Desiccant Based HVAC Dehumidification Systems

The treatment of humidity on HVAC systems is crucial when a satisfactory indoor air quality needs to be reached.Traditional HVAC systems meet the latent cooling load by reducing the air temperature until its dew point, heating subsequently the air in order to reach the supply temperature for user comfort, with the energy waste this entails.On the other hand desiccant wheels requires normally an excessive post-cooling because of employed regeneration temperatures of around 70-80 C.In this paper the design and simulation models and testing results at laboratory scale of a hybrid liquid desiccant system (HLDS), developed in the frame of the EU project nanoCOOl, are presented.The HLDS is especially suited for applications with a low SHR (Sensible Heat ratio) and high ventilation requirements in tropical or subtropical climates.The aim of the project is to validate the developed technology for a good indoor environment quality, achieving the required ventilation needs, a good occupant comfort by the treatment of temperature and humidity to reach comfort conditions, avoiding the generatio... Read More

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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 advanc... Read More

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Solid desiccant dehumidification has proven to be more energy-efficient than traditional condensation dehumidification. However, owing to the complexity and large size of existing solid desiccant dehumidifier systems, their application in residential spaces is limited. In this study, we explore the potential of using small solid desiccant dehumidifiers in residential spaces. The dehumidifier uses a variable frequency fan to replace the two fans of a traditional solid desiccant dehumidifier. Meanwhile, the flow direction of the dehumidified air and regeneration air was adjusted via the air valve such that the air in different working modes flows in the same space, thereby reducing the size of the dehumidifier. Moreover, the dehumidifier used an equalizing orifice to ensure the stability and uniformity of the airflow in a small space and used an electric heating tube for regeneration, as opposed to a heat exchanger, to reduce the size of the system. The experimental results of the prototype device show a dehumidification efficiency of more than 85%. The humidity at the inlet of the deh... Read More

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In comfort, air-conditioning control over the humidity is essential in applications such as pharmaceutical industries, electronic gadgets manufacturing units, the food sector, paper industries, etc. Relative humidity of nearly 50% can effectively prevent the growth and abidance of biological pollutants. There are several methods using which dehumidification can be achieved. The most common method is subcooling air up to the condensation temperature of the moisture trapped and then cooling again, and the condensate is collected. This method is time-consuming and needs to be more effective. On the other hand, desiccants dehumidification process is suitable for maintaining humidity in air-conditioning systems and producing dry air. Desiccants with economical materials, high moisture removal rate, low regeneration temperature, and steadiness after many years make a desiccant system more successful in its performance and cost. The effect of change in process air temperature, process air humidity ratio, and regeneration temperature on the system's performance is studied. This research foc... Read More

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A review of desiccant dehumidification technologies for improving air-quality has been presented, especially focusing on alternatives for air conditioning systems for minimizing the Sick Building Syndrome. The principles and types of desiccant wheels, as well as the existing selection software for these types of equipment, were reviewed and comparatively evaluated. The study focuses on the Brazilian context, therefore, information about air condition systems and laws of this country were evaluated. Possible applications of desiccant wheels are also analyzed, such as their integration into cooling cycles and the sensible heat wheel. Finally, several commercial desiccant wheel selection software were evaluated, which are useful in many situations. Nevertheless, it was evidenced that the available softwares are not capable of performing an operation analysis for only a specific period. Therefore, it is essential to create computational tools to select desiccant wheels, considering the data from the different Brazilian regions for a year.

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Due to its sustainable cooling design and inexpensive operation, desiccant based dehumidification and cooling systems have been popular in recent years for humid areas. In general, the desiccant cooling used in conjunction with evaporative cooling as two separate types of configurations according to direct or indirect cooling. The relative humidity of moist outside air can potentially be controlled by both the systems during dehumidification and cooling to produce indoor thermal comfort. The solid desiccant-assisted evaporative cooling technologies may enable the use of the technique in a wider variety of climates, including those with high humidity. The development of innovative desiccant materials, improvement of the structure and material of the dehumidifier setup, desorption consumption rate and operating strategy of the system are some of the potential research possibilities and recommendations that were made. According to this review study, the desiccant integrated innovative cooling system is found as promising alternative to the traditional vapor-compressed cooling system and... Read More

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Traditional cooling systems based on vapor compression are ineffective in humid climates due to their inability to remove moisture below the dew point of the conditioned air, which involves additional effort in the form of an electrical power supply to run vapor compressors. A solid desiccant cooling system reduces powerusage while simultaneously providing fresh and clean air. It is important toexamine and analyze the performance of desiccant dehumidifiers using the Different pattern in the desiccant wheel that will help to develop a more efficient cooling system. Like ahoneycomb, triangular, sinusoidal.To study different type of material used in desiccant wheeel to adsorp the air moisture. Study different simulation technique used in desiccant.

