Fire safety aspects of PCM-enhanced gypsum plasterboards: An experimental and numerical investigation

New trends in building energy efficiency include thermal storage in building elements that can be achieved via the incorporation of Phase Change Materials (PCM). Gypsum plasterboards enhanced with micro-encapsulated paraffin-based PCM have recently become commercially available. This work aims to shed light on the fire safety aspects of using such innovative building materials, by means of an extensive experimental and numerical simulation study. The main thermo-physical properties and the fire behaviour of PCM-enhanced plasterboards are investigated, using a variety of methods (i.e. thermo-gravimetric analysis, differential scanning calorimetry, cone calorimeter, scanning electron microscopy). It is demonstrated that in the high temperature environment developing during a fire, the PCM paraffins evaporate and escape through the failed encapsulation shells and the gypsum plasterboard's porous structure, emerging in the fire region, where they ignite increasing the effective fire load. The experimental data are used to develop a numerical model that accurately describes the fire behaviour of PCM-enhanced gypsum plasterboards. The model is implemented in a Computational Fluid Dynamics (CFD) code and is validated against cone calorimeter test results. CFD simulations are used to demonstrate that the use of paraffin-based PCM-enhanced construction materials may, in case the micro-encapsulation shells fail, adversely affect the fire safety characteristics of a building.     

相变材料在节能建筑中的应用探究

相变材料具有高效的储能特性,将其应用在建筑中能够降低建筑能耗,调整室内环境舒适度,提升建筑材料的功能,从而实现建筑绿色环保的要求。在对相变材料的性质进行综合分析的基础之上,重点探究了相变材料在墙体、屋顶保温隔热,以及室内地板地采暖等方面应用的可行性,并对相变材料的研究方向和未来发展前景进行了展望。     

Thermal energy savings in buildings with PCM-enhanced envelope: Influence of occupancy pattern and ventilation

Integration of building materials incorporating PCMs into the building envelope can result in increased efficiency of the built environment. A PCM-enhanced wall system is proposed in this paper and a simplified model for the heat exchange between the indoor environment and ambient was developed. The objective of the study was to assess the effect of occupancy pattern and ventilation on the energy savings potential of the wall system. It was found that (1) the occupancy pattern influences the value of the PCM melting point for which maximum energy savings value was reached and (2) the ventilation and its pattern reduces the relative value of the energy savings.     

泡沫混凝土外墙的热工性能测试与分析

随着建筑能耗的不断增加以及能源危机的日益加剧,建筑节能变得尤为迫切。外墙是围护结构节能的重点。泡沫混凝土因良好的保温隔热性能被广泛应用于建筑工程中,但其在建筑外墙的应用还处于探索阶段。本文介绍了新型泡沫混凝土外墙的构造及性能特点,并通过实验对比分析了外保温墙体、实心砖墙体和泡沫混凝土墙体的保温隔热性能。实验结果显示,泡沫混凝土外墙的保温隔热性能远优于其他两种墙体,在空调状态下,其内表面的热流值仅为外保温墙体的30.4%,具有显著的节能效果。不仅如此,泡沫混凝土外墙更为轻质,其质量仅为外保温墙体的49.1%。     

Experimental and modelling study of twin cells with latent heat storage walls

An experimental and numerical simulation study of the application of phase change materials (PCMs) in building components is presented for thermal management of a passive solar test-room. The experimental study was conducted in an outdoor test cell constituted of two small rooms separated with a wall containing PCM. A specific wall made of hollow glass bricks filled with PCM was studied. Three PCMs were tested: fatty acid, paraffin, and salt hydrate whose melting temperatures are 21 °C, 25 °C and 27.5 °C respectively.Indoor and outdoor temperatures were measured with thermocouples. Ten fluxmeters located at the centre of each wall allowed us to measure the heat fluxes across the walls. Tests were carried out in real climatic conditions.A one-dimensional numerical model has been developed to simulate the transient heat transfer process in the walls. Reasonable agreement between the simulation and the experimental results was observed.     

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。     

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.     

定形相变墙体传热性能和力学性能的实验研究

利用液体石蜡-46#石蜡、液体石蜡—月桂酸和癸酸—肉豆蔻酸3种相变材料混合物分别与高密度聚乙烯混合制备定形相变材料.通过直接混合法把定形相变材料加入水泥砂浆制备定形相变墙体.实验研究了相变墙体和普通墙体的传热性能和力学性能.实验结果显示:定形相变墙体表面温度和热流均低于普通墙体;热物性不同的相变材料随着墙体中含量的增加...     

