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• The phenomenon of simultaneous adsorption-evaporation was experimentally tested. • Desiccant dehumidification and M−cycle cooling integrated in a single heat exchanger. • Experiments validate ability of compact air-conditioning towards net zero emissions. • Cycle time analysis reveals solutions to double system cooling capacity. Despite having the potential to be adopted as a solution towards net-zero emission-based air-conditioning systems, desiccant-evaporative cooling systems have limited applications due to the need to combine several systems to achieve the target conditions. This paper, therefore, undertakes an experimental analysis of a compact system that integrates solid desiccant dehumidification and M−cycle cooling in a single heat exchanger. The system then undergoes regeneration and cooling stages, where no air-conditioning occurs. It is observed that the system can achieve thermal comfort for almost all inlet conditions. Parametric analysis also shows that varying the inlet humidity ratio impacts the system output more than the inlet DBT. The overall cooling capacity of the system increases with greater channel velocity and peaks at around 30 % branching ratio. The concept of operational time (dehumidification stage) and downtime (regeneration and cooling stages) has also been investigated. The analysis shows that the operational time is more than the downtime for all cases except when channel velocity increases above 2.4 m/s. It is also observed that the operational time becomes double the downtime when the regeneration temperature exceeds 83 ℃. Therefore, the analyses practically demonstrate the combined reduction of sensible and latent loads through a simultaneous adsorption-evaporation phenomenon as a step towards a net zero emission-based air-conditioning system. [ABSTRACT FROM AUTHOR]

[Display omitted] • Design of a novel desiccant coated circular fin tube energy exchanger (DCCEE). • Use of phase change material-silica gel as working pair instead of water–silica gel. • Novel DCCEE is utilized for air conditioning/thermal energy storage applications. • Assessed sorption kinetics of silica gel employing linear driving force model. • Phase change material temperature is examined for different adsorption parameters. Advancement of air conditioning systems is a key focus because of high energy usage and rising demand for better air quality. Desiccant air conditioning offers enhanced energy management and sustainability features. Phase change material (PCM) based thermal energy storage systems are effective for efficient thermal energy storage applications. Hence, the practicality of integrating PCM with desiccant coated energy exchangers (DCEE) for air conditioning and thermal energy storage necessitates experimental investigation. Therefore, a novel desiccant coated circular fin tube energy exchanger (DCCEE) has been designed and fabricated in this study. DCCEE is integrated with PCM to assess its dehumidification and thermal energy storage characteristics. The key highlight of this work is the use of PCM-silica gel as the working pair instead of conventional water–silica gel. A linear driving force model is used to evaluate the silica gel's adsorption and desorption kinetics. Experiments have been designed by response surface methodology employing the central composite design technique to analyze the effect of independent parameters on the response of DCCEE. The variation in the cooling capacity, adsorption effectiveness, and PCM temperature at different input conditions has been judiciously evaluated. The adsorption capacity of silica gel is 0.332 g/g at a relative pressure of 0.9. Under the air velocity of 2.5 m/s, the total cooling capacity of DCCEE has the highest value of 3.55 kW, which consists of 1.18 kW sensible cooling capacity and 2.37 kW latent cooling capacity. At the 20 °C and 22 g wv /kg da condition, the adsorption effectiveness reaches a maximum value of 0.82. During adsorption, PCM melts in response to different input parameters and reaches phase change point in 490 s (air temperature), 540 s (air velocity), and 570 s (relative humidity), respectively. To conclude, this study elucidates the feasibility of integrating PCM with DCEE and provides a reference for DCEE system design. [ABSTRACT FROM AUTHOR]

[Display omitted] • Mathematical modeling of membrane distillation considering concentration polarization. • Integration of membrane distillation into a liquid desiccant air conditioning system. • The hybrid system driven by solar energy with a batch-wise operation. • Feasibility analysis of the hybrid system in a hot and humid climate area. • System performance evaluation in terms of air dehumidification and water production. Membrane distillation (MD) is a promising method for liquid desiccant (LD) regeneration as it can mitigate LD carryover and produce freshwater as a by-product. Previous research on MD regeneration was mainly focused on performance evaluation and optimization of the regenerator itself. This paper proposed a hybrid solar-driven direct contact MD (DCMD) regeneration-assisted liquid desiccant air conditioning (LDAC) system for air dehumidification, cooling, and freshwater production. A mathematical model for the DCMD regenerator was first developed by considering both temperature and concentration polarizations. This model was validated against the experimental data in terms of the outlet channel temperature and LD solution concentration in the feed tank with relative deviations of ± 9.8 % and ± 0.5 %, respectively. The DCMD model was further integrated into an LDAC system with a batch-wise operation. To investigate the technical feasibility of the proposed system, a one-week simulation was conducted in a residential house during summer in a tropical climate area of Australia. The results showed that the latent heat load was effectively removed from the process air and the regenerated liquid desiccant solution can meet the dehumidification requirement with a concentration over 30.0 wt%. The dehumidification rate and regeneration rate were at 0.49–1.25 kg/h and 0.95–4.25 kg/h, respectively. Solar energy contributed to 52 %-78 % of the total system thermal energy consumption. Furthermore, this system can produce 11.0–12.8 kg of water daily. [ABSTRACT FROM AUTHOR]

• An innovative desiccant-based atmospheric water generator is proposed. • The aim is to remove source/sink reservoirs conventionally needed for desalination. • Humidification dehumidification with liquid desiccant and a moisture extractor. • The system has two loops: one for a desiccant solution and another for airflow. • Model is developed for humidifier, dehumidifier, and moisture extractor. This study introduces a zero-brine discharge approach, eliminating the necessity for continuous seawater input and brine disposal—major drawbacks in traditional desalination methods. This research's core is a humidification-dehumidification (HDH) system operating under variable pressures, significantly boosting efficiency. The system comprises two synergistic components: a variable-pressure HDH unit and a desiccant-based moisture extractor utilizing a lithium chloride solution. After freshwater is extracted, the concentrated desiccant cycles through the moisture extractor to absorb atmospheric water vapor, diluting it for reuse and thus completing the desiccant loop. The heat and mass transfer processes were scrutinized through mathematical modeling, and parameters for maximizing the Gain Output Ratio (GOR) were optimized. The results underscore the system's capacity for sustainable, efficient freshwater production. This methodology offers a feasible solution to challenges in desalination and significantly contributes to alleviating global water scarcity, particularly in coastal areas. Further analysis shows that systematic optimization of key parameters, such as pressure ratios and desiccant temperatures, considerably improves performance metrics. Adjusting the pressure ratio from 1.22, where the GOR peaks at 2.44, to 1.56 directly impacts system efficiency. Modulating the maximum desiccant temperature at an optimal pressure ratio of 1.25 reveals that the GOR can increase from 1.635 at 0.7 to 2.44 at an effectiveness of 0.8. Optimized manipulation of these parameters can potentially enhance the GOR by up to 50% and improve mass transfer efficiency by about 20% within the HDH process. [ABSTRACT FROM AUTHOR]

• A heat pump-boosted desiccant wheel system is proposed for deep dehumidification. • A prototype attains regeneration air over 100 °C and supply air dew point below − 15 °C. • The dehumidification efficiency surpasses traditional systems by more than double. • The exergy efficiency is over twice that of electric heater-boosted system. • Compared to conventional systems, the effective payback period is only 2.81 years. Desiccant wheel systems achieve deep dehumidification with sub-zero dew points for various industrial needs, but the regeneration process using electric or steam heaters requires considerable energy input. Integrating heat pumps improves efficiency, yet conventional heat pump condensing temperatures fall short of deeper dehumidification. This paper proposes a novel heat pump-boosted desiccant wheel system. The regeneration air is heated using a high-temperature heat pump sub-system (HTHP reg), which recovers regeneration exhaust air heat. Additionally, an auxiliary heat pump sub-system (HP prcs) enhances the pre-processing for the desiccant wheel process inlet. Experimental tests of a prototype confirm the system produces stable regeneration air over 100 °C, achieving supply air dew point below − 15 °C. The HTHP reg exhibits a heating efficiency COP h of nearly 3.0 and the overall system's specific moisture extraction rate (SMER) is 1.5 kg/kWh. Compared to the conventional system, the combination of HP prcs and HTHP reg decreases regeneration heat input by ∼ 20 % and power consumption by 75 %. Dehumidification efficiency SMER increases by a factor of 1.13 to 1.17 with HP prcs , 1.72 to 2.36 with HTHP reg , and 2.05 to 2.67 combined. At the 35 °C/80 % condition, system exergy efficiency rises from 5.9 % to 14.4 %. The levelized cost per liter of extracted water over 15 years decreases 27 % and the effective payback period over conventional systems is only 2.81 years. [ABSTRACT FROM AUTHOR]

