A simple model for assessing the energy performance of windows

A simple model for the annual energy balance of the window taking solar radiation and heat losses into consideration has been further developed and analysed. Hourly meteorological data for the solar irradiation and the outside temperature are used together with the optical and thermal performance of the window to evaluate the net energy heat flow through a window. The model renders a very simple way to compare different advanced windows in different geographical locations, orientations and buildings using basically only the balance temperature as building input. The energy balance and the cost efficiency for several glazing combinations are evaluated for buildings with different balance temperatures in a typical mid-Swedish climate. This model has a potential to be used for energy rating of windows.     

Transient three-dimensional window thermal effects

A model is developed, and checked experimentally, to allow reasonably accurate computer calculations for three-dimensional temperature distributions in sunlit, partly shaded windows. The time evolution of surface temperature profiles, the sideways heat flow to and from adjacent walls, and the heating due to solar absorption in the glazing can be calculated. To reduce computation time, only two layers of cells were taken for each glazing pane, and uniform heat transfer was assumed between the panes. Nevertheless, the calculations matched well with experimental temperatures obtained for nine different full-scale windows at different orientations in a rotatable test hut on 27 clear or nearly clear winter days. In some winter experiments, an average of 15% of the 24-hour heat loss through a south window went sideways to the adjacent walls, with a minimum of 10% near noon, and a maximum of 20% near midnight. Near noon, with an ambient temperature of — 7°C (20°F), the centre of the inside of a south-facing triple-glazed window was above room temperature, due to solar absorption in the glass. At the same time, the inside of the shaded edge of the glazing was below room temperature.     

Improvement of thermal environment and reduction of energy consumption for cooling and heating by retrofitting windows

Various techniques for creating a comfortable thermal environment and saving energy have been proposed and employed in residential buildings in many countries, including Japan. For these techniques to be introduced, existing houses should be renovated. Among the techniques available, installation of additional inner windows is effective in creating a comfortable and energy-efficient living environment. In the present research, the effect of additional inner windows on the thermal environment and energy saving was investigated by measuring indoor windows on the thermal environment and energy saving was investigated by measuring indoor concrete building. Air temperatures, the humidity, the global solar radiation on horizontal and vertical surfaces, radiant temperatures, and the electricity consumption of air-conditioners were measured. A comparison of these values before and after the installation of inner windows showed that the thermal environment and energy saving had improved. Results obtained from a thermal model agreed well with measured results by changing the value of solar transmittance and heat transmission coefficient of the glazing following renovation. Furthermore, in a questionnaire survey conducted in summer, more than half of the occupants answered ‘‘comfortable’’ to a question on the overall thermal comfort.     

Description of ParaSol v3.0 and comparison with measurements

ParaSol is a computer program for calculating the solar and thermal properties of windows with sunshades and the energy demands of a room with a window/shading system. The program has three main features. One of them is a calculation of g, T and U for normal incidence of beam irradiation, which is performed as soon as a window or an internal/interpane sunshade is selected. The other two are based on yearly simulations, using DEROB-LTH, a building energy simulation program on which ParaSol is based. One of the applications gives the monthly average of g and T for the window glazing and the glazing/sunshade system. The other application gives the heating and cooling demands for a room with a window, with and without a sunshade, where input data are given for the internal heat, ventilation settings, shading control and temperature set-points. Version 3.0 of ParaSol, which has some new and improved models, is described in this paper. The g-values obtained with this program version are compared with measurements on windows with internal/interpane screens/venetian blinds. The absolute deviation is less than 0.03 for the venetian blinds. The measured values of dark internal screens with closed air gaps exceed those simulated by Parasol, but are lower than the ones simulated with open air gaps.     

建筑负荷预测中太阳辐射透过窗户引起的冷负荷

通过对建筑物玻璃窗所受太阳辐射得热的性能分析,建立了太阳辐射得热模型;根据《民用建筑热工设计规范》中划分的5个建筑热工分区,建立了典型玻璃窗的太阳辐射得热系数（SHGC）数据库,由此构建了透过玻璃窗的瞬时太阳辐射得热模型。参考DeST中的家具平板模型,建立了玻璃窗的室内蓄热平板模型,通过模型将太阳辐射得热量转化为瞬时冷负荷,并与相同条件下冷负荷系数法中的透过玻璃窗的日射得热形成冷的负荷进行对比,其相对误差不超过20％,满足城市规划阶段负荷预测的要求。从而为解决太阳辐射透过玻璃窗形成的冷负荷提供了一个新的思路,为修正用于区域能源规划中建筑负荷预测用的负荷因子模型提供了一个实用方法。     

