Vapor Compression Cycle Research Articles

Technical performance analysis of a micro-combined cooling, heating and power system based on solar energy and high temperature PEMFC

A solar energy and high temperature proton exchange membrane fuel cell (PEMFC)-based micro-combined cooling, heating and power (CCHP) system (named system I) is proposed in this work. This system mainly consists of a PEMFC subsystem, an organic Rankine cycle (ORC) subsystem and a vapor compression cycle (VCC) subsystem. System I would reduce to a high temperature PEMFC-based CCHP system (named system II) if there was no solar energy. With the technical performance analysis models developed, the effects of the current density, operating temperature, solar radiation intensity and ambient temperature on the thermal, economic and environmental performances of the systems are theoretically analyzed. The results show that the current density and solar radiation intensity are the main impact factors that can significantly affect the thermal, economic and environmental performances, while the operating temperature and ambient temperature only have remarkable influences on the thermal performance. The coefficient of performance (COP) of system II is approximately 1.19 in summer and 1.42 in winter, which is always higher than that of system I under the same working conditions. The exergy efficiency of system I and system II are approximately 49.7% and 47.4%, respectively. The primary energy saving rates (PESRs) of system I and system II are 64.9% and 31.8% in summer, and 60.0% and 36.2% in winter, respectively. The payback periods of system I and system II are 9.6 yr and 6.0 yr without government subsidy, respectively. Compared with system II, the pollutant emission reduction rates (ERRs) of system I can be increased by approximately 8.4%–23.5% with the addition of solar energy, which indicates that the development and utilization of clean and renewable energy such as solar energy can significantly reduce pollutant emissions.

Validation of a three-dimensional visual target acquisition system for evaluating the performance effects of head supported mass

Night vision goggles (NVGs) enable aircrew to complete missions in the cover of night, but dramatically increase and alter the distribution of mass borne by the head. Our novel approach to visual target acquisition, based on Fitts’ Law, was used to assess differences across three different performance metrics between low (L) and high (H) head supported mass (HSM) conditions. Fifteen healthy male participants completed time-optimal and reciprocal visual target acquisitions between target pairs arranged in four different movement trajectories. A significant interaction effect was found and subsequent post hoc analysis revealed that participants required more time to acquire the 20 mm target in the H-HSM condition. In the H-HSM condition participants had a higher error index during target acquisition and required more time to move off the target. Our approach demonstrates great promise in distinguishing performance decrements associated with the use of helmeted systems that include NVGs.

Preliminary study of integrating the vapor compression cycle with concentrated photovoltaic panels for supporting hydrogen production

Although implementations of CPVs to support electrolysis to produce hydrogen have recently been established, they often neglect the heat component which is important to improve electrolysis efficiency. Therefore, this research proposes to integrate the vapor compression cycle to concentrated photovoltaic panels to form a combined heat and power system that efficiently supplies such required energy to a water electrolyzer to produce hydrogen. The vapor compression cycle is modified to selectively choose whether the waste heat should support water heating or be discharged into the ambient environment where the latter method is aimed to save power consumption. A preliminary investigation of the proposed system is conducted by analyzing a commercial concentrated photovoltaic panel and simple formulations such as the theoretical Carnot efficiency for the vapor compression cycle. Results suggest that the required compressor power in the vapor compression cycle is very substantial and caused the effective electrical efficiency to drop from 40% to 10% for condenser temperature of 360 K–410 K. Fortunately, the heat available by the vapor compression cycle is much higher than that demanded by water electrolysis. Thus, the modified vapor compression cycle with the selective heat discharge functionality has demonstrated hydrogen production rate improvements of up to 4%.

The chemical looping heat pump: Thermodynamic modeling

The need for more energy efficient heating and cooling technologies will increase over the coming decades. Climatic concerns associated with greenhouse gas emissions as well as energy costs associated with powering heating and cooling systems necessitate more efficient systems. This work presents an alternative to traditional vapor compression cycles used for heating and cooling. The chemical looping heat pump system is an indirect chemical heat pump that utilizes the possibility of condensation after a chemical reaction to allow the working fluid's compression to take place in the liquid phase. A thermodynamic model of the cycle is developed using electrochemical cells as the reaction drivers of the cycle. Sensitivity analysis is used to identify the most critical components of the system. The chemical looping heat pump may provide a potential COP increase of over 20% when compared to traditional vapor compression systems for representative device efficiencies.

