空调房间气流组织的空气动力学研究

提出一种新的CFD热边界条件给定方式,可将室内热源和室外气象信息同时考虑在计算域内。并运用该种热边界条件给定方法针对一个包含外墙和外窗的办公室算例进行模拟,计算结果表明,外墙和外窗内壁面的温度和热流密度分布很不均匀,采用传统的热边界条件给定方式无法给定,但通过本文提出的方法却可容易地获得准确的外墙、外窗内壁面温度和热流密度分布及室内环境温度场等信息,便于研究与设计人员使用,具有一定的工程实用价值。     

贵州省居住建筑复合墙体动态蓄放热特性分析

根据典型气象年数据分析了适宜贵州3个地区的夜间通风时段,应用EnergyPlus软件模拟了外保温外墙的内外壁面温度,通过Matlab编程计算了墙体的节点温度,分析了室外气温周期性变化边界条件下墙体逐时热流密度和逐时蓄热量的变化规律。结果显示:毕节、贵阳、遵义地区的凉爽通风时段分别为17:00至次日10:00,20:00至次日09:00,22:00至次日08:00;在22:00至次日01:00期间,由于外保温层的隔热作用及墙体对温度波的延迟作用,外墙内侧水泥砂浆仍会向室内散热,增大房间的冷负荷。     

通过建筑外壁绿化改善城市热环境的研究

运用CFD的方法，对进行绿化后建筑外墙壁面的漫漫国度以及室外空间的风向、风速、空气温度、相对湿度、平均辐射温度（MRT）的空间分布进行数值模拟，从而对建筑物外壁绿化所产生的城市热环境改善效果进行定量的分析。     

辐射供冷末端不同边界条件下的数值计算对比

以一个由4个壁面构成一体化辐射末端的办公室模型房间为例,基于计算流体力学(CFD)技术对辐射空调末端边界条件分别采用定热流密度和定温两种处理办法计算出相应结果,对比分析研究表明:在室内空气为自然对流的情况下,采用定热流密度边界条件,计算收敛难度大而且室内温度高达30℃以上,难以满足热环境的舒适性;采用定温边界条件,室内的温度场分布较均匀且在22~24℃左右,房间温度处于舒适性合理区域。因此,室内空气处于纯自然对流条件时,对辐射空调系统一类问题的数值计算辐射末端适宜采用定温度边界条件。     

建筑热桥三维非稳态传热数值模拟分析

本文以上海地区冬季典型年室外温度为计算参数,建立外墙与屋面连接处建筑热桥三维非稳态导热偏微分方程。计算了不同保温形式下墙体内表面温度及热流分布,并分析了热桥对负荷及结露的影响。     

航站楼使用阶段钢结构温度取值研究

为了准确确定大跨度钢结构在使用阶段的温度作用和方便钢结构温度变化模拟分析,对厦门高崎机场T4航站楼屋盖钢结构夏季的温度进行了全面测试,提出太阳辐射与室外气象温度的日变化计算模型。根据气象条件、室内分层温度控制方法以及屋面构造做法,通过CFD模拟技术研究高大空间温度场沿高度方向的变化规律,并在天窗部位考虑了太阳辐射的影响。结果表明:金属屋面具有良好的保温隔热性能,室内与室外钢结构的最高温度均与最高气温非常接近,钢结构昼夜温差主要受室外气温变化的影响;受到太阳辐射的影响,天窗部位钢结构的温度明显高于最高气温;CFD模拟计算得到高大空间空气温度沿竖向分布的结果与实测值的变化趋势相一致,顶部热滞留区的温度明显高于等温空调区,计算温度与实测温度相对误差为5%~10%;通过实测与模拟分析,可以较为合理地确定在使用阶段大跨度钢结构的温度,该方法可供类似大型公共建筑设计时参考。     