Influence of thermal insulation position in building envelope on the space cooling of high-rise residential buildings in Hong Kong

At the present time, thermal insulation is almost not used in fabric of tall residential buildings in Hong Kong, as their fabric slabs usually comprise concrete layer covered on each side by plaster layers. This study investigates into the influence of an existence of the thermal insulation layer in the outside walls on the yearly cooling load and yearly maximum cooling demand in two typical residential flats in a high-rise residential building by employing HTB2, detailed building heat transfer simulation software. During the investigations, the thermal insulation layer up to 15 cm thick was placed either at the inside, or at the outside, or at the middle part of the outside wall structure. Then, the concrete layer was up to 40 cm thick. The simulation predictions indicate that the highest decrease in the yearly cooling load of up to 6.8% is obtained when a 5 cm thick thermal insulation layer faces the inside of the residential flat. The highest decrease in the yearly maximum cooling demand of 7.3% is recorded when a 5 cm thermal insulation layer faces either the outside or the inside of the flat; this depends on the flat orientation. However, much weaker reductions in the yearly cooling load and yearly maximum cooling demand are found when the thickness of thermal insulation is increased above 5 cm and the thickness of concrete is increased above 10 cm.     

建筑门窗幕墙框节能研究

建筑门窗幕墙节能对围护结构节能至关重要,尤其是框的节能是建筑门窗幕墙节能性能的关键,同时是门窗幕墙构造设计的重点。本文分析了目前我国常用的铝合金断热窗框、塑料窗框、木窗框、明框幕墙框、隐框幕墙框等的传热系数、线传热系数,总结出节能门窗幕墙框节能设计、应用的一般原则。     

Enhancement of solar thermal energy storage performance using sodium thiosulfate pentahydrate of a conventional solar water-heating system

The time variations of the water temperatures at the midpoint of the heat storage tank and at the outlet of the collector in a conventional open-loop passive solar water-heating system combined with sodium thiosulfate pentahydrate-phase change material (PCM) were experimentally investigated during November and then enhancement of solar thermal energy storage performance of the system by comparing with those of conventional system including no PCM was observed. It was observed that the water temperature at the midpoint of the storage tank decreased regularly by day until the phase-change temperature of PCM after the intensity of solar radiation decreased and then it was a constant value of 45 °C in a time period of approximately 10 h during the night until the sun shines because no hot water is used. Heat storage performances of the same solar water-heating system combined with the other salt hydrates-PCMs such as zinc nitrate hexahydrate, disodium hydrogen phosphate dodecahydrate, calcium chloride hexahydrate and sodium sulfate decahydrate (Glauber's salt) were examined theoretically by using meteorological data and thermophysical properties of PCMs with some assumptions. It was obtained that the storage time of hot water, the produced hot water mass and total heat accumulated in the solar water-heating system having the heat storage tank combined with PCM were approximately 2.59–3.45 times of that in the conventional solar water-heating system. It was also found that the hydrated salts of the highest solar thermal energy storage performance in PCMs used in theoretical investigation were disodium hydrogen phosphate dodecahydrate and sodium sulfate decahydrate.     

Application of latent heat thermal energy storage in buildings: State-of-the-art and outlook

Latent heat thermal energy storage (LHTES) is becoming more and more attractive for space heating and cooling of buildings. The application of LHTES in buildings has the following advantages: (1) the ability to narrow the gap between the peak and off-peak loads of electricity demand; (2) the ability to save operative fees by shifting the electrical consumption from peak periods to off-peak periods since the cost of electricity at night is 1/3–1/5 of that during the day; (3) the ability to utilize solar energy continuously, storing solar energy during the day, and releasing it at night, particularly for space heating in winter by reducing diurnal temperature fluctuation thus improving the degree of thermal comfort; (4) the ability to store the natural cooling by ventilation at night in summer and to release it to decrease the room temperature during the day, thus reducing the cooling load of air conditioning. This paper investigates previous work on thermal energy storage by incorporating phase change materials (PCMs) in the building envelope. The basic principle, candidate PCMs and their thermophysical properties, incorporation methods, thermal analyses of the use of PCMs in walls, floor, ceiling and window etc. and heat transfer enhancement are discussed. We show that with suitable PCMs and a suitable incorporation method with building material, LHTES can be economically efficient for heating and cooling buildings. However, several problems need to be tackled before LHTES can reliably and practically be applied. We conclude with some suggestions for future work.     

我国不同气候区典型外墙的热湿迁移特性及霉菌生长风险评估

针对国家建筑标准设计图集09J908-3中常见建筑外墙的热湿迁移特性及霉菌生长风险展开研究,以5个代表城市(沈阳、北京、上海、福州和昆明)为例,采用WUFI Pro 6.2软件模拟了外墙的非稳态热湿传递过程.结果表明:墙体内部的热湿动态迁移过程受主体材料、保温材料和当地气象条件等多个因素的共同影响;加气混凝土(AAC)...     

