No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Renewable energy for liquid desiccants air conditioning system: A review
... Significantly, in hot and humid regions the demand and energy consumption for applying ACSs is increasing. Currently, in these areas, ACSs include a major sector of building energy consumption (Fekadu and Subudhi 2018;Al-Qawasmi and Tlili 2018;Wang et al. 2018;Lertlakkhanakul, Yoon, and Choi 2010). ACSs assign a large part of the energy consumption of the building in the summer season. ...
... The results indicated that the inhabitants' behaviour of residential buildings in the saving of energy consumption is very effective. One of the effective criteria in utilizing ACSs is the consumer age (Fekadu and Subudhi 2018). Other important criteria are environmental pollution and the noise produced by ACSs that is increasingly significant. ...
... Also, satisfaction with the ACS used by older people to cool the building environment is important. Therefore, the age of household people is considered as a criterion in using ACSs (Fekadu and Subudhi 2018;Yoshino, Hong, and Nord 2017). ...
The present study provides potentially interesting for researchers in the novel integrated method of the fuzzy set qualitative comparative analysis (fsQCA) and digital design methodology to apply in the field of energy and sustainability of socio-technical systems (STSs) used in the building energy management (BEM). The research sample is the air-conditioning system (ACS). The social and technical aspects of ACS are satisfaction and energy consumption. Ten sustainability criteria are applied to assess and monitor the fields of energy consumption and satisfaction with the aim of achieving sustainable consumption in the use of ACSs for BEM. This action can be carried out by nesting a circuit in a microprocessor and microcontroller for use in a building energy management system (BEMS). According to, the circuit obtained from the assessment of the study can be practically implemented and assembled in a BEMS as online. This work can define a sustainability-based BEMS.
... According to the phase, desiccants are categorized as liquid desiccant and solid desiccant. Compared with solid desiccant, liquid desiccant has better moisture absorption ability, lower regeneration temperature, lower system construction cost, better ability in filtering microorganism [6,7]. ...
... Classifications of components, systems, material, cooling/heating methods and energy recovery in LDAS Rafique et al. [9] 2016 Applications of commercially available liquid desiccants and configurations of dehumidifiers Sahlot et al. [23] 2016 Components used in liquid desiccant systems Fu et al. [24] 2017 Impact of liquid desiccant dehumidification on indoor air quality Guo et al. [25] 2017 Photovoltaic thermal (PV/T) heat utilization for desiccant cooling and dehumidification Shukla et al. [26] 2017 Regeneration of liquid desiccant using solar energy Bai et al. [27] 2018 Modelling methods of membrane-based liquid desiccant heat and mass exchanger Fekadu et al. [7] 2018 Renewable energy utilization for LDAS Giampieri et al. [10] 2018 Thermodynamics and economics of typical liquid desiccants in LDAS Gómez-Castro et al. [28] 2018 Solar thermal regeneration for liquid desiccant systems Gurubalan et al. [29] 2019 Classifications and developments in components, materials and mathematical models in LDAS Liu et al. [30] 2019 Materials, components, systems and performances of membrane-based liquid desiccant air dehumidification Ren et al. [12] 2019 Heat and mass transfer improvement techniques for dehumidifiers and regenerators in LDAS Wen et al. [31] 2019 Correlations and enhancement of heat and mass transfer in liquid desiccant dehumidification Chen et al. [6] 2020 Types of dehumidifiers and the integrations of LDAS with different technologies Liu et al. [4] 2020 Electrically driven dehumidification technology in LDAS Qi et al. [5] 2020 ...
... In order to overcome the weakness of specific type of substance, the working pair of mixture-water is presented. For example, LiBr-TEG-H 2 O is raised to alleviate the corrosiveness of LiBr and the volatility of TEG [7]. ...
Liquid desiccant air-conditioning system (LDAS) becomes an attractive option for reducing the energy consumption of conventional air-conditioning systems. Despite lots of published papers on LDAS in various aspects, there is not yet a comprehensive and up-to-date review on the properties of liquid desiccants, while the selection of liquid desiccant plays essential role in the overall performance of LDAS. In this paper, a state-of-the-art review on the properties in regard of energy and environmental performance is delivered for present and potential liquid desiccants, including vapor–liquid equilibrium, specific heat capacity, safety concerns. The current situations and future concerns of liquid desiccant investigation can be obtained, while different kinds of liquid desiccant candidates can be compared and evaluated comprehensively. Existing liquid desiccant of halide salt faces severe drawback of corrosiveness in long-term use. Compared with existing liquid desiccants, the candidates of weak acid salt, ionic liquid and deep eutectic solvent behave low toxicity and friendly corrosiveness, whereas their weak moisture absorption ability, high cost or high viscosity is the bottleneck for further applications. Therefore, the mixture of them can be regarded as a promising candidate in LDAS applications, but the fundamental properties are urged to be measured. The work in this paper provides momentous reference and guidance for the exploration of new liquid desiccant as well as the evaluation of future prospect of LDAS.
... The results show a decrease in RE; a lower refrigeration effect can lower COP [31]. The latent heat of vaporization in the Air Conditioning (AC) system comes from the evaporation of refrigerant [32]. The closed container of R410A has the highest RE value. ...
The growing demand for air conditioning systems has driven research into alternative applications, such as seawater desalination. This study evaluates the performance of a modified window air conditioner (WAC) integrated with a vortex generator for desalination. Experiments were conducted using R410A refrigerant under four conditions: closed container (CC), without vortex (WV), connected vortex (CV), and separated vortex (SV). Seawater was heated via the condenser to 55–60°C, controlled by a thermostat, and data was collected every five minutes over eight hours. The thermodynamic properties of R410A were analyzed using Refprop software to determine refrigeration effect (RE), compression work (CW), and coefficient of performance (COP). Results indicate that the SV configuration achieved the highest evaporation rate (5.01 kg) but led to a lower COP (3.91) due to increased condenser temperature and compressor workload. Conversely, CC yielded the highest COP (5.08) by stabilizing the evaporator air temperature and reducing compressor effort. These findings suggest that vortex generators enhance evaporation rates but reduce system efficiency. Further research is needed to optimize vortex generator configurations to improve desalination efficiency while minimizing COP reduction.
... Where; MCdb -moisture content (% db), MCwb -moisture wet-basis (% wb). The useful energy required to evaporate 9.36 kg of water was estimated using the sensible heating equation (Fekadu & Subudhi, 2018); ...
A mix-mode solar dryer which incorporates a flat plate collector into a framed-rack dehydrator glazed with polythene was developed to address the difficulty encountered in drying tomatoes during bumper harvest times in Zaria, Nigeria. The evaluation results of the rack dryer using 10 kg of fresh tomatoes revealed a dry rate of 0.71 kg/hr and drying efficiency of 65.90 % when dehydrating tomatoes from an initial moisture content of 94 (% wb) to a final moisture content of 4.25 (% db). The efficiency of the dryer indicates its suitability for crop drying especially fruits and vegetables, with high moisture contents. This dryer will find great application in households and among operators of restaurants who can dry and store tomatoes hygienically within two days in batches for use during scarce periods.
... However, liquid desiccants require large volumes in the desiccant air-conditioning system and the liquid desiccant saline solutions face problems of increased corrosion and crystallization. Furthermore, some liquid desiccant materials are environmentally unfriendly and toxic [12]. ...
Air-conditioning (A/C) systems in tropical regions are characterized by significant energy consumption for latent load handling. Decoupling of the latent load from the A/C units can be achieved using a dedicated dehumidification system while the A/C systems handle only the sensible heat at high efficiencies. Desiccants are widely used in industry, and adsorbent materials that exhibit a unique isotherm shape, i.e. "S shape", have been developed extensively. Recently, activated carbons (ACs) have been discussed as effective adsorbents for dehumidification applications. Although pristine ACs are considered to be hydrophobic materials, certain surface treatments initiate surface phenomena that promote water vapour uptake at relative pressures above 0.4 due to microdroplet aggregation. This work reviews and reports the latest developments of sustainable activated carbons for dehumidification using a multiscale approach spanning from the sustainable precursor selection, “green” activation processes and surface functionalization, adsorption thermodynamics, and system-level developments. With the focus on sustainability, we demonstrate that water adsorption and viable adsorption range are gradually improving with the progressing research, and they are reaching operational values required for practical use. The unique adsorption process of water onto ACs is further explained in detail using solvation theory on the microdomains created by the hydrophilic functional groups while providing clarification of thermodynamic properties adopting the specificities of water/activated carbon adsorption pair. The predicted performance of a desiccant dehumidification system utilizing activated carbon is evaluated using the local weather conditions of numerous major cities worldwide. The highest dehumidification performances of activated carbon, as indicated by the unified SDP (specific dehumidification power) value, are reached particularly in cities that suffer from high humidity and temperature the most proving the viability of this cheap and sustainable material.