• A prototype of Renewable Air-Cooling Unit is experimentally evaluated in this work. • This is composed of a desiccant wheel and a dew-point indirect evaporative cooler. • Key performance indicators are developed for these components and the prototype. • 64 experimental tests are carried out to obtain several complete empirical models. • High values of Energy Performance are achieved under severe climatic conditions. Given the escalating energy consumption in cities worldwide, it is crucial to investigate the utilization of sustainable technologies and renewable energy sources. The number of empirical studies on the energy performance of hybrid air-cooling systems is limited. Therefore, the objective of this work is to experimentally study the energy performance of a novel renewable air-cooling unit. This prototype is mainly composed of a desiccant wheel and a dew-point indirect evaporative cooler to independently control the temperature, humidity, and carbon dioxide levels of indoor air. 64 experimental tests are carried out to fit an empirical model of this renewable air-cooling unit, focusing on outlet air conditions and the coefficient of performance. In addition, several performance indices are developed for desiccant wheel and dew-point indirect evaporative cooler: (i) moisture removal capacity; (ii) moisture removal capacity per unit of electrical power-consumption; (iii) dew-point efficiency and (iv) cooling capacity of dew-point indirect evaporative cooler per unit of electrical power-consumption. The highest values of dehumidification capacity, sensible cooling capacity and coefficient of performance for this renewable air-cooling unit are achieved for the most severe outdoor air conditions, namely 19.02 kg·h−1, 21.49 kW and 11.0, respectively. This work can serve as a reference for research on the feasibility of hybrid air-cooling systems in the scenarios of heat events and climate change world. [ABSTRACT FROM AUTHOR]

• Ideal exergy efficiencies of the two regeneration methods are explicitly derived. • The MVR method's exergy efficiency surpasses the AT method by 3.6% in basic case. • Aerodynamic thermal method is applicable to high-temperature and drought areas. • Mechanical vapor recompression excels in high-concentration regeneration. Regeneration is essential for ensuring the continuous and energy-efficient operation of liquid desiccant air-conditioning systems. While the conventional aerodynamic thermal (AT) method is widely used, the mechanical vapor recompression (MVR) method offers an alternative for desiccant solution regeneration. However, existing studies on MVR have primarily focused on applications such as seawater desalination and wastewater treatment, with limited exploration of its performance for regenerating solutions suitable for liquid desiccant air-conditioning systems. In this study, we compare the exergy efficiencies of the AT and MVR regeneration methods through explicit derivation and experimental analysis. Results indicate that, under basic conditions, the MVR method achieves an exergy efficiency of 43.9%, surpassing the 40.3% efficiency of the AT method. Furthermore, the study suggests that the MVR method is well-suited for humid areas where ambient air approaches saturation, whereas the AT method is more applicable in high-temperature and arid regions, making optimal use of free exergy input from ambient dry air. Additionally, the applicable area of MVR regeneration expands with increasing solution concentration. This research aims to serve as a valuable reference for selecting desiccant solution regeneration methods and contributing to enhanced energy performance in the field of air conditioning. [ABSTRACT FROM AUTHOR]

• The concentrated photovoltaic panel is cooled using desiccant material. • Water is harvested from desiccant material. • The heat pipe is used to enhance photovoltaic panel cooling. • Two system designs for concentrated photovoltaic panels are discussed. • The indirect system with a heat pipe performs best in cooling and water harvesting. Energy and water are essential for human beings' life. Researchers tried to find solutions to face the energy crises and water shortages. Solar energy shows excellent potential to generate electricity using photovoltaic panels and generate water using a desiccant atmospheric water harvester. A concentrated photovoltaic panel offers much-generated power compared with a non-concentrated panel for the same panel area; however, it suffers from the very high temperature and non-uniform temperature distribution on the panel, which causes a significant reduction in the electrical efficiency and reduction in the panel lifetime. Nearly uniform temperature distribution can be obtained using a flat heat pipe, which is integrated into the panel's backside and provides the excess panel heat to the heat sink. The desiccant atmospheric water harvester needs heat to desorb water vapor, which is then condensed and collected. This paper offers two hybrid system configurations that cool the concentrated photovoltaic and generate water by providing the excess heat of the concentrated photovoltaic to the desiccant material. The first configuration is a direct cooling technique where the panel's backside is directly attached to the desiccant. In contrast, the second configuration is an indirect cooling technique where a heat pipe interfaces the panel backside and the desiccant. The system model is presented, solved using MATLAB, and validated. The current study evaluates the influence of the concentration ratio of the concentrated photovoltaic panel, the heat pipe condenser area to evaporator area ratio, the thickness of the desiccant layer, and the desiccant type on the cell temperature, cell electric efficiency, generated power, desiccant uptake, the harvested water per day, and the system overall efficiency. It was found that the maximum average cell efficiency has a value of 13.97% when the concentration ratio is 1, the heat pipe condenser area to evaporator area ratio is 2, the layer thickness is 2 cm, and the system uses the silica gel at the indirect cooling technique configuration. The maximum average power is 212 (W/m2) when the system configuration works on an indirect cooling technique and has a heat pipe condenser to evaporator area ratio = 2, concentration ratio = 4, the layer thickness = 1 cm, and the desiccant is silica gel. The minimum average output power, excluding the naturally cooled photovoltaic panel, is 59 (W/m2) when the system configuration works on the direct cooling technique and has a concentration ratio = 1, the desiccant layer thickness = 3 cm, and the desiccant is zeolite. The maximum amount of the harvested water and harvested water per unit area are 0.75(kg/day) and 12.02 (kg/(day m2)) when the heat pipe condenser area to evaporator area ratio is 2, the concentration ratio is 4, the layer thickness is 3 cm, and the system uses silica gel as the desiccant. The proposed systems of photovoltaic panel cooling and water harvesting are designed for areas with water scarcity or limited water resources. [ABSTRACT FROM AUTHOR]

• An adsorption model based on the real microstructure of desiccant coating is developed. • A self-refined algorithm, which can realize automatic mesh optimization is proposed. • A model, which can simulate the transient performances of different SDHP systems is established. • Three SDHP systems based on silica gel, MOF, and hygroscopic salt are simulated and analyzed. The solid desiccant heat pump (SDHP) is a promising air-handling method. Present simulation models of SDHP have two challenges. Owing to the fixed mesh structure, one model should be deeply revised to simulate another SDHP system. Besides, an adsorption dynamic model based on the real mass transfer network of desiccant coating is still lacking. This study proposes a universal SDHP model, which is based on the self-refined mesh algorithm and a new adsorption dynamic model (GP model). Self-refined mesh algorithm can automatically optimize the mesh structure, making it easy to simulate different SDHP systems in variable environmental conditions. GP model, based on the real microstructure of coating is demonstrated to be suitable for MOF, hygroscopic salt (LiCl), and silica gel coatings in our paper. Our model simulates the performances of three SDHP systems (coated with silica gel, MIL-101Cr, and LiCl) in sub-humid and humid conditions. Compared with LiCl, MIL-101Cr is more suitable for situations of sub-humid environment and high dehumidification quantity. For the sub-humid condition, the optimal switch-over period for MIL-101Cr-based SDHP is 13 min to owe the highest COP (5.6). For the humid conditions, LiCl-based SDHP shows the highest COP (10.7) when the switch-over period is 3 min. We believe this work can enlighten other studies on SDHP simulation and mass transfer in desiccants and guide the design of SDHP systems. [ABSTRACT FROM AUTHOR]

[Display omitted] • Solar-driven VMD system with heat pump for liquid desiccant regeneration is proposed. • Energy, exergy, and environmental analysis is performed. • Two operation modes are introduced based on solar radiation and heat demand. • Single and multi-objective optimization are used to find optimal operating conditions. Liquid desiccant air-conditioning (LDAC) system is one of the excellent alternatives to conventional vapor compression refrigeration system due to its great energy-saving potential. However, regeneration of diluted liquid desiccant is the main energy-consuming process, and its performance plays a significant role in LDAC system. Recently vacuum membrane distillation (VMD) is becoming an emerging and promising separation process rely on the advantage of high permeate flux and low energy losses. The interest of usage solar energy techniques for feed solution heating in VMD systems is regarded as a sustainable path for membrane distillation process. In this work, a solar-driven VMD system incorporating a vapor-compression heat pump for liquid desiccant regeneration is introduced. An adapted solar/heat pump hybrid heating strategy has been devised to establish a connection between the heat-demanding process and the solar thermal supply. A comprehensive multicriteria assessment of energy, exergy, and environmental evaluation is conducted, and the influences of crucial parameters on both key components and system performance are evaluated to ensure a systematic examination. Results show that both the COP and STEC decrease obviously with the growth of the inlet solution temperature, whereas SEEC is improved abviously from 410.6 kW·h/m3 to 566.1 kW·h/m3 due to the effect of heat pump. The exergy analysis indicates that exergy losses in solar collector and stratified heat storage tank accounted for over 80 % of the total exergy losses. Additionally, single-objective optimization and multi-objective optimization are employed to explore the optimum operating conditions of key componets and whole system. Results show the ideal optimal solution can be obtained with a COP of 19.92 and a SEEC of 142.89 kW·h/m3 when the weights of COP and SEEC are taken as [0.5, 0.5]. [ABSTRACT FROM AUTHOR]

