Desiccant Air Research Articles

Solid desiccant air conditioning system using desiccant dehumidifiers with cooling technique and thermal recovery unit: Experimental investigation and performance analysis

The displayed experimental investigation pursues to design and fabricate high-efficient desiccant air conditioner that achieves the sustainable development by protecting the environment from harmful emissions, achieving thermal comfort conditions, and rationalizing energy consumption. To achieve this, smart innovative desiccant dehumidifiers and energy recovery unit were incorporated with the suggested air conditioner. The smart innovative desiccant dehumidifiers aimed to improve the air dehumidification capacity and avoid the effect of the adsorption heat by using larger cooling rates to cool the process air. To minimize power consumption, regeneration air was pre-heated using an energy recovery unit. The results showed that the ultra-efficient desiccant air conditioner suggested in the present study represents an effective design because it could achieve thermal comfort conditions and rationalize energy consumption. The ultra-efficient desiccant air conditioner could supply the cooling air with average temperature and humidity ratio varying between 11.9 and 14.6 °C and 6.89–8.9 gw/kgda, respectively. Also, the energy analysis presented that the proposed desiccant air conditioner is high-efficient where the average values of thermal coefficient of performance and electrical coefficient of performance reached 3.68 and 3.79, respectively. Moreover, the average saving in thermal energy was varying between 21.9 and 28%.

Effect of operating parameters on the performance of rotary desiccant wheel energized by PV/T collectors

The main energy input of a desiccant air conditioning system is the low-quality thermal ener-gy required for regeneration, which can be obtained from waste heat, geothermal resources or solar energy. Regeneration thermal energy can be produced as well as energizing components such as fans, pumps, auxiliary air heaters, and control elements of the system by using pho-tovoltaic-thermal solar collectors (PV/T). In this study, parametric analyzes were performed to investigate the effect of regeneration temperature and air frontal velocity on the tempera-ture and dehumidification performance of a solid silica-gel desiccant wheel and on the wa-ter-cooled PV/T collectors used to provide the regeneration thermal energy. The regeneration temperature was varied between 50 and 70°C, and air frontal velocity between 1.3 and 4.1 m/s. The analyzes show that the dehumidification efficiency increases from 13.94% to 33.04% as regeneration temperature increased from 50°C to 70°C at 1.3 m/s air frontal velocity at which dehumidification efficiency is maximum. At 4.1 m/s air frontal velocity, the required regener-ation thermal energy is maximum and increases from 49.64 kW to 132.48 kW at the same re-generation temperature change. The low regeneration temperature resulted in desirable latent performance and undesirable sensible heat transfer performance in DEW. Finally, considering the whole system, it was concluded that the optimum regeneration air temperature for the performance parameters is 60°C.

Water Vapor Adsorption on Desiccant Materials for Rotary Desiccant Air Conditioning Systems

In order to determine the water vapor adsorption performance of a rotary desiccant-based air conditioning system, the behavior of water adsorption on cylindrical pores of different sizes was studied by using classical density functional theory (CDFT) based on perturbated chain statistical associating fluid theory (PC-SAFT). Firstly, the structural parameters of the desiccant material were characterized by scanning electron microscopy (SEM), X-ray Energy Dispersive Spectrum (EDS), and N2 adsorption/desorption isotherms, as well as adsorption equilibrium measurements of water vapor at temperature range 293–308 K. Secondly, the potential energy equation of water molecules in cylindrical pores was determined, and contribution of various terms of PC-SAFT for simulating fluid in cylindrical pores were established. Finally, the pore size distribution (PSD) of the desiccant materials is determined by the PC-SAFT kernel. Moreover, water vapor condensation was investigated with the PC-SAFT model in micropores. The results indicate that the rotary desiccant materials have a large number of micropores with a volume of 0.3669 cm3/g and the amount of water adsorption is about 0.285 g/g. The condensation pressure and the pore width corresponding to the saturated pressure P0 grow with an increase in the temperature, signifying that adjusting the PSD of the material has a significant effect on improving the dehumidification performance. The research concludes that the PSD range of the oxide cylindrical pore between 1.09 and 1.53 nm is particularly beneficial for dehumidification. This study provides valuable theoretical guidance for optimizing dehumidification materials.

