Desiccant Regeneration Research Articles

Regeneration of Spent Desiccants with Supercritical CO2.

Supercritical CO2 (sCO2) dehydrates desiccants such as silica gel, activated carbon, graphite, and molecular sieve by dissolving and emulsifying the water. Despite differences in the surface area of these desiccants, the amount of water removed under comparable conditions is the same. The main advantage of sCO2 dewatering over conventional hot-air regeneration lies in situations where the exhaust contains environmentally sensitive components, e.g., in nuclear detritiation operations where the small footprint and closed cycle benefits of the sCO2 process are especially significant. Calculations show that depressurizing the spent sCO2 to half its initial pressure drops out most of the water, after which the CO2 can be repressurized and reused. sCO2 dewatering requires about half the energy needed for thermal drying because the water is removed nonevaporatively.

Investigating the performance of direct contact membrane distillation for liquid desiccant regeneration and freshwater production: A CFD-based study

Liquid desiccant air conditioning (LDAC) systems offer a promising solution for enhancing indoor thermal comfort, air quality, humidity control, and energy efficiency. This study focuses on the critical aspect of regenerating liquid desiccants in LDAC systems, which has the potential to enhance system efficiency and performance significantly. Using computational fluid dynamics (CFD) to model direct contact membrane distillation (DCMD) for liquid desiccant regeneration and freshwater production, this research paves the way for improving the performance of LDAC systems. The DCMD process, which involves mass transfer across a membrane driven by a temperature gradient between the permeate and feed channels, is a key area of exploration in this study. The findings of this study have significant implications for the design and operation of LDAC systems. The impact of feed inlet velocity and temperature on vapor flux for liquid desiccant regeneration is substantial, with increasing the feed inlet temperature leading to a fourfold increase in water vapor flux. Similarly, increasing the feed inlet velocity boosts flux due to enhanced convective heat transfer. Membrane characteristics, such as porosity and thickness, are key determinants of system performance. These findings underscore the importance of optimizing these parameters for efficient liquid desiccant regeneration and freshwater production in LDAC systems, thereby enhancing their overall performance and energy efficiency. Finally, a mathematical model for water vapor flux was developed to investigate water vapor flux as a function of key factors such as inlet temperature, velocity, liquid desiccant concentration, and membrane characteristics.

Multi-hierarchical structured PTFE membrane for liquid desiccant dewatering via membrane distillation

Poly (tetrafluoroethylene) (PTFE) can be used for robust separation membranes owing to its exceptional chemical and thermal stabilities. Simultaneously achieving construction of hierarchical pore structures and re-entrant surface microstructures during the fabrication of PTFE membrane holds significant importance in addressing the issues of low flux and membrane wetting in membrane distillation (MD). Herein, we proposed a flexible method for manufacturing hierarchically structured PTFE membrane by combining electrospinning/spraying with sintering/welding. The present approach facilitated the controlled fabrication of a superhydrophobic PTFE membrane with slippery surface (exhibiting a water contact angle of 153.5°, and an ultralow sliding angle of 7.5°) without using fluoride-based solvents or external nanoparticles. Moreover, the anti-wetting mechanism and performance stability of the PTFE membranes in MD were thoroughly investigated. In liquid desiccant regeneration experiments, the 20 wt% LiCl solution was successfully concentrated to 28.64 wt%. Furthermore, the PTFE membrane demonstrated a stable flux (>30 kg m−2 h−1) and relatively low permeate conductivity (<15 μs cm−1) during treating simulated seawater for 30 h. The present work offers a new approach to fabricate multi-hierarchical structured superhydrophobic membranes for desalination and regeneration of liquid desiccants.

