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An experimental study of a forced flow solar collector/regenerator using liquid desiccant
Abstract
One of the main components of a liquid desiccant cooling system is the regenerator. In a liquid desiccant air conditioner, outside air is dehumidified by liquid desiccant and cooled within the absorber. The diluted desiccant solution thus obtained has to be concentrated for reuse, by passing through the regenerator and the cycle is, consequently, repeated. The regenerator used in this application is a forced parallel flow type solar collector/regenerator. The regenerator has been designed and optimized and the prototype of the solar collector/regenerator has been built and tested. Calcium chloride has been used as the absorbent solution. The results of the tests conducted as a parametric analysis indicate that the air and solution mass flow-rates and the climatic conditions affect the regenerator performance. Furthermore, a comparison between the experimental data obtained and a previously developed model for a forced parallel flow solar collector/regenerator reveals that the experiments are in good agreement with the model predictions. Finally, it was concluded that the proposed solar collector/regenerator performs satisfactorily under the summer conditions of Adelaide, Australia.
... Gomez-Castro et al. [18] reviewed both theoretical and experimental studies on various direct and indirect solar thermal regeneration methods of dilute LDS. Although regeneration can be carried out in packed beds [14,[19][20][21][22], direct contact solar regenerators, where the solution itself is the fluid collecting the heat from a surface exposed to solar radiation, are preferred due to its higher effectiveness and lower overhead of system components [18,23]. Recent studies on the use of direct solar regenerators in LDCS have been reported by several authors in the literature [23][24][25][26][27][28]. ...
... Although regeneration can be carried out in packed beds [14,[19][20][21][22], direct contact solar regenerators, where the solution itself is the fluid collecting the heat from a surface exposed to solar radiation, are preferred due to its higher effectiveness and lower overhead of system components [18,23]. Recent studies on the use of direct solar regenerators in LDCS have been reported by several authors in the literature [23][24][25][26][27][28]. Alizadeh and Saman [28] presented a theoretical model of a forced parallel flow solar regenerator using an aqueous solution of CaCl 2 as the desiccant and an experimental study on the same reported by Alizadeh and Saman [23] confirmed the accuracy of the theoretical model developed previously and the results were also consistent with other findings reported in the literature. ...
... Recent studies on the use of direct solar regenerators in LDCS have been reported by several authors in the literature [23][24][25][26][27][28]. Alizadeh and Saman [28] presented a theoretical model of a forced parallel flow solar regenerator using an aqueous solution of CaCl 2 as the desiccant and an experimental study on the same reported by Alizadeh and Saman [23] confirmed the accuracy of the theoretical model developed previously and the results were also consistent with other findings reported in the literature. ...
In this paper, we provide thermal analysis and design methodology of a liquid desiccant assisted dew point indirect evaporative cooling system. The purpose of the system is to serve as an alternative for conventional vapour-compression based building air conditioning systems in providing satisfactory human thermal comfort conditions in the hot and humid climatic regions. The main features of the study are the following: i) novel incorporation of a forced parallel flow direct solar regenerator and a dew point indirect evaporative cooler within the same air conditioning unit; ii) detailed thermal modelling of each of the system components with lesser simplifying assumptions with respect to earlier works; iii) large cooling capacity (∼18.8 TR) under harsh climate; and, iv) a comprehensive year-around case study for system operation in a hot and humid location (Kolkata, India). Our thermal model is validated with a reference model study. The maximum room air temperature predicted by the current system for yearlong analysis is 26.7 °C. The thermal COP of the system for diurnal operation in the most humid month of a calendar year (July) varied between 0.40-0.96. The cooling system can prevent overheating of the conditioned space, as specified by ASHRAE Standard 55-2017, throughout the year.
... A summer air conditioning system using aqueous solution of lithium chloride as desiccant and employing evaporative cooling was reported by Scalabrin and Scaltriti (1990), which showed that low heating temperatures in the range of 35-50°C are required for regenerating the desiccant. Alizadeh and Saman (2002a) designed, optimized and provided an experimental study of a forced parallel flow solar regenerator using calcium chloride solution as liquid desiccant. They compared the experimental results with those obtained from a reference model study available in literature (Alizadeh and Saman, 2002b). ...
... In order to regenerate the desiccant solution, a forced parallel flow solar regenerator/collector similar to the one proposed by Alizadeh and Saman (2002a) is used. It consists of a flat inclined blackened surface (a plate of copper sheet metal electroplated using a nickel layer underneath and thin black chrome coating at the top) over which the weak desiccant solution to be concentrated trickles down as a thin film. ...
In this paper, a novel scheme of a partially closed solar regenerated liquid desiccant assisted evaporative cooling system has been proposed. The objective of the system is to provide suitable conditions inside greenhouses for cultivation of high value temperate crops like lettuce throughout the year in hot and humid climates of tropics and subtropics. The partially closed system re-circulated a fraction of return air from the greenhouse and ventilated a certain amount of ambient air. A forced parallel flow solar regenerator has been used to re-concentrate the weak desiccant solution. A thermal model has been developed to predict the greenhouse air temperature, vapour pressure deficit and the coefficient of performance of the system. The predicted greenhouse temperature has been compared with that of a reference model study available in literature. A very good agreement is established on comparing the temperatures predicted by the two models with a root mean square error of 0.82 °C and average percentage difference being 2.4%. The COP of the cooling system varied between 0.64 and 0.74 for daylong operation in the most humid month of the year (July). The maximum greenhouse temperature predicted using our proposed model was about 27 °C for year round system operation for the place under consideration (Kolkata). The predicted vapour pressure deficits were also in the optimum range. Thus, optimum or viable lettuce growing conditions were predicted by our model all year around. The study consequently reinforces the viability of cultivation of target plantation (lettuce) in hot and humid climates prevailing in the tropical or subtropical countries like India with our model.
... Saman and Alizadeh [176] presented a new dehumidifier which is a derivative of the dehumidifier with inner cooling which makes use of direct evaporative cooling unit. This configuration of the system is shown in Fig. 3.9. ...
... To avoid the desiccant carry over with the air, mist eliminators (droplet filters) are utilized. These mist eliminators can decrease carryover of desiccant to parts per billion of process air flow, but air side pressure drop is increased due to these eliminators and more maintenance is required.Saman and Alizadeh[176] tested a liquid desiccant air conditioner with evaporative cooler by using a plastic plates of 0.2 mm thickness and of 600 m 2 as contact surface area inside the dehumidifier. A solution of 40% CaCl2 was used as the desiccant which was sprayed on the plates. ...
... The regeneration chamber is also eliminated. Forced parallel flow type solar collector/ regenerator is designed and tested by Alizadeh and Saman [49]. The regenerator has been designed and optimized and the prototype of the solar collector / regenerator has been built and tested. ...
... Parallel flow desiccant regenerator[49] ...
This paper gives a detailed account of the general features of the major desiccant regeneration techniques and configurations of the related systems; meanwhile, attention has been paid to both technological development of solar powered regenerator, which is a key component of the liquid-desiccant dehumidification system. Studies to improve the system performance have been discussed. Benefits and conditions of the use of liquid desiccant for dehumidification purposes have been stated. It is clear from the survey that the desiccant dehumidification is more energy-efficient compared with the conventional vapor compression system. Moreover, new configurations of the solar regenerator, to improve the system performance, have been demonstrated. Some new hybrid systems that greatly expand the desiccant in residential applications, as well as effectively promoting the single system's performance, are also introduced.
