Harmonic analysis of building thermal response applied to the optimal location of insulation within the walls

The analysis of heat transfer through building walls using Fourier transforms and the matric method are briefly reviewed. The formalism is applied to a simple one-room building. By making a few simplifying assumptions and by considering only one- or two-layer walls and roofs, the equations are kept sufficiently short to preserve the insight of the reader into the effects of a few construction features upon the building's thermal response. Such construction features, mainly the placement of insulation inside or outside the main wall mass, are extensively discussed, with an eye on their potential energy savings.The results are: (1) the placement of insulation outside the wall masonry reduces the amplitude of the internal temperature swing caused by weather conditions and by internal heat gains. If the inside temperature is left free to oscillate within a few degrees, the amplitude of the heating or cooling load is greatly reduced, allowing for substantial energy savings. However, the building is thermally sluggish and inefficient durign thermostat setbacks because of its large wall heat storage. (2) Inside placement of insulation increases the room temperature response to weather conditions and to internal heat gains. Thus, heating or cooling is needed for temperature peak-shaving. In return the building's response to a thermostat setting change is quick and the heat stored in the walls, lost during a setback, is relatively small.     

Passive cooling in hot,arid regions in developing countries by employing domed roofs and reducing the temperature of internal surfaces

Natural ventilation due to wind effects through buildings employing domed roofs was estimated by a flow network analysis. The dome was assumed to have an opening at its crown. When compared with flat roofs, the domed roofs always increase the air flow rate through the building. The increase in natural ventilation becomes significant in buildings with doors and windows all in one wall, or whenever the wind effects on the building envelope do not produce large pressure differences at the openings.The large air flow rate in the buildings with domed roofs may be utilized to store night air coolness in the structure more effectively and keep the mean radiant temperature of the interior surfaces low for thermal comfort in summer. The lowest internal surface temperatures can be obtained when the surfaces are kept moist and evaporatively cooled.Through a one-dimensional energy analysis the inside surface temperature of a horizontal slab was estimated for various slab materials and thicknesses and external and internal conditions. The inside surface temperature was compared with the case of employing a roof pond. It was found that lower temperatures can be obtained by evaporatively-cooled moist internal surfaces than that which can be obtained by unshaded roof ponds: For a building whose internal surfaces (walls and ceiling) are kept moist a large ventilation rate is needed to prevent water vapor build-up in the space. A domed roof with a hole in its crown can produce the necessary ventilation for such a building.     

Periodic heat transfer and load levelling of heat flux through a PCCM thermal storage wall/roof in an air-conditioned building

This communication presents an investigation of the thermal behaviour of a phase changing component material (PCCM) wall/roof which is exposed on one side to periodic solar radiation and atmospheric temperature and on the other side is in contact with room air at constant temperature. A periodic heat transfer analysis for PCCM slab has been developed (assuming effective thermal properties of PCCM) to assess the load levelling of the periodic heat flux and thermal storage characteristics of a PCCM wall/roof. It is found that a PCCM wall of thickness which is even less than that of an ordinary masonry concrete wall is more desirable for providing efficient thermal energy storage and maximum load levelling and hence is suitable for providing excellent thermal comfort in an air-conditioned building. Both the load levelling and storage duration increase with the decrease of melting temperature and increase of the latent heat of fusion of the PCCM.     

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。     

冷桥对墙体平均传热系数的影响

本文基于控制容积法编制了平面温度场分析程序，利用该程序对普通住宅的一个典型开间墙体内部二维温度分布进行了模拟。把按二维温度分布计算出的墙体传热系数与按标准的一维面积加权方法计算的平均传热系数作比较，两者差别很大。可见冷桥对墙体传热的影响只有通过二维、三维的温度场模拟才能比较准确地反映出来。     

