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This paper reviews the current research and advances in humidity control for residential and commercial buildings. Desiccant and hygroscopic buffering zones are summarized. System types, performances and challenges are presented to help the reader select the best cooling dehumidification system for his application or project. More emphasis is put o...
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... are different types of solid desiccants such as silica gels, lithium chloride (LiCl), and molecular sieves ( ). Figure 1 summarizes some common solid and liquid desiccant materials 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 3 used for humidity control purposes. Solid desiccants are usually embedded in a wheel or other means that allow the desiccant material to be in contact with two air streams, as shown in Figure 2. Figure 2 represents a typical rotating wheel dehumidifier where a solid desiccant is contained inside the packing of the wheel. ...
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... liquid desiccant materials, as shown in Figure 1, include lithium and chloride based solutions such as LiCl, LiBr, CaCl 2 , NaCl, tri-ethylene glycol and mixtures of the pre-mentioned liquid desiccants. The performance of liquid desiccant systems is controlled by the effectiveness and operation of the dehumidifier and the regenerator. ...
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... designs for direct contact dehumidifier-regenerator systems are presented in this paper including packed bed, spray tower and falling film types. In the packed bed dehumidifier, shown in Figure In an adiabatic packed bed, shown in Figure 10(a), the temperature of the desiccant solution changes as it flows through the dehumidifier-regenerator due to the heat transfer with the air stream and due to phase change which accompanies the moist transfer. In an internally cooled/heated "isothermal" packed bed, shown in Figure 10(b), the solution is continuously cooled/heated by a third fluid. ...
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... the packed bed dehumidifier, shown in Figure In an adiabatic packed bed, shown in Figure 10(a), the temperature of the desiccant solution changes as it flows through the dehumidifier-regenerator due to the heat transfer with the air stream and due to phase change which accompanies the moist transfer. In an internally cooled/heated "isothermal" packed bed, shown in Figure 10(b), the solution is continuously cooled/heated by a third fluid. This fluid could be water. ...
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... are three configurations associated with falling film dehumidifiers: cross flow, parallel flow, and counter flow. These configurations are shown in Figure 11 ( Abdel-Salam et al., 2016). 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 ...
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... for converting solar radiation into useful energy for usage in the air-conditioning or cooling processes are summarized in Figure 12. Solar regeneration systems are very effective over the long 710 711 712 713 714 715 716 717 718 719 720 721 722 723 724 725 726 727 728 729 730 731 732 733 734 735 736 737 738 739 740 741 742 743 744 745 746 747 748 749 750 751 752 753 754 755 756 757 758 759 760 761 762 763 764 765 766 767 14 term as they provide sustainable and renewable energy sources. ...
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... 2007, Henning presented a solar driven solid desiccant system as shown in Figure 14. The solid desiccant adsorption was utilized for both adsorption cooling and adsorption dehumidification. ...
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... solid desiccant adsorption was utilized for both adsorption cooling and adsorption dehumidification. As shown in Figure 14, as the exhaust air is released out to the atmosphere, it exchanges energy and absorbs the moist from the incoming supplied air. The incoming fresh air is dehumidified in the rotating dehumidifying wheel, precooled in the heat recovery exchanger, then humidified before being cooled further down, during summer time, to the desired temperature using a cooling chiller. ...
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... also concluded that the mass flow rate of air can improve the COP when increased, but this will limit its outlet temperature and, thus, recommended a balance between the system COP and the leaving temperature of air ( Dai et al., 2002). Figure 14. Solar driven solid desiccant system (Henning, 2007) (Ge et al., 2010) simulated a solar driven two-stage rotary desiccant cooling system. ...
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... Liu et al., 2010) investigated liquid desiccant systems that control humidity independent of the supply air temperature similar to the system shown in Figure 15. The results showed that the required chilled water temperature by the system was increased from 7 ˚C to 17˚C17˚C due to the removal of the latent load from the chiller. ...
