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.     

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%.     

Performance analysis on the internally cooled dehumidifier using liquid desiccant

Dehumidifier is one of the most important components in liquid desiccant air-conditioning systems. Previous study shows that the internally cooled dehumidifier may have better mass transfer performance than the adiabatic unit. The effect of flow pattern, especially the flow direction of air to desiccant on the internally cooled dehumidifier performance is numerically analyzed in detail. The result shows that counter-flow configuration of air to desiccant has better dehumidification performance, and parallel-flow configuration performs the poorest with the same conditions, due to more uniform mass transfer driving force expressed in the counter-flow configuration. The decrease of the desiccant concentration is the main factor that influences the internally cooled dehumidifier's performance, while the increase of the desiccant temperature is the main performance restricting factor in adiabatic dehumidifier. Internally cooled dehumidifier has better mass transfer performance compared with adiabatic dehumidifier plus external heat exchanger.     

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.     

新风和回风对液体除湿空调系统的影响

采用十字正交实验法对液体除湿新风处理机组在高温高湿工况下的除湿量进行了测定分析,结果表明：除湿量受新风含湿量、风量影响较大,受新风温度和回风温度、风量影响较小;并随着进口空气流量、含湿量、温度和回风量的增加而增大,随回风温度的升高而降低。     

溶液除湿空调系列文章溶液式空调及其应用

分析了目前空调系统面临的主要问题，提出了基于溶液除湿空气处理方式的解决方案。介绍了溶液除湿空气处理方式的原理和系统构成方式，从改善室内空气质量、改进空调末端装置方式、节省能源、改善城市能源结构等方面讨论了这一方式的优点和特点。分析表明，基于溶液除湿空气处理方式的湿度独立控制空调系统可有效消除空气的霉菌、粉尘，可以根据人员数量调节新风量，并通过独立的吸收或提供显热的末端装置调节温度，实现室内温湿度的分别控制。溶液除湿空气处理方式还可有效地对排风进行全热回收，并在过渡季利用干燥或低温的新风，从而降低空气处理能耗。由于冷水不承担除湿任务，因此只需要18—21℃冷水用于吸收除湿过程释放的热量和室内显热。这就有可能利用各种自然冷源或采用高GOP的冷水机组。溶液除湿方式还可实现高密度的能量蓄存，从而协调各种能源供应中的负荷匹配。     

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。     

溶液除湿空调新风机组冬季工况性能研究

提出了一种由溶液除湿新风机组和空气源热泵装置组合的新系统,利用MATLAB语言对该系统进行数值模拟计算和分析,结果表明:在西安地区冬季空调室外计算参数下,新风机组性能系数COP,TCOP和COPh分别为0.5,0.65和5.1。     

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。     

Exergy performance and thermodynamic properties of the ideal liquid desiccant dehumidification system

In this paper, an ideal liquid desiccant dehumidification system is presented as the idealization of practical liquid desiccant dehumidification systems, along with an exergy analysis that considers the effects of various parameters like dehumidification temperature, water vapor pressure and temperature of surrounding environment on the system performance. Exergy formulations are developed and validated for the ideal system. These results show that the ideal system is strongly influenced by these impact factors, with respect to operating condition and exergy efficiency, and should be used with caution when comparing with condensation-based dehumidification systems.     

Optimization of air-conditioning system operating strategies for hot and humid climates

This paper describes research into the optimal operation of building heating, ventilation, and air-conditioning (HVAC) systems focusing on both temperature and humidity control. While most previous work on HVAC optimization has been limited to evaluation of conventional temperature-based control systems, this study emphasizes the humidity control issue in meeting both sensible and latent building loads. The analysis is based on a combination of a realistic simulation of a direct expansion (DX) air-conditioning system and a direct-search numerical optimization technique. The simulation models have been validated through comparisons with field data. Optimization was performed on five different system control variables to minimize system power consumption while meeting building loads and maintaining comfort. Indoor temperature and humidity are also optimized within standard comfort constraints. Building loads were modeled using an extended bin method that allows consideration of the interactions between loads and indoor conditions. Results indicate that minimum energy use typically occurs at low airflow rates, with indoor humidity levels below the upper comfort limit. Results also show that coil air bypass and evaporator circuiting control are typically not necessary unless operation would otherwise result in overcooling. The optimization results also translate to relatively simple strategies for system control. Significant savings are demonstrated over conventional control strategies used in packaged DX equipment.     

