遮阳型节能玻璃的全年节能评价

提出遮阳型节能玻璃的全年节能评价新方法，即太阳辐射综合节能效率SEC计算公式，将夏季遮阳节能与冬季透光节能同时考虑，不仅包含太阳辐射、建筑体形等常规建筑热工问题，而且还加入供暖空调系统设备的能效问题，该评价方法可用于全国不同地区的建筑玻璃系统选型，对建筑物冬季太阳能的合理利用具有积极意义。     

玻璃幕墙建筑节能措施探讨

本文分析了室内气流速度、设置外遮阳、幕墙朝向、玻璃类型和玻璃夹层的填充气体等因素对玻璃幕墙建筑能耗的影响。结果表明,提高室内气流速度、在建筑室外种植树木或设置外遮阳、合理的玻璃性能组合是玻璃幕墙建筑夏季节能的有效措施。     

低辐射玻璃的节能性能分析

本文结合我国华北地区的气象条件对低辐射玻璃的热舒适性和节能性能进行了分析比较。计算结果表明 ,低辐射玻璃最适合于北方寒冷地区的东、西、北三个朝向的外窗 ,普通中空玻璃是建筑物冬季南向房间日照时刻的最佳节能玻璃。节能玻璃的选型不应忽视建筑物冬季太阳能的合理利用     

水平遮阳方式在住宅建筑南窗遮阳应用上的探讨

太阳辐射得热是夏季空调负荷的重要组成部分,同时也是冬季采暖负荷的安全系数。因此,合理的遮阳就成为暖通空调领域节能的一个途径。该文以平均遮阳系数作为衡量遮阳效果的指标,以住宅建筑的南窗为研究对象,针对水平遮阳方式,定量分析了我国一些地区水平遮阳板构型尺寸对冬夏季遮阳效果的影响程度。并在综合考虑多方面因素的基础上,给出了这些地区南窗遮阳板构型设计的最佳尺寸。     

建筑外遮阳检测系统热负荷的计算与分析

建筑遮阳的目的主要在于节约能源,提高热舒适与视觉舒适性。建筑遮阳分外遮阳和内遮阳。根据实际应用效果来看,外遮阳的遮阳隔热性能明显比内遮阳要好。介绍了建筑外遮阳检测系统的构造原理,通过计算建筑外遮阳检测系统夏季工作时的冷负荷,来确定夏季建筑外遮阳检测系统工作时的制冷量,同时根据计算结果进行空调设备的选型,并在实践中检验了效果。     

建筑遮阳的基本形式选择与比较

采取合理有效的遮阳措施,不但可以降低夏季外窗的太阳辐射透过率,大幅降低空调设备的能耗,还可明显地改善自然通风条件下的室内热环境。建筑遮阳可以分为外遮阳、内遮阳、玻璃自遮阳和绿化遮阳,通过对各种遮阳措施的分析比较,外遮阳是一种较为理想的遮阳方式,是可持续性建筑的首选,而对于夏热冬冷地区,应优先采用活动式的外遮阳。     

节能玻璃在建筑节能设计中的应用

分析了建筑节能玻璃的节能原理及传热系数U﹑可见光透射率T﹑遮阳系数Sc等三大性能指标。提出了在建筑节能设计中,节能玻璃的选择应遵循的原则。在此基础上,对影响建筑节能玻璃性能的主要因素进行了讨论,为节能玻璃在工程实践中的应用作出了指导。     

上海地区外遮阳系数对中层住宅能耗的影响

上海地区是夏热冬冷地区,文中研究遮阳系数对中层住宅制冷能耗、制热能耗、总能耗、单位面积制冷能耗、单位面积制热能耗、单位面积总能耗的影响效果;通过e QUEST能耗模拟软件分析夏热冬冷地区冬季使用空气源热泵等空调供暖还是选择市政供暖方式会更加的节能。经过分析模拟数据发现南向遮阳系数变化对能耗的影响最大、北向遮阳系数的变化对能耗影响较小,东、西方向遮阳系数的变化对能耗的影响最小;上海地区使用空调供暖的情况下较冬季市政供暖更加节能。     

