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In favor of renewable energy and using green refrigerant, the absorption air-conditioning system is a good measure for overcoming energy shortage and environmental deterioration. With the thermal method, its performance is not good enough because of much heat loss in the regeneration process. For optimal performance, capacitive deionization (CDI) regeneration method was proposed by regenerating absorbent with electrodes in electric field. Previous research shows the theoretical COP of the CDI based system could attain 3. However, these results lack experimental support. Therefore, this paper presents the experimental research on the actual performance. The influence of concentration and other parameters has been analyzed in the experiments. Based on the experimental results, the energy recovery characteristic also gets confirmed and it provides a new way to improve the performance of the CDI based system. Electricity and energy models have been developed; some important parameters have been investigated. The experimental results present the actual regeneration capacity and corresponding COP. The theoretical results expose the improvement of COP with energy recovery and the influences of equivalent series resistance, flow rate and capacitance. It found the COP has potential to further increase by 2 or even 3 times, could reach 6 with appropriate energy recovery. [ABSTRACT FROM AUTHOR]

Air-conditioning systems consume a large proportion of energy consumption in buildings, which leads to an important significance of energy-saving in air-conditionings. For liquid desiccant air-conditioning system, a new air-conditioning with good energy-saving potential, electrodialysis (ED) can be a reliable regeneration method, which cannot be affected by hot and wet air. In this paper, an ED regeneration experimental system was conducted to investigate actual effect of concentration difference between dilute and regenerate cells on the performance of ED regenerator. The results show that increase of concentration difference is harmful to performance of ED regenerator. Moreover, decrease of liquid desiccant flow rate in regenerate cells can be a solution to add concentration increase in regenerate cells even when concentration difference is big, but it is harmful to current efficiency of ED regenerator and COP of liquid desiccant air-conditioning system based on ED regeneration. On the other hand, as current efficiency and COP finally tends to be stable with the increase of current and concentration difference, the “final” current efficiency and COP may only depend on liquid desiccant concentration, the structure of ED regenerator and characteristics of membranes, which should be improved to optimize the performance of ED regenerator. [ABSTRACT FROM AUTHOR]

As an important part of urban public transport, how to reduce energy consumption of rail transit becomes a focused issue. Considered with the operating characteristic of air conditioning in subway station, solution method with large temperature difference and high outlet temperature of 10/17 Celsius in evaporator is put forward. Two condensers and evaporators are linked in series and both of them are in countercurrent form, in which condition the energy efficiency can be improved greatly. Simultaneously high efficiency chiller with two different capacities of compressor heads is designed to improve the energy efficiency in part load. Experimental research of high efficiency chiller is conducted and the results show that: With the decrease of load percentage, COP (coefficient of performance) is fluctuated from 6.2 to 7.0. With the increase of outlet chilled water, COP increases greatly; while with the increase of outlet cooling water, COP decreases greatly. In this system at the design condition, COP can reach as high as 7.01, which can supply database for utilization of chiller in subway station air conditioning system. [ABSTRACT FROM AUTHOR]

Liquid desiccant evaporative cooling air-conditioning (LDECAC) system, which combines both advantages of liquid desiccant and evaporative cooling technology, has a great potential to utilize low-grade heat for refrigeration and air conditioning. A novel LDECAC system is proposed to obtain lower supply air temperature and humidity ratio at the expense of less thermal energy consumption when used as a dedicated fresh air system. It consists of a liquid desiccant system with self-cycle solution at dehumidification and regeneration sides, a regenerative indirect evaporative cooler (RIDEC) and a direct evaporative cooler with adjustable by-pass flow. A parametric study on steady-state thermal performance of LDECAC system was performed based on the developed mathematical model. The performance was investigated by varying five key parameters: solution self-cycle ratio ( R s ), working to intake air flow ratio ( R a ), regeneration temperature, ambient air temperature and humidity ratio. The results show that the system can handle the process air to 17.9 °C and 9.2 g/kg with the thermal coefficient of performance of 0.56 under the design condition. The recommended value for R s lies between 0.6 and 0.7 and that for R a is 0.2 under the typical operating condition. The variable R s control method is effective in response to the change of ambient air conditions. Performance comparison with the conventional LDECAC system shows that the novel system can utilize lower temperature heat source and achieve a higher thermal coefficient of performance. [ABSTRACT FROM AUTHOR]

