Performance analysis of a liquid desiccant and membrane contactor hybrid air-conditioning system

The present study examines the performances of a hybrid air-conditioning system in which a vapour-compression inverse cycle is integrated with an air dehumidification system working with hygroscopic solution and hydrophobic membrane. This model may be a valid alternative to traditional summertime air-conditioning system, in which the air is cooled to below its dew-point temperature and subsequently reheated.The proposed hybrid system involves simultaneously cooling and dehumidifying the air conveyed to the conditioned ambient in an air-solution membrane contactor. An LiCl solution is cooled by means of a vapour-compression inverse cycle using the refrigerant KLEA 407C. The solution is regenerated in another membrane contactor by exploiting the heat rejected by the condenser.A SIMULINK calculation programme was designed in order to simulate the system under examination in steady-state conditions. The performances of the system were analysed on varying a few significant operating parameters, and were compared with those of a traditional direct-expansion air-conditioning plant in typical summertime conditions. The results of the simulations revealed significant energy savings, which, in particular operating conditions, may exceed 50%.     

溶液除湿过程热质交换规律分析

除湿器和再生器是溶液除湿系统的重要传热传质部件。建立了一个测试叉流除湿、再生模块性能的实验台,以溴化锂溶液为除湿剂,用除湿量、除湿效率和体积传质系数描述除湿效果,实验测试了溶液和被处理空气的进口参数对除湿器性能的影响。由实验数据得到的准则关联式,可供叉流除湿器设计参考使用。     

溶液除湿系统中除湿塔的设计

对溶液除湿系统中除湿塔填料层直径和高度的设计进行了理论分析,并通过具体参数说明了设计计算的方法和步骤,以积累溶液除湿系统中除湿塔的设计经验,完善除湿塔的设计。     

Analysis on the ideal energy efficiency of dehumidification process from buildings

As dehumidification is one of the most important tasks of environment control of the building, it is necessary to know the energy efficiency of dehumidification processes. The energy efficiency can give the energy cost of drawing moisture from indoor air to the outside environment. This paper presents analysis of the ideal cost of dehumidification process by a liquid desiccant cycle. Formulas to calculate ideal efficiency of dehumidification process are obtained, which is determined by indoor temperature, outdoor temperature, and the temperature of the intersection point of the iso-relative humidity line of indoor air and the iso-humidity ratio line of outdoor air. The ideal efficiency of the condensing dehumidification method is lower than the ideal dehumidification process, due to the fact that condensing dehumidification method must dehumidify the air at the temperature of dew point. Results from this paper can be used as theoretical foundation for the further analysis of various dehumidification methods and the development of new dehumidification processes.     

液体除湿研究与进展

介绍了液体除湿原理、除湿剂的选择、液体除湿器的工作原理和传质模型，以及液体除湿空调系统的优势及其发展。     

Performance comparison between two novel configurations of liquid desiccant air-conditioning system

This paper is concerned with performance investigation and comparison between two novel configurations (type A and type B) of liquid desiccant air-conditioning system driven by low grade thermal energies. Both of these configurations, compared with other liquid desiccant systems, may have some outstanding advantages: leading to improved indoor air qualities, possessing a compact structure and making the best use of space exhaust air to cool the process air. Computer simulation is performed to analyze the cycle performance of these two system configurations under the effect of five key variables. Simulation results show that type B configuration is superior when the supply air temperature and humidity ratio are required to be relatively low or the ambient air absolute humidity is relatively high. In contrast, system of type A configuration has higher performance under the lower ambient air absolute humidity conditions. For a typical hot and humid summer day of Zhuhai, a city of Guangdong Province in southern China, the supply air temperature of type B configuration is more stable.     

Performance analysis of liquid desiccant based air-conditioning system under variable fresh air ratios

In conventional air-conditioning system, fresh air volume is always restricted to save energy, which sacrifices indoor air quality (IAQ) to some extent. However, removing the latent load of air by liquid desiccant rather than by cooling is an alternative way of reducing energy consumption. Therefore, IAQ can be improved by increasing the volume of fresh air introduced into an air-conditioning system. In this paper, a liquid desiccant based air-conditioning system is studied, with the system performance under various fresh air ratios analyzed using simulation tests. In addition, the proposed system and a conventional system are compared. In the proposed system, with the increase in fresh air ratio, the heating load for solution regeneration rises, the dehumidification efficiency increases and the regeneration efficiency drops. The coefficient of performance (COP) of the liquid desiccant based system decreases sharply when the fresh air ratio exceeds 60%. The results also show that the proposed system can save power notably. The maximum power saving ratio is 58.9% when the fresh air ratio is 20%; however, the ratio drops when the fresh air ratio increases. These findings will be beneficial in the selection of fresh air ventilation strategies for liquid desiccant based air-conditioning systems.     

