Desiccant Air Conditioning System Research Articles

Effect of Air Parameters on LiCl-H2O Film Flow Behavior in Liquid Desiccant Systems

The wettability and stability of a solution’s film on the filler surface are the key factors determining heat and mass transfer efficiency in liquid desiccant air conditioning systems. Therefore, this study investigates the effects of different air parameters on the flow behavior of a lithium chloride solution’s film. The effects of air velocity, air flow pattern, and pressure on the wettability and critical amount of spray are discussed. The results show that the main mechanism by which the air velocity affects the wettability is that the shear stress generated by the direction of the air velocity disperses the direction of the surface tension and weakens its effect on the liquid film distribution. In addition, in the counter flow pattern, the air flow blocks the liquid film from spreading longitudinally and destroys the stability of the liquid film at the liquid outlet, which increases the critical amount of spray. The pressure distribution is similar under different operating pressures when the flow is stable; thus, pressure has little effect on wettability. The simulation results under 8 atm are compared with the experimental results. It is found that the sudden increase in the amount of moisture removal when the amount of spray changes from 0.05 to 0.1 m3/(m·h) in the experiment is caused by the change in the liquid film flow state. In addition, the results show that within the range of air flow parameters for the liquid desiccant air conditioning system, air flow shear force is not the main factor affecting the stability of the solution’s film, and there is no secondary breakage of the solution’s film during the falling-film flow process.

Performance predication of a solar assisted desiccant air conditioning system using radial basis function neural network: An integrated machine learning approach

In this Paper solar desiccant air conditioning system integrated with cross flow Maisotsenko cycle (M-cycle) indirect evaporative cooler is used to investigate the performance of whole system in different range of parameters. Solar evacuated tube electric heater is used to supply the regeneration temperature to the desiccant wheel, whereas, Desiccant Wheel (DW) and M-cycle is used to handle latent load and sensible load separately. Major contribution of this research is to predict system level performance parameters of a Solar Assisted Desiccant Air Conditioning (Sol-DAC) system using Radial Basis Function Neural Network (RBF-NN) under real transient experimental inlet conditions. Nine parameters are mainly considered as input parameters to train the RBF-NN model, which are, supply Air temperature at the process side of desiccant wheel, supply air humidity ratio at process side of the desiccant wheel, outlet temperature from the desiccant wheel at process side, outlet humidity ratio from the desiccant wheel at process side, regeneration temperature at regeneration side of the DW, outlet temperature from the heat recovery wheel at process side, outlet humidity ratio out from the Heat Recovery Wheel (HRW) at process side, temperature before heat recovery wheel regeneration side of the system, humidity ratio before heat recovery wheel regeneration side of the system. Four parameters are considered as the output of the RBF-NN model, namely: output temperature, output humidity, Cooling Capacity (CC), and Coefficient of Performance (COP). The results of the RBF-NN model shows that the best Mean Squared Error (MSE) and Regression coefficient (R) for outlet temperature prediction are 0.00998279 and 0.99832 when regeneration temperature is 70 °C and inlet humidity at 18 g/kg. Best MSE and R for predication of outlet humidity are 0.0102932 and 0.99485 when the regeneration temperature is 70 °C and inlet humidity at 16 g/kg. Best MSE and R for predication of COP are 0.0106691 and 0.9981 when the regeneration temperature is 70 °C and inlet humidity 12 g/kg. Best MSE and R for predication of CC are 0.0144943 and 0.99711 when the regeneration temperature is 70 °C and inlet humidity 14 g/kg. Experimental and predicted performance parameters were in close agreement and showed minimal deviation. Investigations of predicted results revealed that trained RBF-NN model was capable of predicting the trend of output result under the varying input condition.

Optimization of solar and heat pump complementary powered desiccant air conditioning system

The effective utilization of renewable heat sources is critical for energy saving in desiccant air conditioning systems. A new solar and heat pump complementary powered desiccant air conditioning system is proposed. The system consists of a solar and water source heat pump complementary reheat subsystem, a two-stage desiccant wheel, a three-stage air cooler, and a two-stage heat pipe exchanger. Simulation are performed in the transient simulation software TRNSYS, and the particle swarm optimization and the Hooke Jeeves algorithm with life cycle cost as the objective function are applied to optimize the collector area, the heat storage tank volume and the water-source heat pump power. The results show that the monthly average coefficient of performance of the system is 5.1, 5.6, 5.5 and 4.8 in June, July, August and September, respectively. Compared to the conventional air conditioning system, the new system has a 58.4% reduction in operation cost and a payback period of 6.6 years. The CO2 emission reduction rate of the new system can reach 65.2% in July and 65.1% in August, while it is the lowest in September at 62.9%. Based on the above, the new system has better energy efficiency, economic and environmental benefits.

