An Ideal Window Area concept for energy efficient integration of daylight and artificial light in buildings

There have been many developments in energy efficiency in buildings in the last few decades, but many new buildings are still not designed whereby daylight is efficiently integrated with the artificial lighting system. In cases where there is integration, the potential for energy savings to be made on lighting is not always assessed. This paper presents a methodology to predict the potential for energy savings on lighting using an Ideal Window Area concept when there is effective daylight integration with the artificial lighting system. The methodology was developed by using rooms of ten different dimensions and five different room ratios. The energy analysis work was performed using the VisualDOE programme for the climatic conditions of Leeds, in the UK, and Florianópolis, in Brazil. Following this, the potential for lighting energy savings was assessed for each room using a method based on Daylight Factors. It was observed that the potential for energy savings on lighting in Leeds ranged from 10.8% to 44.0% over all room sizes and room ratios for an external illuminance of $\text{5000}\text{lux}$; and in Florianópolis, the potential ranged between 20.6% and 86.2% for an external illuminance of $\text{10000}\text{lux}$. The methodology presented can be applied to any location around the world.     

Energy saving potential and strategies for electric lighting in future North European, low energy office buildings: A literature review

This article presents key energy use figures and explores the energy saving potential for electric lighting in office buildings based on a review of relevant literature, with special emphasis on a North European context. The review reveals that theoretical calculations, measurements in full-scale rooms and simulations with validated lighting programs indicate that an energy intensity of around 10 kWh/m² yr is a realistic target for office electric lighting in future low energy office buildings. This target would yield a significant reduction in energy intensity of at least 50% compared to the actual average electricity use for lighting (21 kWh/m² yr in Sweden). Strategies for reducing energy use for electric lighting are presented and discussed, which include: improvements in lamp, ballast and luminaire technology, use of task/ambient lighting, improvement in maintenance and utilization factor, reduction of maintained illuminance levels and total switch-on time, use of manual dimming and switch-off occupancy sensors. Strategies based on daylight harvesting are also presented and the relevant design aspects such as effects of window characteristics, properties of shading devices, reflectance of inner surfaces, ceiling and partition height are discussed.     

Rainwater tank capacity and potential for potable water savings by using rainwater in the residential sector of southeastern Brazil

Rainwater has been used in many countries as a way of minimising water availability problems. In Brazil, it has been reported that the potential for potable water savings by using rainwater may range from 48% to 100% depending on the geographic region. In southeastern Brazil, water availability is about 4500 m³ per capita per year, but it is predicted to be lower than 1000 m³ per capita per year from about 2100 onwards. The main objective of this article is to evaluate the potential for potable water savings by using rainwater in 195 cities located in southeastern Brazil. Rainwater tank sizes are also assessed for some cities in order to evaluate the ideal tank capacity as a function of potable water demand and rainwater demand. Results indicate that average potential for potable water savings range from 12% to 79% per year for the cities analysed. Ideal rainwater tank capacities for dwellings with low potable water demand range from about 2000 to 20,000 litres depending on rainwater demand. For dwellings with high potable water demand, ideal rainwater tank capacities range from about 3000 to 7000 litres. The main conclusion drawn from the research is that the average potential for potable water savings in southeastern Brazil is 41%. It was also concluded that rainwater tank capacity has to be determined for each location and dwelling as it depends strongly on potable water demand and rainwater demand.     

Effect of switchable glazing on discomfort glare from windows

In this paper we report the results of experimental tests carried out to study the effect of electrochromic (EC)-glazing on discomfort glare from windows. The research is performed by a small scale test-cell equipped with a small area double glazing unit (DGU) where one pane consists of an EC device with a visible transmittance τ_v ranging from about 7 to 70% and the other of an ordinary clear float glass (τ_v ∼ 90%), the overall DGU transmittance dynamic range resulting about 4–58%. The performance of the device is investigated under real sky conditions as a function of time, solar radiation intensity, test-cell orientation and switching strategies (static and dynamic). The evaluation methods adopted for assessing the discomfort glare degree are the “New Daylight Glare Index” (DGI_N) and the “Glare Subjective Rating” (SR). Results deriving from application of these two methods are compatible and show that for south facing windows and under the involved climatic conditions EC-glazing can be very effective in reducing discomfort glare caused by high window brightness originating from diffuse skylight. This glare reduction can be realized without compromising much of the available daylight so without necessarily increasing the need for artificial lighting and, at the same time, preserving an unobstructed outside view. Occurrence of glare effects from west (or east) facing windows is more difficult to be controlled due to the lower sun angles which entail the use of EC devices switchable to very low transmittance states (τ_v < 7%) and/or integration of traditional sun protection devices. This would probably compromise indoor daylight availability (and potential energy savings associated to reduced use of artificial lighting) as well as exterior view although the positive effect of the EC-glazing could be a substantial reduction of the frequency of use of these additional shading systems.     

