Chilled ceiling displacement ventilation design charts correlations to employ in optimized system operation for feasible load ranges

This paper expands Ghaddar et al. [N. Ghaddar, K. Ghali, R. Saadeh, A. Keblawi, Design charts for combined chilled ceiling displacement ventilation system (1438-RP), ASHRAE Transactions, 143 (2) (2008) 574-587] design charts of combined chilled ceiling (CC) displacement ventilation (DV) system to operating sensible load ranges from 40 W/m² to 100 W/m². It develops a global correlation of system load and operational parameters, with comfort measured by vertical temperature gradient and indoor air quality measured by the stratification height. The correlations are used for a known transient load profile in generating optimal settings of the CC/DV system operational parameters and associated energy consumption.An example is illustrated to show how the correlation could be used to size the system and to provide optimized control of the CC/DV system operation at low computational cost. Results of the current model are compared to the published case study of an optimized operation based on transient simulations of the space thermal model to achieve minimum operation cost [M. Mossolly, N. Ghaddar, K. Ghali, L. Jensen, Optimized operation of combined chilled ceiling displacement ventilation system using genetic algorithm, ASHRAE Transactions, 143 (2) (2008) 541-554]. The design correlations resulted in good agreement with published data (within 3% error in energy consumption and average 6% error in predictions of comfort and stratification height) at 1/4 of the computational time. The presented methodology provides an alternative for using the correlation for supervisory online controllers for the CC/DV system based on physically derived correlations.     

太阳能液体除湿处理热湿地区冷却顶板新风湿负荷

以广州为例分析了热湿地区冷却顶板空调系统新风冷负荷的特点,显示夏季空调期新风湿负荷占新风总负荷的90%以上.提出了利用太阳能液体除湿处理冷却顶板空调系统新风湿负荷的方案,并将其与常规的冷却除湿方案进行了比较.结果显示,冷却顶板空调系统新风湿负荷的太阳能液体除湿方式比冷却除湿方式节能40%以上,静态投资回收年限为2.2年,认为冷却顶板空调系统新风湿负荷的太阳能液体除湿方式要优于冷却除湿方式.     

空压机进气端除湿及润滑油余热利用研究

为了降低空气压缩机吸气温、湿度以有效降低空气压缩机系统能耗,将膜分离技术、液体除湿技术和热泵技术相结合,并充分利用空压机余热,设计了应用于空压机进气端的中空纤维膜液体除湿装置。应用结果表明:采用进气端除湿方法将空压机系统的热负荷与湿负荷分开处理,改善了压缩机的进气条件,降低了压缩过程的功耗,同时为空压机创造了良好的运行环境,降低了空压机的日常运行、维护成本。     

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.     

Model-based optimal supervisory control of chilled ceiling displacement ventilation system

The aim of this paper is to develop an optimized online supervisory control predictive tool for the chilled ceiling displacement ventilation (CC/DV) system to minimize energy consumption while creating the best indoor air quality (IAQ) and thermal comfort. The online controller is designed to operate under an optimized control strategy with five control set points. A dynamic multi-variable objective cost function is formulated for the supervisory control of the CC/DV system performance indices and constraints, and is solved using genetic algorithm. The design of the optimized controller takes into consideration the response time of three-way valves, reheat, and supply fan to employ signaled changes in set points.The developed online controller response to load changes and its ability to change system set points to optimally meet unknown load and constrains are tested and evaluated under the simulated ‘real life’ environment for a case study. It is shown that the implemented online optimized controller is robust, and its development contributes to improved CC/DV system energy efficiency.     

Performance analysis on a hybrid air-conditioning system of a green building

This paper presents the performance analysis on a hybrid air-conditioning system according to the hybrid building energy system of the green building demonstration project in Shanghai, in which a 150 m² solar collector is used to power two 10 kW adsorption chillers, a vapor compression heat pump is used to cool air in the evaporating end while the condensing heating at about 80 °C is fully used to regenerate a liquid desiccant dehumidification system. In the hybrid system, the sensible cooling to the air is treated mainly by solar adsorption cooling and vapor compression cooling, whereas the latent heat is treated by the liquid desiccant dehumidification system with regeneration from the condensing heat of the heat pump. The results show that the performance of this system is 44.5% higher than conventional vapor compression system at a latent load of 30% and this improving can be achieved by 73.8% at a 42% latent load. The optimal ratio of adsorption refrigerating power to total cooling load for this kind of hybrid systems is also studied in this paper.     

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.     

Application of desiccant systems for improving the performance of an evaporative cooling-assisted 100% outdoor air system in hot and humid climates

The purpose of this study was to enhance the energy-saving potential of an indirect and direct evaporative cooling-assisted 100% outdoor air system (IDECOAS) by integrating it with either a solid or liquid desiccant system. The desiccant system can be installed either at the scavenger air side of the indirect evaporative cooler (IEC) to enhance its effectiveness or at the primary air side of the IEC to reduce the latent load of outdoor air. The operating energy consumption affected by the location and type of the desiccant unit integrated with IDECOAS was simulated under three different hot and humid climates using TRNSYS 17 integrated with commercial equation solver programme. And then, the most energy-conservative configuration was selected for each climate zone as the proposed system. The simulation results showed that configurations with the desiccant dehumidification unit located upstream of the IDECOAS consume 76–85% less cooling coil energy than those with the desiccant unit located downstream of the IDECOAS. It was also found that the liquid desiccant system saves 21–50% more primary energy than the solid one, when it is integrated with IDECOAS.     

