Desiccant Wheel Dehumidification Research Articles

Review on dehumidification technology in low and extremely low humidity industrial environments

Many industrial environments have low-humidity requirements. However, most research focuses on dehumidification systems in civil buildings, while research on industrial low humidity environments is extremely limited. This paper aims to summarize the research of dehumidification systems in low-humidity industrial environments, and provide some suggestions for the selection and improvement of dehumidification systems. Firstly, the environmental control requirements of industrial plants are reviewed and categorized into low humidity and extremely low humidity based on a relative humidity of 45 %. Then, the performance and applicability of condensation dehumidification systems, desiccant wheel (rotary dehumidifier) dehumidification systems and liquid desiccant dehumidification systems in typical industrial environments are summarized. Several preliminary system selection and configuration methods are presented. It is shown that the traditional condensation system is only suitable for low humidity plants. The desiccant wheel-based system is more capable of deep dehumidification, with a humidity ratio of less than 4 g/kg of supply air, while the liquid desiccant-based system can achieve high air volume operation of 10000 m3/h. Furthermore, their ranking under different scenarios is still outstanding issues. Evaluation indicators that weigh factors such as initial investment, operating costs, and control effectiveness need to be urgently proposed. Long term on-site testing is strongly recommended.

Investigation of purge angle on the air inhomogeneity reduction and energy efficiency improvement of the desiccant wheel dehumidification system

ABSTRACT The rotary desiccant wheel dehumidification system has been extensively applied to achieve deep dehumidification in the modern environment with low humidity ratio. The effect of mixing destruction caused by the temperature and humidity inhomogeneity on the thermodynamic performance of the desiccant wheel deep dehumidification (DWDD) system has not been thoroughly illustrated. This research aims to reduce the mixing destruction and improve the overall energy efficiency of the DWDD system. Numerical analyses were carried out to investigate the mixing destruction characteristics of the deep dehumidification process. The results revealed that the mixing exergy destruction gradually becomes a prominent factor as regeneration temperature and humidity ratio increase under deep dehumidification, and there is a significant temperature and humidity ratio gradient in the transition angles from the regeneration side to the process side. The purge angle is regulated to reduce the average temperature and humidity ratio on the process side and lower the air inhomogeneity. The exergy efficiency of the desiccant wheel can be improved from 44.8% to 73.9% at the regeneration humidity ratio of 20 g/kg under the effective purge angle of 30°, indicating a considerable enhancement of exergy efficiency under the effective purge angle at a high regeneration humidity ratio.

Investigation of a Wheel Liquid Desiccant Cooling System Performance via ANSYS CFX

A liquid desiccant cooling system is an alternative air-conditioning system with significant energy-saving potential. This system is commonly used in the industrial sector, such as in dehumidifiers. The key component of the liquid desiccant cooling system is its dehumidification performance. Therefore, a study on a liquid desiccant dehumidifier has been conducted to predict its performance using computational fluid dynamics analysis. In these simulations, the effects of the temperature of the liquid desiccant and the velocity of air flow on the absorption process between the liquid desiccant and air were studied. The same applies to the velocity profile, which helps determine the airflow pattern within the dehumidifier. The model was constructed using ANSYS FLUENT and Autodesk Inventor. The model is the rotary desiccant wheel dehumidifier which was used to dehumidified the air.. ANSYS CFX was used for simulating the velocity profile to achieve the airflow pattern in the dehumidifier. The volume of fluid was selected as the multiphase method for the second simulation process. The temperature and mass fraction of water were monitored within the air during the counterflow simulation between the liquid desiccant and the air. The liquid desiccant chosen for this study was LiCl. The simulations were conducted at specific air velocities, and the behavior within the dehumidifier was observed. The analysis results revealed that the air entering the rotary desiccant wheel dehumidifier experienced a drop in velocity after passing through the desiccant wheel in the middle. Additionally, turbulence occurred after the air passed through the wheel and the dehumidifier’s wall. Based on these findings, the design of an optimal dehumidifier and the selection of an appropriate air velocity for cooling can be carried out.