Review of Solar Cooling Technologies in the MENA Region

The demand for air conditioning and refrigeration has been increasing due to a rise in the global temperature and the burgeoning world population. Conventional electricity-driven vapor compression cycles (VCCs) use refrigerants, which are harmful to the environment, and are responsible for the consumption of huge amounts of electricity leading to high CO2 emissions. Therefore, solar-driven cooling cycles have great potential to address these issues, and the Middle East and North Africa (MENA) region has an abundant supply of solar radiation. In this study, the research carried out within the MENA region on solar cooling technologies is presented. The solar cooling cycles reviewed are the adsorption, absorption, solid desiccant, liquid desiccant, ejector, and solar electric-driven cycles. The interest over time and across countries in each of these cycles is also discussed. This review shows that interest in solar cooling technologies has increased sharply in the MENA region since late 2000s, and there are several issues like subsidized electricity prices hindering their adoption. In addition, this work shows researches where more investigations are needed.

Performance analysis on the charging and discharging process of a household heat pump water heater

In this study, a household heat pump water heater (HPWH) test system was built and a coupling model containing both vapor-compression cycle and water heater was established to analysis the charging and discharging performance. Water temperature distribution, heat transfer coefficient and operating efficiency of the system were three main characteristics to compare the performance of HPWH with fixed/varied-diameter coil. The results of the coupling simulation showed good agreement with experimental results. In the water-charging process, heat transfer coefficient and COP of varied-diameter coil were 20.00% and 10.23% higher than that of fixed-diameter coil, respectively. In water-discharging process, difference of heat transfer coefficient and COP between these two coil designs was relatively small. However, the discharging efficiency and extraction efficiency of varied-diameter coil were 7.74% and 9.70% higher than that of fixed-diameter, respectively. Thus, this work could provide some guideline on optimization of condenser coil designs.

Optimization of a vapor injection refrigeration cycle using hydrocarbon mixed refrigerants

Refrigeration systems are major consumers of electrical energy in many process industries. Hydrocarbons have regained interest as refrigerants because of the increasing restrictions applied to halogenated fluids. In this work, the use of hydrocarbons mixed refrigerants and an alternative flash tank with vapor injection (FTVI) refrigeration cycle were combined. Five different binary mixed refrigerants involving R170 (ethane), R290 (propane), R600 (n-butane) and R600a (isobutane) were studied. Using different refrigerant compositions, the cycle was simulated and optimized for maximum COP, considering a fixed refrigeration capacity in the evaporator to reduce the temperature of a secondary thermal fluid from 281.55 K to 269.15 K. Parameters analyzed were: coefficient of performance, temperature glide in the evaporator and refrigerant mass flow rate. The use of a FTVI led to a COP improvement from 4% to 36% when compared to the traditional vapor compression cycle (VCC). The pair R290/R600 with 60/40 wt% presented the maximum COP of 4.88.

Increasing the air source heat pump efficiency at low ambient temperature by using a two-phase ejector

The use of an ejector as expansion device is one of the alternative ways to improve the performances of an air source heat pump at low ambient temperature. This article presents a theoretical energetic and exergetic analysis of an ejector expansion vapor compression heat pump with on/off control. By using the ejector, the expansion throttling process is replaced by an adiabatic expansion. Furthermore, compressor operation is much improved due to lower compression ratio and reduces the temperature of the working medium at the end of the compression process. It also enables to reduce size of the evaporator, It also enables to reduce size of the evaporator, by using a phase separator. The results show that, by using an ejector instead a throttle vane in basic vapour compression cycle, both the energy efficiency and the exergetic efficiency of the cycle increase. The phase separator placed after the ejector has a significant influence on the cycle performance too. The exergy loss in every heat pump components is calculated. Thus, it can be seen that the process needs to be improved for better performance of the heat pump. The results highlights that the most important exergy loss at low ambient temperature have place in the compressor.

