Vapor Compression System Research Articles

Energy and exergy performance comparison of conventional, dew point and new external-cooling indirect evaporative coolers

External-cooling indirect evaporative cooling is an effective energy saving technology, where air–water finned coils are linked with packed cooling tower by water pipes. However, external-cooling indirect evaporative coolers with different configurations and working air sources are incomprehensively analyzed and compared. This study presented an energy and exergy analysis of five external-cooling indirect evaporative coolers, including conventional configuration, dew point configuration, newly patented dew point configuration, and energy recovery forms of the first two. In order to analyze the evaporative cooler and its hybrid system combined with mechanical vapor compression system, the numerical model and experimental correlation are used. The effect of four selected parameters (ambient temperature, ambient humidity ratio, total number of transfer units and fresh air flowrate), and the summer energy saving potential in three different cities are studied. The analysis results show that the new dew point configuration has the best performance under the conditions of high temperature, high humidity, and high fresh air flowrate. This new dew point cooler’s hybrid system achieves the best energy saving rate in humid and arid climates, between 19.1% and 48.5% compared with the pure mechanical vapor compression system. In this study, the advantages and disadvantages of presented designs are established and their application potential under different climates is estimated.

Development and performance analysis of a PCM based cooling fan for hot climate of Bangladesh

In hot climatic regions, some kind of cooling system is necessary to avoid warmth and humidity. Many of the available cooling systems are not economic and sustainable. In this study, sustainable and feasible space/room cooling systems have been experimentally analyzed. A solar operated cooling system with two options have been designed and their performances are compared. Phase Change Material (PCM) is proposed to store thermal energy instead of a costly battery. A 1200-watt compressor and fin-type condenser are used to construct the vapor compression system. When the incoming air is passed through the cooling coil, it gets cool. For this cooling coil, 50 feet copper tube is used. The front side copper tube diameter of the fan is 3/8 inch and the backside tube diameter is 1/2 inch. It took about 35 minutes and 5 minutes to minimize the room temperature at the desired level in the case of the stand fan and duct fan, respectively. Furthermore, the stand fan and duct fan systems reduced 3 ℃ and 6 ℃ of the outside temperature, respectively.

Absorption Refrigeration Systems Based on Ammonia as Refrigerant Using Different Absorbents: Review and Applications

The interest in employing absorption refrigeration systems is usually related to electricity’s precariousness since these systems generally use thermal rejects for their activation. The application of these systems is closely linked to the concept of energy polygeneration, in which the energy demand to operate them is reduced, which represents their main advantage over the conventional vapor compression system. Currently, the solution pairs used in commercial absorption chillers are lithium bromide/water and ammonia/water. The latter pair has been used in air conditioning and industrial processes due to the ammonia operation’s low temperature. Few review papers on absorption chillers have been published, discussing the use of solar energy as the input source of the systems, the evolution of the absorption refrigeration cycles over the last decades, and promising alternatives to increase the performance of absorption refrigeration systems. There is a lack of consistent studies about designing requirements for absorption chillers, so an updated review covering recent advances and suggested solutions to improve the use and operation of those absorption refrigeration systems using different working fluids is relevant. Hence, this presents a review of the state-of-the-art of ammonia/absorbent based absorption refrigeration systems, considering the most relevant studies, describing the development of this equipment over the years. The most relevant studies in the open literature were collected to describe this equipment’s development over the years, including thermodynamic properties, commercial manufacturers, experimental and numerical studies, and the prototypes designed and tested in this area. The manuscript focuses on reviewing studies in absorption refrigeration systems that use ammonia and absorbents, such as water, lithium nitrate, and lithium nitrate plus water. As a horizon to the future, the uses of absorption systems should be rising due to the increasing values of the electricity, and the environmental impact of the synthetic refrigerant fluids used in mechanical refrigeration equipment. In this context, the idea for a new configuration absorption chiller is to be more efficient, pollutant free to the environment, activated by a heat substantiable source, such as solar, with low cost and compactness structure to attend the thermal needs (comfort thermal) for residences, private and public buildings, and even the industrial and health building sector (thermal processes). To conclude, future recommendations are presented to deal with the improvement of the refrigeration absorption chiller by using solar energy, alternative fluids, multiple-effects, and advanced and hybrid configurations to reach the best absorption chiller to attend to the thermal needs of the residential and industrial sector around the world.

