Thermal performance analysis and economic evaluation of roof-integrated solar concrete collector

This paper examines the thermal performance of a roof-integrated solar concrete collector for reducing heat gain to a house and providing domestic hot water. The solar concrete collector is made of PVC pipes embedded in deck slab or concrete roof. No glazing on the top of the solar concrete collector or insulation at the back has been used as in conventional solar water heaters. To compare the energy saving, two test rooms of 2.3 m width, 2.5 m length and 2.5 m height were built. In the first room, the reinforced cement concrete (R.C.C.) slab was used as deck slab whereas the second room was equipped with a cement concrete solar collector. The experimental results showed that the cement concrete solar collector is extremely interesting as it can produce up to 40 l of hot water per day at water temperatures ranging from 40 to 50 °C. A mathematical model based on the conservation equations of energy is developed to predict the performance of the cement concrete solar collector. There is reasonable agreement from the comparison between measured data and predicted results. The economic analysis indicates that the payback period is rather fast.     

Fuß‐ und Radwegbrücke aus Carbonbeton in Albstadt‐Ebingen

Pedestrian bridge made from carbon‐concrete in Albstadt‐Ebingen – First entirely carbon‐reinforced concrete bridge worldwide The bridge erected in Albstadt‐Ebingen in October 2015 is realized without any steel reinforcement or pre‐tensioning, making it the world's first entirely carbon‐reinforced concrete bicycle and pedestrian‐bridge. The trough section with material thicknesses of 70 mm (trough walls) and 90 mm (slab) respectively has been fabricated as monolithic pre‐cast element. With a span length of 15 m and a width of 3 m, the bridge‐deck requires no further coating and has a total weight of just 14 tons (approximately 310 kg/m2); this is about 50 % of comparable conventional reinforced concrete bridge‐decks. Besides material and weight savings, an exceptionally long service life with minimal maintenance can be expected, as the steel corrosion that is typical in reinforced concrete structures can be entirely avoided. Since the use of carbon‐reinforced concrete (carbon concrete) is not yet approved in Germany, the client had to obtain approval based on individual cases (ZiE).     

Leichte Dachschalen aus Carbonbeton

Light‐weight precast shell elements made of textile reinforced concrete: production, experimental investigations and application potential For single curved barrel‐vault shells made of textile reinforced concrete (TRC) a manufacturing process has been developed that comprises the production of the precast parts as well as tailored solutions for transport and mounting of the filigree shells at the construction site. Furthermore, the load‐bearing capacity of the shells could be verified experimentally using large‐scale tests of prototypes. Saw cuts document the high production quality of the precast parts.The developed methods were successfully applied within the research project by constructing a large‐scale roof structure consisting of five barrel‐vault shells. The cross‐sectional thickness of the 10 m2 large elements amounts to only 2 cm emphasizing the high strength and application potential of TRC.     

Limit analysis of local failure in shallow spherical concrete caps subjected to uniform radial pressure

Many thin-walled shallow concrete shells (or caps or domes) have experienced structural collapse during or subsequent to their erection. Very few experimental investigations have been reported of shallow concrete spherical caps that allow for the effects of geometric and material non-linearities and imperfections to be identified, despite this information being essential for the validation of sophisticated numerical treatments. Classical thin-shell theories for axisymmetric domes predict a global buckling mode, but observations from experimental tests show that failure in concrete spherical caps is usually localised within a relatively small region and at a load significantly less than the classical buckling load. An investigation of the non-linear behaviour of thin-walled concrete spherical caps is currently being carried out both experimentally and theoretically at The University of New South Wales. As part of this study, an approach based on limit analysis has been developed on the basis of a local failure model and it is used for analysis of concrete/mortar spherical caps described in the published literature. The ultimate bending strength of a unit width of a spherical shell section is derived from a typical non-linear concrete stress-strain relationship and the in-plane thrust from shell membrane theory. The analytical results based on a local failure yield line model are compared with the available experimental results in the literature as well as with classical theoretical buckling results.     