Thermoeconomic analysis of optimization potential for CO 2 vapor compression cycle: From transcritical to supercritical operation for waste heat recovery from the steam condenser

Recent research has been focused on the utilization of low-grade waste heat, and the industrial high-temperature heat pump can be an alternative technology because of its simplicity and outstanding performance. However, the use of carbon dioxide in vapor compression heat pumps with high-temperature heat source is still to be optimized because of low critical temperature. In the present study, a system for waste heat recovery from the steam condenser using CO2 vapor compression cycle is modeled from the energetic, exergetic, and economic perspectives, and optimized system performances are obtained by dual-objective Jaya algorithm. Potential optimized operating strategies for transcritical cycle are discussed by the parametric study and T-s diagrams. The transcritical and supercritical cycles are further compared with each other considering different steam temperatures. The optimization strategies of transcritical cycle are based on the main purpose to improve the evaporation potential and achieve transcritical cycles with the critical point inside the closed region surrounded by the process curves, so lower superheating degree and minimum temperature difference of gas cooler, higher evaporating temperature, and more return water cooling should be employed in order to promote the cycle performances. In comparison with transcritical cycles performances, the supercritical operation shows superior performances, which are less sensitive to the variations of return water temperature.

Improving system performance of a personal conditioning system integrated with thermal storage

An innovative personal conditioning system called Roving Comforter (RoCo) comprises of a miniature vapor compression cycle (VCC), storing its condenser heat in a phase change material (PCM) thermal storage with helical refrigerant tubes. In the present study, we analyze its system performance with different PCM by using a validated dynamic model in Modelica®. Mathematical equations and programming decisions for implementation of PCM model in Modelica are discussed. Higher melting temperature of PCM results in higher power consumption during cooling operation, but reduced power consumption during recharge operation (solidification of PCM). Thus, it is necessary to identify the appropriate temperature of PCM that maximizes its coefficient of performance (COP), since RoCo operates with alternating cooling and recharge operations. The PCM melting and solidification from the helical coil geometry is captured with empirical correlations obtained from experiment. Various regimes observed in these asymmetric processes are discussed. An increase of 11% in the COP is observed. The article highlights modeling details and interesting insights of system performance of a vapor compression cycle integrated with PCM, which are increasingly being developed in recent times.

Design and analysis of double pipe counter flow heat exchanger (condenser) to produce hot water as modification of air conditioner split condenser

This study was conducted to design a heat exchanger double pipe counter flow as a condenser to produce hot water that can be used for various purpose like a warm bath. Hot fluid flows in copper with cold fluid flowing in the annulus. The hot fluid used is R-22 while the cold fluid used is water. This pipe double heat exchanger is measuring 112.04 cm in length by 29 cm in width and 20.3 cm in height. Inside of pipe using copper with diameter ¼ inch. And total length of the copper pipe 18.915 m. While on the annular pipe using PVC pipe with ½ inch size. The total length of the annulus pipe is 16.128 m. In addition, heat exchanger is used to determined heat released by the condenser, coefficient of performance (COP) of vapor compression cycle, efficiency vapor compression cycle and temperature of the condenser-generated hot water.

The optimum temperature of single-stages vapor compression refrigeration cycle for Air-Conditioning unit

Vapour-compression cycle is the most widely used refrigeration cycles for Air-Conditioning (AC) units. The system consumes a significant amount of the energy. Thus, any modification to improve the energy efficiency is extremely needed. One of the well-known modification is multistage VC cycles. The objective of this study is to search the optimum high pressure based on environmental temperature of air condition. The single-stage cycle is analysed using for three different refrigerants (R32, R22 and R134a.). Pressure was varied based on ambient temperature. The governing equations and the boundary conditions are solved using Aspen Plus software. COP, refrigeration effect (RE), and compressor power as optimum temperature are plotted. The results show that there exists an optimum temperature for optimum cycle.

