基于CTF系数法的混凝土空心砌块的动态传热计算

本文采用CTF系数法对混凝土空心砌块进行了动态传热计算。首先通过建立空心砌块的频域有限元模型来计算其理论频域热特性,并采用参数辨识的方法获取其传热s多项式函数。然后根据辨识得到的传热s多项式函数进一步求取空心砌块的CTF系数,最后直接计算出空心砌块的动态传热量。同时建立了空心砌块的CFD模型(作为参考模型),并对空心砌块进行了动态传热模拟计算。通过对比发现,CTF系数法计算的空心砌块的动态传热量与CFD模型的模拟结果非常吻合。本文采用的CTF系数法可以准确地计算空心砌块墙体的动态传热量,并且在计算时间和效率上优于CFD等数值方法。     

节能型复合混凝土小型空心砌块的热绝缘系数分析

对外保温空心墙体的静态热绝缘系数计算同时考虑导热、对流和辐射对热绝缘系数的影响,并用非稳态传热理论和计算机模拟分析的方法,利用传递函数法求解节能型复合混凝土小型空心砌块墙体的传热过程,计算某建筑物的围护结构(传统实心砖墙体和节能型复合混凝土小型空心砌块墙体)的全年逐时能耗和总能耗,并根据计算结果进行节能分析,得出:在空调条件下,建筑物采用节能型复合混凝土小型空心砌块墙体比采用传统实心砖墙体,夏季节能57%,冬季节能59%。     

混凝土砌块平均热绝缘系数的数值分析

在回顾并比较分析几种混凝土砌块平均热绝缘系数试验计算方法的基础上,利用数值计算的方法对混凝土空心砌块及复合型混凝土砌块热工性能进行分析与比较。研究分析了不同孔洞排列、填充材料、混凝土材料及应用对混凝土砌块平均热绝缘系数的影响。     

混凝土砌块平均热绝缘系数的数值分析

在回顾并比较分析几种混凝土砌块平均热绝缘系数的方法的基础上,利用数值计算的方法对混凝土空心砌块及复合型混凝土砌块进行了热工性能的分析与比较。研究分析了不同孔洞排列、填充材料、混凝土材料及应用方式对混凝土砌块平均热绝缘系数的影响。     

混凝土空心砌块墙体热绝缘系数理论分析

在混凝土空心砌块住宅中，目前广泛使用的190mm厚单排孔混凝土空心砌块墙体，不能满足《江苏省民用建筑热环境与节能设计标准》（DB／32／478－2001）中对住宅建筑外墙保温隔热和建筑节能的要求。通过对小型混凝土空心砌块墙体热绝缘系数的理论分析计算，为新型住宅墙体材料课题的进一步研究提供依据。     

混凝土空心砌块的孔型对其隔热性能的影响

本文采用有限元法在计算机上对不同规格、孔型的混凝土空心砌块的热阻值进行了大量计算，指出孔洞的排数对砌块热阻值的影响最大，并提出“多排孔、薄孔壁”可作为隔热空心砌块热工设计的准则。     

混凝土空心砌块平衡热阻计算的研究

本文采用有限元法，计算出在稳定传热条件下空心砌块内部的温度场分布及其平均热阻值，并与国内外现行的几个空心砌块平均热阻计算公式的计算结果进行了比较。对我国＜＜民用建筑热工设计规程＞＞中的计算公式提出了改进意见。     

陶粒砌块热工性能计算及孔型优化研究

根据新疆寒冷地区的特点,设计了一系列390 mm×300 mm×190 mm规格的陶粒混凝土空心砌块。从陶粒混凝土基材导热系数、孔洞排列数、孔洞交错排列等方面对砌块的热工性能进行了理论分析和平均热阻的计算。研究发现,陶粒砌块孔洞的排数是影响砌块平均热阻最主要的因素,基材的导热系数对砌块热阻影响次之,孔洞交错排列对改善空心砌块的热阻效果不明显,并提出了基于热工因素的建议优化孔型。     

