Effect of daylight saving time on lighting energy use: A literature review

The principal reason for introducing (and extending) daylight saving time (DST) was, and still is, projected energy savings, particularly for electric lighting. This paper presents a literature review concerning the effects of DST on energy use. Simple estimates suggest a reduction in national electricity use of around 0.5%, as a result of residential lighting reduction. Several studies have demonstrated effects of this size based on more complex simulations or on measured data. However, there are just as many studies that suggest no effect, and some studies suggest overall energy penalties, particularly if gasoline consumption is accounted for. There is general consensus that DST does contribute to an evening reduction in peak demand for electricity, though this may be offset by an increase in the morning. Nevertheless, the basic patterns of energy use, and the energy efficiency of buildings and equipment have changed since many of these studies were conducted. Therefore, we recommend that future energy policy decisions regarding changes to DST be preceded by high-quality research based on detailed analysis of prevailing energy use, and behaviours and systems that affect energy use. This would be timely, given the extension to DST underway in North America in 2007.     

夏时制对北京地区住宅建筑的照明能耗影响研究

本文通过DeST软件模拟北京地区一栋典型住宅建筑的天然采光逐时照度,进而计算该建筑的照明能耗,比较在标准北京时间和实行夏时制时的照明能耗分布特点。通过分析可得出结论:对于北京地区的住宅建筑,夏时制可以节约照明能耗;夏时制的起止日期可以考虑从三月第四个星期开始到九月第三个星期结束;在此期间,采用夏时制可节约照明能耗7.95%。     

Determination of the origin of the illumination vector due to vertical windows under Moon-Spencer sky conditions (uniformly overcast)

This paper provides a procedure of easy approximation to obtain the direction of the illumination vector for a window under an overcast sky.When working with uniform skies, it is simple to demonstrate that the direction of the illumination vector is determined by the centre of the window and the illuminated point.However, when a luminance distribution is produced such as that specified by the Moon-Spencer law, the origin of the vector is no longer the centre of the window, but some point within a fragment of the window. In this paper, this fragment of window is delimited.     

A review of daylight illuminance determinations and energy implications

Daylighting is recognized as an important element in architecture and a useful strategy in energy-efficient building designs. Daylight gives a sense of cheeriness and brightness that can have a significant positive impact on the people. There is a scope for integrating daylight with electric light to reduce building energy use. The amount of daylight entering a building is mainly through window openings, which create in the indoor environment a more attractive and pleasing atmosphere, in addition to maximise visual access to the pleasant views of the outside world. Determinations of the exterior and interior daylight and lighting energy savings are key issues to demonstrate the benefits based on daylighting designs. This paper provides a review of daylight illuminance determinations and the lighting energy reductions due to daylighting schemes. The study includes daylight measurements, prediction of daylight illuminance under various sky conditions and potential electric lighting energy savings from daylight-linked lighting controls. The article aims at providing building professionals, practitioners and researchers more information and a better understanding of daylight for promoting effective daylighting designs and evaluations.     

The importance of interior daylight distribution in buildings on overall energy performance

Simulations of daylight distribution within a house show that there can be significant visual discomfort associated with specific sky conditions. Thermal models of the same building, which include simplified daylight calculations and which calculate annual energy performance of the building, do not reflect extreme visual discomfort and high thermal load associated with these sky conditions. These results illustrate the importance of more detailed interior daylight distribution calculations in assessing the thermal and visual comfort of a building, and in developing energy performance ratings for buildings. Some techniques for incorporating more detailed interior daylight distribution calculations in simplified thermal models are discussed.     

Luminous efficacy of daylight under different sky conditions

Dalighting is recognised as an important and useful strategy in terms of energy-efficient building design in hot climates. However, daylighting is always accompanied by unwanted solar heat gain, particularly during the cooling season. To achieve and evaluate daylighting design, solar radiation and outdoor illuminance data are needed. In 1991, a measuring station was installed at the City University of Hong Kong to measure global and diffuse solar radiation and outdoor illuminance. The measured data are analysed, and empirical models to determine luminous efficacy under different sky conditions are developed and presented. Implications for energy efficiency in building designs are discussed.     

