Glazing energy performance and design optimization with daylighting

This study systematically explores the influence of glazing systems on component loads and annual energy use in prototypical office buildings. The DOE-2.1B building energy simulation program, which contains an integrated daylighting model, is used to determine fenestration energy performance in diverse climates. The sensitivity of total energy use to orientation, window area, glazing properties (U-value, shading coefficient, visible transmittance), window management strategy, installed lighting power, and lighting control strategy are all described. We examine the conditions under which daylighting reduces net anual energy use as well as those conditions under which energy use may increase. Combinations of wall and fenestration properties that minimize net energy requirements as a function of climate and orientation are described.     

基于MIT Design Advisor的门窗设计——窗墙比对建筑采光的影响

外窗设计是建筑立面设计的重要方面,外窗的大小对建筑的采光能耗等有着重要的影响,我国建筑采光设计标准中对建筑的窗地面积比有着不同的要求,在建筑地面面积和墙面面积不变的情况下,窗地面积比也可以通过窗墙比来反映。本文利用MIT Design Advisor模拟计算了不同窗墙比对建筑空间采光和工作面采光性能的影响。     

Estimation of lighting energy savings from daylighting

This paper refines and validates the predictions of a simplified analysis method for evaluating the potential of daylighting to save energy use associated with electrical lighting. Specifically, impacts on daylighting performance are investigated for several combinations of building geometry, window size, and glazing type for several US and international locations. The impact of both dimming and stepped daylighting controls and their settings are also investigated. Predictions from the simplified method are validated using measurements obtained from field-testing of a daylighting control system utilized to operate lighting fixture illuminating an office space.     

外窗尺寸对办公建筑采光影响因素研究

外窗作为建筑重要的外围护结构,不仅会影响建筑采光,同时,还会影响建筑照明、空调、供暖能耗。在相同外窗面积条件下,为获得更好的采光效果,可以在不增加空调及供暖能耗的前提下有效减少建筑的照明能耗,进而降低整体建筑能耗。通过计算机模拟分析办公建筑外窗尺寸对有效采光宽度、有效采光深度、有效采光面积的影响,总结出不同吊顶高度下的采光效果指标的查询图标,供外窗设计参考。     

The New York Times Headquarters daylighting mockup: Monitored performance of the daylighting control system

A 9-month monitored field study of the performance of automated roller shades and daylighting controls was conducted in a 401 m² unoccupied, furnished daylighting mockup. The mockup mimicked the southwest corner of a new 110 km² commercial building in New York, New York, where The New York Times will be the major tenant. This paper focuses on evaluating the performance of two daylighting control systems installed in separate areas of an open plan office with 1.2-m high workstation partitions: (1) Area A had 0–10 V dimmable ballasts with an open-loop proportional control system and an automated shade controlled to reduce window glare and increase daylight, and (2) Area B had digital addressable lighting interface (DALI) ballasts with a closed-loop integral reset control system and an automated shade controlled to block direct sun. Daylighting control system performance and lighting energy use were monitored. The daylighting control systems demonstrated very reliable performance after they were commissioned properly. Work plane illuminance levels were maintained above 90% of the maximum fluorescent illuminance level for 99.9 ± 0.5% and 97.9 ± 6.1% of the day on average over the monitored period, respectively, in Areas A and B. Daily lighting energy use savings were significant in both Areas over the equinox-to-equinox period compared to a non-daylit reference case. At 3.35 m from the window, 30% average savings were achieved with a sidelit west-facing condition in Area A while 50–60% were achieved with a bilateral daylit south-facing condition in Area B. At 4.57–9.14 m from the window, 5–10% and 25–40% savings were achieved in Areas A and B, respectively. Average savings for the 7-m deep dimming zone were 20–23% and 52–59% for Areas A and B, respectively, depending on the lighting schedule. The large savings and good reliability can be attributed to the automatic management of the interior shades. The DALI-based system exhibited faulty behavior that remains unexplained, but operational errors are expected to be resolved as DALI products reach full maturity. The building owner received very competitive bids ($30–75 US/DALI ballast) and was able to justify use of the daylighting control system based on operational cost savings and increased amenity. Additional energy savings due to reduced solar and lighting heat gains were not quantified but will add to the total operational cost savings.     

