顶板辐射供冷房间节能性的探讨

运用Fluent对一个顶板辐射供冷房间进行模拟.模拟发现随着辐射板温度的降低,辐射板换热量和外墙传热量大幅提高,而人体换热量却变化不大.可分析得出辐射制冷系统的节能性是有条件的.     

无保温楼板辐射供冷系统热过程的研究

楼板辐射供冷是一种舒适度很高的新型空调技术：楼板内若不设保温层，天棚和地板均成为冷辐射表面向房间供冷：系统的供冷能力和楼板上下表面温度是空调供冷系统运行和调节的关键参数，研究它们与影响因素之间的关系是十分重要的。本文建立了无保温楼板辐射供冷系统的物理模型和数学模型，并对控制方程进行数值模拟，给出了系统供冷能力和楼板上下表面温度和诸多影响因素之间的关系。研究结果显示：冷水温度越低，天棚和地板的表面温度越低，系统提高的冷量越大；天棚表面温度略大于地板表面温度；随着冷水温度的升高，天棚和地板之间的温度差异将减小，房间的舒适性好；地板辐射换热量远大于对流换热量，天棚辐射换热量略大于对流换热量；天棚提供给房间的冷量大于地板提供的冷量。且冷水温度越低，相差越大；管子埋深越大，天棚和地板表面温度越大，系统供冷量越小，但差别不显著；埋管间距越大，天棚和地板表面温度越大，系统供冷量越小；埋管管径越大，天棚和地板温度越小，系统供冷量越大，但差异不显著。研究结果可为实际工程的设计、运行参数的选择和系统的可行性分析提供依据和指导。     

天棚辐射供冷系统换热过程的研究

天棚辐射供冷是一种舒适度很高的新型空凋技术。系统的供冷能力和天棚表面温度是系统设计和运行的关键，研究它们与影响因素之间的关系是十分重要的：通过建立天棚辐射供冷系统的物理模型和数学模型，对控制方程进行数值模拟，给出了影响系统供冷能力的诸多因素之间的关系。研究结果显示：冷水温度越低，天棚表面温度越低，系统提供的冷量越大。天棚表面与室内环境之间的辐射换热量大于对流换热量，舒适度好。管子埋深越大，天棚表面温度越大，换热能力越小，但差别不显著：埋管间距越大，天棚表面温度越大，换热能力越小，所以埋管间距不宜取得过大。埋管管径的变化对天棚表面温度及换热量的影响不大。研究结果可为实际工程的设计、运行参数的选择和系统的可行性分析提供依据和指导。     

顶棚辐射结合下送风供冷系统运行特性实验研究

本文基于对室内温度、围护结构内表面温度、风口参数等实测数据,分析了顶棚辐射结合下送风供冷系统运行过程中系统换热量、人体热舒适性变化规律,以及操纵量、扰动量对被控量的影响。研究结果表明:系统净辐射换热量、对流换热量和总换热量在系统开启的前1.5 h内递增,之后趋于稳定,系统稳定时,辐射换热量占总换热量的43%,余下57%冷量由风系统承担,此时,PMV和PPD值均在ISO7730的推荐值范围内。室内空气温度和作用温度随着扰动量和操纵量的增加而增加;当室外空气温度相对较低或较高时,室内发热量或平均水温较低时,室内空气温度和作用温度的增加率较小;室内空气温度和作用温度随着送风温度呈近似线性增加。     

辐射吊顶供冷方式节能舒适性研究

利用TRNSYS软件建立办公建筑空调过程计算模型,并分别设置对流供冷与辐射吊顶供冷2种空调方式。用PID控制吊顶水流量来调节辐射板冷量,使室内参数满足设计值。为保证控制的精确性,模拟计算时采用较小的时间步长(0.01 h)。在不同工况下,对建筑辐射吊顶供冷及对流供冷方式的室内舒适性、负荷进行模拟计算。结果表明,相同室内空气温度下,辐射吊顶供冷方式室内舒适性优于对流供冷方式;相同舒适性情况下,辐射吊顶供冷方式房间负荷小于对流供冷房间负荷。因此,辐射吊顶供冷方式具有良好的舒适性和节能性。     

地板辐射采暖房间传热性能研究

建立了地板辐射采暖房间的传热模型。通过实验测量了房间稳态传热时的空气、地板、墙体和顶板的温度，计算了各表面之间的对流、辐射换热量。     

混凝土天棚辐射供冷的应用探讨

介绍了天棚混凝土辐射供冷的优势;分析了混凝土辐射供冷中天棚最大允许换热能力和室内空气参数的关系、天棚辐射换热量的比例;分析了新风除湿对混凝土天棚供冷的影响以及利用冷却塔进行天棚供冷的可行性。得出的结论对工程实际有很好的指导作用。     

毛细管网抹灰安装供冷能力分析

针对采用抹灰安装的毛细管网辐射末端系统,分析了供冷工况下管内流体与管壁之间、管壁与抹灰层之间、毛细管网与室内空气之间换热过程的特点及影响毛细管网供冷能力的因素,计算了每个换热过程的换热量和相关参数,给出了毛细管网供冷能力的相关曲线图,归纳了提高毛细管网供冷能力的措施。     

