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In subtropical Hong Kong, clear glass is normally used as the translucent material for external windows of residential buildings, but it has poor heat insulation performance especially the tremendous solar heat gain in summer. To improve the thermal performance of conventional clear glass, a new heat blocking coating was developed. The coating can effectively absorb the near infrared radiation, so it can reduce the solar heat gain and therefore the energy use from air-conditioning systems. In this paper, the preparation of the heat blocking coating was firstly introduced. Then the optical and thermal properties of different types of window glazing were tested in the laboratory. Based on the experimental data, a combined daylight, thermal environment and building energy numerical model of a public rental housing was established to fully simulate the performance of different types of windows glazing. The results indicated that the heat blocking coating can reduce about 275.4 kWh (14.4%) electricity use per year compared to conventional clear window. [ABSTRACT FROM AUTHOR]

A street canyon pollution dispersion model is described which accounts for a wide range of canyon geometries including deep and/or asymmetric canyons. The model uses up to six component sources to represent different effects of street canyons on the dispersion of road traffic emissions. The final concentration is a weighted sum of the component concentrations dependent on output point location; canyon geometry; and wind direction relative to canyon orientation. Conventional approaches to modeling pollution in street canyons, such as the "Operational Street Pollution Model" (OSPM), do not account for canyons with high aspect ratios, pavements, and building porosity, so are not applicable for all urban morphologies. The new model has been implemented within the widely used, street-level resolution ADMS-Urban air quality model, which is used for air quality assessment and forecasting in cities such as Hong Kong where high-rise buildings form deep and complex street canyons. The new model is evaluated in relation to measured pollutant concentration data from the "Optimisation of modelling methods for traffic pollution in streets" (TRAPOS) project and routine measurements from 42 monitoring sites in London. Comparisons have been made between modeling using the new canyon model; a simpler approach to canyon modeling based on the OSPM formulation; and without any inclusion of canyon effects. The TRAPOS dataset has been used to highlight the model's ability to replicate the dependence of concentration on wind speed and direction, and also to show improved model performance for the prediction of high concentration values, which is particularly important for model applications such as planning and assessment. The London dataset, in which the street canyons are less well defined, has also been used to demonstrate improved model performance for this advanced approach compared to the simpler methods, by categorizing the measurement locations according to site type (background, near-road, and strong canyon). Implications: Currently available air dispersion models do not allow for a number of geometric features that influence air dispersion within street canyon environments. The new advanced street canyon model described in this paper accounts for: emissions from each road carriageway separately; canyon asymmetry; canyon porosity; and pavements. The extensive model evaluation presented shows that the new model demonstrates good performance, better than more basic approaches in which the complex geometries that define "canyons" are neglected. [ABSTRACT FROM AUTHOR]

In this paper, we estimate the energy efficiency of educational buildings with the case study of buildings in City University of Hong Kong by constructing an energy demand stochastic frontier model. The model is estimated by using the university statistical data from 2011 to 2015. For the consistent frequency of data among the variables, we have adopted the quadratic-match sum method to convert annual university report data into a monthly dataset. Our result shows the average energy efficiency is 0.87, implying that 13% of total energy consumption can be saved. We then calculate how much of the energy saving potential has been achieved by constructing the performance score, which increases from 0.08 to 0.17. It implies that the campus performs more efficiently in saving energy over time. We further develop econometric decomposition analysis based on the energy demand frontier model to identify the factors affecting energy consumption. It suggests that research activities account for a large share of overall energy consumption. Analysis on energy end-use shows university should improve efficiency in lab instrument as it is least efficient among the four usages. We expect this paper can provide the fundamental and methodological guideline for university-scale energy efficiency estimation. • Estimating energy efficiency of educational buildings needs to consider the composition of research related factors. • Energy efficiency of campus building presents increasing tendency with seasonal cycle over time. • Research related variables affect significantly on energy efficiency of educational buildings. • Energy use in lab instrument needs to be effectively managed to save energy. [ABSTRACT FROM AUTHOR]