Daylight performance of anidolic ceiling under different sky conditions

The daylight performance of anidolic ceiling for diffuse daylight is the subject of this article. The performance is assessed over a wide range of sky conditions following the new CIE Standard General Sky and compared between locations in Singapore, Japan and the United Kingdom. The criteria illuminance ratio (IR) and daylight glare index (DGI) are used to quantify the daylight performance of a default ribbon window façade with and without an anidolic ceiling. The difference is expressed in new terms IR improvement factor (IR IF) and DGI reduction. These factors are charted over all 15 sky conditions and various sun altitudes and may serve as general references indicating conditions under which anidolic ceilings perform best. The application of these new terms are demonstrated for Singapore, Fukuoka and Sheffield, representing three main latitude bands and different sets of prevailing sky types. It can be concluded that the daylight performance improvement through anidolic ceilings is most significant in Singapore.     

Energy saving and solar energy use in the University of Valencia (Spain)

Recent years have seen increasing public interest in issues related to energy saving and concern for the environment. It is important to highlight the work of public institutions in this respect. This was the motive that led the University of Valencia to finance a pilot project with the objective of studying useful initiatives for optimising energy consumption in accordance with the institution’s needs as well as the incorporation of innovative and more efficient technologies. The approach was to consider various aspects ranging from the analysis of the current energy consumption and the state of the installations, through the substitution of some energy inefficient components, to the study of the possible installation of a photovoltaic solar powered electricity generation station connected to the network. Also purely technical questions on economic efficiency should not be forgotten as this could lead to a reduction in energy consumption and the optimisation of the current energy consuming equipment, since generally, it is this question that limits the possible energy saving actions.     

The impact of daylight saving time on electricity consumption: Evidence from southern Norway and Sweden

This paper examines the impact of daylight saving time (DST) on electricity consumption in southern Norway and Sweden. As DST was implemented in both the countries in 1980, we do not have a clear counterfactual in the form of a control period to identify the impact of DST directly with before and after or with and without analysis. This problem in the study is resolved by using “equivalent day normalization technique” to identify the impact of DST. The difference-in-difference (DID) average treatment effects model suggests an annual reduction of at least 1.0 percent in electricity consumption for both Norway and Sweden due to DST. The average annual electricity consumption reduction corresponding to DST effects equals 519 and 882 GWh for southern Norway and Sweden, resulting in an annual financial saving of 16.1 million Euros and 30.1 million Euros, respectively. The distribution of treatment effects across different hours of the day indicates a small but significant reduction in electricity consumption during the morning and a steep decline during the evening hours in both countries.     

The energy saving index and the performance evaluation of thermochromic windows in passive buildings

The concepts of the energy saving equivalent (ESE) and energy saving index (ESI) are presented in this paper to evaluate the performance of new materials and components in passive buildings. The ESE represents the hypothetical energy that should be input to maintain a passive room at the same thermal state as that when a particular material or component is adopted. The ESI is the ratio of a particular material or component's energy saving equivalent to the corresponding value of the ideal material or component that can maintain the room at an ideal thermal state in passive mode. The former can be used to estimate the effect of the adoption of a certain building component or material on the building's thermal state from an energy standpoint, while the latter can be used to characterize the performance of the actual building component or material from a common standpoint and be used to evaluate the performance of components or materials in different climatic regions or under different operating situations. In this study, the ESI was used to evaluate the performance of a thermochromic window, represented by a single vanadium dioxide (VO₂) glazing, in passive residential buildings in three climatic regions of China (cold zone, hot summer and cold winter zone, and hot summer and warm winter zone).     

A methodology for investigating the effect of a south oriented surface on natural illuminance received on north oriented glazing of a top lighting system under clear sky conditions

A methodology for investigating the effect of a south oriented surface with varying inclination angle in reflecting natural light towards a north oriented glazing of a top lighting system is proposed for use under clear sky conditions. This was done based on mathematical simulation for a top lighting system. Results have shown the importance of the reflective surface in increasing the illuminance received on the glazing of the top lighting system.     