On-site performance investigation of liquid-desiccant air-conditioning system applied in laboratory rodent room: A comparative study

Considerable ventilation rates in laboratory animal rooms indicate huge energy consumption of air-conditioning systems. The liquid-desiccant air-conditioning (LDAC) system is regarded as an energy-efficient system, which can help to save energy in laboratory animal rooms. However, limited studies have applied LDAC systems to this kind of rooms for energy conservation. In this study, a demonstration project is focused on, wherein both the LDAC system and conventional vapor-compression system are used in the laboratory rodent center. On-site measurements were conducted to reveal the energy performance difference between the two systems. The test results reveal that the considerable cooling loads of two rodent rooms air-conditioned by the conventional system and LDAC system are 482.1 W/m2 and 576.8 W/m2, respectively, under the summer conditions in Beijing. The LDAC system can avoid reheating and recover cooling from the exhaust air from indoors. Thus, the coefficient of performance (COPsys) of the LDAC system ranges 3.5–4.5, whereas the COPsys of the conventional system only ranges 1.8–2.3 during the test period. During the entire cooling season, an electric power saving rate of 37.3% can be achieved by the LDAC system. Moreover, although both systems can satisfy all the environment control requirements, the LDAC system is beneficial for particulate matter filtration, yet slightly unfavorable for reducing indoor ammonia concentration, compared to the conventional system.

Performance analysis of refrigerants with various expansion valves in vapour compression refrigeration and air-conditioning system

Abstract The primary role of expansion devices in Vapour Compression Refrigeration System (VCRS) are dropping the pressure, temperature and regulates the mass flow rate of refrigerant gas concerning with evaporator load conditions. Also, proper selection of expansion devices helps to control the degree of super heat to protect the compressor from liquid slugging. The performance of the vapour compression system partially depends on the expansion devices. The different predictions such as theoretical, experimental and simulation which are carried out by various researchers on basis of design, development and selection of the expansion devices concerning with different flow conditions. The present study is describes the performance of different expansion devices involving various refrigerants gases like as R134a, hydrocarbon LPG, R600a, and R22 etc. It is also discussed with proper understanding about the recent development of various expansion devices using for different refrigerant gases.

Exergy analysis and optimization of MED–TVC system with different effect group divisions

Multi-effect distillation-thermal vapor compression (MED–TVC) systems have attracted increasing attention due to their relatively low steam consumption. In this work, comprehensive thermal and exergy analyses of MED and MED–TVC systems were implemented. Besides, a detailed energy utilization diagram (EUD) analysis was conducted to reveal the mechanism of the internal exergy loss. According to the EUD analysis, TVC could solve energy level mismatch and improve energy utilization. However, the system's exergy loss was greatly increased. With the introduction of TVC, the performance ratio (Pr) increased from 10.88 to 14.11, and the energy consumption (Q) decreased from 224.09 kJ/kg-Mp to 181.30 kJ/kg-Mp. In addition, a countercurrent grouping feed was adopted in the system. The influence of the suction position combined with different effect group division methods for the 13-effect MED–TVC system was also investigated. Five different effect group division methods were analyzed in terms of system efficiency, performance ratio, exergy destruction, and energy consumption. The results indicated that a more uniform distribution of effects among the effect groups was beneficial for improving the performance of the MED–TVC system. Furthermore, both the Pr and system exergy efficiency (y) improved with an increase in the suction effect number.

