The transient house heating condition—the building envelope response factor (BER)

In this paper influence of house walls on heating energy consumption and indoor thermal comfort was investigated. The simulations were carried out using an extended dynamical model of building-software ZID under transient conditions, like the first heating day after a long non-heating period. Four simulation cases were considered: two-layered thermal-insulation concrete house walls were used, where the thermal insulation was inserted in the inner, outer or middle positions according to the inside of the house, and one-layered concrete house walls. The influence of the house walls on internal thermal comfort and heating process is presented by two introduced factors: thermal comfort degree-hour and building envelope response factor (BER factor). This new BER factor could be a significant variable in considering house walls as a passive heating energy source. The conclusion is that under certain conditions the BER factor is at a maximum, at which point the influence of house walls on inside thermal comfort and heating energy consumption is also at a maximum.     

添加石蜡的相变水泥墙传热性能分析

利用ANSYS有限元分析软件,模拟添加石蜡的相变水泥墙体和普通水泥墙体的传热性能。通过模拟计算,给出普通水泥墙和相变水泥墙在一侧受到热流时另一侧的表面温度和热流的变化规律,并与实验测试结果进行比较;通过对比研究相变墙体和普通墙体的传热性能,分析相变墙的节能效果和可行性;同时求解相变墙体表面恒温时间随导热系数和相变潜热的变化规律。结果显示:数值模拟结果与实验测试结果较吻合,模拟方法可行;与普通墙体相比,相变墙体的温度变化平缓,热流传递出现滞后,热流量小,节能效果较明显;提高相变材料的导热系数和潜热能提高表面恒温时间,有利于相变材料在墙体中的储能效果。     

Comparative study of room temperature control in buildings with and without the use of PCM in walls

The concept of thermal energy storage in building gains a specific importance in the present energy scenario related to energy consumption and indoor thermal comfort. The material used to store the thermal energy which undergoes a phase change referred as PCM and it is considered as a possible solution for reducing energy consumption in the building by storing and releasing heat within a certain temperature range; it raises the building inertia and also stabilizes indoor air temperature fluctuations. The room temperature is controlled by imposing PCM inside the walls. An attempt has been made to compare room air temperature with and without the use of PCM inside the walls of constructed modular building unit. The PCM imposed modular building shows the reduced temperature fluctuations in room, the PCM absorbs and liberates excess heat which is gained from the outer side of the room and maintains constant inner room temperature. The PCM imposed walls of modular building unit have an ability to reduce 10–30% of heat load in comparison with the plain wall. The results showed that reduction in room temperature is about 2–4°C and it has been concluded that the PCM imposed modular building unit has more energy saving opportunities than normal modular building unit.     

Thermal performance of a non-air-conditioned building with PCCM thermal storage wall

This paper presents a time-dependent periodic heat transfer analysis of a non-air-conditioned building having a south-facing wall of phase-changing component material (PCCM). A rectangular room (6 × 5 × 4 m) based on the ground is considered. The effects of heat transfer through walls and roof, heat conduction to the basement ground and furnishings, heat gain through window and heat loss due to air ventilation have been incorporated in the periodic time-dependent heat transfer analysis. The time-dependent heat flux through the PCCM south-facing wall has been obtained by defining the effective thermal properties of the PCCM for a conduction process with no phase change. Numerical calculations are made for a typical mild winter day (7 March 1979) at New Delhi for heat flux entering through the wall and inside air temperature. Further, a PCCM wall of smaller thickness is more desirable, in comparison to an ordinary masonry concrete wall, for providing efficient thermal energy storage as well as excellent thermal comfort in buildings.     

Analysis on the heat transfer in a square cavity with a semitransparent wall: Effect of the roof materials

A theoretical study on conjugated heat transfer (natural convection, radiation and conduction) in a square cavity with turbulent flow is presented. The cavity is a representation of a room, where the left wall is isothermal, the right wall is semitransparent (glass), the lower wall is considered as insulated and on the upper opaque wall heat conduction is present. Both conductive walls (opaque and semitransparent) interact with the ambient. The semitransparent wall is subject to a constant heat flux (G₂ = 736 W/m²) whereas on the opaque wall a constant heat flux (G₁ = 875 W/m²) falls perpendicularly. The sizes of the cavity under study were 5.0, 4.0, 3.0 and 2.0 m. The upper opaque wall was considered as a mixture of concrete and a composite material (concrete–expanded polystyrene) with different thicknesses and diverse types of water-repellent coatings on top of it. From the results, it was found that the white coating on top of the opaque wall significantly reduces the amount of energy towards the inside of the cavity. It was also determined that the opaque wall with a 20 cm thickness shows the best thermal performance and it is the most adequate to reduce thermal gains inside the cavity. Correlations for the total heat transfer as a function of the cavity size, the type of coating and material of the opaque upper wall are proposed.     