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... mathematical model for a liquid desiccant dehumidifier that dehumidifies a space independent of the air cooling systems was developed by (Keniar et al., 2015). The liquid desiccant regeneration was 829 830 831 832 833 834 835 836 837 838 839 840 841 842 843 844 845 846 847 848 849 850 851 852 853 854 855 856 857 858 859 860 861 862 863 864 865 866 867 868 869 870 871 872 873 874 875 876 877 878 879 880 881 882 883 884 885 16 integrated with a solar energy source as shown in Figure 15. Membrane technology was not investigated as part of this research, but rather the membrane was assumed to be permeable for water vapor only and not for liquid desiccant. ...
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... developed mathematical model was validated by conducting experimental testing. The developed model was used to compare the performance of the system shown in Figure 15 against a conventional AC system. An improvement of 10% in the dehumidification effectiveness was achieved. ...
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... initial cost of the system needed a payback period of 7 years and 8 months compared to conventional AC systems operating under the same conditions. Figure 15. Schematic of the separate dehumidification system integrated with renewable solar energy ( Keniar et al., 2015) ( Angrisani et al., 2015) investigated the dependence of a hybrid liquid desiccant system, operating with a silica gel desiccant rotating wheel and a small regenerator, on several parameters such as outdoor air and regeneration temperatures, outdoor humidity ratio, desiccant wheel rotational speed, and air and liquid desiccant flowrates. ...
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... membrane can be permeable or semi-permeable allowing the passage of water vapor only with no mass transfer. Figure 16 shows a liquid to air membrane technology that is a semi-permeable membrane. It allows the transfer of water vapor but not any liquid. ...
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... allows the transfer of water vapor but not any liquid. Usually, the flat plate "liquid-to-air membrane energy exchange" (LAMEE) consists of several air and solution channels that are separated by semi permeable membranes as shown in Figure 16b. Figure 16a shows a microscopic view of the membrane. ...
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... the flat plate "liquid-to-air membrane energy exchange" (LAMEE) consists of several air and solution channels that are separated by semi permeable membranes as shown in Figure 16b. Figure 16a shows a microscopic view of the membrane. This membrane is characterized by: 1) low vapor diffusion resistance, as low as 97 seconds per meter, that improves the dehumidification process, 2) high liquid penetration pressure that prevents the transfer of any desiccant droplets from the desiccant solution to the air channels, and 3) high modulus of elasticity which decreases the deflection of the membrane and, thus, reduces the flow mal-distribution in the air and desiccant channels. ...
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... Huang et al., 2016) conducted experimental and numerical analysis for an internally cooled membrane-based liquid desiccant arranged in cross-flow with air. Water was allowed to flow vertically and formed falling films, similar to those shown in Figure 11. Air and the desiccant solution were separated by selective permeable membrane. ...
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Citations
... The need for air dehumidification for the preservation of art, products and equipment in different industries has led to the development of various dehumidifying mechanisms over the past few years [1][2][3][4][5][6][7][8]. Many dehumidification technologies are bulky, energyinefficient or noisy, and they cannot be used with precision equipment that requires a small footprint and noise-free operation. ...
Much scientific equipment requires the use of humidity control technologies. This includes instruments with hygroscopic optics, such as infrared spectrometers, OPOs and some lasers. The most common strategies include nitrogen purging or desiccant bag replacement, which involve maintenance and running costs. In this work we present a dual strategy, combining both ionic membranes and silica desiccant, which results in a reusable and maintenance-free scheme for humidity control. The desiccant action of the silica gels, the membrane, and combinations thereafter, are studied. It is shown that the combination of the silica gel desiccants and the membrane is the most efficient configuration, reducing the humidity from 73% to only 15% in 20 h in a 70 L volume and from 80% to 20% in 40 h in a 230 L volume. An experiment over 5 days showed that the status of the silica gel desiccants that had adsorbed high water vapor levels returned to normal after they were enclosed together with the ionic membrane in the 70 L volume. Finally, measurements taken by a commercial infrared spectrometer of the reduction in the H2O lines absorption in the mid-infrared region under the operation of the combined configuration are examined. It was demonstrated that H2O lines with low to moderate absorption almost disappeared when the humidity levels inside the spectrometer dropped from 42.5% to 15.1% in the span of 90 min, while lines with stronger absorption remained present even though they showed the highest percentage of change.