A data-driven model for a liquid desiccant regenerator equipped with an evacuated tube solar collector: Random forest regression, support vector regression and artificial neural network

The application of a solar-assisted liquid desiccant air-conditioning system equipped with evacuated tubes, focusing on the assessment and comparison of various artificial intelligence (AI) models is investigated. Specifically, Support Vector Regression (SVR), Multi-Layer Perceptron Artificial Neural Network (MLP-ANN), and Random Forest Regression (RFR) models are assessed for predicting key performance indicators: mass removal rate, efficiency, and effectiveness. Additionally, different optimizers within the Artificial Neural Network (ANN) framework—such as Adam, Stochastic Gradient Descent (SGD), and RMSprop—are systematically examined and tuned. The study encompasses the selection of the most suitable AI model for each target variable, considering parameters such as ambient temperature, solar radiation, timestamp, airflow rate, and initial solution concentration as influential factors in the modeling process. It is found that the best predictor model for effectiveness is SVR with RBF kernel. For MRR and efficiency, it is MLP-ANN with respectively AdamW and NAdam optimizers. The disparity of prediction of the MRR, efficiency and effectiveness target are respectively 0.72%, 1.07% and 0.5%, on average, indicating a precise prediction. Furthermore, including timestamps as model inputs significantly boosts accuracy, an aspect often neglected in prior research, leading to a noticeable minimum 5% rise in the R2 score.

Solar driven liquid desiccant dehumidification system: Measurements and annual system simulations

Liquid desiccant air conditioning (LDAC) systems are used for dehumidification of air to low dew point temperatures. In the presented study a TRNSYS model of a LDAC unit is developed and validated with laboratory measurements. This model is coupled with a solar thermal system that provides heating water for the regeneration process. With this model dynamic annual system simulations can be carried out to simulate the dehumidification of a building. The solar fraction is evaluated for various infiltration rates of the building and solar collector areas with an internally cooled as well as an adiabatic absorption process.The simulation results reveal that high solar fractions of 70% to 81% can be achieved when dimensioning the solar thermal system to cover the regeneration heat demand on a good summer day. This is due to the good correlation of solar irradiance and dehumidification load. Without internal cooling of the absorption process (adiabatic conditions), the solar fraction is reduced by about 10percent points for the same size and operating conditions.

Dynamic simulation of a novel liquid desiccant air-conditioning system for greenhouse cooling and water recovery

We present dynamic, hour-by-hour modelling of a multi-stage nanofiltration regeneration system for liquid desiccant air-conditioning (NF-LDAC) of horticultural greenhouses in 17 locations covering four climate types. Four technologies are compared: fan ventilation, evaporative cooling (EvapC), conventional air-conditioning (AC), and NF-LDAC. The comparison is based on acceptable conditions for cultivation and coefficient of performance (COP). On average, fan ventilation and EvapC achieve acceptable conditions for 2 months per year, compared to 5.4 and 10.5 months for AC and NF-LDAC respectively. The highest COP value of 7.6 for NF-LDAC is reached at Colombo (Sri Lanka), followed by 5.3 at Mecca (Saudi Arabia). The permeate of the multi-stage regenerator can be recycled for irrigation, providing water savings. The highest water saving of 63% is at Mecca. These results are inferior but more realistic than those from an earlier idealised and steady-state model, which predicted a COP of 12.4 and water savings of 100% at Mecca. Nevertheless, in hot desert climates, NF-LDAC maintains acceptable conditions for year-round cultivation and saves water that is scarce in such climates. Future advances in nanofiltration membrane fabrication could increase the COP of NF-LDAC to 12.1 at Colombo and 7.4 at Mecca.

Experiments and modeling on thermal performance evaluation of standalone and M-cycle based desiccant air-conditioning systems

