Feasibility study of a novel dew point air conditioning system for China building application

The paper investigated the feasibility of a novel dew point evaporative cooling for air conditioning of buildings in China regions. The issues involved include analyses of China weather conditions, investigation of availability of water for dew point cooling, and assessment of cooling capacity of the system within various regions of China. It is concluded that the dew point system is suitable for most regions of China, particularly northern and west regions of China where the climate is hot and dry during the summer season. It is less suitable for Guangzhou and Shanghai where climates are hot and humid. However, an air pre-treatment process involving a silica-gel dehumidification will enable the technology to be used for these humid areas. Lower humidity results in a higher difference between the dry bulb and dew point of the air, which benefits the system in terms of enhancing its cooling performance. Tap water has adequate temperature to feed the system for cooling and its consumption rate is in the range 2.6–3 litres per kWh cooling output. The cooling output of the system ranges from 1.1 to 4.3 W per m³/h air flow rate in China, depending on the region where the system applies. For a unit with 2 kW of cooling output, the required air volume flow rate varies with its application location and is in the range 570–1800 m³/h. For a 50 m² building with 60 W/m² cooling load, if the system operates at working hours, i.e., 09:00 to 17:00 h, its daily water consumption would be in the range of 60–70 litres. Compared with mild or humid climates, the dry and hot climates need less air volume flow rate and less water.     

再循环蒸发冷却技术及其应用

基于直接蒸发冷却和间接蒸发冷却方法,提出了一种再循环蒸发冷却方法。设计了一套再循环蒸发冷却装置,并通过试验测试了它的冷却效果。对再循环蒸发冷却技术在空调行业的应用进行了具体分析,提出了相应的系统应用设计方法。最后指出这种技术为开发节能环保空调设备和空调系统提供了一个新的途径。     

Numerical study of a novel dew point evaporative cooling system

Dew point evaporative cooling system is an alternative to vapor compression air conditioning system for sensible cooling of ventilation air. This paper presents the theoretical performance of a novel dew point evaporative cooling system operating under various inlet air conditions (covering dry, moderate and humid climate) and influence of major operating parameters (namely, velocity, system dimension and the ratio of working air to intake air). A model of the dew point evaporative cooling system has been developed to simulate the heat and mass transfer processes. The outlet air conditions and system effectiveness predicted by the model using numerical method for known inlet parameters have been validated with experimental findings and with recent literature. The model was used to optimize the system parameters and to investigate the system effectiveness operating under various inlet air conditions.     

再循环蒸发冷却中再循环风量的实验研究

介绍了一种再循环蒸发冷却技术,其原理是利用一部分经间接冷却处理的空气作为二次空气直接蒸发制取冷水,用冷水反过来间接冷却室外空气。搭建了相应的实验台,针对夏季实际工况条件,实验研究了再循环风量比例对蒸发冷却效率的影响,给出了合适的再循环风量范围。     

Investigation of a hybrid system of nocturnal radiative cooling and direct evaporative cooling

In this paper, the results of a study on a hybrid system of nocturnal radiative cooling, cooling coil, and direct evaporative cooling in Tehran have been discussed. During a night, the nocturnal radiative cooling provides required chilled water for a cooling coil unit. The cold water is stored in a storage tank. During eight working hours of the next day, hot outdoor air is pre-cooled by means of the cooling coil unit and then it enters a direct evaporative cooling unit. In this period, temperature variation of the conditioned air is investigated. This hybrid system complements direct evaporative cooling as if it consumes low energy to provide cold water and is able to fulfill the comfort condition whereas direct evaporative alone is not able to provide summer comfort condition. The results obtained demonstrate that overall effectiveness of hybrid system is more than 100%. Thus, this environmentally clean and energy efficient system can be considered as an alternative to the mechanical vapor compression systems.     

国内外蒸发冷却空调技术研究进展(3)

介绍了多级蒸发冷却空调系统、除湿与蒸发冷却相结合的空调系统、半集中式蒸发冷却空调系统、建筑物被动蒸发冷却技术、蒸发冷却自动控制系统及蒸发冷却水的水质处理。     

Experimental study of practical applications of a passive evaporative cooling wall with high water soaking-up ability

Aimed at controlling the increase in urban surface temperature and creating comfortable urban environments in summer, the authors have developed a passive evaporative cooling wall (PECW) constructed of porous ceramics. These ceramics enable their vertical surfaces to be wet up to a level higher than 100 cm when their lower end is placed in water. Our previous study has demonstrated the cooling performance and applicability of a prototype PECW constructed of pipe-shaped ceramics (ceramic pipes). The present paper presents a PECW unit system which can be easily installed for practical applications. Experiments were conducted using experimental PECW units. Experimental results show that the ceramic pipe developed in this study possessed a higher water-holding and soaking-up ability than the previous one. Wet surfaces of the new ceramic pipe reached a height of over 130 cm at an outdoor location exposed to solar radiation on sunny summer days. Furthermore, the air passing through the PECW unit was cooled, and its temperature can be reduced by around 2 °C during summer daytime. These results indicate that the proposed PECW can be broadly applied to various urban locations.     

