建筑维护结构表面换热过程辨识数学模型

采用了动态系统的随机型输入,输出离散差分方程,分别建立了以建筑围护结构表面与空气间的温差作为输入信号,建筑围护结构表面热流作为系统输出信号的单输入,单输出建筑维护结构表面换热过程系统辨识离散数学模型;和以辐射强度,墙体表面温度和空气温度作为输入信号,墙体表面热流作为系统输出信号的多输入,单输出建筑维护结构表面换热过程系统辨识数学模型,得出了建筑墙体表面换热过程相应的Z传递函数模型描述。为研究建筑围护结构表面换热过程找到了一种新的方法。     

混凝土对流换热系数的风洞实验研究

提出混凝土表面对流换热系数的实验方案,试件的形式为圆管,从内部加热,安装在TJ-1风洞内,圆管的轴线与风向一致,风速调节范围为1m/s至25m/s,利用专门开发的实验控制系统全自动监控加热过程并自动记录数据。3个试件的实验结果有很好的一致性。实验结果表明,混凝土表面对流换热系数与风速、混凝土表面热辐射系数与温差之间均有很好的线性相关性。由实验结果回归分析得到混凝土表面受迫对流换热系数、混凝土表面热辐射系数、混凝土表面总热交换系数的计算公式,为混凝土结构温度效应分析中热工参数取值提供了依据。     

建筑外表面热流及换热系数现场测试

建筑表面换热系数是建筑热工与节能及能耗模拟的重要参数。为考察实际建筑表面的热流与换热系数动态变化,提高建筑能耗模拟的准确性,为设计标准提供基础参数数据,采用直接热平衡法,对西安某办公建筑外墙进行现场测试,得到外墙的对流、辐射及总换热热流,并在此基础上获得了表面的对流、辐射和总换热系数。结果表明:测试期间外墙表面辐射换热系数与对流换热系数分别在159～2918 W/(m2·K)和014～756 W/(m2·K)之间变化;外墙辐射热流在白天占总热流比例约为85%,夜间约为50%;对低风速的自然风,建议采用最大频率的对流换热系数数值作为设计计算取值。     

建筑墙体表面传热系数辨识研究

对实验房间南向墙体内表面中心区域的换热过程进行实验，发现当风速在0－5．5m/s之间时，表面传热系数在8－18W（m^2.K）之间波动，而风向对墙体表面传热系数影响不大；用辅助变量法分析墙体表面传热过程，并结合实验推导出墙体表面传热系数。模型的预测结果与实测结果吻合良好。     

确定墙体内表面换热系数的实验方法

首次提出了用辅助变量法分析建筑墙体内表面换热过程及推导墙体内表面换热系数的实验方法。实验和预测检验表明：该方法能够真实反映墙体内表面换热过程,为确定墙体内表面换热系数找到一种实用有效的方法。     

高层建筑外表面对流换热系数的数值模拟研究

通过西安市1幢既有高层住宅建立几何模型,以西安地区的自然气候条件为基础,运用CFD软件模拟外墙外表面的对流换热系数情况。研究结果表明风速对高层建筑对流换热系数影响很大,并成正比例关系;建筑高度对对流换热系数也有一定影响,主要表现在迎风面上成正比,背风面上无明显影响;风向投射角也会影响高层建筑表面的对流换热系数,在迎风面上随着夹角的变大对流换热系数也变大,对背风面无太大影响。     

混凝土表面对流换流系数测试研究

根据传热学原理，确定了对流换热系数测试方案，测量了混凝土表面自然对流换热系数和受迫对流换热系数。结果表明，混凝土表面对流换热系数与风速基本呈线性关系。根据该关系所提出的建议计算式，希望能为今后的工程应用和科研提供参考。     

