隔热涂层降低建筑顶层空调动态负荷的数值模拟

建立了屋顶和南外墙涂敷隔热涂层的房间的非稳态传热模型.利用该模型探讨了隔热涂层对房间空调动态负荷、日制冷量和室内热环境的影响,并采用北京、合肥、深圳3地夏季月平均气象数据,对当地建筑使用隔热涂层的节能效果进行了评估.研究发现:给建筑顶层外表面加装隔热涂层可显著降低房间空调负荷和日制冷量;整个夏季的空调平均日制冷量随地区的不同可降低40.0%～60.1%;隔热涂层还能显著降低房间外表面和内表面(尤其是天花板)温度的峰值和波幅,在节能的同时可改善室内热环境.     

不同典型气候区内建筑屋面及外墙使用隔热涂层后节能作用的分析与评价

利用典型气象年逐时数据,讨论寒冷、夏热冬冷和夏热冬暖地区典型城市的建筑在屋顶和外墙上使用低太阳辐射吸收率的隔热涂层后,全年空调和采暖能耗变化的情况。发现在属寒冷地区的北京使用隔热涂层,建筑冬季采暖能耗的增加量超过夏季空调能耗的减少量,这类地区更适合使用降低热损的保温层;在属夏热冬冷地区的上海,隔热涂层对全年能耗的影响与冬季采暖的方式有关:当采暖的能效比(EERh)与空调能效比(EERc)满足EERh/EERc<1.24时,使用隔热层全年没有节能收益;而采用集中暖气供暖方式(EERh=4.3),无保温层的建筑加装隔热涂层后,全年节能收益可达5.54kWh/m2,有保温层的建筑加装隔热涂层,全年节能收益也可达1.28kWh/m2。在属夏热冬暖地区的广州,与使用保温层相比,使用隔热涂层降低建筑空调能耗的效果更显著,全年单位面积节能收益是加装保温层时的2.65倍。     

隔热涂料用于建筑外表的热工性能等效折算方法

基于现有典型气象年气候数据,首先建立室外综合温度的计算模型,并用其考察表面长波发射率和短波吸收率对室外综合温度的影响。结论表明,表面短波吸收率对室外综合温度的影响很大,而长波发射率影响很小。然后,将室外综合温度进行分解,利用传热叠加原理和傅里叶级数展开理论,导出隔热涂料用于建筑外表的附加热阻和附加热惰性指标计算公式。最后,以厦门地区应用为例,计算水平屋面涂刷涂料的附加热阻和附加热惰性指标,提出利用附加热惰性指标和综合附加热阻评判隔热涂料在某地区应用的适宜性。     

双面受热太阳能平板接收器热性能模拟研究

为提高太阳能光热转换效率,建立同轴非完整型平移抛物面聚光系统。分析双面受热平板接收器的能量传递及转换过程,采用热阻网络图的分析方法建立平板接收器的理论计算模型。利用MATLAB 7.0软件编制程序实现了平板接收器的热性能计算。在结构参数、环境参数和进口参数确定的情况下,当吸热板导热系数、厚度和吸热板表面发射率变化时,分析温度、能量及热性能的变化趋势。研究表明：导热系数和吸热板厚度达到一定数值,继续增加对于提高接收器的热性能基本没有太大意义;吸热板表面发射率对热性能影响显著,采用发射率为0.1的选择性涂层可实现能量最大转化;环境温度在0～30 ℃变化时,双面受热比单面受热的热效率提高了8.18%～37.01%。     

极端热环境下被动式遮阳墙体设计与节能特性研究

为了降低空调能耗在建筑能耗中所占的比例,提出了一种基于太阳高度角的被动式遮阳墙体的设计方法,在太阳高度角较大时规避太阳辐射,在高度角较小时利用太阳辐射。以南京地区某住宅为例,采用EnergyPlus软件对建筑全年负荷进行了动态模拟,分析了被动式遮阳墙体节能效果的影响因素。研究结果表明,被动式遮阳墙体能根据太阳高度角调节各个配件的尺寸,同时,采用被动式遮阳墙体的建筑比参照建筑降低了18.82%的建筑冷负荷,节能效果显著。     

南京地区宾馆建筑能耗模拟及节能分析

建筑能耗在社会总能耗中占据了较大比例,并且具有较大的节能潜力.文中对南京地区的某个宾馆建筑的能耗进行了分析,研究了人口密度、外墙热阻、灯具及插座负荷、空调运行策略等因素对宾馆建筑能耗的影响,并针对宾馆建筑提出了相应的节能方案.研究结果表明:在使用节能策略后,宾馆建筑的全年能耗下降了16％,每年可节省约10万元的电费,节...     