冬暖夏凉型双层节能式窗户节能分析

冬暖夏凉型双层节能式窗户属最新国家专利,由外侧窗扇和内侧窗扇组成,内侧窗扇使用白玻璃,外侧窗扇使用遮阳型Low-E中空玻璃。该专利窗户冬暖夏凉,节能远远超过65%目标要求。     

低能耗房屋中窗户面积的优化选择

应用全年能耗模拟软件,分别用不同面积、类型的窗户玻璃对一栋住宅楼进行模拟计算,得到不同窗户玻璃在不同朝向的能耗,以及保持室内温度在20~26℃所需的最大能源。模拟结果表明在低能耗房屋中南向节能窗户的面积不是冬季采暖能耗的主要影响因素,而与夏季制冷能耗密切相关。因此,扩大北向窗户的面积,可获得更好的采光效果。从节能的角度出发,存在一个理想的南向窗户面积。     

Modeling and simulation of a simple glass window

This paper presents a mathematical model with numerical simulations of the heat transfer across a simple glass window. The model is two-dimensional, transient based upon the energy equation with a source term to account for the solar radiation absorbed through the glass sheet. Variable incident solar radiation and external ambient temperature are considered in the numerical simulations. The governing equations and the associated boundary conditions are discretized by the finite difference approach and the ADI scheme. Numerical simulations are realized for the cases of clear and absorbing glass to show the effect of the glass thickness on the total heat gain, the solar heat gain and the shading coefficient.     

Effect of absorption of solar radiation in glass-cover(s) on heat transfer coefficients in upward heat flow in single and double glazed flat-plate collectors

Absorption of solar radiation in the glass cover(s) of a flat plate solar collector increases the temperature of cover(s) and hence changes the values of convective and radiative heat transfer coefficients. The governing equations for the case of single as well as double glazed collector have been solved for inner and outer surface temperatures of glass cover(s) with/without including the effect of absorption of solar radiation in the glass cover(s), with appropriate boundary conditions. The effects of absorption of solar radiation on inner and outer surface temperatures and consequently on convective and radiative heat transfer coefficients have been studied over a wide range of the independent variables. The values of glass cover temperatures obtained from numerical solutions of heat balance equations with and without including the effect of absorption of solar radiation in the glass cover(s) are compared. For a single glazed collector the increase in glass cover temperature due to absorption of solar radiation could be as high as 6°. The increase in temperatures of first and second glass covers of a double glazed collector could be as high as 14° and 11°, respectively. The effect on the convective heat transfer coefficient between the absorber plate and the first glass cover is substantial. The difference in the values of the convective heat transfer coefficients between the absorber plate and the first glass cover (h_cp1) of a double glazed collector for the two cases: (i) including the effect of absorption and (ii) neglecting the effect of absorption in glass cover, could be as high as 49%. Correlations for computing the temperatures of inner and outer surfaces of the glass cover(s) of single and double glazed flat plate collectors are developed. The relations developed enable incorporation of the effect of absorption of solar radiation in glass cover(s) in the relations for inner and outer surface temperatures in a simple manner. By making use of the relations developed for inner and outer surface temperatures of glass cover(s) the convective and radiative heat transfer coefficients can be calculated so close to those obtained by making use of surface temperatures of glass cover(s) obtained by numerical solutions of heat balance equations that numerical solutions of heat balance equations are not required.     