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Abstract Thermally driven desiccant- and evaporative cooling-based technologies are promising greener and cheaper alternatives to compressor-based systems due to the separate handling of latent and sensible loads. Desiccant air-conditioning (DAC) systems comprise a desiccant dehumidifier, a sensible cooling unit, a heat source for regeneration, and a heat recovery unit. These components of a DAC system can be arranged in various ways to give different configurations with varying advantages and disadvantages. In this study, five configurations of thermally driven desiccant dehumidifier- and dew point evaporative cooling (DPEC)-based DAC systems were investigated. Seven evaluation criteria namely regeneration temperature, desiccant moisture removal capacity, COPt, DPEC L/H, heat exchanger UA, system size, and fan power requirement were employed. Results show that the standard cycle in ventilation mode offers the highest COPt despite having the highest regeneration temperature. Recirculation of the return room air can operate at a significantly lower regeneration temperature at the expe... Read More

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A growing environmental Impact of global warming and rapidly increasing cost of the electrical energy cause researchers in the field of refrigeration and air conditioning to develop the sustainable cooling technologies. The aim of this study was to investigate and design a radiant cooling panel with solid desiccant dehumidifier which was suitable for tropical climate to achieve thermal comfort. The influence of an interior ventilation fan to thermal comfort assessment was also examined. The designed system with CFD (Computation fluid dynamics) simulation used ANSYS software to compare with the measured data. The total area of the ceiling and wall radiant cooling panels were 16.83 m2 and 16.32 m2 with 26.28 L/min of supplied water by the cooling tower. The solid desiccant dehumidifier was the pressure-vacuum swing adsorption technology with containing 20 kg of silica-gel. The flow rate of supply air was approximately 90 kg/h. The results indicated that the PMV (Predicted mean voted) could be improving with the uses of cooling panel with dehumidifier during the day. The lower temperatu... Read More

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Cooling has a significant share in energy consumption, especially in hot tropical regions. The conventional mechanical vapor compression (MVC) cycle, widely used for air-conditioning needs, has high energy consumption as air is cooled down to a dew point to remove the moisture. Decoupling the latent cooling load through dehumidification from the sensible cooling load can significantly improve the energy requirement for air-conditioning applications. Solid desiccants have shown safe and reliable operation against liquid desiccants, and several configurations of solid desiccants dehumidifiers are studied to improve their performance. However, the characteristics of solid desiccants are critical for the performance and overall operation of the dehumidifier. The properties of every desiccant depend upon its porous adsorbing surface characteristics. Hence, it has an optimum performance for certain humid conditions. Therefore, for a better dehumidification performance in a specific tropical region, the solid desiccant must have the best performance, according to the humidity range of that ... Read More

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In liquid desiccant-operated evaporative cooling systems (LDECS), the latent heat load of air-conditioning in the confined space is adsorbed by the liquid desiccant, according to the adsorption capacity. Whereas sensible heat load that controls the temperature is handled by the evaporative cooling system. The key difference between conventional vapour compression refrigeration system (VCRS) and LDECS is that latent and sensible heat load of air-conditioning in the confined space are handled separately by different sub-components in LDECS whereas handled by the single cooling coil in VCRS. In review, various components of LDECS such as dehumidifier and regenerator, desiccant heater and cooler, evaporative air cooler, etc., and its features and advancements have been discussed. Further, the influence of distinct input parameters on performance indices of dehumidifier, regenerator, and on the overall performance of LDECS has been addressed through the various state-of-the-art research results and summarized in the form of tables. At the end, the critical conclusion and the future scope ... Read More

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Abstract In recent decades, desiccant dehumidification has been given much interest in the air conditioning industry area. Compared to the conventional vapour compression air conditioning system, desiccant dehumidification has various advantages, including separate humidity and temperature control. In this paper, the analysis of the Rotary Solid Desiccant Wheel System has been performed. Here, we have studied three diffusion coefficients: Ordinary, Knudsen and Surface diffusion coefficients for Rotary Solid Desiccant Wheel System. Also, the analysis has been performed for three different solid desiccant materials: Silica Gel, Molecular Sieve and Activated Alumina to incorporate and to study the effect of pore size on moisture transport and to examine the impact of Tortuosity factor on moisture transport phenomenon. This analysis can correctly select the best desiccant material suitable for the desiccant dehumidification industry.