In this paper the air-conditioning system which combined the inducement ventilation and radiant air-conditioning is proposed. The indoor terminal device is the induction unit which is processed to be combined with the radiant panel on which the copper pipes with rigid aluminum diffusion fins are installed. The radiant panel can be cooled and heated by both water and air. The two-stage evaporator chiller with the non-azeotropic refrigerant is utilized in the system. The experiments of performance test for the novel air type induction radiant air-conditioning system were carried out to verify the feasibility of the system. With the radiation to heat the building envelope of the laboratory, the system can form an overall uniform indoor temperature field both in the vertical direction and the horizontal direction. When the upside return air inlet which shown better performance was used, the space under height 2m had a moderate temperature difference. The system can greatly reduce the sensation of draught which reduces comfort. [ABSTRACT FROM AUTHOR]

Abstract: Liquid desiccant regeneration has important effect on performance of a liquid desiccant air conditioning system. Compared with conventional packed regenerator, internally heated regenerator is proposed to achieve better regeneration performance. This study emphasized on both regeneration rate and regeneration thermal efficiency to evaluate the performance of both regenerators. A validated heat and mass transfer model was used to analyse and compare the performance of internally heated and adiabatic regenerators. The results indicated that internally heated regenerator not only could increase the regenerate rate, but also could exhibit higher energy utilization efficiency. Different from adiabatic regenerator, internally heated regenerator can provide comparable regeneration efficiency and regeneration rate at low desiccant flow rate, so it should be a good alternative to avoid carryover of desiccant droplets. Higher air flow rate would result in a deduction of regeneration thermal efficiency although achieving higher regeneration rate. Suitable flow rate of the air should be considered carefully in liquid desiccant regeneration. The internally regenerator could have considerable prospect in liquid desiccant air conditioning application. [Copyright &y& Elsevier]

Abstract: For providing good performance of dehumidifier and regenerator with certain dimensions, a new type of internally cooled/heated dehumidifier/regenerator based on the plate–fin heat exchanger (PFHE) was designed. To investigate the behavior of the new equipment, an experimental setup was established in an environment chamber with regulable temperature and humidity air. By the internally cooled dehumidification testing, effects of the cooling water temperature, the air flow rate and the desiccant temperature on the dehumidification performance and the cooling efficiency were presented. The behavior of internally cooled dehumidification process was compared with that of the adiabatic dehumidification process. The results suggested that the cooling efficiency decreased with the increasing of the cooling water temperature and desiccant with low temperature could bring more mass transfer coefficients. There is an optimal air flow rate to achieve the maximum absolute humidity decrease of the air. By the internally heated regeneration testing, effects of the air flow rate and the desiccant inlet temperature on the regeneration performance and air outlet parameters were discussed and also compared with those of the adiabatic regeneration process. It was concluded that the regeneration efficiency of internally heated regeneration was more than that of the adiabatic regeneration, and the internally heated regenerator could offer better thermal performance. [Copyright &y& Elsevier]

Abstract: A new type of air conditioning system, the liquid desiccant evaporation cooling air conditioning system (LDCS) is introduced in this paper. Desiccant evaporation cooling technology is environmental friendly and can be used to condition the indoor environment of buildings. Unlike conventional air conditioning systems, the system can be driven by low-grade heat sources such as solar energy and industrial waste heat with temperatures between 60 and 80°C. In this paper, a LDCS, as well as a packed tower for the regenerator and dehumidifier is described. The effects of heating source temperature, air temperature and humidity, desiccant solution temperature and desiccant solution concentration on the rates of dehumidification and regeneration are discussed. Based on the experimental results, mass transfer coefficients of the regeneration process were experimentally obtained. The results showed that the mean mass transfer coefficient of the packing regenerator was 4g/(m2 s). In the experiments of dehumidification, it was found that there was maximal tower efficiency with the suitable inlet humidity of the indoor air. The effective curves of heating temperature on the outlet parameters of the regenerator were obtained. The relationships of regeneration mass transfer coefficient as a function of heating temperature and desiccant concentration are introduced. [Copyright &y& Elsevier]

