Air Dehumidification System Research Articles

Kinetic and cracking analysis of paddy rice drying using refrigeration-assisted air dehumidification system

The presence of high relative air humidity in regions characterized by a humid climate results in a slow drying process and the rehydration of paddy. To address this issue, the utilization of a liquefied petroleum gas refrigeration system for the purpose of dehumidifying the ambient air has been shown to reduce drying time and enhance the quality of the final product. In the present investigation, the impact of ambient air dehumidification on the quality and moisture reduction of the Hashemi rice variety was examined. The drying of paddy was modeled and optimized using the Response Surface Method, taking into consideration three key factors: temperature (40, 45, and 50 °C), air velocity (1.7, 2.2, and 2.7 m/s), and relative air humidity (70, 80, and 90 %) as the variables in the conducted experiments. The findings of this study revealed that under dehumidification conditions, samples with a moisture content of 6 % exhibited the lowest cracking rate of 2 %. Moreover, the use of liquefied petroleum gas resulted in a 13 % reduction in cracking and drying times, ranging from 22.3 % to 68.9 %, depending on the experimental conditions. Irrespective of whether dehumidification was employed or not, the temperature was identified as the most influential parameter, impacting the experimental responses by 73.29 % and 73.09 % for the non-dehumidified and dehumidified conditions, respectively. Under optimal conditions, a cracking rate of 2 % was attained during dehumidification at a temperature of 40 °C, a relative air humidity of 80 %, and an air velocity of 1.7 m/s, yielding a desirability index of 0.958. The Response Surface Method, when applied in the dehumidification case, displayed an excellent fit between the experimental and predicted data for both the moisture content (R2 = 0.99) and the cracking index (R2 = 0.98). These results demonstrate the efficacy of the refrigeration system that employs liquefied petroleum gas inefficiently drying paddy in humid regions, rendering it applicable in industrial settings.

Solar air dehumidification systems

The solar air dehumidification system permits dehydration of air inside buildings using thermal energy. With thermal energy storage it is possible to organize the continuous process of air dehumidification even in the night time. Recently we have developed low cost solar concentrators that can be used for air dehumidification. The concentrators of this type contain a large number of flat triangle mirrors. The support frame for these mirrors has a shape of a parabolic dish. The experiments with two prototypes of flat mirror solar concentrators show that a stagnation temperature of more than 300ºC can be obtained. This temperature is sufficient to regenerate almost all desiccants that are used for air dehumidification. We estimate the cost of flat mirror concentrators in mass production as 20-30 USD per square meter. This cost permits creation of dehumidification systems for residential and district applications.

Analysis of the relevant technical characteristics in indoor comfort terminal units for the purpose of satisfying the demanding energy, functional, hygienic and sustainability requirements of NZEB and ZEB buildings

With a growing number of countries, cities and organizations committing to a carbon neutral society by the middle of this century, zero and nearly zero energy buildings (NZEB & ZEB) and nearly zero carbon emissions buildings (NZCB) are becoming the new standard. These buildings with high energy efficiency and low carbon footprint, together with numerous advantages, lead to the materialization of new needs that have a significant impact on the comfort terminals units located in the various indoor environments. In fact, we are witnessing a growing concern for the phenomena of overheating and in general we are already starting to notice that air conditioning and dehumidification systems, in most cases, must be started already in spring and used until late autumn. Heating, on the other hand, becomes less relevant in quantitative terms, thanks to the greater degree of insulation of the building envelope, but thermal inertia can become a problem. In these new conditions, dictated by constructions with a high energy efficiency criterion, it is becoming strategic to have a new generation of indoor comfort terminals units available that take into account the stringent energy, functional, hygienic and sustainability requirements of decarbonized buildings. In this context, present paper focuses on the analysis of what the relevant technical characteristics could be in indoor comfort terminal units to meet the requirements of NZEB and ZEB in the coming decades.

High-efficiency heating and cooling technology with embedded pipes in buildings and underground structures: A review