混凝土空心砌块多模式非稳态周期传热特性

在建立混凝土空心砌块非稳态导热-自然对流-辐射多模式耦合传热模型基础上,研究了基于稳态热优化的混凝土空心砌块在徐州地区采暖期的非稳态周期传热特性;分析了空心砌块温度场、热流率随时间的变化规律。定义了非稳态周期传热条件下混凝土空心砌块保温性能评价参数—失热量,并与常用的保温性能评价参数—等效导热系数对比。结果显示,非稳态周期传热时空心砌块优化的效果并没有等效导热系数表征的优越;因此,在空心砌块的设计中应该重视非稳态传热的重要性。     

正交试验在混凝土小型空心砌块热阻值优化中的应用

通过FLUENT软件模拟计算混凝土小型空心砌块的热阻值,并采用正交试验方法分析孔宽、孔的交错程度和孔排数对混凝土空心砌块热阻的影响,以优化混凝土空心砌块孔形排列设计。结果表明:孔排数对砌块热阻影响最大,孔宽次之,而孔的交错程度对砌块热阻影响很小。     

Verification for transient heat conduction calculation of multilayer building constructions

Validation and verification of building simulation programs and load calculation programs is of continuing interest. Dynamic thermal behavior data, including conduction transfer function (CTF) coefficients, thermal response factors and periodic response factors, are used to calculate transient heat conduction through building constructions. Computational inaccuracy sometimes occurs in calculating CTF coefficients and response factors. In this paper, a method for verification of the CTF coefficients and response factors over the whole frequency range is introduced. This method is based on the equivalence of dynamic models for a linear system and the frequency characteristics of building transient heat transfer models. Bode diagrams and error criteria are proposed to verify the CTF coefficients and response factors. Some examples are given to demonstrate the methodology.     

Modelling of wall heat transfer using modified conduction transfer function, finite volume and complex Fourier analysis methods

The original conduction transfer function (CTF) method (which was derived from the EnergyPlus source codes), and the present modified CTF method (which uses a higher order discretisation scheme for the surface heat flux as well as finer grids at the layer boundaries for multi-layer constructions) were used to calculate wall surface heat fluxes based on monitored wall surface temperatures as the inputs. At the same time, the finite volume method and the matrix method (based on the complex Fourier analysis) were also used for the numerical predictions. The matrix transfer method was updated to treat the non-linear long wave length thermal radiation and proved to be consistent with the results from the finite volume method for all wall types ranging from single-layer wall, two-layer wall with air gap, cavity brick wall and brick veneer wall. Numerical predictions using the matrix transfer method, the conduction transfer function method and the finite volume method were compared with the long period measurements for single- or multi-layer materials with and without air gaps. At the same time, CTF coefficients for modified CTF methods were tabulated and analysed for all computational cases in this study.     

节能空心砌块选型的正交综合分析

空心砌块以其热工性能好、节省材料等优点广泛应用于建筑外墙中。空心砌块内部空气间层的孔型、排布方式等是砌块热工性能的重要影响因素。编制计算墙体砌块稳态和非稳态热工性能的MATLAB程序,对混凝土空心砌块进行正交设计分析,得到节能空心砌块选型的方向和途径。     

Identification of empirical transfer function coefficients for a hollow tile based on detailed models of coupled heat transfers

Numerical simulation of transient heat transfer through a hollow tile, two air cells deep, is carried out using the SIMPLE algorithm. The coupling between the heat transfers by conduction, convection and radiation is taken into account. The heat fluxes computed for realistic time-varying excitations are used to derive empirical transfer function coefficients using an identification technique. Dynamic responses of the hollow tile predicted using both the transfer function coefficients and the simulation program are compared for thermal excitations that differ from those used to derive the coefficients. The results show a very good agreement between the two procedures’ predictions.     

Transfer function coefficients for time varying coupled heat transfers in vertically heated hollow concrete bricks

This paper describes a two step numerical procedure to determinate empirical transfer function coefficients (TFCs) for vertically heated hollow concrete bricks. For such systems TFCs cannot be generated using the analytical techniques available in the literature such as the z-transfer function method or the space state representation method because of the nonlinear local character of the heat transfer by natural convection and radiation in the air cells of the hollow concrete bricks. The first step of the procedure consists in predicting coupled heat transfer by conduction, convection, and radiation in realistic time varying conditions using a detailed numerical simulation. In the second step, the results of the simulation (the time-varying heat fluxes at the hollow brick surfaces) are used to obtain empirical transfer function coefficients using an identification technique. Transfer function coefficients are generated for three different types of hollow concrete bricks mostly used in practice. It is shown that the empirical transfer function coefficients permit fast and accurate prediction of heat transfer for thermal excitations that differ markedly from those used to generate these coefficients without solving the complex system of equations governing the coupled heat transfer mechanisms.     