Improving Vegetable Seed Quality and Dryer Performance with an Automated Desiccant-Assisted Hybrid Solar Dryer System

A desiccant-assisted automated hybrid solar dryer was developed for vegetable seeds. The dryer consisting two sections, one for drying the air and the other for the regeneration of desiccant. The collector area of the dryer is 1.3 sq.m and three trays of 0.18 m 2 of area each in the drying chamber. The dryer consists of a real-time data acquisition system for recording the temperature, and humidity, and the dryer was equipped with an automatic temperature control unit to maintain the temperature at a preset level(≤40°C). The bottom of the drying chamber was also filled with desiccant for continuous drying after sunshine. The performance of the developed dryer was evaluated by drying fresh onion seeds having an initial moisture content of 18-20% (wb) and compared with the developed dryer without desiccant considering both the drying parameters and quality parameters of the dried seeds. The developed dryer with desiccant was found to produce a significant difference in drying rate (P&lt;0.0001) for onion seeds compared to dryers without desiccant drying. All the quality parameters in terms of germination percentage, and vigor index I and II, found to have a significance difference (P&lt;0.0001) compared to without desiccant drying. The developed solar dryer provides a promising alternative for the continual drying of other materials including onion even after sunshine hours with real-time data acquisition system and also found to be superior in retaining quality.

Sorption Drying of Wheat Seeds Using Kieserite as a Solid Desiccant

The moisture content (MC) of wheat seeds must be reduced before storage using appropriate dehydration processes. Desiccant drying is a promising alternative to conventional drying methods because it improves seed quality while providing overall energy efficiency. This study explores the sorption drying of wheat seeds using granulated kieserite MgSO4·H2O as a solid desiccant, which has a high water capacity and is regenerated at low temperatures &lt;100 °C. Desiccant characterization was conducted using SEM-EDS, XRD, DSC-TG, and particle size analysis. Wheat seeds mixed directly with kieserite in various mass ratios were dried under uniform stirring and controlled temperature conditions. A 240-min drying time was required to reduce the initial MC of wheat from 21.5% to 15.1% at a desiccant-to-grain ratio of 1:1. After 360 min, a final MC of 14.4% was achieved. The germination energy and seed capacity after sorption drying were 91 ± 1% and 97 ± 2%, respectively. Due to the available water capacity of kieserite, several batches of seeds can be dried without intermediate desiccant regeneration. This study is useful for developing low-cost, non-thermal, and sustainable drying technology for various agricultural products.

A hybrid solar-driven membrane distillation-assisted liquid desiccant air conditioning system: Mathematical modeling and feasibility analysis

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

Parametric analysis and multi-objective optimization of a membrane distillation liquid desiccant regenerator with heat/moisture recovery and potable water production

The regenerator plays a crucial role in determining the energy efficiency of green liquid desiccant air-conditioning systems. This paper presents a novel air gap membrane distillation regenerator featuring heat recovery and portable water production. Based on a validated numerical model, performance evaluation of the regenerator combined with an external heat exchanger is conducted in terms of regeneration capacity (RC) and energy consumption (Qin). The comparison of flow patterns demonstrates that the counter-flow has a slightly higher RC, while the parallel-flow has a significantly lower Qin and is therefore preferable from the perspective of COP. The effects of key parameters including feed and coolant desiccant inlet temperatures (Tf,in &Tc,in), mass flow rate (mdil), membrane length (L), air gap thickness (δag), desiccant concentration (Xdil) and solution heat exchanger effectiveness (εshe) on the performance are investigated. The results show that Tf,in is the dominant factor on performance compared to Tc,in and mdil, and increasing L leads to a marked growth in both RC and COP regardless of the raised Qin. Additionally, it is found that narrowing the air gap from 3 mm to 1 mm can improve RC and COP by 69.9 % and 50.1 % respectively. As for εshe, it has no influence on RC but remarkable impacts on Qin and COP. Moreover, the heat recovery by the coolant channel is proved to save nearly 8 % of energy input under the involved conditions. Finally, the NSGA-Ⅱ based multi-objective optimization is performed to obtain the Pareto front for maximizing RC and minimizing Qin. And the optimal solution through TOPSIS decision-making offers a RC = 975.8 g/h and a Qin = 1938 W. The findings provide a basis for design and application of the novel regenerator.

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.

Optimal design of a novel combined heat source system using solar energy and data center waste heat for desiccant regeneration

Nowadays, the raise of a front-loading dehumidified evaporative cooling system has been a key breakthrough in overcoming the application limitations of evaporative cooling technology. However, the desiccant regeneration process of this system still relies on a traditional heating method, coexisting with a single form of heat source and high energy consumption. To solve these problems, a novel heat source system combining data center waste heat and solar energy was proposed in this paper. Through experimental tests and simulation, the performance of this system was investigated and validated, and the collecting-area and inclination angle of system’s collector were reasonably optimized. The results indicate that the novel system not only demonstrates an advantageous performance, but also have the ability to provide regenerative heat in a stable and continuous manner: daily outlet temperature could reach up to 93.36 °C, effective operating hours could be extended by approximately 2 h compared to singular solar heat source, and optimized annual effective operating hours could reach 1036 h with a monthly average outlet temperature ranging from 71.2–90.6 °C. This study can provide a technical support for the application of front-loading dehumidified evaporative cooling system.