Response surface modeling and optimization scheme of an internally cooled liquid desiccant air conditioning system

Applying an internally cooled liquid desiccant air conditioning system (LDAC) is a promising energy-saving and emission-reduction scheme for hot and humid areas. This research investigates the application of an internally cooled LDAC for performance enhancement in hot and humid areas like Hong Kong. The combined system integrates liquid desiccant dehumidification (LDD) and regenerative indirect evaporative cooling (RIEC) without a power-intensive compressor. The internally cooled LDD removes latent heat from the hot and humid air before the RIEC cools it. To ensure efficient energy utilization, the LDD captures the exhaust air to assist in the dehumidification and initial cooling of the fresh air, which alleviates the efficiency deterioration of the desiccant. An all-fresh air system is used for better indoor air quality. To optimize the performance of a system with many influencing parameters, the response surface method (RSM) and multi-objective optimization are used to optimize and assess the potential and performance of the system. The system cooling capacity (C), latent heat removal rate (Qd), and dehumidification efficiency (ηd) are used as the optimization objectives. The response surface model and desirability function approach optimize six critical parameters, achieving a 7.6% improvement in dehumidification performance with low airspeed (1.5 m/s) and high desiccant concentration (40%) during high-humidity months. Increasing the extraction ratio of the RIEC by 20% in warmer months enhances the peak cooling capacity by 23.6%. This research contributes to implementing internally cooled LDAC systems and provides insights into optimizing monthly operation patterns in hot and humid regions.

Sorption property, excess enthalpy, and solvatochromic parameters of choline lactate

Sorption properties, including isotherm shape, adsorption energy, maximum uptake, and cyclic hydrothermal stability, have a significant influence on the optimization of absorbents for diverse desiccant air conditioning systems. The sorption behavior of the water/choline lactate ([ch][lac]) pair was examined using a dynamic vapor sorption (DVS) analyzer. Data analysis identified type-III isotherms. The Dubinin-Astakhov (D-A) formulation, defined by a temperature-independent Polani potential, was successfully applied to the sorption equilibrium curve. The Kamlet-Taft polarity parameters were tested using solvatochromic probes with a UV/Vis spectrophotometer. Multivariate regression analysis was performed to correlate the water affinity coefficient of the D-A model with the Kamlet-Taft polarity parameters using linear solvation energy relationships (ISERs). The solvatochromic parameter of dipolarity/palarizability (π*) had a positive contribution to the water affinity coefficient of ionic liquid (IL) desiccants, and the general trend of influence was hydrogenbondacidity(α)>π*>hydrogenbondbasicity(β). Excess enthalpies were correlated well with solvatochromic parameters. The differential enthalpies and entropies, first virial coefficient (A0), and isosteric enthalpies of sorption at zero surface coverage were also discussed. The enthalpy of activation at zero surface coverage was deduced from sorption kinetics. The hydrothermal cyclic stabilities and ambient regenerabilities were determined by cycle stress tests.

Variable operating conditions characteristics of circulating wheel dehumidification air conditioning system

For its efficient application of low-grade energy, the circulating wheel dehumidification air conditioning system has received a lot of attention and research in response to the shared challenges of environmental protection, energy conservation, and low carbon. Desiccant wheel dehumidification air conditioning systems can recycle waste heat as a desiccant wheel regeneration heat source and improve air quality, which is expected to achieve low energy consumption and high-efficiency dehumidification. The desiccant wheel dehumidification air conditioning system is divided into a treatment air channel and a regenerative air channel. Treated air is directly sent to the air conditioning room after dehumidification and cooling, and regenerative air is directly discharged to the outdoors after the completion of regeneration. Therefore, a new type of recirculated desiccant wheel dehumidification air conditioning system is established. In this paper, the experimental study of the circulating regeneration wheel dehumidification air conditioning system is carried out. Dehumidification characteristics under variable working conditions are quantified and studied. Compared with the water cooling unit, the dehumidification rate of the new circulating wheel air conditioning system is improved effectively. The effects of different treated air temperatures (28 °C–40 °C) and treated air relative humidity (50%–85%) are obtained. The experiment shows that the proposed air conditioning system can effectively improve the dehumidification rate compared with the conventional direct condensation of seawater. Under the same circulating shunt coefficient, the system dehumidification rate increases gradually with the increase of the temperature and humidity of the treated air and the temperature of the reclaimed air. The dehumidification rate has an optimal value, and the corresponding optimal circulation shunt coefficient is 50%–75%, which decreases with the increase of the temperature and humidity of treated air and increases with the increase of the temperature of regenerated air.