Graphical abstract
... An alternative method of dehumidifying air is by using desiccants, which are materials with a high affinity for water vapor and can effectively remove moisture from the air [7]. Thus, desiccants can be used in various applications, such as air conditioning, drying, and water harvesting from the air. ...
... Studies have shown that building energy consumption accounts for 30-40% of the total social energy consumption [1]. Moreover, air conditioning energy consumption accounts for 40-60% of building energy consumption [2,3]. Air source heat pumps constitute the most widely used air conditioning equipment in domestic residential buildings due to their energy saving, environmental friendliness, short investment return period, and low operating cost. ...
Nanoporous alumina sheets can inhibit the growth of the frost layer in a low-temperature environment, which has been widely used in air-conditioning heat exchangers. In this study, nanoporous alumina sheets with pore diameters of 30 nm, 100 nm, 200 nm, 300 nm, and 400 nm were prepared by using the anodic oxidation method with the conventional polished aluminum sheet as the reference. A comprehensive and in-depth analysis of the frosting mechanism has been proposed based on the contact angle, specific surface area, and fractal dimension. It was found that compared with the polished aluminum sheet, the nanoporous alumina sheets had good anti-frost properties. Due to its special interface effects, the porous alumina sheet with a 100 nm pore diameter had strong anti-frost performance under low temperatures and high humidity. In an environment with low surface temperature and high relative humidity, it is recommended to use hydrophilic aluminum fins with large specific areas and small fractal dimensions for the heat exchange fins of air source heat pump air conditioning systems.
... The selection of the proper liquid desiccant solution hinges on meeting certain characteristics related to low equilibrium vapor pressure at relatively elevated temperature, regeneration temperature, heat of absorption, viscosity in addition to low toxicity and corrosiveness [49]. Although conventional halide desiccants have high dehumidification capacity, especially lithium-based desiccants, they are very expensive and highly toxic [50]. Ionic liquid-based desiccants have also been used due to their low toxicity; however, they suffer from high heat of absorption, thus limiting their dehumidification performance in desiccant systems [32]. ...
Indoor humidity management is one of the most challenging aspects of the control of indoor environment and is energy intensive, especially in hot and humid climates. A promising approach is the removal of the water vapor from the room using hygroscopic materials, otherwise known as desiccants. Desiccant cycles are thermally driven but require a heat sink and electricity-driven mechanical parts for desiccant circulation. Accordingly, this work proposes a thermosyphon-driven membrane-based liquid desiccant loop for sustainable humidity pumping between two areas at different humidity conditions. Mathematical models were developed for the different system subcomponents, which were validated with published data and in-house experiments. The models were used in a parametric study to determine the influence of the design and operation parameters on the system performance under different air conditions surrounding its various sections.
It was found that the system was able to pump the air moisture from high to low and low to high humidity areas. Four cases were considered with outdoor conditions raging from moderate and hot and humid to semi-arid climates. The latent load removal density per unit area of the exposed membrane varied between 4 W/m2 to 35 W/m2 over the entire range of considered cases at required heat inputs varying between 150 W and 570 W respectively. The heat input increased with the channel height and the air humidity surrounding both system sides. The added sensible load depended on the heat sink temperature and was more than 65 % lower than removed latent load in most considered cases.
... In Ref. (Golubovic, Hettiarachchi, and Worek 2007), researchers compared the performance of DCHEs and GPHEs with RD (regular density)-type silica gel as a solid desiccant and found that DCHEs have a better output result in terms of lower exit humidity ratio and low processed air temperature. Researchers also found that a desiccant with a lower regeneration temperature has a higher coefficient of performance (COP) (Fekadu, Subudhi, and Reviews 2018;Oladosu, Baheta, and Oumer 2021). Some research work has been carried out on the coating of solid desiccants with metallic fins. ...
Desiccant-coated heat exchangers (DCHEs) allow the simultaneous removal of adsorption heat and moisture from the incoming process air and support the cause of sustainability through energy recovery and energy efficiency. This study investigated the performance of a solid desiccant material namely, metal-organic framework (MOF-A520), by means of static and dynamic experimental processes. The static experiment revealed that under the same environmental conditions, the adsorption capacity of MOF-A520 is at least 12% better than the adsorption capacity of the traditional Sorbead R desiccant. Additional dynamic experiments were conducted by coating MOF-A520 on an industrial type heat exchanger within a controlled air-tunnel environment. Under the process air temperature of 30 °C, 80% RH and regeneration temperature of 80 °C, the maximum total vapor adsorption amounts (Gvap), vapor adsorption amounts per unit contact area of fins (GA), and vapor adsorption per unit mass of MOF-A520 (GD) attain maximum values of 239.96 g, 0.052469 g/cm² and 0.67596 g/g, respectively. Overall, with a lower regeneration temperature of 60 °C and shorter desorption time of 20 minutes, MOF-A520 demonstrates its potential as a suitable desiccant material for air conditioning applications.
... On the other hand, the adoption of desiccant is convinced efficient to deal with dehumidification requirement, whose energy consumption is expected to be cut down up to 50% compared with CDAS [5]. Attributed to better moisture absorption ability, lower regeneration temperature, lower system construction cost and better microorganism filtering, liquid desiccant air-conditioning systems (LDAS) have been well studied by researchers and widely applied in daily life [6][7][8]. ...
Despite the recognition of its energy-saving potential, the promotion of liquid desiccant air-conditioning system is limited by the drawbacks of existing desiccants in long-term or large-scale use. Deep eutectic solvent with good bio- and eco- friendliness has not yet been tested for systematic study in air-conditioning system. In this paper, a deep eutectic solvent, ethaline, is utilized in a heat pump driven liquid desiccant air-conditioning system, whose energy, exergy, exergoeconomic and enviroeconomic performances are studied. Under basic condition of ambient temperature of 35 ℃ and relative humidity of 80%, its systematic coefficient of performance reaches 1.406 with exergy efficiency of 32.65%. Meanwhile, 52.36% CO2 emission can be reduced compared with conventional condensation dehumidification air-conditioning system. The payback period of such system at basic condition with 20 kW cooling load is 14.4 years, and it can be significantly reduced in applications with larger cooling load. Parametric analyses for different requirements and environments are conducted as well. The energy and environmental superiority of ethaline is more significant under more latent loads, higher supply air flow rate and lower fresh air ratio. Under ambient temperature ranging from 28 ℃ to 40 ℃, the effect of CO2 emission reduction for ethaline reaches to extents of more than 38%. The advantages of ethaline are further illustrated in comparison with other potential desiccant candidates, in aspects of toxicity, price and corrosiveness. The potential performance improvement approach for ethaline used as liquid desiccant is also proposed and discussed. The results in this paper demonstrate the promising prospect of ethaline quantitatively, and provide enlightening for exploration of new liquid desiccant. In pace with the broadening application of air-conditioning system, liquid desiccant air-conditioning system using such green desiccants can be promoted, which brings out great prospects in energy saving and CO2 emission reduction.
... These salts are also used to absorb moisture in industrial applications or construction applications. Comparisons of salts prepared using (Studak and Peterson 1988;Jones 2008;Ren et al. 2019;Fekadu and Subudhi 2018; Peladow DG Calcium Chlorıde 2014; Lithium Bromide Lab 2019; Lithium Chloride Granular Reagent 2019; Calcium Chloride Anhydrous 2019) sources are presented in Table 1. ...