Zwei Kuppeln in München: Armeemuseum und Anatomie (1903–1905) – Die ersten Betonschalen Europas

Two domes in Munich: The Armeemuseum and the Department of Anatomy (1903–1905) – The first concrete shells in Europe. In 1903 Wayss & Freytag merged with the Heilmann & Littmann studio establishing the Eisenbeton‐Gesellschaft, a manufacturer of reinforced concrete structures operating in Munich and the surrounding area. In the following two years the company – directed by Ludwig Zöllner – realized the most innovative works of the time: the Isarbrücke near Grünwald and the domes of the Armeemuseum and the Department of Anatomy of the University of Munich. This paper focuses on these two shell structures calculated by the young engineer Emil Mörsch. The innovative realizations – 7 cm thick and with a span of 16 and 22 m – were built at the same time as the Law Court (1891) and the Ministry of Transport (1904) and presented a high level of engineering that marked the final transition from 19th century steel constructions to 20th century reinforced concrete ribbed domes. The Armeemuseum was formally reminiscent of a historicist language, while the Department of Anatomy – designed by Max Littmann and built in exposed reinforced concrete – resulted in an organic unity of form, construction and material, the first such example in Munich and perhaps in Germany.     

中国航海博物馆帆体钢结构吊装技术

中国航海博物馆帆体钢结构为异形双层网壳,长70m,高58m,双帆相对呈合抱状.针对该钢网壳结构高耸直立的特点,以及建造于已施工完毕的标高12m混凝土平台上等复杂施工环境,布置了临时钢构架,结合柔性拉索,以提供钢结构的侧向稳定,并采用"工厂下料切割、现场整体拼装、构件分段短驳、起重机(结合液压提升)吊装就位,支承系统分步卸载拆除"的施工技术路线,取得了良好的效果.     

双水箱太阳能热水系统贮热水箱容积的比较研究

针对设置双蓄热水箱的集中式太阳能热水系统,以辅助热源能耗为目标,分析了不同贮热水箱容积的设置对系统辅助热源能耗的影响。并通过运用TRNSYS软件,建立动态分析模型,比较分析了不同太阳能保证率条件下,单位面积集热器对应的贮热水箱容积对系统性能的影响。分析结果表明:单位面积集热器对应的蓄热水箱容积最优值分布在50~70 L/m~2范围内;贮热水箱的容积对系统能耗的影响较小,在单位面积集热器对应的蓄热水箱容积为40~100 L的推荐值范围内,其辅助热源的最大值与最小值差异在1%以内。     

Analysis on the optimum matching of collector and storage size of solar water heating systems in building space heating applications

The overall thermal performance of a solar water heating (SWH) system is significantly affected by the mismatch between the temporal distribution of solar radiation and the heating load. Therefore, a favorable correlation between the collector and storage size should be generated based on the dynamic characteristics of the system. This study focuses on the optimal matching of solar collector area with storage volume for an SWH system (with short-term heat storage capability) for a space heating application. A simplified model of an SWH system based on hourly energy flow is established. System control strategy is integrated into the model in a simple manner without sacrificing computing speed. Based on this model, the combined effect of collector area and storage volume on system thermal performance and economy is analyzed, and a simple procedure for determining the optimal system size is illustrated. A case study showed that for an SWH system utilized for space heating application, the optimized ratio between storage volume and collector area is dependent on the total collector area of the system, and is dominated by the requirement of overheating prevention. The minimum storage volume for a specific collector area that can prevent the storage tank from being overheated can be adopted as the optimum storage volume for that collector area. The optimum ratio between storage volume and collector area increases as the collector area increases. Therefore, a trade-off between heat collection and heat loss has to be made while attempting to increase solar fraction by improving collector area.     