The thermally activated system utilizes heat exchange pipes embedded in buildings and underground structures to efficiently and stably regulate thermal and humidity environment of building and underground spaces by fully utilizing low-grade energy and heat storage characteristics of the embedded pipe structure. In this review, a comprehensive summary and analysis of the research on embedded pipe heat exchange system are provided, including TABS classification, influencing factors, enhancement strategies, system integration and optimization, application potential, and development trends. The three forms of embedded pipe structures in building enclosures, namely floors, walls, and ceilings, are thoroughly explored. Specifically, to address the demand for environmental regulation in underground spaces, embedding pipes within underground infrastructures is proposed to cater to heating needs in cold region tunnels, cooling requirements in urban tunnels, and deicing/snow melting on road pavements. Various enhancement methods for TABS are suggested to improve operational effectiveness, including utilizing phase change materials, implementing reasonable and effective intermittent operation schemes and control strategies, and integrating with auxiliary air conditioning and dehumidification systems. Future research directions are identified, such as strengthening the prefabrication of embedded pipe thermal activation systems, introducing machine learning algorithms to enhance system intelligence, and combining new technologies to improve system integration as well as integrating the thermo-active system into the fifth-generation district heating and cooling networks. This review work of thermal activation systems with embedded heat transfer pipes will be of some significance in guiding future research and application of embedded pipes heating and cooling of buildings and underground spaces.

Desiccant Dehumidification System Developed Using Additive Manufacturing and Biodegradable Materials

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

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

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

Humidity grade-matched fresh air dehumidification system with adjustable treating stages

Air conditioning systems using liquid desiccants are efficient in dehumidification, but their performance can be further improved under both design and different partial load conditions. In this study, a humidity grade-matched system with adjustable treatment stages is designed based on the use of appropriate humidity sinks to handle loads. The method to determine reasonable treatment stage numbers and packing tower areas is given by optimizing the total system energy consumption and economic performance under different working conditions, based on validated numerical system performance models and device prices from the market or literature. The performance of the proposed system is compared with traditional systems in a case office building in Nanjing. The results are as follows: 1. By optimizing the total system power consumption and economic performance under different conditions, the humidity difference for one-stage and mass transfer humidity difference should be set at 3–5 and 2–3 g/kg to determine the stage number and packing tower area, respectively. 2. The proposed fresh air dehumidification system as applied to an office building without exhaust air in Nanjing reduces 16.6% and 13.5% of the seasonal energy consumption for the entire system relative to single-stage and three-stage systems, respectively. 3. When the system selectively uses exhaust air or outdoor air, 11.0% of additional seasonal energy consumption can be saved for the entire system relative to a system using only outdoor air.

MODELING A SYSTEM WITH SOLAR CONCENTRATORS AND THERMAL ENERGY STORAGE

Global climate change, which has upset the ecological balance, and the rate of population growth, causing an increase in the demand for electricity in the world, are accelerating the gradual transition of states to green energy. Energy generation and energy storage are two important elements in green energy systems. We select parabolic solar concentrators as instrument for energy generation and develop flat facet solar concentrators that approximate a parabolic shape surface. Not only the structure of solar concentrators is proposed, but also the structure of thermal energy storage is described and presented. Using our solar concentrators, small-scale thermal energy storage (TES), it is possible to make power plants for green buildings. Small solar power plants and the air dehumidification system based on solar concentrators have great practical potential, can provide all the energy needs of smart residential buildings in countries with a hot climate, regulate air humidity, improve agricultural productivity in mountainous areas, etc. We describe a small-scale TES and the heater based on a solar concentrator. Water can be used to transfer heat energy. Another variant of TES is based on grave. We describe not only the structure of the system with parabolic solar concentrator and TES but calculate their parameters.

Experimental evaluation of a 3D printed air dehumidification system developed with green desiccant materials

Energy-efficient dehumidification systems are necessary to reduce energy consumption and CO2 emissions into the atmosphere. Desiccant systems could be an alternative to conventional air dehumidification systems based on direct-expansion units. In the present work, the main objective was to develop and experimentally evaluate a 3D printed desiccant system manufactured using green desiccant materials. Hence, the adsorbent capacity of three 3D printed desiccant materials were studied: polylactic acid (PLA), pine wood with PLA (PW-PLA) and olive pit with PLA (OP-PLA). The results showed that PW-PLA was the material with the highest adsorption capacity of those analysed, up to 12.7 % higher than OP-PLA. A fixed bed desiccant system was fabricated using PW-PLA filament and its latent energy performance was investigated under different inlet air conditions and low regeneration temperature, 50 °C. The evaluation of the energy performance of the 3D printed desiccant system revealed adequate moisture removal capacity values, up to 30 g/sm3, with low pressure drop, less than 552 Pa. These results show the promising potential of 3D printing and green desiccant materials for manufacturing ecological air dehumidification systems.

