Evaluation of heat flux reduction provided by the use of radiant barriers in clay tile roofs

In Brazilian towns and cities the greatest thermal gain occurs through the roof of single-storey buildings. In this regard, the use of thermal radiation barriers has the function of minimizing the heat flux through the roof. Even though the use of this type of thermal insulation has increased in recent years; there are still no technical standards which address the subject. Thus, many products have become available on the market which have the appearance of a radiant barrier, but without low emissivity, and not functioning properly as thermal insulation. The objective of this study is to analyze the efficiency of some types of radiant barriers found on the civil construction market, as well as to analyze the efficiency of sheets made from the joining together of a solid urban waste, long-live carton packaging, in loco and in the laboratory. The in loco measurements were carried out in a roof of a residence in the city of Florianópolis, where the heat flux, surface temperatures of the tiles and the ceiling, and the internal and external temperatures, were monitored. The laboratory experiments were carried out with an apparatus which simulates the thermal resistances of a real roof. The results allowed the verification of which is the best type of radiant barrier, that is, which achieves the greatest reduction in heat flux through the roof. This study also allowed a comparison between the in loco and laboratory results.     

Seasonal heat flux properties of an extensive green roof in a Midwestern U.S. climate

Green roofs, or vegetated roofs, can reduce heat flux magnitude through a building envelope as a result of insulation provided by the growing medium, shading from the plant canopy, and transpirational cooling provided by the plants. This study quantifies the thermal properties of an inverted 325 m² retro-fitted extensive green roof versus a traditional gravel ballasted inverted roof in a Midwestern U.S. climate characterized by hot, humid summers and cold, snowy winters. In autumn, green roof temperatures were consistently 5 °C lower than corresponding gravel roof temperatures. Even during chilly and moist conditions, the heat flux leaving the building was lower for the green roof than the gravel roof. Temperatures at the top of the insulation layer were more variable for both green roof and gravel roof on winter days with no snow cover than on days with snow cover. Variation in temperatures between roof types in spring was similar to those in autumn. Peak temperature differences between gravel and green roof were larger in summer than other seasons (sometimes by as much as 20 °C). Over the course of a year (September 2005-August 2006), maximum and minimum average monthly temperatures and heat fluxes were consistently more extreme for the gravel roof than the green roof.     

室内气温对绿化屋顶当量热阻的影响

绿化屋顶在节能设计中以附加当量热阻增大屋顶总热阻值,有效减少由屋顶进入室内的热量,降低室内空气温度。但根据已有的实验研究,绿化屋顶隔热特性与室内气温是耦合关系,随室内气温的变化,绿化屋顶会呈现出不同的隔热特性。用实验测试与数值模拟相结合的方法,分析在不同室内气温下绿化屋顶、参照屋顶与等效保温屋顶内表面温度与热流的变化。结果表明:室内气温会显著改变绿化屋顶的隔热性能,其当量热阻为与室内温度正相关的变量。在被动式建筑中,绿化屋顶更能充分发挥隔热功效,且具有不向室内传热的特性。     

Passive cooling systems for cement-based roofs

In warmer climates, buildings made of cement-based materials often exhibit unfavorable thermal characteristics including higher interior temperature, especially in the absence of an active cooling mechanical system. The purpose of this research project was to investigate the thermal effects of newly designed passive cooling systems on concrete roofs in existing buildings. Each tested passive cooling system consists of a combination of materials that can reduce net heat load in buildings. Commercially available materials such as aluminum 1100 and galvanized steel were used as radiation reflectors; and polyurethane, polystyrene, polyethylene, and an air gap were used as insulation. Experimental results based on laboratory-scale prototypes show that the radiation reflector shape as well as the material selection of each passive cooling system led to reductions in heat conduction between 65 and 88% when compared to a control prototype. Each passive cooling system showed a slow thermal time response when compared to a plain concrete roof, which is a desirable characteristic for controlling thermal fluctuations when heat conduction is also reduced simultaneously. Transient empirical models to predict accurately the midpoint temperature of a cement roof were formulated with and without passive cooling systems in use.     