Coupled heat transfer modes for calculation of cooling load through hollow concrete building walls

A CFD model was developed to study thermal performance of hollow cement wall constructions of buildings under hot summer conditions. The approach employed couples conjugate, laminar natural convective flow of a viscous fluid in hollow building blocks with long-wave radiation between the cavity sides. Realistic boundary conditions were employed at the outdoor and indoor surfaces of the wall. A state-of-art building energy simulation program, ESP-r, was used to determine the outdoor thermal environment that included solar radiation, equivalent temperature of the surroundings and convective heat transfer coefficient. The CFD problem is put into dimensionless formulation and solved numerically by means of the control-volume approach. The study yielded comprehensive, detailed quantitative estimates of temperature, stream function and heat flux throughout the wall domain. A detailed parametric study showed that using a wider cavity within a building block does not necessarily reduce heat flux through the block. Radiation heat transfer between cavity sides may account for a significant fraction of heat flux through the block and neglecting its effect can lead to errors that could be as large as 46%. The geometry of the hollow blocks was demonstrated to affect the heat flux by as much as 30%.     

内插保温层混凝土空心砌块的热工性能与经济性分析

根据国家对建筑能耗节能50%和节材的要求,目前在夏热冬冷地区对建筑围护结构普遍采用空心砌块以满足对热阻的要求。本文分别对某内插保温层混凝土空心砌块以及将保温层取出的砌块的热阻进行了试验研究,分析了两者热工性能的差异,并对砌块内插保温层的有效性和经济性进行了分析,得出砌块内插保温层的投资可在4~5年内收回;并找出该空心砌块存在的不足,分别针对砌块外部结构和内部构造提出了改进方法,使砌体能够满足夏热冬冷地区对建筑围护结构节能的要求。     

A simple time domain calculation method for transient heat transfer models

This paper presents a simple time domain calculation method to derive thermal response factors and conduction transfer conduction (CTF) coefficients of finite differential models for estimating transient heat transfer through building structures. It is developed on the basis of converting the matrix exponential function, which is a part of the solution of the state equation established from the finite differential equations of building finite differential models, to matrix polynomial. The thermal response factors and CTF coefficients can be easily derived from the matrix polynomial with simple arithmetic and integral in time domain. This method avoids the time-consuming root-finding process of conventional methods and the computation of all the internal temperature of the finite differential model, while utilizing the advantage of the thermal response factors/CTF coefficients which relate the desired outputs at a moment to the previous inputs through a set of coefficients. Various case studies were conducted to validate the performance of this time domain calculation method in calculating the thermal response factors and CTF coefficients of various order finite differential models.     

适用于岛礁地区的珊瑚集料砌块热工性能分析

近年来,我国正大力发展海洋岛礁地区的工程建设,但原材料运输成本高故提出一种就地取材的新型珊瑚集料空心砌块。用热线法和DSC法分别测得珊瑚集料的导热系数与比热容,并计算了砌块的热阻、传热系数及热惰性等热工参数,与普通墙体材料进行对比分析。结果表明,珊瑚集料砌体的传热系数比普通墙体材料小,保温性能好;热惰性比普通墙体材料大,热稳定性好。在相同的墙体构造中,珊瑚集料砌体墙的热工性能衰减度和延迟时间均大于普通材料砌体墙,抵抗温度变化的能力比较强。根据06J908—2《公共建筑节能构造(夏热冬冷和夏热冬暖地区)》图集,推荐了4种珊瑚集料砌块墙体用于海岛建筑,可节省运输成本,减少墙体的盐雾侵蚀,提高建筑耐久性和节能效果。     

内插保温层混凝土空心砌块热工性能数值模拟分析

根据国家对建筑能耗节能50％和节材的要求,目前在夏热冬冷地区对建筑围护结构普遍采用空心砌块以满足对热阻的要求。应用模拟软件FLUENT对内插保温层混凝土空心砌块的热工性能进行数值模拟,并分别从热传导、热对流和热辐射三个方面对模拟结果进行了详细的分析,找出存在的不足,从而为改善砌块的热工性能提供了较为有效的途径。