夏热冬冷地区办公建筑自然采光效果模拟分析

选取夏热冬冷地区苏州市某办公建筑作为模拟对象,采用Ecotect结合Radiance软件模拟建筑内自然采光情况,计算建筑内各楼层的平均自然采光系数与全自然采光百分比,分析玻璃可见光透射比、窗墙比对建筑自然采光效果和照明能耗节约量的影响。研究表明,采用可见光透射比较高的玻璃,适当增加建筑外窗面积,有助于提高建筑采光系数,改善自然采光环境,节约建筑照明能耗。     

Development of an optimal daylighting controller

A new lighting and daylighting control strategy is modeled and evaluated against conventional lighting and daylighting controls. The new lighting and daylighting control strategy can be incorporated in an energy management and control system (EMCS) to operate and control lighting fixtures in any indoor space. The new daylighting control can also be modeled and integrated in detailed building energy simulation tools. Through a validation analysis, it was found that the new control strategy provides more energy savings than conventional daylighting controls. Moreover, the validation analysis has indicated that existing daylighting control simulation analysis tools could overestimate lighting energy savings associated with daylighting controls. Moreover, it was also found that if calculated solar and illuminance data are used instead of measured solar radiation data, the errors in predicting lighting energy use when daylighting controls are utilized can be significant.     

Analysis and modelling of window and glazing systems energy performance for a well insulated residential building

The energy performance of a window depends on its thermal transmittance, the glazing solar transmittance, and the air leakage due to the frame and installation airtightness.In new installations air leakage represents a quite small term which is almost independent from the window and in particular from the glazing system selection.The contributions of the two other terms to the building thermal balance are not independent to each other: the most effective thermal insulating glazing, as triple glazings, are generally characterized by low solar transmittance reducing solar gains. The thermal energy balance of the building is then affected not only in summer but also in winter, potentially increasing heating energy need.This work evaluates the impact of different kinds of glazing systems (two double and two triple glazings), window size (from 16% to 41% of window to floor area ratio), orientation of the main windowed façade and internal gains on winter and summer energy need and peak loads of a well insulated residential building. The climatic data of four localities of central and southern Europe have been considered: Paris, Milan, Nice and Rome. A statistical analysis has been performed on the results in order to identify the most influencing parameters.     

Adding advanced behavioural models in whole building energy simulation: A study on the total energy impact of manual and automated lighting control

Behavioural models derived from on-going field studies can provide the basis for predicting personal action taken to adjust lighting levels, remedy direct glare, and save energy in response to physical conditions. Enabling these behavioural models in advanced lighting simulation programs, such as DAYSIM and the Lightswitch Wizard, allows for a more realistic estimate of lighting use under dynamic conditions. The current downside of these approaches is that the whole building energy impact of manual changes in blind settings and lighting use, including its effect on heating and cooling requirements, is not considered. A sub-hourly occupancy-based control model (SHOCC), which enables advanced behavioural models within whole building energy simulation, is presented. The considered behavioural models are the Lightswitch2002 algorithms for manual and automated light and blind control, while the investigated whole building energy simulation program is ESP-r.The enhanced functionality is demonstrated through annual energy simulations aiming at quantifying the total energy impact of manual control over lights and window blinds. Results show that building occupants that actively seek daylighting rather than systematically relying on artificial lighting can reduce overall primary energy expenditure by more than 40%, when compared to occupants who rely on constant artificial lighting. This underlines the importance of defining suitable reference cases for benchmarking the performance of automated lighting controls. Results also show that, depending on the proportion of buildings occupants that actively seek out daylighting, reduced lighting use through automated control may not always produce anticipated savings in primary energy for indoor climate control. In some cases, reduced lighting use is shown to even increase primary energy expenditure for indoor climate control, trimming down initial primary energy savings in lighting alone. This reveals the superiority of integrated design approaches over simpler daylighting guidelines or rules of thumb.     

An analysis of daylighting performance for office buildings in Hong Kong

Daylighting has often been recognized as a useful source of energy savings and visual comforts in buildings. Occupants expect good daylight in their working spaces. The quality and quantity of natural light entering a building depend on both internal and external factors. In Hong Kong, commercial building accounts for the major building energy use and electric lighting is one of the major electricity-consuming items. This paper studies the daylighting performance and energy implications for office buildings. A total of 35 commercial buildings have been selected in the survey. Key building parameters affecting daylighting designs are presented. Two typical office blocks were further analysed based on a lighting simulation program. The daylighting performance was evaluated in terms of daylight factor, room depth and glare index. It has been found that the daylighting performance for office buildings is quite effective. About one-third of the office areas that are near the perimeter regions have an average daylight factor of 5%. For inner region of deep plan offices, some innovative daylighting systems such as light redirecting panels and light pipe could be used to improve the daylighting performance. In general, the office building envelop designs are conducive to effective daylighting and proper daylight linked lighting controls could save over 25% of the total electric lighting use.     

Assessment of daylight in rooms with different architectural features

Results are presented from a parametric study that assessed the amount of daylight in rooms with different architectural features: the orientation, window size and visible glazing transmittance, room depth, external obstruction angle and site. Annual lighting simulations were run in order to understand how the daylight availability within a space changes as a function of the architectural features. A sub-dataset of the full result database is examined in detail for north- and south-facing rooms in Turin, north-west Italy, with a visible glazing transmittance of 70%. Each feature is analysed for its influence on the daylighting conditions. A simple graphical tool is presented to promote an easier reading of the results. This was developed to provide a synthesis of information to the design team. It shows the influence of preliminary design solutions on the amount of indoor daylight. This allows a design team to assess indoor daylighting from the earliest design phases onwards and to determine which combinations of architectural features are able to provide high, acceptable or low daylight levels within a room.     

