0.45, 0.54, and 0.65 with cycle operating periods of 110, 135, 180, 240, and 300 min. The results showed that the electrical current, power consumption, and pressure drop were decreased with the reversed cycle. The maximum energy-saving percentage was 13% for cycle operation time 300 min. The amounts of freshwater reached 19 L for cycle operation times of 300 min from 30 L saline water. It is recommended to run our newly designed system at an ice ratio of 0.45 since these results save 1.5% in the reversed cycle, which is the most used cycle in the new design.

An integrated cooling system comprising passive cooling-thermosyphon loop and active cooling-vapor compression was proposed for the cooling of electronics, especially avionics, under a wide range of heat loads and ambient temperatures. A prototype of the integrated system with the weight of 2.8 kg was developed by microchannel heat exchangers and a micro rotary compressor. The dynamic characteristics of the thermosyphon loop mode and vapor compression mode, and the switching mode were investigated experimentally, with second as time scale. Under the premise that the average wall temperature does not exceed 50 °C, the thermosyphon loop mode can handle a heat load of 600 W with COP of 35.7, and the vapor compression mode can handle a heat load of about 1000 W with COP of 3.1, at the ambient temperature of 20 °C. The developed integrated cooling system can effectively handle the sharp change in heat load (two heat loads of 400 W and 800 W like square wave) and ambient temperature (from 10 °C to 32 °C) by switching working modes. It automatically switched to TL mode at low heat load and ambient temperature for energy conservation, and switched to VC mode at high heat load and ambient temperature for safety.

The overwhelming evidence of global warming caused by human activities documents both contemporary impacts on human life but also extraordinary future risks are also assisted with it. Accretion of global temperatures engenders the extensive use of air conditioning devices to make the surrounding livable in the summer season. Energy consumption for air conditioning is also palpable by the evidence that this industry is the 2nd largest power-consuming sector in the consumer field. High temperatures also affect the performance of the air conditioning system by decreasing their energy efficiency ratio (EER) and cooling capacity (QC). Modifications are made in such a way to lower down the temperature of the surrounding by the use of a honeycomb wet pad which uses evaporative cooling with condensate of the indoor side. Experiments were made to observe the difference in performance efficiency, with modification and sans modification, by operating separately at 40–50 °C temperatures. Results were evident that condensate assisted evaporative cooling shows improvement in cooling capacity by 19% and a reduction in power consumption (P) by 13% as compare to the conventional system. A huge increase in the energy efficiency ratio of 36% was observed with the use of the modified system. The things used for the modification are cheaper and easily available in the market. [ABSTRACT FROM AUTHOR]

This paper presents the investigation of zeotropic binary fluid mixtures containing cyclohexane (critical temperature above 200 °C) as the base fluid with R600, R600a, R601, R601a, R1336mzz(Z), R1234ze(Z), R1233zd(E) and cyclopropane (critical temperatures between 100 °C and 200 °C). For pure components and their mixtures, the performance of the vapor compression system with an internal heat exchanger was analysed at 50 °C and 80 °C heat source and sink inlet, respectively. Variation of the heat source temperature difference and the internal heat exchanger pinch point temperature difference at supply temperatures (140–170 °C) were also investigated. A pinch point temperature difference of 5 K was maintained for the evaporator and condenser. An increase of 6.59 % in COP was obtained with the zeotropic mixture of cyclohexane/cyclopropane compared to that of pure cyclopropane. The design point analysis showed that increasing the heat source temperature difference and internal heat exchanger pinch point temperature difference reduces the COP. The adopted mixture criteria increased the performance between 3.23 % and 3.91 % with respect to standard working fluids like R1233zd(E) and R601, for a 170 °C supply temperature. With this promising thermodynamic analysis in a subcritical operation, the cyclohexane/cyclopropane mixture has prospect of full integration heat pump design. • Siloxane and cyclic hydrocarbon mixtures are suitable for heat pump (up to 170 °C). • Cyclohexane/cyclopropane mixture improved the COP of R601a heat pump by 7.16%. • COP increased at lower heat exchanger pinch point temperature difference. • Increased source temperature glide amounted to reduction in COP. • Heat pump performance strongly correlates with heat exchanger exergy destruction. [ABSTRACT FROM AUTHOR]