On-site measurement and optimization of energy efficiency of the cascading desiccant wheel deep dehumidification systems in the lithium-ion battery manufacturing factory

The desiccant wheel deep dehumidification system in the lithium-ion battery manufacturing factory is significantly energy intensive, which substantially treats the process air from the ambient to the supply air state with a dew point temperature below −20 °C. On-site measurements were conducted in this study to investigate the actual performance of the deep dehumidification systems. The air treatment process and energy consumption during the operation were continuously monitored. The results reveal that the coefficient of performance of the dehumidification process of the systems ranges from 0.54 to 0.63 under basic winter conditions and ranges from 1.15 to 1.25 under basic summer conditions. The deep dehumidification processes of the systems are divided into multiple stages, and with the deepening of the process air humidity ratio from above 6 g/kg to below 0.3 g/kg, the partial energy efficiency of the treatment stages decreases. The efficient operational strategies are further elaborated for the improvement of the deep dehumidification system, including the proper match between the dehumidification gradient and the dehumidification stages, and the appropriate use of outlet process air with low humidity ratio as the regeneration air. The energy consumption of the cascading desiccant wheel dehumidification system can be reduced by lowering the cooling temperature of the cooling coil to undertake more latent load in the preliminary dehumidification stage. The effect of the bypass air state as the regeneration air is revealed, and the energy efficiency of the system is enhanced by up to 32 % by applying appropriate bypass air. This study offers guidance for the future design of the cascading desiccant wheel deep dehumidification system in similar applications.

Performance variation of a desiccant wheel dehumidifier equipped with a sensible heat exchanger due to experimental fluctuations in regenerative heat input

This study investigates the impact of different control strategies on the performance of a single desiccant wheel dehumidifier with a heat recovery in real-world applications. A method to minimize the performance fluctuation as an effect of dynamic system performance response is proposed. First, the effect of regeneration heat input (Qin) changes on the system performance of the above dehumidifier was clarified. Second, the performance behavior was examined in response to transient conditions for different operation modes and was used to determine the most effective operation mode. Qin was assumed to change over time, which would influence the regeneration temperature and airflow velocity. The results showed that fluctuating Qin reduces the dehumidification capacity (ΔX) and coefficient of regeneration performance (COPreg). Therefore, a rotational control speed was implemented in the optimum operation mode, which was effective in preventing the system performance decline and accelerated the emergence of the rotational speed control effect.

Exergy destruction comparison of facial area ratio on dehumidification performance of the rotary desiccant wheel system under conventional and deep dehumidification

The rotary desiccant wheel has been extensively applied for humidity control in air conditioning systems, and it is also capable of deep dehumidification processes in various areas. The differences in the exergy destruction characteristics of the desiccant wheel between deep dehumidification and conventional dehumidification were still unclear. This study conducted numerical investigations to illustrate the impact of operating parameters, especially the facial area ratio, on the transfer exergy destruction and the mixing exergy destruction of the desiccant wheel components. The results revealed that the desiccant wheel with a facial area ratio of 1 has a higher exergy efficiency in conventional dehumidification due to low transfer and mixing exergy destruction. However, it shows a lower exergy efficiency than that of 3 under the deep dehumidification depth when operated at a high regeneration air humidity ratio. In the deep dehumidification process, the mixing exergy destruction caused by the distribution inhomogeneity of temperature and humidity ratio becomes a prominent factor to influence the exergy efficiency along with the transfer exergy destruction. It is concluded that the efficient design of the desiccant wheel dehumidification system highly depends on the dehumidification depth, the operating parameters, and the proper facial area ratio.

An Eco-Energetic Performance Comparison of Dehumidification Systems in High-Moisture Indoor Environments

This study discusses the choice of dehumidification systems for high-moisture indoor environments, such as indoor swimming pools, supported by an eco-energetic performance comparison. Initially, the causes of the high relative humidity and condensation in these spaces are reported, as well as the available dehumidification technologies. Two different solutions are described: desiccant wheel dehumidification and re-cooling. The energy demand required by a refrigeration system is lower than the desiccant wheel; however, the former system requires less maintenance and does not require refrigerant fluid. An eco-energetic comparison is performed between the two systems in two countries with different energy matrices (Brazil and USA). In Brazil, the desiccant wheel is the best choice for the past 10 years, with a predicted 351,520 kgCO2 of CO2 emissions, which is 38% lower than the refrigeration system. In the USA, the best option is the refrigeration system (1,463,350 kgCO2), a 12% more efficient option than desiccant wheels. This model can be considered for energy and CO2 emissions assessment, predicting which system has better energy efficiency and lower environmental impact, depending on the refrigerant type, location and environmental conditions.

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.

