Liquid 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.

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.

Experimental study on passive-mixing strategy of a liquid-desiccant air-conditioning system

In a solution recirculation-type liquid-desiccant system, small fractions of the diluted and concentrated solutions must be mixed to maintain the solution concentration. Active-mixing strategies require many moving parts such as pumps, valves, and pipelines to mix the solutions, which increase the complexity of the system structure and frequency of mechanical breakdowns. This study proposes a new passive-mixing strategy in which a diluted low-density solution and concentrated high-density solution is naturally mixed, without the need for moving parts or complex pipe structures, because of the difference in solution densities. The operating performance of the proposed strategy was experimentally investigated and compared with that of a reference active-mixing strategy. The results demonstrate the feasibility of the proposed passive-mixing strategy in terms of maintaining the solution concentration and achieving the dehumidification and regeneration performance. In addition, the proposed strategy maintained the solution levels in the absorber and regenerator sumps, thereby improving the energy performance by 4% compared with the reference active-mixing strategy. In summary, the proposed passive-mixing strategy is more applicable than the reference active-mixing strategy because of its air-conditioning performance, system durability, practicality, and energy performance.

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.

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].

Applicability of a heat-pump-driven liquid-desiccant air-conditioning system in energy-efficient buildings

Building trend is toward energy-efficiency by reducing building sensible load, while neglecting latent load. A heat-pump-driven liquid-desiccant (HPLD) air-conditioning system has emerged for effectively handling building latent load in energy-efficient buildings with low indoor sensible heat ratio. However, previous studies only investigated one building type, failing to account for the increase in building energy-efficiency. This study estimates building thermal loads of four different energy-efficient high latent load buildings, simulating building trend. Then, as energy-efficiency of buildings increases, the changes in indoor thermal comfort and energy consumption of the HPLD air-conditioning system and reference vapour compression system are compared. Simulation results show that in building with the highest energy-efficiency, the reference system can only maintain thermal comfort for 43.3% and 24% of summer operating hours when primarily meeting supply-air target temperature and humidity, respectively. Contrastingly, the proposed system can maintain thermal comfort in all building types for almost 100% of summer operating hours due to decoupled control of air temperature and humidity. Additionally, the proposed system saves up to 33.2% of operating energy when both systems achieve the same thermal comfort satisfaction. In conclusion, the HPLD air-conditioning system with decoupled control is more applicable as energy-efficiency of buildings increases.

Applicability of a liquid-desiccant air-conditioning system in energy-efficient buildings with high latent load

To reduce global greenhouse gas emissions, the recent building trend is toward energy efficiency, achieved primarily by reducing the indoor sensible load. However, handling the indoor latent load has been overlooked. Reflecting this building trend, heat-pump-driven liquid-desiccant (HPLD) air-conditioning systems have emerged as a promising technology that effectively handles indoor latent loads in energy-efficient buildings with low indoor sensible heat ratios (SHR). However, the aforementioned building trend has not been simulated in previous studies. Thus, the performance analysis of HPLD air-conditioning systems has been investigated for only one type of building. In this study, the indoor thermal loads of four different energy-efficient types of high-latent-load buildings were estimated to simulate building trends. Then, the changes in indoor thermal comfort based on room conditions and energy consumption of the reference air-conditioning system (i.e., the vapor compression system) and the proposed HPLD air-conditioning system were compared as the energy efficiency of the buildings increased. The indoor thermal loads were estimated using TRNSYS18 software, and both air-conditioning systems were modelled via the integration of theoretical analyses and the effectiveness-NTU model. The simulation results show that the indoor SHR decreased from 0.8 on average in the reference building to 0.64 on average in the building with the highest energy efficiency. In the building with the highest energy efficiency, only 43.3% and 24% of summer operating hours were thermally comfortable when the reference system operated to meet only the supply-air target temperature and primarily the supply-air target humidity via the condensation dehumidification process, respectively. In contrast, owing to the decoupled control of air temperature and humidity, the proposed system could maintain a thermally comfortable room in all building types for almost 100% of summer operating hours. Finally, when both systems achieved the same thermal comfort satisfaction, the proposed system could save up to 33.2% of the operating energy compared to the reference system in energy-efficient buildings. Based on the results, it can be concluded that the proposed HPLD air-conditioning system adopting decoupled control is more efficient as the energy efficiency of buildings increases.

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.

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.

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.