Coupling of thermal mass and natural ventilation in buildings

The coupling of thermal mass and natural ventilation is important to passive building design. Thermal mass can be classified as external thermal mass and internal thermal mass. Due to great diurnal variation of ambient air temperature and solar radiation intensity, heat transfer through building envelopes, which is called external thermal mass, is a complex and unsteady process. Indoor furniture are internal thermal mass, affecting the indoor air temperature through the process of absorbing and releasing heat. In this paper, a heat balance model coupling the external and internal thermal mass, natural ventilation rate and indoor air temperature for naturally ventilated building is developed. In this model, the inner surface temperature of building envelopes is obtained based on the harmonic response method. The effect of external and internal thermal mass on indoor air temperature for six external walls is discussed of different configurations including lightweight and heavy structures with and without external/internal insulation. Based on this model, a simple tool is developed to estimate the indoor air temperature for certain external and internal thermal mass and to determine the internal thermal mass needed to maintain required indoor air temperature for certain external wall for naturally ventilated building.     

Thermal performance of a solarium with removable insulation

A thermal model for a solarium with removable insulation has been developed; the air inside the house is assumed to be at constant temperature corresponding to air conditioning). The model enables the evaluation of the temperature of the air in the sunspace and the thermal flux through the south wall into the house as a function of time, from the hourly variation of solar insolation and atmospheric temperature. The effect of various parameters, like the thickness of the thermal wall, its area and the presence of an isothermal mass, on the temperature of zone 1 and the heat flux through the thermal wall into zone 2 has been investigated.     

Ventilation as a means of air-conditioning power saving in reinforced concrete telephone-exchange buildings-analysis and directions for design

The paper presents a computer-aided analysis of the combined use of ventilation and structural heat capacity and insulation as a means of saving air-conditioning power in digital telephone exchanges. It is shown that such savings can be effected by increasing air change with outdoor cool air at night, and when feasible, also in daytime, through the air change unit, in a conventional air-conditioning cycle. The total thermal time constant (TTTC) method of calculation used enables the evaluation of daily or seasonal heat-flow balance for a given indoor temperature, considering the tendency of the heat capacity of the building and of envelope components to flatten the fluctuations of this temperature.     

单侧自然通风条件下强热源附近热环境的试验研究

以某冷轧钢厂房为研究对象,采用模型试验的方法,搭建试验模型小室,研究了单侧自然通风条件下不同热源放置位置对热源两侧迎、背风面温度分布规律的影响,以及热源非中央放置时模型小室两侧内壁面温度和中央温度梯度的分布情况。在不受其他因素影响下,迎风侧空气温度低于背风侧;热源距离侧面墙壁较近一侧空气温度高于较远一侧。指出在热源散热量确定的情况下,合理的热源布置位置和优化的通风方案是改善强热源室内热环境的有效措施。     

空心砌块通风墙体二维简化传热模型研究

空心砌块通风墙体是一种新型的建筑围护结构,该结构可以利用空调系统排风、地道风或夏季夜间凉风对空心砌块墙体的空腔进行通风,实现墙体内部冷、热量的转移。该技术将热回收或可再生能源利用与降低墙体内部冷/热量结合起来,可削弱室外气候对室内环境的影响,减小墙体内表面温度的波动,从而改善人体的热舒适性。为了研究该新型通风墙体的传热特性,建立了空心砌块通风墙体的二维简化传热模型。并且在稳态情形下,计算分析了该通风墙体内表面的平均温度。还进一步研究了空心砌块通风墙体的当量热阻及其影响因素。结果表明空心砌块通风墙体能获得较低的墙体内表面温度和较高的当量热阻,同时,也降低了室内负荷。     

Influence of the internal inertia of the building envelope on summertime comfort in buildings with high internal heat loads

The aim of this study was to assess the influence of thermal mass placed on the inner side of the building envelope, described as the dynamic internal areal heat capacity (International Standard ISO 13786), on the summertime thermal comfort in buildings characterised by high internal heat loads.To that aim, simultaneous monitoring was carried out on rooms with high internal heat loads (school classrooms), varying the internal inertia of the envelope through the introduction of an insulating panel on the interior side. Analytical assessment was performed in order to include different inertia values and combinations of both external and internal heat loads.The study allowed the threshold values of internal areal heat capacity to be determined with respect to the different periodic transmittance values of the walls, assessed according to the adaptive thermal comfort model described in Standard EN15251.These values could be adopted in energy saving regulations which, being based on semi-stationary calculation models, tend to consider the performance of building envelopes as analogous even if there is different thermal inertia.     