Passive room conditioning using phase change materials—Demonstration of a long-term real size experiment

The thermal properties of lightweight buildings can be efficiently improved by using phase change materials (PCMs). The heat storage capacity of the building can be extended exactly at the desired temperature level, which leads to an enormous increase in residential comfort. This is shown in the present paper using the example of a prefabricated wooden house. The house was divided into two identical rooms. One of them was equipped with almost one ton of phase change material based on salt hydrates with a melting temperature of approx. 21°C. The material was encapsulated in 1-l Polyethylene containers and installed in two back-ventilated layers inside of the walls. The house was monitored for a period of 87 days in terms of temperatures, solar radiation and air velocity inside the PCM wall system. A considerable temperature buffering could be observed in the PCM room compared to the reference room. An overall reduction of the temperature fluctuations of 57% and a reduction of the day/night fluctuations of 62% compared to the reference room could be obtained. In addition, a prediction regarding the energy demand of such buildings is discussed on the basis of a simulation program. Thus, the annual cooling capacity can be reduced by 36.5% compared to the regular timber construction technique by introducing PCM. Furthermore, the good correlation of the simulation results with the experimental ones allows using the simulation as a tool to design a house with additional thermal storages.     

Modélisation en régime transitoire des mouvements convectifs dans une cellule d'habitation

This study aims thermal phenomena modelling inside a dwelling cell in order to determine temperature distribution there. A coupling of the zonal method and integral analysis in walls vicinity is carried out. The zonal method lies on breaking up the cell into isothermal zones. Mass and energy balances are established, in transient flow, for each zone. The various convective transfer types are listed and studied: transfer between air and walls, transfer between air layers, transfer between air and cold air jet, transfer between air and transmitter. Conductive transfer through walls and radiative transfer inside the cell are also taken into account. An experimental validation campaign is also achieved in a testing room, two heat transmitter types are tested: distributed and located. Validation results are satisfying and air diffusion importance is emphasised. The influence of air nodes number is also studied.     

Conjugate Heat Transfer Analysis in a Glazed Room Modeled as a Square Cavity

A numerical study of conjugate heat transfer by turbulent natural convection in a room with three different glazed configurations is presented. The room is modeled as a square closed cavity, where the lower wall is adiabatic, the right wall is semitransparent, and the upper and left walls are opaque conductive surfaces. Governing equations of mass, momentum, and energy were solved by the finite volume method with a two equation turbulence model. The results are presented in terms of streamlines, isotherms, heatlines, turbulent viscosity isolines, and thermal parameters, such as indoor temperatures and heat transfer coefficients. From the three cases considered in this study, the reflective glass window was the optimal configuration from the thermal comfort point of view for both design days. On the contrary, the glass-film configuration showed the worst indoor thermal performance inside the cavity despite of being the configuration that allows lower energy transferred into the room through the glazed surface. A set of useful heat transfer correlations are obtained for building design applications and energy codes in temperate climates.     

The transient house heating condition—the daily changes of the building envelope response factor (BER)

The current paper presents a logical extension of previous work [Lukić N. The transient house heating condition—the building envelope response factor (BER). Renewable Energy 2003;28:523–32.]. The daily changes of the earlier introduced building envelope response factor (BER) are shown, under transient heating conditions, during the first three heating days after a long non-heating period. Four simulation cases were studied: two-layered thermal-insulation-concrete house walls where the thermal-insulation had in, out and middle position according to inside of house and one-layered concrete house walls. Three different behaviors of central radiator heating system were simulated. The BER factor is considered an important pointer on influence of house walls to heating/cooling energy consumption and thermal comfort during transient conditions. In numerous simulations, using BER factor presentation, the start heating-period was investigated up to the achievement of defined thermal comfort inside the building walls. Alongside of the expected start peak, local peaks and off-peaks of BER factor appeared during first three heating days. Recognition of the daily changes of BER factor could enable aims, lower energy consumption and a rapid achievement of good thermal comfort. In this attempt, a building envelope, as a passive source of energy, is a critical factor.     

Use of a variable parameter test-cell for the study of latent-heat solar walls

A paraffin Trombe wall with double glazing, is studied experimentally with the help of a test-cell allowing several working conditions to be checked. The efficiency of the wall itself is shown to be very similar whether thermocirculation is on or not. But an important additional contribution comes from the glazing in the first case. The analysis of the results points out that a controlled air circulation would give much better results than the two cases considered. Indeed the overheating due to thermocirculation can be cancelled by some controlled air circulation only, and the important convective front losses observed at the begining of the night have to be decreased by getting the heat back to the room through forced air circulation.     