Collapse analysis of real RC spatial structures using known failure schemes of ferro‐cement shell models

Large‐span reinforced concrete (RC) shells collapses that occurred in the last decade caused many death toll as well as significant losses to national economies. The most famous cases were the collapse of the aqua park cover in Moscow on February 2004 and the 2E terminal roof destruction at Charles de Gaulle Airport near Paris on May 2004. Following the publications of the appropriate commissions that have studied the reasons of these events, the influence of concrete creep and changes in the shell geometry on buckling of RC thin‐walled shells was not properly considered in the design. This study is focused on buckling of such shells, taking into account geometrical and physical nonlinear behaviour of compressed concrete. Other important reasons of concrete shells collapse are also analysed. The study is based on available experimental and theoretical investigations of ferro‐cement shells' models previously performed by the first author. The results of these investigations, obtained for small‐scale ferro‐cement models of thin‐walled shallow RC shells, are discussed. Behaviour of the tested models is compared with that of the above‐mentioned real shells and similar structures, which also collapsed. The critical buckling loads for the shells are obtained. It is shown that these loads are lower than the actual ones; thus, the shells buckling was unavoidable. To prevent brittle shell failure, they should be designed using other dominant failure modes that appear before the buckling. Possible failure schemes of real RC shells can be predicted using dominant failure modes obtained by laboratory testing of scaled models. Copyright © 2012 John Wiley & Sons, Ltd.     

谈太阳能技术在民用建筑中的应用

结合太阳能的定义及工作原理,介绍了目前市场上三种太阳能集热器的功能,用途及特点,以全玻璃真空管太阳能集热器为例进行了系统分类及成本估算,并对相关材料、设备、安装设计要求作了具体说明,以促进太阳能技术在民用建筑中的应用。     

太阳能强化烟囱技术在通风采光装置中的应用研究

通过对室外的通风采光装置的通风管改造成透明玻璃管,形成集热器式太阳能烟囱,测试了烟囱的通风速率和温度变化情况,根据其工作原理计算了从9:00-17:00时之间的室内外空气压力差,证实了太阳能烟囱可以提高室内外的通风速度。     

Design and analysis of reflectivity for Mylar-coated solar dish

Energy is the key driver of the economy but energy crisis is a problem for the present-day source of energy. The concentrated solar power systems make use of different reflector configurations to convert the solar energy into high-temperature heat energy. Parabolic dish system is considered as the best suitable system for achieving high temperature and so it is opted for the study. Here, a solar dish is designed with an open diameter of 1.8?m (which is 2.5?m² in area), and reflective film is being used to reflect the solar irradiance and concentrated it in the focal point. A receiver of 1?mm thickness and 10?cm diameter is used at the receiver end to measure the temperature of the focal point. The setup has made to attain a maximum temperature of 940°C and average temperature of 850°C in the focal point at clear sky in a sunny day.     

Thermal solar water heater with H2O-Al2O3 nano-fluid in forced convection: experimental investigation

This paper describes laboratory experiments with a thermal solar water heater consisting of a flat-plate solar collector and helical coil heat exchanger using Al₂O₃ nano-particles dispersed in water as a working. The experiments were carried out for various nano-particle concentrations, from 0% to 3% (by volume), through forced convection cooling. The experiments were carried out under the climatic conditions of Tanta University, Egypt. The laboratory work has been carried out in actual thermal environment in August 2013. The experiments have an emphasis on the main parameters with impact on the water production temperature. These parameters include the solar radiation, the feed water mass flow rate and the nano-particle volume fraction. The main conclusion is that considerable improvement in the daily solar collector efficiency is obtained with increasing the nano-particle concentration up to 11% for concentration 3% with; this increase in efficiency is bounded by ±10% uncertainty. The outlet water temperature is increased with increasing of nano-particle concentration by 5.46% for concentration 2%. The helical heat exchanger effectiveness is increased by 4.25% for a concentration of 1% with ±13% uncertainty. The helical heat exchanger effectiveness and solar collector efficiency are increased with decreasing the working fluid mass flow rate.     