Combined non-gray radiative and conductive heat transfer in solar collector glass cover

A rigorous approach for the radiative heat transfer analysis in solar collector glazing is developed. The model allows a more accurate prediction of thermal performance of a solar collector system. The glass material is analysed as a non-gray plane-parallel medium subjected to solar and thermal irradiations in the one-dimensional case using the Radiation Element Method by Ray Emission Model (REM by REM).This method is used to analyse the combined non-gray convective, conductive and radiative heat transfer in glass medium. The boundary surfaces of the glass are specular. The spectral dependence of the relevant radiation properties of glass (i.e. specular reflectivity, refraction angle and absorption coefficient) are taken into consideration. Both collimated and diffuse incident irradiation are applied at the boundary surfaces using the spectral solar model proposed by Bird and Riordan. The optical constants of a commercial ordinary clear glass material have been used. These optical constants (100 values) of real and imaginary parts of the complex refractive index of the glass material cover the range of interest for calculating the solar and thermal radiative heat transfer through the solar collector glass cover. The model allows the calculation of the steady-state heat flux and temperature distribution within the glass layer. The effect of both conduction and radiation in the heat transfer process is examined. It has been shown that the real and imaginary parts of the complex refractive index have a substantial effect on the layer temperature distribution. The computational time for predicting the combined heat transfer in such a system is very long for the non-gray case with 100 values of n and k. Therefore, a simplified non-gray model with 10 values of n and k and two semi-gray models have been proposed for rapid computations. A comparison of the proposed models with the reference non-gray case is presented. The result shows that 10 bandwidths could be used for rapid computation with a very high level of accuracy.     

槽式太阳能电站集热管热性能测试

采用硅碳棒加热技术和热平衡法测试了桑普生产的具有自主知识产权的槽式太阳能电站集热管的热性能。在40～300℃温度范围内,共测试8个工况下集热管热性能。实验结果显示,集热管中低温性能与肖特公司的PTR70相差不大,完全满足中低温槽式太阳能电站和其他太阳能中低温利用领域的应用。红外图像结果表明,玻璃-金属封接温度明显高于玻璃外管温度,对集热管进行理论分析时不能忽略此部分漏热量。实验数据的获得为国内太阳能槽式电站的设计、建设提供了实验参数,为集热管漏热测试相关标准的制定提供了基础。     

Comparative performance investigation of integrated collector‐storage solar water heaters with various heat loss reduction strategies

A detailed comparative assessment is reported on the thermal performance of integrated collector‐storage (ICS) solar water heaters with various strategies for reducing top heat losses. The objective of this investigation is to assess and compare heat loss reduction strategies. The shape of ICS solar water heater considered in present investigation is rectangular. The thermal performance of the solar water heater is evaluated and analyzed for the following cases: (1) single glass cover without night insulation; (2) single glass cover with night insulation; (3) double glass cover without night insulation; (4) transparent insulation with single glass cover; and (5) insulating baffle plate with single glass cover. Energy balances are developed for each case and solved using a finite difference technique. The numerical assessment of the system performance is performed for a typical July day in Toronto. Each strategy is observed to be beneficial, reducing top heat losses, and improving system performance. The greatest performance enhancements are observed for the water heater with a single glass cover and night insulation and for the system with a double glass cover and without night insulation. Copyright © 2010 John Wiley & Sons, Ltd.     

The Effect of Climatic Parameters on the Heat Transfer Mechanisms in a Solar Distillation Still

This paper deals with a simple and inexpensive solar desalination configuration. The performance of a simple solar still operating under Maltese climatic conditions is analyzed both theoretically and experimentally. The internal and external heat transfer modes of the distillation unit are examined. This paper concludes that the distillation rate in a simple solar distiller increases with ambient temperature and solar radiation, even though the condensation capacity of the glass is reduced. A higher wind speed decreases the evaporation and condensation processes. The energy fractions within the solar still have also been analyzed. The simulations and the experiments conclude that the glass components handle the bulk of the heat transferred in a solar still, namely, radiation, evaporation, and condensation, and thus the distillation efficiency is enhanced by improving the thermal and optical properties of the glass.     

Thermal modeling of solar stills: an experimental validation

Expressions for water and glass temperatures, yield and efficiency of both single and double slope multiwick solar distillation systems in quasi-steady state conditions have been derived. The analysis is based on the basic energy balance for both the systems. A computer model has been developed to predict the performance of the solar stills. Experimental validation of the thermal model has been carried out by using modified heat transfer coefficients. Internal heat transfer coefficients have been evaluated based on both inner and outer glass cover temperatures for typical days namely January 22, and June 19, 2001 in Delhi. A fair agreement has been observed between theoretical and experimental results by using the modified internal heat transfer coefficients based on inner glass cover temperature.     