Water generation through desiccant using novel‐designed solar still coupled with heat pipe vacuum tube collector: An experimental observation

AbstractIn this article, an experiment has been carried out with heat pipe vacuum or evacuated tube collector to produce water from atmospheric air. In this experiment, the regeneration and adsorption method has been adopted, that is, water has been produced through the adsorption and regeneration of desiccants. The desiccant is heated through a hot surface to facilitate its regeneration. Limited experiments have been conducted to obtain water through the regeneration of desiccant using a hot surface. For the condensation of water vapor, a novel box has been designed, named the “novel‐designed acrylic box.” The water is collected in a measuring flask or beaker to determine its quantity. Silica gel desiccant has been used for the adsorption and regeneration of water vapors. In this experiment, the adsorption process for silica gel was carried out in two different ways. In the first method, 1 kg of silica gel was scattered on the copper tray, that is, inside the system, while in the second method, 1 kg of silica gel was scattered on the paper, that is, outside of the system. In the first case silica gel adsorbed 137 g water vapor, and in the second case, it adsorbed 232 g water vapor. In the first case of adsorption, 70 mL water was produced while in the second case of adsorption, 175 mL water was produced from ambient air. The system's maximum efficiency was found to be 4.9%. Effects of various parameters, such as solar intensity, ambient temperature, wind speed, and so forth, have been studied.

Experimental investigation on mass transfer for regeneration of liquid desiccant

Desiccants can be used in conjunction with solar energy to provide a viable alternative to traditional air conditioning techniques. Liquid desiccant regeneration was proved to be an effective method to extract the moisture from solution with a relatively less energy in order to regenerate the desiccant. An experimental study was carried out to analyze the effect of temperature for regeneration process using an injected air through the liquid desiccant solution (calcium chloride dihydrate) by a dryer. Many tests with different operating conditions such as air temperature, humidity ratio, air velocity and solution level are investigated in order to demonstrate that this salt is capable to absorb moisture and can be regenerated at a low temperature. Experimental results showed that the mass transfer is affected by the air conditions. Also, the vapour pressure difference between the air and liquid desiccant surface is the driving force of the mass transfer process. In this analysis it was also determined that the CaCl2.2H2O could be regenerated at low temperature around 48 to 60°C hence the possibility of using the flat plate solar collectors for its regeneration and this salt can be used in a system (LDCS).

Heat and mass transfer characteristics of vertical falling film cylindrical plastic surfaces under partial wetting conditions for liquid desiccant regeneration

The regenerator plays a dominant role in the overall energy-economic performance of liquid desiccant systems. Nevertheless, very few studies have been reported on falling film liquid desiccant regenerators. Most of the previous studies targeted experimental/numerical modelling needs of regeneration process under design conditions. In the current research workexperimental investigation of regeneration process is carried out to study the coupled heat and mass transfer process for adiabatic regeneration of LiCl liquid desiccant over outer surface of vertical Plain and Modified polypropylene cylindrical surfaces under design (complete wetting) and part load (partial wetting) operating conditions. Modified cylindrical surfaces are developed to compensate the poor wetting of the plastic surfaces. New generalised one-dimensional numerical philosophy is proposed to accommodate the need of part load operating conditions by inclusion of actual wetting of the working surface as well as convective heat transfer happening from dry patches of solid surface to the flowing air. The heat and mass transfer coefficients are determined by solving the governing coupled heat and mass balance non-linear differential equation using the numerical finite difference method. It is found that the Modified surface offered an average improvement of 35.8% in the mass transfer coefficient under partial wetting conditions. New Sh and Nu number correlations are proposed by incorporating heat and mass transfer driving potentials and new parameter wetting factor. The developed correlations predicted the change in humidity and temperature across the regenerator with an average error of 6.2% and 7.5%, whereas from the existing two correlations found in the literature, the first one predicted the same experimental observations with an average error of 54.6% and 36.2%, while second one predicted with an average error of 77.3% and 22.0%, respectively. The results highlighted that the assumption of complete wetting of working surface under part load operating conditions leads to significant error in prediction of air outlet conditions. The proposed correlations will be helpful for numerical modelling and simulation of falling film regenerators under wide range of liquid loading conditions.