Performance improvement of solar-assisted air-conditioning systems by using an innovative configuration of a desiccant dehumidifier and thermal recovery unit

The present study aims to construct an innovative configuration of a desiccant air conditioner that achieves thermal comfort conditions with the lowest electrical power consumption rates. To achieve this, an innovative configuration of a desiccant dehumidifier channel with multi-stages of silica-gel pads and heat exchangers for inter-cooling (DDC-MSSGP&HEI) was incorporated with the suggested air conditioner. The DDC-MSSGP&HEI is characterized by increasing the dehumidification capacity as well as cooling the process air with cooling rates higher than the heat generated by the adsorption heat effect. The thermal recovery unit was also incorporated with the suggested air conditioner to achieve the lowest electrical power consumption rates; it was utilized as a preheating unit to heat the regeneration air before entering into the solar collectors. The results showed that the system could supply air with a temperature of 12.2 °C and a humidity ratio of 7 gw kgda−1, this is because of the positive effect of DDC-MSSGP&HEI. Also, the energy performance of the innovative configuration of a desiccant air conditioner is more efficient where TCOP and ECOP reached 1.96 and 3.14, respectively at a regeneration temperature of 90 °C. Moreover, the energy saving due to the utilization of the thermal recovery unit reached 28.7%. The economic feasibility indicates that the proposed configuration has the potential to save the life cycle cost by a rate of up to 33% compared to the conventional system with a payback period of 5.8 years.

Scalable and high-efficiency lignocellulose sponge-based evaporators for solar-driven desalination and desiccant regeneration

Liquid desiccant air conditioning systems (LDAC) have attracted increasing interest for the high efficiency of temperature and humidity control. Improving the regeneration performance with low-grade energy could make LDAC systems more competitive. In this work, by combining Chinese ink and lignocellulose sponge, we developed an inexpensive, efficient and large-scale evaporator that allows regeneration of desiccant via solar energy. Results show that the evaporator exhibits remarkable salt-resistance capacity, rendering it suitable for effective seawater desalination and regeneration of high-concentration desiccant. Even for the 40 wt% desiccant at about 22 °C, the regeneration rate can reach 0.63 kgm−2 h−1 under 1-sun irradiation. The outdoor experiments further confirmed the high regeneration rate of the evaporator. Additionally, concentrated desiccant presents an alternative means of solar energy storage. Considering the high efficiency, easy preparation, and remarkable salt resistance, the lignocellulose sponge-based evaporators could advance the practical application of solar heat localization for seawater desalination and desiccant regeneration.

Estimation of Evaporation of Water from a Liquid Desiccant Solar Collector and Regenerator by Using Conservation of Mass and Energy Principles

Solar thermal energy-powered air conditioning technologies are receiving increased attention. Among the solar energy-driven cooling technologies, open type liquid desiccant air conditioning (AC) system is emerging as a promising technology, which has a solar driven desiccant solution regenerator. In this type of system, the evaporation of water and concentrating the desiccant or regenerator performance determines the cooling performance of the AC system, which necessitates its development and experimental performance testing under actual operating conditions. The setup is made of a black painted corrugated solar collector of area 0.8 m × 1.84 m covered with glass, and a liquid desiccant solution tank and distribution system over the absorber. Solar regeneration experiments on calcium chloride–water solution were carried out on the setup and a total of five sets of meteorological, collector and solution property data were collected through concentrating the desiccant from 32.9 initially to 51.3% in five days. The evaporation of water from the regenerator was analyzed using energy and desiccant mass conservation. For a typical day, the mass of water evaporated was estimated to be 3.10 and 3.16 kg over a day, as estimated by conservation of mass and energy principles from a 34.8 kg of calcium chloride solution with initial desiccant concentration of 43.6% stored in the tank.