The aim of the present study is to enhance the performance of the refrigeration cycle in a condensate recovery plant existed in Egypt. In the current work, two proposals were suggested to increase the efficiency of the refrigeration system. The first proposal is the optimization of the operating conditions of the current cycle, which uses propane as a refrigerant. The second proposal is based on using vapor compression cycle with ammonia as a refrigerant instead of propane with the same equipment of the current system. The two proposals are simulated using HYSYS software program. Additionally, an economical study is introduced for each proposal based on capital cost, operating cost and expected profit. Regarding the first proposal, the simulation results demonstrated that the flowrate of the refrigerant and the intermediate pressure are the key factors affecting the refrigeration system. These factors are studied to select the optimum operating conditions to maximize the benefit of the present cycle. However, the second proposal results showed that using ammonia as a refrigerant is more economical and more efficient than propane. [ABSTRACT FROM AUTHOR]

• A novel semi-coupled solid desiccant heat pump system is proposed. • A mathematical model of the novel system is established. • Some of the designed parameters is optimized with the model. • Novel system can supply air with lower temperature and temperature variation. Solid desiccant heat pump system (SDHP) can handle sensible and latent heat load simultaneously with high coefficient of performance (COP). However, in such system, supply air temperature is relatively high and unstable due to the frequent switch between desiccant coated heat exchanger as evaporator and condenser. In order to overcome these drawbacks, the concept of semi-coupled solid desiccant heat pump (SCSDHP) system is proposed in this paper, then a mathematical model is established to investigate the feasibility of this novel system. Calculation shows that under ARI (Air-conditioning and Refrigeration Institute) summer condition silica gel coating with density of 0.25 kg m −2 is optimal, and area ratio between desiccant coated evaporator and conventional evaporator of 1:1 is recommended. Furthermore, compared with conventional SDHP system, supply air temperature can be 4.5~7°C lower and the variation range of supply air temperature decreases by 16~21°C. Also, effects of main operating parameters including the temperature and relative humidity of outdoor air on the performance of SCSDHP system are investigated. [ABSTRACT FROM AUTHOR]

This article reports on an experimental analysis and performance assessment of using thermoelectric generators (TEGs) for waste heat recovery from residential vapor compression refrigeration systems. The analysis shows that there is a good opportunity for waste heat recovery using TEGs by de-superheating refrigerant after the compressor. Design and manufacturing of a de-superheater unit consisting of a tube and plate heat exchanger and thermoelectric generator modules (HE-TEGs) have been performed and integrated in an experimental test rig of R134a refrigeration cycle. Experimental assessment of the performance parameters, as compared to the basic refrigeration system, reveals that the overall coefficient of performance (COP) using HE-TEGs desuperheater unit increases by values ranging from 17% to 32% depending on the condenser and evaporator loads. Exergy analysis shows that the enhancement is attributed to reduction in the exergy destruction in the condenser and compressor due to lower values of condenser pressure and pressure ratio of the compressor. The output power of the HE-TEGs unit is found to be sufficient for driving the TEGs heat sinks air cooling fan, thus providing a passive de-superheating system without an additional external source of electricity. Further enhancement of the refrigeration cycle performance can be achieved by installation of additional HE-TEGs units.

• Solar driven vapor compression refrigeration system was analyzed. • The effect of condenser's pressure on performance of the system is studied. • The effect of evaporator's pressure on performance of the system is studied. Photovoltaic (PV) solar refrigeration system is considered as one of the most vital areas in photovoltaic application. This research work aims to study the effect of operating pressures of evaporator and condenser to the performance of directly coupled variable speed solar refrigeration system. Performance parameters which were considered in the study are compressor speed, power consumption, refrigerant mass flow rate, and cooling capacity. The working pressure of the refrigeration system at evaporator and condenser were expressed with the saturation temperatures. In this study, a sensitivity analysis was performed with two cases. In the first case, the working saturation temperature of the condenser was fixed to 49 °C while the working saturation temperature of the evaporator was varied from −13 °C to −34 °C. In the second case, the saturation temperature of the evaporator was fixed to −24 °C while the saturation temperature of the condenser was varied from 38 °C to 60 °C. In the first case, it was found that all the considered performance parameters were sensitive to variation in saturation temperature of the evaporator. In the second case, compressor speed and power consumption showed negligible sensitivity to variation in saturation temperature of condenser but the other two performance parameters (refrigerant mass flow rate and cooling capacity) showed significant sensitivity to variation in saturation temperature of condenser. [ABSTRACT FROM AUTHOR]

