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。     

长沙地区太阳能溶液除湿独立新风系统能耗分析

基于长沙市太阳能资源分布情况,评价了太阳能溶液除湿在该地区的可行性,得到该地区太阳能保证率为89%。计算并比较了太阳能溶液除湿DOAS同常规空调系统的能耗情况:该系统比传统DOAS节电19.1%,比带全热交换器的一次回风系统节电32%,比一次回风系统节电52%。     

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.     

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 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.     

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.     

New type of fresh air processor with liquid desiccant total heat recovery

A liquid desiccant total heat exchanger and small capacity refrigeration cycle combined fresh air processor is proposed here in this paper, in order to improve indoor air quality and decrease the energy consumption of the air-conditioning system. Operating principles of both the total heat recovery device and fresh air processor using liquid desiccant are presented in details. Experimental tests of the fresh air processor installed in a hospital show that energy efficiency ratio (EER) is around 6.3–7.3 in the summer experimental conditions and 4.7–5.0 in the winter experimental conditions. Hour-by-hour simulation, which is based on the climate data in Beijing, shows that the average EER is 5.3 and 4.3 in summer and winter period, respectively. Liquid desiccant has the potential to remove a number of pollutants, avoiding cross contamination. Furthermore, in summer fresh air is dehumidified by contacting liquid desiccant instead of 7 °C chilled water, which avoids wet surfaces in the air-conditioning system and much higher indoor air quality can be achieved.     

Performance of combined displacement ventilation and cooled ceiling liquid desiccant membrane system in Beirut climate

The performance of the chilled ceiling (CC) displacement ventilation (DV) systems is constrained by latent load removal capacity and cost of supply air dehumidification to prevent condensation on the ceiling. In this study, a liquid desiccant dehumidification membrane cycle (LDMC) is mathematically modelled to replace the CC and remove directly latent and sensible load from indoor space through the membrane. The desiccant system is coupled with the DV system. An optimized operational strategy is adopted while allowing ceiling temperature to drop to lower values than conventional CC/DV. The optimized LDMC-C/DV system was implemented in an office space in Beirut climate. It was found that decreasing the membrane liquid desiccant temperature resulted in a significant decrease in the total cooling energy of the system, while increasing the solar heating energy of the desiccant regeneration. At optimal set points, a decrease of 49% in energy consumption was observed compared to the conventional CC/DV system.     

Advancement of solar desiccant cooling system for building use in subtropical Hong Kong

The solar desiccant cooling system (SDCS) had a saving potential of the year-round primary energy consumption as compared to the conventional air-conditioning system for full fresh air application in the subtropical Hong Kong. In order to further enhance its energy efficiency, advancement of the basic SDCS was carried out through a strategy of hybrid design. Six hybrid system alternatives of SDCS were therefore proposed, three for full fresh air design while another three for return air design for the building zone. Year-round performance evaluation of each solar hybrid desiccant cooling system was conducted for typical office application under different climatic and loading conditions. All the six hybrid system alternatives were found technically feasible, with up to 35.2% saving of year-round primary energy consumption against the conventional air-conditioning systems. Among the hybrid alternatives, recommendations were made on the SDCS hybridized with vapour compression refrigeration for full fresh air design; and the SDCS hybridized with vapour absorption refrigeration for return air design, since they had the saving potentials of both primary energy and initial cost. These two hybrid system alternatives used evacuated tubes, a more economical type of solar collectors compared to the PV or PVT panels.     

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.     

Experimental investigation and theoretical analysis of solar heating and humidification system with desiccant rotor

In this paper, a solar heating system, which combines the technologies of evacuated tube solar air collector and rotary desiccant humidification together, has been configured, tested and modeled. The system mainly includes 15 m² solar air collectors and a desiccant air-conditioning unit. Two operation modes are designed, namely, direct solar heating mode and solar heating with desiccant humidification mode. Performance model of the system has been created in TRNSYS. The objective of this paper is to check the applicability of solar heating and evaluate the feasibility and potential of desiccant humidification for improving indoor thermal comfort. Experimental results show that the solar heating system can convert about 50% of the received solar radiation for space heating on a sunny day in winter and increases indoor temperature by about 10 °C. Compared with direct solar heating mode, solar heating with desiccant humidification can increase the fraction of the time within comfort region from about 10% to 20% for standalone solar heating and from about 30% to 60% for solar heating with auxiliary heater according to seasonal analysis. It is confirmed that solar heating with desiccant humidification is promising and worthwhile being applied to improving indoor thermal comfort in heating season.     

A comprehensive review of the solar dryer

ABSTRACT

Drying of agricultural products is an energy-demanding process. High costs, scarcities in fossil fuels and environmental threats attract the use of solar energy as an alternate source, especially in developing countries. Increasing environmental concerns led to the use of clean and green energy resources in the field of drying agricultural products. A solar dryer integrated with a thermal energy storage system is reasonably efficient for continuous and uniform drying of agricultural produce in the temperature range of 40–75°C which is the requisite for drying most of the products. Such dryers have become a natural choice to replace drying systems based on fossil fuels. Many studies have been performed till date by a number of researchers for the last few decades for drying agriculture and food products by a solar dryer. This review paper primarily presents an appraisal of the significant contributions made so far in the field of solar drying systems, with the latest updates in drying technology. Solar dryers which offer drying during off-sunshine hours have been specially mentioned. Some novel ideas like use of phase change materials and desiccant materials which enhance the performance and effectiveness of the dryer have also been attempted.     

