Effective thermal conductivity of vacuum insulation panels

Vacuum insulation panels (VIPs) with evacuated fumed silica as the core material and different barrier envelopes were subjected to a series of tests in a guarded hot plate apparatus. The process was conducted to determine thermal conductivity at the centre-of-panel and the edge effect, i.e. the linear thermal transmittance due to the thermal conductivity of the barrier envelope, which is many orders of magnitude higher than that of the evacuated fumed silica. Numerical simulations using a two-dimensional model were carried out in parallel and compared with measured results. In a further step, the influences of different parameters such as panel size, metal layers in the barrier envelope and the shape of the joint between two adjacent VIPs were quantified. Based on these findings, an effective thermal conductivity can be attributed to a system of VIPs. Investigations were performed within the framework of an international research programme of the IEA, Annex 39 ‘High Performance Thermal Insulation in Buildings and Building Systems’, Subtask B.     

Effective thermal conductivity of a staggered double layer of vacuum insulation panels

The use of vacuum insulation panels in buildings has gradually increased in the past few years and developments in their production have occurred in parallel. This has mainly lead to an optimization of different hygro-thermal properties of both the core material as well as the envelope. The issue of thermal bridges caused by the 300 nm thin metallic layers of the barrier envelope and by the joints between two adjacent panels remains. The present study investigates the influence of these thermal bridges on the effective thermal conductivity of a staggered double-layer of vacuum insulation panels. For this purpose a series of guarded hot plate measurements on single- and double-layers of vacuum insulation panels was carried out. The variety of the existing thermal bridge situations was accounted for by different panel size compositions. The results hereof were compared to those of a simplified numerical model. The target is to determine the effective thermal conductivity by a minimum number of required tests and the simplest numerical model. This will enable the determination of additional heat loss induced by the mentioned thermal bridges for a specific envelope laminate type without knowing the details of its composition especially the metallic layers.     

Vacuum insulation panels for building applications: A review and beyond

Vacuum insulation panels (VIPs) are regarded as one of the most promising high performance thermal insulation solutions on the market today. Thermal performances three to six times better than still-air are achieved by applying a vacuum to an encapsulated micro-porous material, resulting in a great potential for combining the reduction of energy consumption in buildings with slim constructions. However, thermal bridging due to the panel envelope and degradation of thermal performance through time occurs with current technology. Furthermore, VIPs cannot be cut on site and the panels are fragile towards damaging. These effects have to be taken into account for building applications as they may diminish the overall usability and thermal performance.This paper is as far as the authors know the first comprehensive review on VIPs. Properties, requirements and possibilities of foil encapsulated VIPs for building applications are studied based on available literature, emphasizing thermal bridging and degradation through time. An extension is made towards gas-filled panels and aerogels, showing that other high performance thermal insulation solutions do exist. Combining the technology of these solutions and others may lead to a new leap forward. Feasible paths beyond VIPs are investigated and possibilities such as vacuum insulation materials (VIMs) and nano insulation materials (NIMs) are proposed.     

隔热型材等温线分布和传热系数研究

作为衡量隔热性能的重要技术参数,型材传热系数的大小是直接影响甚至决定门窗隔热节能及保温性能的重要因素.本文针对目前行业中普遍认为的隔热型材节能设计理念,利用THERM/WINDOW热工仿真软件对不同设计结构的等温线分布和传热系数进行模拟计算,验证该理念的准确性,并通过对计算结果的分析讨论,得出科学的设计理念,以更好的指...     

Comparing different approaches to in situ measurement of building components thermal resistance

This paper introduces a comparison of different measuring methods of buildings fabric thermal resistance, including the test wall measuring points arrangements and measurement results, conducted in a test chamber in Cagliari (Italy) in summer 2009.Two methods and their measurement uncertainties are presented and compared by the compatibility of measurement study.The non-destructive method involves the heat-flow rate measurement through the test wall and its surface temperatures. The reliability of this method depends on the temperatures difference between the two environments separated by the building envelope. Thus two measurement series with different temperatures were carried out on the test wall.The destructive method instead foresees the acquisition of a sample by the use of a hollow drill, the building envelope layers thickness measurement and the thermal properties assignment to each different material. The wall R-value is the sum of each layer thermal resistance.The comparison shows that the R-values measured by the non-destructive method with a temperature difference of 10 °C and 7 °C and the one calculated from the destructive method obey the compatibility of measurement principle.     