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Liquid desiccant technology is a promising option with a high thermal coefficient of performance (COP), easy storage, and lower regeneration temperature. Single stage static liquid dehumidification approach gave a limited moisture removal rate. Hence, the paper focuses on designing and fabricating a multistage reciprocating desiccant dehumidification system integrated with a conventional vapour compression cycle. The system consists of an absorber unit consisting of calcium chloride liquid desiccant and a duct integrated with Celdek packing for dehumidifying the inlet air. The desiccant concentration is recovered by circulating it to a regeneration unit. Regeneration unit consists of a heating unit, a separator, & a contact device. Experiments are conducted by varying the number of packings, desiccant concentrations, and air Reynolds number. Dehumidification performance parameters such as coefficient of mass transfer (MTC), rate of moisture removal (MRR), sensible heat factor (SHF), dehumidification effectiveness (DE) are evaluated. Energy consumption is determined for varying condit... Read More

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The traditional air conditioners suffer from performance degradation especially in humid conditions. This is due to fact that the excess moisture level in ventilation air considerably increases latent cooling load of the space to be conditioned. The use of desiccant integrated sensible cooling system can alleviate this problem by controlling the temperature and humidity separately. It also reduces energy consumption for obtaining desired thermal comfort. In the present study, TRNSYS simulation studio project has been developed to perform the simulations of the desiccant dehumidifier coupled HVAC system for different configurations in summer cooling season. Measurements are also carried out to observe the influence of operating parameters on system performance. The obtained results show that the proposed system has ensured a substantial reduction in process air humidity at dehumidifier exit while maintaining the conditioned room comfort.

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Desiccant is a hygroscopic substance generally used in the dryer and air-conditioning system as a drying agent. The function of desiccant is to remove moisture from the air to reduce the humidity of the surrounding air been conditioned. This paper presents several works on the performance of desiccant material in the drying and air-conditioning application. It puts focus on the various advantages and disadvantages of the use of desiccant as a drying agent. There are some advantages of using desiccant include consistent drying and low energy usage. However, there are several disadvantages of using desiccants which are low capacity for moisture absorption and pressure drop in solid desiccant. Solar drying applications have some advantages such as being comparatively cheaper than other methods and less risk of spoiling the product. On the contrary, drying applications have disadvantages include being lower in comparison to the original foodstuff and drying foods eventually leads to shrinkage. The advantages of using desiccant in air-conditioning applications offer dehumidified fresh air... Read More

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Abstract To reduce electricity consumption, heating ventilation from the airconditioning sector focuses on developing alternative solution electrically-driven vapour-compression system. The liquid desiccant air-conditioning system represents energy efficiency. It is more environmentally friendly as an alternative technology for the dehumidification process, especially in cases with high latent loads to maintain air quality under reduced conditions for comfortable. This technology is more efficient than the vapour compression system in hot and humid climates like Indonesia. This study carries out an experimental investigation to find out how much moisture removal with using a liquid desiccant to absorb humidity in the air and to know general types of correlations for heat and mass transfer in the contactor for the air solution. In this experiment, liquid desiccant will be passed through wooden slats to determine the physical and thermophysical properties of the air. The general equation will be verified by the experimental results using a curve that fits this expected. The result is a... Read More

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The use of air conditioning systems has seen considerable growth in the last few decades all over the world, especially in commercial buildings. However, it has shown to have adverse effects on the environment as well as increased energy consumption in buildings. Thus, there has been extensive research to identify alternatives to conventional vapour compression air conditioning systems. Desiccant evaporative cooling (DEC) is one such encouraging system, yet research into its use is still at an initial stage and it needs to be investigated further. In this paper desiccant-based evaporative cooling systems are reviewed, focusing mostly on the solid-based desiccant. The study presents one-stage and two-stage dehumidification, and direct and indirect evaporative cooling for application in hot and humid climates. The review has identified that solid-based desiccant evaporative cooling systems have high potential for use in hot and humid weather. Basic desiccant direct evaporative cooling systems having greater effectiveness in term of output temperature compared to indirect types, but any... Read More

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This paper reviews and surveys desiccant technology, which can be used in the optimization of the HVAC system for high indoor air quality. Also, it compares the electricity consumption of both the technologies. Additionally, it aims to demonstrate the capabilities of modern high-performance desiccants and to enhance the cooling efficiency of the system and to provide comfortable airspace for occupants in humid climates, and simultaneously reducing the electricity requirement. Liquid desiccant system and solid desiccant wheels are used for dehumidification and optimization of the HVAC system. Using dehumidification techniques, latent cooling offers significant energy savings, as well as good indoor air quality as the number of pollutants, are removed directly by co-adsorption. In humid climates, the desiccant system can prevent microbial growth which is essential nowadays. Thus, desiccant dehumidification is a suitable technology for advanced humidity control and can provide benefits over conventional cooling-based dehumidification.

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Desiccant-based hybrid air-conditioning technologies are currently being developed to reduce energy consumption and enhance the effectiveness of indoor thermal environmental control in buildings. T...