... It was selected for the experimental study over Lithium Chloride (LiCl) or Lithium Bromide (LiBr) due to its low toxicity and cost which made the study safer for food testing without compromising the system behaviour [30]. Liquid absorption-based desiccants were considered for this study over solid adsorption-based desiccants due to their relatively higher thermal energy efficiency and their ability to be regenerated using lower quality or lower temperature heat, making them more conducive to be integrated with solar thermal systems [31]. The CaCl 2 salt was commercial grade and had 6 % impurities. ...
In this study, a three-stage solar dryer using solar convection, convection-microwave, and solar desiccant
absorption-assisted convection drying was developed and evaluated. This process was designed to reduce energy
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were dried in the first stage using solar convection and the process was assisted by Microwave radiation in the
second stage to increase the drying rate. The final stage combined solar desiccant absorption with solar convection
to maintain the drying rate at a lower temperature, thereby reducing energy use and minimizing thermal
damage to the biomass. Compared to Microwave-Convection drying, the three-stage drying process was found to
consume 46 % lower specific energy and reduced Carbon emissions by 53 %. The Vitamin – C retention and color
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used to improve the overall performance of solar thermal drying methods in terms of temperature control, energy
efficiency, sustainability, and product quality. It also has the potential to be deployed in rural areas with minimal
dependence on grid energy.
... This integration between the vapor compression cycle and thermally driven desiccant systems resulted in advantageous systems in terms of handling latent heat [11]. However, the adsorption process leads to the production of hot and dry air, which produces an added sensible load on the cooling system [12]. Furthermore, the process and regeneration ducting work creates bulky systems with substantial parasitic power consumption due to the high pressure drop [13]. ...
... Desiccant dehumidification and refrigeration technologies can provide energy-efficient solutions for industrial applications and exceptional circumstances requiring controlled humidity levels. It is anticipated that desiccant technology will develop due to its potential applications and benefits [24]. ...
Desiccant agents (DAs) have drawn much interest from researchers and businesses because they offer a potential method for lowering environmental impact, increasing energy efficiency, and controlling humidity. As a result, they provide a greener option to conventional air conditioning systems. This review thoroughly analyzes current issues, obstacles, and future advancements in liquid desiccant agents (LDAs) for drying, air conditioning, and dehumidification applications. The importance of LDAs in lowering energy use and greenhouse gas emissions is highlighted, emphasizing their potential for environmentally friendly humidity control. The current review examines key parameters such as novel materials, enhancing desiccant qualities, integration with technologies, and long-term durability while examining recent developments in LDAs and investigating their applications in diverse industries. The main conclusions from the evaluated publications in this review are also highlighted, including developments in LDAs, new applications, and developing research fields. Overall, this review advances knowledge of LDAs and their potential to shift humidity control systems toward sustainability and energy efficiency.
... On the other hand, low indoor RH levels cause skin dryness and eye irritation [5]. It is therefore important to control indoor humidity levels, which is conventionally carried out by pumping dehumidified air into the space to dilute the indoorgenerated moisture [6]. Such techniques rely on the use of vapor compression cooling either as standalone systems or integrated with desiccant dehumidifiers to generate this dried air. ...
Regulating indoor humidity levels to healthy ranges is important to provide occupants with acceptable thermal comfort and air quality conditions. Conventional techniques relied on the supply of dehumidified outdoor air to dilute the indoor generated moisture. They use vapor compression cooling either as standalone system or integrated with desiccant dehumidifiers to generate the dry air. Such systems are energy intensive and require large footprint areas, especially in hot and humid climates. This work proposes thus an energy-efficient alternative where the indoor humidity is pumped directly from the space and discharged outdoors. This system integrates a metal organic framework-based dehumidifier with the building breathable façade. The dehumidifier dries the outdoor air that is used to ventilate the façade and create the necessary driving gradient for the moisture transfer, irrespective of the outdoor air conditions. Mathematical models are developed to evaluate the system performance for an office space located in the extreme hot and humid climate of Jeddah, KSA. The proposed system resulted in 89 % and 90 % reduction in the system size and energy consumption compared to conventional systems over the peak humidity month.