• This paper integrates bifacial photovoltaics as sunshades into buildings. • The impact of installation and building factors on power generation is studied. • The impact of installation factors of bPV on the energy savings is studied. • The south orientation, small tilt angle and wide bPV are recommended to install. • The buildings with high wall reflectivity and low WWR achieve more energy savings. Solar photovoltaic (PV) shading systems are of great significance for achieving low-carbon buildings. Bifacial photovoltaics (bPV) is a promising technology that can generate electricity from both the front and rear sides of bPV modules. By integrating bPV shading systems into buildings, more power generation and less building energy consumption can be achieved compared to traditional shading systems. This study aims to integrate and optimize bPV shading systems into the building vertical façades in hot and humid regions, considering varying installation and building parameters. The evaluations of electricity generation and energy saving were conducted based on a typical three-story office building in Hong Kong. The evaluation of electricity generation reveals that the optimal installation condition for bPV sunshades in Hong Kong is south orientation with a tilt angle of 35°. Regarding the width of bPV sunshades, as the width increases, the annual electricity generation per unit area (AEGPA) decreases, but the total annual electricity generation (TAEG) increases. Besides, the bifacial gain of optimized bPV sunshades increases from 3.3% to 6.1% as the wall reflectivity increases from 0.15 to 0.7, while being insensitive to window reflectivity. Similarly, when the window-to-wall ratio (WWR) increases, the bifacial gain decreases. Furthermore, the energy-saving evaluation indicates that the south orientation with small tilt angles and wide sunshades tends to achieve much more energy savings benefits. The findings of this study provide practical guidance for maximizing the power generation and optimizing the design of building-integrated bPV sunshades to achieve maximum energy savings. [ABSTRACT FROM AUTHOR]

Buildings are a main contributor to energy consumption and carbon emissions. The approach of low energy or low carbon building has been widely adopted. However, there exist challenges for energy and carbon modeling, particularly of high-rise buildings in high-density urban environments. The aim of this paper is to examine the challenges and develop strategies for energy modeling of high-rise buildings drawing on the case of public housing in Hong Kong. The paper reviews the knowledge barriers to the use of building energy analysis software and proposes a workflow to incorporate energy simulation into the design stage. Considering the urban environmental factors that may contribute to biased results of energy simulation, the technical issues during the conversion of data from BIM model to energy simulation software are investigated. Thermal zones and user behaviors are also examined as technical and subjective assumptions could lead the simulation to a wrong direction. The examined challenges and developed strategies will help achieve building energy simulation and carbon emission estimation of high-rise buildings in Hong Kong with efficiency and accuracy and also inform practices in other relevant urban settings. [ABSTRACT FROM AUTHOR]

Abstract: Prefabrication has been increasingly used in buildings. It is recognised as a solution to reduce waste arising during design and construction phases. However, there is little emphasis on life cycle design issues for prefabricated buildings located in dense high-rise building environments. The purpose of this paper is to review the application and identify benefits and impediments of design for deconstruction and Industrialised, Flexible and Demountable building systems when applied to precast concrete construction. The paper presents the results of a comprehensive literature review, and two case studies of recently completed institutional buildings using prefabrication. The literature review shows that, so far, design for deconstruction is not a common practice in the building industry. The case studies showed some limitations such as the dense urban environment conditions and limited site area. The promotion of a closed-loop material cycle is critical to contribute to sustainability thus minimising CO2 emissions, natural resources consumption. [Copyright &y& Elsevier]

[Display omitted] • Developed an efficient energy-saving building model based on transparent heat-shielding glass and energy-storage cement. • Halloysite nanotubes have been successfully used for energy storage cement. • Transparent heat shielding glass and energy storage cement have a synergistic effect on building temperature regulation. • The energy saving and economic payback period of the best scheme are 23.4% and 4.82 respectively. Transparent heat-shielding (THS) glass based on selective absorbing materials has great application prospects in reducing building energy consumption. However, the heat generated by absorbing near-infrared light will also increase the indoor temperature, meanwhile, a single energy-saving material often causes obvious indoor temperature differences. This paper presents an energy-saving building room based on Cs x WO 3 @TiO 2 coated glass (CG) and polyethylene glycol (PEG)/halloysite nanotubes (HNTs) energy storage cement (CP/F). The Cs x WO 3 (CWO) nanoparticles coating with TiO 2 enhanced the stability of THS materials. The PEG/HNTs energy storage material exhibits a desirable phase change temperature of 28.70 °C, and relatively high latent heat of 74.84 J/g. The test room result shows that the combination of CG and CP/F can reduce the room temperature by about 10 °C, which is greater than the sum of CG and CP working alone owing to the synergistic effect of two materials, that is, CP/F can absorb part of the heat from CG. The combination of CG and CP/F made the indoor temperature distribution more uniform, with the maximum temperature difference decreasing from 6.7 °C to 3.1 °C. The annual energy saving of CP/F-CG in Changsha and Hong Kong is 14.7 % and 23.4 % respectively, and the economic payback period is 6.57 and 4.82 years respectively. The experimental results provide a new perspective on the development of energy-saving buildings. [ABSTRACT FROM AUTHOR]