Multi-objective optimization for capacity matching and energy performance of heat-pump-driven liquid-desiccant air-conditioning system

In heat-pump-driven liquid-desiccant (HPLD) air-conditioning systems, releasing condensing heat from heat pump to regenerator solution and exhaust air (i.e., capacity matching) is important for maintaining dehumidification performance, operational feasibility, and system stability. Therefore, this study optimizes capacity matching, especially focusing on releasing extra condensing heat, which has simply been assumed to be well-treated in previous studies, in conjunction with energy performance. With four design variables under various outdoor air conditions, a multi-objective optimization is conducted to simultaneously maximize system coefficient of performance (COP) and minimize a newly defined capacity-matching index of extra condenser. Pareto front, a set of optimum points, is obtained using a multi-objective genetic algorithm. Final optimum solutions are then determined and discussed based on a decision-making scenario. In optimization results, the regenerator air and solution flow rates should be respectively greater and lower than those of the absorber. The optimum temperature of absorber inlet solution is generally distributed at approximately 18 °C, while that of regenerator inlet solution is significantly influenced by the decision-making scenario. Finally, the system COP was maximally increased by 24 %, and the capacity-matching index of extra condenser was maximally decreased by 55 %, compared with each initial value.

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.

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.

Numerical and experimental study on the regeneration performance of a liquid desiccant system coupled with rotating packed bed and vacuum

High moisture load generated during the air quality control process introduces a considerable energy consumption, liquid desiccant air-conditioning system has some constrains during the application although it provides an opportunity to save energy. Therefore, a novel regeneration system of liquid desiccant coupled with rotating packed bed (RPB) and vacuum technique was proposed in this study. A numerical model of RPB was developed and validated in order to characterize the heat and mass transfer process during the regeneration and correlate to its performance, furtherly, an experimental rig was built to study its feasibility of RPB application in regenerators. To facility the investigation, the moisture removal rate was introduced to evaluate the regeneration performance and thereafter the effects of three key factors, rotating speed, regeneration pressure and initial concentration of liquid desiccant, were investigated accordingly. The results show that the moisture removal rate increases with the rotating speed for which the maximum of 17.395 g·L-1·min−1 was reached; meanwhile it decreases with the regeneration pressure and initial concentration of desiccant, among which the concentration has a greater impact on moisture removal rate. Compared to traditional packed bed regenerators, the rotating packed bed can significantly enhance the heat and mass transfer rate. In overall, the proposed system can reduce the energy consumption by 10.6%, the regenerate performance was improved significantly, and the feasibility of proposed system was verified to prompt its application.

Energy, exergy, exergoeconomic and enviroeconomic (4E) assessment on a liquid desiccant air-conditioning system using green deep eutectic solvent of ethaline

Despite the recognition of its energy-saving potential, the promotion of liquid desiccant air-conditioning system is limited by the drawbacks of existing desiccants in long-term or large-scale use. Deep eutectic solvent with good bio- and eco- friendliness has not yet been tested for systematic study in air-conditioning system. In this paper, a deep eutectic solvent, ethaline, is utilized in a heat pump driven liquid desiccant air-conditioning system, whose energy, exergy, exergoeconomic and enviroeconomic performances are studied. Under basic condition of ambient temperature of 35 ℃ and relative humidity of 80%, its systematic coefficient of performance reaches 1.406 with exergy efficiency of 32.65%. Meanwhile, 52.36% CO2 emission can be reduced compared with conventional condensation dehumidification air-conditioning system. The payback period of such system at basic condition with 20 kW cooling load is 14.4 years, and it can be significantly reduced in applications with larger cooling load. Parametric analyses for different requirements and environments are conducted as well. The energy and environmental superiority of ethaline is more significant under more latent loads, higher supply air flow rate and lower fresh air ratio. Under ambient temperature ranging from 28 ℃ to 40 ℃, the effect of CO2 emission reduction for ethaline reaches to extents of more than 38%. The advantages of ethaline are further illustrated in comparison with other potential desiccant candidates, in aspects of toxicity, price and corrosiveness. The potential performance improvement approach for ethaline used as liquid desiccant is also proposed and discussed. The results in this paper demonstrate the promising prospect of ethaline quantitatively, and provide enlightening for exploration of new liquid desiccant. In pace with the broadening application of air-conditioning system, liquid desiccant air-conditioning system using such green desiccants can be promoted, which brings out great prospects in energy saving and CO2 emission reduction.