Analytical Model for Predicting Thermal Bridge Effects due to Vacuum Insulation Panel Barrier Envelopes

Because of a necessity for sustainability and thus for a reduction of the amount of primary energy generated with fossil fuels, vacuum insulation panels (VIP) have recently caught the attention of practitioners in the building industry. The reduction of layer thickness may be considered among the most promising features for large‐scale application of VIPs in buildings. The high barrier laminate (or casing) with relatively high thermal conductivity envelops the core material, thus introducing a thermal bridge at the panel edges and corners. Especially for barrier laminates containing ‘thick’ metal foils, the thermal bridge effect needs to be considered thoughtfully. In this contribution analytical models are presented which on the one hand allow rapid estimation of the VIP's overall thermal performance and on the other hand show the influence of material and geometric parameters on this performance. The analytical models are validated through numerical simulations.     

非均质围护结构传热系数的简化计算及检测方法

对非均质围护结构等效热阻的两种简化计算方法进行了回顾评述,从热阻等效原理证明了这两种简化算法是基于不同的热阻等效得到的,并串联的等效方法较串并联等效方法更适于非均质围护结构传热系数的简化计算。对现有检测非均质围护结构传热系数方法进行分析讨论,指出用热箱法可以检测流过非均质围护结构的热流量,但不宜直接测量表面温度来计算非均质围护结构等效热阻,提出了“真空屏热箱法”检测非均质围护结构传热系数,并对这一方法的原理进行了说明。     

高庙子膨润土及其混合材料导热性能研究

导热性能是高放废物地质处置库缓冲/回填材料的重要性能之一。采用瞬变平面热源法,研究了我国高放废物地质处置首选缓冲/回填材料高庙子膨润土,及以其为主料,添加不同含量石英砂、北山花岗岩碎屑组成的混合材料的导热性能。分析了添加剂种类和含量、干密度、饱和度等因素对导热系数的影响。研究结果表明:高庙子膨润土及其混合材料的导热系数、热扩散系数都随干密度和含水量的增大而增大;石英砂、北山花岗岩碎屑能够不同程度提高膨润土的导热系数,石英砂的作用优于北山花岗岩碎屑;饱和度对添加剂发挥其提高缓冲/回填材料导热性能的作用影响明显,饱和度越高,添加剂的作用越显著。     

高放废物处置库缓冲材料导热性能研究

 缓冲材料是高放废物深地质处置库中的重要工程屏障,其导热性能参数是高放废物处置系统设计的关键参数之一。利用ISOMET导热仪,研究内蒙古高庙子天然钠基膨润土GMZ01与石英砂和石墨混合材料GMZM不同压实密度和不同含水量样品的导热性能。结果表明,GMZM的导热系数、热容量和热扩散系数随压实密度的增大而显著增大,随着含水量的增大而增大;与GMZ01的导热性能相比,随着压实密度的增大,石英砂和石墨作为添加剂可以明显提高缓冲材料的导热性能和热扩散性能,但对比热没有显著影响。压实干密度大于1.8 g/cm3后,GMZM的导热系数和热扩散系数比GMZ01的导热系数和热扩散系数均提高20%以上。缓冲材料的导热性能与其含水量、干密度、矿物组成和微结构等有关,导热系数随着含水量和干密度的增大而增大,但是导热系数与含水量和压实干密度不具有一致的线性关系。当GMZ01的饱和度大于20%时,不同压实干密度样品的导热系数、比热、热容量、热扩散系数均与饱和度具有线性关系。     

Combined heat transfer of radiation and conduction in stacked radiation shields for vacuum insulation panels