This paper studies the integration of heat pump units (HPUs) to enhance the thermal efficiency of a combined heat and power plant (CHPP). Different solutions of integrate the HPUs in a combined-cycle gas turbine (CCGT) plant, the CCGT-450, are analyzed based on simulations developed on “United Cycle” computer-aided design (CAD) system. The HPUs are used to explore low-potential heat sources (LPHSs) and heat make-up and return network water. The use of HPUs to regulate the gas turbine (GT) intake air temperature during the summer operation and the possibility of using a HPU to heat the GT intake air and replace anti-icing system (AIS), over the winter at high humidity conditions were also analyzed. The best solution was obtained for the winter operation mode replacing the AIS by a HPU. The simulation results indicated that this scheme can reduce the underproduction of electricity generation by the CCGT unit up to 14.87% and enhance the overall efficiency from 40.00% to 44.82%. Using a HPU with a 5.04 MW capacity can save $309,640 per each MW per quarter.

Present work compares and optimizes the performance of cooling tower assisted cascaded and hybrid configurations of vapor compression-absorption integrated refrigeration system. Both the systems are designed to estimate their performance, size, and cost for the cooling capacity of 100 kW. Further, optimization strategies based on the Coefficient of Performance (COP), operational cost, and investment cost are followed to make the systems competitive. Four optimization cases, i.e. the COP single-objective, the total operational cost single-objective, the total investment cost single-objective, and the multi-objective optimization are performed and compared for both the systems. Comparative study of cascaded refrigeration system (CRS) with hybrid refrigeration system (HRS) shows that the COP and second law efficiency of CRS is 82.1% and 25.0%, respectively more as compared to HRS; whereas, the CO2 penalty cost of CRS is almost half of HRS. The efficient energy utilization and lower CO2 emission yields 46.1% lower annual operational cost in HRS as compared to CRS. Further, the economic analysis predicts that the investment cost of CRS is 10% less than that of HRS for same cooling capacity. Therefore, based on combined energy, exergy, environmental, and economic (4E) analyses, it can be concluded that the performance of CRS is better as compared to HRS. [ABSTRACT FROM AUTHOR]

The exergoeconomic analysis was conducted theoretically for a steam turbine driving vapor compression refrigeration system using R134a, R410a, R407c and R717 in this study. Dual-purpose system was designed by eliminating the expansion valve to fulfill the demand for the cooling load of the steam power plant. Primarily steam turbine was investigated by changing turbine inlet parameters. Afterward, the effect of input parameters of the steam turbine on the cooling load, the coefficient of performance (COP), the exergy efficiency of vapor compression cycle (VCC) and equipment, both the exergy destruction ratio and the exergy efficiency was determined. Among all examined working fluids, R134a was the best candidate from thermodynamic and thermoeconomic viewpoints. The COP values were determined to be 2.73, 2.29, 1.8 and 1.15 for R134a, R410a, R407c and R717, respectively. Also, the exergy efficiencies of the vapor compression refrigeration (VCR) system were found to be 18.61%, 13.93%, 14.97% and 10.01% for R134a, R410a, R407c and R717, respectively. Conversely, the general exergy efficiency of the whole coal-fired plant was 39.1%. As a consequence of integrating VCC, overall exergy efficiencies of the complete system were 39.36%, 39.32%, 39.27% and 39.21% for four different working fluids, respectively. [ABSTRACT FROM AUTHOR]

Abstract Drying is a common process in industries and usually discharges much waste heat. Heat pump is an energy efficient approach to upgrading waste heat to a higher drying temperature. In this paper, a novel pressure boost thermochemical sorption heat pump (TSHP) is proposed. Different from existing salt/ammonia heat pump cycles, a compressor is installed between two reactors to drive the cycle so that only one sorbent is needed in the cycle and the exothermic process becomes continuous. Thermodynamic analysis shows that when desorption and sorption temperatures are 70 °C and 120 °C, the COP (coefficient of performance) of the new cycle with working pair SrCl 2 /NH 3 is 6.5, which is remarkably higher than that of conventional vapor compression heat pump (VCHP) cycle under same operating conditions. Furthermore, for higher temperature rise, a hybrid cascade heat pump cycle is proposed as well. The VCHP cycle with refrigerant R134a is selected as the low stage cycle, while the TSHP cycle with sorbent SrCl 2 is chosen as the high stage cycle. For the evaporating temperature 30 °C and sorption temperature 120 °C, the cascade cycle COP is 2.4, relative to 2.0 COP of conventional vapor compression cascade heat pump cycle. Highlights • A pressure boost thermochemical sorption heat pump (TSHP) cycle is proposed. • TSHP is superior to vapor-compression heat pump (VCHP) in high temperature range. • A cascade heat pump cycle consisting of VCHP and TSHP is proposed. • The novel cycle is a new approach to high-efficiency heat pump. [ABSTRACT FROM AUTHOR]