Nowadays, with the rapid increase in world population, potable water shortage has started to create serious problems. Many factors such as increased water consumption, environmental problems and climate change cause the decrease in potable water resources. In this study, a fully automatic system which produces water from ambient humidity developed to provide solutions especially in areas where access to clean and potable water resources is difficult. Moisture and salt are used for raw material. CaCl 2 salt is not very good for moisture absorption, but when compared with other salts, it can provide a great advantage under human health and cost. The machine is also reinforced with electrical equipment and measures the ambient temperature, pressure values and humidity, consumed energy and prints it on the memory card (SD card) in real time. While the system is running, it can be controlled and read over the phone. Experiments have been carried out and the changes in the amount of water produced and the amount of salt consumed depending on the ambient humidity and temperature have been investigated. The amount of energy consumed by the system was also analyzed. It was observed that the amount of water produced was directly proportional to the ambient humidity.
... Desiccant cooling units do not require ozone-depleting refrigerants, and they can use solar thermal energy or waste heat, thus lowering peak electrical demand [15]. Although the concept of solar liquid desiccant air conditioning systems was proposed as far back as 1955 [16], there has been a lack of progress to commercially take advantage of these low-energy systems. ...
There is a need to control air temperature and humidity in humid regions, especially when fresh air is demanded. This study investigates the performance of a hybrid liquid desiccant (LD) air conditioning system with a direct expansion (DX) evaporative cooler. Temperature, relative humidity, and power consumption were measured and reported using a wireless data-logging system at the air conditioning unit's key locations. The results showed that the hybrid unit reached a 34 % saving in the cooling load. In addition, the air hybrid liquid desiccant air conditioning system with the direct expansion evaporative cooler saved about 32% in power consumption, compared to an uncooled desiccant air conditioning system that saved 23%.
... (Abbassi et al. 2017) compared the different desiccant cooling systems where the solar collector was used as the regeneration source. The regeneration of desiccant materials can be done by utilizing solar energy in different ways and also many renewable energy sources (Misha et al. 2012;Cheng and Zhang 2013;Jani et al. 2016;Guo et al. 2017;Shukla and Modi 2017;Speerforck et al. 2017;Fekadu and Subudhi 2018). However, there is a particular limitation on its access throughout the 24-hour operation for a day. ...
This paper proposes a novel scheme of biomass regenerated two-stage desiccant-supported greenhouse cooling in the tropical and sub-tropical countries. The system's goal is to provide the ideal thermal environment inside a greenhouse for the growth of different kinds of Orchid. The two-stage desiccant-based cooling is used in the proposed system to obtain a low humidity ratio inside the greenhouse. The desiccant is regenerated using a biomass-based heating system. The first law analysis and the exergy analysis of the system's individual components have been included in the study. The results of the thermal model (greenhouse temperature) have been compared with that of a reference model study available in the literature. With a mean absolute error for the humidity ratio and greenhouse air temperature of 4.3 percent and 4.5 percent, respectively. The model's predictions are in good agreement with the results of the reference model. The performance study of the proposed system reveals that the maximum temperature of the greenhouse air can be limited within the defined values even during July and September, when both the ambient humidity and the temperature are high. The proposed system COP th varies from a minimum of 0.54 to a maximum of 1.02 for a typical hot and humid day of July. The system can exhibit maximum exergy efficiency of 33% in the morning, while the ultimate exergy destruction occurs at the DW 1 (39.25%) and regeneration heater (21.69%). The payback period of the proposed system is 8.2 years considering 15 years’ life span.
... Under climate change and weather intensity, air conditioning is becoming inevitable for the comfort of human beings. Air conditioning demand is very high in hot and humid tropical regions with high humidity (Samuel et al., 2013;Fekadu and Subudhi, 2018;Burhan et al., 2021a). Such a humid tropical climate demands a higher latent than sensible cooling load. ...
Cooling has a significant share in energy consumption, especially in hot tropical regions. The conventional mechanical vapor compression (MVC) cycle, widely used for air-conditioning needs, has high energy consumption as air is cooled down to a dew point to remove the moisture. Decoupling the latent cooling load through dehumidification from the sensible cooling load can significantly improve the energy requirement for air-conditioning applications. Solid desiccants have shown safe and reliable operation against liquid desiccants, and several configurations of solid desiccants dehumidifiers are studied to improve their performance. However, the characteristics of solid desiccants are critical for the performance and overall operation of the dehumidifier. The properties of every desiccant depend upon its porous adsorbing surface characteristics. Hence, it has an optimum performance for certain humid conditions. Therefore, for a better dehumidification performance in a specific tropical region, the solid desiccant must have the best performance, according to the humidity range of that region. In this article, a theoretical methodology has been discussed to help the industry and chemists to understand the porous structural properties of adsorbent surfaces needed to tune the material performance for a particular humidity value before material synthesis.
... The absorption process holds and attracts moisture by its substances termed desiccants (Assilzadeh et al. 2005). Desiccants are also termed sorbents, which means the materials that can magnetize and handle other liquids or gases with a specified resemblance to water (Fekadu and Subudhi 2018). Moreover, the absorption schemes are the same as vapor compression (Julien et al. 2016) air condition modules but it varies in pressurization stages (Kalkan et al. 2012). ...
In recent times, solar energy has been utilized for refrigeration systems due to its efficiency and clean form of energy. Moreover, the evacuated tube collector (ETC)–assisted vapor absorption refrigeration system plays a significant role in the modern industrial world compared to the traditional electrical system. However, the conventional vapor absorption refrigeration system design is complex in nature and causes corrosion in the system. Therefore, in this research, novel Generalized Approximate Reasoning–Based Intelligent Control (GARIC) and Hybrid Ant Colony African Buffalo Optimization (HACABO) methods based on an ETC-linked 5-kW vapor absorption refrigeration system are proposed depending on lithium bromide-water (LiBr-H2O). Primarily, the Haryana region’s solar radiation and weather parameters were taken over a year to simulate the ETC system. ETC collects the solar energy for the refrigeration cycle, and the efficiency of the ETC is estimated using the GARIC method as per the input of solar radiation, collector area, and used solar energy. Moreover, the efficiency of the ETC is optimized using the proposed HACABO method. The modified polynomial fits curved equation is utilized for performance analysis. The simulation model of the solar cooling absorption system is carried out in the MATLAB platform. The coefficient of performance (COP) rate of the absorption cycle has gained 0.82% with the help of HACABO. Compared to other recent associated models, the proposed model has maximized the COP in the finest range.
This study aims to experimentally demonstrate a liquid desiccant systems effectiveness by using thermo-chemical fluid, such as aqueous solution of calcium chloride. This study evaluated the effect of operating temperatures on air properties (temperature, relative humidity, and moisture content) and system effectiveness by varying air flow rates. The system’s functionality was influenced by the operational temperature and air flow rate, and the dehumidification effectiveness was higher at low operating temperatures and low airflow rates. An ANN metamodel-based control strategy is also proposed for implementation in hybrid thermo-chemical networks with the help of system performance data and real-time data. The suggested ANN model’s results were validated using a variety of measuring techniques, including the RMSE, MAPE, correlation (R), and coefficient of determination (R²). The proposed ANN analysis achieved an excellent correlation between predicted and experimentally measured data.
This paper proposes a novel scheme of biomass-regenerated two-stage desiccant-supported greenhouse cooling in tropical and subtropical regions. The system’s goal is to provide the ideal thermal environment inside a greenhouse for the growth of different kinds of Orchids. Two-stage desiccant-based cooling is used in the proposed system to obtain a low humidity ratio inside the greenhouse. The desiccant is regenerated using a biomass-based heating system. The first law analysis and the exergy analysis of the system’s individual components have been included in the study. The results of the thermal model (greenhouse temperature) have been compared with those of a reference model study available in the literature. The mean absolute error for the humidity ratio and greenhouse air temperature is 4.3% and 4.5%, respectively. The model’s predictions are in good agreement with the results of the reference model. The performance study reveals that the maximum greenhouse air temperature can be restricted within 26 °C even during the peak sunshine hours for a typical day in May which represents the peak summer season in India. The proposed system COPth varies from a minimum of 0.54 to a maximum of 1.02 for a typical hot and humid day of July. The proposed system can exhibit a maximum exergy efficiency of 33% at 6 AM for a representative day in July. The maximum exergy destruction occurs at the DW1 (39.25%) and regeneration heater (21.69%). The payback period of the proposed system is 8.2 years, considering a 15-year life span.