The predicted impact of roof aperture design on the energy performance of office buildings

An investigation has been made of potential lighting electricity reductions and associated thermal impacts of replacing electric light with sunlight admitted through rooftop glazing on a single-story, prototypical office building. Experimental scale models have been used to determine the fraction of the solar radiation entering the aperture which reaches the work plane as useful illumination. This information is used in a developmental version of the building energy analysis computer program BLAST-3.0 to predict reductions in lighting electricity and the impacts on energy consumption for heating and cooling the building. The results indicate that a large fraction of the electricity consumed for lighting a single-story office building can be displaced using modest amounts of glazing in the roof. Also, both heating and cooling energy consumption reductions are possible from a daylighting system, but they are substantially smaller than the potential lighting electricity reductions. The design implications of the results are discussed and future directions for the work are outlined.     

Prospective techniques of effective daylight harvesting in commercial buildings by employing window glazing, dynamic shading devices and dimming control—a literature review

Over a few decades, daylighting has been perceived to possess good potential for energy conservation. In this perspective, there have been significant advances in research methodologies and technologies for optimizing energy consumption through daylight harvesting in commercial buildings. In light of this, a thorough understanding of the application of available technology is very important for daylighting practices for building energy management. The objective of this paper is to examine the status of published research on three key building parameters: window glazing area, dynamic shading devices, and daylighting controls playing a rule on energy conservation. This article may serve as a coherent literature survey that would provide better understanding of the subjacent issues and possibly rejuvenate research interest in this immensely potential field of energy engineering.     

夏热冬冷地区三维空间视角下住宅南向窗节能研究

外窗属于外围护结构之一,是建筑的重要组成部分,也是建筑保温中最薄弱的环节。窗的开设与建筑节能密切相关。夏热冬冷地区南向窗应属整套住宅建筑的主要采光源,其窗户面积大小变化对采光率影响较大。以夏热冬冷地区——桂林市南向窗采光良好条件为基础,以"窗墙面积比"和"窗地面积比"作为研究变量,以能耗模拟软件Ecotect模拟作为研究方法,在三维空间视角下进行建筑热环境模拟研究,确定了南向房间节能的"窗墙面积比"与"窗地面积比"取值范围,为今后的夏热冬冷地区——桂林市住宅建筑的节能设计提供一定的参考依据。     

The impact of daylighting on peak electrical demand

A complete analysis of the cost-effectiveness of daylighting strategies should include the impact of daylighting on peak electrical demand as well as on energy consumption. We utilized an hour-by-hour building energy analysis program to study the thermal and daylighting impacts of fenestration on peak demand. Fenestration properties and lighting system characteristics were varied parametrically for office buildings in Madison WI and Lake Charles LA. Peak electrical demand was disaggregated by component and by zone, monthly patterns of peak demand were examined, and impacts of fenestration performance on chiller size were studied.The results suggest that for daylighted office buildings, the peak electrical demand results from a complex trade-off between cooling load due to fenestration parameters, lighting load reductions due to glazing and lighting system characteristics. Lowest peak demands generally occur with small to moderate size apertures. With daylighting, peak electrical demand is reduced by 10 to 20% for the building configuration studied (37% perimeter zone, 63% core zone). This work indicates that solar gain through fenestration must be effectively controlled in order to realize the potential of daylighting to significantly reduce peak electrical demand.     

Impact of electric lighting efficiency on the energy saving potential of daylighting from roof monitors

A developmental version of the building energy analysis computer program BLAST was used to perform simulations of a prototypical, single-story office building. Total annual energy consumption was computed using Typical Meteorological Year (TMY) [1] weather data from three locations in the United States. For each location, two electric lighting designs were tested on the baseline building (no roof monitors) to compare the energy requirements of current-practice and more efficient electric lighting designs. Then roof monitors were added to evaluate their energy saving potential for each of the electric lighting designs. The roof monitors had highly diffusing, vertical glazings facing southeast and southwest.The results show that improving electric lighting system efficiency and adding roof monitors for daylighting both have the potential for substantially reducing lighting electricity and the energy cost of operating the building. The potential benefits of daylighting are substantially lower for a building outfitted with a more efficient electric lighting system, although still significant. To determine the limits of validity of the simulations, a number of sensitives studies were performed. Among the issues investigated were: dirt deposits, snow accumulation, glazing optical properties, interior design, luminous efficacy of admitted sunlight, and thermostatic controls.     