This study aims to evaluate the performance of standalone and Maisotsenko-cycle based desiccant air-conditioning systems with silica gel through experimental and explainable artificial intelligence methods. In order to examine the desiccant systems' performance, deep neural networks have been constructed based on the optimal hyper-parameters provided by the Bayesian surrogacy. The influential factors, such as regeneration air temperature and relative humidity, primary air temperature and relative humidity, among other system features like regeneration temperature and humidity, are chosen as the inputs using feature engineering and correlation heat maps. The results indicated that with the right framework and training data, the proposed model can forecast the performance of the standalone and M-cycle-based desiccant air conditioning systems with a great accuracy (i.e. R2 = 0.99). In addition, regeneration temperature and humidity, and inlet regeneration air temperature are considered to be the primary parameters that affect the thermal performance of Maisotsenko-cycle and stand-alone desiccant systems. The regeneration conditions are shown to have a positive correlation with the primary and regeneration outlet temperatures while having a negative correlation with the primary and regeneration outlet relative humidity. The primary inlet relative humidity has the greatest impact on the primary outlet relative humidity while the regeneration inlet temperature has the highest impact on the regeneration outlet relative humidity of the system. In addition, the primary inlet relative humidity is found to have positive correlations with the outlet regeneration and primary relative humidity and outlet regeneration temperature. Also, the primary air inlet temperature is found to be directly associated with the outlet primary relative humidity and temperature for the considered systems.

Performance analysis and optimization of a solar assisted heat pump-driven vacuum membrane distillation system for liquid desiccant regeneration

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].

Accelerated Water Desorption of Oligomeric Poly(ethylene glycol) by Addition of Poly(propylene glycol) for Energy-Efficient Water Recovery Systems.

Adsorbents are used to recover water vapor from the atmosphere in desiccant air conditioning (DAC) and atmospheric water harvesting (AWH) systems. Solid adsorbents have been conventionally used in these systems, though liquid adsorbents are considered to be more effective for energy-efficient fluidic thermosystems because of their low regeneration temperatures (45-70 °C). While most previous studies have focused on improving the adsorption performance, the desorption performance of adsorbents can also be a critical factor in improving the energy efficiency of these systems. Thus, this study aimed to improve the water desorption efficiency, focusing on the liquid adsorbents. We found that mixing hydrophobic molecules into a liquid adsorbent decreases the desorption temperature and increases the water-desorption efficiency. Oligomeric poly(ethylene glycol) (PEG), a common moisture-adsorbing liquid oligomer used in detergents and cosmetics, was selected as the liquid adsorbent. Oligomeric poly(propylene glycol) (PPG), which has a structure analogous to PEG and lower hygroscopicity, was selected as the hydrophobic molecule. Water adsorption and desorption experiments showed that the mixture of PPG with PEG promoted the desorption of water molecules beyond that of PEG, while thermogravimetric differential thermal analysis revealed a decrease in the water desorption temperature with increasing PPG content. The improved desorption efficiency was ascribed to the likely water adsorption equilibrium between PEG and PPG in the blend; water molecules are preferentially desorbed from PPG, which has weaker water-adsorbate interactions. The proposed concept is expected to be incorporated into various hygroscopic liquids to develop energy-efficient liquid adsorbents for DAC and AWH.

Performance Evaluation of Different Desiccant Matrix Materials Coated with Silica Gel

ABSTRACT Excessive cooling of air is required in conventional air conditioning systems to reduce the humidity, leading to the development of desiccant wheel-based air conditioning systems. The desiccant wheel consists of desiccant material which is deposited on matrix material. In this study, aluminum, magnesium alloy, Teflon and fiberglass have been considered matrix materials of the desiccant wheel. A one-dimensional mathematical model has been developed to evaluate the effect of these matrix materials. The results show that fiberglass can be selected as a suitable matrix material for drying applications because it has maximum moisture removal (1.92 g/kg) and temperature difference (4.72 °C) at optimal rotational speed, which are desirable for drying. While aluminum can be selected as a suitable matrix material for air conditioning applications because, at the optimal rotational speed, it has lower maximum moisture removal (1.26 g/kg) and temperature difference (3.14 °C) as compared to other matrix materials. As moderate maximum moisture removal and lower temperature difference are the requirements for air conditioning. A similar trend of results has been also obtained for other parameters (volume ratio, regeneration velocity, regeneration temperature, etc.) of this study.

Performance Assessment of Solar Desiccant Air Conditioning System under Multiple Controlled Climatic Zones of Pakistan