This paper presents multi-objective optimization of a biomass heating-based two-stage desiccant-supported greenhouse cooling system used for Orchids cultivation in hot and humid weather conditions. The simulation model has been developed considering thermodynamics, economic, and environmental aspects. The thermal coefficient of performance (COPth) of the system and greenhouse temperature have been predicted for the five most impactful months (March, May, August, September, and December) corresponding to the respective seasons of Spring, Summer, Monsoon, Autumn, and Winter of a calendar year. The system maintains the peak average greenhouse temperature at a maximum of 26°C during the prominent sunshine period (12 hours) in May while ensuring a minimum of 18°C during nighttime. In terms of system components, the residue boiler stands out as the significant contributor to exergy destruction (45%), followed by regeneration heater 1 (22%), DW1 (7%), and the heat recovery water heater (6%) during the critical operational month of August. Multi-objective optimization has also been conducted using the optimization toolbox provided in MATLAB-R2017a to determine the optimal performance and operating conditions of the Two-stage Desiccant Cooling System (TSDC) system. The optimal conditions display the corresponding total cost rate, considering capital and maintenance costs, operating cost, CO2 penalty costs, and exergetic efficiency.
To avoid problems such as low efficiency of liquid desiccant processes in high humidity environments, vacuum membrane distillation (VMD) solution regenerators are proposed. This study investigates the conjugate heat and mass transfer mechanism in the vacuum membrane distillation solution regeneration. The study reveals that the solution temperature and concentration in the hollow fiber membrane tube exhibit a tower-shaped distribution, with the lowest temperature near the membrane surface and the highest concentration at the outlet. The membrane flux decreases along the direction of the solution flow, ranging from 0.62 to 0.36 g/(m2·s). Increasing the solution flow rate and vacuum degree enhances the heat and mass transfer, while increasing the solution concentration reduces the heat and mass transfer. The Nusselt and Sherwood number formulas applicable to the VMD solution regeneration process were fitted, which is more accurate than the empirical formulas at atmospheric pressure. The resistance distribution during the solution regeneration process in VMD shows that the membrane-side resistance has a significant impact on the heat and mass transfer during solution regeneration, with the membrane-side thermal resistance accounting for 91% of the total resistance in the heat transfer process and 67% in the mass transfer process. The findings in this paper can more accurately guide the design of vacuum membrane distillation solution regenerators.
Thermal management, including heating and cooling, plays an important role in human productive activities and daily life. Nevertheless, in the actual environment, almost all the ambient scenarios come with the challenge that the objects are located in a quite dynamic and variable environment, which includes fluctuations in aspects such as space, time, sunlight, season, and temperature. It is imperative to develop low-energy or even zero-energy thermal-management technologies with renewable and clean energy. In this review, we summarised the latest technological advances and the prospects in this burgeoning field. First, we present the fundamental principles of the daytime passive radiative cooling (PDRC) thermal management device. Next, In the domain of dual-mode systems, they are classified into various types based on the diverse mechanisms of transitioning between cooling and heating states, including electrical responsive, mechanical responsive, temperature responsive, and solution responsive. Furthermore, we conducted an in-depth analysis of the principles and design methodologies associated with these categories, followed by a comparative assessment of their performance in radiative cooling and solar heating applications. Finally, this review presents the challenges and opportunities of dynamic dual mode thermal management, while also identifying future directions.
Desiccant agents (DAs) have drawn much interest from researchers and businesses because they offer a potential method for lowering environmental impact, increasing energy efficiency, and controlling humidity. As a result, they provide a greener option to conventional air conditioning systems. This review thoroughly analyzes current issues, obstacles, and future advancements in liquid desiccant agents (LDAs) for drying, air conditioning, and dehumidification applications. The importance of LDAs in lowering energy use and greenhouse gas emissions is highlighted, emphasizing their potential for environmentally friendly humidity control. The current review examines key parameters such as novel materials, enhancing desiccant qualities, integration with technologies, and long-term durability while examining recent developments in LDAs and investigating their applications in diverse industries. The main conclusions from the evaluated publications in this review are also highlighted, including developments in LDAs, new applications, and developing research fields. Overall, this review advances knowledge of LDAs and their potential to shift humidity control systems toward sustainability and energy efficiency.
The world is facing a rapid increase of air conditioning of buildings. It is the motivation of Annex 80 to develop, assess and communicate solutions of resilient cooling and overheating protection. Resilient Cooling is used to denote low energy and low carbon cooling solutions that strengthen the ability of individuals and our community to withstand, and prevent, thermal and other impacts of changes in global and local climates. It encompasses the assessment and Research & Development of both active and passive cooling technologies of the following four groups: Reduce heat loads to people and indoor environments. Remove sensible heat from indoor environments. Enhance personal comfort apart from space cooling. Remove latent heat from indoor environments. The present review sums up the state of the art in cooling solutions which may be regarded as resilient. Its main objective is to systematically describe the available cooling solutions, their physical basis, their benefits and limitations, their technology readiness level, their practical availability, and applicability. Doing so, the State-of-the-Art Review forms the basis for the work of EBC Annex 80.
The poor heat transfer performance of the heat exchanger leads to low heat storage efficiency of the latent heat storage device. To improve the heat transfer performance of the heat exchanger, a novel annular fin with inclined angle is proposed to enhance heat transfer of the heat exchanger. 12 fins with different structural parameters are designed and welded to the inner tube wall of the heat exchanger. The simulation model is in good agreement with the literature and the model is considered to be reliable. Based on the enthalpy-porosity model, the liquid fraction, temperature distribution, melting front, energy storage density and heat storage rate were used to compare and optimize the structural parameters of the annular fins. Results demonstrated that the difference in complete melting time due to the number of fins, fin arrangement, fin length and fin angle were 43 min, 85 min, 17 min and 10 min, respectively. The fin arrangement was the most significant in reducing the heat storage time. Compared to N = 4 and uniformly distributed fins, non-uniformly distributed fins reduced the total melting time of stearic acid by 53.13 % and 20.54 %. To be conclusive, the addition of non-uniformly distributed annular fins with 70° inclination enhanced the heat transfer in the heat exchanger and saved a significant amount of heat storage time.
This study provides a high-level overview of alternative energy sources that can be harnessed to power agricultural operations, focusing on renewable energy technologies. When thinking about the overall economy around the globe, agriculture is vital. Energy is required at each step of production, from fertilizer production to fueling tractors for planting and harvesting. The high energy prices and unpredictable energy market significantly affect the input energy costs. Energy efficiency methods, when properly applied, and the use of farm’s renewable energy sources could assist agricultural producers in saving energy-related costs. Renewable energy resources in the form of solar, biomass, wind, and geothermal energy are abundantly available in the agriculture sector. This review aims to explore renewable energy as an alternative energy source for efficient energy management in agriculture. It discusses the potential benefits, challenges, and opportunities associated with adopting renewable energy technologies in the agricultural sector. Our research adds value by presenting a comprehensive overview of alternative energy sources and their applicability in energy management. By highlighting the benefits and potential challenges associated with each option, we provide valuable insights for agricultural stakeholders and researchers aiming to transition toward sustainable energy practices in the sector. Better energy management is intertwined with problems that need a broader strategy than has so far been used. In a nutshell, transitioning to alternative energy sources for energy management in agriculture holds great promise for reducing greenhouse gas emissions, improving energy efficiency, and promoting sustainability in food production. However, successful implementation requires addressing technical, economic, and policy barriers while fostering knowledge dissemination and capacity building among farmers and stakeholders
Internal space cooling technology is pushing toward promoting alternatives from conventional vapor compression systems to mitigate global warming. Many innovative cooling systems are currently focusing on Research and development (R&D) and commercialization. An evaporative cooling system is one of the possible solutions for vapor compression systems. Despite showing a promising alternative to vapor compression systems, their market penetration is insignificant in society. This stems from the challenges inherent within its operation in diverse climate conditions. In this critical review, various evaporative cooling systems along with their recent developments, were presented and discussed. In search of best outcome and limitation of evaporative cooling systems, a comparison of the performance of selected evaporative cooling system were discussed further. The current review also encapsulates the fundamentals and working principles of various dehumidification systems used in the industrial, residential, and agricultural sectors. Then, the solid and liquid desiccant dehumidification systems were further explored, and their effects on the evaporative cooling system were analyzed. Finally, the liquid desiccant and membrane dehumidification systems were comprehensibly reviewed with their effects on the evaporative cooling system. Based on the energy-saving potential analysis, it was found that independent dehumidification before cooling is an effective method to improve the efficacy of the evaporative cooling system in comparison to the conventional approach at different outdoor conditions. Also, an enhanced evaporative cooling system was found to be a promising replacement for vapor compression system. To provide thermal comfort in hot and humid conditions, membrane dehumidification with a dew point evaporative cooling system shows promise as a substitute air-cooling technology with reduced power usage.