重庆地区夜间通风条件下西外墙动态蓄热分析

针对重庆地区高温湿热的气候特征,提出采用贴附射流冷却墙体内壁面的方式进行夜间通风,并进行了实验测试和模拟分析。对比室外气象条件相近的无通风工况和采用贴附射流夜间通风工况的实测结果,分析了夜间通风对墙体壁面温度的影响。通过测试室外气象条件近似、通风速率相同、通风开启时刻不同的2个工况的数据,采用Fluent软件建立非稳态三维模型,计算了西外墙的热流密度和蓄热量。计算结果表明,该夜间通风方式可以有效降低墙体蓄热量。     

墙体材料对农村民居围护结构传热影响分析

以大庆市农村民居的外墙为和当地气候的特点为研究对象,计算得出该地区冬季的室外综合温度,并以此温度为输入条件循环作用于墙体,并根据实际情况建立多种材料的墙体模型,利用CFD软件计算在该温度下的不同种墙体材料对应的逐时热流密度,进而得出各种墙体材料的保温性能。     

套管封装相变材料准稳态传热模型研究

本文建立了套管封装相变材料的准稳态简化传热模型,对定温边界条件下相变套管凝固、熔化过程的传热特性进行了模拟分析。进一步将准稳态简化模型的模拟结果与套管封装相变材料CFD数值传热模型的计算结果进行对比分析。结果表明,在相变过程中,准稳态简化模型计算的套管内工质(不流动)的温度与通过内、外套管表面热流及其变化趋势与数值计算结果一致,温度平均误差小于0.5℃,热流平均误差小于10%,模型准确性较好。准稳态简化传热模型的计算时间不到数值模型计算时长的1%,计算效率高,易于嵌入建筑热湿软件包进行集成模拟分析。     

夏热冬冷地区动态传热保温设计室外典型气象参数确定方法

GB50176-2016《民用建筑热工设计规范》中围护结构外墙保温设计采用稳态方法,但夏热冬冷地区由于特有的建筑运行模式,使外墙传热方向发生逆转,故稳态方法难以满足冬季室内热环境水平提升的实际需求。提出一种基于动态传热的冬季外墙保温设计室外计算温度确定方法,探究室外干球温度和太阳辐射逐时波动的最不利组合,将保温设计的目标由“日”提升到“时”。基于典型城市2007-2017年逐时气象数据,以外墙内表面温度的累计不保证天数作为热工设计指标,将累计不保证天数恰好不为0(指各朝向外墙内表面温度低于室内基本热舒适条件下所能允许温差的天数)时作为典型日挑选的依据,并将典型日出现频率最高的日期作为室外计算温度选取的依据,获得冬季保温设计典型日,并获得了典型日计算时长的影响。可为夏热冬冷地区围护结构外墙保温设计室外计算参数的挑选提供理论支撑。     

几种建筑外墙隔热性能的比较分析

建立了几种建筑外墙结构的数学模型,结合南京夏季室外综合温度,采用FLUENT软件对几种墙体的热工性能进行对比,并从传热学的角度对墙体的内部传热机理进行分析。研究结果表明：添加保温材料或者空气问层均能够提高墙体的隔热性能;墙体采用外保温时,其保温层较高的热阻使热量集中墙体外表面,减小向室内侧的传热量,同时也提高了墙体的耐久性;通过对比几种具有不同隔热措施的建筑墙体,外保温墙体对温度波的衰减度最大,内壁面温度的波动幅度最小,抵御室外温度影响的能力强,热稳定性能好。     

Temperature and Vapor Pressure Gradients Across Wall Assemblies Using Microcomputer Graphics

An educational microcomputer graphics program for predicting the temperature and vapor pressure gradients across external wall assemblies is developed to assist designers in evaluating the performance and selection of materials. A large number of constructional types and combinations of materials are available to satisfy the various functional requirements such as structural, thermal, acoustic, etc., of an external wall. This paper presents the methodology used in organizing the material properties information in a data base within a general purpose drafting program for diagnosing the problem of condensation within the wall assembly. Specifying the thickness and the material properties used for structure, insulation, cladding, etc., one can obtain the variation in temperature across the different layers of the wall for a set of given indoor and outdoor design temperatures. The condensation problem in the wall assembly can be investigated by knowing the relative humidity of the indoor and outdoor environment. Many different wall types such as cavity walls, walls with interior and exterior insulation, metal and timber clad walls can be analyzed for a number of different combinations of materials and various thicknesses. AutoLISP in the AutoCAD environment is used for the material properties data base, calculations, and drafting. A program of this kind is an effective tool for the students of building science in the analysis of external walls for design and retrofitting, and understanding the principles involved.     