Over the past decade, the integration of desiccant technology with evaporative cooling methods has proven to be highly effective and efficient in providing comfortable indoor environments. The performance of desiccant-based direct evaporative cooling (DEC) systems is strongly influenced by environmental conditions, and their output behavior varies across multiple climatic zones. It is not easy to assess the system performance in numerous climatic zones as it is a time-consuming process. The current study focuses on determining the feasibility of a solid desiccant integrated with a direct evaporative cooler (SDI-DEC) for three different climatic zones of Pakistan: Lahore (hot and humid), Islamabad (hot and semi-humid) and Karachi (moderate and humid). To serve this purpose, a specially designed controlled climate chamber with an integrated air handling unit (AHU) was installed to create multiple environmental conditions artificially. It could also provide global climatic conditions under temperature and absolute humidity ranges of 10 °C to 50 °C and 10 g/kg to 20 g/kg, respectively. The weather conditions of the selected cities were artificially generated in the climate chamber. Based on different operating conditions, such as inlet air temperature, humidity and regeneration temperature, the performance of the system was estimated using performance indicators like COP, dehumidification effectiveness, solar fraction and supply air conditions. Results showed that the maximum temperature achieved from solar collectors was about 70 °C from collectors with an area of 9.5 m2. Moreover, the observations showed that when the regeneration temperature was increased from 60 °C to 80 °C, the COP of the system decreased about 41% in a moderate and humid climate, 28% in a hot and semi-humid environment and 23% in a hot and humid climate. The results revealed that an SDI-DEC system has the potential to overcome the humidity and cooling loads of the multiple climatic scenarios of Pakistan.

Energy Performance and Thermal Comfort Delivery Capabilities of Solid-Desiccant Rotor-Based Air-Conditioning for Warm to Hot and Humid Climates—A Critical Review

There has been considerable research worldwide on desiccant-based air-conditioning during the past 30 years. The rationale for the push for this new research focus has been twofold: (a) the need to provide an alternative to conventional refrigerative air-conditioning systems which rely heavily on fossil fuels as their energy sources, and (b) the need to provide better thermal comfort in air-conditioned spaces in warm to hot and humid climates. A desiccant air-conditioning system consists of several components to cool and dehumidify the air before it is supplied to a conditioned space. Earlier research work has identified the potential advantages of this technology, which include the following: (1) working fluids that do not impact on the ozone layer, (2) reduced electricity consumption, (3) improved indoor air quality, (4) simpler construction and less maintenance, and (5) integral provision of heating and cooling for cold/temperate climates. On the other hand, the authors of this paper identified the following drawbacks: (1) inevitable heating of air while being dehumidified, (2) the need for desiccant regeneration and low thermal COP paradox, (3) limited options for regeneration heat sources, (4) limited options for reliable cooling, and (5) low electrical coefficient of performance (COP). This paper presents a critical review of the energy and thermal comfort performance of solid-desiccant rotor-based air-conditioning systems, and discusses in detail their potential advantages and drawbacks. This critical review found that the drawbacks of the systems outweigh their identified advantages. The main reason for this is the inevitable heating of air while being dehumidified and counterintuitive addition of moisture to air during the evaporative cooling process. During the past 30 years of research and development efforts, no significant innovations have been discovered to resolve these crucial issues. Unless future research and development is directed to find a breakthrough, this technology will have limited commercial application.

Performance evaluation of an innovative liquid desiccant air-conditioning system directly integrating a heat pump with two membrane energy exchangers

For high moisture removal applications with improved indoor air quality, the use of liquid-to-air membrane energy exchangers (LAMEEs) in liquid desiccant (LD) air-conditioning systems has been suggested in the literature. This study introduces a novel configuration for a heat pump LD system to improve its dehumidification and energy use. The evaporator and condenser coils of the heat pump (HP) are embedded in the LD channels of two LAMEEs; one is an internally cooled dehumidifier (ICD), and the other is an internally heated regenerator (IHR). These LAMEEs are designed to directly use the HP condenser coils for the IHR's regeneration process while also effectively controlling the local temperature rise of the LD solution inside the ICD. An integrated CFD model for both the ICD and the IHR is simultaneously solved, considering the coupling of the HP components and the closed loop of the LD solution. This model, which counts all existing balances of energy, mass, and salt content in various components, determines the condensing temperature employed in the regeneration process at each operational condition. This system-level model, which requires few inputs, is novel and very reliable for evaluating the overall performance of the proposed system in terms of specific dehumidification rates and COP. Case studies were carried out using the annual dehumidification design conditions of five Middle Eastern cities known for their hot and humid climates. For the cities of Sharm El Sheikh and Dammam, respectively, the system achieved promising results with specific dehumidification rates of 130.3 and 172.2 g/(m2.h) and system COPs of 6.38 and 5.67, when the temperature and specific humidity of outside fresh air of (30 °C, 19 g/kg) and (32.8 °C, 23.2 g/kg) were cooled and dehumidified to (20.18 °C, 6.52 g/kg) and (21.0 °C, 6.61 g/kg). Using the regeneration air flow rate as high as possible boosts the performance of the proposed HPLD system, concluding that the system is preferable for all-fresh-air handling units.

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.

Seasonal analysis of a desiccant air-conditioning system supported by water-cooled PV/T units

Seasonal analysis of a desiccant air-conditioning system supported by water-cooled PV/T units

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.