Solar thermal modelling of a non-airconditioned building: Evaluation of overall heat flux

This paper presents an investigation of the thermal behaviour of a non-airconditioned building with walls/roof being exposed to periodic solar radiation and atmospheric air while the inside air temperature is controlled by an isothermal mass, window and door in the walls of the room. The effects of air ventilation and infiltration, the heat capacities of the isothermal storage mass inside air and walls/roof, heat loss into the ground, and the presence/absence of the window/door have been incorporated in the realistic time dependent periodic heat transfer analysis to evaluate the overall heat flux coming into the room and the inside air temperature. A numerical computer model using typical weather data for Delhi has been made to appreciate the analytical results quantitatively. It is found that the heat fluxes through different walls have different magnitudes and phase lags w.r.t. the corresponding solair temperatures. The overall heat flux coming into the room as well as the room air temperature are sensitive functions of the number of air changes per hour, closing/opening of the window and the door ventilation. The effects of the heat capacity of the isothermal mass and the basement ground are found to reduce the inside air temperature swing and the presence of a window is found to increase the inside air temperature even when the window area is much smaller than the wall/roof area. The model presented would be an aid to a building architect for good thermal design of non-airconditioned buildings.     

Experimental study on the thermal properties of the phase change material wall formed by different methods

The thermal properties of the shape-stabilized phase change material walls with different structure were studied. The phase change material is composed of paraffin mixture and high-density polyethylene. The walls including concrete and shape-stabilized phase change material were prepared respectively by different methods. Preparation methods include direct mixing method and lamination interpolation method. Heat transfer process in the shape-stabilized PCM walls was studied by comparing with traditional wall. The results showed that the surface temperature and the heat flow through the phase change material walls prepared by different methods are lower than that of traditional wall and the change is small. Energy-saving effect of the shape-stabilized PCM walls prepared by lamination interpolation method is better than that of the shape stabilized PCM walls by direct mixing. Results in this paper can provide the basis for the application of the shape stabilized PCM walls in the buildings.     

Nonlinear thermal optimization of external light concrete multi-holed brick walls by the finite element method

In this work, an analysis and numerical study have been carried out in order to determine the best candidate brick from the thermal point of view by the finite element method. With respect to the ecological design and the energy saving for housing and industrial structures, there is also a great interest in light building materials with good physical and thermal behaviours, which fulfils all thermal requirements of the new CTE Spanish rule for further energy savings. The conduction, convection and radiation phenomena are taking into account in this study for four different types of bricks varying the material conductivity obtained from the experimental tests. Based on the previous thermal analysis, the best candidate was chosen and then a full 1.05 × 0.35 × 1.0 m. wall made of these bricks was simulated for fifteen different compositions and temperature distribution is also provided for some typical configurations. The major variables influencing the thermal conductivity of these walls are illustrated in this work for different concrete and mortar properties. The finite element method (FEM) is used for finding accurate solutions of the heat transfer equation for light concrete hollow brick walls. Mathematically, the nonlinearity is due to the radiation boundary condition inside the inner recesses of the bricks. Optimization of the walls is carried out from the finite element analysis of four hollow brick geometries by means of the average mass overall thermal efficiency and the equivalent thermal conductivity. In order to select the appropriate wall satisfying the CTE requirements, detailed instructions are given. Finally, conclusions of this work are exposed.     

Experimental study of small-scale solar wall integrating phase change material

Solar walls have been studied for decades as a way of heating building from a renewable energy source. A key ingredient of these wall is their storage capacity. However, this increases their weight and volume, which limits theirs integration into existing building. To aleviate this problem, storage mass is replaced by a phase change materials. These allow to store a large amount of energy in a small volume, which brings the possibility of retrofit trough use of light prefabricated module.This article presents an experimental study of a small-scale Trombe composite solar wall. In this case, the phase change material was inserted into the wall in the form of a brick-shaped package. While this material can store more heat than the same volume of concrete (for the same temperature range), it shows a very different thermal behavior under dynamic conditions. A particular attention is focused on the delay between the absorption of solar radiation and the energy supplied to the room. The energy performance of the wall from heat flux measurements and enthalpy balances are also presented.     

Numerical study on a low energy architecture based upon distributed heat storage system

Basic performance of a hybrid heating system was investigated numerically through several case studies including examinations of effects of PCM as a heat storing materials. A simple test room assuming passive utilization of solar energy was used with a thermal storage wall (Trombe wall) inside it. Unsteady simulation was performed with a CFD code developed by authors. As the outdoor conditions, standardized weather data of Sapporo city, a cold climate district in Japan, were used. In the simulation, the room air was controlled with the heater operations setting the target air temperature at 18 degree Celsius. Simulated results indicate the effectiveness of PCM and suggest the possibility of developing low energy houses with hybrid system introduced in this study.     