Human thermal adaptation is widely recognized to achieve building energy saving. However, the energy-saving potential of traditional dwellings based on adaptive thermal comfort of residents in cooling and heating periods has not been fully explored. This paper takes the traditional dwellings in the Small West Lake area in Nanjing, China as an example, and explores the thermal comfort of local residents. Then, based on the annual thermal neutral temperature of local residents, a dynamic control strategy of temperature setting points throughout the cooling and heating periods was proposed, and compared with the traditional constant indoor condition from the perspective of heat transfer. The results show that the proposed dynamic controlling method can reduce the energy consumption for maintaining heating or cooling by 26.87%–36.51% in the whole year under the climatic environment of Nanjing, China. The average thermal neutral temperatures are 27.63 °C in summer and 14.44 °C in winter. The thermal sensitivity of residents in traditional Chinese dwellings in winter is lower than that in summer. This study shows the applicability of the adaptive thermal comfort model to traditional Chinese dwellings and a relaxation in the presence of strict set-point temperatures. It is recommended to consider the adaptive thermal comfort of residents into the design of air conditioning or heating systems, which can achieve great energy-saving effect. • The field study of thermal comfort of residents in traditional Chinese dwelling was carried out. • The neutral temperature of residents in traditional Chinese dwellings is 27.63 °C in summer and 14.44 °C in winter. • A dynamic control strategy of indoor setting temperature was proposed. • The proposed control strategy was proved to have energy saving potential. [ABSTRACT FROM AUTHOR]

Dehumidifier and regenerator are the key components of a liquid desiccant dehumidification system. This paper examines the heat and mass transfer processes of a counter-flow packing tower using entransy analysis. Under ideal thermodynamic conditions, if NTU m of the counter-flow packing tower is infinite, the reversible process only exists when the inlet states of air and solution lie on the same iso-relative humidity line. In actual heat and mass transfer processes, the relative position of the inlet parameters of air and solution in the psychrometric chart will influence the entransy dissipation in the packing tower. Based on the analytic solution of temperature difference and humidity ratio difference between air and solution, minimum entransy dissipation is determined when the states of inlet air and solution lie on the same iso-relative humidity line. The influence of inlet characteristics can be quantified using an unmatched coefficient of inlet parameter (γ). This parameter is an indicator of the flow-path design and the system optimization. Furthermore, a practical application is presented by comparing three typical flow paths. The flow path with the smallest γ value reduces the required temperature of heat sources from 60 °C to 45 °C. The realization of such low-grade heat sources not only means high/efficient utilization of heat or solar energy, but also results in less waste heat. [ABSTRACT FROM AUTHOR]

• Two hybrid regeneration methods are proposed for absorption system. • Both charge efficiency and refrigerant purity are enhanced in hybrid systems. • Models are developed to evaluate and optimize the performance of hybrid systems. • Operating parameters are optimized to achieve the optimum system performance. • The hybrid regeneration methods improve the system COP by around 30%. Absorption air-conditioning system is considered as sustainable but its performance is limited by the low efficiency of conventional thermal boiling method. This study proposes two hybrid regeneration methods: one combines capacitive deionization (CDI) and solar steam (SS) process for regeneration, the other combines CDI and reverse osmosis (RO) process for regeneration. These two regeneration methods can overcome the inherent limitation of conventional absorption system. Absorbent is regenerated by electrosorption and refrigerant is obtained by solar interfacial evaporation or water permeation, which circumvents the inefficient separation of thermal boiling method. The processes of new systems have been designed. Models have been established to evaluate and optimize system performance and experiments have been conducted to acquire the corresponding performance indexes. Based on models and experimental results, the influence of some key parameters has been revealed. For CDI-SS system, a real-time control strategy has been developed to achieve its optimum performance. For CDI-RO system, the optimum inlet concentration of RO regenerator has been determined from energy and economic viewpoints. Both systems exhibit a better performance than conventional absorption system. Compared with CDI-SS system, CDI-RO system has advantages in operation and application but its COP is lower. [ABSTRACT FROM AUTHOR]

