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.     

水冷式表冷器传热研究(6):机器露点表达式的建立

建立了水冷式表冷器冷盘管表面平均热状态在干工况和湿工况下的数学表达式，通过理论和实验分析了各影响因素及影响程度。指出结构特性一定的表冷器，干工况下冷盘管表面平均热状态温度和进风干球温度、冷水初湿成线性关系；湿工况下在空调常用范围内，冷盘管表面平均热状态焓值和进风焓值，冷水初温成线性关系，且两种工况下冷盘管表面平均热状态温度（或焓值）都随迎面风速增大而增大，随水流速增大而减小。     

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.     

基于湿球温度的逆流闭式冷却塔换热模型分析

根据热力学和传热学理论分析,建立了逆流闭式冷却塔热传递过程的微分方程组,并利用湿球温度与湿空气饱和温度在空气-水系统中数值上相等以及湿空气饱和线线性两种合理的假设推导得到了基于空气湿球温度的数学模型。对某逆流闭式冷却塔基于湿球温度的换热模型应用Matlab作四阶Runge-kutta数值求解,得到了冷却循环水、喷淋水、空气干湿球温度的变化规律,基于此模型可分析湿球温度对逆流闭式冷却塔冷却效率的影响,同时为今后此类冷却塔的开发提供理论支撑。     

掘进工作面降温参数拟合分析

为了掌握矿井掘进工作面降温参数变化规律,更好的指导现场实施与应用,以存在高温热害现象的长距离掘进巷道(掘进巷道长度1 000 m)为研究对象,现场实际测定矿井降温系统运行后部分测点风流温度,拟合分析得到了部分参数之间较准确的定量关系。拟合结果表明:赵楼煤矿掘进工作面迎头温度与风筒出口风流温度(干、湿球温度)近似呈线性关系;与空冷器后处理风流温度(干球温度,相对湿度近似为100%)在一定范围内近似呈二次抛物线关系。此外,掘进工作面附近干湿球温度差值较大,最大可达5~7 ℃。风流在回头过程中热湿交换严重,很容易形成放大的回头增热、增湿现象。     

Numerical study of a M-cycle cross-flow heat exchanger for indirect evaporative cooling

In this paper, numerical analyses of the thermal performance of an indirect evaporative air cooler incorporating a M-cycle cross-flow heat exchanger has been carried out. The numerical model was established from solving the coupled governing equations for heat and mass transfer between the product and working air, using the finite-element method. The model was developed using the EES (Engineering Equation Solver) environment and validated by published experimental data. Correlation between the cooling (wet-bulb) effectiveness, system COP and a number of air flow/exchanger parameters was developed. It is found that lower channel air velocity, lower inlet air relative humidity, and higher working-to-product air ratio yielded higher cooling effectiveness. The recommended average air velocities in dry and wet channels should not be greater than 1.77 m/s and 0.7 m/s, respectively. The optimum flow ratio of working-to-product air for this cooler is 50%. The channel geometric sizes, i.e. channel length and height, also impose significant impact to system performance. Longer channel length and smaller channel height contribute to increase of the system cooling effectiveness but lead to reduced system COP. The recommend channel height is 4 mm and the dimensionless channel length, i.e., ratio of the channel length to height, should be in the range 100 to 300. Numerical study results indicated that this new type of M-cycle heat and mass exchanger can achieve 16.7% higher cooling effectiveness compared with the conventional cross-flow heat and mass exchanger for the indirect evaporative cooler. The model of this kind is new and not yet reported in literatures. The results of the study help with design and performance analyses of such a new type of indirect evaporative air cooler, and in further, help increasing market rating of the technology within building air conditioning sector, which is currently dominated by the conventional compression refrigeration technology.     

水冷式表冷器传热研究（3）：半干半湿工况热力计算

将已较成熟的水冷式表冷器干工况和湿工况热力计算理论与干、湿工况的分界是点“表冷器空气初状态的露点温度”结合起来,建立了半干半湿工况热力计算公式。其特点在于把湿工况段转换为等价干工况处理。     

西北干旱地区的空调系统节能设计

针对西北地区独特的气候特点,分别提出了蒸发冷却+置换通风和蒸发冷却+干式风机盘管2种空调系统形式可在喀什地区实际工程中应用。通过对比发现,第1种系统形式比传统电制冷空调系统节能53%,第2种系统形式比传统电制冷系统的制冷机房内设备节能71%,2种系统节能效果显著。通过对送风状态点露点分析,蒸发冷空调系统无凝结水产生,可避免室内环境污染。蒸发冷却空调系统的独特优势决定了其在西北地区的广泛应用前景。     

夏季空调室外计算参数的修正研究

本文对5个典型城市建筑在"干湿球温度分别统计,干球温度为基础耦合同期湿球温度,湿球温度为基础耦合同期干球温度,干湿球温度之和与湿球温度分别统计"四种参数选取方法条件下的空调设计负荷及典型气象年夏季逐时冷负荷分别进行计算,以最大逐时冷负荷为指标,获得该地区适用的空调室外设计参数,进而对干、湿球温度分别统计所得的参数做出修正。结果表明,计算湿球温度的变化对空调设计负荷的影响较大。"干球为基准耦合湿球温度"的参数选取方法适用于干空气能资源较丰富的地区,"湿球为基准耦合干球温度"的参数选取方法适用于干空气能资源较贫乏的地区,给出了五个区域的室外计算参数修正系数。     