Design and performance analysis of a thermoelectric air-conditioning system driven by solar photovoltaic panels

Solar cooling technologies can play a vital role in renewable energy applications development. Thermoelectric systems have shown promising advantages over traditional refrigeration systems such as high thermal comfort, active adaptability, no moving parts, and refrigerants free. In this work, a novel thermoelectric air-conditioning system (TEACS) driven by photovoltaics (PV) is experimentally and theoretically investigated under the hot climate conditions of Sohag city (30°26′N, 42°31′E), Egypt for air conditioning of a typical small-size office room under different thermal loads. During day time, PV panels produce electricity which utilized to drive the TEACS directly and to charge batteries that store electricity to be exploited during nighttime. Moreover, a numerical model implemented in TRNSYS coupled with MATLAB software is developed to evaluate the performance of the proposed TEACS. The influences of varying the input electric current on the coefficient of performance (COP), cooling capacity, and average air room temperature are also studied. The results showed that a design point with an input current of 2.5 A for a cooling capacity of 30 W could be selected to maximize the cooling performance, in which the COP of the TEACS is found to be 2.2. Moreover, the daily average air temperature of the conditioned room was found to be 23.5, 25.5, 27.5, 28.5, and 30.5 °C for internal thermal loads of 0.0 W, 65.0 W,130.0 W, 195.0 W, and 260.0 W, respectively, at average air intake temperature of 36 °C, daily average input current of 4.28 A and air volume flow rate of 14.4 m3/h. It can be concluded that the TEACS powered by PV could be considered as a proper alternative to the traditional vapor compression systems.

A tripartite graph based methodology for steady-state solution of generalized multi-mode vapor compression systems

The vapor compression system is the dominant technology in providing cooling and heating for residential, commercial, and industrial applications, and thus has significant energy and environmental impact. To predict the steady-state performance of vapor compression systems with a wide variety of configurations and operating modes, a general-purpose representation and solution methodology for vapor compression systems was developed using a component-based simulation architecture. The proposed methodology uses mass flow sign propagation to determine the working fluid flow directions. A tripartite-graph based tearing method was applied to reveal the most efficient component execution order, and to identify the corresponding tearing variables and residual equations. The resulting equations are solved using quasi-Newton method. The representation and solution methods are applied to six test systems: five R410A systems and one CO2 system, with capacities ranging from 10 to 100 kW. The test systems were chosen to represent a wide range of HVAC&R applications and operating modes, including residential heat pump, dual-circuit chiller, vapor injection system, supermarket system, and VRF system. The steady-state solutions of the test systems were verified and/or validated against existing simulations and experimental data. The observed worst case simulation energy imbalance across all cases was 0.91%, and the maximum system performance deviation was 8.94% compared to existing data.

Upper-limit of performance improvement by using (quasi) two-stage vapor compression

Both quasi two-stage and two-stage compressions are important ways for improving the energy efficiency of the vapor compression heat pump system, especially for high compression ratio conditions. Many experiments and simulations have been conducted to investigate the performance improvement of two-stage or quasi two-stage systems. In most occasions, positive results were obtained. However, the performance improvements reported by different studies vary significantly. Actually, the results obtained by different researchers are barely comparable, because operating conditions, refrigerants, cycles, and economizers heavily affect the performance of (quasi) two-stage system, which hinders the potential evaluation in cycle-selection period and perfectness assessment of developed (quasi) two-stage systems. In this study, a general analytical expression for the (quasi) two-stage vapor compression system is proposed, by which the upper-limit of performance improvement of (quasi) two-stage systems using different refrigerants under different operating conditions can be calculated quickly. Based on that, the potential of adopting (quasi) two-stage cycle and the maturation of the developed prototypes can be easily identified by comparing the test performance with the upper-limit improvement.