Combined heat transfer of radiation and conduction considering depthwise conduction phenomena in stacked radiation shields for vacuum insulation panels (VIPs) having an artificial core structure is investigated. The purpose of this study is to establish a reliable analysis method for actual shield design. A one-dimensional problem is first analyzed. Actual two-dimensional problem is simplified for theoretical modeling and the depthwise conduction around contact spot is further considered. Test radiation shields are manufactured using press molding process with SUS 304 (AISI grade 304) plates, since this sample depicts the parametric effects well. Measurement of the effective thermal conductivity is performed with a VGHP apparatus. While various analytical and numerical models predict the effective thermal conductivity in the case of this specific specimen within about 40% error, the combined heat transfer analysis considering depthewise conduction phenomena is accurate within 10% error and it is thus recommended in estimating the effective thermal conductivity of stacked radiation shields.     

多元胶凝体系泡沫混凝土性能研究

采用正交试验研究了粉煤灰、矿粉、硅灰及减水剂对泡沫混凝土力学性能的影响,设计了泡沫混凝土配合比,研究了在不同干密度下泡沫混凝土的抗压强度、孔隙率和导热性能。初步探究了利用珊瑚砂制备泡沫混凝土的可行性。结果表明:复掺矿粉和硅灰能有效提高泡沫混凝土的强度;泡沫混凝土的抗压强度、导热系数与干密度存在非线性关系,孔隙率与泡沫混凝土干密度呈线性负相关。珊瑚砂的掺入对泡沫混凝土性能存在不利影响。     

二氧化硅气凝胶棉毡保温性能的研究

根据圆管导热仪的原理,建立实验台,通过试验测量二氧化硅气凝胶毡的导热系数,得出计算温差与导热系数的曲线,并进行误差分析,再与传统保温材料的导热系数进行对比,体现出二氧化硅气凝胶毡在同类产品中的优越性.     

含湿量对混凝土导热系数的影响分析

掌握混凝土导热系数与含湿量的定量关系是准确计算混凝土传热传质性能及建筑能耗的前提.通过试验分析了含湿量对3种常见混凝土导热系数的影响,并给出了两者之间的定量关系.研究结果表明:混凝土孔隙率越大,含湿量对其导热系数的影响越明显;在低含湿量范围内,混凝土导热系数随含湿量增加而增加的幅度较大,而在高含湿量范围内其增幅变小,且孔隙率和孔径越大时,此变化趋势越明显;获得了混凝土导热系数与质量含湿量的幂函数关系.     

Gas-filled panels for building applications: A state-of-the-art review

With their thermal conductivity down to 10 mW/m K, gas-filled panels (GFPs) are regarded as possible high performance thermal insulating solutions for building applications. However, thermal conductivities of respectively 46 and 40 mW/m K have so far been achieved for prototype air-filled and argon-filled panels, values slightly higher than currently traditional building insulation materials. Compared to other high performance thermal insulation materials and solutions, e.g. vacuum insulation panels (VIPs), the future of GFPs may therefore be questioned. Nevertheless, the application of a low-conductive gas and reflective barriers may have a potential in the development of new high performance thermal insulation materials. Within this work, a state-of-the-art review is given on the knowledge of GFPs for building applications today.     

Design strategy for low-energy ventilation and cooling within an urban heat island

Natural ventilation is a proven strategy for maintaining thermal comfort in non-domestic buildings in the UK. The energy consumption and thus the carbon dioxide emissions that contribute to global warming are lower than in conventional air-conditioned buildings. However, the ambient temperatures in the UK have risen over the last decade and new climatic data for use in the design of naturally ventilated buildings has been published. Using these data and dynamic thermal modelling, it is shown that passive stack ventilation alone was unlikely to maintain summertime comfort in a proposed University College London building within an urban heat island. The stack ventilation strategy was evolved by the introduction of passive downdraught cooling. This low-energy technique enables cooled air to be distributed throughout the building without mechanical assistance. The underlying principles of the technique were explored using physical models and the anticipated performance predicted using thermal modelling. The architectural integration is illustrated and the control strategy described. The resulting building is believed to be the first large-scale application of the passive downdraught cooling technique; construction began in late 2003.     

