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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