[Display omitted] • Two-stage direct solar-regenerated desiccant dehumidification rotating belt is studied. • Mathematical model of the system was developed and experimentally validated. • System performance is optimized to enhance air quality & minimize energy consumption. • The system maintained an indoor RH of 58 ± 1.5 % and CO 2 concentration of 780 ± 41 ppm. • The system consumed 26 kWh during cooling season for fan & cooling coil operation. Conventional vapor-compression cooling for outdoor air dehumidification is energy intensive, especially in hot and humid regions. To reduce energy consumption, desiccant dehumidification wheels and packed beds are integrated with the air conditioning systems. However, these systems have large pressure drops and require external heating sources for regeneration. In this study, a two-stage direct solar-regenerated desiccant dehumidification rotating belt (SR-DDRB) system is proposed. The aim is to sustainably dehumidify the outdoor air while meeting the indoor humidity levels at enhanced indoor air quality and minimal energy. The system was sized, and its operation was optimized using artificial neural network for a case study of a typical office space located in hot and humid climate. The supplied outdoor air flowrate varied between 0.055 kg/s and 0.085 kg/s, which is much higher than the minimum required of 0.0392 kg/s. During months of high humidity, the operating conditions were affected by outdoor air humidity conditions such that higher outdoor air flowrate and bypass factor were achieved at low outdoor humidity, and vice versa. During months of low humidity, the operating conditions were primarily influenced by the outdoor air temperature rather than outdoor air humidity to minimize energy consumption. Over the cooling season and while operating at optimal conditions, the SR-DDRB system was able to meet an indoor relative humidity (RH) of 58 ± 1.5 %. Additionally, it maintained the CO 2 concentration of 780 ± 41 ppm, well below the allowable 1,000 ppm, whereas electrical energy consumption was 78.8 kWh over the entire cooling season. [ABSTRACT FROM AUTHOR]

• New desiccant dehumidification cycle has coefficient of performance values up to ∼4. • Energy efficiency improved via liquid–liquid versus liquid–vapor phase transition. • New method of regenerating liquid desiccants using two-phase liquid separation. • Flory-Huggins modeling identifies desiccant properties for improved efficiency. We describe a liquid desiccant dehumidification cycle that regenerates via liquid–liquid phase separation instead of the typical liquid–vapor phase separation. Liquid-liquid phase separation is enabled by the use of thermoresponsive liquid desiccants that exhibit a "U-shaped" immiscibility curve in their phase diagram with water. Crossing this immiscibility curve causes a single-phase liquid to transform into a two-phase liquid mixture, which then facilitates the liquid-state removal of the absorbed humidity. In order to systematically explore this cycle's dehumidification coefficient of performance (COP deh), we employ the Flory-Huggins theory of mixing to systematically vary the immiscibility curve. The Flory-Huggins theory uses two key parameters, the lower critical solution temperature (LCST) and the enthalpic interaction parameter (χ H) to define the position and shape of the immiscibility curve, respectively. We show that LCST temperatures close to the cycle's heat rejection temperature improve COP deh by reducing the necessary sensible heat during regeneration. We also show that enthalpic interaction parameters with larger negative magnitudes lead to flatter immiscibility curves that improve COP deh. This improves COP deh by better directing regeneration heat toward liquid–liquid demixing as opposed to increasing temperature. Our modeling indicates that COP deh values up to ∼4 are possible using this cycle whereas traditional non-thermoresponsive liquid desiccant cycles would achieve COP deh values of <1. This large increase in COP deh is due to the fact that the demixing enthalpy associated with liquid–liquid phase separations is much smaller than the enthalpy of vaporization associated with liquid–vapor phase separations. [ABSTRACT FROM AUTHOR]

• Study of ceiling cascaded liquid desiccant system and displacement ventilation for humidity control. • A model of the cascaded liquid desiccant system is developed to predict system effectiveness. • The validated model was applied to case study in humid climate and was able to control humidity. • Membrane exchanger with cascaded system performed better than conventional dehumidification. • The cooling and heating energy were lower by 21.25% and 16.23% respectively in the cooling season. Displacement ventilation (DV) combined with liquid desiccant membrane cooled ceiling (LDMC-C) is an efficient Heating, ventilation and Air conditioning (HVAC) system. However, the LDMC-C/DV has limited performance in office spaces located in hot and humid climates or characterized by high internal latent loads due to the inability to control the humidity. This study proposes a cascaded liquid desiccant system in which the liquid desiccant flow exiting the LDMC-C is directed into a liquid desiccant heat and mass exchanger in the DV supply duct to control the humidity in the space and conserve energy. To achieve this goal, an integrated model for different components of the cascaded liquid desiccant system is developed to predict the comfort level and the air quality inside the space as well as the energy consumption of the system. The model was validated experimentally in a climatic chamber. The validated integrated system model was applied to a case study to assess the effectiveness of the system in hot and humid climate. Two configurations of the LDMC-C and mass exchanger were simulated and found to provide acceptable humidity for comfort in the occupied zone of the space. Moreover, the cascaded system cooling and heating energy were found lower by 21.25% and 16.23% respectively in August when compared to a LDMC-C/DV, and to DV membrane exchanger system with different configuration. The cooling and heating energies were also lower in the cascaded system compared to a LDMC-C/DV while using conventional supply air dehumidification method. [ABSTRACT FROM AUTHOR]

• A hybrid heat recovery system based on liquid desiccant is proposed for boilers. • System thermal efficiency can reach 104.0% when return water temperature is 60 °C. • A better inlet temperature and flowrate of the desiccant solution are recommended. • The formation of white smoke is avoided due to lower flue gas relative humidity. In district heating, conventional flue gas heat recovery systems do not perform well anymore when the return water temperature is high. In this paper, a hybrid heat recovery system based on vapor compression refrigeration and liquid desiccant dehumidification is then proposed, with proper refrigerants and desiccants recommended. A simulation model of this system is established and a typical case is studied based on the model with a return water temperature of 60 °C. Then, an equivalent thermal efficiency is introduced to evaluate the system performance. Parametric analyses are conducted by changing the liquid-gas flowrate ratio and the inlet solution temperature in the second stage of the absorber in the system. According to the parametric analyses, a liquid-gas mass flowrate ratio of 3.2–3.4 and an inlet solution temperature of 45 °C are recommended as the best working conditions considering the economic and ecological effects. Under these conditions, the equivalent thermal efficiency of a boiler can be increased from 90% to 104%. For a boiler with a rated heating capacity of 7 MW, about CNY 236,000 (USD 34,000) can be saved per month. Besides, the flue gas is finally discharged at a relative humidity of only 33%. The formation of white smoke can thus be avoided and the contaminant attachment in the atmosphere around can be alleviated. The proposed system is efficient and environmentally friendly and the simulation results can offer references to real applications under variable working conditions. [ABSTRACT FROM AUTHOR]

• A hybrid desiccant deep dehumidification system with a compact structure is proposed. • No extra regeneration air or corresponding air ducts are required in the proposed system. • Supply air with a humidity ratio of 2.1–4.5 g/kg was obtained with a COP sys of 2.4–3.2. • The proposed system can reduce energy consumption by 13.8% compared with the reference system. • An improved system was developed to increase the supply air temperature. Desiccant-based hybrid air-conditioning systems have recently become popular owing to a reduction in their energy consumption. In addition to the dehumidification process, regeneration is a necessary process in a hybrid system, and in all previous studies the regenerator (REG) has been separated from the liquid desiccant dehumidifier (DEH), which implies the need for a complex duct configuration and a large equipment space. In the present study, a novel hybrid liquid desiccant–heat pump air-conditioning system combined with a cooling coil is proposed for deep dehumidification with a supply air humidity ratio of below 5 g/kg, where the REG, condensing DEH (cooling coil), and liquid desiccant DEH are cascaded. This system not only maintains the energy performance advantages of hybrid systems over conventional systems, it also simplifies the layout of the entire system and guarantees a compact system structure, particularly for buildings with an existing central air-conditioning–chilled-water system. Using the proposed system, a coefficient of system performance (COP sys) of 2.4–3.2 has been obtained experimentally with an supply air humidity ratio of 2.1–4.5 g/kg. Despite the compact system structure, when the air is processed from 30 °C and 20 g/kg to 4 °C and 3.6 g/kg, the proposed system achieves a superior COP sys of 3.3 with an improvement of 13.8% when compared with a conventional liquid desiccant dehumidification system. [ABSTRACT FROM AUTHOR]

