Solar Coefficient Of Performance Research Articles

Optimal working pairs for solar adsorption cooling applications

This article suggests a detailed comparison of 7 working pairs intended for use in solar adsorption cooling systems. The performance analysis was based on two indicators: adsorption capacity and solar coefficient of performance. Based on a reformed form of the Dubinin–Astakhov equation, a 3D graph was constructed to show the adsorbate concentration in the appropriate adsorbent as a first step to determine the adsorption capacity. A MATLAB program was developed to solve the system equation to predict the solar coefficient of performance for a typical summer day in a Moroccan city Fez. It was found that maximal adsorption capacity is obtained by activated carbon fibre/methanol (0.3406 kg kg−1) followed by activated carbon/methanol (0.2565 kg kg−1) and activated carbon/ethanol (0.2008 kg kg−1). At a condenser temperature of 25 °C, with an adsorbent mass of 20 kg, and an integrated collector-reactor configuration, the couple silica gel/water for air conditioning purpose can reach an SCOP of 0.3843. Activated carbon fibre/methanol is the following more efficient couple and can be used in the different cooling applications with an SCOP ranging from 0.1726 to 0.3287.Furthermore, adequate indicators are evaluated addressing the economic, environmental and safe aspects associated with each working pair.

Experimental performance investigation of small solar air-conditioning systems with different kinds of collectors and chillers

Different types of solar collectors should be integrated with different sorption chillers. Traditional evacuated tube U pipe solar collector, high efficient CPC (Compound Parabolic Concentrating) solar collector and PTC (Parabolic Trough Collector) solar collector can provide 60–85°C, 85–125°C and 125–150°C of hot water. So, they can drive silica gel–water adsorption chillers, single-effect LiBr absorption chillers and double-effect LiBr absorption chillers, respectively. This paper will present the experimental performance investigation and economic analysis of three small solar cooling systems with these different kinds of collectors and chillers. The test results show that the solar COP (Coefficient of Performance) of the solar cooling system with adsorption chiller and U pipe solar collectors is about 0.15 and the silica gel–water adsorption chiller can be driven by 55°C of hot water. The solar COP of the system with CPC solar collector and single effect absorption chiller can reach 0.24 in the sunny weather condition. The solar COP of the solar cooling system with PTC solar collectors is about 0.5 and the double-effect LiBr absorption chiller is more attractive because of its higher solar COP (Coefficient of Performance) and better economy.

Modeling of a thermal adsorber powered by solar energy for refrigeration applications

In this paper, we introduce a dynamic model of a thermal adsorber powered by solar energy. The system operates with silica gel (as an adsorbent) and water (as a refrigerant). The Finite Difference approximation was used; the obtained numerical model was then incorporated in a MATLAB code in order to solve the system of algebraic equations modeling heat and mass transfers. The real ambient temperature and solar radiation variations relative to a typical summer day in Fez (Morocco) are taken into account. The system is characterized by its simple design and can reach a SCOP (Solar Coefficient of Performance) of 0.15 under a condenser and evaporator temperatures of 27 °C and 5 °C respectively. Consequently, this installation can be an attractive solution to meet positive cooling needs (medicine and food storage) in off-grid electricity regions. It can be also proposed in humanitarian actions in Africa.

Experimental based energy performance analysis and life cycle assessment for solar absorption cooling system at University of Californian, Merced

Traditional air conditioning and heating systems in buildings are fossil fuel based energy systems, which take the main responsible for the carbon emissions. In contrast, using solar energy for air conditioning becomes one of the promising approaches to reduce energy consumptions and negative environmental impacts from buildings. University of California, Merced built a test facility to investigate the technology: solar cooling. The solar system has 54m2 external compound parabolic concentrator (XCPC) solar collectors to drive a 23kW double-effect absorption chiller. This paper first provides the detailed energy performance analysis of the experiments conducted in August, 2012. The data collected from the experiments shows that the system could provide adequate cooling for a test facility between 11AM to 5PM in both sunny and cloudy days. The daily average collector efficiency is at the range of 36% to 39%. The average coefficient of performance (COP) of the LiBr absorption chiller is between 0.91 and 1.02 with an average of 1.0, and the daily solar COP is approximately at 0.374.In addition to the experimental investigation, a detailed life cycle economic and environmental assessment was also performed by comparing the solar systems to the conventional systems in two types of office buildings at three locations at California. Two different solar cooling system configurations were considered: (i) configuration 1 sizes the area of solar collectors and absorption chiller to meet the peak cooling demand, and uses natural gas as the only backup energy source; (ii) configuration 2 sizes the area of solar collectors and absorption chiller to meet half of the peak cooling demand, and uses natural gas as the backup energy source for the absorption chiller, while incorporates an electrical vapor compression chiller to meet the rest half of peak cooling demand. The annual performance predicts that the systems can achieve the annual solar fraction around 55–68%. And the configuration 2 achieves better life cycle economic and environmental performance than the configuration 1. Specifically, the configuration 2 can achieve lower present worth cost during the entire life span than the conventional systems. And both configuration 1 and 2 can reduce the life time carbon footprint by 35–70%.