Investigating the impact of flow rate and moisture content for different concentration of liquid desiccant solution

The desiccant air conditioning system consists of two processes, namely cooling and dehumidification, in which the air temperature and humidity are controlled in order to provide comfortable thermal conditions. A typical system includes a dehumidifier, indirect evaporative cooler, and regenerator. The desiccant is selected depending on its ability to absorb water vapor present in the air. In this study, calcium chloride solution was used as a desiccant for the desiccant solution regeneration process, and a flat plate solar collector was employed. Different variables, such as the primary air flow rate, desiccant flow rate, and the concentration of the desiccant solution, were changed during the experiments. The impact of these variables on the performance parameters of the desiccant system such as moisture removal rate, moisture efficiency, enthalpy efficiency, sensible heat ratio, and the mass transfer coefficient was studied. The obtained results revealed that as the solution concentration and the flow rate of primary air increase, the moisture removal rate, sensible heat ratio, and mass transfer coefficient increase. A particular value of inlet primary air flow rate (0.18Kg/s), an increase in the inlet concentration of calcium chloride solution from 0.85 to 0.95 leads to a rise in moisture removal rate, sensible heat ratio, and mass transfer coefficient of (1.1 _1.65) g/s, (0.18-0.25), and (0.01075-0.0123) m/s respectively. While at a certain inlet concentration of a desiccant solution (0.95), increasing the inlet primary air flow rate from 0.1Kg/s to 0.18Kg/s leads to an increase in the moisture removal rate, sensible heat ratio, and mass transfer coefficient o (0.94-1.26) g/s, (0.24-0.26), and(0.0038 -0.011) m/s respectively.

Modeling comparison and theoretical study of mass transfer characteristics for desiccant coated air channel under isothermal dehumidification

Coupled heat and mass transfer phenomena are encountered in desiccant coated dehumidifier, and their numerical modeling is becoming indispensable. In this study, three conjugate heat and mass transfer models were compared to clarify the effects of interparticle mass transfer and local kinetic non-equilibrium on modeling accuracy, and the models were validated by experiment results of silica gel and FAM Z01 coated dehumidifiers with single one air channel. Furthermore, a parametric study on the separate mass transfer characteristics of the dehumidifier under isothermal dehumidification was conducted based on one of the improved models. Results demonstrated that the effect of interparticle mass transfer should be involved, while the local kinetic non-equilibrium tends to be considered for desiccants with steep isotherm shape. Parametric study revealed that as air velocity increases, both air- and solid-side mass transfer change significantly, while desiccant layer thickness, interparticle porosity and isotherm shape mainly affect solid-side mass transfer. The average mass transfer Biot numbers Bim of desiccant layer with relative low thickness of 0.1 mm under various parameters are in the same order of magnitude as 1, indicating that the mass transfer resistance on solid side cannot be ignored generally.

Performance enhancement of electrodialysis regeneration of deep eutectic solvent for liquid desiccant air conditioning systems

Despite the promising energy-saving potential of the electrodialysis regeneration technique for liquid desiccant regeneration in air conditioning systems, there are still issues that need to be resolved in electrodialysis separation systems, such as the high initial cost owing to the complexity of the cell gaps, over-limiting current, and electro-osmotic flow effects. This study utilized stereolithography (SLA) 3-D printing technology to manufacture a low-cost scalable model of an electrodialysis system. An electrodialysis system with a cell gap of 5 mm and serpentine flow feed spacers was investigated to regenerate deep eutectic solvent (DES) developed from choline chloride and ethylene glycol as a bio-friendly liquid desiccant for air conditioning systems. Ammonium chloride electrode rinsing solution with about 250 mS/cm electric conductivity was utilized to enhance the conductive properties of the system. The optimum parametric operating conditions for the system are found to be around 0.0058 m/s for the circulation flow rate, 0–4 wt.% for the concentration difference of the diluted and regenerated solutions' cells, and 6–8 V voltage supply energy input. In 60 minutes of operation, the current efficiency value of the constructed model was discovered to be as high as 65.82%. Matching the performance threshold of the commercial electrodialysis equipment described in the literature for regenerating lithium chloride conventional liquid desiccant.