Highlights • Energy consumption of desiccant coated heat exchanger systems are analyzed. • Effects of climatic conditions and sensible heat ratios are discussed. • R410A and R32 are promising refrigerants. • Desiccants with adsorption heat of 2300–3000 kJ/kg satisfies most conditions. • Desiccants with adsorption heat more than 4000 kJ/kg need a careful decision. Abstract DCHE (Desiccant coated heat exchanger) based heat pump systems can handle sensible and latent loads simultaneously and separately within one single component via flowing refrigerant and coated desiccant. Their characteristics have a crucial impact on the performance of the whole system. To ensure energy efficiency of DCHE based systems, the restriction between refrigerant and desiccant is discussed based on energy consumption analysis. Results show that energy consumption of the DCHE based heat pump is intimately related with its coefficient of performance and adsorption heat of coated desiccant. R410A and R32 are found to be promising refrigerants for DCHE systems. Maximum allowable values of adsorption heat under different ambient air conditions and sensible heat ratios are obtained. Desiccant materials with adsorption heat of 2300–3000 kJ/kg such as various silica gels, all-silica zeolites and salt supported composites are within maximum allowable values of adsorption heat for most conditions. When applying the majority of zeolite type desiccants that possess adsorption heat more than 4000 kJ/kg, great attention should be paid to the determination of supply-air temperature difference. This paper provides the underlying insights needed to guide a fast and proper selection of refrigerants and desiccants for DCHE based systems. [ABSTRACT FROM AUTHOR]

• A CFD approach is developed to study desiccant coated heat exchangers' performance. • Fundamental laws of mass, momentum, energy, and species conservation are employed. • Parametric study investigates the effects of desiccant characteristic properties. • Impact of fin-tube configurations on dehumidification performance is analyzed. • New fin-tube configurations show 7–40% improvement in moisture removal capacity. A solid-desiccant coated heat exchanger (DCHE) technology can be applied to many heat transfer/exchange systems such as air-conditioners, heat pumps, adsorption chillers, and atmospheric water harvesters. Although the existing mathematical models can sufficiently predict the performance of the DCHEs, they are inapplicable for designing a new DCHE as the heat and mass transport coefficients used are derived from pre-determined empirical correlations. Therefore, in this paper, we developed a new mathematical platform to simulate the simultaneous heat and mass transfer phenomena that occur during DCHEs' dehumidification/regeneration processes. Unlike existing models, the current model considers fluid flow, temperature, and moisture distributions across different domains. The effectiveness of the model was established by validating the performance of silica gel and composite polymer coated heat exchangers under different cooling and hot water temperatures. The maximum discrepancies between the model predictions and experimental data for outlet air humidity ratio and temperature were ±14% and ±12% respectively. A parametric study was then conducted to investigate the effects of key characteristic properties and fin-tube configurations on dynamic performance of DCHE. The respective dehumidification performance of two tube-fin and annular-fin DCHE configurations was observed to record 7% and 40% improvement in moisture removal capacity over the single-fin tube configuration. [ABSTRACT FROM AUTHOR]

Highlights • A desiccant cooling system is proposed for coproduction of cooling and water. • Ability of providing comfort conditions in hot and humid climate was investigated. • This system covers its water use and produces excess water for domestic usage. • Energy and carbon saving of the proposed was investigated. • Economic evaluation indicates feasibility of the proposed system. Abstract Although evaporative coolers consume much lower electricity than the vapor compression systems, they are not applicable in humid climates. Combination of desiccant wheels and evaporative coolers, known as desiccant-based evaporative cooling systems, allows evaporative coolers to be used in humid climates, which provide significant energy and environmental advantages with respect to vapor compression systems. However, one of the main disadvantages of evaporative cooling is the high water. Regarding the global water crisis, a cooling system which saves both water and energy will be an attractive alternative to the current cooling systems. To this aim, this paper presents a novel desiccant-based evaporative cooling system for co-production of water and cooling. In this system, the moisture content of exhaust regeneration air is recycled to cover all of the evaporative cooler water consumption, and also part of the domestic water usage. To evaluate the system performance, dynamic hourly simulation of the proposed system as well as a reference vapor compression system was performed for a typical 60 m2 building in hot and humid climate of Bandar Abbas, Iran. The simulation results show that the proposed system is able to provide comfort temperature and relative humidity in a hot and humid climate. Moisture harvesting produce about 590 L water during a week, which covers all of the evaporative cooler water consumption, and provides an excess amount of 289 L for domestic usage. Monthly integrated results indicate that electricity consumption of the proposed system is 60% lower than the reference system, while its natural gas consumption is 30% higher than VCS, which is due to the high regeneration temperature in some hours. In other worlds, this system replace electricity consumption, a high-exergy and expensive energy carrier, with heat consumption. This system leads to 18.7% saving of CO 2 emissions over a month. Economic evaluation proves the economic feasibility of proposed system with a payback period of 3 years. In conclusion, proposed system provide a more environmental friendly cooling system for water, energy and carbon saving. [ABSTRACT FROM AUTHOR]

Highlights • Optimal design of desiccant cooling with energy generation and storage is presented. • The optimization was achieved using a neural network and a genetic algorithm. • Specific net electricity generation was used as the optimization objective. • A dimension reduction method was used to determine key design parameters. • Design solutions identified by this method outperformed a baseline design. Abstract A design optimization strategy for rotary desiccant cooling (RDC) systems integrated with a photovoltaic thermal collector-solar air heater (PVT-SAH) and a phase change material based thermal energy storage (TES) (named RDC-PVT-SAH-TES) is presented in this paper. The optimization method was developed using a multilayer perceptron neural network (MPNN) and a genetic algorithm to maximize the specific net electricity generation (SNEG) of RDC-PVT-SAH-TES systems while maintaining the required cooling demand with the assistance of an electric heater. A dimension reduction method was used to determine the main design parameters of the RDC-PVT-SAH-TES system. An RDC-PVT-SAH-TES system was simulated using TRNSYS and the simulation data were utilized for training and validation of the MPNN model and for dimension reduction analysis. A comparison of the design solution identified by this optimization method with a baseline design showed that the SNEG and the solar thermal contribution of this RDC-PVT-SAH-TES system can be increased from 3.77 kWh/m2 to 10.32 kWh/m2 and from 91.5% to 99.4%, respectively. The optimization method developed could be potentially adapted to facilitate optimal design and size of other engineering systems with onsite energy generation and thermal storage. [ABSTRACT FROM AUTHOR]

• Solid oxide fuel cell system integrated with hybrid desiccant cooling is proposed. • Numerical analysis of two system were performed at three climatic conditions. • System optimization for design and operational strategy is achieved. • System without burner at load following mode has the highest electrical efficiency. • System with burner at load following mode has the highest total efficiency. Solid oxide fuel cell systems are advantageous in distributed power generation and are commonly utilized in residential buildings. However, since commercialized small-scale solid oxide fuel cells generally produce hot water using high-temperature exhaust gas, it is difficult to utilize thermal energy in high-temperature areas and during the summer. The exhaust heat from the solid oxide fuel cell system can be effectively utilized by integration with the hybrid desiccant cooling system. In this study, a numerical model of a solid oxide fuel cell system integrated with a hybrid desiccant cooling system has been developed to determine the optimal system configuration and operating strategy. As for the Hot-dry, Hot-humid, and Mixed-humid, which are representative climatic conditions of summer in the United States, were selected. The system model has been simulated at a period of the highest electrical demand in a year with each climate. The solid oxide fuel cell-hybrid desiccant cooling system model has been simulated to compare the system efficiency at 4 case. The simulation results show that the solid oxide fuel cell-hybrid desiccant cooling system without a burner has the highest total efficiency of 77.7 % and the highest total coefficient of performance of 1.528 under electric load following operation. This study can provide the basic insight to establish the parametric analysis and control strategy in integrating the solid oxide fuel cell system and the desiccant cooling system. [ABSTRACT FROM AUTHOR]

• Combining membrane dehumidification and dewpoint evaporative cooling (M−DPEC) • Thermodynamic model based on first and second laws to assess energy performance. • M−DPEC achieves up to 50–90% energy savings compared to desiccant wheels. • Up to 50% carbon emissions reductions compared to conventional technologies. • System dehumidification step self-supplies up to 12x the water required for cooling. Investigating new energy efficient and sustainable designs for air conditioning has become imperative due to air conditioning's contribution to global warming. The combination of membrane-based dehumidification and dewpoint evaporative cooling provides a possible solution that eliminates the energy-intensive process of condensation dehumidification, while also avoiding the use of harmful refrigerants. This paper is the first to present a straightforward thermodynamic model and initial assessment of a hybrid system that combines a vacuum membrane dehumidifier inspired by the Claridge-Culp-Liu (CCL) cycle with a dewpoint evaporative cooler with the additional investigation of reusing the dehumidification water to provide the evaporative cooling. A parametric study is performed for different ambient conditions. Results show the maximum achievable coefficient of performance (COP) for cooling and dehumidification with the system to be as high as 15 for very dry climate conditions, with a median value in the range of 4 over the range of typical ambient conditions. The system also displays the potential for having a self-sustaining water supply for evaporative cooling, producing up to 12x the amount of water required for the evaporative cooling portion of our system in highly humid conditions. An energy savings analysis yielded positive savings at low humidity conditions when compared to a baseline vapor compression system. Additionally, the system outperformed a baseline desiccant wheel system under all conditions. The absence of harmful refrigerants lowers overall (direct and indirect) greenhouse gas emissions associated with the M−DPEC system to as low as 50% of the baseline vapor compression system. Therefore, the model shows potential for the technology to efficiently fulfill building cooling demands while employing an environmentally friendly system to reduce greenhouse gas emissions. [ABSTRACT FROM AUTHOR]