燃气驱动的三级液体除湿空调系统及其特点分析

介绍了液体除湿空调系统的原理及其特点。基于分级除湿思想和能量梯级利用原则，提出了一种燃气驱动的三级液体除湿空调系统，系统由风机、除湿器、蒸发冷却器和再生器组成。除湿器采用三级液体除湿，通过对室内回风直接蒸发冷却进行全热回收，用回收的冷量冷却除湿过程，移去处理空气的潜热；蒸发冷却器由间接蒸发冷却器和直接蒸发冷却器两部分组成，前者间接冷却除湿后的空气，移去空气的显热，后者调节空气的温湿度；再牛器采用燃气驱动，实现沸腾蒸发和非沸腾蒸发结合的两效再生。该系统是一种节能环保的新型空凋系统，具有优化城市能源结构的功能。     

Achievable working range for solid all-desiccant air-conditioning systems under specific space comfort requirements

Solid desiccant air-conditioning systems present a promising solution, in terms of performance level and environmental protection, pointing out their potential to be coupled with thermal solar or waste heat energy source. Nevertheless, these systems are characterized by constraints to the load they can satisfy, through the trade-off between the dehumidification cooling capacity and the latent load of the conditioned space. On that level, one has to note that, for steady environmental conditions, the conditioned space does not present unique value of load, but range of load, corresponding to an array of acceptable temperature and (usually relative) humidity values. In this work a methodology is proposed for the definition of the system's achievable working range under specific set of space (comfort) requirements. Through this approach, the systems present greater potential for covering the space requirements, thus presenting more possibilities on a design basis, and more flexible control strategies, as well. The proposed methodology is presented and discussed through the case study of a solar desiccant air-conditioning system coupled to a typical residential building.     

Energy savings potential of a desiccant assisted hybrid air source heat pump system for residential building in hot summer and cold winter zone in China

In hot summer and cold winter zone in China, air conditioning system has four running modes yearly including cooling with dehumidification, cooling, dehumidification and heating in residential buildings. The conventional air source heat pump (ASHP) system is not designed to independently control temperature and humidity, and is not very suitable for the dehumidification mode in the view of building energy consumption. A novel ASHP system combining radiant cooling/heating for residential buildings was presented. The main feature of this hybrid ASHP system is that desiccant wheel and cooling coil accomplish dehumidification process together, and the regenerative heat needed by the desiccant wheel is supplied by the condenser dissipated heat. Based on simulation studies and performance analysis, this paper predicts the primary energy consumption of the hybrid ASHP system in comparison with the conventional ASHP system during the cooling and heating seasons. It was found that primary energy requirement can be reduced by more than 8% in cooling with dehumidification mode, by 50% in dehumidification mode, and by more than 14% in heating mode. The study results prove that the hybrid ASHP system can keep great energy saving and running cost saving yearly, especially in the dehumidification process.     

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.     

Experimental study on dehumidifier and regenerator of liquid desiccant cooling air conditioning system

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 4 g/(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.     

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.     

主动除湿转轮在民用建筑空调领域的发展

主动除湿工艺利用干燥剂吸附水分的特性,可实现温湿度精确调节,干燥剂利用低位能源再生,与常规方式相比,在达到同等舒适状态下能减少能耗。介绍了主动除湿原理,认为其技术合理,在民用建筑空调中很具推广潜质。     

冷却顶板对置换通风系统的影响:CFD研究

以计算流体力(CFD)的模型为基础,采用有限容积法对带有冷却顶板的置换通风系统和不带冷却顶板的普通置换通风系统的温度场、气流分布及人体的热舒适性进行了模拟分析,模拟结果表明,冷却顶板-置换通风系统可以减小室内温度梯度,提高人体热舒适性。     

溶液调湿技术在昆明南站的应用

分析了昆明南站的溶液调湿通风系统,通过通风满足室内温度要求,通过溶液调湿系统满足室内湿度要求,并对溶液调湿通风系统进行数值模拟和运行工况分析。     

GHP与除湿相结合的复合空调系统

介绍了一种燃气发动机热泵（GHP）与除湿转轮的复合空调系统，夏季将回收的发动机余热用于除湿转轮再生、承担湿负荷；冬季通过排热回收减小空调系统的采暖负荷。对比了复合空调系统、单独使用GHP、电动空调系统的能耗情况。     

溶液除湿空调在高温高湿地区的应用研究

设计了一种新型的溶液除湿装置。综合利用太阳能、天然水源、热回收和溶液除湿技术,对新风进行分阶段除湿,同时,利用太阳能和室内排风对溶液进行再生,克服了传统溶液除湿空调技术在高温高湿地区应用过程中的局限性。结果表明,与传统溶液除湿方案相比,该系统的溶液循环量减小,运行能耗降低,对太阳能的依赖程度降低,溶液的吸湿效率和再生效率提高。     

转轮除湿复合式空调系统

介绍了转轮除湿与常规冷却及蒸发冷却相结合的两类复合式空调系统。指出了在要求低湿或湿负荷较大的场合,采用前者既可避免制冷机的蒸发温度过低影响制冷效率,又可避免凝结水排放不当造成渗漏等问题,利于节能;采用后者,节能效果更显著,而且既无ＣＦＣ问题,又能缓解夏季电力供应紧张的压力。