Analytical Performance Evaluation of Hybrid Desiccant Air Conditioning Systems (Dept.M)

Atheoretical evaluation of a hybrid desiccant air conditioning in post and pre· cooli ng arrsngemenls is studied and compared versus the trad',tional vapor compression system {VeSl- The periormance of the rotary desiccant wheel Is also studied as the hean of the hybrid desiccant cooling syste m. Lithium ' chloride IS applied as the worning desiccant malerial In Ihls investigalioll. A mathemati cal model of coupled heal and mass Iransfer of the desiccant wheel is presented and numerica lly solved. The model validity is check.ed 8galnslP' other work and results are in good agreement. Effect!J01 rotary wheel speed , number of transfer units (NTU) and the desiccant surface area to volume on Ihe performance of the wheell sre investigated. The ellecl of regeneration air velocily and temperature, slot diameter, evaporator an d condenser effectiveness and dehumidification effectiveness on the system perlorrnance is also studied. The post cooling hybrid system is found 10 be an energy efficient system, it saves up to 30% of cooling coit capaCity compared to traditional VCS _ The COP of the post cooling arrangement,is nearly Iwice thai of VCS with reheat. Thelpre cooling arrangement supplies air at lower dew point lemperalure (down to 6°C) with an increase of COP up 10 80% compared to VCS wilh reheat.

Novel compound waste heat-solar driven ejector-compression heat pump for simultaneous cooling and heating using environmentally friendly refrigerants

This work investigates the theoretical performance of a novel compound waste heat-solar driven ejector-solar assisted heat pump for simultaneous heating and cooling purposes. The system utilizes waste heat from three different sources, PV/T (photovoltaic thermal) with flat plate collector, milk pasteurization process, and condenser exchange heat. Real weather data is employed to determine the hourly performance of the system in three European cities, Valencia (Spain), Berlin (Germany), and Stockholm (Sweden) representing warm, middle and cold climates, respectively. Moreover, R450A and R513A alternative refrigerants are compared to the greenhouse gas R134a. The results show that the proposed system improves cooling COP by 7% using R450A in comparison with a conventional R134a vapor compression system. Furthermore, the utilization of waste heat recovery enhances the system COP from 3.7 to 4 in the absence of solar intensity. On the other hand, the results of the heating mode show that the system with PV/T and using R450A has a COP increase over the adopted solar time, ranging from 2 to 5% in Valencia; 2 to 2.5% in Berlin, and1 to 1.5% in Stockholm. However, R513A shows a COP reduction of about 5% in comparison to R134a. Regarding the heating mode with waste heat utilization from milk pasteurization, the system based on R450A results in the highest system COP, increasing COP up to 75% compared to the R134a baseline scenario. Overall, the proposed R450A systems show the highest equivalent carbon dioxide emission reduction and, therefore, it is recommended from an environmental point of view.

Effect of various parameters on the performance of vortex tube cooling system

Conventional vapour compression systems prove to be expensive for continual, specialized usage and require maintenance as there are several moving parts. A vortex tube cooling system has no moving parts and operates as a small cooling machine by separating the compressed gas into two different streams namely cold and hot streams. The thermal performance of the system was studied as function of a geometrical parameter i.e. L/D ratio of the vortex chamber, under various inlet pressure conditions. The study was oriented towards obtaining the maximum possible temperature drop across the system. Experiments were carried out by varying the L/D ratio and an inference was drawn on the cold fraction. Results proved that the length to diameter ratio plays an important role in the performance of the vortex tube cooling system.

Optimized Refrigerant Flow Rate and Dimensions of the Ejector Employed in a Modified Ejector Vapor Compression System

This paper presents the analysis of a modified vapor compression cooling system which uses an ejector as an expansion device. Expanding refrigerant in an ejector enhances the refrigeration effect and reduces compressor work. Therefore, it yields a better coefficient of performance. Thermodynamic analysis of a constant area ejector model has been done to obtain primary dimensions of the ejector for given condenser and evaporator temperature and cooling capacity. The proposed model has been used to design the ejector for three refrigerants; R134a, R152a and R1234yf. The refrigerant flow rate and the diameters at various sections of the ejector have been obtained by doing numerical modeling in Engineering Equation Solver (EES). Refrigerant R1234yf demanded the highest diameter requirements at a fixed 5∘C evaporator temperature and 40∘C condenser temperature for a given range of cooling load. Both primary and secondary refrigerants flow rates are higher for R1234yf followed by R134a and then R152a.