The energy performance of the Central Sunlighting System

This article presents a simulation study to predict the energy performance of the Central Sunlighting System (CSS) installed in open-plan offices. Several simulation tools are combined to conduct the simulations. SkyVision calculates the daylight luminous flux and the lighting and solar heat gains of the CSS. A set of coefficients pre-calculated using Radiance relates the desktop illuminances to the CSS luminous fluxes. DaySim is used to compute the daylight illuminance from the perimeter windows. ESP-r is used to compute the heating and cooling energy use of the office spaces. The results show that the CSS may save a significant amount of energy in North American climates. Energy savings from the combination of daylighting from windows and the CSS for typical, four-cubicle, open-plan offices range from 44% to 57% for lighting, 8% for cooling and from 14% to 23% for the total (lighting, cooling and heating) energy.     

The mathematisation of daylighting: a history of British architects' use of the daylight factor

British post-war planning guidance proposed that cities be rebuilt according to scientific principles. Mathematical tools were devised to determine built form; daylight levels within buildings were to be evaluated using a metric called the daylight factor. The daylight factor is still the principal metric used in daylighting guidance, despite recent calls to replace it with other metrics. This article explores whether the Modernist ambition, for buildings to be designed according to mathematically verifiable principles, was realised in relation to daylighting. Specifically, the article explores post-war architects' usage of the daylight factor in designing housing. The article draws on eleven semi-structured interviews with practising and retired architects, lighting consultants and a planning officer. Architects interviewed for the study reported that they did not routinely evaluate daylight factors at the design stage. Interviewees described the process as time-consuming, and often unnecessary as windows can be designed without undertaking a calculation or a photometric model study. Also, planning authorities rarely required architects to prove that proposed dwellings achieved specific daylight factors. However, those architects who were knowledgeable about daylight factors reported that this knowledge enhanced their understanding of the principles of daylighting. The daylight factor also helped to establish objective standards.     

Turning-off line in perimeter areas for saving lighting energy in side-lit offices

A method of determining the depth of an area where one can turn off electrical lighting to utilize daylight in perimeter areas has been developed for standard offices with side-lit windows and typical artificial lighting. A graph of cumulative occurrence rates of the unobstructed sky illiminance is combined with the various distribution curves of daylight factors on the working planes in the standard rooms through the intermediary of the required illuminance. This graph makes it possible to decide the depth of the area easily and quickly by considering room widths, window-width ratios and obstructed angles of buildings opposite to the window across the street.Several limitations to this method are discussed and the problems for future research outlined.     

The use of DOE-2 to determine the relative energy performance of daylighted retail stores covered with tension supported fabric roofs

With increasing interest amongst the architectural and engineering community in daylighted buildings, there is a need to evaluate the relative energy performance of those buildings. One means of daylighting a building is to use a coated glass fiber fabric roof. With such a roof, it has been found that sufficient daylight is admitted to allow most artificial lighting to be turned off during the daytime hours. However, solar cooling loads and conductive loads may be greater than for conventionally roofed commercial buildings. With the fabric roofed buildings capable of using considerably less energy for artificial lighting, yet possibly requiring greater use of energy for space heating and cooling, the relative energy performance is a matter of trade-offs.To determine this relative energy performance of fabric roofed and conventionally roofed retail stores, a modified version of DOE-2.1A was used with weather data from 19 cities located within the United States. In the analyses, both single-layer and double-layer roofs were studied as were stores with different levels of electric power for artificial lighting. In general, the results suggest that a fabric roofed store will use less total energy than a conventional roofed store in a geographic area with a mild climate but that it will use more energy in a cold climate area.     

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.     

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.     