Parametric space distribution effects of wall heat capacity and thermal resistance on the dynamic thermal behavior of walls and structures

The present work aims at the investigation of the combined space distribution effects of heat capacity and thermal resistance on the transient thermal behavior of a wall, seen as a continuum of distributed parameters. The physical system is compared with the idealized wall lumped parameter model and its thermal time constant is related to its effective wall heat capacity, defined as the fraction of the wall heat capacity which participates in a transient thermal process. The effect of the space distribution of heat capacity and thermal resistance on the effective wall heat capacity is investigated for a wide range of homogeneous and multilayer thermally insulated walls. It is derived that the decrease of thermal resistance in homogeneous walls leads to an increase of their effective heat capacity. However, the effects are remarkably stronger on the effective heat capacity of thermally insulated multilayer walls, in which when the thermal insulation layer is at the ambient side, it leads to a significant increase of effective heat capacity, although when it is installed at the room side it leads to very low effective heat capacity, irrespective of the wall thermal resistance. Based on the first order results from a simplified room model, it was subsequently found that the influence of these parameters on the effective heat capacity of the building envelope leads to significant effects on the transient thermal behavior, thermal time constant and stability of structures.     

建筑门窗玻璃幕墙传热系数现场测试研究

建筑门窗玻璃幕墙是建筑围护结构节能最薄弱部位,其传热系数目前只能在实验室通过热箱法测定,在现场准确、快捷地测试该值对于建筑的节能评估改造具有重要意义。在现场测试门窗幕墙内外空气温度和表面温度的基础上,推导出了基于"准稳态"测试原理和"热阻法"、"表面温度法"、"传热系数法"3种传热系数现场测试方法,现场测试值与实验室检测值的较高一致性表明了该现场测试方法的准确性,连续测试数据与平均值的较小偏差表明了该测试方法的稳定性。研究结果表明,建筑门窗玻璃幕墙传热系数可通过该方法在现场准确、快捷地测试得到。     

Time-domain transient thermal response of structural elements

An analytical solution of one dimensional unsteady heat conduction applicable to heat transfer through structural elements forms the basis of a mathematical model to describe transient response while absorbed heat flux is constant. This is useful for determination of starting transients or time delays in heat transfer. It also enables simple calculation of thermal time constant as a first step to predict frequency response before proceeding to analysis in the frequency domain.Solar absorption and simultaneous forced convection at exterior building surfaces together with the linked conduction through homogeneous wall etc., plus convection at inside surfaces contributes to an overall heat balance for heat gains and losses. Calculations show the extent to which a house wall is a governing thermal resistance.Analytical work is finally presented in normalized graphical form to illustrate transient temperature profiles across homogeneous structural elements and the related transient heat flux at inside surfaces.     

Night cooling with a Ventilated Internal Double Wall

This study investigates the feasibility of a device to improve summer comfort in wood-frame houses using a Ventilated Internal Double Wall (VIDW). The idea is to increase the house's thermal inertia and to evacuate accumulated heat during the night with a mechanical ventilation system. The VIDW is a cooling wall. Numerous studies on night ventilation have been conducted, but the active ventilation inside the air gap of a double wall with high thermal inertia has not been studied. The first part of this study examines the impact of VIDWs on the thermal comfort in a timber-frame house. The VIDW is modeled in transient mode based on an electrical analogy with the assumption that the exchange coefficients are constant for a given air velocity. In addition, modeling a stationary CFD in forced convection of the VIDW air gap allowed us to study the cooling potential and the benefit of installing obstacles.     