... Another conventional dehumidification strategy consists of using thermally driven desiccant systems [9,10]. By treating the exhausted room air, the hybrid desiccant systems result in a hot and dry airstream, whose temperature depends on the regeneration temperature as well as the amount of adsorbed water [11]. An additional sensible load is thus imposed on the cooling system to provide the needed supply temperature to the space. ...
Indoor humidity management is vital for both building and occupant health. Conventional methods that decouple the latent and sensible load use desiccant dehumidifiers integrated with vapor compression systems to supply cool dry air to the space and dilute the indoor generated moisture. Such methods remain energy-intensive, especially for high latent load spaces located in hot and humid climate. Direct removal of the indoor generated moisture via moisture migration through naturally ventilated building façade, proved to be a more energy-efficient alternative. However, this strategy suffers from different drawbacks in humid conditions, which impose an intermittent operation on the moisture control system. In this work, a continuous humidity pump system is proposed that integrates a metal organic frameworks-based desiccant dehumidifier to supply dry air to the ventilated building façade provided with breathable insulation. This creates a water vapor pressure gradient between the indoor and dry air to actively drive the indoor moisture to the outdoor environment, irrespective of its humidity conditions. Mathematical models are developed for the system’s subcomponents, which are then experimentally calibrated. Design and control strategies are presented for the proposed system and applied for a case study of a high latent load space located in the hot and humid climate of Beirut. Over the entire cooling season, the proposed system resulted in 66 % reduction in the investment cost and 86 % in the operating cost compared to conventionally employed hybrid desiccant – vapor compression cooling systems.
... Besides temperature, humidity is an important weather metric as dehumidification in buildings remains as a primary contributor to cooling load in hot-humid climate regions, thereby consuming much energy, and contributing to environmental impact through greenhouse gas emissions [29,30]. Shehadi [31] discusses humidity control in a building to meet the comfort level of building occupants. Since high levels of thermal comfort come at the expense of high energy demands, researchers are focusing on adaptive approaches to achieve thermal comfort. ...
Thermal-Energy-Storage Air-Conditioning (TES-AC), a sustainable form of Air-Conditioning (AC) operates by storing thermal energy as chilled water when energy demand is low during nighttime. Later it uses the stored thermal energy during the daytime to cool the indoor air of the building the next day. However, the stored thermal energy in the form of water in the tanks of the chiller plant might be affected by external weather factors. It is essential to understand whether there is a relation between external weather conditions and water consumption in the TES-AC system. Without verifying the relation, applying computational intelligence for Thermal-Energy-Storage (TES) in Heating, Ventilation, and Air Conditioning (HVAC) would not be appropriate. However, not much research has focused on applying such techniques in HVAC for facility management and maintenance. Moreover, identifying these features by discovering the relation between weather and water consumption is a crucial part to apply computational intelligence such as machine learning techniques for predictive maintenance of this facility as it heavily relies on water volume for TES-AC charging. During warmer weather, the stored thermal energy might have an effectual loss due to evaporation which would mean more water consumption by TES-AC for cooling. Hence, this research investigates whether external weather data has any effect on the water consumption of TES-AC and discusses how external weather may affect the water consumption of TES-AC and if it is important to factor it in whilst utilizing computational intelligence for charging load prediction of TES-AC.
... Control Materials (HCMs) can adjust indoor relative humidity through absorbing/releasing moisture for building applications [18,19]. In reality, there are several types of HCMs, such as inorganic salts [20], inorganic minerals [21] and composite biomass [22], and many existing studies have thoroughly demonstrated that using HCMs can both improve indoor humidity environment and reduce energy consumption of buildings [23,24]. ...
