Lighting Power Density Research Articles

Analysis of high-energy performance residences in Nigeria

Households account for over 80% of the total energy consumed in Nigeria. This paper evaluates optimal and cost-effective energy efficiency measures for residential buildings in Nigeria. Specifically, several energy-efficient design measures are considered in the optimization analysis including window types and sizes, wall and roof insulation levels, lighting power densities, cooling set point temperature, and high energy-efficient cooling systems. A sequential search optimization technique is utilized to determine the best energy efficiency measures that minimize life-cycle costs while maximizing source energy savings. Optimized energy-efficient measures for a typical residential building are identified for three cities to account for a wide range of climatic conditions within Nigeria. The optimization results indicate that utilizing energy-efficient lighting fixtures and high efficient air-conditioning system was required to design high-energy performance residential buildings throughout the tropical climatic zones in Nigeria. Combined with optimal energy efficiency measures and PV systems, residential buildings can be designed to be net-zero or net-positive energy assisting Nigerian households to have access to electricity especially in the rural areas.

Estimating the influence of occupant behavior on building heating and cooling energy in one simulation run

Energy performance contracting (EPC) aims at guaranteeing a specified level of energy savings in the built environment for a client. Among the building energy performance uncertainties that hinder EPC, occupant behavior (OB) plays a major role. For this reason, energy service companies (ESCOs) may be interested in including OB-related clauses in their contracts. The inclusion of such a clause calls for an efficient, easy-to-implement method to provide a first estimate of the potential effect of various aspects of OB on building cooling and heating energy demand. In contrast with common sensitivity analysis approaches based on a high number of scenarios, a novel simulation method requiring only a single simulation run for both heating and cooling seasons is presented here. The estimate is provided by evaluating the newly developed impact indices (II) based on the results obtained by means of the simulation run. A set of 16 building variants differing in floor height, climate, construction vintage and equipment and lighting power density was investigated to test the method. All II were calculated for the 16 building variants. In order to verify their significance, the results of a one-at-a-time sensitivity analysis mimicking simplified variations in occupant behavior (OB) were plotted against the II. The R2 values were above 0.9 when evaluating the effect of equipment use, lights use, and occupant presence, confirming the significance of the developed II. For blind use and temperature setpoint setting, the R2 values were ca. 0.85. Subsequently, the method was applied to an existing office building in Delft, The Netherlands, to evaluate its potential for EPC. This study confirms the high variability of the effect of OB on heating and cooling energy demand according to the case at hand. The developed method is useful for practitioners to evaluate the potential effect of OB on a given design in a time-effective manner.

Field data and simulations to estimate the role of standby energy use of lighting control systems in individual offices

This paper investigates the effectiveness of lighting control systems (LCSs) in 57 individual office rooms of an educational building located in Lund, Sweden. The study uses simulations based on actual occupancy data. The simulations, performed with Daysim via the Honeybee interface, focus on the portion of standby energy use on total lighting energy use considering different combinations of LCSs and lighting power density (LPD). The results show that standby energy use accounts for about 30% of the total lighting energy use, but it can raise up to 55% in extreme cases. The portion of standby energy use increases with lower occupancy rates and lower LPD. As a conclusion, a complete switch-off of systems during unoccupied hours is fundamental to preserve savings from LCSs. In addition, the article argues that, when standby energy use cannot be minimized or eliminated, daylight design and very efficient light sources may reduce the need for complex LCSs in individual office rooms or the like.

Estimation of the daylight amount and the energy demand for lighting for the early design stages: Definition of a set of mathematical models

A set of logistic mathematical models to estimate the daylight amount and the energy demand for lighting of a room is presented. The models were built upon a database of results obtained for a sample room through Daysim simulations: features such as site, orientation, external obstructing angle, window size, glazing visible transmittance and room depth were parametrically changed, resulting in 102 cases. For each case, the target workplane illuminance and the lighting power density were also changed, producing a final database of 408 cases. Two groups of models were built, for two different external obstructions: a building ahead and an overhang used as shading system. Each group contains a set of models for different daylighting metrics (daylight autonomy, continuous daylight autonomy and spatial daylight autonomy) and for the energy demand for lighting, considering a manual on/off switch or automated daylight responsive lighting control. The estimates that were obtained using the models showed, compared to the corresponding simulations results, a coefficient of variation CV lower than 16% for all the models, with one exception, having a CV up to 30%.The aim of the study was to elaborate models that could be used to incorporate daylighting strategies since the earliest stages of the building design process. Using the models, it is possible to predict the annual daylight amount in a room and the corresponding energy consumption of the lighting systems starting from some given room features (for instance the room depth or the window area) or, the other way around, estimate the suitable values of room features (glazing area, visible transmittance or room depth) to guarantee a target value of energy demand for lighting or of a daylighting metric.