Recently, Egypt is facing an energy problem due to the increase in consumption and population. There are two ways to face this issue; first, the world should be more interested in renewable energy resources and the second is the efficient use of energy. Refrigeration and air conditioning systems have a high rate of electrical power consumption. For that, the objective of the present work is to enhance the performance of the vapor compression cycle as well as to reduce the energy consumption resultantly. To achieve these goals, the performance of a vapor compression cycle with nanomaterials additives to the primary loop of refrigeration (refrigerant loop) is investigated experimentally. Mineral oil and polyol ester oil with Al2O3 nanomaterials additives are used to enhance the performance in the vapor compression cycle with R-143a refrigerant. The stability of nanofluids was first tested by using sedimentation test. The results showed that the optimum concentration for nanolubricant is 0.1% mass percentage. Results revealed that the refrigerant heat transfer coefficient increased by 22% maximum when nanofluids were used. Moreover, exergy efficiency increases by 20% when mineral oil and Al2O3 nanoparticles were used. The experimental results indicate that R-134a and mineral oil with Al2O3 nanoparticles enhance the vapor compression cycle performance by 22.5% theoretically and 10% actually with 10% less energy consumption. These results were obtained with 0.1% mass fraction of nanolubricant oil. Moreover, experimental results indicate that the polyester oil with Al2O3 nanoparticles mixture has better performance than mineral oil with Al2O3 nanoparticles mixture by 7.5% in theoretical COP and 19.5% in actual COP. [ABSTRACT FROM AUTHOR]

Caloric refrigeration is an emerging class of cooling technologies based on caloric effects detected in ferro-caloric solid-state materials. Depending of the nature of the driving field, it is possible distinguishing four main caloric refrigerations: magnetocaloric, electrocaloric, elastocaloric and barocaloric. Therefore, caloric refrigeration is based on solid-state materials, unlike vapor compression, nowadays still the most diffused cooling technique, whom employs fluids as refrigerants. Solid-state materials do not provide a direct contribution in global warming, since they do not disperse in the atmosphere, but only an indirect impact is registered when they are employed as refrigerants in cooling systems. On the other side, a vapor compression plant is characterized by both direct and indirect contributions to global warming. The main parameter to evaluate global warming impact and carbon-dioxide emissions coming out from a cooler is the Total Environmental Warming Impact (TEWI) index, which accounts both the direct and indirect contributions produced. In this paper a numerical ?TEWI analysis is presented, comparing the environmental impact of a caloric refrigerator, operating with different caloric materials, with the one of a vapor compression cooler working with HFC134a. [ABSTRACT FROM AUTHOR]

• New post-combustion capture process (PCCP) using amine-based solvent is proposed. • Four configurations of PCCP (Design-1, Design-2, Design-3, Design-4) are presented. • The side intercooler absorber could increase the CO 2 capture ability by MEA solvent. • The side interheater stripper with internal heat integration reduces energy consumption up to 62%. The post-combustion capture process (PCCP) using amine-based solvent was the most mature and adequately researched carbon capture and storage (CCS) technology. Monoethanolamine (MEA) solvent regeneration in the stripper (desorption process) usually takes high energy consumption and a MEA make-up is required before re-entering the absorber (absorption process). To improve the CO 2 capture efficiency and reduce the overall energy consumption of PCCP, four configurations (Design-1, Design-2, Design-3, Design-4) are presented, where Design-1 is denoted as the base case design. Design-2 is an extension of Design-1 by adding the side intercooler in the absorber. Design-3 is an extension of Design-2 by using internal heat integration in the stripper. Design-4 is an extension of Design-3 by adding the side interheater in the absorber. By using response surface methodology (RSM) in conjunction with central composite design (CCD), operating parameters (MEA solvent flowrate, MEA concentration, pressure) including side intercooler/side interheater locations of Design-2 to Design-4 are optimized. It is successfully validated that the side intercooler absorber could increase the CO 2 capture ability by MEA solvent and the side interheater stripper with internal heat integration could effectively reduce energy consumption about 36% to 62%. [Display omitted] [ABSTRACT FROM AUTHOR]