玻璃长波透射率对普通双层中空玻璃热特性的影响

依据稳态热流平衡原理,采用理论分析和数值迭代的方法建立了考虑玻璃长波辐射透射率和室内外空间环境耦合条件下普通双层中空玻璃的稳态传热模型,并对普通双层中空玻璃在冬季典型室内外气温和空间环境几何边界条件下的总热流密度、总传热系数、有效长波辐射透射系数和内、外表面辐射换热系数进行了计算分析.结果表明:每层普通透明玻璃的长波辐射透射率达到01时,冬季典型室外气温范围（-40~0℃）内双层中空玻璃的有效长波辐射透射系数达到0167~0177,内表面辐射换热系数相比不计玻璃长波辐射透射率时的增大25%左右,外表面辐射换热系数相比不计玻璃长波辐射透射率时的增大10倍以上,玻璃的长波辐射透射作用对双层中空玻璃节能性能的不利影响明显,玻璃的长波辐射透射率在设计与计算时不可忽略.此外,冬季随着室内外气温温差的减小,双层中空玻璃的总热流密度逐渐减小,而总传热系数则逐渐增大,内、外表面辐射换热系数也逐渐增大.     

混凝土表面对流换热系数测试方法探讨

根据传热学原理，通过对混凝土表面对流换热系数进行测试，得到了混凝土表面换热系数与风速之间的关系，希望能为今后的工程应用和科研提供参考。     

神经网络法求解墙体传热系数关键输入变量的分析

在应用神经网络法求解墙体传热系数过程中,合理确定训练样本的输入变量是准确得到墙体传热系数的关键。分析了加热功率、内外侧环境温差、内外表面温差、内外表面热流密度、总厚度等对边界可测量量的影响,进而得出它们是确定墙体传热系数的关键输入变量。并对用它们作为输入变量的样本进行了训练和测试,得到了较满意的结果。     

超高层建筑外微气候参数垂直变化的实验研究

通过对某超高层玻璃幕墙建筑外表面的微气候参数的监测,发现高度是影响各参数垂直变化的主因。随着高度的增加,温度和湿度的变化均呈多"S"型变化,且为互补,顶层的温度较高而湿度最低;11∶00时建筑外表面垂直温差最大为6.7℃,而16∶00时垂直温差最小为0℃,测量时间段内平均垂直温差为2.7℃。随着高度的增加,建筑外表面的贴附气流速度逐渐增加,直至顶层有所回落,在建筑高度85%左右的平均风速最大,约为地面风速的7倍。温湿度和风速之间存在相互影响,较大的风速可以强化热湿交换,利于湿热地区夏季的通风降温和除湿。     

New external convective heat transfer coefficient correlations for isolated low-rise buildings

Building energy analyses are very sensitive to external convective heat transfer coefficients so that some researchers have conducted sensitivity calculations and proved that depending on the choice of those coefficients, energy demands estimation values can vary from 20% to 40%. In this context, computational fluid dynamics calculations have been performed to predict convective heat transfer coefficients at the external surfaces of a simple shape low-rise building. Effects of wind velocity and orientation have been analyzed considering four surface-to-air temperature differences. Results show that the convective heat transfer coefficient value strongly depends on the wind velocity, that the wind direction has a notable effect for vertical walls and for roofs and that the surface-to-air temperature difference has a negligible effect for wind velocity higher than 2 m/s. External convective heat transfer coefficient correlations are provided as a function of the wind free stream velocity and wind-to-surface angle.     

Performance of phase change material boards under natural convection

The high thermal storage capacity of phase change material (PCM) can reduce energy consumption in buildings through energy storage and release when combined with renewable energy sources, night cooling, etc. PCM boards can be used to absorb heat gains during daytime and release heat at night. In this paper, the thermal performance of an environmental chamber fitted with phase change material boards has been investigated. During a full-cycle experiment, i.e. charging–releasing cycle, the PCM boards on a wall can reduce the interior wall surface temperature during the charging process, whereas the PCM wall surface temperature is higher than that of the other walls during the heat releasing process. It is found that the heat flux density of the PCM wall in the melting zone is almost twice as large as that of ordinary wall. Also, the heat-insulation performance of a PCM wall is better than that of an ordinary wall during the charging process, while during the heat discharging process, the PCM wall releases more heat energy. The convective heat transfer coefficient of PCM wall surface calculated using equations for a normal wall material produces an underestimation of this coefficient. The high convective heat transfer coefficient for a PCM wall is due to the increased energy exchange between the wall and indoor air.     