... The thermal performance of the solar C/R is measured by the amount of The analytical procedures for calculating the mass of water evaporated from the weak solution as a function of inlet conditions and climate parameters have been developed by Collier (1979) and S. Alizadeh and W. Y. Saman (2002). Recently, a simplified model has been developed for indirect evaporative cooler (Chenqin Ren and Hongxing Yang, 2006) and packed bed liquid desiccant air contact system . ...
... water evaporated from the diluted solution. Many studies were dedicated to investigate the performance of the open cycle solar C/R(Collier, 1979;Alizadeh S. and W. Y. Saman, 2002;Conlisk A. T., 1995;Habib Hamza M. and B. D. Wood, 2001;Gandihdasan P. and A.A. Al-Farayedhi, 1995). Several different theoretical models have been developed for this kind of regenerator, namely finite difference model, empirical model and simplified model. ...
... In order to use the desiccant material again, thermal energy is required for the regeneration process. Generally this thermal energy can be supplied by gas or solar [6,9]. Solar desiccant cooling systems can deliver a dryness enough to treat 7.5 l of wet air per second per person and the personal moisture load of 70 W latent (0.1 l per hour) [10,11]. ...
... Present worth factor is used to compare the future cost of a solar system to today's cost taken into account an obligation recurs each year at i inflation rate and d discount rate over N years or time period as in Eq. (8). Payback period is the total time that the system will cover its installation cost as expressed given by Eq. (9). ...
Institutional buildings contain different types of functional spaces which require different types of heating, ventilating and air conditioning (HVAC) systems. In addition, institutional buildings should be designed to maintain an optimal indoor comfort condition with minimal energy consumption and minimal negative environmental impact. Recently there has been a significant interest in implementing desiccant cooling technologies within institutional buildings. Solar desiccant cooling systems are reliable in performance, environmentally friendly and capable of improving indoor air quality at a lower cost. In this study, a solar desiccant cooling system for an institutional building in subtropical Queensland (Australia) is assessed using TRNSYS 16 software. This system has been designed and installed at the Rockhampton campus of Central Queensland University. The system's technical performance, economic analysis, energy savings, and avoided gas emission are quantified in reference to a conventional HVAC system under the influence of Rockhampton's typical meteorological year. The technical and economic parameters that are used to assess the system's viability are: coefficient of performance (COP), solar fraction, life cycle analysis, payback period, present worth factor and the avoided gas emission. Results showed that, the installed cooling system at Central Queensland University which consists of 10 m 2 of solar collectors and a 0.400 m 3 of hot water storage tank, achieved a 0.7 COP and 22% of solar fraction during the cooling season. These values can be boosted to 1.2 COP and 69% respectively if 20 m 2 of evacuated tube collector's area and 1.5 m 3 of solar hot water storage volume are installed.
... The experimental results show a regeneration efficiency varying between 38% and 67%. Alizadeh and Saman [20,21] developed a computer model to evaluate the thermal performance of the solar collector and regenerator. They used a forced parallel flow prototype of a solar collector and regenerator and conducted experimentation. ...
Solar thermal energy-powered air conditioning technologies are receiving increased attention. Among the solar energy-driven cooling technologies, open type liquid desiccant air conditioning (AC) system is emerging as a promising technology, which has a solar driven desiccant solution regenerator. In this type of system, the evaporation of water and concentrating the desiccant or regenerator performance determines the cooling performance of the AC system, which necessitates its development and experimental performance testing under actual operating conditions. The setup is made of a black painted corrugated solar collector of area 0.8 m × 1.84 m covered with glass, and a liquid desiccant solution tank and distribution system over the absorber. Solar regeneration experiments on calcium chloride–water solution were carried out on the setup and a total of five sets of meteorological, collector and solution property data were collected through concentrating the desiccant from 32.9 initially to 51.3% in five days. The evaporation of water from the regenerator was analyzed using energy and desiccant mass conservation. For a typical day, the mass of water evaporated was estimated to be 3.10 and 3.16 kg over a day, as estimated by conservation of mass and energy principles from a 34.8 kg of calcium chloride solution with initial desiccant concentration of 43.6% stored in the tank.
... Their performance has been consistently investigated and improved by coupling solar collectors to different cooling processes [4,108,109]. As was detailed in the previous sections, several experimental and numerical studies were performed on solar systems that were based on the evaporative or desiccation cooling processes [3,121,123,124,133,137]. The results show that solar cooling systems that are adapted for greenhouse units are showing satisfactory results in terms of the efficiency and the economic income. ...
This work is motivated by the difficulty of cultivating crops in horticulture greenhouses under hot and arid climate conditions. The main challenge is to provide a suitable greenhouse indoor environment, with sufficiently low costs and low environmental impacts. The climate control inside the greenhouse constitutes an efficient methodology for maintaining a satisfactory environment that fulfills the requirements of high-yield crops and reduced energy and water resource consumption. In hot climates, the cooling systems, which are assisted by an effective control technique, constitute a suitable path for maintaining an appropriate climate inside the greenhouse, where the required temperature and humidity distribution is maintained. Nevertheless, most of the commonly used systems are either highly energy or water consuming. Hence, the main objective of this work is to provide a detailed review of the research studies that have been carried out during the last few years, with a specific focus on the technologies that allow for the enhancement of the system effectiveness under hot and arid conditions, and that decrease the energy and water consumption. Climate control processes in the greenhouse by means of manual and smart control systems are investigated first. Subsequently, the different cooling technologies that provide the required ranges of temperature and humidity inside the greenhouse are detailed, namely, the systems using heat exchangers, ventilation, evaporation, and desiccants. Finally, the recommended energy-efficient approaches of the desiccant dehumidification systems for greenhouse farming are pointed out, and the future trends in cooling systems, which include water recovery using the method of combined evaporation–condensation, as well as the opportunities for further research and development, are identified as a contribution to future research work.
... Alizadeh and Saman [8] studied a solar collector's thermal performance as a regenerator and used a computer model for CaCl2. They found that the theoretical model and experimental results had a good agreement [9]. Qiu et al. [10] used a system with a biomass boiler that supplied 554 Watts for regeneration. ...
Corrosive fluids such as lithium chloride are often used in liquid desiccant air conditioners. Corrosion in enthalpy exchanger is one of the design problems. Some solutions are studied in this research, and based on them; an experimental setup is investigated. In this design, a counter-flow enthalpy exchanger is used to exchange moisture between the air and the liquid desiccant. First, the inlet air is preheated or precooled by an aluminium heat exchanger. Then, the liquid desiccant is preheated or precooled by thin-walled plastic tubes. By contacting this processed air and liquid desiccant, heat, and mass exchanging occurs. The variation of the air moisture content is investigated in laboratory conditions, and the rate of regeneration and dehumidification is studied. The results indicate that in general, the ambient air moisture content decreased around 20% during the dehumidification process and it enhanced around 14.28% during the regeneration process. Furthermore, the moisture content variation in the dehumidification process improved at least 9.92%, but the regeneration process decreased at least 10.76% compared to the previous study. In addition, utilizing the particle swarm optimization algorithm is desirable to identify the system's transient behavior and obtain the fitting parameters of a curve that is closely similar to the experimental data of the rate of dehumidification and regeneration and the average errors of the fitted curve were 10.43 and 1.52%, respectively.