A comparative life cycle assessment of two desiccant wheel dehumidifiers for industrial applications

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

Performance Analysis of a Hybrid Dehumidification System Adapted for Suspension Bridge Corrosion Protection: A Numerical Study

A commonly adopted dehumidification system on a suspension bridge is the desiccant wheel dehumidification system (DWDS), which demonstrates ineffectiveness and energy-intensiveness in high temperature and humidity scenarios. This paper proposes a suspension bridge hybrid dehumidification system (HDS) as a better alternative for corrosion protection. A numerical model of HDS was first established. Then, the effects of the main operating parameters on HDS were analyzed, and the dehumidification performance of HDS and DWDS was further compared to illustrate the superiority of HDS to apply on a suspension bridge. In addition, the air supply parameter was discussed, and a low-energy operation strategy of HDS in summer cases was proposed. Finally, limitations and adaptations of heat pump dehumidification system (HPDS) and DWDS on suspension bridges were discussed. The results showed that: (1) HDS realizes the utilization of waste energy from suspension bridges, enhancing the system efficiency. Its specific moisture extraction rate (SMER) reaches 3.16 kg kW−1 h−1 in a high-temperature and -humidity environment (35 °C, 30.82 g kg−1) of the suspension bridge. (2) In the same inlet air conditions, HDS has greater dehumidification capacity than DWDS, and this advantage is enlarged with the increment of inlet air temperature and moisture content. In addition, HDS can strengthen dehumidification ability by decreasing the evaporation temperature and increasing the regeneration temperature to meet peak moisture loads of the suspension bridge. (3) Considering the anti-corrosion effects, energy consumption and drying time, the authors recommend that the moisture content corresponding to the atmospheric temperature and RH of 45% be used for air supply on a suspension bridge. (4) HPDS has poor adaptability to temperatures below 20 °C, while DWDS has poor adaptability to some high temperatures of 24~40 °C and high humidities of 19~30 g kg−1. None of them can meet the air supply requirements of a suspension bridge’s main cable alone.

Experimental investigation and effectiveness analysis of a desiccant wheel dehumidification system with low air humidity

The desiccant wheel dehumidification system is a feasible approach to realize the deep-dehumidification process to produce supply air with dew point temperature below 0 °C in modern architecture fields. However, actual dehumidification performance of the desiccant wheel system under low humidity condition and its difference from normal humidity dehumidification process have not been experimentally demonstrated. This study, therefore, carried out experiments to investigate the dehumidification performance as well as the thermodynamic effectiveness of the desiccant wheel deep dehumidification system. The results reveal that the desiccant wheel dehumidification system show relatively higher relative dehumidification capacity under low inlet process air conditions, reaching 77.4% under the regeneration air state of 75 °C and 4 g/kg by supplying air humidity under 1 g/kg. The sensitivity of dehumidification performance varying with regeneration humidity is reduced when the desiccant wheel is operated at high regeneration temperature. The deep dehumidification process also shows much greater isenthalpic deviation and surplus temperature deviation than normal dehumidification process due to larger irreversible heat loss, and the thermodynamic effectiveness is also highly related to the regeneration parameters. The study provides theoretical and experimental reference for the effective and efficient design of the desiccant wheel assisted deep dehumidification system.

Experimental Investigation on Heat Transfer Performance of Rotatory Desiccant Dehumidifier

Dry air plays an essential role in achieving human comfort and in other applications like product drying, food storage, etc. one of the best methods to produce dry air is by employing a desiccant dehumidifier. A rotatory desiccant wheel with silica gel is used in the present work. Current work involves the optimization of the desiccant wheel performance in terms of airflow rates along with ambient temperatures. Optimization of desiccant wheel is suggested by maximum value of various performance parameters involved in this study. Required conditions have been set up by the pre-treatment section installed before the desiccant wheel. At the regeneration section two electric heater (250 watt each) is fitted through which the desiccant material is regenerated. This work is conducted for humid and hot conditions and found that the optimum functioning of desiccant wheel dehumidifier is found at 31°C ambient temperature and at the inlet 3.5 m/s velocity of air.