Performance rating of glass windows and glass windows with films in aspect of thermal comfort and heat transmission

This article is about a study on glass window and glass window with film of different types in aspect of thermal comfort and heat transmission. Different types of glass window, clear glass, tinted glass, reflective glass, double pane glass, and low-e glass were investigated. Films with different spectral optical properties were then adhered to the glass windows of different types and studied. The analysis was done based on the outside design weather condition which selected from 12 years of Bangkok meteorological data. Predicted percentage of dissatisfied (PPD) was selected as the thermal comfort index. The relative heat gain (RHG) based on local weather condition was selected as the heat transmission index. The PPD can be subdivided into the PPD due to surface temperature effect and the PPD due to solar radiation effect. The analysis indicated that, for most of the glass windows considered except the reflective glasses, the values of PPD due to solar radiation effect were much larger than the values of PPD due to surface temperature effect. And the most discomfort condition occurred when using a clear glass as window. Adhered films to the glass windows caused the PPD due to surface temperature effect increase and cause the PPD due to solar radiation effect decrease. It was also found that the PPD values due to solar radiation effect for glass windows and glass windows with films were varied linearly with the total transmittance of glass windows and glass windows with films. The PPD values due to surface temperature effect were varied with the total absorptance of glass windows and glass windows with films in an almost linear fashion. The heat transmission index, RHG, based on chosen design weather condition can be subdivided into the RHG due to conduction effect and RHG due to solar radiation effect. The analysis indicated that the values of RHG due to solar radiation effect were larger than the values of RHG due to conduction effect for all glass windows and glass windows with films considered in this study. Adhered film to the glass windows resulted in lowering the relative heat gain due to solar radiation in the amount corresponding to the film properties. But the film had very few effect on the relative heat gain due to conduction. The relative heat gain values were varied linearly with the total transmittances of the glass windows and glass windows with films. The relative heat gain values were also varied inversely with the absorptances of glass windows and glass windows with films in a linear fashion.     

Experimental determination of thermal performance of glazed façades with water film,under direct solar radiation in the tropics

An experimental investigation of a glazed façade oriented west has been conducted utilizing the Sustainable Glazed Water Film (SGWF). The experiments involved the following three parameters namely: the water flow rate, the type of glazing, and the solar radiation intensity. Two full-scale rooms were used, one as a reference room, with a fixed configuration, and the other as a test room, which could be configured in different ways. The ability of the SGWF to reduce the passage of the solar energy during the sunny hours and hence to limit the heat passage through glazing was analyzed. The aim of this paper is to examine the improvement in thermal performance obtained by the flowing water film over glazed façades. It has been found that the flowing water film on the glazed façade lowers the glazing surface temperature by 7.2–14 °C (average) and absorbs a portion of the solar energy resulting in decreasing indoor temperature by 2.2–4.1 °C (average). However, with increased solar radiation intensity, the SGWF provides a better level of efficiency in reducing the heat transfer indoors.     

夏热冬冷地区居住建筑房间得热量分布及节能方向

采用多层板壁热力系统的反应系数法分析计算了典型气象条件下4个典型房间各围护结构的逐时传热量及其在房间得热量中所占比例。结果显示,在夏季典型气候条件下,单位面积围护结构对房间得热量的影响从大到小依次为外窗太阳辐射、外窗传热、屋顶传热、东西墙传热、南墙传热;白天由太阳辐射引起的得热量一直是房间得热量的主要部分;随着西向窗墙面积比的增大,西窗逐时传热得热量和辐射得热量呈线性显著增加;在夏热冬冷地区,必须提高窗户的遮阳性能,并降低窗户的传热系数,适当控制南向窗户面积,严格控制东西向窗墙面积比,建议西向窗墙面积比不大于0.2。     

Convective heat transfer coefficients in a full-scale room with and without furniture

The convective heat transfer coefficient at an outer ambient wall with a window exposed to natural climate was measured in a room with and without furniture. The method used was to estimate the heat flow from measured temperatures and solar radiation. The convective heat transfer was calculated as the difference between the heat flow through the building element and the calculated long-wave radiation. Even though the accuracy was at best ±15%, the effect of different heating and ventilation strategies could clearly be detected. Local coefficients may be more than 10 times the expected, due to ventilation or position of the radiator.     