... The glass cover fixed at 70 mm optimized the mass exchange performance. On the other hand, the air-desiccant temperatures are inversely proportional to the desiccant flow rate [25,26]. ...
In this paper, a comprehensive technical review of liquid desiccant (LD) dehumidification and regeneration techniques is presented. The operational features, processes and performance indices of various flow configurations of adiabatic dehumidifier and regenerator are extensively covered. The heat and mass transfer assessment is presented in terms of past experimental and modelling evaluations and procedures. The existing adiabatic dehumidifier/regenerator heat and mass transfer models are categorized into finite difference, effectiveness-number of transfer units and simple empirical correlation models. The respective performance prediction models are critically analysed in details and compared in terms of assumptions, iterative procedures, solution methods, accuracy, computation time, output variables and applications. The solar regenerator models are also highlighted with a focus on the collector module. The ideal settings, formulation procedures, current state-of-the-art and opportunities for improvements are outlined. The review provides meaningful insight into the research status and available opportunities in the LD adiabatic dehumidifier and regenerator modelling and optimization as well as conceptualization of the applicable models. Finally, some very impactful suggestions for improvement and further research are outlined.
... Since then, various modifications of solar regeneration systems have emerged in the forms of experimental evaluations and validations on glazed and unglazed flat plate modules [3], enclosed and open zones, forced flow arrangements [4], psychometrics, feasibility and actualization [5][6][7]. The heat and mass exchange correlation constants found from investigational assessments of an open-cycle forced convection solar regenerator are obtainable in [8][9][10][11][12][13]. Combinations of theoretical examination and experimental justification of heat and mass exchange factors during chemical dehumidification and regeneration in different configurations using various desiccant solutions such as lithium chloride (LiCl) [14][15][16][17], triethylene glycol (TEG) solution [18], H2O/KCOOH [19], lithium bromide (LiBr) [20,21] have been explored in details in packed columns. ...
Coupled heat and mass transfer performance of an adiabatic solar-powered liquid desiccant dehumidification and regeneration scheme using lithium bromide(LiBr) solution has been conducted experimentally as well as numerically under subtropical climatic conditions. The application of a vacuum insulated photovoltaic and thermal module to provide desiccant regeneration heat as well as electrical power to drive the air fans and liquid pumps have been explored. A square channelled ceramic cordierite packing with a varying channel density of 20–80 m/m has been used to establish the optimum direct air-LiBr contact ratio for maximum effectiveness. The aggregate crammed vertical dehumidifier and regenerator operational indices featured were effectiveness, moisture removal rate (MRR), heat and mass transfer constants and Lewis number. The influence of solar radiation, humidity and L/G ratios, air–desiccant flow rates and concentration on the indices have been scrutinized in details. A 3D predictive numerical thermal model based on falling liquid stream with constant thickness in counter-flow configuration has been developed and solved by a combination of separative appraisal and stepwise iterative technique. The heat and mass exchange coefficients significantly increased with the increase in Lewis number, air and desiccant flow rates for both the dehumidifier and regenerator vessels. The predicted results of heat and mass transfer coefficients, effectiveness and MRRs have been validated with experimental measurements within a general acceptable conformity of less than 10%.
... Generally, this thermal energy can be supplied by gas or solar. Figure 5 explains the operational concept of desiccant cooling technologies [25,26]. ...
Indoor air quality as always is the centre of attention for researchers, architect developers and public health officials. As everyone know. The human exposure to a variety of indoor pollutants and the high cost of energy are the motivation for these kinds of studies. Fungus and mould growth has always been a problem in subtropical climate areas due to the high temperature and high humidity. Generally, in institutional buildings, most of the internal heat load is generated by human body and thermal comfort is achieved with extensive usage of recycled air and air conditioning. The main considerations in any air conditioning system economisers are based on the usage of recycled air and air ventilation. The current practice in an institutional building cooling system under subtropical climate is to curb the mould issue by overcooling large recirculation airflow to remove the moisture content from the air, which is considered as an expensive practice. The use of a solar desiccant cooling system to reduce moisture from the air and to improve indoor air quality is found to be economical, environmentally friendly and readily achievable in the tropics. This technology is the future alternative to the conventional vapour compression cooling system to maintain human thermal comfort conditions and enhance indoor air quality. Solar desiccant cooling systems are also environmentally friendly and energy efficient. This paper presents review on a solar desiccant cooling system and its effect on indoor air quality. It first introduces the issue of air moisture, mould growth and indoor air quality and then the development and application of thermally activated desiccant cooling technologies.
... The LDS after dehumidifying the process air becomes diluted due to the absorption of moisture and heats up due to the released latent heat of condensation. It is then preheated in the desiccant-desiccant heat exchanger (HEX 1) before being supplied to the forced parallel flow direct solar REG [5] where it loses moisture to the regenerating air stream. Thereafter, the hot concentrated LDS at the REG outlet is pre-cooled in the HEX 1 and desiccant-water heat exchanger (HEX 2) before being supplied to the DEH. ...
In this paper, exergy analysis of a novel solar powered liquid desiccant assisted air
conditioning system is presented and simulated. The system aims to provide suitable thermal
comfort conditions inside large office buildings with high internal loads situated in the hot and
humid tropical/subtropical countries of the world. The system consists of process and
regenerating air streams, a liquid desiccant solution loop and a cooling water loop. The primary
objective of this study is to present the exergy of cooling capacity along with the overall
exergy efficiency of the proposed system. The study helps to quantify the optimum operating
and design parameters for system operation based on the second law of thermodynamics. For
the base case, which is representative of a hot and humid climatic condition, the proposed
system is able to maintain the room air conditions within the moderate thermal acceptability
criterion. The exergy of cooling capacity and exergy efficiency for the base case is about 2900
W and 2 % respectively. Parametric analyses show that the system performs the best under
conditions of high ambient insolation and temperature, low ambient humidity and a process air
to desiccant solution mass flow rate of about 3 in the dehumidifier.
... Innovations are required in the liquid desiccant dehumidification technique in industrial and residential applications as well as effectively ameliorating the system's performance. Finally, future study and application for liquiddesiccant dehumidification techniques are need following research and development [17][18][19][20][21][22][23][24][25][26][27][28]: ...
Presently the air conditioning industry is confronted with some major challenges regarding use of halogenated Liquid desiccant based building cooling technology is an environment friendly which can be used to condition the outdoor air to produce thermal comfort. Unlike traditional vapor compression based air conditioning systems, which completely rely on use of high grade electricity to drive the cooling cycle, liquid desiccant cooling is a freely available renewable solar energy heat driven cycle. Liquid desiccant based air conditioning systems have been used successfully in many parts of the world exposing hot and humid climate conditions especially in tropical region since very long time. The present review enables use of solar energy to drive liquid desiccant cooling in various applications. The study demonstrates the application of solar energy is feasible in many parts of the world, provided that the latent heat gains experienced are excessive. To this extent use of freely available renewable solar energy for dehumidification and cooling applications is desirable. It is appreciated that this source of energy can at best be complementary rather than being competitive to conventional energy sources.