High-resolution CFD simulations for forced convective heat transfer coefficients at the facade of a low-rise building

High-resolution 3D steady RANS CFD simulations of forced convective heat transfer at the facades of a low-rise cubic (10 × 10 × 10 m³) building are performed to determine convective heat transfer coefficients (CHTC). The focus is on the windward facade. CFD validation is performed based on wind tunnel measurements of velocity and heat transfer for reduced-scale cubic models. The CFD simulations employ a high-resolution grid with, for the 10 m cubic building, cell centres at a minimum distance of 160 μm from the building surface to resolve the entire boundary layer, including the viscous sublayer and the buffer layer, which dominate the convective surface resistance. The results show that: (1) the wind flow around the building results in highly varying CHTC values across the windward facade; (2) standard and non-equilibrium wall functions are not suitable for CHTC calculation, necessitating either low-Reynolds number modelling or specially-adapted wall functions; (3) at every facade position, the CHTC is a power-law function of the mean wind speed; (4) the CHTC distribution at the windward facade is relatively insensitive to wind direction variations in the 0–67.5° angle range; (5) the CHTC shows a stronger spatial correlation with the turbulent kinetic energy than with the mean wind speed across the facade; and (6) the CHTC distribution across the windward facade is quite similar to the distribution of wind-driven rain (WDR), with both parameters reaching high levels near the top edge of the facade. This suggests that also the convective moisture transfer coefficient will be higher at this location and that the facade parts that receive most WDR might also experience a higher drying rate.     

Newspaper sandwiched aerated lightweight concrete wall panels—Thermal inertia, transient thermal behavior and surface temperature prediction

Experimental investigation on aerated lightweight concrete (ALC) wall panels in terms of thermal inertia, transient thermal behavior and surface temperature prediction using finite difference method (FDM) are the main focus of this study. ALC wall panels of different density and different aerial intensity of newspaper sandwiched were produced and installed on a prototype house. The ALC wall panels were facing east direction and subjected to Malaysia natural environment condition. The inner and outer surface temperatures of the wall panels were recorded at 3 min interval, 24 h a day for a period of one year. Time lag and decrement factor were computed from the surface temperatures recorded. The results showed that thermal diffusivity has a positive relationship to the thermal inertia of ALC wall panels. FDM was used to predict the surfaces temperature and the predicted temperature was close to the observed temperature. The average differences between the observed and the predicted outer wall surface temperature lied between 1.4 and 2.4% whereas for the inner wall surface, the range was 1.3-2.2%. Greater deviations were detected on the predicted outer surface temperature could be due to some unaccounted factors such as wind direction and relative humidity in the present FDM.     

膜式全热换热器换热效率影响因素实验研究

为了研究膜式全热换热器换热效率影响因素,本文采用一种有机超滤膜设计制作了两种新型膜式全热换热器,通过实验分析了迎面风速、温湿度以及通道长度对换热器换热效率及阻力的影响。结果表明,随着迎面风速的减小、温湿度的增大及通风通道长度的提高,换热器换热效率有着不同程度的增加,但通风阻力随着通道长度及风速的增加而增大。这一系列的研究结果为全热换热器的设计和应用提供了依据。     

混凝土砌块墙体检测中的几个问题

墙体主体传热系数通常使用热流计进行测量.本文分析了热流计的使用条件,提出对于砌块墙体等表面温度分布不均匀的墙体,不适宜使用热流计测量其主体传热系数的观点.而后以混凝土砌块墙体为例,分别模拟了不同室外温度时,不保温、外保温和内保温3种情况下,墙体内外表面温度分布的情况.并针对保温墙体改变其保温层厚度.得出墙体内外表面温度及温差变化的趋势,进而得到应将热流计粘贴在保温层一侧对保温墙体进行检测的结论.模拟结果还显示,当室外温度大于0℃时,对于保温层厚度大于70 mm的内保温墙体,也可将热流计贴在不保温的一侧进行检测.     

高层建筑室外风速简化计算方法研究

由于地表摩擦的结果,使接近地表的风速随着离地面高度的减小而降低,而大部分建筑物都在这个范围内。因此,室外风速对高层建筑热负荷的计算有重要意义。但是室外风速随高度变化呈对数曲线状,因此,不适合直接应用于高层建筑板壁传热量计算。通过根据不同层高进行分段直线拟合来代替曲线和计算出风速均值,从而达到简化的目的。