A two dimensional thermal network model for a photovoltaic solar wall

A two dimensional thermal network model is proposed to predict the temperature distribution for a section of photovoltaic solar wall installed in an outdoor room laboratory in Concordia University, Montréal, Canada. The photovoltaic solar wall is constructed with a pair of glass coated photovoltaic modules and a polystyrene filled plywood board as back panel. The active solar ventilation through a photovoltaic solar wall is achieved with an exhaust fan fixed in the outdoor room laboratory. The steady state thermal network nodal equations are developed for conjugate heat exchange and heat transport for a section of a photovoltaic solar wall. The matrix solution procedure is adopted for formulation of conductance and heat source matrices for obtaining numerical solution of one dimensional heat conduction and heat transport equations by performing two dimensional thermal network analyses. The temperature distribution is predicted by the model with measurement data obtained from the section of a photovoltaic solar wall. The effect of conduction heat flow and multi-node radiation heat exchange between composite surfaces is useful for predicting a ventilation rate through a solar ventilation system.     

Theoretical approach of a flat-plate solar collector taking into account the absorption and emission within glass cover layer

A rigorous theoretical approach of a flat-plate solar collector with a black absorber considering the glass cover as an absorbing–emitting media is presented. The glass material is analyzed as a non-gray plane-parallel medium subjected to solar and thermal irradiations in one-dimensional case using the Radiation Element Method by Ray Emission Model (REM²). The optical constants of a clear glass window proposed by Rubin have been used. These optical constants, 160 values of real part n and imaginary part k of the complex refractive index of a clear glass, cover the range of interest for calculating the solar and thermal radiative transfer through the glass cover. The computational time for predicting the thermal behavior of solar collector was found to be prohibitively long for the non-gray calculation using 160 values of n and k. Therefore a suitable semi-gray model is proposed for rapid calculation. The profile of the efficiency curve obtained in the present study was found to be not linear in shape. Indeed, the heat loss from the collector is a combination of convection and radiation and highly non linear. The effect of the outside convective heat transfer on the efficiency curve is also studied. In fact, when the convection is the dominant heat transfer mode compared with the radiation one, the profile of the efficiency curve is more or less straight line. Consequently, the heat loss coefficient could be calculated using Klein model. It has been also shown that the effect of the wind speed on the glass cover mean temperature is very important. This effect increases with the increase of the mean absorber temperature.     

Heat losses from parabolic trough solar collectors

Parabolic trough solar collector usually consists of a parabolic solar energy concentrator, which reflects solar energy into an absorber. The absorber is a tube, painted with solar radiation absorbing material, located at the focal length of the concentrator, usually covered with a totally or partially vacuumed glass tube to minimize the heat losses. Typically, the concentration ratio ranges from 30 to 80, depending on the radius of the parabolic solar energy concentrator. The working fluid can reach a temperature up to 400°C, depending on the concentration ratio, solar intensity, working fluid flow rate and other parameters. Hence, such collectors are an ideal device for power generation and/or water desalination applications. However, as the length of the collector increases and/or the fluid flow rate decreases, the rate of heat losses increases. The length of the collector may reach a point that heat gain becomes equal to the heat losses; therefore, additional length will be passive. The current work introduces an analysis for the mentioned collector for single and double glass tubes. The main objectives of this work are to understand the thermal performance of the collector and identify the heat losses from the collector. The working fluid, tube and glass temperature's variation along the collector is calculated, and variations of the heat losses along the heated tube are estimated. It should be mentioned that the working fluid may experience a phase change as it flows through the tube. Hence, the heat transfer correlation for each phase is different and depends on the void fraction and flow characteristics. However, as a first approximation, the effect of phase change is neglected. Copyright © 2013 John Wiley & Sons, Ltd.