中温太阳光谱选择性PbS涂层制备

对现有的中温太阳光谱选择性PbS涂层制备方法加以改进,直接在预处理过的铜片上化学镀PbS。首先,考察了反应温度、反应物浓度、加碱量和反应时间等对PbS涂层太阳吸收率α的影响,得到了制备PbS涂层的优化条件;然后,在PbS涂层上涂敷TiO2作为保护层,以延缓PbS涂层的氧化,对两种涂层表面进行了XPS和SEM分析。实验结果证明,在不明显影响吸收率的情况下,TiO2/PbS涂层的耐热性能、耐腐蚀性和耐磨性能比单纯PbS涂层有明显提高,从而达到既降低发射率又延缓涂层寿命的目的。     

涂层导热系数变化对换热器传热的影响

采用换热器效能法,对不同种类换热器进行校核计算.研究换热工质为气气、气液、液液时,不同种类换热器的换热性能随涂层导热系数的变化趋势.结果表明,各种换热器的总传热系数皆随涂层导热系数的增加而增大,且在不同低温侧流体雷诺数下增加程度不同,雷诺数越大,增加程度越大.设定涂层厚度为200.000 μm,涂层导热热阻所占比例随着...     

太阳吸收率与热发射率

现已知道,如果在太阳集热器的吸热表面上涂以一种特殊的材料——选择性吸收涂层,它不仅能使集热器最大限度地吸收太阳辐射能,而且可以大幅度地减少集热器向周围环境的辐射热损失,从而显著地提高太阳集热器的效率。两个重要的测量参数对于任何一种太阳能吸收涂层来说,都可以用两个重要的参数——太阳吸收率和热发射率来衡量它的热辐射性能。当太阳辐射能投射到涂层表面之后,一部分被吸收,一部分被反射。涂层的太阳吸收率,就是指涂层吸收到的太阳辐射能与投射在它上面的太阳辐射能之比值,通常用α_s表示。     

窗墙比和体形系数对办公建筑能耗的影响

济南地区某公共办公建筑,其围护结构按照高效节能的设计方法进行设计。运用Dest软件对该建筑进行能耗模拟,模拟该建筑的逐时能耗,分析不同体形系数和窗墙比对建筑物能耗的影响,以及两者共同作用下的影响。通过模拟结果得出:窗墙比对夏季负荷的影响要大于对冬季的影响,冬季窗墙比越大,能耗变化率相对较小;而体形系数的不同对建筑物空调能耗的影响变化较小。     

Performance of a coupled cooling system with earth-to-air heat exchanger and solar chimney

Buildings represent nearly 40 percent of total energy use in the U.S. and about 50 percent of this energy is used for heating, ventilating, and cooling the space. Conventional heating and cooling systems are having a great impact on security of energy supply and greenhouse gas emissions. Unlike conventional approach, this paper investigates an innovative passive air conditioning system coupling earth-to-air heat exchangers (EAHEs) with solar collector enhanced solar chimneys. By simultaneously utilizing geothermal and solar energy, the system can achieve great energy savings within the building sector and reduce the peak electrical demand in the summer. Experiments were conducted in a test facility in summer to evaluate the performance of such a system. During the test period, the solar chimney drove up to 0.28 m³/s (1000 m³/h) outdoor air into the space. The EAHE provided a maximum 3308 W total cooling capacity during the day time. As a 100 percent outdoor air system, the coupled system maximum cooling capacity was 2582 W that almost covered the building design cooling load. The cooling capacities reached their peak during the day time when the solar radiation intensity was strong. The results show that the coupled system can maintain the indoor thermal environmental comfort conditions at a favorable range that complies with ASHRAE standard for thermal comfort. The findings in this research provide the foundation for design and application of the coupled system.     