Experimental investigation of two-stage indirect/direct evaporative cooling system in various climatic conditions

Cooling performance of two-stage indirect/direct evaporative cooling system is experimentally investigated in the various simulated climatic conditions. For this purpose, a two-stage evaporative cooling experimental setup consisting of an indirect evaporative cooling stage (IEC) followed by a direct evaporative cooling stage (DEC) was designed, constructed and tested. Due to the wide variety of climatic conditions in Iran, two air simulators were provided to simulate outdoor design condition of different cities in primary and secondary air streams. Results show that under various outdoor conditions, the effectiveness of IEC stage varies over a range of 55–61% and the effectiveness of IEC/DEC unit varies over a range of 108–111%. Aspects of achieving comfort conditions and power saving have been investigated with related excess water consumption. Considering the evaporative comfort zone, this system can provide comfort condition in a vast region in Iran where direct evaporative alone is not able to provide summer comfort condition. More than 60% power saving could be obtained by this system in comparison with mechanical vapor compression systems with just 55% increase in water consumption with respect to direct evaporative cooling systems. This system can fill the gap between direct evaporative cooling systems and mechanical vapor compression systems as an energy efficient and environmentally clean alternate.     

A two-stage system of nocturnal radiative and indirect evaporative cooling for conditions in Tehran

In this paper, the results of an investigation on a two-stage cooling system have been studied. This system consists of a nocturnal radiative unit, a cooling coil, and an indirect evaporative cooler. During the night in summer, requisite chilled water for a cooling coil unit is provided by nocturnal radiative cooling and is stored in a storage tank. During the next day, the water in the tank provides chilled water for the cooling coil unit and hot outdoor air passes through two-stages: the cooling coil unit and an indirect evaporative cooler. Three sources provide secondary air for the indirect evaporative cooler. The sources are outdoor air, the air leaving from the cooling coil, and the air leaving from the indirect stage (regenerative). The investigation has been conducted in weather conditions in the city Tehran. The results obtained demonstrate that the first stage of the system increases the effectiveness of the indirect evaporative cooler. Also, the regenerative model provides the best comfort conditions. Therefore, this environmentally friendly and energy-efficient system can be considered as an alternative to the mechanical vapor compression systems.     

燃气轮机进气蒸发冷却系统的设计及效果分析

论述了燃气轮机发电机组进气蒸发冷却系统的工作原理、主要设计参数,采用典型气象年逐时气象参数对其全年运行效果进行了分析。采用进气蒸发冷却系统后,发电量增加,发电效率提高,热耗率减小。     

某车间蒸发冷却通风降温系统的设计及运行测试

介绍了蒸发冷却降温技术在某工厂空冷配电室的应用,对其系统运行情况进行了测试分析,结果表明在干燥地区采用直接蒸发冷却通风降温方式消除工业余热可以满足生产需求.     

基于再循环蒸发冷却塔和地源热泵热/冷源的辐射空调系统初探

将再循环技术与冷却塔、地源热泵技术和辐射供暖/冷技术互相结合,充分利用自然热/冷源,提出了新型的节能空调系统模式,并根据技术特点提出了该系统模式的发展趋势.     

蒸发冷却在南方地区发电厂配电装置室的应用

通过分析蒸发冷却适用的气象条件,认为在南方地区类似发电厂配电装置室的热车间可以采用蒸发冷却装置进行降温。以广州某发电厂配电装置室为例,分析了采用蒸发冷却式空调进行降温通风的可行性。系统运行效果分析表明其节能作用显著。     

Design and performance of solar powered absorption cooling systems in office buildings