Investigation of the most suitable location of insulation applying on building roof from maximum load levelling point of view

In this study, the maximum load levelling of periodic heat flux entering a room through a composite roof consisting of different insulation layer has been evaluated for different insulation positions in the roof. A numerical model based on implicit finite difference scheme was applied for 12 different roof configurations during typical winter and summer days. For this purpose, total insulation thickness was kept constant and insulation was placed as equally two pieces and as equally three pieces in different locations within the roof thickness. Then, insulation layers were moved 1 cm at a time across the roof thickness for 12 different configurations. Maximum and minimum values of periodic heat fluxes for each sweeping process in the roof were calculated for achieving the maximum levelling of the heat flux entering through the roof. It was found that the best load levelling was achieved in the case where three pieces insulation of equal thickness were placed one at the outdoor surface of the roof, the second piece of insulation was placed in the middle of the roof and third piece of insulation was placed at the indoor surface of the roof.     

广州国际体育演艺中心屋面工程施工技术

广州国际体育演艺中心屋面工程施工面积约16000m2,由下至上设7个构造层,以满足防水、保温隔热、防火、隔气、隔声等多种功能要求,施工工序较繁琐,工艺复杂。该屋面还采用了覆铝箔酚醛发泡保温板和TPO防水卷材。施工中抓重要工序及节点施工质量控制,高效率、高质量地完成了屋面施工。     

现浇有网聚苯乙烯板外墙外保温抗裂施工技术

外墙保温面层裂缝是保温建筑的质量通病，防裂性能是墙体保温体系要解决的关键技术之一。介绍一种既经济，又能有效解决有网聚苯乙烯板抹灰找平层开裂，减轻面层荷载，提高保温体系安全性及解决“热桥”等问题的施工技术。     

土壤含湿量对绿化屋顶隔热性能影响的数值研究

绿化屋顶因其特有的蒸发作用而展示出独特的隔热性能,其能力就如同给建筑增加了被动降温装置一样。本文用数值模拟的方法来分析土壤水分在绿化屋顶隔热系统中的作用,比较分析了间歇灌溉、连续灌溉和不灌溉三种模式下不同含湿量对屋顶传热的影响。研究得出：绿化屋顶隔热能力与土壤湿度呈正相关;采用间歇灌溉,屋顶热流密度对土壤湿度反应更敏感,在土壤含湿量不超过0．2时,随着湿度的增大,热流显著降低,在含湿量超过0．3后,热流反应较为迟钝;采用连续灌溉,屋顶的隔热性能较间歇灌溉提高3—4倍。     

玻化微珠保温砂浆屋面保温技术研究

结合目前屋面保温材料存在的问题,探索使用具有良好保温、防火作用的玻化微珠保温砂浆作为屋面的保温层。主要介绍了玻化微珠保温砂浆的性能、屋面保温层的构造做法、与普通保温材料的热工性能对比以及工程应用,证明了玻化微珠保温砂浆在屋面节能中的可行性。     

Suitable roof constructions for warm climates—Gazimağusa case

This research aims to find the suitable roof constructions for warm climates. The research has been carried out at Gazimağusa, North Cyprus. With the limited research budget 14 different roof constructions were selected and tested on a test house. These constructions included the types which are widely used in Cyprus and also the new ones. The roof constructions were tested under continuously air-conditioned and non-acclimatised regimes. They were also tested for the risk of condensation.Most of the research on similar aspects were done in terms of energy loss and gain. This research has been designed to study the roof constructions in terms of thermal comfort of the users. Naturally, the roof constructions which have the highest thermal resistance will result in lowest heat gain and loose. In this study instead of finding the roof constructions which gain the least amount of heat during the hottest days of summer or the ones which loose the least amount of heat during the coldest days of winter, it was aimed to find how much they provide thermal comfort throughout the year.In this respect, the roofs with thermal insulation showed the best performance. The location of the thermal insulation materials towards the inner surface of the section increased the performance. Inclined timber roof constructions on reinforced concrete ceiling save the buildings from solar bombarding in summer. However, to prevent the humidity accumulated, the attic space should be very well ventilated. On flat roofs, not only the thermal resistance of the roof section, but also the light reflectance of outside surface materials effected the thermal performance. Outside surface materials with very high light reflectance reduced heat gain in summer considerably.In buildings which are air conditioned in summer, there is condensation risk. The defects due to this condensation can be avoided by the use of thermal insulation materials which are not effected from water. There is also condensation risk for winter. However, it was found that this condensation can dry if the building is ventilated.     