Highlights • A novel hybrid desiccant cooling system with a condenser is studied. • Thermal balancing technique is applied for zero and single extraction systems. • A mathematical model of the proposed system using enthalpy pinch method is explained. • The coefficient of performance is improved by 85% using the single extraction. • The investigated hybrid system also produces fresh water as a by-product. Abstract This paper focuses on thermodynamic balancing of the regeneration process in a hybrid liquid desiccant cooling/desalination system. The thermal balancing technique is investigated by adding a single extraction between the system regenerator and condenser. This technique is considered as a potential method to reduce energy consumption and increase the hybrid system performance, dramatically. The mathematical procedure to model the proposed system using enthalpy pinch is outlined to study the effect of extraction on the hybrid system performance. The hybrid system, with a single extraction and without extraction (zero extraction), is analyzed in terms of the normalized entropy generation, local enthalpy losses, the coefficient of performance, and proper extraction location. The results show that at enthalpy pinch of 20 kJ per kg of dry air, single extraction system performance is 85.7% better than zero extraction. In addition, the single extraction produces 103.2 kg of fresh water per hour as a by-product compared to 94.2 kg per hour for the zero extraction system. [ABSTRACT FROM AUTHOR]

Air dehumidification is widely applied in the civilian and industrial use, however, conventional vapor compression air-conditioning system consumes substantial power. Using renewable energy in the air handling process has potential to further reduce the power consumption, meanwhile ease the carbon emission. This paper proposes a novel liquid desiccant system integrated with a concentrated photovoltaic/thermal collector for deep dehumidification. The generated electric power drives a vapor compression chiller for cooling the desiccant solution for a two-stage dehumidification, and the released heat from the collector is used for the desiccant regeneration. Simulation studies indicated the proposed system has a superior power saving ability of 55.65% comparing with the conventional one, besides the equivalent power generation efficiency reaches 8.7% in the base design condition. A comparative driven force analysis showed the two-stage dehumidification has a better match of driven force compared with the single-stage liquid desiccant dehumidification, thus leading to a reduced irreversible loss of 65.43%. Sensitivity analysis indicated that the dehumidification temperature has a decisive effect on the system performance. The exergy efficiency has a maximum value of 13% as the dehumidification temperature is 22.3 °C. The economic studies showed that the investment on the concentrated photovoltaic/thermal collector account for the largest share of the total initial investment, and has a significant effect on the payback period. The payback period would be reduced further if the benefit of the clean development mechanism ( CDM ) is considered. [ABSTRACT FROM AUTHOR]

[Display omitted] • Performed a comparative cradle-to-grave LCA for adsorption dehumidifiers. • Identified the key influencing factors of selected environmental impact categories. • The usage phase contributes the most (65% − 99%) in all impact categories. • Supply humidity, climatic data, and operational hours are the key parameters. Desiccant wheel dehumidification technology is essential within industrial applications to maintain indoor humidity levels and provide low dew points. While the need for desiccant wheel dehumidification has increased in several industrial sectors, it is still an energy-intensive method undergoing rapid technological development. The lack of comprehensive life cycle assessment studies and recently introduced taxonomy by the European Union (EU) prompt the urgency of evaluating the environmental impacts of dehumidification systems. This study performs a comparative life cycle assessment for two desiccant wheel dehumidifiers for industrial applications. We identify the key influencing factors of selected environmental impact categories, e.g., climate change, ozone depletion, and fine particulate matter formation. The study reveals that the usage phase contributes the most, varying between 65% and 99% of the overall impact in all categories, with electricity consumption as the key driver. The cradle-to-gate stage, which shows the second biggest impact (up to 26%), has its most significant share in fine particulate matter formation. The end-of-life (disposal) contributions are insignificant, with an average impact of less than 1%. The scaling factor, operational hours of the systems, the target supply humidity, and the climatic data are the critical parameters for environmental performance. Potential for improvement is seen for an increased recycled content during the cradle-to-gate stage to reduce the impact from raw material inputs and the integration of sustainable energy technology as well as the connection of the systems to energy-efficient equipment during the operational phase. The study could serve as an example on how the EU Taxonomy can be applied for investigating the environmental sustainability of dehumidification systems. [ABSTRACT FROM AUTHOR]

In this study, the performances of a solar energy assisted hybrid desiccant air conditioning system integrated with humidification–dehumidification (HDH) desalination system are numerically investigated. The aim of this study is to benefit from the temperature rise of the regeneration air outside of the desiccant conditioning system as well as the water vapor content in this regeneration air by feeding it to the humidification-dehumidification water desalination unit to produce distillate water. The distillate water productivity, human thermal comfort issues, and energy saving represent the main objective of the present numerical study. The simulated results developed for subsystems are validated with the published experimental results. The effects of regeneration air temperature and flow rate on supply cooled air temperature, distillate water productivity, the cooling coefficient of performance and overall daily coefficient of performance of the proposed system are investigated. The results show that (i) the distillate water productivity increases from 3.175 to 5.011 L/h and overall daily coefficient of performance decreases from 4.392 to 3.636 with increasing the regeneration air temperature from 75 to 95 as (ii) the increase in the regeneration air flow rate from 70 to 130 m 3 /h, increases the distillate water productivity from 2.988 to 4.78 L/h and decrease the overall daily coefficient of performance from 4.66 to 3.386. The study demonstrates that the proposed system represents the best options in hot and humid regions. [ABSTRACT FROM AUTHOR]

This paper proposed and investigated a new no-frost air source heat pump (ASHP) combined with liquid desiccant dehumidification and compression-assisted regeneration. In the system, an additional vacuum compressor is introduced in the regeneration cycle to recover the regenerated heat, which could improve the performance the hybrid no-frost ASHP system. A mathematical model of the novel system is constructed to further study the characteristics of the system under various operating parameters and climatic conditions. Based on the simulation model, the results show that the COP anverage of the system varies from 2.811 to 3.242 when ambient air temperature rises from −10 to 0 °C at a constant relative humidity of 80%. And with the ambient air RH increasing from 70% to 90% the COP anverage decreases slightly from 3.285 to 3.20 when the temperature is at 0 °C. In addition, the effects of air-to-solution mass flow rate ratio in the dehumidifier and regeneration temperature on the performance of the system are discussed. Finally, a comparison study between the proposed system and typical reverse-cycle defrosting system is presented, which indicates that the COP anverage of the novel system is at least 36.05–61.19% higher than that of the COP reverse in the variation ranges of the analyzed parameters. [ABSTRACT FROM AUTHOR]

Liquid desiccant air conditioning systems are cost-effective, environmentally friendly and energy efficient techniques, especially in coastal areas. In the conventional liquid desiccant air conditioning system, the scavenging air is expelled into the atmosphere carrying a considerable amount of energy and water vapor. Thus, there is plenty of room to improve the system performance by recovering these losses. The proposed system consists of a conventional liquid desiccant air conditioning system plus a condenser. The aim of this study is to reduce the energy consumption by recovering the heat from the scavenging air using the condenser while also producing freshwater in addition to space cooling. Lithium chloride (LiCl) is used as the liquid desiccant for this study. The mathematical formulation for simultaneous heat and mass transfer between the condenser and the regenerator was developed to establish a comparison between the performance of the conventional and modified systems. Using the generated model, it is found that the modified system performance is 11.25% better than the conventional system and that it produces 86.4 kg of freshwater per hour as a by-product under the given conditions. [ABSTRACT FROM AUTHOR]

In recent years, liquid desiccant air-conditioning system (LDAC) has shown a great potential alternative to the conventional vapor compression systems. LDAC not only greatly improves the indoor air quality by controlling the humidity and temperature independently, but also deceases the electrical energy consumption of the conventional air conditioner. In this work, the liquid desiccant and humidification cycle is driven by the exhaust heat of the compressor. Cycle performance of a small-scale heat pump type air conditioner coupled with a liquid desiccant/humidification cycle has been theoretically and experimentally evaluated by the present study. Parametric analysis on cycle performance of the present cycle is carried out through both theoretical and experimental methods, and lithium chloride aqueous solution is used as the working fluid of the solution cycle. The thermodynamic analysis results show that while the evaporating temperature of the present cycle increases to 15 °C, the energy consumption decreases by about 22.64% when compared with conventional air conditioner. Theoretical results also indicate that the coefficient of performance (COP) of the novel system has a potential improvement of about 35.3%. Based on the theoretical results, experimental analyses of this novel cycle under summer and winter working conditions are carried out. In addition, comparison of the humidification and dehumidification ability as well as COP of the present novel system and the traditional one are carried out. Researching results of the present study provide important reference for investigator of this field. [ABSTRACT FROM AUTHOR]