The variation of daylight levels across atrium walls: Reflectance distribution and well geometry effects under overcast sky conditions

Daylight plays a major role in making atrium spaces appealing to building users. This appeal is also evident in the spaces adjoining the atrium. A key component of atrium daylighting, especially in tall atria, is the daylight reflected on to the atrium walls. This study examines the impacts of well geometries and different diffuse reflectance distributions of walls on variations of vertical internally reflected daylight across the walls of atria. The square atrium models used in the study have a very wide range of well index (WI) values, ranging from 0.25 (shallow atrium) to 2.0 (deep atrium). In addition, two well wall reflectance distribution patterns were used, namely horizontal and vertical bands. Validated by scale model measurements, the lighting package Radiance was used to predict vertical internally reflected daylight levels. It was found that different reflectance distributions do have an impact on the vertical internally reflected components across the wall of the square atrium models under overcast sky conditions. The impact relates to the orientation of the band with different reflectance distributions on the wall. For central wall areas at locations greater than one third of atrium height the horizontal distributions of the reflectances significantly affect the vertical internally reflected components. For the wall area near the atrium corner the effects are quite complicated, being decided by both the horizontal reflectance distributions and vertical positions. For an atrium with a height more than 0.5 its well width the reflectance distribution influence tends to increase with increasing well index. The vertical distributions of the reflectance, however, do not substantially affect the vertical daylight levels in atria except for some special reflectance distribution patterns.     

Energy savings of office buildings by the use of semi-transparent solar cells for windows

The study investigated a PV window that consists of a double glazed window with semi-transparent solar cells. The window provides natural light transmission as well as electricity production. The effect of the PV window on energy consumption of office buildings was analyzed in terms of heating and cooling loads, daylighting, and electricity production. The purposes of the study were to find the optimum solar cell transmittance and window to wall ratio (WWR), and to estimate energy savings of the building. A standard floor of an office building was modeled to run computer simulation, and annual energy simulation was performed with EnergyPlus. The results showed that the solar cell transmittance of 40% and WWR of 50% achieved the minimum electricity consumption in the building when artificial lighting was controlled with daylighting. The optimum solar cell transmittance for PV windows in different orientation was also presented. By using the optimum PV window, the electricity consumption was reduced by 55% compared to the single glazed window with WWR of 30% and no lighting control.     

Analysis of interactions among the barriers to energy saving in China

Since China became the second largest energy consumer and carbon dioxide emitter, the problem of energy consumption and environmental pollution has drawn the world's attention. Meanwhile, Chinese government has put high emphasis on the problem. One project of energy saving initiated by Chinese government has been put into practice. However, many difficulties need to be dealt with to meet the expected aim of social development. The objective of this article is to investigate the interactions among the major barriers which prevent the practice of energy saving in China. Obviously, a clear definition of relationships among the barriers to energy saving helps top leaders make relevant decisions to solve the problem of economic sustainability, energy security and environment pollution in the future. To date, studies specifying energy-saving barriers have often focused on analyzing these barriers separately. As a result, a holistic view in understanding the barriers to energy-saving project is lacking. Interpretive structural modeling (ISM) is utilized to summarize the critical barriers hindering the project of energy saving in China and to explain the interrelationships among them. Suggestions for energy-saving practice and future research are provided.     

Electric energy saving potential by substitution of domestic refrigerators in Mexico

We evaluate the potential for electric power saving in Mexico that would follow the substitution of old, low efficiency domestic refrigerators with modern, high efficiency ones. Our results indicate that a total substitution of domestic refrigerators would save 4.7 TWh/year, which represents 33% of the annual total consumption of 14.1 TWh. Assuming an average daily use of 14 h for domestic refrigeration, 900 MW of electricity would be saved. An annual substitution of 20% over 5 years would save approximately 1 TWh a year and almost 180 MW would be released. It is recommended that this program of replacement should be supported by the Federal and State governments, beginning with the States (which have more direct influence), and with the oldest, least efficient refrigerators along the lines followed in programs that introduced fluorescent compact lamps.     