... A heat pump is utilized in the air driven solution regeneration system by Wen et al. 7 In the system, the condensing heat of the heat pump is used to heat the weak solution for regeneration, and simultaneously the evaporator of the heat pump is put into the warm and humid air after solution regeneration for efficiency improvement. Some experts have proposed to utilize the solar energy [8][9][10] and the industrial waste heat 11 to heat the solution. The advantage of the air driven type of solution regeneration is that the regeneration system is simple, and the natural resource or the waste heat could be utilized as the heat source. ...
Solution regeneration of the heat-source tower is significant to guarantee the normal operation of the heat-source tower. Mechanical vapor recompression system is an efficient system for evaporation of solution. In this paper, mechanical vapor recompression system is applied to regenerate solution of heat-source tower. To clarify the merits of mechanical vapor recompression solution regeneration system, several typical solution regeneration systems are modelled. As a result, mechanical vapor recompression shows 35.7%, 73.5% and 91.2% energy saving compared to air-driven heat pump, three-effect evaporating system, and single effect evaporating system, respectively. Furthermore, a heat-source tower heat pump with solution generation system is installed in a typical building in Yangtze river region. The whole heating season performance is simulated to find the effects of different solution regeneration system on the whole heat pump system. As a conclusion, the seasonal coefficient of performance of heat pump is decreased 1.6% by mechanical vapor recompression regeneration system. Comparatively, the seasonal coefficient of performance of heat pump is decreased 2.6%, 4.2% and 10.0% by air-driven heat pump, three-effect evaporating system, and single effect evaporating system, respectively. Practical application: Solution regeneration systems for heat-source tower heat pump systems have been applied in building projects especially in hot summer and cold winter zone in China based on previous investigation. A heat-source tower heat pump system combined with heat pump solution regeneration system has been applied in an office building in Changsha, Hunan Province in China. And its practical operation energy consumption has been reduced obviously compared with traditional single effect evaporation system. Therefore, it is of vital importance to demonstrate the operating performance of different solution regeneration systems applied in heat-source tower heat pump systems in building. © The Chartered Institution of Building Services Engineers 2018.
... In order to regenerate the weak desiccant solution, a forced parallel flow solar regenerator similar to that proposed in literature [5] is used. The regenerator is installed in two halves to allow a fraction of incident ambient solar insolation on the roof into the greenhouse as shown in Fig. 1. ...
A scheme of a partially closed solar regenerated desiccant assisted evaporative cooling system has been proposed for the cultivation of temperate crops like lettuce in hot and humid climates. The partially closed system re-circulated a fraction of return air from the greenhouse and ventilated a certain amount of ambient air. A thermal model has been developed to predict the greenhouse air temperature and vapour pressure deficit. The same was compared with a reference model study available in literature. Re-circulation of a fraction of return air decreased the greenhouse air temperature and increased the vapour pressure deficit, thereby augmenting lettuce yield quality. Year around, the maximum greenhouse temperature predicted using our proposed model was about 27 °C. The predicted vapour pressure deficits were also in the optimum range. Thus, optimum or viable lettuce growing conditions were predicted by the proposed model throughout the year for the climatic conditions of Kolkata.
... One may find out that this work is basically focuses on vapour pressure, one of the leading parameters for finding system effectiveness. Alizadeh et al.[78]used parallel flow type forced flow solar collector/regenerator as shown inFig. 11for the regeneration of CaCl 2 LD at Adelaide, Australia. ...
In a global era, continuous increment in energy requisition with its associated cost and relevant climate problems is causing accentuation in exploring more efficient ways to provide air conditioning in enclosed space without degradation of the environment. In the hot and humid area, major part of conventionally produced electrical energy is consumed by air conditioning. Also in the rapidly growing world scarcity of clean water is dilemma as equal as greenhouse and ozone layer depletion. Thus, there is emergence of dehumidified air for human comfort conditions with having potable clean water same time. In summer with largely available solar radiation, use of hybrid solar system is viable option to overcome problems of dehumidification of liquid desiccant as well as of potable water. Up till now the conventional dehumidification with desiccant solution has been improved or replaced by less costly new systems. This paper provides an extensive literature review on development of liquid desiccant regeneration using solar energy. The paper also includes the recent findings of hybrid solar system in which either two sources of heat is used for regeneration of liquid desiccant or solar energy is used for regeneration of liquid desiccant along with other application.
... Alizadeh et al. [11] designed, optimized and constructed a prototype of a forced flow solar collector/Regenerator. They emp loyed an aqueous solution of calciu m chloride as desiccant and studied the influence of parameters, such as air and desiccant solution flow rates as well as the climat ic conditions on the regenerator's performance. ...
With the drastically change in climatic conditions in recent years, demand for air conditioning is spreading all over the world. This causes a primary consumption of energy in high quantity. In order to provide the best indoor air quality and thermal comfort with minimum consumption of energy, the hybrid desiccant cooling system is one of the options in our daily life. In this paper, an experimental performance study has been done on the hybrid desiccant cooling system. The effects of various parameters on performance of the system have also been observed. It is found that the influence of the parameters studied on the dehumidification rate is similar to those reported earlier.
... The study suggested that, when the latent load constitutes 90% of the total cooling load, the system can generate up to 80% of energy savings. Alizadeh et al. [27] designed, constructed and optimized an investigational setup of a forced flow solar collector/regenerator. They utilized an aqueous solution of calcium chloride as desiccant and studied the various influence of parameters, such as air and desiccant solution flow rates as well as the climatic (environmental) conditions on the regenerator's performance. ...
This term paper presents a review based study of the solar desiccant evaporative cooling technology, which was undertaken from a selection of aspects including background, history, current status, concept, types, system configuration, operational mode, research and industrialization, as well as the future focuses on R&D and commercialization. This review work indicated that the DEC technology has prospective to be an alternative to conventional mechanical vapor compression refrigeration systems to take up the air conditioning duty for buildings and transportation also. Owing to the continuous progress in technology innovation, particularly the heat and mass transfer and material optimization, the DEC systems have obtained significantly enhanced cooling performance over those the decade ago and now a days it is using with Solar apparatus also.
... For example, Kessling et al. [3] conducted experiments for absorbers using LiCl and were the first to point out the benefit of energy storage thanks to the use of liquid desiccants. Jaina et al. [4], Pietruschka et al. [5], and Alizadeh et al. [6] proposed experimentally validated models of As cooling process using liquid desiccant combines dehumidification-humidification processes of the airstream with absorption-desorption processes related to the desiccant solution, we can categorize some experimental works on the basis of the technique used for bringing the desiccant solution into contact with the process air. The contact surface can be a wetted wall/falling film absorber [4,7,8], a spray chamber [9,10], or a packed tower [11][12][13]. ...