Experimental investigation on a compact fresh air humidification/dehumidification system based on desiccant coated heat pump

Widely used vapor-compression heat pump system can provide both heating and cooling capacity, considering it cannot realize humidification and efficiency of condensation dehumidification is relatively low. In this paper, a fresh air humidification and dehumidification system based on desiccant coated heat pump is established. In which the condenser and evaporator of the heat pump system are replaced by desiccant coated heat exchangers. By using the 4-ventilation valve, the system is very compact. The feasibility of humidification and dehumidification of the system has been theoretically analyzed. The performance of the system under GB Shanghai summer conditions and GB winter conditions is experimentally verified. The results show that the system can realize dehumidification and humidification in summer and winter efficiently and the COP under these two conditions is 5.16 and 5.06 respectively. The dehumidification and humidification rates of the system in the two chosen conditions are 2.99 L h−1 and 1.99 L h−1 respectively. The results also show that under Shanghai summer conditions, by changing the compressor frequency, the system can get a dehumidification of 2.40 L h−1 to 3.05 L h−1 with a COP of 7.80 to 3.56. The optimized switchover period is 6 min.

Steady-state performance assessment and geometrical optimization of packed-bed liquid desiccant air dehumidification systems

Steady-state performance assessment and geometrical optimization of packed-bed liquid desiccant air dehumidification systems

Review of liquid desiccant air dehumidification systems coupled with heat pump: System configurations, component design, and performance

Vapor Compression Systems (VCS) are the most common air conditioning technology. VCS cool the air to its dew point temperature (overcooling) to remove water vapor in the air through condensation and then reheats the air back to the comfort temperature for direct use. The VCS process is inefficient due to overcooling and reheating. Liquid Desiccant Dehumidification (LDD) is a potentially energy-efficient air conditioning. LDD removes water vapor in the process air using liquid desiccant’s high-water affinity. It hybrids with sensible cooling to control temperature and humidity separately. The LD in the LDD becomes weak after dehumidification. The LDD needs additional heating to regenerate the weak Liquid Desiccant (LD) to a high concentration for dehumidification.Earlier versions of the LDD systems use highly concentrated liquid desiccant (large water removal capability) to dehumidify the air by only dealing with latent load. It leads to highly elevated temperatures above 60 °C of heat sources (combustion or electric resistance-based heating) for regeneration. The energy needed for the elevated temperature heat resource significantly reduces or demolishes the benefit of LDD systems. In the recent two decades, researchers have investigated a new configured LDD system that couples an LDD with a heat pump at both dehumidification and regeneration sides for better efficiency.The heat pump provides cooling (from the evaporator) for both dehumidification and sensible cooling and simultaneous heating from the condenser for regeneration. The highly integrated system (HP-LDD) with improved efficiency enables the LDD to operate at lower concentrations and temperatures in dehumidification and regeneration.This paper depicts the working principle behind HP-LDD and its heating and cooling requirements. It reviews the comparison between the HP-LDD systems and the conventional LDD systems regarding system configurations, component design, energy efficiency, and dehumidification performance characteristics. The main findings from the review include the preferred use of packed bed over membrane-based dehumidifiers, the use of internally cooled dehumidifiers enabled by the HP cooling capacity, the high dispersion of HP operation conditions, and the dependence of dehumidification performance on various dehumidifiers. An outlook for future research on HP-LDD strategies is presented based on the reviewed works and their limitations.

Experimental study of dehumidification performance and solar thermal energy enhancement properties on a dehumidification system using desiccant coated heat exchanger

Due to the high dehumidification performance realized by removing adsorption heat by inner cooing, desiccant coated heat exchanger (DCHE) has been proposed and widely studied. The heat pump is usually used as the cooling and heat sources of the dehumidification system composed of DCHE because the cooling and heat capacity could be provided by the heat pump at the same time. Moreover, considering the advantage of low-grade thermal energy utilization, solar thermal energy can be used to further enhance the regeneration of DCHE to improve dehumidification performance and energy efficiency. In this paper, the solar-enhanced fresh air dehumidification system using DCHE driven by heat pump was proposed and a series of experiments were conducted under typical Shanghai summer high humidity conditions. The typical moisture removal of the system can be increased by about 15% to 10.14 g/kgDA and the COP could be further increased by over 25% to 5.39. In addition, the influence of different regeneration temperatures enhanced by solar thermal energy on the system has also been studied. Considering the dehumidification performance improvement and energy utilization efficiency, the optimal regeneration temperature is between 60 °C and 65 °C for the system proposed in this paper.