Control strategies for a liquid desiccant air-conditioning system

Liquid desiccants are energy efficient in air dehumidification. A significant amount of research has been conducted on liquid desiccant systems, but little attention has been paid to the control issues surrounding such system. In this study, a novel dedicated outdoor air-conditioning system that adopts liquid desiccant dehumidification is proposed. A simulator of the proposed system is built on the TRNSYS platform. Control methods for the supply air dehumidification and solution regeneration processes are presented, and their effectiveness is evaluated. Two control strategies are developed for the proposed liquid desiccant system based on the evaluation results. The control performances of these two strategies are compared under different operation conditions using simulation tests.     

转轮除湿能力的测试分析

介绍了除湿转轮的性能测试原理与方法,重点讨论了湿度测量方法对测量结果不确定性的影响,同时分析了流量仪表精度对性能测试的影响。介绍了测试中的若干细节问题并给出了一个测试实例。     

溶液除湿方式对室内空气品质影响的初步研究

在溶液除湿空调空气处理过程中，因溶液与空气直接接触，可能对室内空气品质产生负面影响，但同时也可以去除空气中的有害物质。以溴化锂溶液为例，进行了室内空气溴、锂离子的测定，溴化锂溶液对甲醛的吸收实验，除湿溶液对细菌和病毒生长的影响实验，并初步探讨了气液交换模块的除尘作用。     

夏热冬暖地区溶液除湿独立新风空调系统的运用实验研究

建立溶液除湿独立新风空调系统的实验装置,实现温湿度独立控制的空调系统,对实验装置所采用的集热泵、溶液全热回收和溶液除湿技术于一体的新风处理机的工作原理进行分析,由此建立了溶液除湿独立新风空调系统的实际工程模拟实验系统。对受控对象的空调房间进行溶液除湿新风空调系统的工作特性测试。通过对测试工况数据的分析,得知室外新风温度与所要求的除湿溶液的入口温度、密度存在一定的线形关系。通过测试广州地区某典型工况下除湿新风机组温度、含湿量的运行参数变化,表明夏季完全能满足设计工况下的室内设计参数温湿度的要求。同时此溶液除湿独立新风空调机组的节能效果明显,EER值在5．0-60之间。     

Performance of a solar-regenerated liquid desiccant ventilation pre-conditioning system

A solar-regenerated liquid desiccant ventilation pre-conditioning system has been proposed for use in hot and humid climates. The system aims to dehumidify the ventilation air which is the major source of latent load. A heat exchanger is used to cool the dehumidified air instead of typical evaporative cooling to maintain the dryness of the air. The use of solar energy at the regeneration process and cooling water from a cooling tower makes the system more passive. The simulation procedure for the proposed system has been presented. By inputting the climatic data and the physical parameters of all equipments, the operating parameters at each equipment and the performance parameters of the system can be evaluated. The simulation procedure is demonstrated by showing the daily profiles of the operating and performance parameters on a typical day as well as investigating the influence of the selected operating parameters on the system performance. The results suggest that the most influential parameters are solar radiation, ventilation rate, and desiccant solution concentration. The balance between the water removed at the dehumidifier and that evaporated at the regenerator needs to be considered to maintain uniform performance during continuous operation.     

液体除湿的经济性分析

介绍了液体除湿系统的原理，比较了液体除湿与冷冻除湿系统的初投资，认为液体除湿是一种经济节能的空调方式。     

一种新型液体除湿空调的应用

分析了常规液体除湿空调的不足,开发了一种新型液体除湿空调装置,介绍了其系统原理及流程。在上海高温高湿的气候条件下的实际应用表明该系统在节能和低品位能源利用方面有重要意义。     

Field performance measurements of a heat pump desiccant unit in dehumidification mode

The variable refrigerant volume (VRV) air conditioning system needs to be operated in conjunction with a ventilation system, because the VRV system cannot provide any fresh air. The common ventilation unit used with the VRV system is the heat recovery ventilation (HRV) unit. In this study, a new ventilation unit, a self-regenerating heat pump desiccant (HPD) unit, was introduced and the characteristics of the HPD unit was experimentally investigated over a wide range of operating conditions in a field performance test. In addition, the energy saving contribution of the HPD and HRV units to the VRV system was compared. It was found that the HPD unit maintained the target indoor humidity ratio of 10 g/kg throughout the cooling season resulting in a better indoor thermal comfort than the HRV unit. Besides, it was found that the outdoor unit of the VRV system consumed 26.3% less energy for the operation in conjunction with the HPD unit as compared to the operation in conjunction with the HRV unit.     