Solar energy technology is an option for energy saving in building air conditioning. A theoretical investigation of an open cycle solar air cooling system using aqueous Lithium Chloride solution as liquid desiccant is presented in this paper. The purpose of this work is to analyze the influences of both internal loads and external forcing, on the studied system by developing a computational code related to its mathematical model. The simulation results justify the choice of the system design. Indeed, it was highlighted that the higher is the outdoor temperature; the better is the coefficient of performance (COP) of the system. Furthermore, a global sensitivity analysis of the system model, achieved using Fourier Amplitude Sensitivity Test method, allowed us to identify the most influential factors that were ranked in a decreasing order of their influence degree on the system COP. Hence, key factors to be controlled for improving the system overall performance are specified.
... Liquid desiccant cooling systems have been proposed to replace the conventional vapor compression cooling systems in hot and humid areas. Many researchers [2][3][4][5] have shown that the liquid desiccant cooling systems can reduce the overall energy consumption as well as shift the energy use away from the electricity and toward renewable energy such as solar energy and waste heat since Lof [6] developed the first liquid desiccant system. Recently Fumo and Goswami [7] gave a brief summary on the liquid desiccant systems, and Younus et al. [8] presented a thermodynamic analysis of different liquid desiccants. ...
EXPERIMENTAL STUDY FOR COMPACT LIQUID DESICCANT DEHUMIDIFIER/REGENERATOR SYSTEM
... Besides, liquid desiccant materials are usually corrosive and simple handling of the working media is difficult. Thanks to fast advancement in the field, the potential of the liquid desiccant is remarkable [9,10]. Ever since Lof [11] investigated liquid desiccant solar cooling concept, a number of researchers have conducted number of studies on liquid desiccant dehumidification systems for solar cooling applications. ...
Cooling by solar energy is one of the key solutions to the global energy and environmental degradation issues. Solar liquid desiccant based on evaporative cooling is proposed as an eco-friendly alternative to the conventional vapour compression systems due to its huge untapped energy savings potential. In this paper, the recent works on solar assisted liquid desiccant cooling and its various applications combined with evaporative airconditioning under different climates are reviewed and advantages the system may offer in terms of energy savings are underscored. A basic description of the principles of hybrid solar liquid desiccant with direct and indirect evaporative cooling is provided. Finally, solar regeneration methods and recent developments for the liquid desiccant air conditioning system are presented.
... Solar energy can be used directly to regenerate the desiccant wheel not only in warm temperatures, but also in hot and humid climates (Joudi and Madhi, 1987;Kabeel, 2007;White et al., 2009). Alizadeh and Saman (2002) studied the relationship between direct solar collection and desiccant regeneration. They found that surges in solution mass flow rate ended in the fall of the water loss rate. ...
... A study of Manley, Bowlen, and Cohen (1985) reveal that the integration of commercially available dehumidifiers for latent heat removal and conventional VCS for sensible heat removal for supermarket applications is an economical option. Alizadeh and Saman (2002) designed, optimised and constructed a prototype of a forced flow solar collector/regenerator. They employed an aqueous solution of calcium chloride as the desiccant and studied the influence of parameters, such as air and desiccant solution flow rates as well as the climatic conditions on the regenerator's performance. ...
In this paper, an experimental study has been conducted on the hybrid desiccant cooling system by removing the latent heat and sensible heat of air separately by mixing it with the desiccant solution in a counter flow manner. This makes air totally dry and thus saves the energy to cool the air in the refrigeration system. The desiccant chosen here is the aqueous solution of calcium chloride. The packed bed inside the absorber as well as the regenerator consists of a polypropylene cascade ring for the efficient mixing of air and desiccant solution. The effects of various parameters such as desiccant inlet temperature, air inlet temperature, mass flow rate of air and desiccant solution have been studied to investigate the performance of the system. Comparing the results with previous studies, a fair agreement has been reported.
... Although many researchers investigated on the energy performance of LDAC or SLDAC in buildings [1][2][3], most of them concerned the packed-bed or solar collector/regenerator liquid desiccant system, and the research on the internally cooled/heated liquid desiccant system is limited. Additionally, only several researchers have been conducted on the operation performance of LDAC applied in buildings under the hot climate like Hong Kong [4,5]. Therefore, it is necessary to find a way to reduce the energy consumption of AC system in buildings in Hong Kong. ...
Volume 61, 2014, Pages 2686-2689
... Although many researchers investigated on the energy performance of LDAC or SLDAC in buildings [1][2][3], most of them concerned the packed-bed or solar collector/regenerator liquid desiccant system, and the research on the internally cooled/heated liquid desiccant system is limited. Additionally, only several researchers have been conducted on the operation performance of LDAC applied in buildings under the hot climate like Hong Kong [4,5]. Therefore, it is necessary to find a way to reduce the energy consumption of AC system in buildings in Hong Kong. ...
Solar-assisted liquid desiccant air-conditioning system (SLDAC) has been considered as a promising application as traditional AC systems have many problems. In this paper, the operation performance of the SLDAC of a typical commercial building in Hong Kong was investigated, for evaluating the energy-saving potential. Combing the numerical model of individual component and inputting the weather data and load profile, the annual energy consumptions of SLDAC and traditional system could be obtained. The simulation results show that the electricity driven LDAC is not suitable for the commercial building due to the high energy demand in the regeneration. But, the solar-assisted system with thermal storage could provide promising energy saving potential. However, with the cooling tower as the only cooling source of the dehumidifier, the dehumidification capacity could not satisfy the requirement and only up to 12.5% of electricity consumption could be saved annually compared to traditional systems. Therefore, to improve the energy-saving potential, extra cooling source should be supplied for the application of SLDAC of buildings in Hong Kong.
... Considerable laboratory experiments, computational analysis and design work has been carried out on a liquid desiccant system at the Sustainable Energy Centre of the University of South Australia [2][3][4][5][6], and the Queensland University of Technology [7,8]. These involved modelling and experimental work on both cross flow and packed-bed dehumidifier as the absorber unit as well as the solar regenerator [9]. ...
... 22 is one typical dehumidification/indirect evaporative cooling unit (W.Y.Saman and S. Alizadeh, 2002). Two tunnels constitute one heat exchanger group. ...
The global air temperature has increased by 0.74± 0.18 °C since 1905 and scientists have shown that CO2 accounts for 55 percentages of the greenhouse gases. Global atmospheric CO2 has been sharply increased since 1751, however the trend has slowed down in last fifty years in the Western Europe. UK and EU countries have singed the Kyoto agreement to reduce their greenhouse gas emissions by a collective average of 12.5% below their 1990 levels by 2020. In the EU, 40% of CO2 emission comes from the residential energy consumption, in which the HVAC system accounts for 50%, lighting accounts for 15% and appliances 10%. Hence, reducing the fossil-fuel consumption in residential energy by utilizing renewable energy is an effective method to achieve the Kyoto target. However, in the UK renewable energy only accounts for 2% of the total energy consumption in 2005.
A novel heat recovery/desiccant cooling system is driven by the solar collector and cooling tower to achieve low energy cooling with low CO2 emission. This system is novel in the following ways:
• Uses cheap fibre materials as the air-to-air heat exchanger, dehumidifier and regenerator core
• Heat/mass fibre exchanger saves both sensible and latent heat from the exhaust air
• The dehumidifier core with hexagonal surface could be integrated with windcowls/catchers draught
• Utilises low electrical energy and therefore low CO2 is released to the environment
The cooling system consists of three main parts: heat/mass transfer exchanger, desiccant dehumidifier and regenerator. The fibre exchanger, dehumidifier and regenerator cores are the key parts of the technology.