Liquid desiccant air‐conditioning system has received increasing attention due to the urgent demand for humidity control and antibacterial in today's medical environment. In this system, the main parameters affecting the dehumidification performance are the specific surface area, hydrophilicity and wettability of the packing material, and the nanofiber membrane has those characteristics. Here, polyacrylonitrile/lithium chloride nanofiber membrane was fabricated by electrospinning with island nozzle. The nanofiber membrane had the dehumidification capacity with moisture absorption of 3.72 g/g. Simultaneously, the antibacterial rate against Escherichia coli and Staphylococcus aureus was higher than 99%, which satisfied the specifications for air purification antibacterial materials in the medical and health sectors (GB/T 18801‐2015). More importantly, the weight per unit time and the thickness per unit area of the nanofiber membrane fabricated with island nozzle were 2.4 times and 3.4 times of those fabricated with single nozzle, respectively, indicating that the preparation efficiency was significantly improved, which provided a scheme for the rapid formation of nanofiber membranes.
Abtstract
Significant focus has been placed on improving Indoor Air Quality (IAQ) due to the emergence of the large-scale severe acute respiratory syndrome (SARS) virus epidemic in the air conditioning system of buildings. There is also a need for an adequate air ventilation system that balances energy needs with air quality. This led to the discovery of liquid desiccants which have the ability to enhance air quality and lower primary energy usage as an alternative to the standard air dehumidification technology. Therefore, this study was conducted to investigate the dehumidification and regeneration processes in a Fin and tube liquid desiccant system. This involved flowing air horizontally while the ionic liquid flowed through the cooling or heating coil vertically downward to create a cross-flow fin and tube configuration. In the testing process, we obtained measurements of relative humidity and dry bulb temperature inlet and outlet from ducting by varying the input parameters. Moreover, the differential humidity ratio of the inlet and output process for the dehumidification and regeneration was observed to be essential for the dehumidifier performance indices. The experimental result showed that the system absorbed a humidity ratio of 5.5 g/kg during the dehumidification process and released 10.7 g/kg during regeneration.
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.
Air-conditioning (AC) systems, which operate on traditional vapor compression refrigeration (VCR) systems, consume a substantial proportion of the world’s electricity consumed by the building industry. In the scope of decreasing greenhouse gas emissions, energy consumption, heating, ventilation, and air conditioning industries have focused on finding alternatives to electrically operated VCR systems. A combination of a liquid desiccant dehumidification system (LDDS) with a VCR system has been recommended as a superior substitute in warm and moist climates. The focus of this research article is to design and fabricate a small-scale 5 kW hybrid LDDS system by integrating the distinct technologies mentioned above. Additionally, data collected on the vapor pressure of potassium formate (KCOOH) at various solution concentrations and temperatures is being collected to assist in encouraging research and determine the optimal concentration range. In this study, experimental analysis and comparison of dehumidification performance was conducted between two desiccants by analyzing the effects of input variables ((Formula presented.), (Formula presented.), and (Formula presented.)) on the output response ((Formula presented.), (Formula presented.), and (Formula presented.)). The results showed that the solution with a 69.92% KCOOH concentration had nearly the same vapor pressure as a solution with a 35% LiCl concentration. Moreover, it was revealed that the lowest values of (Formula presented.) and (Formula presented.) and the highest value of (Formula presented.) yield maximum values of the output responses. At the same combination of input variables, the KCOOH desiccant has a much higher hybrid system coefficient of performance than the LiCl desiccant.
The overall performance of photovoltaic (PV) panels is prejudiced by the operating temperature of the solar cell owing to the absorbed solar radiation. In this experimental study, the in-house hybrid PV/thermal (PV/T) system is designed, fabricated, and parametrically studied for effective and practical applications of the solar panels. The water and water-based nanofluids are used for the active cooling of the PV/T system. The effect of phase change material (PCM) along with the active cooling is also studied, and results are comprehensively discussed. The in-house stable water-based Al2O3 and TiO2 nanofluids are engineered by the two-step method with two different nanoparticle concentrations of 0.05 and 0.1 vol.%. The thermal conductivity and stability of the nanofluids are experimentally measured and discussed to understand their effects on heat transfer from the PV panel. The thermal conductivity of nanofluids is increased with the concentration of nanoparticles in the base fluid. The maximum enhancement of around 30% is observed with Al2O3-water nanofluid at a concentration of 0.1 vol.%. The PV/T system is experimentally simulated in the indoor experimental setup with the solar simulator to provide the variable intensity of solar irradiance from 450 to 1050 W/m². The maximum decrement in the panel’s temperature is found to be around 25% using both active and passive cooling simultaneously and the electrical efficiency is improved by approximately 10.3% at the 1050 W/m². The electrical efficiency has found 13% more with Al2O3-water nanofluid of 0.1 vol% as compared to water cooling at 450 W/m². The use of nanofluids also improved the system’s thermal efficiency compared to the water, and the maximum improvement of around 10% is achieved with the Al2O3-water nanofluid at 0.1 vol.% concentration. These results are significant for the design of the PV/T system from the application viewpoint.
Liquid desiccant dehumidification technology as an efficient way of handling moisture load has attracted much attention, while the performance of liquid desiccant dehumidifiers has characteristics of uncertainty and time-varying in actual runtime, limiting its application fields. Thus, it is necessary to develop dynamic control methods to achieve stable and efficient operation. As the liquid desiccant dehumidification process is a multi-parameter, time-varying and large delay nonlinear dynamic process, therefore it is difficult to achieve the dynamic control. In this paper, dynamic control methods of the liquid desiccant dehumidification process were studied experimentally for the first time and main difficulties in the dynamic control of the liquid desiccant dehumidification process were presented clearly, helping to learn more knowledge on dynamic control process and facilitate the development of control methods. PID control as a classic control method was applied to control the liquid desiccant dehumidification process firstly, the result showed that it requires long adjusting time to follow the command and is not suitable to control nonlinear dynamic process with large delay. Novel fuzzy logic control (FLC) as an advanced control method was implemented as well, the result demonstrated that it follows command quickly while is unable to maintain the new set point accurately. Then reasons for shortcomings of each control method were analyzed. Along with the above analysis, a new control method, combining the PID control and novel FLC was developed. The command following experiment and disturbance rejection experiment for the newly developed control method were conducted. Control performances are great and validate the feasibility of the new control method. Besides, the newly developed control method also provides a good reference for achieving the dynamic control of a multi-parameter, time-varying, nonlinear dynamic process with large delay.
Desiccant systems have found applications in a very large variety of industrial and daily usage products including the new HVAC installations. The dehumidifier is one of the essential parts of those systems, which severely affects the whole system performance. This paper theoretically and experimentally studies the performance of the cross flow dehumidifier, which has been less studied than the counter flow dehumidifier, although it is more applicable in practice. Channel gauze structured packing was used in the dehumidifier and a LiCl aqueous solution was used as the liquid desiccant. The humidity reduction and dehumidifier effectiveness were adopted as the dehumidifier performance indices. The effects of the dehumidifier inlet parameters, including inlet air and desiccant flow rates, inlet air and desiccant temperature, inlet desiccant concentration and inlet air humidity ratio, on the two indices were investigated. The characteristics of the dehumidifier performance agreed well with the other studies reported in the open literature.