Temperature and humidity independent control (THIC) systems demonstrate promising energy-saving potential compared with the conventional air conditioning systems. One type of THIC systems is proposed to use dual cooling sources with different temperatures since they could be produced easily by traditional vapor compression refrigeration chillers. This paper investigates the applicable condition of the THIC system based on dual cooling sources (DCSTHIC system). It is found that the DCSTHIC system has limited conditions (such as scopes of the heat moisture ratio and the fresh air rate) when applied, otherwise the indoor air temperature and humidity can’t be fulfilled, and further available scope of the heat moisture ratio realized by the DCSTHIC system is disclosed for air conditioned spaces. The minimum realized heat moisture ratio depends on the temperature of low-temperature cooling sources ( t LCS ). A parametric study is also conducted to analyze effects on the energy efficiency of DCSTHIC systems. These parameters include the heat moisture ratio ( ε ) and temperatures of dual cooling sources. Results show that DCSTHIC systems show more significant energy-saving potential in the air conditioned spaces with higher ε . The system COP improvement ranges from 3.1% to 17.5% compared with conventional air conditioning systems when the heat moisture ratio changes from 8000 kJ/kg to 15,000 kJ/kg. This study helps to guide the design and optimization of DCSTHIC systems. [ABSTRACT FROM AUTHOR]

Highlights: [•] A temperature and humidity independent control air-conditioning system is proposed. [•] Liquid desiccant with low concentration and temperature is used in dehumidification. [•] Condensation heat is used for the liquid desiccant regeneration. [•] The performance of the system under different operation conditions is investigated. [•] Performance improvement of the new system to the conventional system is studied. [ABSTRACT FROM AUTHOR]

Abstract: Liquid desiccant dehumidification technology is becoming increasingly attractive due to its high efficient utilization of low-grade heat and its effectiveness in dehumidification. Using this technology, energy-efficient air conditioning systems have been developed, which demonstrated superiority over the traditional vapor compression type system by allowing both temperature and humidity to be controlled independently. This paper presented a state-of-the-art review of the research and development in this field, covering the topics of heat and mass transfer models, performance evaluation of liquid desiccant dehumidification and regeneration, and technology development of dehumidifiers and regenerators as the most important components of liquid desiccant systems. Meanwhile, many detailed systems using solar energy in desiccant cooling was reported, and some new applications of liquid desiccant dehumidification were also introduced. [Copyright &y& Elsevier]

Abstract: This paper presents an adaptive Smith predictor-based self-tuning PI controller and its application to the air-conditioning system of a test room. The significant time delay of air-conditioning processes can lead to degradation of performance and instability of the control loop. The parameters of air-conditioning processes vary due to the changes in the operation conditions. By using a recursive least squares (RLS) algorithm combined with a z-domain fitting method, the parameters of the air-conditioning process in the closed loop including time delay can be estimated online. Based on the estimated dead-time, a Smith predictor, which uses a reference model, is adopted to reduce the unfavorable effects of the time delay in the air-conditioning system. Based on the predicted error and estimated values, the control signal of the control loop is calculated by a self-tuning PI controller using ITAE tuning rules. The performance, robustness and effectiveness of the proposed control method are validated in the experimental platform. The corresponding performance of the proposed control method is compared with an adaptive PI controller. Experiment results demonstrate that the proposed strategy achieves better performance compared with the adaptive PI controller considering the effects of set-point changes, parameter variations or load disturbances in HVAC systems. [Copyright &y& Elsevier]

An energy conservative air-conditioning system is critical to promoting energy conservation and emission reduction. One promising alternative is liquid desiccant cooling system (LDCS), which can be driven by low-grade heat and has superior dehumidification performance. However, energy waste from traditional regeneration process restricts its application from widespread use. To overcome this disadvantage, a wood-based heat localization regenerator is presented: it localizes the thermal energy on the regeneration surface avoiding the unnecessary heating of bulk solution. The real performance of this new regenerator has been investigated theoretically and experimentally in this paper. The regeneration process of desiccant solution has been analyzed and a regeneration performance prediction model has been developed. Some performance indexes have been derived from experimental data. A regeneration performance comparison has been conducted between the heat localization method and the traditional heating method. The results show that the new method improves regeneration thermal efficiency by above 50% and the maximum value can achieve 43.6%. Besides higher performance, the reduction of energy consumption, initial cost and complexity has achieved with the heat localization regenerator. The overall improvement makes LDCS such a competitive alternative to the current air-conditioning system. [Display omitted] • A wood-based heat localization regenerator is presented for efficient regeneration. • The actual performance of heat localization regeneration method has been revealed. • The heat localization method improves regeneration thermal efficiency by more than 50%. • The heat localization based LDCS has advantages on performance, initial cost and complexity. [ABSTRACT FROM AUTHOR]