In this study, the performance of three nano-composite energy storage absorbents; Vermiculite-CaCl 2 (SIM-3a), Vermiculite-CaCl 2 -LiNO 3 (SIM-3f), and the desiccant Zeolite 13X were experimentally investigated for suitability to domestic scale thermal energy storage. A novel 3 kWh open thermochemical reactor consisting of new meshed tube air diffusers was built to experimentally examine performance. The results were compared to those obtained using a previously developed flatbed experimental reactor. SIM-3a has the best cyclic behaviour and thermal performance. It was found that 0.01 m 3 of SIM-3a can provide an average temperature lift of room air, Δ T = 20 °C over 180 min whereas for SIM-3f, Δ T < 15 °C was achieved. Zeolite provided high sorption heat in close approximation with SIM-3a, however, the higher desorption temperature requirements coupled with poor cyclic ability remain as obstacles to the roll out this material commercially. The study results clearly show that the concept of using perforated tubes embedded inside the heat storage material significantly improves performance by enhancing the contact surface area between air → absorbent whilst increasing vapour diffusion. The results suggest a linear correlation between thermal performance and moisture uptake, Δ T –Δ w . Determining these operating lines will prove useful for predicting achievable temperature lift and also for effective design and control of thermochemical heat storage systems. [ABSTRACT FROM AUTHOR]

A novel combination of phase change material (PCM) and a solid desiccant layer is proposed for the aim of maintaining dry cool microclimate air adjacent to wet warm skin and hence improve PCM performance in cooling vests used in hot humid environment. A fabric-PCM-Desiccant model is developed to predict the temperature and moisture content of the microclimate air layer in the presence of a PCM-Desiccant packet. The developed model is validated through experiments conducted on a wet clothed heated cylinder for the two cases of using (i) a PCM only packet and (ii) a PCM-Desiccant packet. Microclimate air temperatures and humidity content as well as PCM and desiccant temperatures were measured experimentally and were compared with predicted values by the fabric-PCM-Desiccant model. Good agreement was attained with a maximum relative error of 7% in measured temperatures. A decrease is observed in the humidity content of the microclimate air in the presence of the solid desiccant from 21.23 g/kg dry air to 19.74 g/kg dry air and an increase in the melted fraction of the PCM at the end of the experiment from 0.24 to 0.5. [ABSTRACT FROM AUTHOR]

Desiccant cooling systems are spreading as a promising technology to reduce the energy consumption and environmental impact of conventional electric driven vapour compression systems for air conditioning purposes. Desiccant wheels (DWs) are the key component of the desiccant cooling systems which have received substantial attention. Desiccant Wheel if equipped with a purge section will show better performance, however in most cases purge section is not considered or a fixed purge angle is assumed. In this study, analysis of the purge angle effects on energy and dehumidification performances of DW is carried out and a novel optimal purge angle definition is introduced. A mathematical model is developed and validated in order to model the coupled heat and mass transfer processes in a DW. In addition, the effect of process and regeneration air velocities, regeneration air temperature, rotational speed, desiccant layer thickness, channel length (DW length) and channel hydraulic diameter on the purge angle are studied. The results showed that purge angle is a function of outlet air humidity profile, while the process air velocity as an operating parameter and channel length as a design parameter presented the most substantial effect on the profile. Furthermore, implementation of the optimal purge angle, improves the DW coefficient performance (DCOP) and results in desired conditions of outlet process air without the necessity of substantial increase in the DW size. [ABSTRACT FROM AUTHOR]

• A membrane-integrated solar still as a regenerator has been proposed for LDeACS. • Hydro-phobic semi-permeable membrane in solar still was used to separate LD and air. • Impact of inlet operating conditions of solar still on sub-components of LDeACS was studied. • Proposed LDeACS is capable to provide comfortable conditions for humans in office. • Most sensitive parameter for LDeACS is inlet mass flow rate of LD at solar still. A liquid desiccant-based evaporative air-conditioning system (LDeACS) is one of the excellent alternatives to conventional vapour compression refrigeration system. The liquid desiccant (LD) requires less thermal energy at low temperatures for regeneration, therefore, the use of renewable (solar) energy is a promising source for the regeneration of LD. The prime motive of the research is to assess the applicability of novel solar still (SS) regenerated LDeACS for an office located at tropical savanna humid climate using numerical simulation. The novel solar still provides the combined function of a regenerator and LD heater. The simulation was carried out to evaluate the performance of sub-components of proposed LDeACS by varying the various input operating conditions (inlet mass flow rate of LD; inlet temperature of LD; temperature of absorber plate of SS) of SS. For the simulation, the mathematical model of sub-components of the proposed LDeACS is interlinked using commercial equation solver software. Simulated results indicated that the proposed LDeACS is capable to provide the required human comfort conditions. The parametric analysis of the system revealed that variations in performance parameters of sub-components of LDeACS are more sensitive to the inlet mass flow rate of LD at SS. An increment in the inlet temperature of LD at SS indicates an adverse effect on the performance indices of LDeACS. An increase in absorber plate temperature of SS enhances performance of SS, contrary to expectations, it degrades the performance of the dehumidifier. [ABSTRACT FROM AUTHOR]

• Desiccant coated heat exchangers are promising for atmospheric water harvesting. • Parametric study for various operational and geometric parameters. • Evaluation of the specific water production and specific energy consumption. • The silica gel coating at inlet and outlet regions of channels were underutilised. • The cycle time and air velocity significantly affected performance. Water scarcity is a significant issue in developing countries and remote locations, however, atmospheric water vapour is a widely available and yet underutilised water reservoir. Desiccant coated heat exchangers are a potential sorption reactor for multicyclic atmospheric water generation due to the enhanced heat and mass transfer to the desiccant. This study utilised a transient one-dimensional mathematical model for a plate-fin desiccant coated heat exchanger and adapted the model for atmospheric water generation. From this, a heat and mass transfer analysis and parametric study were conducted to determine the effect of the operational and geometric parameters on the specific water production and specific energy consumption. The heat and mass transfer analysis found that the coating at the inlet and outlet regions of the channels were underutilised. The parametric study found that the adsorption and desorption cycle times should be optimised independently, the primary air velocity should be high during adsorption and low during desorption, and secondary channel cooling during adsorption did not significantly improve performance. The highest specific water production and the lowest specific energy consumption recorded in this study were 5.8 L kg−1 day−1 and 7.7 MJ L-1 respectively. The recorded specific water production values were higher than most desiccant based atmospheric water generators in the literature. However, the performance was significantly reduced at higher ambient temperatures. [ABSTRACT FROM AUTHOR]

• A liquid desiccant air-conditioning system using ethaline is simulated. • Energy, exergy, economic and environmental performances are studied. • Parametric studies confirm the advantage of ethaline at variable conditions. • The advantages of ethaline is illustrated compared with other desiccant candidates. • Ethaline has great prospects in energy saving and CO 2 emission reduction. 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% CO 2 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 CO 2 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 CO 2 emission reduction. [ABSTRACT FROM AUTHOR]

The paper provides a performance analysis assessment of a novel solid oxide fuel cell (SOFC) liquid desiccant tri-generation system for building applications. The work presented serves to build upon the current literature related to experimental evaluations of SOFC tri-generation systems, particularly in domestic built environment applications. The proposed SOFC liquid desiccant tri-generation system will be the first-of-its-kind. No research activity is reported on the integration of SOFC, or any fuel cell, with liquid desiccant air conditioning in a tri-generation system configuration. The novel tri-generation system is suited to applications that require simultaneous electrical power, heating and dehumidification/cooling. There are several specific benefits to the integration of SOFC and liquid desiccant air conditioning technology, including; very high operational electrical efficiencies even at low system capacities and the ability to utilise low-grade thermal energy in a (useful) cooling process. Furthermore, the novel tri-generation system has the potential to increase thermal energy utilisation and thus the access to the benefits achievable from on-site electrical generation, primarily; reduced emissions and operating costs. Using empirical SOFC and liquid desiccant component data, an energetic, economic and environmental performance analysis assessment of the novel system is presented. Significant conclusions from the work include: (1) SOFC and liquid desiccant are a viable technological pairing in the development of an efficient and effective tri-generation system. High tri-generation efficiencies in the range of 68–71% are attainable. (2) The inclusion of liquid desiccant provides an efficiency increase of 9–15% compared to SOFC electrical operation only, demonstrating the potential of the system in building applications that require simultaneous electrical power, heating and/or dehumidification/cooling. (3) Compared to an equivalent base case system, the novel tri-generation system is currently only economically viable with a government’s financial support. SOFC capital cost and stack replacement are the largest inhibitors to economic viability. Environmental performance is closely linked to electrical emission factor, and thus performance is heavily country dependent. (4) The economic and environmental feasibility of the novel tri-generation system will improve with predicted SOFC capital cost reductions and the transition to clean hydrogen production. [ABSTRACT FROM AUTHOR]