Recently, solid desiccant air conditioning system has been proposed as an alternative to the conventional vapor compression refrigeration air conditioning systems for efficient control over humidity of conditioned air especially in hot and humid areas. The solid desiccant cooling can be more favorable over the traditional vapor compression refrigeration air conditioners, because it assures more accessible, economical and cleaner air conditioning. It is still more important when it is powered by free energy sources like solar energy and waste heat with temperatures of between 60°C and 80°C. In addition, it can significantly reduce the operating cost as well as save energy. In the present paper, principle of solid desiccant cooling system is recalled and its technological applications and advancements are discussed. Through a rigorous literature review, different configurations of desiccant cooling cycles, conventional and hybrid desiccant cooling cycles, different types of mathematical models of rotary desiccant dehumidifier, performance evaluation of desiccant cooling system, technological improvement and the advantage it can offer in terms of energy and cost savings are highlighted. This paper also gives a detailed account of the general features and performance of the solid desiccant cooling system when it is powered by solar energy or industrial waste heat for regenerating the desiccant. This review is useful for making opportunities to further research of solid desiccant cooling system and its feasibility which is becoming common in the coming days.
Electrically-driven compression chillers are the commonly used technology for cooling and dehumidifying air. Open sorption systems driven by solar heat are an alternative to conventional air dehumidification technology and may reduce primary energy consumption. For air dehumidification, liquid desiccant systems may exhibit some process engineering and thermodynamic advantages in comparison to solid desiccant systems. The liquid desiccant must exhibit low equilibrium water vapour pressures at the available heat rejection temperature level to achieve low air dew point temperatures and thus a strong air dehumidification with comparably low driving temperatures. Desiccant mass fractions should be as low as possible, but in order to achieve low vapour pressures required desiccant mass fractions may surpass the solubility limit.
The dehumidifier is one of the main components in open-cycle liquid desiccant air-conditioning systems. An experimental study was carried out to evaluate the performance of a solar thermally driven, low-flow, falling-film, internally-cooled parallel- plate liquid desiccant air-conditioner in Kingston, Ontario at Queen’s University. A solution of LiCl and water was used as the desiccant. Unlike high-flow devices, the low-flow of desiccant solution flowing across the unit’s dehumidifier and regenerator sections produces large variations in solution concentration. In this study, a series of tests were undertaken to evaluate the performance of the dehumidifier section of the unit.
Results presented are based on mass flow and energy transport measurements that allowed the moisture transport rate between the air and liquid desiccant solution to be determined. Based on these results, a relationship between the desiccant concentration and the rate of dehumidification rate was found and the effect of inlet-air humidity on the dehumidification effectiveness identified. The moisture removal rate of the system was found to range from 1.1 g/s to 3.5 g/s under the conditions evaluated. These result corresponded to an average dehumidification effectiveness of 0.55.
In this work a novel energy efficient air-conditioning system utilizing lithium chloride (LiCl) solution as liquid desiccant has been proposed and simulated. The simulation of this system is mainly formulated with two packed columns, one for regenerating the weak desiccant and the other for the dehumidification of ambient air. The air is first dehumidified in the dehumidifier and then sensibly cooled in the indirect and direct evaporative coolers. First and second laws of thermodynamics have been used to analyze the effect of five key variables on the performance of the system. High efficiency could be achieved if proper values of these variables are selected.
Energy is inevitable for human life and a secure and accessible supply of energy is crucial for the sustainability of modern societies. Continuation of the use of fossil fuels is set to face multiple challenges: depletion of fossil fuel reserves, global warming and other environmental concerns, geopolitical and military conflicts and of late, continued and significant fuel price rise. These problems indicate an unsustainable situation. Renewable energy is the solution to the growing energy challenges. Renewable energy resources such as solar, wind, biomass, and wave and tidal energy, are abundant, inexhaustible and environmentally friendly.
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.
This paper presents a numerical analysis of three desiccant air-conditioning systems equipped with different indirect evaporative air coolers: (1) the cross-flow Maisotsenko cycle heat and mass exchanger (HMX), (2) the regenerative counter-flow Maisotsenko cycle heat and mass exchanger and (3) the standard cross-flow evaporative air cooler. To analyze the desiccant wheel and the indirect evaporative air coolers, the modified ε-NTU-model was used. The simulations were performed under assumption that the desiccant wheel is regenerated with air heated to relatively low temperature values (50–60 °C), which can be produced with solar panels in typical moderate climatic conditions. It was established that the main advantage of the presented solutions is that they can provide comfort conditions even with less effective dehumidification. The different systems were compared under variable selected operational factors (i.e. inlet air temperature, humidity and regeneration air temperature). The analysis allowed establishing the advantages and disadvantages of presented solutions and allowed estimating their application potential.
Liquid desiccant air-conditioning system is a novel air-conditioner with good energy saving potential. For the liquid desiccant air-conditioning system, the energy consumption mainly relies on the regeneration process of desiccant solution. As the regeneration process of the liquid desiccant air-conditioning system only needs low-grade energy, solar energy (a kind of renewable energy) can be used to regenerate the desiccant solution and the solar desiccant regeneration system has attracted many attentions. In this paper, recent theoretical and experimental works on solar thermal regeneration method and solar electrodialysis regeneration method of the liquid desiccant air-conditioning system are extensively reviewed. Moreover, the comparison of solar TH regeneration method and solar electrodialysis regeneration method is discussed. The results showed that compared to the solar thermal regeneration system, the solar electrodialysis regeneration system is more energy-efficient but expensive.
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.
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.
The corrosion problem of traditional liquid desiccants hinders the development of solar liquid desiccant air conditioning system. Ionic liquids (ILs) could be a possible substitute because of their low corrosion to metals. According to the characteristic of cation and anion, two ILs 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim]BF4) and 1,3-dimethylimidazolium acetate ([Dmim]OAc) were selected for possibility investigation. The experimental results demonstrated that the surface vapor pressure of [Bmim]BF4 aqueous solution was so high that it was not suitable for dehumidification. With comparing the structure of [Bmim]BF4 and 1-ethyl-3-methylimidazolium tetrafluoroborate ([Emim]BF4), it was found that for imidazole salts with the same anion, as the alkyl chain of the cation becomes shorter, the surface vapor pressure of its aqueous solution would be lower. In addition, simulation model was used to compare the dehumidification performance of [Dmim]OAc and [Emim]BF4 with that of the traditional desiccants lithium Chloride (LiCl) and lithium bromide (LiBr). The results showed that in the same condition, [Dmim]OAc with an inlet mass concentration of 81.7% and [Emim]BF4 of 85.5% could reach the same dehumidification rate as LiCl of 40.9% and LiBr of 45.0% mass concentration. Better dehumidification performance of [Dmim]OAc than that of [Emim]BF4 was achieved, thus, like [Emim]BF4, [Dmim]OAc can also be a promising substitute for traditional desiccant.
This paper studies the feasibility of using a solar-powered liquid desiccant system to meet both building cooling and fresh water needs in Beirut humid climate using parabolic solar concentrators as a heat source for regenerating the liquid desiccant. The water condensate is captured from the air leaving the regenerator. An integrated model of solar-powered calcium chloride liquid desiccant system for air dehumidification/humidification is developed. The LDS model predicted the amount of condensate obtained from the humid air leaving the regenerator bed when directed through a coil submerged in cold sea water. An optimization problem is formulated for selection and operation of a LDS to meet fresh water requirement and air conditioning load at minimal energy cost for a typical residential space in the Lebanon coastal climate with conditioned area of 80m2 with the objective of producing 15l of fresh drinking water a day and meet air conditioning need of residence at minimum energy cost. The optimal regeneration temperature increases with decreased heat sink temperature with values of 50.5°C and 52°C corresponding to sink temperatures of 19°C and 16°C.