Performance of the Merced Demonstration XCPC Collector and Double Effect Chiller

A solar thermal cooling system using novel nontracking external compound parabolic concentrators (XCPC) has been built at the University of California, Merced and operated for two cooling seasons. Its performance in providing power for space cooling has been analyzed. This solar cooling system is comprised of 53.3 m2 of XCPC trough collectors which are used to power a 23 kW double effect (LiBr) absorption chiller. This is the first system that combines both XCPC and absorption chilling technologies. Performance of the system was measured in both sunny and cloudy conditions, with both clean and dirty collectors. It took, on average, about 2 h for the collector system to reach operating temperatures between 160 and 180 °C. When operated in this temperature range, the XCPC collector array collected solar energy with an average daily efficiency of 36.7% and reached instantaneous efficiencies up to 40%. The thermal coefficient of performance (COP) of the system (including thermal losses and COP of absorption chiller) averaged at 0.99 and the daily solar COP of the entire system averaged at 0.363. It was found that these collectors are well suited at providing thermal power to drive absorption cooling systems and that both the coinciding of available thermal power with cooling demand and the simplicity of the XCPC collectors compared to other solar thermal collectors makes them a highly attractive candidate for cooling projects. Consequently, the XCPC technology is currently being commercialized in the U.S. and India. The XCPC's numerous potential applications include solar heating, cooling, desalination, oil extraction, electricity generation, and food processing.

Design and Realization of a Solar Adsorption Refrigeration Machine Powered by Solar Energy

This work aims to the experimental realization of a refrigerator prototype that uses an adsorption tube collector for cooling, in which solar energy can be directly absorbed. The development of a software giving an estimate of the activated carbon and methanol quantities in the refrigeration system, the quantities of energy used in its various parts, their design, the refrigeration and solar performance coefficient was carried out, and this according to the temperature data, total radiation and the dimension of the refrigeration compartment to be cooled. The thermal COP of the prototype was founded equal to 0.49 depending thus on the refrigerating effect and the energy absorbed in the collector-adsorbor. The solar COP was founded equal to 0.081 depending on the refrigerating effect and the solar radiation.

A stand-alone solar adsorption refrigerator for humanitarian aid

Solar adsorption ice makers are devices which could prove a great help in sustaining the cold chain in third world countries. The use of such devices could be extended also in supporting humanitarian aid actions for vaccines storage. However, further development and optimization of the system design are still required. In this paper a new, versatile, solar driven ice maker operating with the activated carbon/methanol adsorption pair has been developed and tested. The field tests carried out on February and March 2013, showed that the prototype is able to produce up to 5kg of ice, with a solar Coefficient Of Performance (COPs) of about 0.08, and to preserve it for whole next day. The overall dimensions of the realized prototype are 1.7×1.5×0.95m. Solar radiation is collected by a solar collector with an exposed area of 1.2m2.

PERFORMANCE STUDY AND EXPERIMENTAL CYCLES OF TWO STAGE SOLAR HYBRID ADSORPTION REFRIGERATION SYSTEM

The performance parameters and experimental cycles of a solar adsorption refrigeration system working with the activated carbon-methanol working pair are presented here. Such a system has been fabricated and tested under the conditions of National Institute of Technology Calicut, Kerala, India. The performance parameters such as specific cooling power (SCP), coefficient of performance (COP), solar heating COP, solar cooling COP, uptake efficiency and exergy efficiency are studied. The dependency between the exergy efficiency and cycle COP with the driving heat source temperature for two thermal compressors is also studied. The optimum heat source temperature for the thermal compressor one is determined as 71.4oC and for the other thermal compressor it is 68.20C. The system has a mean cycle COP of 0.196 during day time and 0.335 for night time. The mean SCP values during day time and night time are 47.83 and 68.2, respectively. Experimental results also demonstrate that the adsorption refrigerator has cooling capacity of 47 to 78 W during day time and 57.6 W to 104.4W during night time. This study also presents the analysis of experimental thermodynamic cycle of solar adsorption refrigeration system. Two cycles have been analysed experimentally, one with clear sky and the other with partly cloudy. Use of artificial neural network model is proposed in order to predict the performance of the system. After training, it was found that LM algorithm with 9 neurons is most suitable for modeling solar adsorption refrigeration system. The ANN predictions of performance parameters are in good agreement with the experimental values with R2 values close to one and maximum percentage of error less than 5%. The RMS and covariance values are also found to be within the acceptable limits.