The regeneration of aqueous electrolyte solutions is a critical and energy-intensive process in air-conditioning systems. In this work, the minimum energy required for regenerating aqueous electrolyte solutions was derived and analyzed from the perspective of the driving force. The thermodynamic efficiency of electrodialysis and thermal regeneration was evaluated and compared. The results show that the minimum energy consumption of the thermally-driven method involving water vapor removal, such as traditional packed-bed thermal regeneration, is lower than that of pressure- and electrically-driven methods that involve liquid water removal, such as electrodialysis and reverse osmosis. Utilizing dry air, such as indoor exhaust and return air, proves to be an effective approach to saving energy during thermal regeneration. For pressure- and electrically-driven regeneration methods, multi-stage processes are necessary to achieve feasibility at high concentrations. However, the complexity and cost of such systems would be considered unacceptable for air-conditioning applications. Instead, single-effect thermal processes can attain high thermodynamic efficiency at high concentrations. The analysis indicates that the thermodynamic efficiency of actual thermal processes studied ranges from 9.1 % to 40.1 %, which is significantly higher than the thermodynamic efficiency of actual electrodialysis processes (which is lower than 4.7 %). • The minimum energy required for regenerating aqueous solutions is derived. • Thermodynamic efficiency of different actual regeneration processes is analyzed. • Thermodynamic efficiency of studied thermal processes ranges from 9.1 % to 40.1 %. • Utilization of available dry air can help save energy for thermal regeneration. [ABSTRACT FROM AUTHOR]

Electrodialysis (ED) is an alternative to the conventional thermal regeneration of high-salt solutions used in air conditioning systems (ACSs). In this work, a simplified mathematical model was developed to describe the solute and water transport. The solute hydration number and free water content were proposed to characterize the solute hydration properties. A laboratory-scale ED regeneration system was set up to investigate the regeneration performance of three kinds of high-salt solutions (aqueous LiCl, LiBr and CaCl 2 solutions) at various initial concentrations and current densities. The results demonstrate good agreement between numerical and experimental findings. The initial concentration and applied current density have great impacts on ED performance. Firstly, higher initial concentration generally results in lower membrane permselectivity, current efficiency, solute and water transfer rate, and higher energy consumption. Secondly, higher current density has a positive effect on solute and water transport but leads to more energy consumption. The solute hydration number and free water content both decrease with increasing initial concentration. The appropriate mass concentrations of 15%, 25% and 15% are respectively suggested for aqueous LiCl, LiBr and CaCl 2 solutions when applying ED in ACSs to ensure responsible performance. • Performance of regeneration of high-salt solutions was experimentally investigated. • Idea based on the solute hydration number and free water content was proposed. • Simplified model was established to describe the solute and water transport. • Solute hydration number and free water content were quantified based on model. [ABSTRACT FROM AUTHOR]

The purpose of air-conditioning systems is to provide a suitable indoor environment with respect to temperature, humidity and fresh air. Liquid desiccant dehumidification constitutes an effective method for extracting moisture from humid air with less energy consumption. Current studies mainly focus on dehumidification system under certain heat and mass transfer ability (number of mass transfer units NTU m ). This paper will investigate NTU m of counter-flow packing tower and its influence on system performance. An experiment including a counter-flow packing tower was conducted. When the height of tower was 0.7 m, the volumetric mass transfer coefficient was between 1–4 kg/(m 3 ·s) and NTU m presented a range between 0.9–1.4, when air flow rate changes from 1 kg/(m 2 s) to 2.5 kg/(m 2 s). When the height changed to 2.1 m, the NTU m of the tower presented a variation from 3.3 to 4.3. Furthermore, a simulation model is developed, which is validated by experimental data and past research results. The influence of NTU m on total circulation flow path is mainly caused by heat and cold offset and an NTU m value approximately of 4 constitutes a suitable value of increasing heat and mass transfer ability. Comparing three typical flow paths, when NTU m is lower than 3.5, inter-stage circulation presents improved performance in system COP. When NTU m is large, total circulation is efficient. The system COP cross points of flow paths are caused by heat and cold offset and concentration difference of the solution circulation between the dehumidifier and the regenerator, which can be quantified by loss coefficient ε and χ respectively. The heat and mass transfer ability of the system should be considered in the designing process of flow path configuration to obtain an efficient performance for different range of NTU m . [ABSTRACT FROM AUTHOR]