Comparison of four building archetype characterization methods in urban building energy modeling (UBEM): A residential case study in Kuwait City

Significant research effort has gone into developing bottom-up, physics based, urban building energy modeling (UBEM) tools, which allow evaluating district-wide energy demand and supply strategies. In order to reduce the simulation inputs required in UBEM, groups of buildings are typically classified into representative “archetypes”. This approach necessarily simplifies the real diversity of occupant behaviors and construction variations, reducing in turn the variety of predicted building energy demands. To further understand the limitations of archetype-based modeling, this paper evaluates four characterization methods of increasing complexity, by comparing simulation results to measured Energy Use Intensity (EUI) distributions of 336 residential buildings in a district in Kuwait City. The first two methods follow a typical deterministic approach, organizing buildings into one and four archetypes respectively, while the third method introduces probabilistic uncertainty modeling for occupant related parameters. The fourth method introduces a new “Bayesian” calibration technique for archetype parameters, and applies it to occupant parameters in method three. In a first step, frequency calibrated distributions for occupancy, lighting power density, plug load density and cooling set points are generated through parametric modeling from a test set consisting of about half of the 336 buildings. The resulting joint distribution of parameters is then sampled using Latin Hyper Cube (LHC) for the probabilistic simulation of the remaining urban model. The comparison of simulated EUI distributions with measured data suggests that the proposed probabilistic Bayesian calibration leads to significantly closer predictions, with a maximum error in the 10th and 90th percentiles of 15% against 55%, 60% and 29% for the other three methods.

Energy saving potential and visual comfort of task light usage for offices in Malaysia

In the wake of the recent green building aspiration in Malaysia, this article explores the energy saving potential and user behaviour towards task lights in two office spaces in Malaysia; one is daylight assisted, and another is the conventional design of full reliance on the overhead electrical light. The lighting usage patterns were monitored with 5min interval over a month’s period during office working hours. Task lights with 8W CFL daylight bulbs were provided after the initial two weeks of measuring period and comparison of lighting power density LPD (W/m2) was made. 15 samples of each office space were given visual comfort survey before and after the task lights were distributed to each’s workspace. The result reveals that the addition of task lights only contributes to 0.60W/m2 of LPD. It further concludes the operational LPD of the daylight assisted with task light equipped office space achieves 78% of lighting energy saving (3.04W/m2) when compared to the recommended base case of MS1525:2014 (14.00W/m2). It also reveals that the provision of task light will not necessarily improve the current LPD if the lighting control system is not responsive to it to create the desirable luminous environment. Interestingly, both offices’ occupants show significant improvement in evaluating their satisfaction towards paperwork brightness and colour rendering with the usage of task light. However, this does not apply to computer work. There is no correlation established between the usage rate of task light and the distance of workspace from the nearest window.

A method for creating maps of recommended window-to-wall ratios to assign appropriate default values in design performance modeling: A case study of a typical office building in Japan

To support the appropriate default value assignment in design performance modeling (DPM), which is defined as energy/performance simulations in the concept and schematic stages of the design process, a methodology for creating maps of the recommended window-to-wall ratio (WWR) is proposed using integrated simulations and optimizations. A case study is conducted to create maps of recommended WWR in Japan. The distribution of the optimal WWR under varying design conditions exhibits three distinct patterns: (i) As the WWR decreases, the CO2 emissions decrease. (ii) An appropriate WWR value exists (30–50%) at which the CO2 emissions are minimized. (iii) As the WWR increases, the CO2 emissions decrease. Five design conditions of lighting power density, climate, window orientation, internal gains, and building scale are examined in this investigation. The results of the quantitative evaluation indicate that the lighting power density, climate, and window orientation significantly impact the optimal WWR configuration. The optimization results of 10 locations in four main orientations with two lighting power densities (10W/m2 and 5W/m2) are processed according to the optimal WWR distribution patterns to generate the recommended WWR maps for Japan. The maps provide architects with the information needed to determine the setting direction of default WWR values for DPM. For example, a larger WWR is recommended for buildings in zones 6–8 of the Japanese climate regions for the current lighting power density (10W/m2), except for eastern facades. In contrast, a moderate or smaller WWR default value should be carefully assigned according to the window orientation in zones 4–8 when the lighting efficiency improves (i.e., for a lighting power density of 5W/m2).