Evaluation of effects of windows installed with near-infrared rays retro-reflective film on thermal environment in outdoor spaces using CFD analysis coupled with radiant computation

Recently, windows with low-e double-glazing or heat-shading films often have been installed to the exterior surfaces of buildings to reduce the cooling load of the buildings. These windows specularly reflect solar radiation into pedestrian spaces. It has been pointed out that the increase in the incident solar radiation reflected at the windows degrades the thermal comfort levels of pedestrians. The installation of near-infrared rays retro-reflective film to window surfaces may both reduce the cooling load of the building and reduce the impacts on the thermal environment in outdoor spaces. Hence, it is expected that the installation of this film will counteract this problem and have positive effects. To assess the feasibility of installing retro-reflective materials to the exterior surfaces of the building walls and ground forming part of a city block, for improving the thermal environment in outdoor spaces, computational methods could serve as a powerful tool for analyzing the radiant environment in urban and building spaces. In this paper, a computational method is outlined for considering the directional reflections from the exterior surfaces of building walls and windows. The method is used to estimate the effects on the outdoor thermal comfort of pedestrians in the summer season.     

Effects of radiant temperature on thermal comfort

The aim of this paper is to investigate the local differences between body segments caused by high radiant temperature, and to analyze the interior surface temperatures for different wall and ceiling constructions with their effect on thermal comfort. For the segment-wise thermal interactions between human body and its surrounding, simulations have been conducted by appropriately modifying Gagge 2-node model to multi-segment case to demonstrate the local differences. Simulation results are found to be in good agreement with experimental and simulation results reported in the literature. To calculate the interior surface temperatures of the wall and ceiling, the sol–air temperature approach is used for convenience. It is shown in the paper that the body segments close the relatively hot surfaces are more affected than others and interior surface temperatures of un-insulated walls and ceilings exposed to a strong solar radiation reach high levels, all of which cause thermal discomfort for the occupants in buildings.     

The effect of south wall's outdoor absorption coefficient on time lag,decrement factor and temperature variations

In this study, the effect of outdoor absorption coefficient of an opaque wall on time lag, decrement factor and temperature variations is investigated by employing a dynamic thermal-network model. The model simulates heat transfer by conduction through the wall and considers convection boundary conditions under detailed forcing functions on the wall outer and inner surfaces. The transient analysis is based on the fundamental principles of thermal circuits and the well-known analogies between the thermal and electrical laws are employed. The effect of the solar absorptivity, is examined for representative wall formations including masonry, insulation and coatings on both surfaces. The insulation is placed as one or two layers on the outer, the inner or in the mid-center of the masonry. The investigation is carried out for a wall with south orientation during the cooling season in the Mediterranean region. The analyses presume a non-sinusoidal periodical excitation that simulates precisely the effect of the outdoor environmental conditions. Computer results show how these varied aspects affect thermal inertia parameters and outdoor/indoor temperature peaks.     

Hygrothermische Wirkungen von Raum‐ und Außenoberflächen

The hygrothermal effect of inside and outside building envelope surfaces. In the past the protection of building constructions under outdoor and indoor climate conditions was one of the most important subjects building physics. Nowadays the energy balance and the hygrothermal performance of building envelopes are current topics. This paper deals with the coupled heat and moisture transfer on the internal and external envelope surfaces. By means of numerical simulation and laboratory investigation the influence of the internal surface of exterior walls on the indoor air humidity is demonstrated. The influence of evaporation cooling on the energy transfer in winter time and during the warm season requires investigations on dewing and driving. It depends on the hygroscopic parameters of the outside wall coating. The effect of infrared reflecting coating is determined. It is shown in which way heat sources integrated in exterior walls could be a possibility to avoid microbiological growth on building envelopes.     