Feasibility and performance analysis of a desiccant solution regenerator using hot air

This paper investigated a desiccant solution regenerator using hot air to concentrate diluted desiccant solution, aiming to utilize the waste heat of hot air, such as the hot air from the condensers of vapor compression refrigeration systems. To verify the feasibility of the utilization of the hot air for the desiccant solution regeneration and disclose the performance of such kind of regenerators, performance analysis was conducted numerically by a validated mathematical model and parametric distribution of the air in a typical case was explored. The results showed that it was possible to use hot air for the desiccant solution regeneration when the requirement of the lowest inlet solution temperature was met and a typical case showed that the suggested hot air temperature was around 65 °C. Effects of main operation parameters on the regeneration thermal efficiency and regeneration rate were discussed and the result showed the regeneration thermal efficiency could achieve the maximum (η_{reg, max}) when the R was around 8 and lower flow rate of the desiccant could achieve higher η_{reg, max}. In addition, effects of dimensions of the regenerator on the regeneration performance were disclosed and some suggestions of design of the regenerators were introduced based on the study.     

A combined system of chilled ceiling,displacement ventilation and desiccant dehumidification

Different types of heating, ventilation, and air-conditioning (HVAC) systems consume different amounts of energy yet they deliver similar levels of acceptable indoor air quality (IAQ) and thermal comfort. It is desirable to provide buildings with an optimal HVAC system to create the best IAQ and thermal comfort with minimum energy consumption. In this paper, a combined system of chilled ceiling, displacement ventilation and desiccant dehumidification is designed and applied for space conditioning in a hot and humid climate. IAQ, thermal comfort, and energy saving potential of the combined system are estimated using a mathematical model of the system described in this paper. To confirm the feasibility of the combined system in a hot and humid climate, like China, and to evaluate the system performance, the mathematical model simulates an office building in Beijing and estimates IAQ, thermal comfort and energy consumption. We conclude that in comparison with a conventional all-air system the combined system saves 8.2% of total primary energy consumption in addition to achieving better IAQ and thermal comfort. Chilled ceiling, displacement ventilation and desiccant dehumidification respond consistently to cooling source demand and complement each other on indoor comfort and air quality. It is feasible to combine the three technologies for space conditioning of office building in a hot and humid climate.     

溶液调湿技术在既有建筑空调系统改造中的应用

针对既有建筑空调系统改造中存在的问题,提出采用溶液调湿空调系统的改造方案,以达到降低改造难度,保证改造后空调系统节能、舒适的目的.以某大型三甲医院综合服务楼为例,对其空调效果不佳的现象进行了测试分析,对溶液调湿空调改造方案和传统改造方案进行了分析比较,指出了溶液调湿空调在既有建筑改造中应用的可行性和优势.     

溶液调湿型空调系统在某博物馆建筑中的应用及节能分析

本文介绍溶液调湿空调技术在博物馆建筑中的应用。通过比较分析得出,溶液调湿空调技术用于博物馆建筑,在空气质量及能耗方面均具有优势。     

Exergetic modeling and experimental performance assessment of a novel desiccant cooling system

New approaches to space conditioning of buildings are required to resolve economic, environmental, and regulatory issues. One of the alternative systems that is brought to agenda is the desiccant cooling systems, which may provide important advantages in solving air conditioning problems. This study deals with the performance analysis and evaluation of a novel desiccant cooling system using exergy analysis method. The system was designed, constructed and tested in Cukurova University, Adana, Turkey and has been successfully operated since 2008. This system consists of a desiccant wheel, heat exchangers, fans, evaporative cooler, electric heater unit and refrigeration unit. The exergy transports between the components and the destructions in each of the components of the desiccant cooling system are determined for the average measured parameters obtained from the experimental results. Exergy efficiencies of the system components are determined in an attempt to assess their individual performances and the potential for improvements is also presented. The exergetic efficiency values for the whole system on the exergetic product/fuel basis are calculated to range from round 32% to 10% at the varying dead (reference) state temperatures of 0-30 °C.