Owing to its proper pore size and porosity, fibre is selected out as the exchanger membrane to execute the heat/mass transfer process. Although the fibre is soft and difficult to keep the shape for long term running, its low price makes its frequent replacement feasible, which can counteract its disadvantages. A counter-flow air-to-air heat /mass exchanger was investigated and simulation and experimental results indicated that the fibre membranes soaked by desiccant solution showed the best heat and mass recovery effectiveness at about 89.59% and 78.09%, respectively.
LiCl solution was selected as the working fluid in the dehumidifier and regenerator due to its advisable absorption capacity and low regeneration temperature. Numerical simulations and experimental testing were carried out to work out the optimal dehumidifier/regenerator structure, size and running conditions. Furthermore, the simulation results proved that the cooling tower was capable to service the required low temperature cooling water and the solar collector had the ability to offer the heating energy no lower than the regeneration temperature 60℃.
The coefficient-of-performance of this novel heat recovery/desiccant cooling system is proved to be as high as 13.0, with a cooling capacity of 5.6kW when the system is powered by renewable energy. This case is under the pre-set conditions that the environment air temperature is 36℃ and relative humidity is 50% (cities such as Hong Kong, Taiwan, Spain and Thailand, etc). Hence, this system is very useful for a hot/humid climate with plenty of solar energy. The theoretical modelling consisted of four numerical models is proved by experiments to predict the performance of the system within acceptable errors.
Economic analysis based on a case (200m2 working office in London) indicated that the novel heat recovery/desiccant cooling system could save 5134kWh energy as well as prevent 3123kg CO2 emission per year compared to the traditional HVAC system. Due to the flexible nature of the fibre, the capital and maintenance cost of the novel cooling system is higher than the traditional HVAC system, but its running cost are much lower than the latter. Hence, the novel heat recovery/desiccant cooling system is cost effective and environment friendly technology.
... Thus efficiency of using the combination of desiccant cycle and evaporative cooling system can be boosted by integrating this technique with other conventional cooling systems. Examples of this integration are desiccant cooling system and conventional vapour compression cooling systems [174], desiccant cycle within an associated chilled ceiling cooling system [175] and desiccant cycle with rooftop cooling system [176]. The hybrid systems will reduce compressor electricity consumption, water condensations in the building envelop, the size of the vapour compression cooling system, and it will improve the overall cooling system COP. ...
journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues. Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier's archiving and manuscript policies are encouraged to visit: a b s t r a c t Australia has a very sunny climate, with a very high demand for air conditioning. Relying on electricity to drive, buildings' HVAC systems will cause a significant negative impact on the environment. In this paper, recent developments in solar assisted air conditioning technologies are reviewed and presented. The conceptual basis of the technologies including open and closed cycles cooling technologies, capabilities and limitation are discussed. Energy demand, energy consumption by Australian buildings sector and economic and environ-mental problems associated with the usage of fossil fuel resources are reported. Second the issue of mould growth and indoor thermal comfort and indoor air quality is highlighted. Finally the technology fundamentals and theories involved with solar energy and solar collector's technologies are summarised and discussed.
In liquid desiccant-operated evaporative cooling systems (LDECS), the latent heat load of air-conditioning in the confined space is adsorbed by the liquid desiccant, according to the adsorption capacity. Whereas sensible heat load that controls the temperature is handled by the evaporative cooling system. The key difference between conventional vapour compression refrigeration system (VCRS) and LDECS is that latent and sensible heat load of air-conditioning in the confined space are handled separately by different sub-components in LDECS whereas handled by the single cooling coil in VCRS. In review, various components of LDECS such as dehumidifier and regenerator, desiccant heater and cooler, evaporative air cooler, etc., and its features and advancements have been discussed. Further, the influence of distinct input parameters on performance indices of dehumidifier, regenerator, and on the overall performance of LDECS has been addressed through the various state-of-the-art research results and summarized in the form of tables. At the end, the critical conclusion and the future scope of various promising technologies have been elaborated concisely.
Vapour Compression Refrigeration (VCR) cycle which consumes electrical energy dominate air conditioning market today. Production of electrical energy is generally associated with fossil fuel consumption, emission of greenhouse gases and pollution. Air conditioning systems which use waste or renewable energy sources should be investigated as alternative solution. Liquid desiccant based air conditioning system (LDAC) is one such potential candidate. The heat from a solar thermal collector can be supplied to regeneration process LDAC systems.
A novel solar collector with goal of no electrical power consumption, simplicity, low cost, and high efficiency was developed in this work for regeneration of LD (aqueous calcium chloride solution). Condensate output in this device used for water desalination was 3.7 kg/m², which is comparable with the best in literature. An area of 7.5 m² of such a device with no parasitic power would be needed per kW of latent cooling.
The appropriate design of the flow path and operating parameters is needed to improve the efficiency of liquid desiccant systems. This study compared the operation of 30 liquid desiccant systems with different flow paths, which include 6 cooling/heating modes and 5 solution circulation types. The models of the packing tower were established to simulate the heat and mass transfer processes between the air and the solution, and the average absolute deviation was within 9.8%. The analytical results reveal that the systemic flow path is a crucial factor influencing the air state changes and a key research direction. Based on reasonable parameter design for each liquid desiccant flow path, the comparison considers cooling/heating capacity, cooling/heating source temperature and energy consumption. With a certain supply air state, the cooling and heating capacities both depend on the heat exchange loss caused by the cold and heat offsets of the solution. Solution Circulation Type Ⅰ was first adopted because it had the largest potential for reducing the heat exchange loss and cooling/heating capacity, and the corresponding heat exchange loss was less than 2.9 kW. Then, under the determined cooling mode and solution circulation type, the heating of the solution reduced the requirement of the heating source temperature. When the residual heat exhaust temperature was lower than 32 ℃, the Ⅰ-③ flow path was preferred through the calculation of the systemic power consumption; otherwise, the Ⅰ-① flow path was preferred. The power consumption of the Ⅰ-① and Ⅰ-③ flow paths was equal at 2.6 kW when the residual heat exhaust temperature was 32 ℃.
In this paper, a self-preheated solar collector/regenerator (C/R) is proposed to conquer the anti-regeneration phenomenon of traditional solar C/R in order to increase its regeneration efficiency. Through numerical simulation, the applicability of the self-preheated C/R in Northern and Southern cities of China and parameter optimization as well as the performance comparisons with the traditional C/R are conducted. The research results show the self-preheated C/R has good applicability for the 24 cities chosen in China, but the length of collector section is selected in the optimum ranges. The optimal proportion of collector length in the southern China is in the range of 0.4–0.55 while it focusing on 0.35–0.5 in the northern China. In the optimization of parameters, the best flow-rates of air and solution for the unit area of C/R fall into the ranges of 50–100 kg/(m²·h) and 3–6 kg/(m²·h) respectively, and the height of C/R glazing should be maintained at 0.04–0.06 m for higher regeneration efficiency of the device. By comparing to the performance of traditional C/R, the self-preheated solar C/R has greater superiority at higher ambient relative humidity, lower solution temperature and higher solution concentration as well as lower solar radiation intensity. The increased extent can reach as much as 22% at ξin = 0.4 kg/kg. The total length of self-preheated C/R has an optimal value on the performance of device. All these results can provide guidance for performance analysis and application of the novel solar collector/regenerator.