Application of the control methods for radiant floor cooling system in residential buildings

In applying radiant floor cooling, its control system must prevent the floor surface condensation in hot and humid weather conditions. With no additional dehumidification system, only the radiant floor cooling system prevents floor condensation. In this case, the effects of the control of the cooling system on the indoor conditions can be changed because of the thermal inertia of the systems. Also different types of control system can be composed according to the control methods, which can affect the construction cost in the design stage. Therefore, the control methods for the radiant cooling system with respect to floor surface condensation must be studied. Furthermore, because Korean people's lifestyle involves sitting on the floor, it is necessary to evaluate if a floor cooling system will influence the thermal comfort of the occupants. This study intends to clarify the control methods of the radiant floor cooling system and to analyze the control performance and applicability of each control method with regard to the floor surface condensation and comfort by computer simulations and experiments on the control methods of the radiant floor cooling system. The results of computer simulations and experiments show that water temperature control is better than water flow control with respect to temperature fluctuations in controlling room air temperature. To prevent floor surface condensation, the supply water temperature could be manipulated according to the dew point temperature in the most humid room, and in individual rooms, the water flow rate (on/off control) can be controlled. Also, the results of radiant cooling experiments show that the floor surface temperature remained above 21 °C, the temperature difference among surfaces remained below 6 °C, and the vertical air temperature difference remained below 1.9 °C, conforming well to comfort standards.     

管式间接蒸发冷风机性能测试及分析

本文搭建了1个管式间接蒸发冷风机实验台,对其进行了性能测试与分析,研究了其冷却效果、压降变化规律及水气比和一二次空气风量比对冷却效率的影响.通过实验可知,当冷风机的入口干球温度和干湿球温差较大时,降温效果明显;间歇供水比持续供水能创造出更高的蒸发冷却效率;随着一次风量的增加,冷风机的压降呈上升趋势;随着水气比和一二次空...     

On-site experimental testing of a novel dew point evaporative cooler

Technologies which utilise the advantages of evaporative cooling to reduce the temperature of air without the addition of moisture have existed for some time. These systems use a heat exchange media between the evaporation of water process and cooling of air. Research has been conducted on a number of systems utilising these technologies in various configurations and it has been demonstrated that temperatures of the incoming air can approach its dew point temperature. This is considerably lower than the wet bulb temperature which is the limit achieved with conventional direct evaporative cooling systems. Prototypes have been built to demonstrate the principles and temperatures achievable, but the technology has never been developed due to its high cost and complexity. These disadvantages have been addressed in a newly developed indirect evaporative cooler. The paper presents results obtained from testing a prototype cooler installed in both a commercial and residential application in a wide range of ambient conditions. The performance characteristic of the indirect evaporative cooler in regards to its outlet temperatures and electrical energy efficiency is presented.     

夏季新风"逐时"冷负荷计算方法的探讨

认为计算夏季空调冷负荷时,将新风焓值按常量考虑,既与新的空调冷负荷计算方法不匹配,又增大了空调计算冷负荷,提出了以日为周期的夏季新风（ 包括渗透风）“逐时”冷负荷计算方法,给出了全国几个主要城市的夏季空调室外空气逐时湿球温度和逐时焓值     

基于湿能理论的空气能量转换方法和实践

运用湿能理论探讨了利用自然空气,在无需外界能量输入的情况下实现制冷与制热,包括直接蒸发冷却、间接蒸发冷却、多级间接蒸发冷却、液体除湿蒸发冷却,以及利用自然空气的能量实现液体再生等.该方法突破了传统的蒸发冷却露点温度的限制,同时将自然空气的利用由制冷拓展到制热.     

蒸发冷却在我国不同区域地下工程中的适用性分析

以送风状态点的干球温度、湿球温度及含湿量为基准,建立了蒸发冷却适用区域的6区模型,并以室内状态点的上限值作为送风状态点,分别以夏季空调室外设计参数、地下工程夏季空调设计参数、夏季空调干球温度及不满足200 h含湿量作为室外状态设计参数,计算并分析了各种形式的蒸发冷却系统在我国不同区域地下工程中的适用性,为蒸发冷却在地下工程中的应用提供基本设计依据。     

风机盘管干工况运行判断及水系统设计

介绍了判断风机盘管空调系统中风机盘管运行工况的方法———等效干球温度法,讨论了露点的计算,探讨了冷水系统特别是混水站的设计方案。     

应用于兰州的直接蒸发冷却空调性能测试分析

本文测试了兰州市内一台金属填料直接蒸发冷却器,获得了干湿球温度、相对湿度、冷却效率、阻力等技术参数。分析了进口处空气干球温度和相对湿度对蒸发冷却效率的影响,发现被测试的机组蒸发冷却效率较低,蒸发冷却段阻力较大,因此,需要改善设计。由于兰州属于干燥地区,因此通过优化设计,蒸发冷却效率有提升的空间。     

蒸发冷却空调技术的研究状况

重点介绍了两级蒸发冷却及露点蒸发冷却空调技术的研究状况,此外还介绍了水蒸发冷却技术的两个较新的应用实例研究.     

地板供冷研究的新进展

对国内地板辐射供冷的研究和应用状况进行了简要总结,对地板辐射供冷的供冷量、防结露措施、新风与卫生条件、热舒适性等方面进行了介绍,研究结果表明,在一定条件下,地板供冷的使用效果良好。     

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.