Indoor thermal environmental conditions near glazed facades with shading devices – Part II: Thermal comfort simulation and impact of glazing and shading properties

This second part of the study uses a validated dynamic building thermal model for perimeter zones with glass facades (described in Part I) and combines it with a transient two-node thermal comfort model. The objective is to investigate the impact of varying exterior climatic conditions, glazing properties and shading properties on indoor thermal comfort and heating demand in such spaces under the presence of transmitted solar radiation. It is evident that selecting appropriate fenestration components becomes a trade-off between energy, thermal comfort, and lighting needs. Facades with insulating and low transmittance glass create more comfortable and stable conditions; however, there is a relationship between lower transmittance of the glazing and increased demand of primary heating needed, as well as with lighting energy use. Regardless of glazing type, shading can improve comfort conditions by decreasing radiant temperature asymmetry and extremes in operative temperature. The results show that perimeter building zones with high-performance facades (glazing and shading) can maintain comfortable conditions and even eliminate the need for secondary perimeter heating in cold climates.     

Simplified daylighting energy savings for non-daylighting building energy simulation programs

The California Legislature mandated the California Energy Commission (CEC) to establish and periodically update energy efficiency standards for new buildings. To this end, a sensitivity analysis was conducted by the Standards Development Office of the California Energy Commission for nonresidential buildings. The purpose of this parametric analysis was to determine which variations in building parameters actually have significant energy impacts.A “generic” building model was developed and implemented in conducting this sensitivity analysis. The generic model was used as an analytical tool in modeling the energy impact of building parameter variations, as well as architectural and mechanical energy-saving measures on the energy use of each module. It is recognized that the level of significant energy impact is equivalent to, or bounded by the accuracy of the energy analysis tools in predicting energy usage in actual buildings. For the computer program used, DOE 2.1A this accuracy is within ±5%.Since DOE 2.1A and most of the other building energy simulation programs do not have daylighting algorithms, another calculation tool was used to determine daylight availability and lighting power reduction on an hour-by-hour basis for each orientation. This is accomplished with a daylight reduction factor (DRF).Quicklite, a simplified daylighting program, calculated footcandle (lux) levels based on outdoor ambient light levels, physical room dimensions and properties. To assess the impact of the Quicklite calculated footcandle (lux) levels on artificial lighting use, a control scheme was assumed, and a DRF was calculated based on annual sky conditions by climate zone.Once the DRF values are known for each orientation, the electric lighting schedule can be modified. A new profile number, representing the proportion of installed lighting switched on at that hour, replaced the daily lighting schedules when daylighting was utilized (09:00 – 17:00). To test this methodology, a sensitivity analysis was conducted between DOE 2.1A with Quicklite modifications and DOE 2.1B which has a daylighting preprocessor. The results displayed a 3.6% variation in total energy use.We conclude that daylighting calculations for design days using simplified programs can be used to approximate daylighting energy savings in building energy simulation programs that allow zoned lighting schedules but do not calculate daylight contributions.     

Sun-control options in a high-rise office building

The DOE-2 building energy analysis computer program has been used to study the life-cycle cost and annual energy use for a wide range of glazing and sun-control options in a 25-story office building with 50% glazing. Four climates in the U.S. have been analyzed: Miami, Los Angeles, Washington, DC, and Chicago. The impact of daylighting in the perimeter zones for the various sun-control options has also been investigated. Double glazing was found to have little effect on energy use in Miami and Los Angeles, but reduced energy use 11–23% in Washington, DC, and 16–32% in Chicago, Daylighting reduced energy use 10–22% and had a simple payback period of 3.7–8.9 years depending on climate and type of fenestration. Of the alternatives considered, the lowest life-cycle cost and energy use were obtained with daylighting coupled with clear glazing and exterior sun-control blinds.     

Prediction of energy savings with anidolic integrated ceiling across different daylight climates

The subject of this article is building energy saving on electrical lighting by anidolic integrated ceiling (AIC), compared in different daylight climates. This particular device collects diffuse daylight with an anidolic external collector and channels it into a reflective ceiling plenum. The exit apertures located at the rear of the room will discharge the daylight to the deep and gloomy zones of the room and thus reduce demand for electrical lighting. This paper analyses the savings on building energy for different locations. Two cases were studied with Singapore representing a location of high sun altitude and high building density, while Sheffield representing a location of lower sun altitude and moderate urban density. The performance criteria Daylight Autonomy (DA) was used to quantify the energy saving, after the AIC was integrated into the default ribbon window façade of a standard office room. Computational simulations show that more than 20% of energy for electrical lighting can be saved. The energy savings are quite similar for both locations, with 21% for Singapore and 26% for Sheffield. Therefore, it is valid to conclude that AIC is a universal remedy to improve daylighting and energy efficiency in deep buildings.