• The performance of solar interfacial regeneration method was investigated. • Drilling holes of wood regenerator can promote the salt resistance ability. • Sunlight absorption ability can be enhanced by drilling holes. • Regeneration rate can reach 0.64 kgm−2h−1 for 40 wt% CaCl 2 solution at 30 °C. Liquid desiccant air-conditioning (LDAC) systems are one of the most promising alternatives to conventional air conditioning systems due to the high energy efficiency. The most energy-consuming part of LDAS system is desiccant regeneration, while traditional regeneration methods often fail to balance the energy grade and energy efficiency. Inspired by solar heat localization for seawater desalination, the regeneration performance of this novel method has been investigated. Here, we fabricated a wood-based regenerator by drilling holes and spaying Chinese ink, which features high sunlight absorption and strong water transportation ability. Owing to the high hydraulic conductivity of drilled holes and low thermal conductivity of wood substrate, liquid desiccant can be regenerated efficiently with a low-temperature rise. Even for 40 wt% CaCl 2 solution at 30 °C, the regeneration rate and efficiency can reach 0.64 kg·m−2·h−1 and 43.2 %. Comparisons between solar interfacial regeneration method and other traditional regeneration methods were also conducted. Results show that the solar interfacial method can significantly improve the regeneration rate at the same temperature. Given the low manufacturing cost and operating cost, high regeneration rate and efficiency, superior salt-rejecting property, and low-temperature rise, the wood regenerators based on solar interfacial regeneration show great potential in LDAC systems. [ABSTRACT FROM AUTHOR]

Liquid desiccant air conditioning system (LDAS) was considered a promising air conditioning system due to the advantages of low-grade heat utilization, effective humidity control and environment-friendly. The performance of LDAS significantly depends on the heat and mass transfer components, namely dehumidifier and regenerator, while the regeneration process of traditional regenerator is energy-inefficient. Inspired by the high-efficiency solar interfacial evaporation which can produce drinking water from seawater, this method was introduced in this work for liquid desiccant regeneration to overcome the inefficiency of the regeneration process. Wood was prepared as the regenerator by alkali-assisted method and surface carbonization. The regeneration performance of solar interfacial regeneration was experimentally investigated and compared with that of packed-bed tower regeneration and membrane distillation regeneration. Results show solar interfacial regeneration is very competitive due to the high regeneration rate and efficiency, which can reach 0.57 kg m−2 h−1 and 42.5% for 40% LiCl solution under 1-sun irradiation. Moreover, the low temperature rises of concentrated solution, cheap construction costs and operating costs make LDAS more energy-saving. This work is expected to supply a novel method for liquid desiccant regeneration. • A novel regeneration method based on solar interfacial evaporation was studied. • Regeneration efficiency (42.5%) was achieved for 40 wt% LiCl solution under 1-sun. • Diluted solution can be regenerated with a low temperature rise. • Excellent salt-rejecting is conducive to improving regeneration performance. [ABSTRACT FROM AUTHOR]