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Solid desiccant dehumidification is a promising alternative to vapor compression-based air-dehumidification to reduce energy consumption and improve air quality. Desiccant coated heat exchanger (DCHE), as one type of solid desiccant dehumidification system, can improve system performance and efficiency. The thermal performance and moisture removal capability of the DCHE greatly influence its dehumidification performance. The present work aims to critically analyze the designs, materials, and manufacturing methods of heat exchangers used for solid desiccant coating and look into recent developments in regular heat exchangers, potentially deployed as a substrate for DCHE applications. A comprehensive literature review of publications regarding solid desiccant materials, heat exchangers, manufacturing and coating methods, binder materials, and the performance of heat exchangers has been developed. Alternative heat exchangers are described as better options than fin and tube heat exchangers that have been considered thus far for DCHE applications. Additionally, the heat exchanger's manuf... Read More

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Separate handling of sensible and latent components of building loads can be an energy efficient approach compared to simultaneous management of both. This paper presents a detailed experimental analysis of an energy efficient air conditioning system using solid desiccant integrated with absorption system for separate building thermal load handling. The experimental system consists of silica-gel based solid desiccant for latent load handling, whereas the gas fired air-cooled NH3-H2O absorption chiller is used to handle sensible load of the space. A chilled water-cooling coil heat exchanger is installed on the process side of desiccant cooling system to integrate it with the absorption chiller. The performance of integrated absorption- solid desiccant system is compared with a standalone conventional desiccant air conditioning system with a direct evaporative cooler considering it as baseline system under wide range of operating conditions including air temperature, air humidity, and regeneration temperature. The comparative analysis is performed in terms of supply air temperature, co... Read More

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Desiccant coated heat exchanger (DCHE) has shown great potential for dehumidification in vapor compression cooling systems and has been widely concerned in the research field of air conditioning, as well as heat and mass transfer in recent years. This paper is aimed at providing fundamental knowledge and research progresses on DCHE for dehumidification and cooling. Initially, DCHE dehumidification is chosen as the research object in this review due to its superiority of the principle by comparing with other two typical dehumidification processes, which are condensation dehumidification and rotary-wheel dehumidification. Then, intermittent dehumidification and continuous dehumidification as two operation modes of DCHE are compared. Finally, the variation characteristics of temperature and humidity during operation are discussed. The current studies of DCHE are reviewed from four aspects, including desiccant coating, cooling source, regeneration heating source and basic heat exchanger. The performance analysis of DCHE is then conducted, according to the different effects of above aspec... Read More

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Desiccant cooling cycle utilizes waste heat as energy source. In this paper, a conceptual solid desiccant cooling cycle with lower increase in air temperature during dehumidification is presented. The ratio of temperature rise during dehumidification at desiccant bed is proposed. It is predicted that a lower ratio of temperature rise may improve the ability of the cycle to reduce the temperature of supply air. Then, three configurations of dehumidifier/desiccant bed that could mitigate the rise in air temperature are briefly discussed. Although this paper does not include any mathematical models to predict the performance of those proposed configurations, the conceptual strategies presented may contribute to a breakthrough in desiccant cooling cycle.

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Membrane-based liquid desiccant dehumidifiers avoid the desiccant carryover, which is better than the packed bed. In the process of liquid dehumidification, the dehumidification performance is reduced due to heat release, and internally cooling dehumidification is a method to improve the dehumidification performance. This study develops an internally cooled hollow fiber membrane-based liquid desiccant dehumidifier(IHFMLDD). IHFMLDD is composed of two tubes. The inner tube is not permeable to moisture but only permeable to heat, while the outer tube is a hydrophobic semi-permeable membrane, which can transmit moisture and heat simultaneously. The advantage of this technology is that the liquid desiccant does not directly contact the air in the process, preventing the problem of droplet carryover in the air stream. In addition, cold water reduces the temperature of the solution and improves the dehumidification performance. This paper studies the heat and mass transfer characteristics of IHFMLDD, which uses a staggered triangle arrangement and takes LiCl solution as a cycling fluid. He... Read More

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Liquid desiccant air conditioning systems (LDAS) are an energy-efficient and eco-friendly alternative to conventional air conditioning systems. The performance of a LDAS significantly depends on its simultaneous heat and mass transfer components, namely dehumidifier and regenerator. These components are referred to as liquid desiccant energy exchangers (LDEEs) since the working fluids (air and desiccant) exchange both heat and moisture. There has been a lot of research on LDEEs over the last two decades to improve their performance, thereby enhancing the efficiency of the LDAS. The main objective of this comprehensive review paper is to summarize the developments of LDEEs. The desiccant material, and design, operating, and performance parameters of LDEEs are explained in detail. Even though a lot of research has been done on LDEEs, they are not much utilized in the practical heating, ventilation, and air conditioning (HVAC) systems. To address this issue, future research should prioritize its focus on (i) practical problems of LDEEs such as cross contamination, and leakage and blocka... Read More

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Hybrid solid dessiccant -vapor compression air conditioning system represents an alternative solution of the energy problem in the world. In this article, three configurations of this technology of refrigeration for a test room of cooling capacity 1.8 kW have been studied under hot and dry climate of Gabes. It is found that the configuration which consists of a dessiccant wheel coupled with conventional vapor compression system has the best COP equals to 2.48. Moreover, the sensitivity of the performance. the regeneration temperature to the various outdoor conditions have been evaluated. Results show that the increase of ambient temperature causes the increase of temperature of regeneration and the decrease of the coefficient of performance for different humidity ratio.