A Comprehensive Evaluation on Energy,Economic and Environmental Performance of the Trombe Wall during the Heating Season

Trombe wall is a passive building energy saving technology that uses solar energy to reduce buildings' heating load and adjust indoor thermal environment. In recent years, much research has been done to increase the thermal efficiency of Trombe wall, but little is focused on the evaluation of Trombe wall from energy, economic and environmental aspects comprehensively. Based on the thermal performance calculation method in ISO 52016-2:2017(E), the authors proposed a concise method to evaluate the energy, economic and environmental performance of ventilated and non-ventilated Trombe walls during a heating season. Firstly, non-iteration calculation methods were introduced for the energy evaluation of Trombe wall and conventional wall during the heating season. Then the economic and environmental evaluation models were brought out according to the energy performance of Trombe wall. After that, a residential building was presented as the case building to evaluate Trombe walls' performance in five building climate zones of China. The calculation results showed that both heating degree days and solar radiation had significant impact on the energy saving effect of Trombe walls. In comparison with non-ventilated Trombe walls, ventilated ones displayed more obvious energy saving potential in all five climate regions, which can provide averagely 62% more heating for the room in the case study. Though the heating degree days of Guangzhou(hot-summer and warm-winter zone) was the smallest in the five zones, ventilated Trombe wall in the zone had the poorest economic performance due to the scarcest solar radiation during the heating season.     

A model of the thermal transient state of a wall of a room during the heating by a heating system

After turning on a room heating system (e.g. central heating) a thermal transient phenomenon takes place on the wall–room system, until it reaches a final thermal equilibrium state. The temperature profiles on the wall cross‐section, starting from an initial profile, corresponding to the initial thermal equilibrium state, come gradually through successive intermediate temperature profiles, to a final temperature profile corresponding to the final thermal equilibrium state. These intermediate, nonlinear and time‐dependent temperature profiles characterize the wall thermal transient state and describe the dynamic thermal behaviour of the wall–room system. The mass of the air in the room is negligible, compared to the mass of the surrounding walls, so the dynamic behaviour of the room–wall system is imposed by the corresponding thermal dynamic behaviour of the walls. The influence of this thermal transient state is important for the room heating behaviour because it acts as a thermal flywheel attenuating and smoothing the room temperature variations. In the present work, using the integral method, analytical expressions yielding the temperature profiles, and the duration of the transient state as a function of thermal and structural characteristics have been developed. Conclusions were drawn on the dynamic thermal behaviour of the room–wall system. Copyright © 2000 John Wiley & Sons, Ltd.     

带有透明蜂窝太阳房的模拟计算

对一种新型带有透明蜂窝府能墙式太阳房进行了模拟计算。该房在透明隔热系统与储能墙之间高有一层薄金属吸热板，室内空气借助风机在吸热板与储能墙夹层中流动，空气受热后，将一部份能量加热储能墙，另一总份由它自身传入室内。模拟计算表明，该太阳房具有良好的热性能，且克服了传统Ｔｒｏｍｂｅ墙的积灰，热惯性大及热损大等缺点。     

Experimental and numerical model of wall like solar heat discharge passive system

The present work raises the use of solar energy as an aid for air conditioning by means of architectural envelope parts such as walls, basically as heat discharge systems. Using a thermal balance applied to these systems, an analytic model was formulated to simulate its behavior and to consider the time variation of the environmental temperature, solar radiation, heat storage in the wall and the temperature of the room to be ventilated. The analytical results were compared against experimental data, creating an experimentally validated model that gives confidence on the accuracy and trustworthiness of the analytic proposal. Six tests were carried out in the experimental model. In four of them, the heat flux simulation was performed with electrical resistors; in the other two, solar radiation was directly employed. The results show that the thermal performance of the system can be appropriately determined and described by the analytical model, within a small margin of error. The proposed analytic model can calculate the behavior of a heat discharge system in walls by simply knowing the dimensions of the prototype and the environmental conditions.     

Maximum thermal load levelling in a double hollow wall/roof

The effect of a metal sheet in the middle of a hollow concrete slab, on the thermal performance of the concrete slab has been studied; one face of the wall/roof is exposed to solar radiation and ambient air and the other is in contact with room air at constant temperature. the optimum distribution of inside and outside concrete thicknesses for maximum thermal load levelling has been obtained; it is seen that this is achived when the outer concrete thickness is as small as possbile. These result have also been compared with the results corresponding to single hollow and double hollow concrete slabs.