[Display omitted] • Liquid desiccant regeneration process and performance evaluation index are explained. • Properties and developments of liquid desiccant materials are examined. • Developments in various liquid desiccant regenerators are reviewed. • Various combinations of liquid desiccant regeneration systems are discussed. • Improvements in the performance of regenerative system are reviewed. Liquid desiccant air-conditioning (LDAC) system is being considered as a promising alternative to vapor compression refrigeration system owing to its effective temperature and humidity independent control and great energy-saving potential. Regeneration of liquid desiccant is an important desalination process in the LDAC system, which aims at re-concentrating the diluted desiccant solution to renew its dehumidification capacity for system continuous operation. This review provides a comprehensive overview of the developments in liquid desiccant regeneration to date, focusing on its application for LDAC systems. The operation principle and evaluation index of liquid desiccant cooling system and regeneration process are firstly presented. Then, attention has been paid to various developments in liquid desiccant materials and regenerators, which play a pivotal role in the liquid desiccant regeneration process. Furthermore, hybrid liquid desiccant regeneration systems with various driven energy sources and the enhancement technologies for improving the regeneration performance are summarized and reviewed. Finally, future needs and recommendations for liquid desiccant regeneration technologies are discussed. This review may help to identify the research gaps and explore promising approach for future study to further enhance the efficiency of liquid desiccant regeneration for the LDAC system. [ABSTRACT FROM AUTHOR]

• An improved system is proposed based on multi-fans with frequency conversion. • The improved system meets pressure control requirement in non-working modes. • The energy saving and cleanliness can be achieved by switching operation modes. Pressure control for cleanrooms in the pharmaceutical industry is a necessary means to avoid the cross-contamination. The pressure control of traditional air conditioning can only handle the working stage. In the non-working stage, the system cannot reduce the air change rate per hour (ACH) in order to alleviate the problem of high energy consumption. This paper proposes an improved air conditioning system, which focuses on the ability to control pressure gradient of the system in working and non-working mode. By theoretical derivation of the combined fan frequency conversion, when the impedance and volume of the infiltration air satisfy S i G Z , i = S j G Z , j = S k G Z , k = c o n s t a n t , the pressure gradient in multi-zone cleanrooms can remain stable. A mathematical model of the system has been established, which includes five modules: air pipe network, fan characteristic curve, fan operating point solution, variable volume damper characteristic curve and multi-zone network pressure gradient solution. The correctness of the model is verified by field measurements. Taking a clean workshop as case study, the room pressure can be stabilized in the range of ± 3 Pa by switching the working and non-working mode, which can save 39.8% of the energy consumption in non-working mode, while ensuring cleanliness. This paper demonstrates the process of the air pipe network's influence on cleanrooms pressure and proves the effectiveness of improved purification air conditioning system in pressure gradient control and energy saving potential. [ABSTRACT FROM AUTHOR]

In this paper, a liquid regeneration method by vacuum membrane distillation (VMD) is proposed for the liquid desiccant air conditioning system (LDACs), and the experimental study on this method is carried out. VMD regeneration experiments were carried out with LiCl solution. The effects of temperature, concentration of feed solution, length, number of fiber membranes and vacuum pressure on the membrane flux, mass transfer coefficient, rejection rate and regeneration ability were studied. The results show that the error between experimental and calculation results is reduced from less than 15% to less than 5% by the optimized calculation model. The temperature of feed solution has a great influence on the regeneration performance of VMD, and the regeneration ability of VMD process increases approximately exponentially from about 0.1% to 0.8–1.2% with the increase of regeneration temperature. The VMD regeneration process of LiCl solution is the result of Poiseuille flow and Knudsen diffusion, and Poiseuille flow dominates. Under the same regeneration capacity, the regeneration temperature of 30 wt% LiCl solution is about 7 °C higher than that of 20 wt% LiCl solution, and this temperature difference also increases as the target regeneration amount increases. In order to improve the regeneration effect of high concentration solution, the regeneration temperature can be increased appropriately. The water flux of the membrane decreases with the increase of the length of the membrane. The membrane length of Type1 is 2.1 times longer than Type 2, but regeneration capacity of Type 1 is only 1–1.7 times higher than Type 2. Further, both the water flux and regeneration ability of the solution decrease first and then increase with the increasing number of membranes. Therefore, the reasonable selection of number of fiber membranes can significantly save materials and also improve the regeneration ability. • A liquid regeneration method by vacuum membrane distillation is proposed for LDACs. • The effects of various influence parameters on regeneration ability were studied. • The mathematical model of membrane flux was optimized, and its accuracy was verified. [ABSTRACT FROM AUTHOR]