In this study, a composite double-layer wallboard with shape-stabilized phase change humidity control materials (PCHCM) has been proposed for building usage. This novel PCHCM can absorb/release both heat and moisture to moderate indoor hygrothermal environment. Based on a numerical analysis in an office building in Wuhan (30.52°N, 114.32°E), China, the effects of PCHCM on both building energy consumption and indoor hygrothermal environment has been investigated. Firstly, a simulation model has been developed for the building integrated with PCHCM wallboards in EnergyPlus, combining both heat and moisture transfer finite solution algorithms. After a validation of the model, both heat and moisture transfer characteristics of the proposed composite wallboards were simulated, and its effects on indoor temperature, humidity and building energy consumption were analyzed. The simulation results showed that this novel PCHCM wallboard can effectively improve indoor hygrothermal environment, with reduced energy consumption by about 8.3% in summer and 24.9% in winter, comparing to the actually used materials in the case study building.
... Over the years, liquid desiccant systems have gained significant interest as they utilize the desiccant material a hygroscopic substance to dehumidify the air and provide favorable comfort conditions by improving the indoor air quality while reducing the power consumption of vapor compression air conditioners specifically. Liquid desiccant systems are more promising than solid desiccant systems as they provide more advantages and control flexibility over solid desiccants (Shehadi 2018). Many works related to liquid desiccant system integration with other conventional systems has been reported that C.O.P of the combined systems is found to be increased (Yamaguchi et al. 2011). ...
The liquid desiccant systems are one of the promising technologies in dehumidification applications. The experimental study on dehumidification performance of a counter flow structured packing liquid desiccant system is done with Aqueous HCO2K as working fluid. The HCO2K solution at different mass flow rate of air and solution is tested. The airflow rate is varied from 0.187 kg/s to 0.272 kg/s and the solution flow rate is varied from 0.053 to 0.115 kg/s. The output parameters, specific moisture change, moisture removal rate, dehumidification effectiveness and latent heat removal capacity varied in following ranges 3-4.2 g/kg of dry air, 2.4-3.1 kg/h, 0.12-0.21 and 1.7-2.1 kW respectively. Particularly when air flow rate increases from 0.187 kg/s to 0.272 kg/s the moisture removal performance improves about 11% whereas when the solution flow rate increases from 0.055 to 0.115 kg/s, improvement in moisture removal performance about 20%. The results imply that increase in solution flow rate always have the positive impact on dehumidification performance. The increase in airflow rate has the negative impact on specific moisture removal and effectiveness, but the impact is positive in case of the moisture removal rate and latent heat removal capacity. The Overall results show a promising dehumidification performance and further improvement is possible by incorporating a cooling system.
... Romdhane S. et al. [123] conducted a review on using PCMs in passive buildings. However, Shehadi M. [124] presented a review on humidity control in buildings. She et al. [125] completed a comprehensive review of energy-efficient and -economic technologies for air conditioning with VCR. ...
Energy has become the backbone of humanities daily activities. Heating, ventilating, and air conditioning systems (HVAC), which consume around 39% of energy in the residential sector, have turned into an essential constituent for providing fresh air, especially after COVD-19, not only in hospitals but also in any simple construction. Thus, decreasing this percentage or recovering part of the energy lost is an essential issue in today’s energy management scenarios. In this context, the present manuscript suggests a comprehensive review, classifications, critical analysis, and potential recommendations for energy recovery in air conditioning systems. It classifies energy recovery into two main categories: using lost energy for external uses, such as heating domestic water, or with other devices; and using lost energy for internal uses, such as the hot airflow which can be reused again for increasing efficiency of HVAC. In addition, this paper presents a summary of previous research and undertakes a review of the devices used for recovering energy. Furthermore, this review identifies superior devices in terms of climate and weather conditions. These objectives are accomplished by investigating around 190 published papers to conclude that energy recovery devices show a considerable effect on energy consumption in HVAC, mainly the heat pipe, fixed plate, and rotary wheel devices.