Highlights • Building two hybrid refrigerators including vapour compression and thermoelectric cooling technologies. • Focusing on thermal analysis of the thermoelectric coolers' influence on the refrigerator performance. • Testing serial and hybrid refrigerators according to different standards. • Hybrid refrigerators have three to four times higher energy consumptions at different ambient temperatures compared to serial ones. • 40% less cooling time and more accurate temperature control can be achieved with thermoelectric coolers. Abstract Two different hybrid refrigerators which include vapour compression and thermoelectric (TE) cooling technologies were built and tested. Serial refrigerators, which use vapour compression only were first tested to collect reference data for comparisons. Then, the hybrid prototypes were constructed by attaching thermoelectric coolers (TECs) to different compartments of these serial units. Among the chill, fresh food and freezer compartments of the refrigerators, the TECs were only used at chill and fresh food compartments, which have different cooling power requirements. Energy consumption, cooling and freezing capacity, and noise tests were conducted in compliance with three different standards. All hybrid refrigerators operated successfully in various ambient temperatures and loading conditions. The test results showed that the hybrid refrigerators had at least three times higher energy consumption levels over those of serial ones, because of the lower operating efficiencies of the TECs and higher transmission losses. Moreover, their noise levels are extremely high, at least 25 dB(A) higher than those of serial ones. However, the TECs provided a more sensitive temperature control in the compartment in which they were used. Additionally, the hybrid refrigerators' performance in terms of cooling capacity was very promising. They were able to cool 17.5 kg of loads from an ambient temperature of 25 °C to the desired temperatures faster than the original serial refrigerators. Since the freezer compartments of both the serial and hybrid units are cooled by compressor-based cooling systems, the freezing capacity results were identical. [ABSTRACT FROM AUTHOR]

In present work, a novel configuration of vapor compression-absorption integrated refrigeration system (VCAIRS) is analyzed. Unlike previous vapor compression-absorption cascaded refrigeration system (VCACRS), proposed configuration works at lower generator temperature of 60 °C. Thus, allowing the use of low grade waste heat for its operation. The performance of VCAIRS is also compared with the equivalent vapor compression refrigeration system (VCRS) and VCACRS for the same cooling capacity of 100 kW. The comparative study result shows that electrical energy requirement in VCAIRS is 21.4% more as compared to VCACRS but it is still 63% less as compared to the equivalent VCRS. Further, the second law efficiency of VCAIRS, VCACRS and VCRS are determined to be 27.9%, 32.7% and 18.8%, respectively. Thus, both the VCAIRS and VCACRS are energy and exergy efficient configurations; but, VCACRS results in more energy efficient cooling technology in the foreseeable future as it utilizes heat at lower generator temperature as compared to VCACRS. After the comparative performance study, the exergetic performance of VCAIRS is further explored based on the coefficient of structural bonds (CSB) and advanced exergy analysis methods. Highest CSB of 4.39 is obtained for high pressure solution heat exchanger but its overall contribution in total irreversibility rate is merely 0.2%; whereas, the highest contribution of 17.4% in total irreversibility rate is by compressor 1 but CSB value computed for it is merely 1.73. Further, advance exergy analysis results show that 35.2% of total irreversibility rate of VCAIRS can be avoided by improving the efficiency parameter of components of system. [ABSTRACT FROM AUTHOR]

Summary: In this study, two novel high‐temperature heat pump systems based on vapor compression cycles are introduced and examined. Three fluids (water, cyclohexane, and biphenyl) are selected and analyzed thermodynamically as prospective working fluids for the high‐temperature heat pumps. These working fluids are used in cascaded cycles to upgrade the heat to a temperature of 600°C. The equations of state used in performance analysis are Peng‐Robinson, non‐random two‐liquid model, and International Association for the Properties of Water and Steam 95. A parametric analysis is carried out to study the effects of isentropic efficiency, sink temperature, source temperature, and ambient temperature on the system performance. Both energetic and exergetic coefficients of performance (COPs) of the overall and individual cycles are determined. The COP values obtained are found to range from 2.3 to 3.8, depending upon the cycle and temperature levels. The high COP values in some instances make these systems promising alternatives to fossil fuel and electrical heating. As a possible sustainable scenario, these pumps can utilize low‐grade heat from geothermal, nuclear, or thermal power plants and derive work from clean energy sources (solar, wind, nuclear) to deliver high‐grade heat. The high delivery temperatures make these heat pumps suitable for processes with corresponding needs, like high‐temperature endothermic reactions, metallurgical processes, distillation, and thermochemical water splitting. [ABSTRACT FROM AUTHOR]