高大空间空气载能辐射末端热环境与传能研究

本文以内设空气载能辐射空调系统的某火车站候车厅为研究对象,利用FLUENT数值模拟的方法,分析研究了房间人体活动区域内空气工况参数和系统传能过程。模拟结果显示,该房间室内空气温湿度分布较均匀,未出现结露现象。且在传能过程中,系统总冷负荷约为119 KW,空气载能辐射空调系统承担92%的冷负荷;其中,辐射换热占房间总负荷64.2%,对流换热占29.1%,由此可得系统以辐射换热为主;相较于金属平板辐射空调系统,该系统新增的对流换热量包括载能空气与辐射孔板间的对流换热量以及循环流动的交换能量;经计算,在相同模拟条件下,该系统总换热量较金属平板辐射空调系统超出约10%以上。综上,该系统在理论上基本符合高大空间建筑夏季负荷大,强调舒适节能的要求。     

辐射顶板供冷性能测试方法及计算方法

辐射顶板供冷以其节能、良好的热舒适度、无吹风感、改善室内空气品质、降低峰值能耗、节省建筑空间等优点,已经被越来越多地选作空调末端。辐射顶板供冷市场需求不断增大同时对辐射顶板制冷量的测试提出了更高的要求。本文对两种顶板辐射供冷性能实验测试方法(DIN EN 14240标准和ANSI/ASHRAE 138标准)和两种辐射顶板制冷量的计算方法(ASHRAE手册和BS EN 1264标准)做了介绍,并对辐射板供冷量的两种实验测试方法和两种计算方法分别做了比较;在按EN 14240标准搭建的实验台中对金属辐射顶板进行了测试,将辐射板单位面积供冷量两种计算值与实验测试值进行了比较并分析了误差原因。     

辐射板供冷性能影响因素与计算方法

通过对现有计算方法的分析,提出了以室内等效辐射温度作为辐射换热计算参数的方法。通过实例计算定量地分析了室内热源环境对辐射板供冷能力的影响。提出将辐射板热阻作为衡量辐射板供冷性能优劣的参数。     

An experimental investigation of application of radiant cooling in hot humid climate

This paper reports an experimental and simulation study of application of radiant cooling using natural air for ventilation under hot and humid climate of Thailand. To avoid condensation of moisture on the cooling panel, the temperature of water supplied to the panel was limited to 24 °C. This led to the expectation that the low heat reception capacity of the panel would limit its use only to situations when loads were low. Experiments were conducted in an experimental room over the hot and dry period of March, the humid period of May, and the cool period of December. The results generally confirm the good potential for application of radiant cooling. However, the room was served by radiant panels with a total area of 7.5 m². Its capacity was grossly inadequate during the hot period, even for night time application only. A special configuration was devised to achieve thermal comfort for the area served by the panel. The well-known TRNSYS program was used to simulate the use of cooling panels and conventional air-conditioning in the experimental room. Simulation results match experimental results very well. Using comfort criterion adopted by ASHRAE and International Standards Organization, results from experiments and simulation show that thermal comfort could be obtained with application of radiant cooling.     

Practical cooling capacity estimation model for a suspended metal ceiling radiant cooling panel

The main thrust of this research was to develop a simplified cooling capacity estimation model for a suspended (free-hanging type) metal ceiling radiant cooling panel. By statistically analyzing panel performance data generated by a validated analytical panel model, the impact of various design parameters and their combinations on the panel cooling capacity was estimated. And then a linear regression equation was derived as a function of major design parameters and interactions which have significant effects on the panel capacity. In this analysis, eight single parameters and 13 two-factor interactions showed significant impact on the panel cooling capacity. Consequently, a simplified regression model for a free hanging panel was derived as a function of those selected parameters. The proposed model could estimate the panel cooling capacity not only for the natural convection but also for the mixed convection condition present in a mechanically ventilated space.     

A full-scale experimental set-up for assessing the energy performance of radiant wall and active chilled beam for cooling buildings

Full-scale experiments under both steady-state and dynamic conditions have been performed to compare the energy performance of a radiant wall and an active chilled beam. From these experiments, it has been observed that the radiant wall is a more secure and efficient way of removing heat from the test room than the active chilled beam. The energy saving, which can be estimated to around 10%, is due to increased ventilation losses. The asymmetry between air and radiant temperature, the air temperature gradient and the possible short-circuit between inlet and outlet play an equally important role in decreasing the cooling need of the radiant wall compared to the active chilled beam. It has also been observed that the type and repartition of heat load have an influence on the cooling demand. Regarding the comfort level, both terminals met the general requirements, except at high solar heat gains: overheating has been observed due to the absence of solar shading and the limited cooling capacity of the terminals. No local discomfort has been observed although some segments of the thermal manikin were slightly colder.     

Evaluating the low exergy of chilled water in a radiant cooling system

In this paper, in order to make guidelines for designing a low-energy radiant cooling system with an air-handling unit (AHU) for dehumidification, we investigated the impact of various air-conditioning parameters on the exergies of chilled water supplied to radiant panels and a cooling coil. The cooling load, thermal comfort index PMV, relative humidity, area of radiant panels, sensible heat factor (SHF), temperature and air-flow rate of supply air of the AHU, and presence/absence of total heat exchanger were considered. We used computational fluid dynamics (CFD) code in order to analyze the indoor air-flow and thermal environments, and added models for the calculation of thermal transfer to radiant panels and a cooling coil. Furthermore, a feedback control algorithm was introduced to calculate the surface radiant panel temperature, targeting the average PMV of the task area in an office room. As a result, the impact of various air-conditioning parameters on the exergies of chilled water were demonstrated quantitatively. As an example, by reducing the cooling load rate from 100% to 57% and 27%, the exergy of chilled water decreased by 47% and 67%, respectively.