Progressive development in hybrid liquid desiccant-vapour compression cooling system: A review

Over the past few decades, the air-conditioning (AC) sector has seen significant growth in liquid desiccant air-conditioning (LDAC) system technologies. The LDAC system has been considered as a viable substitute to vapour compression system (VCS) as a result of its exceptional temperature and humidity control and energy-saving ability. This study provides an overview of the developments associated with the incorporation of liquid desiccant technologies into VCS units to date. Various configurations of dehumidifiers and hybrid technologies have been compiled and analysed according to economic and environmental considerations. The operating principle of dehumidification and the regeneration process of a LDAC system are initially discussed. Afterwards, the numerous advancements in materials for liquid desiccant and dehumidifiers, which play a crucial part in the dehumidification and regeneration processes, are discussed. Numerous studies have demonstrated that by incorporating liquid desiccant systems with the VCS units, a comfort level of cooling can be achieved by employing a dehumidification process while providing 40–80% energy savings. This review article is beneficial to researchers since it identifies research gaps and explores prospective future research techniques to further enhance the performance of hybrid liquid desiccant-vapour compression systems..

A comparative study on the regeneration performance of traditional heating and heat localization methods

Liquid desiccant air-conditioning (LDAC) system is a promising alternative to the traditional vapor compression system. The most energy-consuming part of LDAC system is desiccant regeneration. An urgent issue that needs to be addressed is the inefficiency of traditional regeneration method. Solar heat localization is a novel and high-efficiency strategy for seawater desalination. However, the wide application is confined due to the low-efficient of water condensation and harvesting. In this work, the regeneration performance of heat localization method was investigated and an electric heating sheet was adopted to circumvent the effect of solar reflection. Compared with traditional heating method, the regeneration performance can be significantly improved by heat localization method. The regeneration efficiency of desiccant with 40 % concentration was significantly improved by 6 times (about 23.15 %) through heat localization method. Heat localization method allows immediate concentration of high-concentration desiccant with a low-temperature rise of regenerated desiccant. The low-temperature rise is beneficial for LDAC system due to less cooling energy is needed. This work is expected to extend the application of solar heat localization and provide some new information for liquid desiccant regeneration.

Economic and Experimental Assessment of KCOOH Hybrid Liquid Desiccant-Vapor Compression System

A liquid desiccant dehumidification cooling system is a promising, energy-saving, high-efficiency, environmentally friendly technology that maintains thermal comfort effectively indoors by utilizing renewable energy sources or waste heat to enhance system efficiency. In this research, a small-scale (6 kW cooling capacity) hybrid liquid desiccant air-conditioning system (HLDAC) is proposed to evaluate the dehumidification performance of a non-corrosive potassium formate (KCOOH) solution. For this, four input parameters, namely, inlet air flow rate, inlet desiccant temperature, inlet desiccant concentration, and inlet specific air humidity, were selected. Moreover, the different combinations of experiments were designed by employing response surface methodology (RSM) to evaluate the dehumidification performance parameters, namely, dehumidifier latent heat load, coefficient of performance of hybrid system, and moisture removal rate (MRR). Further, a comparative performance analysis between the hybrid system and a standalone vapor compression system (VCS) unit was carried out. The result showed a remarkable increase in coefficient of performance, which was observed at about 28.48% over the standalone VCS unit. Furthermore, the economic assessment of the proposed hybrid system is presented in this paper. Finally, from the economic analysis, it was concluded that the hybrid system had a payback time of 2.65 years compared to the VCS unit.

A state-of-the-art review on the liquid properties regarding energy and environmental performance in liquid desiccant air-conditioning systems

Liquid desiccant air-conditioning system (LDAS) becomes an attractive option for reducing the energy consumption of conventional air-conditioning systems. Despite lots of published papers on LDAS in various aspects, there is not yet a comprehensive and up-to-date review on the properties of liquid desiccants, while the selection of liquid desiccant plays essential role in the overall performance of LDAS. In this paper, a state-of-the-art review on the properties in regard of energy and environmental performance is delivered for present and potential liquid desiccants, including vapor–liquid equilibrium, specific heat capacity, safety concerns. The current situations and future concerns of liquid desiccant investigation can be obtained, while different kinds of liquid desiccant candidates can be compared and evaluated comprehensively. Existing liquid desiccant of halide salt faces severe drawback of corrosiveness in long-term use. Compared with existing liquid desiccants, the candidates of weak acid salt, ionic liquid and deep eutectic solvent behave low toxicity and friendly corrosiveness, whereas their weak moisture absorption ability, high cost or high viscosity is the bottleneck for further applications. Therefore, the mixture of them can be regarded as a promising candidate in LDAS applications, but the fundamental properties are urged to be measured. The work in this paper provides momentous reference and guidance for the exploration of new liquid desiccant as well as the evaluation of future prospect of LDAS.