Energy efficiency opportunities in Hotels

According to the statistics in Egypt (2013), the number of hotels is 1193, about 407 of them have contracted power greater than 500 kW. Air conditioning, lighting, water heating and refrigeration represent the main activities demanding electrical energy in hotel business. The energy consumption per night spend changes a lot, depending on various factors; facilities provided, category of hotel, occupancy , geographical situation, weather conditions, nationality of clients, design and control of the installations. Energy benchmarking is an internal management tool designed to provide ongoing, reliable and verifiable tracking on the hotels performance. The most useful performance indicator (or Energy Efficiency Benchmarking) of hotels are: Lighting Power Density (LPD) in W (for lighting)/m2, and energy intensity (kWh/m2/ y). There are multiple benefits for improving energy in hotel business; reduces the hotel's operating cost, reduces climate change risks and promotes green tourism. Energy efficiency opportunities are low-cost measures and cost- effective investments. There are many energy saving opportunities for lighting in hotel's guest rooms as well as the more obvious savings in lobbies and exterior lighting areas. Behavior campaigns can yield substantial energy savings, both through the guests and housekeeper behavior. Encouraging housekeepers to use natural light during room cleaning is a simple first step to implement energy saving program. This paper presents the energy efficiency guidelines and energy benchmarking for hotels. Also a case study showing how the energy efficiency program implemented is presented.

Impacts of building operational schedules and occupants on the lighting energy consumption patterns of an office space

This paper considers pre-retrofit and post-retrofit lighting energy end-use of two sub-metered office spaces. Building lighting retrofits are typically installed to reduce energy consumption and operational costs of buildings. This traditionally includes replacing lights and introducing Building Management System (BMS). Through this process, an occupant’s ability to override new computerized controls could be compromised, which can dramatically affect the overall success of the project. Therefore, the analysis focuses on the effectiveness of the lighting retrofit, influence of the BMS upgrade, occupant behavior, and the lessons learned. The analysis comprises three different phases including one pre-retrofit and two post-retrofit phases. Each of the retrofit phases lasted approximately one year, leading to the monitoring of three years of sub-metered lighting energy end-use. The results showed that when the occupants had access to the lighting switches while BMS managed the operational lighting schedule, the office area with the responsible occupant saved 23.2% compared to the pre-retrofit phase. For the second lighting retrofit phase when the occupants did not have access to the light switches, the lighting schedule operated for more than two hours after the typical work day and the occupant was not able to turn off the lights upon departure. It should be noted that there are limited numbers of studies that consider three years sub-metered lighting retrofit data with the presented granularities in this study. Similar lighting retrofit projects could benefit from the findings of this study. Finally, the results of this sub-metered lighting data could address uncertainty in the selection of lighting power density and associated schedules of building energy simulations.

Practicality and Performance of Daylight Trough in The Tropics: A Case Study

The field of office daylighting is vital for both energy efficiency practice and occupants’ visual comfort. With the emergence of green building in Malaysia, building designers are exploring avenues for energy efficiency design; one common strategy is daylighting. The majority literature reviews on daylighting are skewed towards temperate or developed countries, where sky luminous condition is different from that of the Tropics. Conventional daylighting system designs redirect daylight from the envelope or atrium openings, such as light shelves. Presumed to be the pioneer daylight trough in the Tropics, this paper presents the simulated and in-situ lighting level measurements prior to occupancy. This case study presents an as-built daylight trough design which is able to daylight the office space as deep as 6 meters sufficiently. It achieves a lighting power density 1.90W/m2 and saves 39.2% of lighting energy over conventional office lighting energy. Discussed further is the practicality of working with such a system, including cost implication, return on investment and contractual challenges in reaching a consensus on the design. The results reinforce that the effectiveness of daylighting design is very dependable on the sun path and obstacles surrounding the office tower. The RADIANCE simulation correlates well to field measurement results. Further investigation into the light trough, its lighting energy savings, users’ interaction, visual comfort, and glare is still ongoing.