CFD analysis for predicting cooling time of a domestic refrigerator with thermoelectric cooling system

Abstract In this work, Computational Fluid Dynamics (CFD) analysis was conducted considering three different turbulence (viscous) models for a fresh food compartment of a domestic refrigerator (DR), in order to not only gain idea on cooling down time rate of fresh food compartment but also present air and temperature distribution inside the compartment when it is loaded. The refrigerator composes of three compartments: Fresh food (FFC), chill (CC) and freezer (FC). The FFC compartment is cooled by a thermoelectric/Peltier cooler (TEC) while the other compartments are handled by a vapour compression (VC) system. To measure cooling times, tests were conducted according to new IEC62552:2015 standard in climatic chambers and the cooling time was measured as 146.5 min. The predictions of developed CFD model clearly visualize the airflow and temperature fields inside the FFC. Concerning numerical predictions for the packages in the upper regions were in better agreement (below 10%) with measurements than the predictions for the packages in the lower regions mainly due to convective heat transfer behaviour.

Model-Based Condenser Fan Speed Optimization of Vapor Compression Systems

Vapor compression systems (VCS) cover a wide range of applications and consume large amounts of energy. In this context, previous research identified the optimization of the condenser fans speed as a promising measure to improve the energy efficiency of VCS. The present paper introduces a steady-state modeling approach of an air-cooled VCS to predict the ideal condenser fan speed. The model consists of a hybrid characterization of the main components of a VCS and the optimization problem is formulated as minimizing the total energy consumption by respectively adjusting the condenser fan and compressor speed. In contrast to optimization strategies found in the literature, the proposed model does not relay on algorithms, but provides a single optimization term to predict the ideal fan speed. A detailed experimental validation demonstrates the feasibility of the model approach and further suggests that the ideal condenser fan speed can be calculated with sufficient precision, assuming constant evaporating pressure, compressor efficiency, subcooling, and superheating, respectively. In addition, a control strategy based on the developed model is presented, which is able to drive the VCS to its optimal operation. Therefore, the study provides a crucial input for set-point optimization and steady-state modeling of air-cooled vapor compression systems.

Cooling in a warming world.

The planet is warming from greenhouse gas emissions, with increases in both peak and average temperatures. Consequently, the demand for cooling will intensify, driven by climate change as well as improving economic conditions. Cooling requirements for data centers and new technologies may also call for innovative solutions. Developing a wide array of cooling strategies will be vital for human comfort and prevention of heat-induced medical emergencies. A growing number of materials and methods are being designed to improve technologies, meet the temperature needs of data centers and other facilities, and reduce harmful emissions. Vapor compression systems supply much of the residential and industrial cooling infrastructure. These systems rely on compressing gases, many of which contribute to the greenhouse effect if released into the atmosphere. Finding replacements is a priority but requires balancing trade-offs between toxicity, flammability, and lower efficiency. An alternative approach involves the use of caloric materials—i.e., solids that effectively pump heat as they are electrically, magnetically, or mechanically manipulated. A completely different cooling strategy is to use materials that regulate heat in the form of infrared radiation. Passive radiative cooling materials take advantage of an atmosphere window for infrared radiation to eject heat into space. When deployed on rooftops, these systems can potentially cool buildings by a few degrees, even in the daytime. Along the same lines, textiles may be modified so that heat can more efficiently radiate through them, allowing people to be more comfortable at higher thermostat set points. As the planet warms, keeping cool without increasing greenhouse gas emissions will be a challenge, but new materials and technologies are poised to meet this goal.