基于Therm的不同标准条件下传热系数分析

目前国际上门窗传热系数的计算存在着北美ASHRAE和欧洲ISO10077—2两种不同的计算方法,而广泛应用的 Therm／Window软件和新近颁布实施的中国行业标准JGJ/T151—2008分别隶属于上述两种不同的算法,为了探讨ASHRAE和JGJ/T151-2008两种不同算法条件下,采用 Therm／Window计算整窗传热系数之间的差别,分析计算了铝固定窗、平开窗和推拉窗三种窗型在十种不同尺寸条件下整窗的传热系数。结果显示,对于所有窗型和尺寸来说,采用ASHRAE算法计算的整窗传热系数都比采用JCJ/T151—2008的要大,且两者之间的差值随整窗尺寸的增大而减小,固定窗为1．88％～0．04％,平开窗为3．71％-0．03％,推拉窗为4．91％-0．27％,大尺寸条件下两者计算结果近似相等,差值可忽略不计。采用理论分析的方法揭示了造成整窗传热系数存在差异的原因,认为不同的玻璃间隔条处理方法造成的窗框边角面积和玻璃边缘面积引起了计算结果的差异。     

Modeling windows in DOE-2.1E

The most recent version of the DOE-2 building energy simulation program, DOE-2.1E, provides for more detailed modeling of the thermal and optical properties of windows. The window calculations account for the temperature effects on U-value, and update the incident angle correlations for the solar heat gain properties and visible transmittance. Initial studies show up to a 35% difference in calculating peak solar heat gain between the detailed approach and a constant shading-coefficient approach. The modeling approach is adapted from Lawrence Berkeley Laboratory's WINDOW 4 computer program, which is used in the National Fenestration Rating Council (NFRC) U-value rating procedure 100-91. This gives DOE-2.1E the capability to assess the annual and peak energy performance of windows consistent with the NFRC procedure. The program has an extensive window library and algorithms for simulating switchable glazings. The program also accounts for the influence of framing elements on the heat transfer and solar heat gain through the window.     

The function of solar absorbing window as water-heating device

While window glazing will be more and more extensively used in modern architecture, the increase in space thermal load as a result will deteriorate the global environment, incurring problems of air pollution and climate change. By connecting the cavity of a double pane window to a water-flow circuit, absorbed solar heat at the window glasses can be readily removed by the water stream. The water passage in this way can effectively lower the glass pane temperature, reduce room heat gain and therefore, the air-conditioning electricity consumption. Thermal comfort can be enhanced. Furthermore, the water-flow window can function as a hot-water preheating device. This article reports the integrative thermal performance of a water-flow absorbing window as compared to the conventional single and double pane absorptive glazing. The results based on the operation in health club environment are very encouraging. This demonstrates its good application potential in domestic–commercial buildings with stable hot-water demands.     

Comparison between PCM filled glass windows and absorbing gas filled windows

From the thermal point of view, windows represent the weak link between the internal and external ambients of a room. In cold climates, they are responsible for 10–25% of the heat lost from the heated ambient to the external atmosphere. In hot climates, the excessive solar radiation entering the internal ambient through the windows leads to increasing the cooling load of the refrigeration system. The use of absorbing gases filling the gap between glass sheets appears to be an alternative solution for thermally insulated glass windows. The other options one may incorporate filling materials such as silica aerogel or a PCM. In this work, a comparison between the thermal efficiency of two glass windows one filled with an absorbing gas and the other with a PCM and exposed to solar radiation in a hot climate is done. To model double glass window filled with infrared absorbing gases, a CW real gas model is used. A radiative convective conductive model and a radiative conductive model were investigated. Three mixtures of gases were used; a strongly absorbing gas mixture, an intermediate absorbing gas mixture and a transparent to infrared radiation mixture. To model the double glass window filled with a PCM, a relatively simple and effective radiation conduction one dimensional formulation is used. Heat transfer through the window is calculated and the total heat gain coefficients are compared and discussed.     

双层窗的复合传热过程研究

应用不可逆热力学分析双层窗的复合传热过程,得出：在不考虑日射得热的条件下,自然对流换热及其对辐射换热的耦合传热是传热过程的主要因素,说明降低窗间气体的自然对流将是提高外窗的绝热性能的主要方向之一     

炎热地区夏季窗户的热过程研究

以重庆地区为例，探讨了炎热地区夏季南向和西向窗户的太阳辐射得热问题。认为辐射得热是导致室内热环境恶化的首要原因，西向铝合金双玻窗的辐射得热高达520W／m^2，而基于室内外温差的热流最大也不超过50W／m^2；对于南向窗，太阳直射对室内热环境影响相对较小，天空散射与环境反射是窗户得热的主要来源。对炎热地区的窗户节能而言，有效控制辐射得热、采用遮阳装置是问题的关键。     