Enhancement of vapor compression cycle performance using nanofluids

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.

Investigation of a solar-biomass polygeneration system

The objective of this work is the investigation of a polygeneration system which is driven by solar energy and a biomass boiler. Parabolic trough solar collectors coupled to a storage tank are used in order to produce useful heat at high-temperature levels (∼350 °C). The system includes an organic Rankine cycle and a vapor compression cycle in order for electricity and cooling to be produced respectively. Moreover, useful heat is produced at two temperatures levels (50 °C and 150 °C) and so there are totally four useful energy outputs. The system is optimized in steady-state conditions and then the most suitable design is investigated in dynamic conditions for all the year period. According to the final results, the yearly energetic efficiency of the system is 51.26% while the yearly exergetic efficiency is 21.77%. The net present value is found 165.6 k€, the payback period 5.13 years, the internal rate of return 21.26%, while the yearly CO2 avoidance to 125 tn. Finally, the results of this work indicate that the suggested configuration can provide various useful outputs with high efficiency and the total investment is characterized as viable due to the suitable financial index values.

Comparative investigation and multi objective design optimization of a cascaded vapor compression absorption refrigeration system operating with different refrigerants in the vapor compression cycle

This study aims to comparatively investigate the performance of a cascaded vapor compression absorption refrigeration system (CVCARS) operated with different refrigerants such as R1234yf, R134a, R717 and R290 in vapor compression cycle. Two design objectives are considered for performance evaluations. Total annual cost is the first design objective which includes investment and operational cost along with the social cost associated with carbon emissions. Exergy efficiency is the second considered objective which is related to thermodynamic issues. These problem objectives are individually and concurrently optimized by means of Artifical Cooperative Search metaheuristic algorithm and best results are compared for each cycle configuration. Single objective optimization results reveal that CVCARS working with R717 in vapor compression cycle has the lowest total annual cost whereas the maximum second law efficiency is obtained by the refrigeration system operated with R290 in vapor compression cycle. Following that, multi objective optimization is applied to acquire the Pareto optimal solutions which are nondominated to each other and no solution between them prevails over the other. Reputed decision making method TOPSIS is applied to choose the final best answer among the Pareto curve. It is seen that solution found by TOPSIS is skewed towards the minimum total annual cost and second law efficiency for each cycle configuration. Sensitivity analysis is then put into practice to observe the influences of variations of decision variables on design objectives as well as performance coefficients of the different cycles in the refrigeration system.

ABSIM–modular simulation of advanced absorption systems: Recent software enhancements

ABSIM (an acronym for ABsorption SIMulation) is a computer code for simulation of absorption systems in flexible and modular form. It may be applied to closed and/or open absorption cycles operating at steady state, as well as to vapor compression and other thermodynamic cycles. This modular code is based on unit subroutines containing the governing equations for the system's units/components and on property subroutines containing thermodynamic properties of the working fluids. The units are linked together by a main program which calls the unit subroutines according to the user's specifications to form the complete cycle. When all the equations for the entire cycle have been established, a mathematical solver routine is employed to solve them simultaneously.As the simulated system becomes more complex, it is increasingly difficult to find a suitable initial guess. If the user obtains one, there is no guarantee that this guess will be adequate for simulating a different system state, even with but a slight change in its parameters (small change in temperature, and/or flow rate, heat transfer coefficients, etc.). To deal with this problem, an automatic initial guess generating algorithm was developed. This algorithm aids the user by automatically selecting the initial guess for the solver to work with. This is to achieve convergence for different operating conditions, given that at least one good initial guess was already obtained for a certain operating point.An additional new feature of the ABSIM software is the implementation of a genetic optimization algorithm. It is enabled by the above automated initial guess algorithm.