The processes occurring in a packed bed dehumidifier, which is part of a liquid desiccant solar cooling system, are mathematically simulated. The air flows in a counter flow direction to the liquid desiccant (CaCl2). The effect of varying the air, liquid flow rates and bed geometry are studied in addition to studying the effect due to varying the air and liquid desiccant inlet coditions. The inlet temperature of the liquid desiccant during the air dehumidification process has a strong effect on the other parameters, while the air inlet temperature has a negligible effect. It is also noticed that higher temperatures of air and while the air inlet temperature has a negligible effect. It is also noticed that higher temperatures of air and liquid desiccant enhance the liquid desiccant regeneration processes but by different ratios. The study showed that both the air and liquid desiccant flow rates have negligible effect on the bed exit humidity ratio of air whereas the liquid flow rate has a strong effect on the bed exit moisture content of the liquid. It is also observed that increasing the air flow rate enhances the liquid desiccant regeneration (air humidification) process. Regardless of the inlet moisture content of the liquid desiccant, it is found that as the product (LAs) gets larger, the exit air humidity gets less.
Liquid desiccant cooling systems are especially suitable for solar energy applications. The liquid desiccants can be regenerated at temperatures below 80°C and the concentrated and diluted desiccants can easily be stored to provide a high energy storage capacity for air dehumidification and cooling. Special absorption processes are necessary to achieve an optimal air dehumidification and simultaneously a high energy storage capacity. The dominating effects on the absorption process are discussed in detail. For efficient dehumidification the temperature of the absorption process and the inlet concentration of the salt solution are of major importance. For a high energy storage capacity a high air to solution mass ratio is required to achieve great differences between salt inlet and outlet concentrations. A high mass ratio corresponds to a small desiccant flow. New dehumidifiers have been developed and tested, to achieve an efficient air dehumidification and high storage capacity. They dehumidify air by a very small flow of a hygroscopic aqueous salt solution, e.g. LiCl–H2O in an internally cooled absorption process. Experimental results of air dehumidification and storage capacities are reported. Mass transfer coefficients, used in numerical models, have been identified by absorption experiments and enable the reliable sizing of dehumidifiers.
Heat and mass transfer between air and falling desiccant film is investigated for inclined parallel and counter flow configurations. Two different configurations are proposed and parametrically analyzed. Effect of inclination angle is examined to study enhancements in dehumidification and cooling processes of the air and regeneration of liquid desiccant in terms of pertinent parameters. Cu-ultrafine particles are also added to the desiccant film to investigate the enhancement in heat and mass transfer between the air and the desiccant film. The pertinent parameters are air and desiccant Reynolds numbers, inlet conditions for both air and liquid desiccant, Cu-ultrafine particles volume fraction, and thermal dispersion. It is shown that inclination angle plays a significant role in enhancing the dehumidification, cooling, and regeneration processes.
Some ionic liquids have dehumidification capacity and are non-corrosive to metals. Based on the Finite Difference Method, the heat and moisture transfer model of the counter-flow dehumidifier was established. Using this model, the dehumidification capacity of one kind of ionic liquids 1-Ethyl-3-methylimidazolium Tetrafluoroborate ([EMIM]BF4) and traditional desiccant lithium bromide (LiBr) was compared in equivalent conditions. The results show that the dehumidification performances of the two solutions both improve with the increase of air flow rate, solution flow rate and air humidity. Even though the dehumidification rate of [EMIM]BF4 is a little lower than that of LiBr, such difference could be reduced by increasing the mass concentration of [EMIM]BF4. Meanwhile, compared with traditional desiccants, [EMIM]BF4 solution has significantly lower corrosion to metals and does not crystallize at high mass concentration, which render it a possible substitute of existed desiccants in liquid desiccant air conditioning systems.
Liquid desiccants are energy efficient in air dehumidification. A significant amount of research has been conducted on liquid desiccant systems, but little attention has been paid to the control issues surrounding such system. In this study, a novel dedicated outdoor air-conditioning system that adopts liquid desiccant dehumidification is proposed. A simulator of the proposed system is built on the TRNSYS platform. Control methods for the supply air dehumidification and solution regeneration processes are presented, and their effectiveness is evaluated. Two control strategies are developed for the proposed liquid desiccant system based on the evaluation results. The control performances of these two strategies are compared under different operation conditions using simulation tests.
In this paper, the principles underlying the operation of desiccant cooling systems are recalled and their actual technological applications are discussed. Through a literature review, the feasibility of the desiccant cooling in different climates is proven and the advantages it can offer in terms energy and cost savings are underscored. Some commented examples are presented to illustrate how the desiccant cooling can be a perfective supplement to other cooling systems such as traditional vapour compression air conditioning system, the evaporative cooling, and the chilled-ceiling radiant cooling. It is notably shown that the desiccant materials, when associated with evaporative cooling or chilled-ceiling radiant cooling, can render them applicable under a diversity of climatic conditions.
A solar-regenerated liquid desiccant ventilation pre-conditioning system has been proposed for use in hot and humid climates. The system aims to dehumidify the ventilation air which is the major source of latent load. A heat exchanger is used to cool the dehumidified air instead of typical evaporative cooling to maintain the dryness of the air. The use of solar energy at the regeneration process and cooling water from a cooling tower makes the system more passive. The simulation procedure for the proposed system has been presented. By inputting the climatic data and the physical parameters of all equipments, the operating parameters at each equipment and the performance parameters of the system can be evaluated. The simulation procedure is demonstrated by showing the daily profiles of the operating and performance parameters on a typical day as well as investigating the influence of the selected operating parameters on the system performance. The results suggest that the most influential parameters are solar radiation, ventilation rate, and desiccant solution concentration. The balance between the water removed at the dehumidifier and that evaporated at the regenerator needs to be considered to maintain uniform performance during continuous operation.
The rapidly growing world energy use has already raised concerns over supply difficulties, exhaustion of energy resources and heavy environmental impacts (ozone layer depletion, global warming, climate change, etc.). The global contribution from buildings towards energy consumption, both residential and commercial, has steadily increased reaching figures between 20% and 40% in developed countries, and has exceeded the other major sectors: industrial and transportation. Growth in population, increasing demand for building services and comfort levels, together with the rise in time spent inside buildings, assure the upward trend in energy demand will continue in the future. For this reason, energy efficiency in buildings is today a prime objective for energy policy at regional, national and international levels. Among building services, the growth in HVAC systems energy use is particularly significant (50% of building consumption and 20% of total consumption in the USA). This paper analyses available information concerning energy consumption in buildings, and particularly related to HVAC systems. Many questions arise: Is the necessary information available? Which are the main building types? What end uses should be considered in the breakdown? Comparisons between different countries are presented specially for commercial buildings. The case of offices is analysed in deeper detail.
The regenerator is one of the essential components in a liquid desiccant air-conditioning system, whose efficiency directly influences the system performance. A performance test-bed for a cross-flow regenerator was established in the present analysis. Celdek structured packings were used in the regenerator and LiBr aqueous solution was used as the liquid desiccant. Moisture removal rate and regenerator effectiveness are adopted to describe the mass transfer performance of the regenerator. Effects of air and desiccant inlet parameters on the regenerator performance are experimentally investigated, and performance comparisons between present cross-flow regenerator and other counter-flow configurations available in the literature are also carried out. The comparison results show that the impacts of air and desiccant inlet parameters show similar tendency with those of counter-flow regenerators. A dimensionless mass transfer correlation is proposed, which gives results in good agreement with the experimental findings.
The paper presents a new desiccant cooling cycle to be integrated in residential mechanical ventilation systems. The process shifts the air treatment completely to the return air side, so that the supply air can be cooled by a heat exchanger. Purely sensible cooling is an essential requirement for residential buildings with no maintenance guarantee for supply air humidifiers. As the cooling power is generated on the exhaust air side, the dehumidification process needs to be highly efficient to provide low supply air temperatures. Solid rotating desiccant wheels have been experimentally compared with liquid sorption systems using contact matrix absorbers and cross flow heat exchangers. The best dehumidification performance at no temperature increase was obtained in an evaporatively cooled heat exchanger with sprayed lithium chloride solution. Up to 7 g kg−1 dehumidification could be reached in an isothermal process, although the surface wetting of the first prototype was low. The process then provides inlet air conditions below 20 °C for the summer design conditions of 32 °C, 40% relative humidity. With air volume flow rates of 200 m3 h−1 the system can provide 886 W of cooling power.A theoretical model for both the contact absorber and the cross flow system has been developed and validated against experimental data for a wide range of operating conditions. A simulation study identified the optimisation potential of the system, if for example the surface wetting of the liquid desiccant can be improved.