An empirical validation of the daylighting algorithms and associated interactions in building energy simulation programs using various shading devices and windows

Empirical validation of building energy simulation programs is an important technique in examining the effectiveness and accuracies of implemented algorithms. In recent years, daylighting algorithms incorporated in building energy simulation programs have become increasingly sophisticated in their abilities to predict the illuminance, light power reductions, and the associated thermal load interactions. The focus of this study was to examine measured and simulated light levels in an actual building constructed for research purposes. Daylighting models were constructed in EnergyPlus and DOE-2.1E and the predicted illuminance and light power were compared with measurements; an assessment of heating and cooling interactions using a variable-air-volume reheat (VAVRH) system was also performed by analyzing reheat coil powers for the VAV boxes. The average differences from EnergyPlus for reference point daylight illuminance, light power, and reheat coil power predictions were within 119.2%, 16.9%, and 17.3%, respectively. DOE-2.1E predicted reference point daylight illuminances were within 114.1%, light powers were within 26.3%, and reheat coil power were within 25.4%.     

Current situation of energy consumption and measures taken for energy saving in the iron and steel industry in China

A survey of the key issues associated with the development in the Chinese iron and steel industry and current situations of energy consumption are described in this paper. The apparent production of crude steel in China expanded to 418.78 million tonnes in 2006, which was about 34% share of the world steel production. The iron and steel industry in China is still one of the major high energy consumption and high pollution industries, which accounts for the consumption of about 15.2% of the national total energy, and generation of 14% of the national total wastewater and waste gas and 6% of the total solid waste materials. The average energy consumption per unit of steel is about 20% higher than that of other advanced countries due to its low energy utilization efficiency. However, the energy efficiency of the iron and steel industry in China has made significant improvement in the past few years and significant energy savings will be achieved in the future by optimizing end-use energy utilization. Finally, some measures for the industry in terms of the economic policy of China's 11th five-year plan are also presented.     

Analysis of energy saving optimization of campus buildings based on energy simulation

The energy consumption of campus buildings has specific characteristics, because of the concentrated distribution of people’s working time and locations that change in line with distinct seasonal features. The traditional energy system design and operation for campus buildings is only based on the constant room temperature, such as 25°C in summer and 18°C in winter in China, not taking into consideration the real heating or cooling load characteristics of campus buildings with different functions during the whole day and whole year, which usually results in a lot of energy waste. This paper proposes to set different set-point temperatures in different operation stages of public and residential campus buildings to reduce the heating and cooling design load for energy station and total campus energy consumption for annual operation. Taking a campus under construction in Tianjin, China as an example, two kinds of single building models were established as the typical public building and residential building models on the campus. Besides, the models were simulated at both set-point room temperature and constant room temperature respectively. The comparison of the simulation results showed that the single building energy saving method of the peak load clipping could be used for further analysis of the annual energy consumption of campus building groups. The results proved that the strategy of set-point temperature optimization could efficiently reduce the design load and energy consumption of campus building groups.     

燃气隧道窑热工测试与节能分析

我国工业炉窑是能耗大户,总体水平较低,具有相当大的节能潜力。以某高铝砖隧道窑为测试对象进行了详细的热工测试,测量了炉气温度、烟气参数、干燥段的气流参数以及各主要壁面的温度,通过计算窑车及物料带出的热量、干燥段排气热损失、排烟热损失和壁面散热损失等参数,对隧道窑进行了热平衡分析。结果表明,所测试隧道窑的热效率为33.4%,造成热损失的原因包括,砖坯码放方式、干燥段气流组织不合理、助燃空气量过大、围护结构保温性能差等,通过改善急冷段和干燥段气流组织,减小预混空气量,增强窑顶和烧成段保温等措施可实现该类隧道窑的节能。     

A model for estimation of daylight factor for skylight: An experimental validation using pyramid shape skylight over vault roof mud-house in New Delhi (India)

A model to estimate daylight factor was investigated and validated using experimental hourly inside and outside illuminance data of an existing skylight integrated vault roof mud-house in composite climate of New Delhi. The daylight factor model was found in good agreement with experimental value of daylight factor. This model was modified for different practical horizontal surface levels inside the big and small dome rooms and validated using experimental measured data. The yearly average value of percentage daylight factor for big and small dome skylight rooms was determined as 2% and 6%, respectively. The total annual average artificial lighting energy saving potential of the skylight illuminance in the existing building was estimated as 973 kW h/year; corresponds to 1526 kg/year of CO₂ emission mitigation. Hence, the annual carbon credit potential from skylight mud-house building is € 15.3/year.