The impact of town planning on the microclimatic conditions and energy consumption of residential buildings

An inexpensive conversion of a mirrored artificial sky from an overcast sky source to a clear sky source allows more extensive model investigation. For a solar altitude angle of 40°, the model sees the relative CIE standard clear sky luminance distribution away from the sun caused by a low perimeter source illuminating a cloth drape covering the mirrored walls. Problems in calibrating the “sky” are explained and compared to a model in a similar real sky and a computer calculation. The errors due to a shifts in angular relationship to the luminance distribution of a close artificial sky source are calculated for different room locations, window types and model sizes.     

A simplified method to estimate energy savings of artificial lighting use from daylighting

This paper provides a simplified analysis method to evaluate the potential of daylighting to save energy associated with electric lighting use. Specifically, impacts on daylighting performance are investigated for several combinations of building geometry, window opening size, and glazing type for four geographical locations in the United States. Four building geometries with various window-to-floor areas, along with different glazing types have been analyzed. It was determined that for most commercial buildings with glass transmittance values above 0.5, increasing window area to floor area ratio above 0.5, daylighting does not provide significant additional lighting energy savings. A direct correlation has been established between window transmittance and window area on annual lighting reductions. A model is proposed to estimate lighting energy savings given perimeter area, window area, and window type. Verification and validation of the model's predictions are demonstrated using results from building energy simulation as well as experimental data.     

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.     

Glazing daylight transmittances: a field survey of windows in urban areas

The effect of urban air pollution on glazing daylight transmittance was investigated by measuring the percentage loss in glazing transmittance of a number of windows throughout a large city in the UK. A total of 430 windows in a range of building types and locations were used to create the database for this window survey. The measurements were taken under overcast sky conditions to minimise errors that could occur during periods of rapidly changing sky luminance. In addition, two adjacent photocells were used so that simultaneous comparative measurements were taken. In general it was observed that the loss in transmittance for a vertical window did not usually exceed 10%. The factors that most significantly reduced glazing daylight transmittance were (i) the function/use of the building or the rooms within, (ii) the inclination of the window and (iii) the shading of the window by overhangs. It is, therefore, suggested that future daylight design guidelines should include these factors.     

Thermal performance of an electrochromic smart window tested in an environmental test cell

This paper describes the results of experimental tests and computer simulation modelling aimed at evaluating the performance of an electrochromic (EC) window with respect to solar control in buildings. The research is carried out by a test-cell equipped with a small area EC double glazing unit (EC-DGU) where one pane consists of an EC device and the other of a clear glass. The performance of the device on global light transmittance control, internal temperature control and solar heat gain control, is investigated in summer-time under real sky conditions as a function of time, test-cell orientation and switching strategies (static and dynamic). Both experiments and numerical analysis show that the decrease of the heat load affecting the test-cell, normalized respect to a clear float glass, is maximum when the EC-DGU is set to its lowest transmitting state and amounts to about 50% for west orientation and about 60% for south orientation. In this latter, thermal load reduction registered when the EC DGU is driven in the dynamic mode (31%) is similar to that of a reflective low-e glazing.     

Aussteifung von Gebäudehüllen durch randverklebte Glasscheiben

Stabilisation of building envelopes by the use of circumferential glued glass panels. The pursuit of maximum transparency with increasingly filigree bearing structures fuels the possibility of using the glazing as a load bearing element that is able to transmit both lateral and in plane forces. Space grid structures with rectangular glass panes seem to be very capable for this purpose. In this case the linear bars are normally pin‐joint at nodes to minimise both cross sections and erection cost. It is common to triangulate space grid structures with rods or prestressed steel cables. These bracings could be omitted if the stiffening forces would be transmitted by the glazing. In the here considered system the glass panes are used as shear panels to stabilize the envelope. Therefore, the panes are glued to the space grid members along their perimeter. Details were designed and the load bearing behaviour of the connections and the glass elements were investigated and design rules developed. These rules consider the shear interaction in laminated glass elements, and the interaction of in plane and out of plane loads.     

Optical and thermal performance of glazing with integral venetian blinds

Shading devices have long been used to control solar gain and daylighting through windows. The optimal design and use of such devices requires a detailed knowledge of their optical and thermal properties, including their variation with the angle of incidence of the solar radiation. We describe the experimental methods used to characterise two types of double-glazing units (DGU) incorporating Venetian blinds. The first consists of a DGU with an adjustable blind located in the space between the panes. The second incorporates a fixed blind element bonded between two glass sheets. The spectral bi-directional transmittance functions (BRTF) were measured for a range of incidence angles, using the Cardiff goniospectrometer. The thermal properties were measured with an illuminated hot box. These measurements are laborious, and it is desirable to develop simple models, that could be used for product development to estimate the effect of changing the properties of the blind material and its design, without the need to make detailed measurements on each variation. A model is described, that calculates the properties of the DGU using as input the optical properties at normal incidence of the component elements (glass and the blind’s slats). The model is applied to the variable blind DGU, varying the angle of rotation of the blind. Despite the simple nature of the model, it is shown to satisfactorily predict the properties of the DGU. The model can easily be incorporated in building energy simulation programs.     