Conventional air source heat pump system faces several challenges when adopted in winter season. Solid desiccant air conditioning system can provide humidification and heating power simultaneously and can be driven by low grade thermal energy; it provides a good alternative for air source heat pump systems. However, conventional solid desiccant air conditioning system adopts desiccant wheel with high cost as core component, which hinders the development of such system. Recently, desiccant coated heat exchanger (DCHE) with low initial cost and high efficiency was developed and this paper aims to investigate performance of DCHE air conditioning system adopted in Shanghai winter season. Performance of the system is predicted by a developed mathematical model where supply air states, mass of humidification and coefficient of performance (COP) are adopted as performance indices to evaluate the feasibility and energy utilization ratio of the system. Effects of regeneration water temperature on system performance are analyzed. It is found that under the simulation condition, relatively low regeneration temperature (such as 20 °C) cannot meet the designed standard and relatively high regeneration temperature (such as 40 °C) provides too much extra heating power, thus moderate regeneration temperature around 30 °C is recommended. Meanwhile, switch time is a crucial operation parameter for the system to obtain satisfied supply air, switch time from 40 s to 80 s and from 70 s to 240 s are recommended for transient and average supply air states, respectively. Both mass of humidification and COP increase with increasing regeneration temperature under simulation condition. Also, influences of ambient air temperature and humidity ratio on system performance are discussed to study the feasibility of such system regarding different climatic conditions. Results show that higher humidity ratio of ambient air results in increased humidity ratio of supply air, temperature of ambient air has neglectable effect on supply air. In conclusion, DCHE air conditioning system can be adopted for winter operation with moderate selection of regeneration temperature as well as switch time. [ABSTRACT FROM AUTHOR]

Renewable energy is one of the most promising solutions to both energy and global warming crisis. Energy consumption can be minimized considerably by utilizing solar energy in air conditioning systems operation. One of the popular solar air conditioning technologies is desiccant air conditioning. Nonetheless, conventional desiccant air conditioning systems have a relatively low coefficient of performance (COP). In consequence, two-stage desiccant air-conditioning systems are proposed to improve desiccant air conditioning systems’ COP. Moreover, a recently commercialized cooling method named Maisotsenko cooling cycle which is capable of cooling air near to its dew point temperature is considered to be integrated within the proposed multi-stage desiccant cooling systems. In this paper, three new two-stage desiccant air conditioning systems incorporating Maisotsenko cooling cycle are proposed and investigated in details for hot and humid climates such as UAE. Furthermore, air precooling is considered to improve two stage desiccant air conditioning systems’ COP. Moreover, full transient analysis and optimization are carried out in UAE within June–October. The proposed system can minimize the required solar heating during noon time as the ambient air dry bulb temperature rises. Average COP of the system during electricity load peak hours (10:00–14:00) for all five considered and combined months is 1.77. Average rate of heat input required to operate the system and average building cooling load are determined to be 100.3 kW and 46.2 kW, respectively. Therefore, system average COP is computed to be 0.46. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Desiccant-based air handling units can provide significant operational advantages and can use solar energy as the main heat source. Hereinafter a plant equipped with a silica-gel desiccant wheel is analyzed for two Italian locations (Benevento and Milano). A parametric study involving collectors types, surfaces, tilt angles and installation site has been performed. The proposed system has been compared with a conventional HVAC unit, through dynamic simulations. In terms of energy and environmental analysis, solar desiccant systems should always be preferred to conventional ones, even when the solar thermal energy surplus is fully dissipated. A maximum primary energy saving of about 10% and 20% with flat plat and evacuated tube collectors, respectively, occurs in both locations. The savings increase up to about 58% and 72% in Benevento and 43% and 58% in Milano, when the solar heat excess is completely used for further energy demands. One observes that systems with evacuated tube collectors are preferable where the available space for the solar field is small, instead with larger surfaces flat plate collectors are advantaged. In terms of economic analysis, the shortest payback periods are 6 and 8 years for Benevento and Milano, respectively. [ABSTRACT FROM AUTHOR]

Polymer Electrolyte Membrane Fuel Cell (PEMFC) based systems have recently received increasing attention as a viable alternative for meeting the residential electrical and thermal demands. However, as the intermittent demand profiles of a building can only be addressed by a tri-generative unit which can operate at partial loads, the variation of performance of the system at partial loads might affect its corresponding potential benefits significantly. Nonetheless, no previous study has been carried out on assessing the performance of this type of tri-generative systems in such conditions. The present paper is the first of a two part study dedicated to the investigation of the performance of a tri-generative system in which a PEMFC based system is coupled with a desiccant wheel unit. This study is focused on evaluating the performance of the PEMFC subsystem while operating at partial loads. Accordingly, a detailed mathematical model of the fuel cell subsystem is first developed and validated using the experimental data obtained from the plant’s and the fuel cell stack’s manufacturer. Next, in order to increase the performance of the plant, two modifications have been proposed and the resulting performance at partial load have been determined. The obtained results demonstrate that applying both modifications results in increasing the electrical efficiency of the plant by 5.5%. It is also shown that, while operating at partial loads, the electrical efficiency of the plant does not significantly change; the fact which corresponds to the trade-off between the increment in the gross electrical efficiency and the lower slope of decrement in the auxiliary losses. The obtained results are suitable to be employed to assess the performance of the overall tri-generative system, conducted in the second part of the study, while meeting intermittent load profiles. [ABSTRACT FROM AUTHOR]

In this work the use of a desiccant wheel for air humidification is investigated through a numerical and experimental approach. In the proposed humidification system, water vapour is adsorbed from outdoor environment and it is released directly to the air stream supplied to the building. Such a system can be an interesting alternative to steam humidifiers in hospitals or, more generally, in applications where air contamination is a critical issue and therefore adiabatic humidifiers are not allowed. Performance of the proposed system is deeply investigated and optimal values of desiccant wheel configuration parameters are discussed. It is shown that in the investigated conditions, which are representative of Southern Europe winter climate, the system can properly match the latent load of the building. Finally, power consumption referred to the primary source of the proposed humidification system is compared to the one of steam humidifiers. The present analysis is carried out through experimental tests of a desiccant wheel in winter humidification conditions and through a phenomenological model of the device, based on heat and mass transfer equations. [ABSTRACT FROM AUTHOR]

[Display omitted] • An attempt has been made to design and develop a sustainable fluidized bed dryer. • Solar thermal system was found to be reliable as fulfilled the heat energy demand. • LiCl + CaCl liquid desiccant dehumidifier was found feasible as it reduced the RH by 5 %. • Intermittent FBD shortened the active drying time and retained dried ginger quality. Higher energy demand for ventilating higher mass flux of hot air in fluidized bed drying (FBD) and SDG-7 of the UN has been actuated the researchers towards solar energy intervention in FBD. However, the thumb rules and systematic design calculation of the solar system for FBD have not been reported in the literature. In view of that, a novel solar thermal system was designed and developed by thermo-hydrodynamic analysis, considering the variable physical properties of bioproducts and fluctuating weather. The key design parameters were fresh and desired dried product's moisture content, physical properties of products, dryer capacity, desired drying temperature, ambient conditions, etc. In order to enhance the drying effectiveness, state-of-the-art technology for air dehumidification was integrated by using an aqueous blend of LiCl (35 %) + CaCl (5 %) desiccant. A solar photovoltaic system was also estimated for recirculating the moisture-saturated desiccant over an unglazed solar absorber to regenerate it. From the experiment of ginger drying, it was explicitly found that the developed solar FBD could supply sufficient heat energy (173.06–604.12 W/hr.) compared to the required heat load (124.65 W/hr.), which justifies the operational flexibility. The obtained solar heat fraction (∼1) and solar fraction (0.52–0.64) imply that the solar energy could fulfill the heat energy demand by 100 % and total energy demand (heat + electrical) up to 64 %. The energy efficiency, exergy efficiency, and sustainability index of the solar thermal system were obtained up to 48 %, 2.96 %, and 1.03, respectively. Aiming for effective energy utilization, an intermittent heat supply strategy was associated. Compared to continuous drying, intermittent drying reduced the active drying time (2–2.5 hrs.) and specific energy consumption (33.47–43.83 %) and fortified the dried ginger by reducing shrinkage (11–12 %) and increasing the rehydratability (up to 22.15 %). [ABSTRACT FROM AUTHOR]