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In the present work, a novel circulating desiccant air dehumidifier is numerically and experimentally investigated.Experimental tests and numerical analysis are conducted to investigate the adsorption and desorption processes in fluidized and packed bed columns which are connected via two inclined tubes.The dehumidification process occurs in the packed bed and regeneration process is carried out in the fluidized bed.Silica gel is used as a working desiccant, and its flow rate is controlled using manual valves.The experimental setup is designed, constructed and described.Silica gel is transferred continuously by gravity to the fluidized bed and particles fluidization to the packed bed.A simulation computer code was developed to predict the performance of the system and analyze its sensitivity to the main operating parameters.Results show that when applying intercooling between the two columns a significant improvement in adsorption process is observed.A satisfactory regeneration rate is confirmed at a regeneration temperature of o C. The adsorption and desorption rates are dependent o... Read More

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Air conditioning is one of the large energy consuming sectors, as it comforts the human in closed environment. Especially, in coastal regions where both temperature and humidity are high, it demands for air conditioning. Usually, in such cases, cooling and dehumidification of outside air is done by cooling coils. Such cooling and dehumidification coils requires relatively large amount of energy. In the era of energy saving technologies, Liquid desiccant system (LDS) has proved to be one of the best alternatives for controlling the humidity, economically and efficiently. Different liquid desiccants are available for dehumidification purpose with their own advantages and disadvantages. This paper summarizes the different liquid desiccants used by researchers in their study and the performances analysis of dehumidification process. An attempt is also made to summarize the characteristics of the different hybrid or composite desiccants developed by researchers in order to improve the desiccant properties for the better dehumidification process.

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Desiccant air conditioning systems are using the concepts of desiccant dehumidification and evaporative cooling. Apart from desiccant material, the flow characteristics and inlet conditions also play vital role in improving the dehumidification performance of a desiccant bed. This paper communicates the experimental adsorption characteristics of two layer hollow cylinder silica bed that is used in desiccant-cooling systems for warm and very humid climates, during adsorption processes. Air velocity varied between 1 and 5 m/s and experimental investigation concluded that moisture adsorption ability is increased respect to air velocity for hollow desiccant arrangement. 3.7 m/s air velocity illustrated 2.2 times higher dehumidification rate than 1 m/s.

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Abstract NOTE: The first page of text has been automatically extracted and included below in lieu of an abstract Session 2333 A Desiccant Instruction Module for HVAC Courses J. W. Stevens, B. K. Hodge, and A. Jalalzadeh-Azar Mississippi State University Abstract An instruction module covering introductory aspects of desiccant dehumidification for space conditioning is described. The module is self-contained and is suitable for use in university-level heating, ventilating, and air conditioning (HVAC) courses. It contains information that can be tailored by an instructor for a particular class, an extensive bibliography for additional information, and page-sized figures from which overheads can easily be made. Experiences in incorporating desiccant material into the Mississippi State University HVAC technical elective course are related. Background Desiccants, substances which extract water vapor from a moist air stream either by adsorption or absorption, have been available for a number of years, with the most familiar being silica gel. Likewise, HVAC desiccant systems have had niche ... Read More

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Desiccant cooling mechanism is one of the alternate methods to control the humidity of air and temperature, compared to the conventional vapor compression method of air conditioning. Desiccant cooling doesnt use harmful chemicals which effect the ozone layer and it saves lots of energy. Summer air condition system can use this technology since it removes the latent heat load from the room effectively and this process is economical. Selection of the appropriate liquid desiccant and packing material is very vital to obtain maximum dehumidification. This paper focuses on the different desiccants and packings used by different researchers to enhance the dehumidification. Simple and hybrid systems are also reviewed, and their comparison are presented based on the construction and dehumidification performance.

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Meeting thermal comfort in buildings with high latent loads requires the treatment of the air humidity with specific technologies. Desiccant based systems have proved to be effective in removing ventilation latent load in heating-ventilation and air conditioning systems. Typically, desiccant based systems are part of the air-handling units, which control both temperature and humidity. Based on the above, this paper presents an innovative solution designed to be integrated in the building envelope. It consists of a honeycomb desiccant block placed inside a ventilated faade. The regeneration of the desiccant material is carried out by a solar air collector, which is also integrated in the faade. The aim of the system is to dehumidify the ventilation air before entering the air-handling unit using the faade as an active element of the system. The solution is built at a pilot scale and tested under Mediterranean climate conditions. The experimental tests lead to a numerical model implemented in TRNSYS. This model is used to evaluate the performance of the solution in an office buildin... Read More