A first approach to discomfort glare in the presence of non-uniform luminance

This study aims to elucidate the difference in glare sensation between uniform and non-uniform glare sources. In the experiment, the degree of discomfort glare is examined using simulated windows of uniform and non-uniform surface luminance. The window plane is divided into two parts, the upper and lower surfaces, and the luminance and solid angle of each surface are set differently. The upper and lower parts are assumed to be the sky and obstacle, respectively. Two conclusions follow from this study. First, the degree of discomfort glare for the uniform window is higher than it is for the non-uniform window, when the luminance of the uniform window is the same as the average luminance of the non-uniform window. Therefore, the discomfort glare sensation of the non-uniform window is different from that of the uniform window. Second, the glare source in the non-uniform window is restricted by luminance and originates from parts ranging from the highest level of luminance down to a level that is 61% of the highest level of luminance. These results may be useful for selecting the glare source in a window with a non-uniform luminance distribution.     

Experimental analysis of energy performance f a ventilated window for heat recovery under controlled conditions

A ventilated window in cold climates can be considered as a passive heat recovery system. This study carried out tests to determine the thermal transmittance of ventilated windows by using the Guarded Hot Box. By testing under defined boundary conditions, the investigation described the heat balance of the ventilated window and clarified the methodology for thermal performance evaluation. Comparison between windows with and without ventilation using the window-room-ventilation heat balance revealed that a ventilated window can potentially contribute to energy savings. In addition, it was found that a significant part of preheating occurred through the window frames, which positively influenced the heat recovery of the window but increased the heat loss. Results also showed that increasing air flow decreased the recovery efficiency until the point when the additional thermal transmittance introduced by the ventilation was higher than the effect of heat recovery. Accordingly, the use of the ventilated windows might be most suitable for window unit with low ventilation rates. The results correlated with theoretical calculations in standards and software. However, the concept of a window thermal transmittance (U_w) value is not applicable for energy performance evaluation of ventilated window and requires deeper analysis.     

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。     

中空窗玻璃贴低辐射膜的性能研究

热阻和太阳能透过率是分别反映窗玻璃热工性能和光学性能的参数.在不贴膜和室内贴低辐射膜2种情况下,对中空窗玻璃的热阻和太阳能透过率进行实验研究,分析和比较2种情况下的窗玻璃性能及其对节能性的影响.结果表明,实验所用中空窗的固定窗和推拉窗2部分,贴膜后传热阻分别增大31.1%和40.7%,传热系数分别降低23.7%和28.8%.对于玻璃的太阳能透过率,贴膜后从40%减少到28.6%,透过玻璃的辐射热减少28.5%.     

Spreadsheet-based calculation tool for direct daylight illuminance adaptable for different glazing properties and sky models

The methods normally used to calculate daylight illuminance of rooms are limited in their capacity to model different sky luminance distributions and different window glazing properties. A spreadsheet-based model is presented in this paper using first-principle calculations, which allows for a free choice of sky luminance distribution and glazing material properties. The glazing is specified in terms of material refractive index, absorption coefficient and thickness, and may be either single or double glazed. The calculations need to be repeated for each of a large number of small elements of window area, which is easily achieved using a spreadsheet. Use is illustrated by comparing the calculation of sky components with standard published data, and demonstrating the effect of substituting double for single glazing. The model was developed for educational use, but would also be useful for designers who need to investigate quickly the effect of altering glazing properties and sky conditions, without recourse to specialist software.     

单片建筑用玻璃光热性能浅析

玻璃作为建筑材料,在满足采光性能要求的同时,具有不同的光学热工性能,从建筑产品角度促进了绿色建筑发展.本文对各类单片建筑用玻璃产品的主要光学热工参数进行分析和讨论.     

Spannungsermittlung punktgelagerter Verglasungen unter Beanspruchung in Scheibenebene

Determination of the stress distribution of point supported glass structures under in‐plane loads. In this article a method for the determination of the stress distribution of point supported glass structures under the application of in‐plane loads is presented. To specify and calculate the load bearing of bolted connections in glass panels exact knowledge of the contact mechanisms and the parameters which influence the stress distribution around the hole is necessary. Due to the complex determination of the stress distribution mostly the structural safety is verified by full‐scale tests so far. An alternative is the numerical verification by finite element analysis (FEA). But therefore adequate program verifications are necessary. At first an approach for verifying the numerical model with an analytical solution is developed. To determine relevant results for design the verified FE‐model is used to examine the influences of different parameters on the stress distribution around the hole.     