Numerical analysis of outdoor thermal environment around buildings

Simulation of thermal environment around buildings is of great importance for residential microclimate study. In this article, a numerical method is proposed to simulate the outdoor thermal environment around buildings. By the method, temperature distributions of the outdoor air, building surfaces and ground surfaces are achieved by combining computational fluid dynamics (CFD) calculation of air flow and energy balance equations calculation of surfaces. In every computing time step, the outdoor air distribution is calculated as quasi-steady condition. And the surface temperatures of buildings and ground are simplified as “shadow zone temperature” and “sunshine zone temperature” to reduce the calculating time and memory space. Response factor method is employed to deal with the transient heat transfer between outdoor air and surfaces of buildings and ground. The numerical method is validated by the measured data of outdoor thermal environment around one single building and the simulated temperature distributions are illustrated and analyzed at different time in a day.     

Experimental approach to the contribution of plant-covered walls to the thermal behaviour of building envelopes

The use of vegetation has an important impact on the thermal performance of buildings and on the modification of the urban climate as well, both in winter and summer. Plants absorb a significant amount of solar radiation for their growth and biological functions, functioning as a solar barrier that prevents solar radiation absorption extensively. Their utilization is essential and can considerably improve the microclimate of the built environment. Vegetation planted to cover the external surface of a building is common practice in urban areas. However, up to now, it has not been fully approved as an energy-saving method. Climbers can provide a cooling potential on the building surface, which is very important during the hot periods of the year, especially in warm climates. Hence, the peak temperatures that appear are essentially lower, in addition to the decrease of heat flow losses. In this study the thermal analysis concerns two equivalent building floors that incorporate non-covered and covered with plants wall sections (insulated wall surfaces), respectively. The investigation is carried out during the cooling period in the Greek region. A comparison between the bare and plant-covered surface sections of the walls is conducted via an experimental setup (stationary method). Results are focused on the developed temperature variations and dynamic thermal characteristics of wall surfaces for both cases under investigation. As it is shown, the contribution of plant-covered wall sections is important so that the thermal behaviour of the building envelope can be improved.     

Untersuchung des Wärmeschutzes von Außenecken über unbeheizten Kellern in Wohngebäuden – die Achillesferse von massiven Außenwänden mit äußerer Wärmedämmung?

Examination of the thermal insulation characteristics of external corners above unheated basements in dwellings – the Achilles' heel of heavy‐weight external walls with thermal insulation on the outside? External walls in dwellings consist often of a heavy‐weight wall and a thermal insulation fixed outside. With this construction the insulation of the external wall is separated by the plinth of the external wall from the thermal insulation incorporated in the slab above an unheated basement. This results in a thermal bridge along the edge of the basement slab. The most critical point of the construction with regard to thermal protection occurs at the exterior corner at ground floor level, where two linear thermal bridges overlay. For this reason the minimum inner surface temperature of the corner is used to estimate the heat protection of the construction. A number of calculations of the minimum temperature at the interior surface of this three dimensional thermal bridge is performed to evaluate the parameters of the adjacent construction details which affect the minimum temperature at the inner surface of the corner. To reach the minimum temperature at he inner surface of the corner of 12.6 °C demanded by the German standard DIN 4108‐2 as the minimum requirement of heat protection for thermal bridges, thermal resistances of the whole wall construction much higher than 1.2 m²K/W are necessary. For this construction type of exterior walls a thermal resistance of 1.2 m²K/W as demanded in table 3 of the German standard DIN 4108‐2 as a minimum heat insulation for exterior walls can be shown to be insufficient to assure a minimum temperature of 12.6 °C at the inner surface of the corner at ground floor level. Thus it is proposed to add additional notes concerning this construction type in this standard.     

夏热冬暖地区复合墙体内表面温度响应特性

根据建筑复合型外墙在室外气象参数周期性变化的边界条件,建立了复合墙体内表面温度在一维非稳态导热控制方程作用下的计算模型,结合夏热冬暖地区复合墙体的结构特点及该地区的夏季气象参数,分析了不同朝向复合墙体随室外气象参数变化的内表面温度响应特性及变化规律,为复合型墙体在隔热和室内舒适性方面的研究提供了理论指导.