[Display omitted] • A sustainable humidity pump system is proposed for indoor relative humidity control. • It integrates desiccant dehumidifier to supply dry air for building ventilated façade. • Metal organic frameworks desiccant is used to enhance the dehumidification stage. • Design and control strategies are proposed for the system, applicable to all climates. • It resulted in 86% reduction in the operation cost compared to conventional systems. Indoor humidity management is vital for both building and occupant health. Conventional methods that decouple the latent and sensible load use desiccant dehumidifiers integrated with vapor compression systems to supply cool dry air to the space and dilute the indoor generated moisture. Such methods remain energy-intensive, especially for high latent load spaces located in hot and humid climate. Direct removal of the indoor generated moisture via moisture migration through naturally ventilated building façade, proved to be a more energy-efficient alternative. However, this strategy suffers from different drawbacks in humid conditions, which impose an intermittent operation on the moisture control system. In this work, a continuous humidity pump system is proposed that integrates a metal organic frameworks-based desiccant dehumidifier to supply dry air to the ventilated building façade provided with breathable insulation. This creates a water vapor pressure gradient between the indoor and dry air to actively drive the indoor moisture to the outdoor environment, irrespective of its humidity conditions. Mathematical models are developed for the system's subcomponents, which are then experimentally calibrated. Design and control strategies are presented for the proposed system and applied for a case study of a high latent load space located in the hot and humid climate of Beirut. Over the entire cooling season, the proposed system resulted in 66 % reduction in the investment cost and 86 % in the operating cost compared to conventionally employed hybrid desiccant – vapor compression cooling systems. [ABSTRACT FROM AUTHOR]

Deep dehumidification of the feed air is expected for the energy saving and stable operation of the air compression process in large-scale industries. Liquid desiccant-based dehumidification technology provides an alternative solution mainly featuring the continuous operation and low regeneration temperature, but the conventional systems still face a challenge to achieve the deep air dehumidification at high air-to-solution flow ratios, especially under high humidity conditions. Based on the cascade matching of driving forces, this study first presents a cascade deep air dehumidification system integrating a direct-contact cooling module (DCCD) and multi-stage internally-cooled liquid desiccant module (MILDD). In particular, the DCCD uses a novel internal matrix structure where the moist air is in direct contact with the cooling water with low hygroscopic. To evaluate the proposed system, a complete thermodynamic model is developed based on the newly-fitted general empirical correlation for mass transfer coefficient between the moist air and cooling water. The numerical model is validated against the initial experiment of the DCCD–MILDD test bench with a mean relative discrepancy of 6%–9%. The supplied air states and energy performance of the cascade system are evaluated at low humidity and high humidity conditions. The cooling water utilization is further improved by two series-looping schemes of cooling water allocation. Numerical results show that the DCCD–MILDD cascade system can achieve deep air dehumidification with the outlet air humidity ratio lower than 6.2 g/kg and the air-to-solution flow ratios over 4.0 even at high humidity conditions. This attributes to an improvement of the coefficient of performance and exergy efficiency, respectively 1.90 and 0.57. This work may provide an effective design of the liquid desiccant-based deep air dehumidification systems applied to the large-scale air compression process. • A cascade system with direct-contact cooling and liquid desiccant is proposed. • Deep dehumidification is achieved at high gas–liquid flow ratios and high humidity. • Correlation for mass transfer coefficient of the direct-contact cooling is developed. • The optimal proportion of cooling water parallel allocation is determined. • Two schemes of cooling water series loop are superior to the parallel one. [ABSTRACT FROM AUTHOR]

This work focuses on the dynamic simulation of an air conditioning system of an airport located in the Mediterranean coast of Andalusia–Spain. It incorporates a desiccant dedicated outdoor air system that operates under variable air volume control strategy. This unit is coupled to a solar source thermal system and to a source heat pump. Several versions of the effectiveness method, applied to the desiccant wheel and based on variable and fix effectiveness parameters, are tested. It is clearly demonstrated that simple approaches based on constant effectiveness parameters, which have been commonly adopted by several authors, provide questionable results. A parametric study investigating the influence of imposing different ranges for the regeneration temperature (minimum of 50 °C and maximum of 80 °C) and for the airflow rates (maximum inlet mass velocity of 3 kg s −1 m −2 ) on the performance results of the system is conducted by considering a suitable approach based on variable effectiveness parameters. Depending on the version of the case simulated: (i) the electrical coefficient of performance of the system varies from 1.22 to 4.07 and (ii) the fraction of time period on August that the system is not able to control the humidity of the zone ranges from 0 to 0.2715. The best case providing controllability of the humidity of the zone during the whole period is characterized by a regeneration temperature range of 50–70 °C and constant airflow rate (inlet mass velocity of 3 kg s −1 m −2 ). The coefficient of performance in this case is 3.2. [ABSTRACT FROM AUTHOR]

Rotary wheel dehumidification is an effective air drying method. This paper analyzes the factors influencing the regeneration temperature from the perspective of exergy. When the dehumidification capacity is fixed, there are two main ways to reduce the regeneration temperature. One is to decrease the exergy destruction during heat and mass transfer in the desiccant wheel, and the other is to decrease the thermal exergy obtained by the processed air after dehumidification. For the first way, the exergy destruction is influenced by the uniformity of the heat and mass transfer driving forces in the desiccant wheel, which can be described by the unmatched coefficient ς . The wheel should be evenly divided, and the two streams of air should have the same flow rate to reduce the exergy destruction. The regeneration temperature can be reduced from above 130 °C to below 70 °C when the air is dehumidified from 20 g/kg to 11 g/kg. For the second way, the thermal exergy obtained by the processed air is influenced by the temperature variation range during dehumidification. Multi-stage dehumidification and pre-cooling are effective mode, with required regeneration temperature lower than 40 °C. [ABSTRACT FROM AUTHOR]

A desiccant dehumidification system with air can be driven by low grade (<80 °C) waste heat. In this paper, which is based on experimental data, the air flow at the outlet of the gas cooler of a trans-critical cycle is forced through a desiccant wheel regenerated by the air flow itself. The hybrid trans-critical refrigerator-desiccant system improves COP by approximately 77% as compared to a classical transcritical. The economical analysis suggests that the investment return-time is acceptable (lower than about 8 years) only at ambient temperature exceeding 35 °C. The ecological analysis indicates that the TEWI of the classical transcritical cycle exceeds that of the hybrid system, by approximately 60%. [ABSTRACT FROM AUTHOR]

Energy saving still and continue a major seek in our life, due to the continuous increase in energy consumptions. So, a desiccant air conditioning system with geothermal energy is conducted in the current study. The thermal analysis of air conditioning system with its different components desiccant wheel, solar collector, heat exchanger, ground heat exchanger and water spray evaporative cooler is presented. Three different air conditioning cycles are simulated in the current study for different zones like: hot-dry zone, warm-dry zone, hot-humid zone and the warm-humid zone. The results show that the desiccant air conditioning system successfully provides a better thermal comfort condition in different climates. This hybrid system significantly decreases the supplied air temperature from 12.7 to 21.7 °C at different climate zones. When ω in , air and T Reg increasing, COP decreases and the ventilation cycle provides the better COP. The highest COP value of the desiccant air conditioning system is about 1.03 while the lowest value is about 0.15. The SHR of makeup cycle is higher than that ventilation cycle at warm and hot-humid zone and vice versa at warm and hot-dry zone. The highest SHR value of the desiccant air conditioning system is about 0.99 while the lowest value is about 0.2. The T sup,air , ω sup,air , COP and SHR isolines may easily be used for pre-evaluating of various cooling cycles in different climates. The hybrid system provides a human thermal comfort at different climates. [ABSTRACT FROM AUTHOR]

• Applying composite superabsorbent polymers for heat transformation applications. • Simplified mathematical model evaluates performance of DCHPs. • DCHPs achieve 30–40% higher COP than conventional heat pumps. • ETC and PV/T solar heating systems are suitable for regenerating DCHEs. • Regeneration with PV/T achieves 10% higher energy efficiency than ETC. Composite superabsorbent polymer desiccants have emerged as a more suitable choice for open-cycle heat transformation applications, namely, heat pumps and dehumidifiers as they record remarkably high sorption capacity at high relative humidity conditions. Existing mathematical models that predict the desiccant coated heat pump's (DCHP) performance exhibit up to 60% discrepancy with experimental findings and are not applicable for variations in experimental conditions/desiccant materials. A simplified mathematical model has been developed in this study to predict DCHP's performance, which records ± 12% and ± 10% discrepancies in outlet air specific humidity and temperature, respectively. In conducting a parametric analysis, the DCHP demonstrated 30–40% improvement in energy efficiency compared to conventional heat pumps. Additionally, the composite superabsorbent polymer desiccant regenerates at 40–50 °C. Integrating either a solar evacuated tube (ETC) and photovoltaic thermal (PV/T) system to provide for thermal regeneration marks an extraordinary potential to achieve significant improvement in energy efficiency. The dynamic performance experiments revealed that although the PV/T was capable of producing hot water at 40 °C, around 10 °C lower than the ETC, the moisture removal ability of the desiccant coated heat exchanger (DCHE) remained identical. Further, the PV/T recorded 11% improved thermal efficiency when compared to the ETC, while providing the electrical power that is required to operate the auxiliary components of the dehumidifier. [ABSTRACT FROM AUTHOR]