Minimizing annual energy consumption using innovative cooling system architecture for diverse climatic conditions

Separate sensible and latent cooling (SSLC) is a promising technology for enhancing the energy efficiency of space cooling systems. In this paper, we propose an SSLC configuration consisting of an indirect evaporative cooling (IEC) device and vapor compression cycle (VCC) for handling space sensible load, and a desiccant wheel for handling space latent load. The performance of the proposed configuration is investigated using physics-based or empirical models for each component. A year-round simulation study of the proposed SSLC system is performed for 12 different cities with diverse climatic conditions. This study considers electrical, thermal, or solar energy for desiccant wheel regeneration. Parameters governing the system performance such as the air flowrate ratio in the IEC and the DW, DW regeneration air temperature, and supply temperature are studied. The proposed SSLC configuration is superior to the conventional system in all cities. The enhancement of seasonal coefficient of performance (sCOP) ranges between 50 and 261 %, 67 and 387 %, and 60 and 2072 % with yearly electrical energy savings of 33 and 72 %, 40 and 79 %, and 38 and 95 % for electrical, thermal, and solar energy for regeneration of DW, respectively.

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].

Atmospheric water harvesting by osmotic distillation and direct contact membrane distillation using hydrophobic hollow fiber membranes

The use of a liquid desiccant air dehumidifier is an energy-efficient technology that can improve both indoor air temperature and humidity. However, the risk of concentrated liquid desiccant leakage into the air conditioning system during dehumidification can corrode the system, negatively impact indoor air quality, and potentially harm residents. To address this issue, this study investigates the effectiveness of osmotic distillation (OD) and direct contact membrane distillation (DCMD) for dehumidification and regeneration, respectively. The study analyzes the impact of inlet operating parameters, including liquid desiccant concentration, temperature, and flow rate, and air flow rate on the dehumidification performance and stability of the OD process. Calcium chloride was utilized as the liquid desiccant in this study. The results indicated that the dehumidification performance of the OD process improved with a higher desiccant concentration and lower desiccant temperature. However, the desiccant flow rate did not have a significant impact on dehumidification performance. Furthermore, the dehumidification performance decreased with a higher inlet air flow rate, but the moisture removal rate increased. The OD process demonstrated stable operation during the dehumidification process. DCMD was effective for desiccant regeneration, and no scaling occurred due to the deposition of calcium chloride crystals. However, the permeation flux of DCMD decreased as the feed concentration increased due to a decline in the feed vapour pressure and an increase in concentration polarization effect. In conclusion, the experimental results indicated that OD can effectively dehumidify humid air, while DCMD is a viable option for desiccant regeneration.

A study of preheating liquid desiccant and its effect on the performance of a PV/T system

When photovoltaic (PV) cells operate, their electrical efficiency decreases due to a rise in temperature. To counteract this, Photovoltaic/thermal (PV/T) systems have been created to maintain PV cell electrical performance and utilize the heat they release to warm fluids. A low temperature is required for liquid desiccant regeneration, which allows for the possibility of using the heat released by PV cells to preheat a unit prior to the main heating unit. This study investigates the use of an aluminum cold plate with a serpentine tube placed behind a PV panel to transfer heat dissipated by PV cells to a desiccant solution. Two desiccant solutions were tested: lithium chloride (LiCl) and potassium formate (KCOOH). Using COMSOL Multiphysics, three-dimensional CFD simulations were conducted to analyze the temperature of both the photovoltaic cells and the solution exiting the cold plate. The simulation results were then used to determine the hybrid system's electrical, thermal, and overall efficiencies. Under nominal operating cell temperature (NOCT) conditions, the total efficiency of the hybrid system was 57.15 % and 55.28 % when using LiCl and KCOOH solutions, respectively, with a cold plate inlet temperature of 25 °C and a mass flow rate of 30 g.s-1. Given the similar efficiency of the system and the lower corrosiveness and cost of KCOOH solution compared to LiCl solution, the study concluded that using KCOOH solution is more appropriate. Simulations were conducted under NOCT conditions to compare the system's performance using desiccant solution and water. As expected, the thermodynamic properties of water resulted in a greater decrease in temperature and increased cell efficiency, but using the desiccant solution directly in the cold plate for cooling eliminated the need for an additional heat exchanger in the system.