A simplified procedure for determining indoor daylight illuminance using daylight coefficient concept

The first step in evaluating the visual performance and energy efficiency provided by daylight requires an accurate estimation of the amount of daylight entering a building. The actual daylight illuminance of a room is mainly influenced by the luminance levels and patterns of the sky in the direction of view of the window at that time. The daylight coefficient concept, which considers the changes in the luminance of the sky elements, offers a more effective way of computing indoor daylight illuminances. Recently, Kittler et al. have proposed a new range of 15 standard sky luminance distributions including the CIE (International Commission on Illumination) standard clear sky. Lately, these 15 sky luminance models have been adopted as the CIE Standard General Skies. This paper presents a graphical method to calculate interior illuminance for the CIE standard clear sky using the daylight coefficient approach. The simplified techniques in the form of a nomograph and Waldram diagram were established and described. The performance of the proposed approach was evaluated against the results obtained by an independent calculation approach and a computer simulation program. It was shown that the daylight illuminances estimated by our graphical tool were in reasonably good agreement with those produced from the other two methods. The findings provide building professionals and students a reliable and simple alternative that incorporates the daylight coefficient concept to estimate the interior daylight illuminance and assess daylighting performance.     

低辐射节能玻璃窗最佳镀膜位置的选择

将Low-E中空玻璃窗划分为单框双玻璃和单框三玻璃,利用WINDOW6.1软件建立单框双玻、单框三玻系统在不同镀膜位置和数量时的模型,并计算两种系统的传热系数、太阳得热系数、遮阳系数、可见光透射比和内表面温度等参数,分析以上参数对窗户能耗的影响,确定单框双玻窗和单框三玻窗玻璃系统的最佳镀膜位置。     

夏热冬暖地区中庭玻璃能耗分析

建筑中庭具有玻璃幕墙和玻璃顶棚,热阻较小,透射系数较大,不利于夏季的防热和冬季的保温。通过计算分析,得出不同玻璃类型产生的中庭能耗。正确选择玻璃类型,可以降低建筑中庭的能耗,达到节能目的。结果可为中庭设计提供依据。     

Analysis of the influence of installation thermal bridges on windows performance: The case of clay block walls

The building's energy performance is the result not only of material and component performances, but also of the way the components are interconnected. Concerning windows, their energy performance, which is usually evaluated by using the glass and frame heat transfer coefficients and the linear heat transfer coefficients of the glazing spacer, depends also on the frame installation. In this paper the entity of thermal losses due to the frame installation has been evaluated in terms of linear thermal transmittance calculated in accordance with the standard EN ISO 10211:2007 using THERM 5.2. The analysis of thermal bridges between a wooden frame window installed into two different kinds of external clay block walls has been carried out. The linear thermal transmittances have been calculated for three cases regarding the position (external, internal, and intermediate) and three concerning the insulation of the hole perimeter (non insulated, insulated and with insulation over fixed frame). The impact of the window installation on thermal losses has been estimated and its dependence on different sizes has been evaluated. A new graphical representation has been suggested. The frame position and the configuration of the window hole insulation result to have a relevant impact on the overall thermal performance of the considered window.     

Materials for reflective coatings of window glass applications

Special glass with reflective coatings has found wide applications in architecture. Thin coatings deposited on glass panes modulate the glass optical properties. Some of the coatings operate as a mirror for long-wave infrared radiation of building interiors. The thin films have high transmittance in visible range and very high reflectance in long-wave infrared range. These coatings limit absorption of infrared radiation in the glass. They have low emissivity. It means radiation heat losses of the coated glazing are reduced. The design of coatings for window glazing applications should be based on the study of optical spectral properties of glass and thin film materials. Optical properties of thin films are determined by spectral characteristics as reflectance, transmittance and absorptance for wavelength in a defined spectral range. Visible and long-wave infrared ranges are important for architectural glass. The article presents results of a study focused on the selection of convenient materials for thin reflective films and optimisation of their composition in coatings. Data from spectral measurements of transmittance and reflectance of selected types of architectural glass were compared with spectral characteristics of the designed coated glass simulated and optimised in the computer program FILM*CALC. The experimental vacuum deposition of the designed thin reflective coating on the glass substrate was carried out and spectrally measured. Apart from the spectral measurements the effect of the special glass reflectance was thermally evaluated in a testing box with the temperature sensor. Results from experiments, computer simulations and spectral measurements brought design recommendations for the optimised composition of thin infrared reflective coatings for window glazing applications.     

Appraisal of thermal performance of a glazed office with a solar control coating: Cases in Mexico and Canada

The use of solar passive strategies such as new solar control coatings on windows for buildings with large glazed areas, have recently become important and helpful tools, mainly because these developments help to reduce heat gains and/or losses through transparent materials, diminishing energy loads, and improving the environment inside buildings. This paper shows an assessment of the thermal performance for an office on top of a building with four different configurations of window glass, and their influence on the indoor conditions. The window glass configurations are: clear glass, glass-film (SnS–Cu_xS solar control coating), double-glass-film, and double clear glass. The simulations were carried out using weather data from Mexico City and Ottawa, which are a good representation of two extreme weather conditions, in order to assess the thermal behaviour inside offices, such as energy loads, costs for air conditioning, and the influence of interior heat transfer coefficient correlations. The results indicate that the glass-film proves to be the less appropriate configuration due to the high temperatures reached on the film surface, which has an impact on the air temperatures inside the office and contributes to increase the energy consumption. In general, the double glass-film configuration results to be adequate for both climates, nevertheless it shows a better performance for Ottawa than Mexico City, where a simple double clear glass would work the same way.