Influence of Lighting Loads upon Thermal Comfort under CBAD and UFAD Systems

Under-floor air distribution (UFAD) systems are occupied-area-based air conditioning systems that generally offer advantages over ceiling-based air distribution (CBAD) systems in terms of energy efficiency and thermal comfort; accordingly, UFAD systems have become more popular lately. The purpose of this study is to provide reasonable UFAD application conditions by comparing and analyzing the influences of cooling loads when UFAD and CBAD are applied to thermally control indoor environments. A chamber experiment was conducted to allow comparisons of the indoor thermal environment under CBAD and UFAD, with the experimental variables of the thermal load of the occupied area and the supply airflow rate. In conclusion, the lower the supply airflow and the higher the lighting power density, the more the thermal comfort of the indoor environment could be improved by using UFAD instead of CBAD. In the lighting power density range of 0–30 W/m2, correlations were calculated whereby the lighting power density levels could be predicted that would ensure thermal comfort at a desired level.

Simulation and Analysis of a University Library Energy Consumption based on EQUEST

The energy situation in China remains troubled, with building energy consumption continuing to dominate a large proportion of the total amount. In such case, it is important to analyze the data and issue recommendations on energy uses in public buildings of university towns. By selecting appropriate simulation software, namely eQUEST, information of actual buildings, including public utility rates and meteorological parameters, can be simplified. Some control variables was chosen to be simulated by eQUEST, such as lighting power density, indoor personnel density, summer indoor design temperature and summer air supply temperature. We summarize the impact on the power consumption of buildings based on the different variables. The respective effect of every aspect on the total power consumption is studied through the method of control variables.

基于反应时间的中间视觉道路照明功率密度分析及显色性能研究

A research method of analysis of the road lighting source safety and energy-saving properties under the human mesopic conditions was given. By constructing the reaction time test system for road lighting under the mesopic vision,the luminous efficiency model was established and luminous efficiency curve was obtained. By using this model,the evaluation method of energy efficiency based on the lighting power density was given. Using the calculation and analysis method of the color-rendering properties based on the color-rendering index,the effect of the changes in relative spectral power distribution on the color of light source was discussed under Luv uniform color space,and the function expression between the dominant wavelength of the light source and color-rendering index was established,which can be used to obtain the relationship between human sensitivity and light source color of each wavelength point. The above method was verified by the reaction time simulation test and the definition of the road lighting picture calculation experiment. The results show that the green-white light source with dominant wavelength of 540- 550 nm has the best power-saving and color-rendering properties under the mesopic vision.

Assessment and Strategies to Reduce Light Pollution Using Geographic Information Systems

Light pollution is a negative lighting condition because it prevents views of the night sky from the general population and astronomers. As a solution to light pollution, proper lighting system design is vital. The location, mounting height, and aim of exterior luminaries need to be taken into consideration for efficient use of lighting energy. In line with the effort, this paper presents the assessment results on light pollution at the port area, which is one of the brightest spots on Earth. In doing so, a GIS model is created to determine the level of light pollution at the study areas. The lighting power densities of ASHRAE 90.1-2007 are applied in order to find a way to reduce the level of light pollution. The effect of light pollution generated from the Long Beach Port area is examined by comparing against the sky glow generated from the Port of Long Beach area and other areas throughout the coast of Southern California, as well as comparing how deep the sky glow penetrates the ocean. The results are validated by comparing against the lighting specification used in the study areas. The lighting strategies proposed include the decreased height of light poles and increased spacing between light poles. This study will serve as a platform in which future researchers may continue and expand on the designs of heights and spaces of lighting poles in order to make severe light pollution areas better sustainable places.

Potential of Energy Saving from Daylight Usage under Ministerial Regulation

To enhance the use of daylight, lighting power density (LPD) load in building can be deducted by designing for energy conservation according to ministerial regulation’s conditions. However, the methods and benefits are not clearly defined. These problems also affect architectural design framework. This is an experimental research aims to explore the potential of daylighting by using DIALux software to simulate daylight level in office building. The results indicate that 1) within the room depth of 1.5 times window head height; most of the results from 4 types of studied windows cannot provide adequate illuminance (300 lux) on workplane. Artificial lights are still needed to be turned on to maintain minimum illuminance level. Therefore, the energy saving purpose is unachieved. 2) The orientation of windows affects on both illuminance and distance of useful daylight. 3) With proper design integration, it is possible to reduce glazing area. 4) Skylight is an effective mean to introduce and distribute daylight into building. 5) For visual comfort issue, daylight quality should be concerned. Finally, the results of this research will propose guidelines for developing design criteria and evaluation method in the future. This will reflect the actual energy consumption and saving.