Parametric investigations on a novel bubble column liquid desiccant dehumidifier with internal cooling

Increasing demand for space cooling and proportionate demand for electrical power call for less power intensive technology with lower carbon footprint. The liquid desiccant (LD) based air conditioning systems can remove latent heat more efficiently, mainly using heat energy coming from waste or renewable energy source. A novel, simple and corrosion-free bubble column liquid desiccant air dehumidifier (BCLD_ADH) with provision for internal cooling of LD has been developed in this work. The advantages of providing internal cooling and effect of LD concentration as well as ambient conditions are evaluated in this experimental work. Two new type of effectiveness, one based on ambient wet bulb temperature and the other on crystallization temperature of LD are proposed here to give due credit to higher potential of moisture removal available in internally cooled dehumidifier. At 40% concentration of LD, the dehumidifier effectiveness at wet bulb temperature was 67% for adiabatic dehumidifier, but could be increased to 95% using internally cooled dehumidifier. Using higher concentration is necessary for adiabatic dehumidifier but less important for internally cooled dehumidifier as lower LD temperature helps retain higher potential for mass transfer. The inlet air humidity ratio helps to increase change in humidity ratio while higher mass flow rate also helps increase moisture removal rate proportionately.

Steady-state performance assessment and geometrical optimization of packed-bed liquid desiccant air dehumidification systems

Steady-state performance assessment and geometrical optimization of packed-bed liquid desiccant air dehumidification systems

Thermoeconomic Optimization of a Polygeneration System Based on a Solar-Assisted Desiccant Cooling

This paper presents a thermoeconomic analysis of a polygeneration system based on solar-assisted desiccant cooling. The overall plant layout supplies electricity, space heating and cooling, domestic hot water, and freshwater for a residential building. The system combines photovoltaic/thermal collectors, photovoltaic panels, and a biomass boiler coupled with reverse osmosis and desiccant air conditioning. The plant was modeled in TRNSYS and simulated for 1 year. A parametric study defined the system’s setup. A thermoeconomic optimization determined the set of parameters that minimize the simple payback period. The optimal structure showed a total energy efficiency of 0.49 for the solar collectors and 0.16 for the solar panels. The coefficient of performance of the desiccant air conditioning was 0.37. Finally, a sensitivity analysis analyzed the influence of purchase electricity and natural gas costs and the electricity sell-back price on the system. The optimum simple payback was 20.68 years; however, the increase in the energy cost can reduce it by up to 85%.

Deep learning artificial intelligence framework for sustainable desiccant air conditioning system: Optimization towards reduction in water footprints

Deep learning artificial intelligence framework for sustainable desiccant air conditioning system: Optimization towards reduction in water footprints

Simulation study of membrane distillation regenerator based on reduced pressure air gap

To reduce the regeneration energy consumption and improve the regeneration effect of liquid desiccant in membrane-based liquid desiccant air conditioning (M-LDAC), this paper combines the widely used Vacuum Membrane Distillation (VMD) and Air Gap Membrane Distillation (AGMD) methods, and innovatively proposes a reduced pressure air gap membrane distillation regeneration system, and applies the control variable method to simulate the influencing factors (desiccant temperature, flow rate, and air gap side vacuum) in the system. The results showed that the desiccant temperature and air-gap side vacuum had more influence on the system membrane flux than the flow rate, and the simulation showed that there was an optimal range of vacuum, and the membrane flux reached 12.55 kg/(m2·h) when the desiccant temperature was 90 °C, the flow rate was 0.2 m/s, and the vacuum was 40 Kpa, which increased the membrane flux by 14.8% compared with 10 Kpa. The analysis proves that the use of vacuum on the air gap side can effectively improve the membrane flux, which provides a reference for the optimal design of future liquid desiccant regenerator modules.