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。     

泡沫玻璃外保温墙体窗口周边传热试验研究

采用大型耐候性试验装置实测2种泡沫玻璃外保温墙体窗口周边的热流密度的结果表明,2种泡沫玻璃外保温墙体的窗口周边热流密度偏差"面砖系统"窗口周边达29.59%";涂料系统"窗口周边热流密度差达34.51%,传热不均匀性较大。当试验温差△t≤10℃时,窗口周边的传热能力相差近35%,热应力及其衍生问题不容忽视。因此,在外保温墙体窗户设计、施工、材料选用时,应尽量采用断桥窗框,降低热桥效应,提高节能效果。     

Solar heating and night radiation cooling by a Roof Radiation Trap

The paper describes a new system, the Roof Radiation Trap, which utilizes solar energy for heating of buildings in winter and nocturnal radiation for cooling in summer. The radiation trap consists of fixed insulating layer separated from the flat roof and glazing, protected by hinged insulating panel, in the southern gap between the roof and the fixed insulation. This fixed insulating layer is covered by corrugated metal sheets, painted white, which serve as nocturnal radiators in summer.The radiation trap is integrated with the building, thermally as well as architecturally. In winter the sun energy penetrates through the glazing and is absorbed directly in the roof, which serves as a combined collector, storage for one night and heat distribution system.The hot air in the space between the flat roof and the fixed insulation is blown into a thermal storage of gravel, under the floor or inside the building. The stored heat is “recovered” by forced convection during cloudy days.In summer the penetration of solar radiation during daytime is prevented by the hinged insulating panel. At night the painted external metal layer is cooled by outgoing radiation and the air under the corrugations is blown into the space of the radiation trap and cools the roof, which, in turn, serves as a heat sink during the next day. Nocturnal evaporative cooling can supplement the radiant cooling.     

Passive cooling of cement-based roofs in tropical climates

In tropical climates, dwellings are made of cement-based materials like concrete to be able to withstand tropical storms and severe weather conditions. However, cement-based materials exhibit undesirable thermal properties including low thermal conductivity and thermal diffusivity which make living conditions almost unbearable. The purpose of this research project was to investigate the impact of a newly designed passive cooling system which can minimize heat transfer through concrete roofs. The passive cooling system consists of a corrugated aluminum sheet with a unique orientation to promote heat dissipation. A layer polyurethane is also used to minimize heat transfer. Experimental results based on lab-scale prototypes show that the well-designed roof insulation system can reduce the typical thermal load by over 70%. The passive cooling system also shows a desirable slow response time to irradiation, which is a desirable characteristic necessary to effectively control thermal fluctuations and reduce thermal loads simultaneously. The results also indicate that the cement-based roof midpoint temperature can be modeled accurately using an appropriate empirical model.     

Reduction of heat flux by a flowing water layer over an insulated roof

This communication presents an investigation of the reduction of heat flux by the flow of water over an insulated roof; the water surface is exposed to periodic solar radiation and atmospheric air while the bottom of the insulation is in contact with the room air at a constant temperature (corresponding to an air conditioned building). The heat conduction equation characterizing the temperature distribution in the roof/insulation, has been solved using appropriate periodic boundary conditions. It is seen that as the flow velocity increases, the heat flux coming into the room decreases while the heat taken away by the flowing water increases. It is concluded that the maintenance of a flowing water layer over an insulated roof is to a great extent more effective than a roof pond system; to some extent it is also more effective than a water film spray system over the roof for reduction of the cooling load of a building.     

