Desiccant System Research Articles

Study on the optimal solution recirculation ratio of liquid desiccant dehumidification system based on matching rate evaluation

The recirculation of dehumidification and regeneration solutions has shown promising moisture removal rates and energy-saving effects in liquid desiccant dehumidification systems. The different combinations of dehumidification solution recirculation ratio and regeneration solution recirculation ratio under varying operating conditions can have different impacts on the system. Nevertheless, the system performance under full operating conditions has not been comprehensively studied. To address this research gap, this study proposes a liquid desiccant dehumidification system with a solution recirculation structure, defines a new evaluation index — matching rate, and conducts a parameterized study and optimization of the steady-state performance of the liquid desiccant dehumidification system with a solution recirculation structure within the range of solution recirculation ratios under all operating conditions, by integrating the system cooling capacity and energy effectiveness ratio. The performance of the system is studied by varying seven key parameters: dehumidification solution recirculation ratio, regeneration solution recirculation ratio, total solution mass flow rate, dehumidification solution inlet temperature, regeneration solution inlet temperature, and ambient air temperature-humidity ratio. The results show that under design conditions, the solution recirculation ratio within the full operating range can process air to a range of 17.8℃～18.5℃ and 12.5 g/kg～17.4 g/kg. The maximum system cooling capacity, energy effectiveness ratio and matching rate values are 21.5 kW, 0.21 and 0.42 respectively. The recommended (dehumidification solution recirculation ratio, regeneration solution recirculation ratio) schemes for high, medium and low demand of system cooling capacity are (0.7～0.9, 0～0.5), (0.4～0.6, 0～0.7) and (0～0.3, 0.4～0.7) respectively, based on the requirements of system cooling capacity.

Performance Evaluation of Different Desiccant Matrix Materials Coated with Silica Gel

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

Desiccant Dehumidification System Developed Using Additive Manufacturing and Biodegradable Materials

Traditional dehumidification equipment is based on vapour compression units. However, they depend mainly on electrical energy and use polluting gases. An alternative to this equipment is desiccant dehumidification systems, which is based on adsorbent materials. These desiccant systems are an efficient way of removing moisture from the air in buildings with high latent loads. This work presents a new way to manufacture fixed-bed desiccant elements that can remove moisture from an air flow. The desiccant element is obtained by material extrusion-based additive manufacturing (fused filament fabrication or FFF). This technology is cost-effective and provides a precision and finish suitable for the intended use. The filament used is Pine, consisting of an easy printable thermoplastic matrix (polylactic acid, PLA, 80 wt%) and a filler based on pine wood powder (20 wt%). This composite material reached a water absorption capacity of 11.5 %. The experimental results of the desiccant air unit demonstrated high dehumidification capacity, up to 39 mg/s, for a regeneration air temperature of 50 °C. The volumetric adsorption rate was also high, up to 30 g/s·m3, for low pressure drop values, below 522 Pa. The proposed method allows the customised, on-demand and just-in-time manufacturing of air dehumidification systems based on the use of biodegradable desiccant materials of organic origin. Such solutions contribute to the circular economy promoted by The United Nations in the Sustainable Development Goals.

Artificial neural network-based modeling for the prediction of heat and mass transfer coefficient of the adiabatic liquid desiccant system

This work, based on the data obtained from the literature reported by (Varela et al., 2018), aims to use the artificial neural network approach to predict the heat and mass transfer in a dehumidifier system, using lithium chloride as a liquid desiccant. A neural network model was developed in MATLAB environment based on multilayer perceptron that included an input, hidden, and output layer. The network input parameters are air velocity, air temperature, air humidity ratio, liquid desiccant temperature, liquid flow rate, and liquid desiccant concentration. The network output includes two variables which are the heat transfer coefficient (Kh) and mass transfer coefficient (Km). The performance of the ANN model was evaluated using the statistical parameters between the prediction results and experimental values. The performance regression yields R2 and MSE values of 0.9344 and 9.0032, respectively, for the test data set of heat transfer coefficient (Kh). Moreover, for the mass transfer coefficient (Km), the regression parameter R2 and MSE values for the ANN tests were found to be 0.9657 and 2.0414, respectively. In addition, air velocity, air temperature, solution mass flow rate, and solution concentration are the most influential parameters on the heat and mass transfer between the air and liquid desiccant.