Investigation of a compact hybrid liquid-desiccant air-conditioning system for return air dehumidification

In some automatic workshops, pharmaceutical warehouses, etc., there are control requirements for indoor air temperature and humidity, yet almost no occupants or no fresh air demand in the rooms. In this study, a hybrid liquid-desiccant air-conditioning (LDAC) system is proposed for the unoccupied rooms without fresh air demand. In the proposed system, the liquid dehumidifier and regenerator are cascaded, and the regeneration process is creatively moved to indoors. Two systems are selected as the reference systems, i.e., conventional vapor-compression system (reference system I) and conventional LDAC system using outdoor air for regeneration (reference system II). The simulation results reveal that, under the typical summer condition in Guangzhou of China, the coefficients of performance (COPsys) of the proposed system, reference system I, and reference system II are 2.6, 1.8, and 2.3, respectively, when the air is dehumidified from 13.0 to 7.7 g/kg. Compared to the reference system I, the reheating process can be avoided, and higher-temperature chilled water at 16 °C can be used in the proposed system. Compared to the reference system II, using indoor air for regeneration helps to reduce the regeneration temperature. Thus, the proposed system demonstrates energy and space advantages than the reference systems.

Recent progress and outlook of solar adsorption refrigeration systems

Solar adsorption refrigeration systems are indispensable in the areas of cooling such as air conditioning, ice making, food preservation, medicine and vaccine storage etc in remote areas. It is cheaper than other devices and lack in noise and corrosion. It is completely an eco-friendly system which could be driven by low grade waste heat. Consumption of electricity is very less in this system as compared to other fields due to the elimination of compression process in adsorption refrigeration. Most of the adsorption system delivers a COP between 0.1 and 0.2 and exceptions are also there. Because of the technical, economic and environmental problems, researches are going on in these areas. Nowadays it is incorporated with vapour compression system to make hybrid system in order to achieve a greater COP and efficiency. This paper presents the basic and advanced aspects of adsorption refrigeration cycle and its hybrid arrangements with pre-existing system. This paper described the different types of conventional and novel adsorbent – adsorbate working pairs and provides detailed review about the past and present state of art research in this field.

A review on the operational instability of vapor compression system

Operational instability, or hunting, is widely observed in vapor compression systems (VCSs), negatively affecting the operational safety and efficiency. As one of the most significant challenges present in VCS operation and control, operational instability has been extensively studied for decades. This paper reviews the current research state on the operational instability of VCSs, including the mechanisms for triggering hunting, the measures to mitigate hunting and the related unsolved issues. Two different views, i.e. the inherent characteristics of two-phase evaporating flow and dynamic characteristics of expansion (EV)-evaporator control loop, were classified for explaining the causes of hunting. As the typical characteristics of two-phase evaporating flow, the present of slug flow upstream in an evaporator, the sudden variation of heat transfer mechanism or two-phase flow instability would trigger the unexpected change of refrigerant temperature at evaporator exit. Consequently, operational instability will be resulted in. The dynamic behaviours of the EV-evaporator control loop in terms of its nonlinearities were considered as another essential factor that would cause system instability. Superheat setpoint adjustment and adaptive superheat control were suggested as two effective measures for mitigating hunting. With the increasing applications of vapor compression cycle for electronic cooling and the multi-evaporator VCSs, more effects should be done to investigate their operational instability with the consideration of two-phase flow instability and the coupling influences of each EV-evaporator control loop.

Vapour absorption refrigeration system for rural cold storage: a comparative study.

Value addition of agro products improves the livelihood opportunities for rural farmers. Cold Storage is one of the techniques to improve the shelf life of agro product. With the increase in the utilization of refrigeration and air cooling using vapour compression refrigeration technology, global warming and ozone depletion due to the refrigerants have also been increased. So, to overcome this problem, several restrictions were placed on the refrigerant by the United Nations Framework Convention on Climate Change (UNFCCC). There is no way to slow down the growth of this technology, so the focus should be shown on finding an alternative. Various studies have been carried out on an alternate refrigeration system. This paper attempts to study the power quality challenges in the conventional vapour compression system. A comparative analysis of vapour compression refrigeration (VCR) and vapour absorption refrigeration (VAR), power factor analysis and temperature measurement on both technologies has also been carried out and reported.