建筑门窗玻璃幕墙传热系数现场测试研究

建筑门窗玻璃幕墙是建筑围护结构节能最薄弱部位,其传热系数目前只能在实验室通过热箱法测定,在现场准确、快捷地测试该值对于建筑的节能评估改造具有重要意义。在现场测试门窗幕墙内外空气温度和表面温度的基础上,推导出了基于"准稳态"测试原理和"热阻法"、"表面温度法"、"传热系数法"3种传热系数现场测试方法,现场测试值与实验室检测值的较高一致性表明了该现场测试方法的准确性,连续测试数据与平均值的较小偏差表明了该测试方法的稳定性。研究结果表明,建筑门窗玻璃幕墙传热系数可通过该方法在现场准确、快捷地测试得到。     

玻璃窗在建筑节能中的作用及其特性分析

本研究根据中国不同地区的气候特点,利用玻璃窗模拟软件Window5.1和建筑环境设计模拟分析软件DeST2,以一个典型住宅建筑模型为研究对象,通过模拟计算9种典型玻璃窗的热工特性以及冬季供暖和夏季供冷的能耗,分析并评估了不同类型玻璃窗的节能特性和对建筑能耗的影响。从而可得出如下结论:在严寒和寒冷地区建议采用中空高透射Low-e玻璃窗;在夏热冬冷地区选用中空 内遮阳窗户类型可比普通单窗节能近20%;而在夏热冬暖地区可以选择低透射Low-e玻璃窗、中空 内遮阳模式或者普通单玻 内遮阳模式均可达到理想的节能效果。为将来的建筑外窗节能设计以及玻璃窗的合理选型设计提供参考依据。     

Real climate experimental study of two double window systems with preheating of ventilation air

This paper aims to characterize the thermal performance of a window system that consists in doubling an existing window, converting it into a ventilated double window. The air coming from the outside circulates upwards through the channel between windows and enters the building through a vent on the top of the window's case. A series of experimental measurements was conducted in a test cell exposed to real outdoor weather conditions located in a mountain region at Centre of Portugal, during heating season in order to determine how this window system can act as a heat exchanger. It was found that such window system act as an efficient heat exchanger using transmission heat losses and solar radiation to preheat ventilation air, thus reducing the building's operational energy costs. An average of about 19 m³/h of air flow rate was found with an air temperature increment within the air gap of about 6 °C, during night-time, for an indoor/outdoor temperature difference of about 16 °C. Air temperature increment reached up to 12 °C using a plastic shutter. With solar radiation, the average of that increment was about 10 °C. This is a simple and cheap building technology which can be implemented both in new and existing buildings.     

Calculation of the thermal response of buildings by the total thermal time constant method

This paper describes the theoretical development and experimental proof of the total thermal time constant (TTTC) method for calculation of the thermal response of buildings. The output is obtained in the form of time sequences of temperature, under given time-variation of internal heating load, or in the form of time dependent heating (or cooling) loads, under given patterns of internal temperature variation in time.TTTC method considers ventilation conditions, internal heating, metabolic heat production, cooling, solar radiation absorption on, and longwave i.r. radiation loss from, the external surfaces, solar radiation penetration through windows and the external air temperature and humidity variations in time. The main feature of this method is that each component of the building is represented here, as a heat transfer path, only by two easy to calculate numbers: the thermal resistance and the TTTC (this includes thermal resistances and heat capacities and their relative position in the heat transfer path, including partitions and ceilings) [1–3]. The two parameters characterize the influence of the element on the thermal response of a building as a whole.Experimental demonstration of the accuracy of the TTTC method in computing the thermal response of buildings is presented and compared with measured temperature time patterns both in models and actual buildings under various external conditions. The method is useful not only for the thermal design of buildings and the selection of building materials, but also for the design of passive methods of climatization, e.g. by the use of solar radiation for heating, and conversely, the cooling of a structure by longwave radiation loss (to the outer space through the atmosphere) and by ventilation. Thermal storage and insulation properties are also considered.     

Energy performance assessment of a window with a horizontal Venetian blind

This study examines the effects of the presence of a Venetian blind on the thermal performance of a window. The blind is positioned adjacent to the indoor surface of either a single or double glazed window and the coupled convection and radiation heat transfer problem is solved using a two-dimensional finite volume model. The numerical model is validated with published experimental and numerical results in the literature. The results show that the presence of a Venetian blind significantly improves the energy performance of a single and double glazed window. The blind reduces the overall heat transfer rate through the window by reducing the thermal radiation from the indoor glazing. The improved understanding of the benefits of Venetian blinds may lead to better designs of window/shading systems.