Computer simulation of solar cooled buildings in Khartoum

The transient state heat transfer formulation has been used to determine the air conditioning cooling load for two selected one room buildings in Khartoum: one made from brickwork and the other from wood. This formulation has been achieved by applying an explicit finite difference numerical techniques and adopting thermal network of electrical analogy to solve the transient conduction heat transfer equations. A computer program was developed to analyse the thermal network and to determine the cooling load for the wall, roof, window, ventilation and the total cooling load for each building for a typical hot summer day in Khartoum.A solar cooling system comprising mainly of a flat plate solar collector, a Lithium Bromide-Water absorption air conditioner, a storage and auxiliary tanks was integrated in the building and the energy equation for each component was obtained. A general simulation program for the solar cooled buildings has been developed and it was found that about 65% of the total cooling load demanded by the brick building could be supplied by energy from the solar collector, the other 35% portion had to be met by the auxiliary tank compared with 70% of the total cooling load demanded by the wood building which could be supplied by energy from the solar collector.     

Simulation–optimization of solar-assisted desiccant cooling system for subtropical Hong Kong

Solar cooling is a novel approach, which primarily makes use of solar energy, instead of electricity, to drive the air-conditioning systems. In this study, solar-assisted desiccant cooling system (SADCS) was designed to handle the cooling load of typical office in the subtropical Hong Kong, in which half of the building energy is consumed by the air-conditioning systems. The SADCS mainly consisted of desiccant wheel, thermal wheel, evaporative coolers, solar air collectors and gas-fired auxiliary heater, it could directly tackle both the space load and ventilation load. Since the supply air flow is same as the outdoor air flow, the SADCS has a feature of sufficient ventilation that enhances the indoor air quality. Although it is inevitable to involve the auxiliary heater for regeneration of desiccant wheel, it is possible to minimize its usage by the optimal design and control scheme of the SADCS. Through simulation–optimization approach, the SADCS can provide a satisfactory performance in the subtropical Hong Kong.     

Performance of a building integrated photovoltaic/thermal (BIPVT) solar collector

The idea of combining photovoltaic and solar thermal collectors (PVT collectors) to provide electrical and heat energy is an area that has, until recently, received only limited attention. Although PVTs are not as prevalent as solar thermal systems, the integration of photovoltaic and solar thermal collectors into the walls or roofing structure of a building could provide greater opportunity for the use of renewable solar energy technologies. In this study, the design of a novel building integrated photovoltaic/thermal (BIPVT) solar collector was theoretically analysed through the use of a modified Hottel-Whillier model and was validated with experimental data from testing on a prototype BIPVT collector.The results showed that key design parameters such as the fin efficiency, the thermal conductivity between the PV cells and their supporting structure, and the lamination method had a significant influence on both the electrical and thermal efficiency of the BIPVT. Furthermore, it was shown that the BIPVT could be made of lower cost materials, such as pre-coated colour steel, without significant decreases in efficiency.Finally, it was shown that by integrating the BIPVT into the building rather than onto the building could result in a lower cost system. This was illustrated by the finding that insulating the rear of the BIPVT may be unnecessary when it is integrated into a roof above an enclosed air filled attic, as this air space acts as a passive insulating barrier.     

Solar cooling for small office buildings: Comparison of solar thermal and photovoltaic options for two different European climates

We present a comparison of solar thermal and solar electric cooling for a typical small office building exposed to two different European climates (Freiburg and Madrid). The investigation is based on load series for heating and cooling obtained previously from annual building simulations in TRNSYS. A conventional compression chiller is used as the reference system against which the solar options are evaluated with respect to primary energy savings and additional cost. A parametric study on collector and storage size is carried out for the solar thermal system to reach achieve the minimal cost per unit of primary energy saved. The simulated solar electric system consists of the reference system, equipped with a grid connected photovoltaic module, which can be varied in size. For cost comparison of the two systems, the electric grid is assumed to function as a cost-free storage. A method to include macroeconomic effects in the comparison is presented and discussed.Within the system parameters and assumptions used here, the grid coupled PV system leads to lower costs of primary energy savings than the solar thermal system at both locations. The presumed macroeconomic advantages of the solar thermal system, due to the non-usage of energy during peak demand, can be confirmed for Madrid.     