A Polygeneration System Based on Desiccant Air Conditioning Coupled with an Electrical Storage

This study presents an extension of a previous paper recently published by the authors. In particular, the current paper focuses on adding electrical storage to a polygeneration system developed for residential applications. Different from the previous work, it aims to design an off-grid facility. The polygeneration plant provides electricity, space heating and cooling, domestic hot water, and freshwater for a single-family dwelling in Almería, Spain. The main system technologies are photovoltaic/thermal collectors, reverse osmosis, and desiccant air conditioning. Lead-acid battery storage was added as a backup for the electrical system. The system was performed in the TRNSYS simulation environment for one year with a 5-min time step. A parametric study was carried out to investigate the grid dependence according to the number of batteries installed. Design optimization was also performed to provide the optimal system configuration for the off-grid case. A solar collector efficiency of 0.55 and a desiccant air-conditioning coefficient of performance of 0.42 were obtained. All demands were fully supplied, and the primary energy saving and CO2 saving achieved 100%. A minimum battery state of charge of 30% was reached for a few hours all year long.

Review of liquid desiccant air dehumidification systems coupled with heat pump: System configurations, component design, and performance

Vapor Compression Systems (VCS) are the most common air conditioning technology. VCS cool the air to its dew point temperature (overcooling) to remove water vapor in the air through condensation and then reheats the air back to the comfort temperature for direct use. The VCS process is inefficient due to overcooling and reheating. Liquid Desiccant Dehumidification (LDD) is a potentially energy-efficient air conditioning. LDD removes water vapor in the process air using liquid desiccant’s high-water affinity. It hybrids with sensible cooling to control temperature and humidity separately. The LD in the LDD becomes weak after dehumidification. The LDD needs additional heating to regenerate the weak Liquid Desiccant (LD) to a high concentration for dehumidification.Earlier versions of the LDD systems use highly concentrated liquid desiccant (large water removal capability) to dehumidify the air by only dealing with latent load. It leads to highly elevated temperatures above 60 °C of heat sources (combustion or electric resistance-based heating) for regeneration. The energy needed for the elevated temperature heat resource significantly reduces or demolishes the benefit of LDD systems. In the recent two decades, researchers have investigated a new configured LDD system that couples an LDD with a heat pump at both dehumidification and regeneration sides for better efficiency.The heat pump provides cooling (from the evaporator) for both dehumidification and sensible cooling and simultaneous heating from the condenser for regeneration. The highly integrated system (HP-LDD) with improved efficiency enables the LDD to operate at lower concentrations and temperatures in dehumidification and regeneration.This paper depicts the working principle behind HP-LDD and its heating and cooling requirements. It reviews the comparison between the HP-LDD systems and the conventional LDD systems regarding system configurations, component design, energy efficiency, and dehumidification performance characteristics. The main findings from the review include the preferred use of packed bed over membrane-based dehumidifiers, the use of internally cooled dehumidifiers enabled by the HP cooling capacity, the high dispersion of HP operation conditions, and the dependence of dehumidification performance on various dehumidifiers. An outlook for future research on HP-LDD strategies is presented based on the reviewed works and their limitations.

Experimental investigation on air dehumidification performance of metal organic frameworks and its application potential for solid desiccant air conditioning systems

In this paper, the air dehumidification performance of MIL-101(Cr) and MIL-101(Cr)-SO3H used for solid desiccant air conditioning (SDAC) system is experimental investigated, and compared with conventional desiccant materials including silica gel, molecular sieve and activated carbon. The results show that the moisture saturated adsorption capacity of MIL-101(Cr) is 1206–1392 mg/g at 25.0–33.5 °C/95%RH which is 4–6 times of the conventional adsorbents. MIL-101(Cr) presented an S-shaped isotherm with steep point between 30% and 50%RH which provide the possibility for low temperature regeneration. The water vapor desorption measurement results show that MIL-101(Cr) could have 96.3% (93.5%) desorption rate at 45 °C/15.95%RH (45 °C/30.60%RH) after saturated adsorption at 33.5 °C/58.0%RH. The modified material MIL-101(Cr)-SO3H didn’t show better moisture adsorption and desorption performance than MIL-101(Cr) at moderate relative humidity range but higher moisture adsorption capacity at low relative humidity cases. Its saturated adsorption capacity for moisture is 2–3 times of traditional adsorbents. MIL-101(Cr) has shown excellent moisture adsorption capacity and low-temperature regeneration property which makes it be a potential option for SDAC system optimization.