基于热探针测试的橡胶-砂颗粒轻质混合填料#br# 导热系数影响因素研究

导热系数是岩土材料热学特性的一个重要参数,文章对橡胶-砂颗粒混合物的进行了大量的热针试验。详细分析含砂率、含水率和干密度对导热系数的影响。结果表明：当含砂量小于20%时,橡胶-砂混合物的导热系数逐渐增加,但砂粒含量超过80%后,导热系数立即出现较高的增加速率;随着干密度的增加,导热系数在低含砂率时呈现抛物线增长,在高含砂率时呈现线性增长;橡胶-砂混合物导热系数随含水率的变化可分为增长区域和稳定区域,6%含水率可作为临界含水率。该文可为地热相关结构周围的轻质回填材料提供更合理的热学参数,此外,废旧轮胎的有效利用可以减少环境污染,促进可持续的基础设施。     

轻质保温墙体导热系数现场测试的研究

墙体保温是实现建筑节能的一项重要措施。现场实测是判定墙体是否保温的有力手段,进一步开发建筑热工性能检测技术也是我国未来建筑节能工作的一个重点。利用防护热板法对轻质保温墙体导热系数进行了现场测试,通过数值分析和实验,并进行了对比测试,证明了该方法应用于此类墙体热工性能测试的可行性。     

幕墙框的传热系数计算方法

幕墙整体传热系数的计算是通过一个面积加权的方法求得的。而幕墙中框及各种面材传热系数需要分别进行计算,在框与面材之间存在一个边界,这个边界不仅存在室内外纵向的传热,还存在框与面材之间的横向传热。如何准确的考虑这个边界的传热,是幕墙传热系数计算的关键问题。本文着重讲述一套框的传热系数计算方法,使其充分考虑边界传热在幕墙传热中的影响,仅供大家借鉴参考。     

不同前驱体浓度柔性气凝胶性能研究

以甲基三乙氧基硅烷（MTES）为前驱体,乙醇（EtOH）为溶剂,通过（酸碱）溶胶-凝胶法和超临界干燥技术制备柔性超疏水二氧化硅气凝胶,并研究不同前驱体浓度溶胶-凝胶工艺柔性气凝胶的物理性质、化学组成、微观结构、柔性和回弹性。结果表明,随着前驱体浓度降低,柔性增强但强度逐渐降低,回弹次数减少;导热系数逐渐降低,当MTES/EtOH摩尔比为1:13时,其导热系数最低为0.0270W/(m·K);平均孔径及孔体积逐渐增大;Si-O-Si, Si-C,C-H键增加,带来更多的三官能团有机硅的交联。     

New equipment for testing steady and transient thermal performance of multilayered building envelopes with PCM

Thermal properties of the different building envelopes, such as thermal transmittance in steady state, heat storage capacity and dynamic thermal responses, must be taken into account during the design phase of buildings. The evaluation and measurement of these parameters in multilayered samples are difficult because of the irregular morphology of the used materials and the difficulty in providing the well-controlled environment needed for the measurements. A new equipment has been designed to measure the thermal response and heat capacity of composite walls of different materials simulating real building envelopes.The equipment presented in this paper was used to test the improvement in the thermal response of a building envelope due to the incorporation of PCM. This study is focused on wood structural panels attached to a gypsum board, which is either impregnated or not with PCM. The four edges of the composite sample are properly insulated to ensure one-dimensional heat flow. The two faces of the sample are exposed to controlled environments heated and cooled by copper coils with thermo stated water supplied by water baths. The measured surface heat fluxes at both surfaces of the sample and temperature distribution in the sample provide accurate assessment to thermal mass and dynamic response of the composite wall, while the steady state measurements provide an accurate estimate of its effective thermal transmittance.