The paper contributes to the system design of solar thermal absorption chillers. A full simulation model was developed for absorption cooling systems, combined with a stratified storage tank, steady-state or dynamic collector model and hourly resolved building loads. The model was validated with experimental data from various solar cooling plants.As the absorption chillers can be operated at reduced generator temperatures under partial load conditions, the control strategy has a strong influence on the solar thermal system design and performance. It could be shown that buildings with the same maximum cooling load, but very different load time series, require collector areas varying by more than a factor 2 to achieve the same solar fraction. Depending on control strategy, recooling temperature levels, location and cooling load time series, between 1.7 and 3.6 m² vacuum tube collectors per kW cooling load are required to cover 80% of the cooling load.The cost analysis shows that Southern European locations with higher cooling energy demand lead to significantly lower costs. For long operation hours, cooling costs are around 200 € MWh⁻¹ and about 280 € MWh⁻¹ for buildings with lower internal gains and shorter cooling periods. For a Southern German climate, the costs are more than double.     

蒸发式冷气机性能参数的试验研究

在改造后的风管式焓差法试验台上对样机进行了热工性能试验。试验分两个阶段:将喷淋水温度设定为进口空气湿球温度,试验研究不同空气流速和水汽比对阻力和效率的影响,得出最佳空气流速和水汽比;在此基础上测试喷淋水温度对水蒸发冷却器效率的影响。试验数据的整理与分析结果表明,最佳迎面空气流速为1.0m/s,最佳水汽比为0.1,蒸发冷却效率和显热制冷量随着喷淋水温度的升高而降低。根据冷气机制冷量实测值不低于明示值95%的规定,经计算得出,喷淋水温度的波动范围为20.13～25.86℃。     

开粒度与保水性沥青路面铺装材料表面蒸发冷却效果的比较

表面铺装是影响城市热岛现象的重要因素之一,而蒸发冷却是可以降低铺装表面温度的一种有效方法.研究可知现今采用的一般表面铺装材料不具有吸水性和保水性,而蒸发冷却效果仅仅在表面洒水后的短暂时间内产生作用.本文通过对蒸发冷却效果的定量分析,研制开发出了具有吸水性和保水性的表面铺装材料,具有长时间稳定的蒸发冷却效果,可在一定程度上缓解城市热岛现象.     

蒸发冷却与毛细管辐射供冷复合式空调

本文介绍了蒸发冷却与毛细管辐射供冷的概况,并根据西北地区的气候特点,提出了一种将两者相复合的半集中式空调系统方案,阐述了该方案中蒸发冷却与毛细管辐射供冷相复合的特点,同时指出该空调系统在我国西北地区具有十分广阔的应用前景.     

Effect of mass recovery evaporator temperature and condenser temperature on the performance of a solar adsorption-based desalination plant

Water scarcity increases alarmingly as the population increases. Over the years, a number of salt water desalination techniques have been proposed and reached limitations. The requirement of minimum energy is very well satisfied by an adsorption system, since it can operate with low-grade energy and waste heat exhaust from most industries. The first part of this work discusses the effect of condenser and evaporator temperatures on the performance of silica-gel adsorption cycle mathematically. The second part discusses the performance variations due to mass recovery in the two-bed adsorption system mathematically. It was found that the reduction in condenser temperature and increase in the evaporator temperature both increase the fresh water productivity and cooling capacity of a plant. A desalination plant with mass recovery assistance is superior in performance than the conventional plant. Portable water productivity of 8?m³/day/ton is achieved with the condenser temperature of 15°C and the evaporator temperature of 30°C.     

Raising evaporative cooling potentials using combined cooled ceiling and MPCM slurry storage

Evaporative cooling is able to generate the cooling medium at a temperature approaching to the ambient wet bulb temperature. In this paper, a low-energy air-conditioning strategy is proposed, which is a combination of cooled ceiling (CC), microencapsulated phase change material (MPCM) slurry storage and evaporative cooling technologies. The assessment of evaporative cooling availability and utilization is done for five representative climatic cities, including Hong Kong, Shanghai, Beijing, Lanzhou and Urumqi in China, and the energy saving potential of the proposed air-conditioning system is analyzed by using a well validated building simulation code. The results indicate that the new system offers energy saving potential up to 80% under northwestern Chinese climate and up to 10% under southeastern Chinese climate. The optimal design method of the slurry storage tank is also proposed based on the slurry cooling storage behaviors and cooling demand variations of the ceiling panels.     

蒸发冷却与置换通风相结合空调系统的应用分析

介绍了蒸发冷却和置换通风的工作原理,提出了温湿度独立控制的蒸发冷却空调系统,分析了在全空气空调形式下蒸发冷却 置换通风空调系统在室内空气品质及节能上的优越性,指出了此空调系统在我国西北地区具有广泛的应用前景.