Experimental analysis of an adsorption air conditioning with micro-porous silica gel–water

In this paper, one novel heat pipe solar adsorption chiller with mass-heat recovery was designed. 65 kg of micro-porous silica gel was used as adsorbent in each adsorbent bed. The influence of operating conditions on the chiller was investigated. The chiller was applied in Green Building in Dezhou city (north latitude of 36°41′) in China. Under the typical summer weather conditions, the average thermal efficiency of solar collector, the average COP (coefficient of performance) of the adsorption refrigerator and the average solar COP of the system are 0.36, 0.44 and 0.16, respectively. The results show that the adsorption cooling performance rises as the hot water inlet temperature, chilled water outlet temperature rise, and it declines as the cooling water inlet temperature rises. The performance can be improved by mass-heat recovery significantly. When the hot water inlet temperature, cooling water inlet temperature, chilled water outlet temperature are 79.0 °C, 25.4 °C, 13.7 °C, respectively, the cooling capacity and COP are 17.9 kW and 0.63, respectively.

Simulation of an adsorption solar cooling system

Abstract A more realistic theoretical simulation model for a tubular solar adsorption refrigerating system using activated carbon–methanol (AC/M) pair has been introduced. The mathematical model represents the heat and mass transfer inside the adsorption bed, the condenser, and the evaporator. The simulation technique takes into account the variations of ambient temperature and solar radiation along the day. Furthermore, the local pressure, and local thermal conductivity variations in space and time inside the tubular reactor are investigated as well. A C++ computer program is written to solve the proposed numerical model using the finite difference method. The developed program covers the operations of all the system components along the cycle time. The performance of the tubular reactor, the condenser, and the evaporator has been discussed. Time allocation chart and switching operations for the solar refrigeration system processes are illustrated as well. The case studied has a 1 m2 surface area solar flat plate collector integrated with a 20 stainless steel tubes containing the AC/M pair and each tube has a 5 cm outer diameter. In addition, the condenser pressure is set to 54.2 kpa. It has been found that, the solar coefficient of performance and the specific cooling power of the system are 0.211 and 2.326 respectively. In addition, the pressure distribution inside the adsorption bed has been found nearly uniform and varying only with time. Furthermore, the AC/M thermal conductivity is shown to be constant in both space and time.

Study of the effect of finned tube adsorber on the performance of solar driven adsorption cooling machine using activated carbon–ammonia pair

Solar refrigeration represents an important application of solar energy due to the excellent matching between the high sunshine and the refrigeration needs. Solar adsorption refrigeration devices are among the significant techniques used to meet the needs for cooling requirements. Several solar refrigeration systems have been proposed and are under development such as sorption systems including liquid/vapor, solid/vapor absorption, adsorption, vapor compression and others. The purpose of this paper is to identify the influence of a cylindrical adsorber on the performances of a solar adsorption refrigerating machine. The adsorber heated by solar energy contains an activated carbon–ammonia pair; it is composed by many cylindrical tubes welded using external fins. A model based on the conservation equations of energy and mass in the adsorber has been developed and well described. Using real solar irradiance data as well as many initial conditions, the model computes for each point and in the considered time interval during the day, the temperature, the adsorbed mass, the pressure inside the adsorber and the solar performance coefficient (COP). The results show that the optimal diameter of the adsorber with fins is greater than the one without fins. Moreover the mass cycled in the case of an adsorber equipped with external fins is more significant than the one without fins, and the maximal temperature reached in the adsorber with fins attains 97 °C while in the adsorber without fins reaches 77 °C. Thus, the performances of the solar adsorption refrigerating machine with an adsorber equipped with fins are higher than the machine without fins.

Study of an adsorption refrigeration system powered by parabolic trough collector and coupled with a heat pipe

The aim of the current paper is to propose a study of a novel solar adsorptive cooling system, using activated carbon–ammonia pair, coupled with a parabolic trough collector (PTC) and a water-stainless steel heat pipe. A theoretical model, based on the thermodynamics of the adsorption process, heat and mass transfer within the porous medium and energy balance in the hybrid system components, is developed and a simulation code, written in FORTRAN, is carried out. This model, which has been validated by experimentation results, computes the temperature, pressure and adsorbed mass inside the adsorbent bed. The performance is assessed in terms of specific cooling power (SCP) and solar coefficient of performance (COPs). Furthermore, the effect of some important parameters on the system performance is discussed, and an optimization of these parameters is given. The simulation results have shown that there exists, for each aperture width value of the collector ( W), an optimum external radius of adsorbent bed ( R 2). Under the operating and design conditions of evaporation temperature T ev = 0 °C, condensing temperature T con = 28 °C, adsorption temperature T ads = 24 °C, W = 0.70 m, R 2 = 0.145 m and reactor length of 0.5 m, an optimal corresponding COPs is found to be of the order of 0.18.