• A POE-integrated simulation method is proposed to address energy occupant behavior. • Opening windows and operating AC were found to co-exist which affects simulation accuracy. • The new method improves energy simulation accuracy by 14% for domestic areas. • The method improves energy simulation accuracy by 16% for total building areas. Occupant behavior plays a critical role in building energy consumption, particularly in residential buildings. However, occupant behavior is complicated and varies significantly from case to case. Also, energy modeling of high-rise buildings is far less explored than that of low- or medium-rise buildings. This paper aims to improve accuracy in building energy simulation by utilizing Post Occupancy Evaluation (POE) data to calibrate energy model. Drawing on a review of the literature of occupant behavior and building energy modeling, the paper provides a calibration method of integrating POE data into an energy model, which is demonstrated using a real-life typical 40-storey residential building in Hong Kong. The developed method addresses seven updated input parameters, namely, schedule, devices, air-conditioners, windows, lights, domestic hot water, and cooking. By comparing the two energy modeling processes, i.e. with and without POE input, and their resultant estimated energy consumption, the paper quantifies the impact of occupant behavior on building energy consumption. Annual metered data together with energy bills obtained from the POE were utilized to validate the models. The results show that the use of the developed POE-integrated method helped to improve accuracy in energy consumption prediction by 14% for the total building floor area and by 16% for the total residential area. From examining the impacts of the seven input parameters, the paper reveals the key energy use sensitive occupant behaviors within high-rise residential buildings in Hong Kong. These include: the number of residents in each unit; adoption of window type and split type of air-conditioners; window and air condition operation modes; cooking time on weekdays and weekends; and time spent on hot water showering. The developed method can assist building designers and services engineers to estimate building energy use more accurately and provides a scenario analysis tool for clients and facility managers to develop effective energy conservation strategies. [ABSTRACT FROM AUTHOR]

Inter-building effect (IBE), which refers to the shading effect from surrounding buildings, plays an important role in building energy use in high-density cities. However, it is customary to neglect the IBE during energy simulation. Four issues are observed on previous research: 1) it has been controversial whether the IBE significantly affects energy consumption, 2) most studies used low-rise or medium-rise residential buildings as references, 3) most studies were conducted with hypothesised buildings, 4) most studies did not consider window blinds effect on IBE. These issues inhibit the theoretical understanding of high-rise building energy performance in cities and jeopardise the achievement of accurate simulation. This paper thus aims to investigate the IBE on the energy use of high-rise office buildings in Hong Kong as a typical high-density city. The IBE of ten selected real-life office buildings in their real-life communities was analysed. Four scenarios were compared, namely, simulation of building with both IBE and window blinds (base case), simulation of building with IBE but no window blinds, simulation of isolated building with window blinds, and simulation of isolated building without window blinds. The results show that the IBE influences the total energy use by up to 13.1%. Compared with the base case, heating, ventilation, air-conditioning (HVAC) and the lighting consumption deviation with different scenarios fluctuated largely, ranging from −11.8% to 18.8% in HVAC consumption, and from 0.1% to −27.6% in lighting consumption. An offset effect was found between the decreased lighting consumption and the increased HVAC consumption. From the floor-level analysis, with real communities, lighting energy use decreased with height among all the buildings generally. A multi-variant regression model was established to evaluate the relationship between IBE variables and building energy deviation caused by IBE. In addition, the results conclude that shading blinds cannot be overlooked when examining IBE on building energy use. These findings reveal the importance of considering IBE on building energy consumption in high-density contexts on a case-by-case basis. [ABSTRACT FROM AUTHOR]