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。     

Effect of solar storage wall on the passive solar heating constructions

Three different greenhouse prototype designs: gable, flat and semi-circle roof shapes were investigated at the Faculty of Agriculture, Suez-Canal University, Egypt. Investigations were carried out to find out the effect of using the adobe (trombe) wall as solar heat storage used for greenhouse passives heating. The study was conducted under controllable weather conditions and outdoor under the prevailing weather conditions of the site of experiments. A range of cheap and readily available materials were said to form the adobe or adobe wall, i.e. clay (13.3%), clay painted with matt black paint (which has absorbability of 0.95%), sand (96.7% sandy attached by 2.5% gypsum, on the weight basis) and the sandy wall was painted black. These walls were compared with the controlled greenhouse without the wall. Investigations were carried out on greenhouse sandy soil (96.7%) with five different moisture contents of air dry, 25, 50, 75, and 100% from the field capacity. Greenhouse air temperature, soil-depth and solar wall temperatures gradient were investigated for the different walls of the different greenhouses deign under different investigation conditions. The study revealed that, the flat shape greenhouse surfaces gives higher air temperatures when the direction of the greenhouse was north–south, while the span surfaces shape for the east–west direction at the same investigation conditions.     

Five-year data of measured weather,energy consumption,and time-dependent temperature variations within different exterior wall structures

This paper presents coherent 5-year measured data that have been gathered for analyses of building energy consumption and thermal performance of exterior walls. The data is also very suitable for calculations and simulations of heating and cooling energy need of buildings. The data was collected from six identical test buildings, having exterior walls that are constructed of different building materials. The data include the following: indoor–outdoors temperatures; temperatures at various depths within the northern, southern, eastern, and western exterior wall facades; indoor–outdoors relative humidity, heating energy, wind speed and direction; air tightness, infiltration, and horizontal global solar radiation. A computer system (data logger) was used to monitor, check, calculate, integrate, and save the data acquired from approximately 520 sensors in each test building. Measurements were taken with a time interval of 20 s. The 20 s values were then integrated over a time interval of 30 min and the minimum, maximum, and mean values were subsequently stored to a computer database. Analyses of the results indicated that temperatures within the buildings’ exterior walls are constantly changing and, that occasionally the flow of conduction heat is reversed (i.e. outside–inside) due to solar radiation. For accurate results of temperature distribution and the actual heat losses through building envelopes, none steady-state calculations are essential. Depending on the intensity of solar radiation and the material characteristics of the walls, temperature gradient at the inner surfaces of exterior walls may become milder compared to that of the outer surfaces.     

相变墙体冬季传热性能评价及相变参数优化

本文从相变墙体冬季的传热过程出发,提出“保温因子”和“放热因子”评价其传热性能。然后,利用热阻法建立相变墙体在冬季的传热模型,并利用单因素分析的方法研究相变墙体内外层热阻和相变温度对“保温因子”和“放热因子”的影响,结果显示当相变墙体的作用是保温的情况下,相变层应布置在墙体的外侧,相变温度应该接近室内空气温度。当相变墙体的作用是放热的情况下,相变层应布置在墙体的内侧,相变温度应该尽量高一些。本研究可以为相变墙体的应用提供理论支持。     

Thermal Barrier as a technique of indirect heating and cooling for residential buildings

The paper presents a concept of an indirect heating and cooling technique of residential buildings driven by solar thermal radiation called Thermal Barrier (TB), which is composed of polypropylene U-pipes located inside of external walls. Fluid flows inside a U-pipes system with a variable mass flow rate and variable supply temperature. This creates a semi-surface parallel to wall surfaces and a spatially averaged temperature almost constant and close to the reference temperature of 17 °C all year round. The TB technique is used to stabilize and reduce heat flux normal to the wall surface and to maintain its direction from internal air out to ambient air during the entire year. The main intention of this paper is to investigate the thermal performance and stability of Thermal Barrier. A 3D FE model of a prefabricated external wall component containing a TB U-pipe system with flowing fluid is developed using the FE code of ABAQUS. The FE analysis is supported by a novel SVC control system implemented in FORTRAN to simulate real-working conditions. The advantages of the TB heating/cooling technique are outlined.