Performance evaluation of regeneration of high-concentration liquid desiccant using direct contact membrane distillation

Membrane-based absorptive dehumidification is an attractive technique for humidity control that reduces energy consumption. The process involves a dehumidifier that absorbs moisture with a liquid desiccant, and a regenerator that concentrates the desiccant solution to complete the process cycle. In this study, a regeneration module employing a membrane distillation (MD) mechanism was developed, and its performance was evaluated theoretically and experimentally. Detailed theoretical investigations demonstrated the impact of the spacer on the convective thermal and material transport at the membrane surface at a high desiccant concentration. The module employs a hydrophobic and microporous composite membrane consisting of a polypropylene support layer and an active layer composed of polytetrafluoroethylene. For all the experiments, the desiccant solution used was an aqueous solution containing 25 wt% of lithium chloride. The transmembrane flux of the regeneration module was evaluated at different feed and permeate flow rates from 0.6 to 1.4 L/min at solution temperatures of 45 to 80 ℃ and a permeate temperature of 25 ℃. The permeate flux of the regeneration module with the spacer-filled channel increased by more than 50 % compared with that of the empty channel. The regeneration module using spacers achieved a permeate flux ranging from 1.9 to 4.3 kg/m2h during desiccant regeneration at a solution temperature of 50 ℃.

Specific energy analysis of using fertilizer-based liquid desiccants to dehumidify indoor plant environments

Controlling humidity in indoor plant environments is crucial to plant growth, but traditional dehumidification methods can be energy intensive. In this study, we evaluate the energy efficiency of a novel dehumidification concept that uses cold concentrated fertilizer solution as a liquid desiccant agent. This closes the water cycle by recovering water vapor for plant fertigation, and eliminates the need for energy-intensive desiccant regeneration. A theoretical transport model is used to conduct a parametric analysis of the specific energy performance of the system in response to desiccant temperature and other operating conditions. Specific energy of dehumidification is defined here as the ratio of the cooling load to the water vapor removal. Minimum specific energy results between 0.16 and 0.24 Wh/g are achieved at liquid desiccant temperatures between 7 and 14 °C. These results compare very favorably with other dehumidification technologies on the market, and satisfy new energy efficiency standards for indoor plant cultivation. The vapor flux associated with the minimum specific energy ranged from 1.2 to 1.6 g/m2/h. Controlling liquid desiccant temperature is shown to be critical to achieving high dehumidification rates at optimal specific energies. These encouraging results suggest that future research and development along this track can contribute to energy efficient greenhouse cultivation for sustainable food production.

Experimental investigations on a solar assisted packed bed regeneration system for building air conditioning applications

In the current study, an experimental investigation carried out on a binary liquid desiccant-based adiabatic counter flow regenerator is presented. The heat harvested from solar collector was supplied into the desiccant for desiccant regeneration. The corrosion characteristics of the binary desiccant solution on stainless steel material were studied using potentiodynamic test. Subsequently, the effects of various inlet process parameters on the performance parameters of the regenerator were studied employing structured pads as packing material. The effect of the phase change phenomena involved in a desiccant regeneration system was also assessed experimentally, along with the system performance under the inlet solution temperatures of 53, 55, 60, 65 and 70 °C at a constant desiccant solution of 50 wt%. It was observed that the corrosion rate of lithium bromide (LiBr), calcium chloride (CaCl2) and LiBr + CaCl2 (85:15) was found to be 0.0303 mm/year, 0.0144 mm/year and 0.0161 mm/year, respectively. The results showed that with the increased solution temperature and air mass flux rate, the desorption rate was increased, whereas the regeneration effectiveness was decreased. The highest desorption rate was found to be 6.8 g/m2-s at the desiccant solution temperature of 70 °C, whereas the highest regeneration effectiveness of 0.85 was obtained at the air mass flux rate of 1.1 kg/m2-s.

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.