Improvement of a liquid air energy storage system: Investigation of performance analysis for novel ambient air conditioning

Liquid air energy storage (LAES) is a grid-scale energy storage technology that utilizes an air liquefaction process to store energy with the potential to solve the limitations of pumped-hydro and compressed air storage. A challenge it faces itself is its high compression work during the charging process. Thus, attempts to increase the performance of the system need to include reducing the compression work. This study investigates the possible performance improvement of a LAES system through inlet air dehumidification and cooling. A simulation is performed on a 40 MW/320 MWhe LAES system which uses a desiccant wheel dehumidifier and a cooling coil for inlet air conditioning. The results show that the system can save 9521 MWhe in compression work annually which will translate to $761,680 annual cost savings in charging the system. The maximum performance improvement achieved during the summer period when the ambient conditions are unfavorable is 11.7%. Financial analysis also shows that the simple payback period of the desiccant wheel dehumidifier modification is 11.5 years and the levelized cost of storage (LCOS) of the LAES system is $237/MWh which is competitive compared to other storage systems.

Parametric number of transfer unit analysis of a photovoltaic thermal coupled desiccant dehumidifier

Conventionally, desiccant wheels are operated with regeneration temperatures around 70–80°C, which are difficult to achieve using photovoltaic thermal collectors. Matching the design and operation of photovoltaic thermal collectors with desiccant wheels at low regeneration temperatures is complex due to the influence of many different parameters. This study investigates a comprehensive approach to parametrically analyse a flat plate photovoltaic thermal collector and a desiccant wheel dehumidification system to find the optimal range of operating conditions to work at a low regeneration temperature of 50°C. This is achieved using the concept of “number of transfer units”, a dimensionless parameter that describes the key design and operational characteristics of the photovoltaic thermal collector as well as the desiccant wheel. This study found that for a silica gel desiccant wheel with equal volume of air flow for the supply and regeneration air, the desiccant wheel has optimal number of transfer unit values between 6 and 10 and optimal rotational speeds between 6 and 8 revolutions per hour for a regeneration temperature of 50°C. This optimal range increases to 10–14 for the number of transfer unit values and 7.5–9.5 revolutions per hour for the rotational speeds at a higher regeneration temperature of 80°C. For a glazed photovoltaic thermal collector to regenerate the desiccant wheel, the optimal range of the number of transfer unit values is found to be 0.13–0.23 for the PV/T collector to achieve low energy consumption. Using these optimal values, with a regeneration temperature of 50°C, a good dehumidification performance (3.5–5.2 g/kg) and system cooling coefficient of performance (2.5–2.7) can be achieved for inlet air temperatures from 26°C to 38°C. For temperate climates and solar irradiance greater than 800 W/m2, with a 15 m2 photovoltaic thermal collector, the desiccant cooling system can achieve 100% energy savings in comparison to a dewpoint dehumidification and cooling process. However, for humid climates where a deep dehumidification of 6–8 g/kg is required, a higher regeneration temperature of 80°C is required.

Effect of Changes in the Regeneration Heat Input on the Dehumidification Performance of a Desiccant Wheel Dehumidifier Equipped with a Heat Recovery Unit

Effect of Changes in the Regeneration Heat Input on the Dehumidification Performance of a Desiccant Wheel Dehumidifier Equipped with a Heat Recovery Unit

Research on Energy-Saving Experimental of Critical Dehumidification of Combined Drying by Dehumidification Wheel and Heat Pump

In order to further decrease the energy consumption of desiccant wheel dehumidification, the drying medium circulation characteristics of a system combining heat pump drying with desiccant wheel dehumidification were investigated. Moreover, the critical dehumidification conversion mechanism was studied. The analysis of the heat pump hot air circulation system demonstrated that the heat pump system has the best dehumidification efficiency. Through the analysis of the system combining heat pump drying with desiccant wheel dehumidification, the critical conversion point was determined. The critical dehumidification mechanism was further verified using an online temperature and humidity measurement system. To investigate the effect of the critical point on energy consumption and drying quality and develop a drying model, response surface experiments were performed based on the effects of regeneration temperature, drying temperature, and conversion point relative humidity on rehydration, color difference, and specific moisture extraction rate (SMER). The optimal conversion point humidity was determined to be about 46% RH, which was slightly different from the test optimization value of 45.6% RH. In addition, comprehensive optimization and experimental verification of the influencing factors were conducted. The results demonstrated that the R2 values of the three models were greater than 0.98, and the experimental factors had a significant effect on drying quality and energy consumption. When the regeneration temperature was 96°C, the drying temperature was 53°C, the relative humidity of the conversion point was 46%, the color difference was 46.3, the rehydration ratio was 5.75, and the SMER was 1.62 kg/kW·h.