The large electricity consumption due to the extensive use of vapour compression machines in the air conditioning and industrial sectors dramatically increases the emissions of greenhouse gases. Besides, the synthetic halocarbon refrigerants used in said machines are responsible for ozone depletion. These environmental concerns give an opportunity to solar thermally-driven liquid sorption systems, whose energy consumption primarily lies on the regeneration heat of liquid sorbents. This paper surveys both theoretical and experimental studies on solar thermal regeneration methods of the hygroscopic solutions used in liquid sorption systems. A brief review of some conventional and alternative liquid desiccants utilised in said systems is firstly presented. Furthermore, information about several configurations of regenerators and their performance is covered in detail, putting special emphasis on solar collector/regenerators, which use directly solar energy to reconcentrate the weak desiccant solution. A comparative assessment of relevant thermophysical properties of some hygroscopic liquids is realised in order to determine their suitability for use in sorption systems. The results show that the aqueous solutions of potassium formate and ionic liquids are very promising desiccants due to their low vapour pressures, specific heat capacities and dynamic viscosities, as well as their non-corrosiveness. A performance comparison between typical regeneration units and solar collector/regenerators is also carried out. It could be shown that solar collector/regenerators have a high potential for enhancing the water desorption rate from a diluted desiccant solution and, consequently, the capacity of the air dehumidification process within the absorber.
A new liquid regeneration equipment — solar air pretreatment collector/regenerator for liquid desiccant cooling system is put forward in this paper, which is preferable to solution regeneration in hot and moist climate in South China. The equipment can achieve liquid regeneration in lower temperature. When the solution and the air are in “match” state in collector/ regenerator, a match air to salt mass ratio ASMR* is found by theoretical study in which there is the largest theoretical storage capacity SC max. After two new concepts of the effective solution proportion (EPS) and the effective storage capacity (ESC) are defined, it is found by theoretical calculation that when ESP drops from 100% to 67%, ESC raises lowly, not drops and liquid outlet concentration C str.sol increases from 40% to 49% in which its increment totals to 90%. All these data explain fully that air pretreatment liquid regeneration equipment enables to improve the performance of liquid desiccant cooling system.
A regenerator is one of the main components of a solar liquid desiccant cooling system. The regenerator used in this application is a forced counter flow type solar collector/regenerator(C/R). Experimental results of the tests indicate that there occurs a maximum value for regeneration efficiency at some air flow-rate. The regeneration efficiency of solution at ambient temperature decreases with the increase in solution flow-rate, instead of increasing at moderate temperature. The inlet temperature of solution has great influence on the regeneration efficiency and a higher concentration of solution is accompanied by a lower efficiency of regeneration. Compared with the regeneration efficiency at Ya,in = 20 g/kg, the regeneration efficiency was increased by about 40% at Ya,in = 10 g/kg. Higher solar radiation intensity will better regeneration performance of the C/R. Air flow-rate has far more effect on heat and mass coefficients between air and solution than solution flow-rate. The solution inlet temperature and salt concentration have contrary effects on heat and mass transfer coefficients with increase in their values. By Simpson numerical integration, two correlations on heat and mass transfer characteristics were given. Finally, it was concluded that the proposed solar collector/regenerator performs satisfactorily in humid climates of the Southern China.
Dehumidifier is the main component of liquid desiccant dehumidification system. Effect of the inlet parameters on various outlet parameters of the dehumidifier is studied in the present paper with structured pads as packing material and calcium chloride as liquid desiccant to process the air. The outlet parameters are change in specific humidity, mass transfer coefficient, moisture removal rate, air temperature, solution temperature, effectiveness and the corresponding inlet process parameters; mass flow rate of air, temperature of air, temperature and flow rate of desiccant solution. It is observed that mass transfer coefficient and moisture removal rate increase with increasing mass flow rate of the air and desiccant while these parameters decrease with increasing temperature of air and desiccant solution. Dehumidifier effectiveness gets increased with increasing solution flow rate. The present investigations are compared with the results of the researchers in the past.
A countercurrent solar solution collector/regenerator (C/R) with experiment platform the size of 1 m(wide)×2 m(long)×0.35 m(high) was used for analyzing the factors influencing regeneration efficiency of solar C/R. It is found that there is an obvious two-stage distribution for regenerating solution at normal temperature. The regeneration efficiency of solution increases first and then decreases with the increase of air mass flow rates and there exists a maximum value. The regeneration efficiency always decreases with the increase of solution flow rates. Heating solution leads to an increase of integrated regeneration efficiency; however, heating regeneration air decreases the integrated regeneration efficiency. The regeneration efficiency is decreased by 0.16 by using humid air of 20 g/kg instead of using humid air of 10 g/kg. The regeneration efficiency increases correspondingly with the increase of the solar radiation intensity. The countercurrent solar solution C/R can operate better in dry air and high solar radiation conditions and a suitable air flow-rate should be selected to achieve better performance.
Definition of the Subject and Its ImportanceCooling is needed for two main fields of application. On the one hand, it is needed in buildings and other closed spaces, for example, vehicles, which are occupied by human beings. Cooling assures that occupants feel comfortable. On the other hand, in industrial and commercial applications, cooling is needed to cool commodities or processes. In a wider sense, cooling in buildings refers to both control of temperature and control of humidity. In the following, it is referred to as air-conditioning. Cooling of commodities or processes is referred to as refrigeration. Cooling in a thermodynamic sense means to withdraw heat. Any heat flux is always directed from a source of high temperature to a sink of lower temperature. Unless a natural heat sink is available – such as the ground or outside air – a thermodynamic cycle has to be employed in order to provide a low-tem ...
To improve indoor air quality, volatile organic compounds (VOCs) absorbed by absorbent solution were tested in a packed-bed absorber. On the basis of the principle that organics dissolve into organic solution easily, the triethylene glycol (TEG) solution was used as the working solution to discuss mass transfer performance of VOCs absorbed by the TEG solution in this study. Toluene, methanol, ethyl ether, and methyl ethyl ketone were absorbed by the TEG solution, and the mass transfer coefficients were calculated. The flow rates of liquid and gas were controlled in the ranges 1.24-1.43 kg/min and 2.9-2.97 kg/min. According to the volatile properties of VOCs and the environmental standard, the concentrations of toluene, methanol, ethyl ether, and methyl ethyl ketone were operated in the ranges 62-110, 210-369, 58-155, and 105-205 ppm, respectively. The concentrations of the TEG solutions were controlled to between 91.5 and 96.5 wt %. After experimental runs, effects of operating variables on mass transfer coefficients were discussed, and the influence of interfacial disturbance on mass transfer performance was also analyzed in this study. The interfacial disturbance occurred because the surface tension difference prompts the surface to renew and increases the contacting probability for liquid and gas phases, which leads to enhancement of the mass transfer performance. Finally, four correlations were regressed to predict the mass transfer coefficient, and the average error was +/- 12%.