Cascade deep air dehumidification with integrated direct-contact cooling and liquid desiccant absorption

Deep dehumidification of the feed air is expected for the energy saving and stable operation of the air compression process in large-scale industries. Liquid desiccant-based dehumidification technology provides an alternative solution mainly featuring the continuous operation and low regeneration temperature, but the conventional systems still face a challenge to achieve the deep air dehumidification at high air-to-solution flow ratios, especially under high humidity conditions. Based on the cascade matching of driving forces, this study first presents a cascade deep air dehumidification system integrating a direct-contact cooling module (DCCD) and multi-stage internally-cooled liquid desiccant module (MILDD). In particular, the DCCD uses a novel internal matrix structure where the moist air is in direct contact with the cooling water with low hygroscopic. To evaluate the proposed system, a complete thermodynamic model is developed based on the newly-fitted general empirical correlation for mass transfer coefficient between the moist air and cooling water. The numerical model is validated against the initial experiment of the DCCD–MILDD test bench with a mean relative discrepancy of 6%–9%. The supplied air states and energy performance of the cascade system are evaluated at low humidity and high humidity conditions. The cooling water utilization is further improved by two series-looping schemes of cooling water allocation. Numerical results show that the DCCD–MILDD cascade system can achieve deep air dehumidification with the outlet air humidity ratio lower than 6.2 g/kg and the air-to-solution flow ratios over 4.0 even at high humidity conditions. This attributes to an improvement of the coefficient of performance and exergy efficiency, respectively 1.90 and 0.57. This work may provide an effective design of the liquid desiccant-based deep air dehumidification systems applied to the large-scale air compression process.

Effect of Geometry and Operational Parameters on the Dehumidification Performance of a Desiccant Coated Heat Exchanger

Solid desiccant dehumidification systems are an alternative to vapor-compression-based air dehumidification systems. They use solid desiccant materials to adsorb air moisture in space cooling. DCHE can integrate the cooling component in the heat exchanger to achieve higher dehumidification capacity. Comprehensive numeric modeling would be necessary to assist in the design and operation of the DCHE under development to achieve maximum performance. This paper provides the details of a heat and mass transfer model developed for this purpose. The model aims to cover a gap in existing models by independently modeling heat transfer on the solid desiccant, fin, and tube. The model results were compared with an experimental reference for validation. The air outlet humidity and temperature results for dehumidification and regeneration showed a deviation lower than 15% from the experiment. The validated model was used to perform a parametric study for a series of design and operating conditions. The parametric analysis showed that an increase of 25% in desiccant layer thickness and thermal contact resistance between solid elements reduces moisture removal by 9.1% and 1%, respectively. These results indicate the need to independently model the desiccant layer.

Wickability-optimized textured liquid-desiccant air dehumidifiers for independent moisture management in energy-efficient buildings

Liquid-desiccant-based air conditioning systems are envisioned to enable independent humidity management, thereby improving the energy efficiency of future buildings. Existing liquid-desiccant-based air conditioning concepts, however, suffer from a poor liquid flow distribution deteriorating moisture removal rate. They are consequently flooded with the liquid-desiccant solution, which significantly degrades the energy efficiency of the dehumidification process. Here, the capillary forces and wickability effect of textured air dehumidifier surfaces are altered to minimize the liquid-desiccant flow rate of the fully wetted state, thereby transforming the physics of interfacial desiccant flow distribution. Consequently, the wickability-optimized air dehumidifier surface maximizes both moisture removal rate and dehumidification energy efficiency. It was interestingly found that the length scale of a textured air dehumidifier surface concept is optimized at an intermediate pattern density. Dry solid-air menisci appear at length scales exceeding the optimum pattern distance while the effective liquid–air interfacial area is reduced at smaller length scales, both of which degrade the moisture removal rate. At the optimum pattern density, the effective liquid–air interfacial area increases with the solution flow rate, thereby increasing the dehumidification rate. At a water vapor pressure potential of 3 kPa and a solution flow rate of 2.8 g/s, experimental results indicated a moisture removal rate of 0.16 g/m2-s for a textured surface concept with a capillary length scale of 3 mm, a 28% improvement compared with that of smooth-plate dehumidifier surfaces. A high moisture removal rate of the textured surface at a low desiccant flow rate led to a high thermal efficiency of 0.75 at a water vapor pressure potential of 5.6 kPa and a LiBr flow rate of 2.8 g/s. The insights gained from the present study accelerate the development of advanced textured surface concepts for next-generation liquid-desiccant-based air dehumidification systems offering independent humidity management for future energy-efficient buildings.