Exergy analysis of dehumidification systems: A comparison between the condensing dehumidification and the desiccant wheel dehumidification

This paper presents a framework of exergy analysis to evaluate the performance of the condensing dehumidification and the desiccant wheel dehumidification. The performance of two dehumidification methods are compared for pure dehumidification purposes based on proposed dehumidification systems that undertake only the latent load. An air-source heat pump is adopted in the dehumidification systems to serve as the cold and heat source. Based on thermodynamic perfectibility theory and the laboratory experiment of the desiccant wheel, the power requirements and exergy efficiency of the two dehumidification methods are analyzed and compared under 17 sets of operating conditions. The coefficient of performance of the heat pump in the condensing dehumidification system is 2–3 times higher than in conventional air-conditioning systems. Environmental factors that influence the performance of each dehumidification method are identified. The performance of condensing dehumidification is affected mostly by the humidity ratio of indoor air, whereas the outdoor air temperature has a minor impact. The humidity ratio difference between indoor and outdoor air is the most influential factor in the desiccant wheel dehumidification, followed by the outdoor air temperature. Under the operating conditions examined in the present study, the condensing dehumidification shows 3–4 times higher exergy efficiency than the desiccant wheel dehumidification. Therefore, the condensing dehumidification should be preferred over the desiccant wheel dehumidification for typical indoor dehumidification applications.

Experimental investigation of desiccant wheel dehumidification control method for changes in regeneration heat input

Abstract This study discusses the effects of changes in the regeneration heat input on the dehumidification performance of a desiccant wheel to confirm its effective operation mode. The quantity of heat input to the regeneration air is assumed to change from 100% to 42%, assuming that the inlet regeneration air at 26 °C can be heated to the maximum regeneration temperature of 75 °C with a regeneration airflow velocity of 2 m/s. For this reason, the constant regeneration airflow velocity mode and the constant regeneration air temperature mode were studied experimentally. The results show that the constant regeneration temperature operation mode produced a smaller drop in dehumidification performance when the regeneration heat input was reduced. Furthermore, the transient responses of the dehumidification performance to long and short changes in the heat input were analyzed in both operating modes. The results confirmed that the constant regeneration temperature mode with proportional control of the rotor rotation speed was effective in stemming the decline in dehumidification performance when the heat input change was relatively long. However, the rotation speed control effect disappeared during short changes in the heat input because the buffer effect of the adsorption capacity of the rotor became much larger.

Drying in a desiccant wheel dehumidification system-assisted hot air dryer: desiccant wheel effectiveness and carrot drying

A desiccant wheel dehumidification system was used in this study to reduce humidity of the air supplied to a hot air dryer. Desiccant wheel effectiveness was determined based on the ideal adiabatic dehumidification process. Best results of adiabatic dehumidification effectiveness and adiabatic enthalpy effectiveness in the range of 0.89 to 0.99 were achieved. Specific adsorption of silica gel in the desiccant wheel was rotational speed dependent. The desiccant wheel system could reduce the relative humidity from 70 to 44%. Drying of cylindrical carrot in the desiccant wheel dehumidification system-assisted hot air dryer was also conducted in this study. The drying temperatures were varied from 80 to 120˚C. The desiccant material regeneration process reused exhaust drying air for heat exchanging with the regenerating air, higher drying temperature caused higher moisture evaporated from the desiccant material. Comparing between dehumidified hot air drying and conventional hot air drying, greater drying rates of dehumidified hot air drying were achieved at the drying temperatures of 100 and 120˚C.

Experimental and model based performance investigation of a solid desiccant wheel dehumidifier in subtropical climate

This paper presents real time performance analysis of a silica gel based desiccant wheel dehumidifier. Thermodynamic model is also validated through comparison under a wide range of operating conditions for subtropical climate conditions. Initially, a mathematical model is developed by using various set of equations for desiccant wheel dehumidifier in engineering equation solver. After-wards, a parametric analysis of the system is performed including various design and climate parameters such as: inlet air humidity ratio, inlet air temperature, regeneration inlet humidity ratio, regeneration temperature, and rotation speed of the wheel. Then, an experimental set-up of the system is established in Taxila Pakistan for the real-time performance assessment. The results revealed that the optimal rotation speed of desiccant wheel ranged from 15-17 rph. The maximum model based and experimental effectiveness is 0.45 and 0.43, respectively at re-generation temperature of 80°C. The maximum and minimum root mean square error values for effectiveness are 3.2% and 2.1%, respectively. Thus, the comparison between experimental and model results showed a good agreement.