相变材料和隔热材料降低顶层房间空调能耗效果之比较分析

针对合肥地区顶层房间,建立了在屋顶内外侧分别加装相变材料或隔热材料的房间的非稳态传热模型,比较分析了两种材料降低空调能耗的效果.研究发现:无论空调运行于恒温模式还是蓄冷模式,相变材料均未能完成一次凝固、熔解循环过程,相变材料利用率低,降低房间空调能耗的效果较隔热材料差;结合峰谷电价政策,房间空调蓄冷模式下日运行费用较小;综合考虑相变材料和隔热材料的节能性和经济性,选择隔热材料更为合理;在屋顶外侧加装隔热材料可使空调耗电量最大降幅为27.2%,空调日运行费用减少28.9%.     

Development of a numerical simulation system toward comprehensive assessments of urban warming countermeasures including their impacts upon the urban buildings'' energy-demands

One of the detrimental effects caused by the urban warming phenomena is the increase of energy consumption due to the artificial air-conditioning of buildings in summer. In greater Tokyo, the temperature sensitivity of the peak electricity demand reaches up to 3%/°C in recent years, and about 1.5 GW of new demand is required as the daily maximum temperature increases by 1.0 °C. This huge demand for summer electricity is considered to be one of the common characteristics of big cities in Asian countries. In order to simulate this increase in cooling energy demands and to evaluate urban warming countermeasures from the viewpoint of buildings' energy savings, a numerical simulation system was developed adopting a new one-dimensional urban canopy meteorological model coupled with a simple sub-model for the building energy analysis. Then, the system was applied to the Ootemachi area, a central business district in Tokyo. Preliminary verification of the simulation system using observational data on the outdoor and indoor thermal conditions showed good results. Simulations also indicated that the cut-off of the anthropogenic heat from air-conditioning facilities could produce a cooling energy saving up to 6% with the outdoor air-temperature decrease by more than 1 °C in the summer urban canopy over Ootemachi area.     

On optimal zone heating and energy conservation in passive solar buildings

Strategies for reducing the energy consumption of buildings include energy conservation, passive solar, and zone heating systems. In this paper, the constrained and global interzonal and overall building load coefficients, and the optimal mix of energy conservation, passive solar and zone heating are calculated as a function of economic and thermal parameters. Results are presented for the sensitivities of the optimal cost fractions to changes in the cost of passive solar and zone heating. For representative costs, the analysis indicated the largest component is energy conservation, followed by passive solar, zone heating and interzonal insulation.     

THE APPLICATIONS OF RENEWABLE ENERGY TECHNOLOGIES IN BUILDINGS

Considerable opportunities exist, most particularly (though by no means exclusively) in the design of new buildings, to integrate renewable energy technologies and thus reduce or even replace conventional energy sources. These technologies can include passive and active solar heating and cooling, and photovoltaic power. Such strategies to improve the energetic performance of buildings and to reduce their environmental impact will always be complemented by conservation and energy efficiency measures.

Passive heating, natural cooling and daylighting represent a spectrum of strategies whose applicability is modified by region and building type, and whose contribution varies from the modest fraction by which most buildings already benefit, to that in well-designed new buildings where the solar energy contribution may represent more than half (and in suitable cases, when combined with other solar techniques, all) of the energy conventionally required to provide comfortable thermal and visual environments. Active solar heating systems have achieved considerable maturity, and developed commercial markets already exist in a number of countries. And building-integrated photovoltaic systems promise to make significant impact within the coming decade.

This paper outlines R&D programmes undertaken within the European Communities to improve our understanding of the science and engineering of these technologies, and to advance the design and industrial adaptation necessary to bring about widespread implementation of renewable energy technologies in European buildings.