Performance analysis of a modified two-bed solar-adsorption air-conditioning system

This paper presents the description and operation of a solar-powered modified two-bed adsorption air-conditioning system with activated carbon and methanol as the working pair. A simple lumped parameter model is established to investigate the performance of this continuous adsorption cycle consisting of a twin adsorber immersed in water tanks, which is measured in terms of the temperature histories, gross solar coefficient of performance and specific cooling power. In addition, the influence of some important design and operational parameters on the performance of the system has been studied. Compared with the conventional system, it is found that the modified system can operate more cycles and at a higher efficiency. The parametric study also shows that the adsorbent mass and the solar collector area have significant effect on the system performance as well as on the system size. Finally, when the system uses gas heater as an auxiliary heat source, it is found that the system can provide a stable cooling effect for a longer period of operation. Copyright © 2008 John Wiley & Sons, Ltd.

Modelling and performance study of a continuous adsorption refrigeration system driven by parabolic trough solar collector

This article suggests a numerical study of a continuous adsorption refrigeration system consisting of two adsorbent beds and powered by parabolic trough solar collector (PTC). Activated carbon as adsorbent and ammonia as refrigerant are selected. A predictive model accounting for heat balance in the solar collector components and instantaneous heat and mass transfer in adsorbent bed is presented. The validity of the theoretical model has been tested by comparison with experimental data of the temperature evolution within the adsorber during isosteric heating phase. A good agreement is obtained. The system performance is assessed in terms of specific cooling power (SCP), refrigeration cycle COP (COP cycle) and solar coefficient of performance (COP s), which were evaluated by a cycle simulation computer program. The temperature, pressure and adsorbed mass profiles in the two adsorbers have been shown. The influences of some important operating and design parameters on the system performance have been analyzed. The study has put in evidence the ability of such a system to achieve a promising performance and to overcome the intermittence of the adsorption refrigeration systems driven by solar energy. Under the climatic conditions of daily solar radiation being about 14 MJ per 0.8 m 2 (17.5 MJ/m 2) and operating conditions of evaporating temperature, T ev = 0 °C, condensing temperature, T con = 30 °C and heat source temperature of 100 °C, the results indicate that the system could achieve a SCP of the order of 104 W/kg, a refrigeration cycle COP of 0.43, and it could produce a daily useful cooling of 2515 kJ per 0.8 m 2 of collector area, while its gross solar COP could reach 0.18.

An adsorptive solar ice-maker dynamic simulation for north Mediterranean climate

This paper presents a model for dynamic simulation of an adsorptive ice-maker. The model describes the different phases of the thermodynamic cycle of the ice-maker components: solar collector, adsorbent bed, condenser and cold chamber (evaporator and water to be frozen). The adsorbent/adsorbate working pair is active carbon/methanol. The simulations were performed for a whole year using measured climatic data of Messina (38°12′N). The detailed results of a week of June and December 2005 are shown, as representative of typical summer and winter conditions. These simulations showed that the ice-maker is able to freeze 5 kg of water during all days of June, and, if the weather conditions are not too unfavourable, also during December. Further simulations, carried out for the whole year 2005, demonstrated that during the most part of the year (from April to October) a daily ice production (DIP) of 5 kg can be obtained, and an equivalent daily ice production (DIP eq) near to 5.5 kg can be reached. During the months of February and March the average monthly DIP is about 4 kg. Finally, for the coldest months (January, November and December) the DIP was 2.0–3.5 kg. The average monthly solar coefficient of performance (COPs) varies from a minimum of about 0.045 (July) to a maximum of 0.11 (January), with an annual mean of 0.07.

Simulation of a solid sorption ice-maker based on the novel composite sorbent “lithium chloride in silica gel pores”

In this paper, a novel composite sorbent “lithium chloride in silica gel pores” is proposed for application in solar-powered adsorptive ice makers. A mathematical model was used in order to calculate the performance of an ice-maker using this material as adsorbent and methanol as adsorbate. The results of the model showed that a maximum solar coefficient of performance (COPs) of 0.33 and a maximum daily ice production (DIP) of 20 kg m −2 can be obtained for an ice-maker equipped with a solar collector area of 1.5 m 2 and 36 kg of adsorbent material. Such performance are noticeably higher than those obtained using commercial activated carbon, that is the adsorbent mostly proposed till now.