Experimental performance and evaluation of direct evaporative cooling system coupled with a desiccant wheel in a closed greenhouse

The greenhouse is one of the most advanced technologies protecting products against inconvenient climates. However, high humidity and temperature throughout the summer, particularly in closed greenhouses, have a reverse effect on the crops. In such conditions, reducing the temperature inside the greenhouse seems indispensable. Therefore, in this study, two different patterns of cooling systems, namely, direct evaporation and mixed direct evaporative desiccant rotatory wheel, were designed and developed in Tehran. The results of these models were evaluated, compared, and modeled in TRNSYS. Subsequently, for performance prediction of these models, they were examined in closed greenhouses located in 5 regions in Iran: Astara, Ahvaz, Bandar-abbas, Tehran, and Shiraz. The temperature and humidity in different parts of the greenhouse were measured and reported to assess the performance of these two systems in terms of the capability to supply the required cooling load, energy consumption, and functional expenses. The experimental results indicated that the direct evaporative cooling system isn't acceptable for cooling the closed greenhouse in the preceding regions. This system in conventional greenhouses can be applicable only in Astara, Tehran, and Shiraz. Although all traditional greenhouses in Tehran use a direct evaporative cooling pad system, such a system cannot be used for cooling the closed greenhouses. Also, findings of the present study indicated that despite the 10% increase in radiation intensity and 7% increase in temperature in the case of evaluating the mixed evaporative desiccant rotatory wheel system, the temperature changes of greenhouse in this system followed a similar behavior, and 8% reduction in functional expenses was also confirmed.

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

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

Thermal and economical performances analyses of a desiccant wheels-assisted atmospheric water harvesting system used in humid climate regions

The thermal and economic performance of an atmospheric water harvesting system that uses four-stage desiccant wheels to pre-humidify processed air was analyzed. A vapor-compression refrigerator was used as the cold source. Two types of heat sources, i.e., heat pump and solar water heater, were considered, and their performance was evaluated. First, thermal performance of the system using different heat sources was analyzed under humid ambient conditions (relative humidity was 40–90 %, dry bulb temperature was 15–35 °C). The results showed that the water harvesting rate was 25.1–94.1 kg/h under these ambient conditions. When a heat pump was used, the water harvesting efficiency with heat recovery was 0.97–2.48 kg/kWh, and 2.41–4.59 kg/kWh when the solar water heater was used. The economic performance of the system was investigated by using diesel generators as the power source. To provide drinking water for 100 people, who consume 3–8 kg/day/person, as compared with bottled water sold in the market, the recovery period of the systems with heat recovery were 0.97–2.58 years and 0.34–0.91 years when the heat pump and solar water heater were used, respectively.

Membrane-based packed-sheet liquid desiccant dehumidification system

Humidity control plays a vital role in both buildings and greenhouses. The thermally-driven liquid desiccant dehumidification systems are getting an increasing traction because of their high moisture removal capacity and the possibility of their integration with waste-heat or renewable energy sources. In this work, a novel design concept for liquid desiccant dehumidification systems is proposed to overcome the practical challenges of the conventional systems, such as solution carryover, crystallization, and corrosion. The presented system utilizes a compact “packed-sheet” sorption bed that houses spherical membrane-based micro-absorbers with LiBr as a liquid desiccant. A bench-scale system is designed and tested under the typical dehumidification working conditions. The experimental results showed that the proposed design has up to two-fold higher moisture removal rate per volume (MRR = 75 g/s-m3) than a conventional LiBr liquid desiccant dehumidification system (MRR = 35 g/s-m3). In addition, a one-dimensional coupled heat and mass transfer mathematical model is developed to simulate the transient behavior of the proposed system. An optimization study, using the validated model, suggested that the performance of proposed design can be maximized to realize moisture removal rates of up to 135 g/s-m3 (270% higher than the conventional liquid desiccant systems) with a coefficient of performance of 0.25.

Performance characteristics of a compact self-circulating liquid desiccant air dehumidification system coupled with a heat pump: A comprehensive parametric study

Integration of a heat pump with a liquid desiccant system for air dehumidification has received growing attention in recent years in view of its more compact size and lower electricity consumption. This paper presents a compact combined heat pump and self-circulating liquid desiccant air dehumidification system targeted at small cooling load applications. The compactness lies in the integration of the dehumidifier and evaporator as well as the integration of the regenerator and condenser. Besides, the design of solution self-circulation (SSC) is intended for energy savings and the auxiliaries are employed to help achieve energy matching between the heat pump and the air dehumidification system. First, a comparative study is performed to identify the more energy efficient one of the two strategies for energy matching. Based on this, a thermodynamic model-based parametric study is conducted to investigate the effects of various influencing factors on the energy matching relationship and performance of the proposed system, as well as the energy-saving potential relative to the basic system without SSC. The results show that there exists an optimum solution self-circulation ratio (SCR) to achieve the maximum COP under a given condition. Basically, the proposed system with a proper SCR could yield a significant energy-saving effect regardless of the performance variations under studied operation conditions. It is found that a reduction of 29.68 % in energy consumption and an improvement of 42.20 % in COP are achieved under the ambient condition of 30 ℃ temperature and 20 g/kg humidity ratio. Furthermore, a correlation analysis is used to reveal the association strength and direction between any two main operation and performance parameters. Finally, the heat recovery is proved to effectively reduce the cooling coils load. This paper provides an in-depth understanding of the energy matching relationship and demonstrates the energy-saving performance benefiting from SSC for future practical applications of the proposed system.