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Energy conservation and emission reduction have become a global consensus. As a novel promising energy-saving dehumidification technology, desiccant coated heat exchanger (DCHE)-based air conditioning systems have attracted immense attention recently. This paper provides a quick and reasonable selection of desiccant materials for DCHE systems using water as the cooling medium in different buildings and climates. By the theoretical calculation of moisture needed to be removed in three types of buildings (offices, residential buildings and restaurants) and the analysis of the dehumidification capacity of desiccants in DCHEs reported in the literature, optimal desiccants for different building types and ambient air conditions under given parameters are recommended. Salt-supported porous composite desiccants possess flexible dehumidification performance and can be utilized in most climates and building types, except for extremely humid indoor environments with high requirement for fresh air. Zeolites are especially suitable for return air states, American Air-Conditioning and Refrigerati... Read More

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The main objective of this study was to conduct an experimental analysis to investigate the performance of a new desiccant bed. Therefore, tests were carried out in a desiccator filled with a porous media, i.e. silica gel used as desiccant enhanced with phase change material, using variable inlet climate conditions. Experimental tests were performed to assess the effect of the new packed bed on the adsorption capacity and this by evaluating the outlet evolutions of temperature, relative humidity and absolute humidity. The experimental setup used in this study is a blower enabling to adjust the flow rate, temperature and relative humidity. The amount of adsorbed mass of moisture is also measured and discussed.

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Experiments are conducted under typical humid ambient conditions of Singapore on an advanced airconditioning system wherein desiccant coated fin-tube heat exchangers (DCFTHX) are retro-fitted within the ducting of a conventional HVAC system with a watercooled condenser.The desiccant is regenerated using room-return air (specific humidity of 0.0109 kg/kg d.a.) and the low-grade heat (warm water at 35.5 o C) from the condenser unit.During dehumidification, water from the cooling tower helps in maintaining low air temperature, thereby improving the adsorption performance of the DCFTHX.It is found that DCFTHX managed 39% of the cooling load thereby reducing the compressor load by the same percentage.The experiments prove the efficacy of such internally cooled/heated desiccant systems for practical applications.

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Desiccant coated heat exchanger (DCHE) was proposed for highly efficient dehumidification process due to the adsorption heat could be eased by inner cooling during the sorption process. Meanwhile, heat pump is probably used with DCHE together in humidity control processes because cooling and heating generated by vapor compression heat pump system match with the energy demand of DCHE well. A fresh air heat pump desiccant dehumidification system using rejected heat with desiccant coated heat exchanger (DCHE) was set up and experimentally tested in this paper. Near isothermal dehumidification process could be realized due to the utilization of DCHE which could convert the sensible cooling provided by vapor compression heat pump subsystem to latent cooling to increase the moisture removal of the system. The optimal average moisture removal and COP are 7.02 g/kgDA and 4.10, respectively, under the near ARI humid condition. Most of the total cooling generated by vapor compression heat pump subsystem is used for dehumidification. The moisture removal per kilowatt hour electric power consump... Read More

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Desiccant cooling systems have been regarded as alternative residential air conditioning systems, owing to their potential for considerably reducing electricity power consumption. In particular, when they are combined with distributed power generations, the overall efficiency of the system can be significantly enhanced by utilizing the system exhaust heat for the adsorption of water from the solid desiccant. However, desiccant cooling systems have a limited cooling capacity and consume an extremely high amount of thermal energy. Hybrid desiccant cooling (HDC) systems can extend their cooling capacity to satisfy the cooling load on the hottest day in the summer season by combination with an electric heat pump (EHP). In this study, one-dimensional steady state models of desiccant cooling systems were developed using MATLAB-Simulink. Three types of desiccant cooling system models, direct evaporative cooling (DEC), indirect evaporative cooling (IEC), and HDC systems, have been simulated, and their cooling performance under various temperatures ranges from 25 C to 50 C and various humi... Read More

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Desiccant coated heat exchanger (DCHE), which can be adopted to construct a solar cooling system or desiccant heat pump system, can realize both sensible and latent load removal to provide comfortable supply air. Although it is difficult to avoid condensation in a practical application, the condensation condition of DCHEs is rarely studied. In this paper, a series of condensation experiments are carried out on the desiccant coated microchannel heat exchanger (DCMHE) under conditions with high temperature and high humidity ratio. First, by changing the temperature of cooling water, the unique dynamic characteristics of condensation different from non-condensing conditions are discussed, and the influence of desiccant coating is analyzed. Then, the parametric effects of inlet air velocity and fluid temperature on the mass transfer, heat transfer, and pressure drop performance of DCMHE are analyzed. The results show that the changing trend of the dynamic curve can be used as a sign to judge whether condensation exists or not. And the performance of DCMHE is still stable under continuous... Read More