An analysis of measured and simulated daylight illuminance and lighting savings in a daylit corridor

Lighting control integrated with daylighting is recognised as an important and useful strategy in energy-efficient building designs and operations. Prediction of the internal daylight levels is a key stage in daylighting designs. With the advances in computer technology, the computation of daylight illuminances can be conducted via lighting simulation program. This paper presents a study of the daylight coefficient (DC) approach using RADIANCE lighting software in simulating the indoor daylight illuminance of a corridor. The interior daylight illuminance data measured in the corridor were compared with the simulated results based on the computer software. It was found that the DC approach could give satisfactory results especially for the sun-shaded surface and sun-facing surface receiving a large amount of direct sunlight. Further, the daylight illuminance detected by the photosensor was also simulated in conjunction with measured daylight illuminance, dimming ratio and electric lighting power to predict the lighting energy savings. The findings suggested that the measured and predicted data showed a good agreement when large electric lighting savings resulted. The probable reasons causing the discrepancies were discussed.     

现代住宅与天然采光

通过科学的设计把天然光引入建筑已成为一种时尚,它不仅可以降低建筑能耗,还能利用阳光提高室内的环境质量.本文从四个方面探讨住宅建筑中的采光设计问题,包括室内天然光设计标准分析、采光窗对居室内部光环境的影响、天然采光系统主要技术手段的应用和住宅获得良好天然光的具体要求及其应注意的问题.     

昼光照明在教学楼建筑设计中的应用

昼光照明较之人工照明呈现的诸多优势使得昼光照明设计一直在建筑设计中处于重要位置。随着高校教学楼建筑规模化、多样化、智能化的发展,其照明设计的要求自然更高。本文针对教学楼这一类建筑,探索了建筑设计中昼光照明的实施策略。     

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.     

Using dynamic simulation to quantify the effect of carbon-saving measures for a UK supermarket

A standard UK supermarket design is used to simulate the energy performance, and subsequent CO₂ emissions, of a modern-day UK supermarket building. Retrofit measures are proposed to reduce these CO₂ emissions by over 50%, mostly due to demand-side measures but also accounting for likely onsite supply-side solutions. The influence of refrigeration and lighting in such buildings is explored and the possible use of heat recovery systems discussed. The air-tightness of supermarket buildings is also highlighted as a potential area for significant energy savings. Finally, the reliance on grid electricity is demonstrated for non-domestic buildings with a high electrical energy use. A combined approach of energy efficiency and low-carbon offsite electrical generation is suggested from the described case study as the most successful strategy to achieve large carbon savings (i.e. >50%) in existing supermarket buildings.     

Energy consumption and the potential of energy savings in Hellenic office buildings used as bank branches—A case study

Energy performance of non-residential buildings and in particular of office buildings used as bank branches is very limited. This paper presents new data from 39 representative bank branches and results from a more in-depth analysis of information from energy audits in 11 typical bank branches throughout Greece. The data was used to derive practical energy benchmarks and assess various energy conservation measures. Accordingly, the average annual total energy consumption is 345 kWh/m². The breakdown of the different end-uses reveals that HVAC averages 48% of the final energy consumption, lighting averages 35% and other office and electronic equipment average 17%. The most effective energy conservation measures reach annual energy savings of 56 kWh/m² by regulating the indoor set point temperature, while the use of HF electronic ballasts and CFL lamps may save about 22 kWh/m² and 29 kWh/m² with and without the use of the external marquee sign, respectively.     

Lighting energy savings in offices using different control systems and their real consumption

This paper compares the potential of lighting energy savings in office rooms by using different control systems, for three locations in Europe and the four main orientations. The method is based on DAYSIM simulations to perform daylight calculations, on laboratory measurement to evaluate precise system energy consumptions and on the implementation of a new algorithm to simulate a close-loop daylight dimming system. It appears that the control of the electrical power in function of daylight leads to very high savings; they slightly depend on the room orientation and the location. Savings vary from 45 to 61%. The performances of an occupancy sensor are also tested. Threshold values of occupancy rate for which daylight dimming leads to higher gains than an occupancy control system vary between 27 and 44% depending on location and orientation. The measurements of the energy consumption of the sensors and detectors also permit to conclude that systems with embedded DALI-compatible ballast controllers should be abandoned in favour of a centralized DALI-compatible ballast controller or embedded analogue systems.     

自然光光导照明在建筑采光中的应用

介绍了自然光光导照明系统的原理与结构,包括采光装置、导光装置、漫射装置的工作原理、外观样式、材料性能要求、特性曲线等,阐述了国内外自然光光导照明在建筑采光中的应用场所和生产企业。通过分析比较自然光光导照明相对于侧窗采光、天窗以及电力照明的照明效果,说明自然光光导照明在建筑采光中的应用与前景。     

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.