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.     

利用盐溶液制备冷水的冷水机组

在间接蒸发冷却装置的基础上，设计了利用盐溶液制备冷水的冷水机组，使得间接蒸发冷却技术能够应用于非干燥地区，并运用了热回收技术达到节能目的。通过对不同室外工况下冷水机组性能的模拟，发现COP对室外空气含湿量最敏感。最后模拟分析了在北京地区使用时此冷水机组的整体性能。     

溶液除湿空调系统在工业厂房应用的能耗分析

通过对深圳某工业厂房分别选用常规冷凝除湿空调系统和溶液除湿空调系统进行系统设计和理论计算分析,比较了两类空调系统的能耗及COP。在夏季室外设计工况下,常规冷凝除湿空调系统的COP为2.94,溶液除湿空调系统的COP为5.42。室外空气含湿量越小,对提高溶液除湿系统的性能越有利。溶液除湿空调系统在节能方面具有较大的优势。     

Experimental investigation of a novel desiccant cooling system

Desiccant based air conditioning systems are a suitable way to improve indoor air quality due to its superior humidity control. In this study, a novel desiccant based air conditioning system is designed and tested experimentally to improve the indoor air quality and reduce energy consumption. In the system studied, a heat exchanger, which is not used in this type of systems, for pre-heating the regeneration air with exhaust air is used. This paper reports results of initial operation and operational procedures. The performance of the system and its components is discussed.     

TRNSYS simulation for solar-assisted liquid desiccant evaporative cooling

ABSTRACT

Recently, desiccant cooling systems are well thought of as a competent method for controlling the water content in the air. A solar flat-plate collector has been used as it decreases the dependency on non-renewable resources. Solar-aided liquid desiccant systems have been used to reduce the dependency of air-conditioning systems on non-renewable sources of energy. Manipal’s humid and searing climate provides certain benefits in setting up such a system. The suggested system has reliability and equipment life and also takes complete advantage of the available solar energy for the renewal of the liquid desiccant. TRNSYS simulation is used to predict the efficiency and feasibility of the system. The temperature and energy-load variations were successfully obtained. An effective simulation was developed whereby the solar air conditioning of a room was indicated.     

一种余热驱动溶液调湿新风机组冬季运行研究

测试分析了一种余热驱动溶液调湿新风机组的冬季运行情况,得出了这种机组在冬季工况下的运行性能。在测试数据的基础上,分析了机组的送风参数随热水温度、热水流量和溶液浓度的变化情况。基于这些变化关系,得出了冬季工况下机组送风参数控制的基本原理和方法。     

Proposal for a new hybrid control strategy of a solar desiccant evaporative cooling air handling unit

Correctly controlled solar desiccant evaporative cooling is an interesting option for achieving savings in building air-conditioning consumption. The operation of this system (open loop cooling cycle) is strongly influenced by indoor and outdoor air conditions. This influence is characterized using numerical simulations. First the air conditioned room and the cooling system are simulated using a validated model of the desiccant wheel. Then the influence of each parameter of the desiccant air handling unit is evaluated. The third step is to assess the system cooling power for each operating mode with fluctuating outdoor and indoor air conditions. This allows for making relevant choices for a new control strategy taking into account both indoor and outdoor air conditions. This control strategy is tested for a whole cooling season and compared to a reference compression system with promising results, allowing for energy savings of about 40% for French climate.     

液体除湿再生性能的理论与实验差异性分析

以实际液体除湿空调系统为对象,进行了数值模拟和实验对比研究,结果表明,实验值和模拟值有相同的变化趋势;在诸多的入口参数中,溶液的温度、浓度以及空气含湿量对再生溶液浓度变化影响较大;溶液出口温度的实验值偏小于理论值,浓度变化的实验值偏大于理论值.重点分析了理论数据和实验数据产生差异的原因.