长沙地区几种屋面隔热性能的测试研究

屋面的隔热性能对顶层住户夏季室内热环境影响很大,因此对几种常用屋面的实际隔热效果进行测试研究,具有实用价值。选择长沙市区某住宅小区两栋相邻的住宅,在2013年夏季按住宅屋面常用构造做法设置了几种实验模块,在外界条件、层高、墙体等都相同的情况下,连续测试各模块屋面的内表面温度、室内空气温度、室外空气温度并进行对比分析。结果表明:种植屋面的隔热效果最好;无隔热措施传统屋面的隔热效果较差,增设保温层后,其隔热效果有一定提高,如果外表面再刷白,隔热性能明显改善;通风屋面有一定的隔热效果,加设保温层后效果更好。     

屋顶绿化层对屋顶热环境影响测试研究

为研究屋顶绿化层对住宅楼屋顶热环境的影响效果,对某小区单元住宅楼有无绿化层屋顶进行连续测试。分析测试结果发现,在屋顶隔热板上设置绿化层后,白天,隔热板下表面平均温度、隔热层中空气平均温度、屋顶上表面平均温度分别降低7℃、3.6℃、2.8℃;隔热板下表面、隔热层空气、屋顶上表面最高温度也明显偏低,其中隔热板下表面最高温度昼间降低高达12.2℃,屋顶上表面最高温度昼间降低高达5.1℃。在屋顶设置绿化层能有效缓解阳光直射屋顶造成的屋顶过热现象,从而改善室内热环境,达到较好的建筑节能效果。     

The relative performance of different approaches to the passive cooling of roofs

This communication presents a discussion of the relative performance of five different approaches to the reduction of heat flux through the roof. These are roof shading by plants, use of removable canvas, evaporative cooling, a roof garden and use of earthen pots over the roof. Explicit expressions have been obtained for the time-dependent heat flux entering into the living space through the roof; the living space is assumed to be at constant temperature (corresponding to air conditioning). Results of numerical calculations corresponding to a typical hot day (16 May 1981) at New Delhi have been presented. For optimum thermal load levelling and least average heat flux into the room, a shaded roof (due to a vegetable pergola) with a water film is the best choice.     

建筑多样化下外墙保温防火发展形式分析

城市建筑模式正随着科学技术的推进不断的发展,建筑理念也在多样化的形势下朝着科学化、创新化推进.建筑外保温材料在建筑领域地位越来越重要,科学研发推进了保温材料在建筑领域发挥着巨大的作用.高效、节能、薄层、隔热、防水外护一体化的外保温材料正在形成,建筑物隔热保温是节约能源、改善居住环境和使用功能的一个重要方面,当今在发展新型保温隔热材料的同时,也要符合结构保温节能技术特点,按标准规范设计及施工,强调有针对性使用保温绝热材料,不断提高保温效率及降低成本.外墙保温材料最重要的环节应该是防火部分,外墙外保温系统的防火安全是事关民生安全的重要且紧急课题.     

双层铝板通风坡屋顶在湖南农村住宅节能改造中的应用

房屋建筑物顶部屋面全年受阳光热辐射,是建筑物受热最多也是最集中的部位。对于普通单层建筑,夏季屋面所得热量占建筑各面总热量的37%左右,而在冬季则能占到50%以上,导致屋顶面隔热能力的强弱直接影响了屋内的内热环境和能耗状况。湖南中北部农村的村民民房绝大部分使用小青瓦或机制瓦铺顶,下方形成阁楼与内屋相通,在没有采取隔热措施的情况下,夏季室温需要另外耗能降温。对此,以湖南农村住宅为实例,对双层铝板通风坡屋面的隔热改造技术在农村建筑节能工程中的应用进行了阐述分析。