Overall cooling efficiency of a solar desiccant plant powered by direct-flow vacuum-tube collectors: simulation and experimental results

Using solar thermal energy is an interesting option for heat-driven air conditioning, e.g. desiccant cooling. In this article, the autonomous operations of a solar desiccant cooling plant powered by direct-flow vacuum-tube collectors are investigated. A model of the solar installation and the desiccant air handling unit is presented and implemented in the SPARK simulation environment and then it is validated experimentally. The overall cooling efficiency of the system is evaluated using simulation for humid and moderately humid climates and the effect of increasing the regeneration temperature on the cooling capacity, the overall cooling efficiency is studied and finally the overall efficiency of the collectors is calculated for the studied cases.     

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.     

溶液除湿空调系统蓄能性能分析

介绍了溶液除湿蒸发冷却空调系统的蓄能原理,分析了蓄能密度的影响因素。与冰蓄冷、水蓄冷和气体水合物蓄冷等常规蓄冷方式的比较结果表明,溶液除湿空调系统在蓄能方面有明显的优势,其蓄能密度远大于常规蓄冷方式。该系统可以利用太阳能作为再生能源,白天蓄存浓溶液用于夜间制冷,节能效果显著。     

Simulation and experimental analysis of a fresh air-handling unit with liquid desiccant sensible and latent heat recovery

This article introduces a liquid desiccant fresh air processor. Its driving force is low-grade heat (heat obtained from 65 – 75°C hot water). Inside the processor, the air is dehumidified by the evaporative cooling energy of the indoor exhaust air. A four-stage structure is used to increase the efficiency of the combined sensible and latent heat recovery from the exhaust air. A mathematical model of the fresh air processor was set up using Simulink®. A liquid desiccant fresh air processor was constructed and tested for outside air conditions of 29.1 – 33.6°C, 13.7 – 16.7g/kg humidity ratio, and supply air conditions of 23.6 – 24.2°C, 7.4 – 8.6g/kg humidity ratio. The average measured COP _f was 1.6 (cold production divided by latent heat removed) for the range of conditions tested. The corresponding average COP _sys of the system including the regenerator was 1.3 (cold production divided by heat input). The detailed operating parameters of each part of the test unit were also measured. The test data was compared with the simulated performance. The characteristic coefficients (such as the volumetric mass transfer coefficient of the air-water evaporative cooling module, etc.) in the mathematical model were modified to calibrate the model output to the measured data. The calibrated simulation model was used to investigate the control strategy of the fresh air processor. The flow rate of the strong solution into the unit and the number of operation stages may be controlled separately or together to meet different indoor air requirements at different outdoor conditions. The hot water driven liquid desiccant air conditioning system was compared with a typical vapor compression system with an average COP of 4.5; the pump and fan power of the proposed system was 40% of the combined chiller, pump, and fan consumption. We achieved savings of over 30% of the power consumption compared with the traditional system under the designed outdoor air conditions.     

Experimental investigation of solar heating and humidification system based on desiccant bed heat exchanger

In this article, an experimental investigation has been made on a solar heating and humidification system. In this system, an evacuated tube solar water heater is connected to the desiccant bed heat exchanger (DBHE) by connecting pipes. The evacuated tube solar water heater supplies required heat to the DBHE for the regeneration of desiccant material. Various types of solid and composite desiccant materials have been used in the DBHE to investigate their effect on the system performance. It has been found that the system obtained its best performance with silica gel with average humidification rate of 0.63?kg/h. The maximum temperature difference of process air has been found as 16°C at the flow rate of 295.2?kg/h.     

香港地区溶液除湿与蒸发冷却复合系统的节能分析

本文提出了溶液除湿与蒸发冷却相结合的复合系统,并根据香港地区的气候条件和相关的空调设计参数,将该复合系统的能耗与一次回风空调系统的能耗进行对比.计算结果表明,在设计工况下复合系统的节能率为21.3%.当采用太阳能、地热等可再生能源或其它废热时,系统的节能率更大.结果表明该复合系统在香港具有较好的运用前景.     

Water generation from atmospheric air by using different composite desiccant materials

In this communication, new composite desiccant materials having 37% concentration of CaCl₂ have been compared for water production from atmospheric air. The vermiculite–saw wood, jute and burnt-clay have been used as host materials and CaCl₂ as a hygroscopic salt. All the desiccant materials have been tested with the solar glass desiccant box type system (SGDBS) with a collector area of 0.36?m². Design parameters for water production are: height of the glass from the desiccant bed to be 0.22?m, an inclination angle of 30°, the effective thickness of the glass as 3?mm and the number of glazing is single. It has been found that on the experimental day, the maximum amount of fresh water generated by the vermiculite–saw wood/CaCl₂ is 130?ml/kg/day.     

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。