Automated air dehumidification system for pigsty

The article presents an up-to-date technical solution of the air dehumidification system for pig breeding premises. The analysis of the existing ventilation systems used in pig breeding is presented. The influence of microclimate parameters on pigs is considered. The required values of microclimate parameters make it possible to obtain maximum productivity from pigs, reduce feed consumption, and also reduce potentially dangerous diseases to a minimum. In turn, the microclimate also affects the pigsty and the equipment installed in it. Compliance with the required values of microclimate parameters is a difficult task, since for small farms the purchase of an air conditioning system is unaffordable. Therefore, it is necessary to develop and design systems that would be economically profitable. The main parameters of the microclimate that affect the productivity and health of pigs are temperature and relative humidity. These parameters affect animals both separately and in a complex. It is known that at high humidity, both high and low temperatures have a negative effect on the body of pigs. If the relative humidity is 85% or more, and the indoor air temperature is below 10 0C, then the animals gain less weight, but the feed consumption increases. To create and maintain a microclimate in a pigsty, it is necessary to design inexpensive and productive installations operating in automatic mode. By draining the air in the pigsty, with the help of natural cold, it is possible to increase the productivity of animals, as well as reduce energy consumption. An installation has been developed to maintain optimal relative humidity.

Transient performance study of an internally-cooled plate membrane liquid desiccant air dehumidification system

• An internally-cooled plate membrane liquid desiccant air dehumidification system has been applied. • A dynamic model for the novel dehumidification system is built up. • The transient performances of the system in a typical summer day are studied. • The temperatures of the solution in the solution tanks vary rapidly after starting up. • Increasing cooling water flow rate or reducing its temperature can improve the system performance. An internally-cooled plate membrane liquid desiccant air dehumidification system has been adopted for air dehumidification due to its excellent ability of removing moisture. In this study, a dynamic model for the novel system is built up by coupling the model of each component. Based on the experimental data and the steady-state model, the dynamic model is validated to prove its accuracy. The transient performances of the system in a typical summer day are investigated. It is found that the operation process of the system during the daytime includes the start-up period and the stable running period. Owing to the rapid change of system parameters, the performances of the system during the start-up period are studied in detail. The results show that the temperatures of the solution in the solution tanks vary rapidly after starting up because of the low thermal inertia. Increasing cooling water flow rate or reducing cooling water temperature can improve the SDP of the system. The initial solution concentration and the volume of solution in the tank have a great effect on the start-up time, while the initial solution temperature has little influences.

Physical characteristics analysis and performance comparison of membranes for vacuum membrane dehumidifiers

The present study pertains to an experimental measurement investigation of membrane physical properties for vacuum membrane dehumidifiers. The membrane material used in an air dehumidification system is a key role for the dehumidification efficiency. To find the most suitable membrane for dehumidification, the membrane physical characteristics are examined by using three critical indexes of air permeance (AP) and water vapor permeance (WP), and selectivity (SE). Two categories of dehumidification membranes, i.e. composite and dense membranes, are applied in the vacuum membrane dehumidifier with a serpentine flow channel. Firstly, the vapor transfer rates of both composite and dense membranes are determined and the experimental data discloses that the composite membranes, such as Sulfone and Metal–organic framework (Mof) membranes, provide higher vapor transport ability, which is not suitable for the vacuum membrane-based dehumidifier. Then, the measurement of AP, WP, and SE is further performed for the dense membranes of Nafion. The result shows that the order of either AP or WP is N.211, N.212, N.115, and N.117, but the SE defined as WP/AP has a different tendency and the order is N.117, N.115, N.212, and N.211. Finally, the results of AP, WP, and SE in this dehumidifier are also compared with the previous experiment.

Performance Investigation of a Hollow Fiber Membrane-Based Desiccant Liquid Air Dehumidification System

The membrane-based desiccant liquid air dehumidification system is a promising technology for efficient humidity control in buildings. The use of a membrane module allows, among other things, for a compact design with a relatively large heat and mass transfer area and eliminates carryover of solution droplets. In this paper, a cross-flow, hollow-fiber membrane module was proposed for air dehumidification and regeneration of lithium chloride. A two-dimensional heat and mass transfer model for cross-flow in a membrane module used for air dehumidification and liquid desiccant regeneration was developed. The effectiveness, moisture removal rate and moisture removal rate were studied numerically and validated against experimental results. Based on the numerical simulations, the most favorable ranges of operating conditions were determined. It was found that the operating conditions significantly impact the dehumidification performance. The proposed dehumidifier maintains its performance in a wide range of inlet air humidity ratios. For dehumidification, the recommended temperature of the incoming solution was in the range of 14–18 °C, while for regeneration the solution range was 40–50 °C. The packing fraction was suggested in the range of 0.30–0.40. These results can help design membrane-based liquid dehumidification systems.