集中太阳能供热水系统研究

介绍了采用集中太阳能热水器的优点,以北京某小区为例,分析探讨了太阳能系统设计的基本要求和太阳能集热面积的设定,并将其与常规能源进行经济效益分析,指出太阳能热水系统具有良好的经济效益和社会效益。     

Numerische Simulation des Verhaltens von Betontragwerken unter Brandeinwirkung

Numerical Simulation of the Response of Fire Exposed Concrete Structure The proposed numerical model for concrete and reinforced concrete structures subjected to fire comprises the transient thermal and mechanical analysis considering the temperature dependent material properties of concrete and reinforcing steel within the framework of the phenomenological approach of the Eurocode 2, part 1‐2. A concrete model, based on the combination of plasticity and damage theory, serves as the basis for the material model of concrete for high temperatures. For reinforcing steel a standard elastic‐plastic material model is employed. The proposed model is validated by the numerical simulation of fire tests on plain concrete specimens and by the numerical simulation of a large scale fire test on a reinforced concrete slab. Furthermore it is used to determine the structural integrity of a tunnel structure, put up by the cut‐and‐cover method, exposed to fire.     

Energiespeicherbeton – ein Beton mit integriertem Latentwärmespeichermaterial

Energy storage concrete – a concrete with integrated latent heat storage material. In times of solar architecture and increased utilisation of renew‐able energy, building components with high thermal heat storage capability are becoming increasingly important. One of the areas future research in building physics and building services will focus on is the development of energy storage units. A particularly interesting research area is latent heat storage. This essay describes the development of a concrete with integrated latent heat storage material (phase change material, PCM) as part of a thesis. This innovative concrete offers significantly improved thermal characteristics. For example, it was possible to more than double the heat capacity within a temperature range of 10 Kelvin around the melting point of the PCM. The PCM has a melting point between approx. 22 °C and 35 °C, depending on application. A highly versatile material such concrete offers a wide range of application options. In principle, it is possible to use latent heat storage concrete to supplement heating systems, to extend the scope of passive solar systems, or to protect against overheating in summer.     

昆明学院洋浦校区综合教学大楼跨越结构设计

昆明学院洋浦校区综合教学大楼共9层,总高度为43.68m,主楼跨越结构部分有3层楼面及斜屋顶,跨度32.40m。在跨越结构的两端均设有钢筋混凝土剪力墙支撑体系,支撑体系及跨越结构均采用型钢混凝土。通过结构方案选择、计算结果分析、主要抗震措施的采用以及施工阶段的结构验算,研究了该种结构在设计及施工时应考虑的问题及采取的措...     

窗户型特殊温室太阳能热水系统热性能试验测试数据

本文用"特殊结构多重温室"来提高平板太阳能集热器的外部环境温度,并使环境温度高于集热器水温,则集热器不再向环境散失热量、热量反而从环境向集热器内的水倒流。试验测试结果:热效率达90%左右,外加"倒流热量",最后使"日有用得热量"达22.09MJ/m(2真空管最高仅9.87MJ/m2),实际热水产量冬季达80～116kg/m(2真空管冬季只有30～50kg/m2)。文中还分析测算了倒流热量。     

混凝土孔结构和渗透性能关系研究

混凝土材料从本质上讲是一种成分复杂的多孔材料,孔隙分布错综复杂,孔径分布很广,混凝土渗透性能和的微观孔结构有很强的相关性,而混凝土的渗透性能是影响结构耐久性的重要因素,通过概述混凝土的微观孔结构,包括孔隙率、平均孔径、临界孔径等对渗透性能的影响,参照国内外研究结果分析了不同参数作用的相关性.     

Modeling of an integrated solar system

The feasibility of using low-cost solar collection and storage technology to provide energy for residential units is investigated. Different construction strategies were compared including traditional housing practice against newly innovative ideas such as low radiant heating system, desiccant dehumidification, integrated low-cost solar collection, and phase-change material (PCM) storage. The selected building, located in Blacksburg, VA, integrated a solar thermal roof collection system consisting of a low-temperature flat-plate collector integrated within a concrete building envelope linked to a PCM storage tank. For the considered location and weather conditions (Blacksburg, VA), the proposed collection and storage solar system can supply 88% of the building's space heating and hot water needs averaged throughout the year saving the homeowner approximately 61.5% of the annual heating bills. However, the use of a storage system is not economical for the considered conditions. The paper also shows a month-by-month demand and supply distributions for the modeled building's heating and hot water needs.