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The liquid desiccant air-conditioning system has been identified as a promising technology that has the potential of decoupling and preciously controlling the latent and sensible cooling loads of air-conditioning spaces. The issues of moulds and bacteria growth on the wet surface of chilled water coils of conventional air handling units can be resolved by employing liquid desiccant systems, where moisture is absorbed by antibacterial desiccant solutions instead of condensing at low temperature. Considerable progress has been made by researchers to enhance the dehumidification and cooling performances of liquid desiccant systems, which are coherently presented in this chapter. The thermophysical properties of several liquid desiccants have been evaluated and the opportunities for improving the desired properties by mixing different desiccant materials are explored. Techniques for improving the wettability and flow characteristics of the packing materials are also discussed. In addition, several theoretical models and solution techniques to study heat and mass transfer enhancement oppo... Read More

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Air-cooled desiccant coated cross-flow heat exchanger (DCCFHE) system provides a simple and effective approach to improve dehumidification performance by using cooling air to remove adsorption heat during adsorption process. In this study, a novel numerical model validated by experimental data was established to predict the performance of a conventional silica gel DCCFHE system. The fin efficiency, as a variable due to the release of adsorption heat, was taken into account in the model. Parametric study for various air velocity and structural parameters was conducted to reveal their effects on the dehumidification performance. Results show that the smaller process air velocity is conducive to improve dehumidification performance, but the performance increases with the increase in cooling air velocity. Compared to the operation case without cooling air, the moisture removal capacity and dehumidification coefficient of performance can obtain about 35% improvement at the cooling air velocity of 1 m/s. The results also indicate that thicker desiccant layer thickness and smaller fin pitch... Read More

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Studies related to membrane technology have been attracting attention because of low cost, eco-friendliness, and compactness. This paper describes the potential use of hydrophobic membranes in semi-direct evaporative cooling applications for heating, ventilation, and air conditioning (HVAC) systems with the air sweeping membrane evaporation method and vacuum membrane evaporation method. The vacuum membrane evaporation methods with desiccant and without desiccant were conducted to assess the impact of the desiccant. The evaporation rate and the cooling rate of each method increased with the higher air volume flow rate and the higher vacuum pressure difference. In this study, experimental comparison of cooling methods was conducted respectively. Test results from this study will be used for design of membrane evaporative cooling system.

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Desiccant-based dehumidification and air conditioning systems are considered as an energy efficient alternative to traditional vapor compression based air-conditioning systems for green building cooling technology especially in tropical hot and humid ambient climates. It is a novel green cooling technology that makes use of low-grade heat for building air conditioning. It is seen that the desiccant based dehumidification and cooling can efficiently provide comfort conditions in subtropical and especially hot and humid tropical climates. The desiccant integrated novel cooling system has a significant higher coefficient of performance compared to the conventional vapor compression system resulting to substantial electrical energy savings during the summer season by use of renewable solar energy, which also resulted in to major reduction in CO2 emissions. Therefore, these results demonstrate that there is a good potential in desiccant-based dehumidification and cooling system for energy and carbon savings while carry out building air-conditioning. Through a literature review, the feasib... Read More

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The solid desiccant based dehumidifier used in conjunction with the conventional HVAC combines the dehumidification of solid desiccant system and with the cooling capacity of the conventional air conditioning system. This hybrid cooling system provides thermal comfort to the occupants of the conditioned space. The hybrid systems main appeal lies in the fact that, it consumes much lesser high grade electrical energy as compared to the dedicated standalone traditional air conditioning systems. The electrical energy usage is possible still lower by use of primary energy sources for to supply the thermal energy needed for the desiccant regeneration. For this purpose freely available renewable solar energy or industrial waste heat can also be used for the regeneration heat source. Sometimes it is also possible to provide condenser waste heat for the part of desiccant reactivation heat supply may increase the overall performance of the system. It was also found that this cooling system with use of air to air waste heat recovery wheel performed better than without it in terms of dehumidific... Read More

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A desiccant cooling system is among the best options to overcome future energy demand issues while considering human comfort by its ability to control both temperature and humidity. Although desiccant materials remarkably affect the performance of desiccant-based cooling systems, most studies focus on the design. This paper presents a review of the recent investigations on advanced desiccant materials regarding the improvement of the material properties for desiccant cooling application, emphasizing other important parameters, such as environmental conditions, cost, and design to achieve optimal performance. The preparation and performance of silica- and carbon-based desiccant materials are discussed. The current most suitable desiccant materials under different conditions for desiccant air conditioning systems and suggestions for future works are presented.