Techno-economic and emission analysis of solar assisted desiccant dehumidification: An experimental and numerical study

In humid climates, it is challenging to maintain moisture content in the air for human thermal comfort and industrial applications. Commercial dehumidifiers rely on conventional electric heaters to regenerate desiccant material, which accounts for significant energy consumption by such dehumidifiers. As a green solution to this problem, the present study integrates a flat plate solar air collector (FPSAC) with a desiccant dehumidifier to effectively use solar thermal energy and reduce electrical consumption. Performance evaluation of glazed and unglazed FPSAC-assisted desiccant dehumidifier has been conducted at process air flow rates of 33, 51 and 62 m3/h with a constant regeneration flow rate of 42 m3/h. Both glazed and unglazed FPSAC assisted desiccant dehumidification systems had the highest dehumidification effectiveness and percentage increase in temperature at the flow rate of 33 m3/h, while the highest moisture removal capacity was at 51 m3/h. Maximum dehumidification effectiveness, percentage temperature increase, and moisture removal capacity for the glazed case were 0.4, 66.67%, and 6.14 kg/h, respectively. Experimental results showed that the glazed FPSAC-integrated desiccant dehumidification system outperforms unglazed FPSAC in all performance evaluation parameters. Using Transient System Simulation software (TRNSYS), the proposed glazed and unglazed assisted desiccant dehumidification system was modeled and validated with experimental results. Furthermore, a techno-economic analysis of the solar hybrid desiccant dehumidification system has been carried out. The FPSAC used in this study showcased a 33.57% yearly solar fraction with a solar hybrid system having a payback period of 4.23 years. In addition, the hybrid system can reduce greenhouse gas emissions yearly by 0.352 tons of CO2 equivalents.

Experimental evaluation of metal–organic framework desiccant wheel combined with heat pump

Reducing the consumption of high-grade energy on the regeneration side is crucial to decreasing the energy consumption of the desiccant wheel system. Metal-organic framework desiccants exhibit superior moisture absorption performance. However, there has been no research on the application of metal–organic framework materials in desiccant wheel systems for low-grade heat source regeneration. To address this research gap, this study applied a composite adsorbent of the metal–organic framework in a heat pump-desiccant wheel system and experimentally evaluated the performance of the heat pump-metal–organic framework desiccant wheel system using low-grade heat sources under different operating conditions. A comparison was made with electrically heated desiccant wheel systems and heat pump-desiccant wheel systems using traditional silica gel adsorbents. The results showed that the optimal desiccant wheel rotational speed was 8.63 r·h−1, and the optimal airflow was 300 m3·h−1. The energy consumption of the heat pump-metal–organic framework desiccant wheel system was only 42.77% of that of the electrically heated desiccant wheel system, and its dehumidification energy factor was 2.07, which is higher than that of the heat pump-silica gel desiccant wheel system. This demonstrates the feasibility and efficiency of utilizing low-grade heat sources for regeneration using metal–organic framework desiccants in practical applications.

Study on the optimal circulation structure of liquid desiccant dehumidification system based on composite model

Liquid desiccant dehumidification systems have demonstrated good energy savings and dehumidification effects in extremely hot and humid areas. However, to improve system performance, the matching problem between the desiccant-regeneration solution recirculation ratio and system performance has not been thoroughly investigated. Therefore, in this study, we constructed a liquid desiccant dehumidification system with solution recirculation and set four circulation modes: NS mode without solution recirculation, CS mode with only desiccant solution recirculation, RS mode with only regeneration solution recirculation, and CRS mode with both desiccant and regeneration solution recirculation. The orthogonal test method was used to determine the influence of solution recirculation on the evaluation indicators, and multi-objective optimization of the major parameters under the four circulation modes was performed based on the NSGA-II and TOPSIS algorithms. The results showed a clear conflict between the moisture removal rate (MRR) and energy consumption (Q). In extremely hot and humid areas, a high air flow rate is suitable for use in the regenerator to process small-flow-rate solutions or set larger sizes. Under typical environmental conditions, it is recommended to set up a liquid desiccant dehumidification system with a solution recirculation structure: when MRR demand is high, the CS mode should be used, where MRR is 6.72 g/s; when Q demand is high, the RS mode should be used where Q is 35.34 kW; considering both MRR and Q effects, the CRS mode should be used where unit energy consumption moisture removal rate is 0.1196 g/(s·kW).

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.