Solar liquid collector/regenerator (C/R), combining the functions of solar collector and regenerator of absorbent solution together, can be effectively utilized in solar energy-driven liquid desiccant cooling systems. Based on thermal balance of the glazing of solar C/R, a group of modified heat and mass transfer models, validated by experimental results to reflect solution regeneration process more truly, were put forward in this paper. Numerical simulation showed only preheating air stream, keeping an equal humidity ratio, did raise the performance of solar C/R, but preheating solution increased the regeneration efficiencies to reach twice that of preheating air stream. There occurred optimum mass flow rates for both air stream and solution film reaching 36-48 kg m(-1) h(-1) and 4-6 kg m(-1) h(-1) respectively for solar C/Rs of 3 similar to 6 m long. As for effect of the length of solar C/Rs, the regeneration efficiency eta(x) reached a maximum value at about 4 m and shorter or longer solar C/Rs failed to increase solution regeneration efficiencies.
In this research study the economical performance of a solar desiccant cooling system has been assessed. The economical parameters that used to assess the system viability are life cycle analysis and system payback period. The optimisations are carried out for a solar cooling system that has been designed and installed under Central Queensland subtropical climate in Central Queensland University, Rockhampton campus, Australia. The desiccant cooling system consists of a solid desiccant machine, an evaporative cooler and a backup Conventional system. The building cooling load and the system component were modelled using TRNSYS16 under a typical meteorological year of Rockhampton climate TMY. Results showed that by installing 10 m2 of solar collectors a 22% of solar fraction will incur and the annual avoided gas emission will be 4.4 tone of Co2. However the payback period will be 22 years if the system resale value was 20% of the total installing cost.
Indoor air quality (IAQ) has recently received increased attention by researchers, architect developers and public health officials. The human exposure to a variety of indoor pollutants and the high cost of energy are the motivation for these kinds of studies. Fungus and mould growth has always been a problem in subtropical climate areas due to the high temperature and high humidity. Generally in institutional buildings, most of the internal heat load is generated by human body and thermal comfort is achieved with extensive usage of recycled air and air conditioning. The main considerations in any air conditioning system economisers are based on the usage of recycled air and air ventilation. The current practice in an institutional building cooling system under subtropical climate is to curb the mould issue by overcooling large recirculation airflow to remove the moisture content from the air, which is considered as an expensive practice. The use of a solar desiccant cooling system to reduce moisture from the air and to improve indoor air quality is found to be economical, environmental friendly and readily achievable in the tropics. This technology is the future alternative to the conventional vapour compression cooling system to maintain human thermal comfort conditions and enhance indoor air quality. Solar desiccant cooling systems are also environmentally friendly and energy efficient. This paper presents review on a solar desiccant cooling system and its affect on indoor air quality. It first introduces the issue of air moisture, mould growth and indoor air quality and then the development and application of thermally activated desiccant cooling technologies
Institutional buildings contain different functional spaces which require different types of heating and ventilating air conditioning HVAC. In order to provide a suitable work environment for the occupants of an institutional building, the buildings (HVAC) system must provide a thermal comfort level and a healthy living environment. However the extensive use of conventional cooling systems in institutional building consider as the biggest energy consumer. Building designer’s main task is to maintain the optimal indoor comfort condition with minimal energy consumption and minimal environmental negative impact. Now a day there is a big interest in non conventional HVAC system especially in solar thermal cooling technologies. The most common types of solar cooling technologies are: solar absorption cooling system and solar desiccant cooling system. The use of a solar desiccant cooling system to reduce moisture from the air and to improve indoor air quality is found to be economical, environmental friendly and readily achievable in the tropics. In this study a feasibility study of solar desiccant cooling system in an institutional building under Queensland subtropical climate namely the city of Rockhampton will be presented using different types of solar collectors. The study will focus on system technical performance using TRNSYS 16 under a typical meteorological year TMY. It first introduces the issue of Indoor air quality, thermal comfort standards, humidity, air moisture, mould growth and then the technical performance of thermally activated desiccant cooling technology. Results showed that during cooling season 1.2 Coefficients of performance COP can be achieved with 60% of annual solar fraction if a 20 m2 of evacuated tube collectors area and 1.5 m3 of solar hot water storage volume installed section
Two solar collector / regenerators of the air circulation type have been designed, constructed and tested. Two new features are incorporated in a falling film type generator, in one of the designs. They are the use of atomizers to spray the solution and inclusion of wire meshes to increase the wetted area. The second model, which is of a basic falling film type, was used for comparsion purposes. The two models were tested side by side under Baghdad summer conditions. In addition to specifying the effects of the various operating parameters, the regeneration and collection efficiencies for both models are compared.
This paper presents an experimental study of the performance of a forced convection glazed solar collector/regenerator (C/R) operated under the meteorological conditions of Kaohsiung, Taiwan. The C/R is the key component of an open-cycle absorption solar cooling system because its performance directly indicates the system performance. The present results show that the counterflow case can improve the C/R efficiency when inlet solution concentration is low. The effects of individual parameters on the C/R performance are analyzed. Dimensionless heat and mass transfer coefficients are given.
A forced flow solar collector/regenerator is one of the effective ways of regenerating the weak liquid solution in an open cycle liquid desiccant air conditioner using solar energy. In this system, the weak solution flows over the absorber plate of a tilted collector/regenerator as a thin liquid film. The forced air stream, which flows parallel or counter to the solution film, removes the moisture which is evaporated from the liquid solution due to absorption of solar energy. The absorber plate of the collector/regenerator is blackened and glazed to enhance the solar energy absorption and protect it from the environment. To evaluate the thermal performance of the solar collector/regenerator, a computer model has been developed using calcium chloride as the desiccant. A parametric analysis of the system has been performed to calculate the rate of evaporation of water from the solution as a function of the system variables and the climatic conditions.
Preliminary results are presented from an analysis of the forced flow solar regenerator used for regenerating weak absorbent solutions, whose thermal performance depends on the rate of evaporation of water from the weak solution. A simple expression is derived to determine the desorption rate of water, assuming that solution temperature, concentration, and vapor pressure are constant at the arithmetic average of these values at the start and end of the regenerator. It is found that the effect of preheating the solution, or air, increases the rate of desorption due to the mass transfer potential increase, although solution regeneration is more effective while preheating the air than while preheating the solution.
An open cycle absorption refrigeration system is simulated and analyzed. The open cycle differs from the closed cycle in that the open cycle regenerates the weak absorbent solution by evaporating refrigerant to the earth's atmosphere rather than to a condenser. The solar collector used for the open cycle is one in which the weak absorbent solution flows as a fluid film over a flat, open, black surface. The absorbent solution is heated by the black surface and is regenerated by water evaporating to the atmosphere. It was found that the relationship between the collector length and the solution mass flow rate was tied to environmental factors such as wind and humidity when optimizing system performance. The system performance was simulated for five cities using actual weather data. The overall daily cooling COP's (cooling/incident solar) ranged from 0.09 to 0.45 for various conditions.
Absorption solar regeneration unit with open regeneration of solution
- Kakabayev
A large scale solar air conditioning pilot plant and its test results
- Kakabayev
Performance enhancement study of solar collector/regenerator for open-cycle liquid desiccant regeneration
- L J Ji
- B D Wood