Experimentation of a solar adsorption refrigerator in Morocco

For countries with a high potential of solar energy, producing cold using solar energy is a promising way to sustainable development since the energy used is free and not harmful for the environment. This work proposes a solar adsorption refrigerator using the pair activated carbon–methanol, which has been totally built and is under experimental tests in the solar laboratory of the Faculty of Sciences of Rabat, the capital of Morocco with Mediterranean climate. The solar adsorption refrigerator is mainly composed of a collector containing the adsorbent, an evaporator and a condenser. The results show that the refrigerator gives good performance in Rabat. The unit produces cold even in rainy and cloudy days and the temperatures achieved by the unit can be less than −11 °C for days with a very high irradiation. The solar coefficient of performance (COP) (cooling energy/solar energy) ranges between 5% and 8% for an irradiation between 12,000 and 28,000 kJ m −2 and a daily mean ambient temperature around 20 °C.

Experimental results of a solar powered cooling system at low temperature

A solar thermochemical prototype producing low-temperature cold has been built and tested during the summer and autumn 2005 in Perpignan, France. It cools a 560 L cold box down to about −25 °C using only low-grade heat produced by two simple flat plate solar collectors. The process involves two cascaded thermochemical systems using BaCl 2 salt reacting with ammonia. Its working mode is discontinuous, as it alternates between one decomposition mode at high pressure (daytime) and one cold production mode at low pressure (nighttime). Experimental results prove the feasibility of this new concept of solar cold production, with temperatures as low as −30 °C, demonstrate its potential use in housing, by the acceptable size and weight of the system and show the system performances during the sunniest months of the year, with a rough solar coefficient of performance (COP) of about 0.031 over the test period. The major meteorological parameters influencing the process efficiency are the solar irradiation and the outside temperature.

Design of a thermochemical process for deep freezing using solar low-grade heat

A deep-freezing process has been designed and experimented to cool a cold box down to about −30 °C using only low-grade heat produced by simple flat plate solar collectors operating at 70 °C. The original process involves two cascaded thermochemical systems using BaCl 2 salt reacting with ammonia. It works discontinuously, with one day phase of regeneration at high pressure and one night phase of cold production at low pressure. A global dynamic model allows the simulation of the different system components functioning depending on the hourly weather conditions. It takes into account the transient periods and shows the temperature changes of the components, the chemical reactions in the system and its performances. This system will cover the cooling needs of a 560 L cold box at −20 °C during the 3 sunniest months of the year and provide more than 60% of the total yearly cooling needs of this box for the weather conditions of Perpignan (South of France). The prototype is expected to show a system coefficient of performance (COP) of about 0.07 over the 10 sunniest months of the year, and a net solar COP of 0.05, taking into account the collectors efficiencies.

06/01215 Energy optimisation model for a CCHP system with available gas turbines: Kong, X. Q. et al. Applied Thermal Engineering, 2005, 25, (2–3), 377–391

This paper presents the achievements gained in solid sorption refrigeration prototypes since the end of the l970s, when interest in sorption systems was renewed. The applications included are ice making and air conditioning. The latter includes not only cooling and heating, but also dehumidification by desiccant systems. The prototypes presented were designed to use waste heat or solar energy as the main heat source. The waste heat could be from diesel engines or from power plants, in combined cooling, heating and power systems (CCHP). The current technology of adsorption solar-powered icemakers allows a daily ice production of between 4 and 7 kg m−2 of solar collector, with a solar coefficient of performance (COP) between 0.10 and 0.16. The silica gel–water chillers studied can be powered by hot water warmer than 55 °C. The COP is usually around 0.2–0.6, and in some commercially produced machines, it can be up to 0.7. The utilization of such chillers in CCHP systems, hospitals, buildings and grain depots are discussed. Despite their advantages, solid sorption systems still present some drawbacks such as low specific cooling power (SCP) and COP. Thus, some techniques to overcome these problems are also contemplated, together with the perspectives for their broad commercialisation. Among these techniques, a special attention was devoted to innovative adsorbent materials, to advanced cycles and to heat pipes, which are suitable devices not only to improve the heat transfer but also can help to avoid corrosion in the adsorbers. Recent experiments performed by the research group of the authors with machines that employ composite adsorbent material and heat pipes showed that it is possible to achieve a SCP of 770 W kg−1 of salt and COP of 0.39 at evaporation temperatures of −20 °C and generation temperature of 115 °C.