Sunlight-driven synthesis of anisotropic silver nanoparticles

Abstract Photoinduced shape conversion of silver nanoparticles was realized using sunlight. The silver seeds were transformed to silver nanoprisms under sunlight when the concentration of citrate was low (⩽5.0 × 10 −4 M). Nevertheless, sunlight converted the obtained silver nanoprisms to silver nanodecahedrons when the concentration of citrate in reaction system was increased. It was found that the ultraviolet light from sunlight played a vital role in the shape conversion from nanoprism to nanodecahedron. Lighting power density did not influence the shape conversion except for reaction rate. Besides, the silver nanodecahedrons were synthesized in the mixed solution of AgNO 3 and citrate in absence of silver seeds through irradiation by simulated sunlight. The mechanism on the sunlight induced synthesis of silver nanoparticles was discussed. Anisotropic silver nanoparticles including nanoprisms and nanodecahedrons were obtained through controlling the citrate concentration and irradiation time by sunlight from green light source.

Energy Saving Design of a Training Center in Dongguan

A training center design as an example, the impact of building energy-saving design on building energy consumption are showed. Energy-saving design options of air conditioning system and refrigerator are given. Lighting power density of the lighting system energy-saving design and the project of energy-saving design are provided.

Spatial mapping of occupant satisfaction and indoor environment quality in a LEED platinum campus building

This paper reports a post-occupancy evaluation study of a LEED Platinum building on a university campus. A multiple-tool POE approach with GIS-based spatial mapping method was used to analyze and visualize the survey results of building occupant satisfaction and the measured indoor environment quality.The occupants were overall satisfied with the indoor environment in their workspaces in the building of study, though thermal comfort was comparatively low with high percentage of occupants reporting their workspaces too cold. Air movement was found to be lower than preferred by the occupants, especially in interior offices where CO2 level was also predominantly higher. Light levels in the building were found higher than preferred. Electric lighting power density installed did not reflect the fact that daylight is available for most of the lab and office spaces. Satisfaction with speech privacy was found lower in individual offices related to the construction detail of the connection between curtain wall and interior walls.Linking performance outcomes with spatial information improves POE data management. Spatial mapping allows reasons that cause occupant discomfort and dissatisfactory measured performance to be identified more intuitively and makes it potentially easier to communicate POE results with architects, engineers and facility management professionals, in order to engage them in the collaborative effort of continuous building performance improvement.

A multivariate non-linear regression model to predict the energy demand for lighting in rooms with different architectural features and lighting control systems

Abstract The paper presents a set of logistic mathematical models to quickly estimate, since the earliest design stages, the electric lighting energy demand for a generic room with different architectural features (site, orientation, external obstructing angle, window size, glazing visible transmittance and room depth), lighting system characteristics or users’ lighting requirements (working plane illuminance, lighting power density, type of lighting control). The models were built upon the data obtained from a parametric study, based on simulations carried out through Daysim of 828 case-studies. Two dataset were obtained: one for rooms with a manual on-off switch lighting control and one for rooms with an automatic daylight responsive lighting control. Consistently, two specific models were derived, one for each control system. The average error of the mathematical models in estimating the lighting energy demand with respect to the results of Daysim simulations was quantified in terms of the normalized Mean Bias Error value (0.66% – for the manual control system model and 0.29% – for the automatic daylight responsive control system model) and of the Coefficient of Variation of the Root Mean Squared Error (3.45% and 5.34% for the two models, respectively).

Understanding the risks and uncertainties introduced by common assumptions in energy simulations for Australian commercial buildings

Building performance simulation has a key role in facilitating effective retrofitting of commercial buildings, an essential task to reduce Australia's greenhouse gas emissions. Simulation users commonly rely on assumptions for certain ‘hard-to-measure’ building and behaviour inputs, and the range of values use can significantly affect predicted energy consumption. New financing methods in Australia may attach financial risk to this simulation uncertainty. This paper reports on a study examining the sensitivity of total predicted building energy consumption to hard-to-measure simulation inputs for two template Australian office buildings; a 10-storey office tower located in a Central Business District (CBD), and a 3-storey office on the fringe of a CBD. The predicted energy consumption for the archetypes varied by more than 50% from baseline consumption for all Australian capital cities, using high and low assumptions. The input parameters that significantly influence energy consumption were found to be; cooling set-point, Information and Communications Technology (ICT) power density, ICT usage schedule, and lighting power density. A case study of a simple lighting upgrade to a 10-storey office building in Sydney showed that the payback period could vary from 2.4 to 10.3 years depending on the simulation assumptions used.