Growing demand for air conditioning in recent years has caused a significant increase in demand for primary energy resources. Solar-powered cooling is one of the environmentally-friendly techniques which may help alleviate the problem. A promising solar cooling method is through the use of a liquid desiccant system, where humidity is absorbed directly from the process air by direct contact with the desiccant. The desiccant is then regenerated, again in direct contact with an external air stream, by solar heat at relatively low temperatures. The liquid desiccant system has many potential advantages over other solar air conditioning systems and can provide a promising alternative to absorption or to solid desiccant systems.Earlier work by the authors included theoretical simulations and preliminary experiments on the key components of the liquid desiccant system. The objective of the present study has been to construct a prototype system based on the knowledge gained, to monitor its performance, identify problems and carry out preliminary design optimization. A 16 kWt system was installed at the Energy Engineering Center at the Technion, in the Mediterranean city of Haifa. The system comprises a dehumidifier and a regenerator with their associated components operating together to dehumidify the fresh (ambient) air supply to a group of offices on the top floor of the building. LiCl-water is employed as the working fluid. The system is coupled to a solar collector field and employs two methods of storage – hot water and desiccant solution in the regenerated state. The performance of the system was monitored for five summer months under varying operating conditions. The paper describes the operation of the experimental system and presents the measured data and the calculated performance parameters.
Goal of this contribution is to draw a picture about some general issues for using solar thermal energy for air conditioning of buildings. The following topics are covered:–A basic analysis of the thermodynamic limits for the use of heat cooling in combination with solar thermal energy is drawn; thereby fundamental insights about control needs for solar thermal driven cooling are obtained.–A short overview about the state-of-the-art of available technologies, such as closed thermal driven cooling cycles (e.g., absorption, adsorption) and open cooling cycles (e.g., desiccant employing either solid or liquid sorbents) is given and needs and perspectives for future developments are described.–The state-of-the-art of application of solar assisted air-conditioning in Europe is given and some example installations are presented.–An overview about new developments of open and closed heat driven cooling cycles for application in combination with solar thermal collectors is given and some of these new systems are outlined more in detail.
Air conditioning system based on liquid desiccant has been recognized as an efficient independent air humidity control HVAC system. To improve thermal coefficient of performance, a novel two-stage liquid desiccant dehumidification system assisted by calcium chloride (CaCl2) solution is developed through exergy analysis based on the second thermodynamic law. Compared with the basic liquid desiccant dehumidification system, the proposed system is improved by two ways, i.e. increasing the concentration variance and the pre-dehumidification of CaCl2. The exergy loss in the desiccant–desiccant heat recovery process can be significantly reduced by increasing desiccant concentration variance between strong desiccant solution after regeneration and weak desiccant solution after dehumidification. Meanwhile, the pre-dehumidification of CaCl2 solution can reduce the irreversibility in the regeneration/dehumidification process. Compared to the basic system, the thermal coefficient performance and exergy efficiency of the proposed system are increased from 0.24 to 0.73 and from 6.8% to 23.0%, respectively, under the given conditions. Useful energy storage capacity of CaCl2 solution and LiCl solution at concentration of 40% reach 237.8 and 395.1 MJ/m3, respectively. The effects of desiccant regeneration temperature, air mass flux, desiccant mass flux, etc., on the performance of the proposed system are also analyzed.
Desiccant systems find applications in a very large variety of industrial and daily usage products including the new HVAC installations. An overview of liquid desiccant technology has been presented in this paper along with a compilation of experimental performance data of liquid desiccant dehumidifiers, empirical dehumidification effectiveness and mass transfer correlations in a useful and easy to read tabular format. The latest trends in this area suggest that hybrid systems are of current interest to HVAC industry, not only for high latent load applications but also for improving indoor air quality. The paper presents a comprehensive comparative parametric analysis of packed bed dehumidifiers for three commonly used desiccant materials viz. triethylene glycol, lithium chloride and calcium chloride, using empirical correlations for dehumidification effectiveness from the literature. The analysis reveals significant variations and anomalies in trends between the predictions by various correlations for the same operating conditions, and highlights the need for benchmarking the performance of desiccant dehumidifiers.
Climate change 2007: the physical science basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change
- P Forster
- Ramaswamyv
- Artaxop
- Berntsent
- Bettsr
- Faheydw
Forster P, RamaswamyV, ArtaxoP, BerntsenT, BettsR, FaheyDW, et al. Changes in
atmospheric constituents and in radiative forcing. In: SolomonS, QinD, ManningM,
ChenZ, MarquisM, AverytKB, TignorM, MillerHL, editors. Climate change 2007: the
physical science basis. Contribution of Working Group I to the Fourth Assessment
Report of the Intergovernmental Panel on Climate Change. Cambridge, United
Kingdom and New York, NY, USA: Cambridge University Press; 2007.
World HVAC equipment demand
- The Freedonia Group
- Inc
The Freedonia Group, Inc.. World HVAC equipment demand. OH, USA: Cleveland;
2012.
A review of desiccant based cooling systems using silica gel
- Yadav Mishra Gaurav Kumar
- Kumar Laxmikant
- Mahesh
Mishra Gaurav Kumar, Yadav Laxmikant, Kumar Mahesh. A review of desiccant
based cooling systems using silica gel. Imperial Journal of Interdisciplinary
Research (IJIR) 2016;
Sorbents and desiccants. Refrigeration and airconditioning engineers, inc
- Ashrae Handbook-Fundamentals
ASHRAE Handbook-Fundamentals. Sorbents and desiccants. Refrigeration and airconditioning engineers, inc. Atlanta, GA: American Society of Heating; 2005.
Thermal Comfort. Passive and Low Energy Architecture International design tools and techniques
- Steven V Andrisauliciems
- Szokolay
AndrisAuliciems and Steven V.Szokolay. Thermal Comfort. Passive and Low Energy
Architecture International design tools and techniques.
Synergization of clean energy utilization, clean technology development and controlled clean environment through thermally activated desiccant cooling system
- N Enteria
- Yoshinoh
- Mochidaa
- Takakir
- Satakea
- Yoshier
- Babas Mitamurat
Enteria N, YoshinoH, MochidaA, TakakiR, SatakeA, YoshieR, MitamuraT, BabaS.
Synergization of clean energy utilization, clean technology development and controlled clean environment through thermally activated desiccant cooling system. In:
Proceedings of the 2nd international conference on energy sustainability; 2008.
Performance of solar photovoltaic plant installed In IIT Roorkee campus. A Case Study
- Sangram Kunwar
- Pundir Singh
- S K Singal
- R P Saini
Sangram Kunwar, Pundir Singh, Singal SK, Saini RP. Performance of solar photovoltaic plant installed In IIT Roorkee campus. A Case Study, IJARSE 2015;Vol.
No.4(01) Special Issue.
Cooling with solar energy
- O G George
- Lof
George O.G.Lof, Cooling with solar energy, In: Proceedings of the congress on solar
Energy 1955; 171-189.
Selection of the liquid desic cant in a run-around membrane energy exchanger. Saskatoon: University of Saskatchewan
- M Afshin
Afshin M. Selection of the liquid desic cant in a run-around membrane energy exchanger. Saskatoon: University of Saskatchewan; 2010. ttp://ecommons. usask. ca/
handle/ 10388/etd-05262010-175310.
Solar powered dehumidification systems using desert evaporative coolers
- Kassem Talal
- Alosaimy Ali
- Hamed Ahmed
- Fazian Mohammad
Kassem Talal K, Alosaimy Ali S, Hamed Ahmed M, Fazian Mohammad. Solar
powered dehumidification systems using desert evaporative coolers: Review.
International Journal of Engineering and Advanced Technology (IJEAT) 2013;3(1).
ISSN: 2249-8958.