Theoretical investigation on energy storage characteristics of a solar liquid desiccant air conditioning system in Egypt

This work presents theoretical study of a standalone outdoor liquid desiccant air conditioning (LDAC) system assisted by solar energy. The liquid desiccant dehumidification cycle was integrated with a double indirect evaporative air cooler and a regenerative air heat recovery. The double indirect evaporative air cooler was used to recover heat from the return air, while air-air heat exchanger was used to recover heat from air leaving the regenerator. A water-in-glass evacuated tube solar collector was used to supply the system with solar heat. The remaining required heat is provided by natural gas fired boiler. The system was simulated by transient model under thermal energy storage, thermochemical energy storage and combined thermal and thermochemical energy storage modes.The theoretical results show that the mean daily thermal coefficient of performance (TCOP) is a strong function of the difference between absolute humidity ratio of outdoor air and saturated air. Results also show that, each tube of solar collector can deliver 30-Watt to operate the LDAC system under thermal energy storage mode for 16 h daily. While in the LDAC system under thermochemical energy storage mode, each tube would deliver 38.5-Watt for 16 h operation.It has been found that, to rise the solar fraction from 90% to 100% in the thermal energy storage mode, the required size of tubes array will be increased by 20%. Also, an analysis was carried out on the TCOP and required storage volume of the different energy storage modes. It shows that the combined energy storage method is the most energy efficient method.Finally, life cycle cost analysis (LCCA) was carried out for the LDAC system using various types of energy storage modes. The comparison indicated that 90% solar fraction LDAC system is the most economic system related to unit prices of solar collector and gas prices in Egypt. The total annual cost for the 90% solar assisted LDAC system is found to be lower than that of a vapor compression cycle (VCC) by about 50.5%. At the second order, the thermal energy storage mode by 49%. On the other side, the thermochemical energy storage mode is the least cost saving energy storage mode.

A comprehensive study of two-stage vapor compression cycles with vapor-injection for heating applications, taking into account heat sink of finite capacity

ABSTRACT This paper presents a comprehensive study of two-stage vapor compression cycles with vapor-injection for several refrigerants considering that the heat sink has a limited capacity. The key parameters of the cycle performance are identified and the influence of these parameters on the heating COP is analyzed. The optimum intermediate conditions of the cycle are evaluated using a general model of the cycle, considering two configurations (flash tank and economizer). Based on the optimization results, a correlation is proposed in order to estimate the optimum intermediate pressure, taking into account the temperature lift in the secondary fluid imposed by the application. The correlation uses cycle subcooling as an input, which is a novelty from the current correlations proposed in the literature. In addition, an optimum subcooling control strategy is proposed and finally, the influence of the size of the system components on the COP is studied.

Experimentally validated modeling of a turbo-compression cooling system for power plant waste heat recovery

Waste heat recovery systems utilize exhaust heat from power generation systems to produce mechanical work, provide cooling, or create high temperature thermal energy. One system that provides a cooling effect is the turbo-compression cooling system, which operates by using low-grade waste heat to vaporize a fluid and spin a turbine in a recuperative Rankine cycle. The turbine power is used to directly drive a compressor in a traditional vapor-compression cycle. This study presents a theoretical modeling approach that uses compressor and turbine efficiency maps and a heat exchanger UA scaling methodology to make performance predictions over a range of ambient temperatures and cooling loads. The results of experimental testing for a 250 kWth TCCS showed good correlation (maximum error of 2.0%) for power and cooling cycle mass flow ranges of 0.35 kg s−1–0.5 kg s−1 and 0.65–0.85 kg s−1, respectively. The validated modeling approach was used to predict system performance for a Natural Gas Combined Cycle power plant application.

Thermodynamic analysis of different oil flooded compression enhanced vapor injection cycles

Oil flooded compression has been found to be able to improve the energy efficiency of vapor injection cycle significantly by reducing the specific compression work. In order to optimize the coupling and study the thermodynamic characteristics, six coupled cycles were proposed and studied in heating conditions. A detailed analysis on each cycle using R32 working fluid was conducted. COP and heating capacity at various conditions were obtained and compared to the respective values of the vapor injection cycle. The respective COP improvement of oil flooded compression in the coupled cycles were investigated and compared to that of oil flooded compression in the single stage vapor compression cycle. The effects of oil temperature and regenerator efficiency on the cycles were also investigated and revealed. The results can provide theoretical guide to the design of a coupled cycle system.