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。     

相变蓄能材料在建筑节能领域的应用研究

介绍了应用于建筑节能领域的相变蓄能材料,探讨了相变蓄能材料在建筑围护结构、相变蓄热供暖系统与相变蓄冷空调系统中的应用。研究表明,相变蓄能材料在建筑领域的应用可以有效地利用太阳能等清洁型能源,缓解建筑物热量供需双方不平衡矛盾,提高室内舒适度,减小建筑能源消耗。总结并展望了未来相变蓄能材料在节能建筑领域应用的研究方向和发展前景。     

相变材料应用于建筑外墙的温度与能耗模拟

使用EnergyPlus能耗模拟软件对相变材料作为外墙表面隔热材料的应用效果进行模拟,在小空间和小型办公室的模型上,改变相变材料的相变温度、材料结构和用量等使用条件,并进一步考虑室内热源和不同气候区的影响,对比分析在空调季节里空间内部温度的变化情况和空调节能效果。模拟结果表明:相变温度稍高的相变材料更有利于夜间散热蓄冷,同时,结合双层复合结构可获得更好的温度抑制和节能效果;内热源的存在会提高房间空调能耗的基数,从而使相变材料空调节能率计算值降低,并且在一定程度上掩盖了相变材料对室内平均温度的抑制作用,尽管如此,相变材料在有内热源环境下使用时空调节能量仍与无内热源时相当。     

室内空调条件下建筑围护结构屋面(墙、窗)的节能控制--建筑热环境与节能研究(之三)

在围护结构(屋顶、墙、窗)隔热控制的基础上，提出了屋顶、墙、窗的节能控制条件，窗——墙作用因子(算符)和隔热一节能作用因子(算符)。在已知墙的隔热控制指标条件下，可简单地计算出窗的隔热控制指标；同时，在已知墙、窗的隔热控制指标情况下，也可简单地计算出墙、窗的节能控制指标。     

What are the hygrothermal consequences of applying exterior air barriers in timber frame construction in Europe?

Moisture-induced damage is one of the major causes of degradations and reduced thermal performance in wood frame buildings. It is therefore crucial to incorporate the hygrothermal assessment of new timber frame building envelopes systems from the early development phase onwards. The article at hand presents the simulation results studying the hygrothermal performance of various timber frame wall configurations with exterior air barrier systems. A parameter analysis explores the impact of different European climates, insulation materials, exterior air barrier materials and verifies in addition to the impact of bad workmanship in the installation of the insulation layer. This study reveals that the application of mineral wool (MW) insulated timber frame walls in combination with exterior air barriers results in increased moisture loads. Moreover, small air gap channels between the MW and the adjacent exterior air barrier significantly increase natural convection and add up to harmful moisture levels. Yet the simulations indicate that the use of blown-in cellulose insulation can avoid these issues. The study further indicates that the technique of exterior air barrier is more suitable for continental climates rather than for moderate sea climates in Europe.     

Effectiveness of vertical barriers in preventing lateral flame spread over exposed EPS insulation wall

Insulation panels made of organic, combustible materials are frequently used in the exterior thermal insulation systems (ETIS) for buildings. Such combustible insulation panels have been involved in several catastrophic building fires in recent years in China. One potential strategy to mitigate this fire hazard is to limit fire spread over the ETIS. The present work evaluates the effectiveness of vertical fire barriers in inhibiting fire spread over exposed insulation walls made of expanded polystyrene (EPS) panels. Reduced-scale experiments were carried out indoors using EPS panels with or without two vertical barriers made of non-combustible mineral wool, the fire started at the bottom center of the middle panel. The interval and width of the barriers were varied systematically, while the temperature distribution on the wall, the radiation heat flux from the fire, and the infra-red (IR) images were recorded. To demonstrate the validity of the concept, an outdoor, full-scale experiment was carried out using a 7-floor building. Our reduced-scale experiments showed that the installation of two vertical fire barriers successfully stopped the lateral flame spread, decreasing the peak temperatures of the two side panels by about 300 °C for all barrier configurations tested. When barrier width was fixed at 5 cm, an increase of the barrier interval from 30 to 90 cm led to increases in the peak temperatures, radiation heat flux, and the maximum rate of upward flame spread. By contrast, when barrier interval was fixed at 90 cm, an increase of the barrier width from 2 to 5 cm had little influence on the combustion dynamics of the middle panel but the peak temperature on the side panels dropped, consistent with the smaller heat transferred with wider fire barriers. In the regions of the side panels next to the barriers, pyrolysis and deformation could be observed with barrier widths of 2 and 3 cm, but not 5 cm. Finally, our outdoor, full-scale experiment demonstrated that a 30 cm wide vertical barrier made of air-filled cement successfully stopped the lateral flame spread over exposed EPS wall. The study highlights the effectiveness of vertical fire barriers in preventing the lateral flame spread over the exposed EPS insulation wall and provides another option for enhancing the fire safety of the combustible insulation systems.