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Desiccant dehumidification refers to the use of chemical for absorption of water vapor to dehumidify air, and thus reduce the latent cooling load in a building's Heating, Ventilation and Air-Conditioning system.There are two types of desiccant systems: liquid and solid.Liquid desiccant systems remove more moisture from air than the dry desiccant systems.Some of the commonly used liquid desiccants include lithium bromide and lithium chloride.The paper presents a comparative analysis of three desiccants, namely, calcium chloride, lithium chloride and potassium formate.Calcium chloride and lithium chloride are commonly used whereas potassium formate is a new desiccant.The wetted wall column is used to study the dehumidifying property of each chosen desiccant.The gas enters in a counter-current fashion allowing gas-liquid contact.The analysis is used to understand the variations in the dehumidifying nature of the desiccants.

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Nowadays, comfortable and efficient heating, ventilation, and air conditioning (HVAC) systems in buildings are highly desirable. Traditional vapor-compression devices exhibit a low coefficient of performance (COP) (typically 2.83.6) due to the cooling-based dehumidification. Temperature-and humidity-independent control (THIC) systems have been proposed to overcome the challenges; however, their COP is hindered by the sorption heat effect. Here, we report on a solid desiccant heat pump (SDHP) based on desiccant coated evaporators/condensers (DCEs/DCCs). The desiccants adsorb moisture almost isothermally and can be regenerated by the condensation heat. With the optimized refrigerant and desiccant, our proposed DCCs/DCEs feature a weakly-coupled heat and mass transfer. The system exhibits a COP of 6~7, doubling the efficiency of heat pumps currently used in household, which opens a window for the future development of HVAC systems and also a broad range of THIC applications.

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Controlling the temperature and humidity is important to achieve a comfortable space for occupants. Numerous studies have shown that the desiccant air conditioning system offered great potential to solve this problem. However, to guaranty the continuous working of the system, desiccant air conditioning is required a regeneration process which always needs a high temperature. Most literature has shown that its required desorption temperature more than 60C. From this motivation, with the humidity control consideration, in this present work, we performed an experimental investigation on desiccant dehumidification system for low desorption temperature. The aim of this study is to evaluate the capabilities of the desiccant system as a dehumidifier particularly focus on the dehumidifying rate and relative humidity limitation. The system was developed as a solid desiccant block which made of polymer material. The ratio between the adsorption and desorption area was equal to control the constant value of the mass flow rate of 0.1 kg/s. The alternating process between the desorption and adso... Read More

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Low cost and environment friendly air conditioning system are required for many applications like human thermal comfort and industrial process. Conventional vapor-based air condition (VCAC) are not feasible solution due to high energy consumption and harmful effects on environment e.g. ozone layer depletion (OLD), global warming potential (GWP). Water based cooing system (direct and indirect evaporative cooling) can achieve cooling load in dry conditions but in humid conditions not found efficient. In this regard, Desiccant air conditioning (DAC) is a promising technology in order to achieve the required load for air conditioning. In this study, a lab scale silica gel based desiccant unit is developed and its heat and mass transfer characteristics are evaluated in the form of Nusselt number (Nu) and the Sherwood number (Sh). The working principle, important features and experimental procedure of DAC is described. Data is collected at the inlet and outlet of desiccant unit in the form of Temperature (T) and Relative Humidity (RH). Obtained data is used for calculation of the Nu and Sh... Read More

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Desiccant-based hybrid air-conditioning systems have recently become popular owing to a reduction in their energy consumption. In addition to the dehumidification process, regeneration is a necessary process in a hybrid system, and in all previous studies the regenerator (REG) has been separated from the liquid desiccant dehumidifier (DEH), which implies the need for a complex duct configuration and a large equipment space. In the present study, a novel hybrid liquid desiccantheat pump air-conditioning system combined with a cooling coil is proposed for deep dehumidification with a supply air humidity ratio of below 5 g/kg, where the REG, condensing DEH (cooling coil), and liquid desiccant DEH are cascaded. This system not only maintains the energy performance advantages of hybrid systems over conventional systems, it also simplifies the layout of the entire system and guarantees a compact system structure, particularly for buildings with an existing central air-conditioningchilled-water system. Using the proposed system, a coefficient of system performance (COPsys) of 2.43.2 has ... Read More

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DCHE (Desiccant coated heat exchanger) based heat pump systems can handle sensible and latent loads simultaneously and separately within one single component via flowing refrigerant and coated desiccant. Their characteristics have a crucial impact on the performance of the whole system. To ensure energy efficiency of DCHE based systems, the restriction between refrigerant and desiccant is discussed based on energy consumption analysis. Results show that energy consumption of the DCHE based heat pump is intimately related with its coefficient of performance and adsorption heat of coated desiccant. R410A and R32 are found to be promising refrigerants for DCHE systems. Maximum allowable values of adsorption heat under different ambient air conditions and sensible heat ratios are obtained. Desiccant materials with adsorption heat of 23003000 kJ/kg such as various silica gels, all-silica zeolites and salt supported composites are within maximum allowable values of adsorption heat for most conditions. When applying the majority of zeolite type desiccants that possess adsorption heat more ... Read More

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