Hybrid membrane dehumidification and dewpoint evaporative cooling for sustainable air conditioning

Investigating new energy efficient and sustainable designs for air conditioning has become imperative due to air conditioning’s contribution to global warming. The combination of membrane-based dehumidification and dewpoint evaporative cooling provides a possible solution that eliminates the energy-intensive process of condensation dehumidification, while also avoiding the use of harmful refrigerants. This paper is the first to present a straightforward thermodynamic model and initial assessment of a hybrid system that combines a vacuum membrane dehumidifier inspired by the Claridge-Culp-Liu (CCL) cycle with a dewpoint evaporative cooler with the additional investigation of reusing the dehumidification water to provide the evaporative cooling. A parametric study is performed for different ambient conditions. Results show the maximum achievable coefficient of performance (COP) for cooling and dehumidification with the system to be as high as 15 for very dry climate conditions, with a median value in the range of 4 over the range of typical ambient conditions. The system also displays the potential for having a self-sustaining water supply for evaporative cooling, producing up to 12x the amount of water required for the evaporative cooling portion of our system in highly humid conditions. An energy savings analysis yielded positive savings at low humidity conditions when compared to a baseline vapor compression system. Additionally, the system outperformed a baseline desiccant wheel system under all conditions. The absence of harmful refrigerants lowers overall (direct and indirect) greenhouse gas emissions associated with the M−DPEC system to as low as 50% of the baseline vapor compression system. Therefore, the model shows potential for the technology to efficiently fulfill building cooling demands while employing an environmentally friendly system to reduce greenhouse gas emissions.

Numerical investigation and comparison on energy performance and exergy destruction of cascading deep dehumidification systems with dehumidification amount exceeding 95%

Liquid desiccant and desiccant wheel systems are feasible approaches for the dehumidification process in modern buildings. Some specialized buildings and industrial fields have the demand for deep dehumidification process to produce supply air with low dew point temperature below 0 °C. In this study, the numerical investigation has been conducted to evaluate the energy and exergy performance of multiple cascading deep dehumidification systems assisted with liquid desiccant and desiccant wheel under a great dehumidification gradient. To process the air from 21 g/kg to 1 g/kg, the results indicate that the cascading liquid desiccant and desiccant wheel deep dehumidification system (LD-DW system) driven by two stages of heat pump exhibits the lowest demand of power consumption compared with the conventional dehumidification systems. It also shows less exergy loss and significantly higher exergy efficiency than other systems. The effects of influencing parameters on the dehumidification performance are also evaluated. The LD-DW system can effectively match the air state with the proper treatment dehumidification process, thus achieving a superior coefficient of system performance (COPsys) of 3.70, and it is an energy and exergy efficient method for advancing the deep dehumidification process.

Hardware-in-the-loop testing of control of a precooled desiccant air-cooling system

Increasing the energy efficiency of cooling in buildings is an important component of the management of global energy consumption. A super-efficient cooling system based on the evaporation concept has been developed, and initial simulation results using the MATLAB/Simulink software tool have already been published by our team. In this paper, we present the results of hardware-in-the-loop (HIL) testing of the real-time controller for the cooler. HIL testing is an engineering process in which the actual controller hardware and software are implemented and interfaced with a real-time simulated model of the controlled system. Using HIL testing, many real-world problems can be fixed before testing on the actual prototype. The controller design is implemented on a small-footprint industrial PC with CODESYS RTE and application code, while control software is implemented using IEC 61131-3 programming languages. Similarly, a real-time thermodynamic and input–output variable-based model of the room, environment, and cooler and its mechanical components (sensors and actuators) are modeled using another industrial PC with the same software tools. HIL test results show very good agreement with the offline simulations.

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.

Review on Polymer Materials for Solid Desiccant Cooling System

AbstractAs an alternative form of vapor compression air conditioning devices, solid desiccant cooling (SDC) techniques have increasingly been explored recently. The overall performances of SDC primarily rely on the capability of dehumidification and regeneration of desiccant. A desiccant with a great uptake capability and excellent regeneration potential is preferred in an SDC system. Although traditional desiccants like silica gels and zeolites are able to absorb moisture at moderate levels, hygroscopic polymers show a superior ability in moisture sorption and desorption. Significant research has been conducted to investigate the hygroscopic polymers in SDC for household and industrial applications. Here, first, an introduction to SDC systems is presented, and then hygroscopic polymers from natural and synthetic origins are discussed. Synthetic polymers discussed are metal–organic frameworks (MOFs), covalent organic frameworks (COFs), covalent triazine frameworks (CTFs), amorphous porous organic polymers (POPs), polyelectrolytes, and polymer‐based composites. Their dehumidification behaviors in SDC systems, primarily desiccant‐coated heat exchanger (DCHE) systems, are compared and summarized. Binders employed in SDC systems are also summarized, as a proper binder enhances the overall performance of the desiccant system. It can be anticipated that hygroscopic polymers and binder materials would witness extensive applications in the future.

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.

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.