Semi-transparent photovoltaic (STPV) windows, which can not only admit daylight into space but also generate electricity, have been widely used as a part of building components in recent years. This paper compares the overall energy performance between STPV windows and commonly used energy-efficient windows, viz. double-pane and Low-E windows, in Hong Kong. A new type of see-through amorphous silicon (a-Si) photovoltaic (PV) module was adopted, and this PV module has higher efficiency compared with other commercialized a-Si PV modules with the same visible transmittance. First, a series of testing were carried out to get the technical parameters of this PV module. Second, the simulation models were developed theoretically, and power, thermal and daylighting performance of different windows were analyzed by EnergyPlus accordingly together with the input weather data of typical meteorological year (TMY) in Hong Kong. Then, based on the simulated energy uses of the air-conditioning and the artificial lighting of the room, as well as the power generation of the STPV windows themselves, the overall energy performance was evaluated. The results indicate that STPV glazing can save up to 18% and 16% total electricity per year respectively in comparison with the clear single and double-pane glazings in cooling dominated areas like Hong Kong. The overall energy performance of Low-E glazing and STPV glazing is very close to each other, which means that STPV glazing is quite energy-efficient. In Hong Kong, southwest is the best orientation for power generation for STPV windows and south is the optimum orientation for STPV window installation in terms of achieving the best overall energy performance. [ABSTRACT FROM AUTHOR]

The estimation of solar heat gain via vertical fenestration is important in energy-efficient building design and operation especially for subtropical Hong Kong. Being one of the most populated cities in the world, buildings in Hong Kong tend to be densely constructed. In this regard, the shading effect of surrounding buildings could significantly limit solar radiation from the sun and sky to the window while certain amount of solar radiation would be reflected from the opposite façades. This paper presents a calculation approach to compute solar radiation on obstructed fenestration for both overcast and non-overcast skies. Performance of the proposed method is evaluated by comparing with simulated results of a sophisticated lighting program and field measurements. The findings are essential for the assessment of both active and passive building energy saving techniques including shading and building integrated photovoltaic systems in metropolitan environment. [ABSTRACT FROM AUTHOR]

Modeling buildings’ energy use is an effective strategy for identifying energy saving potential and seeking for energy efficient building solutions. However, there exist significant challenges for such modeling, particularly of high-rise buildings. The aim of this paper is to examine such challenges drawing on the case of high-density high-rise office buildings in the hot and humid climate of Hong Kong. The challenges are examined in relation to four aspects, namely, modeling approach, modelling tools, data availability and atmospheric conditions. A framework of strategies is developed for addressing the challenges. The strategies are then illustrated through a case study with a hypothesized high-rise office building in Hong Kong. Essential to achieving accuracy of modeling buildings’ energy use are found to be the collection and verification of building information and specification of thermal zones and schedules for modeling. The lack of usable data of energy use in high-rise buildings is considered to be a major barrier to verifying modeled results. To establish an integrated model with energy modelling and CFD software should effectively address the challenges. [ABSTRACT FROM AUTHOR]

Application of the shading-type Building-Integrated Photovoltaic (BIPV) claddings is one of the most effective approaches for reducing energy use in buildings and making buildings environment-friendly. PV modules are used as external shading devices and insulation panels as well. In this paper, the energy performance of the shading-type BIPV claddings is investigated under dynamic conditions. The design parameters of the shading-type BIPV claddings, including the tilt angles and azimuth angles of PV modules, the window to wall ratio of the building and the overhang length, are discussed based on the meteorological conditions of Hong Kong. Optimum designs of the shading-type BIPV claddings are reported for buildings with different orientations and window to wall ratios. [ABSTRACT FROM AUTHOR]

Abstract: This paper develops an overall methodology for investigating the thermal and power behaviors of semi-transparent single-glazed photovoltaic window for office buildings in Hong Kong. In order to estimate its overall energy performance, this study is conducted in terms of total heat gain, output power and daylight illuminance. Three simulation models are established, including one-dimensional transient heat transfer model, power generation model and indoor daylight illuminance model. A typical office room reference is chosen as case study, and the weather data from 2003 to 2007 from the Hong Kong Observatory are used as the simulation inputs. By incorporating the simulation results, the overall energy performance can be evaluated in terms of electricity benefits corresponding to five orientations of the studied typical office. The priority of office orientation considering overall energy performance is: south-east, south, east, south-west and west. The findings show that thermal performance is the primary consideration of energy saving in the entire system whereas electricity consumption of artificial lighting is the secondary one. The overall annual electricity benefits are about 900 kWh and 1300 kWh for water-cooled and air-cooled air-conditioning systems respectively. The application of semi-transparent PV glazed window can not only produce clean energy, but also reduce building energy use by reducing the cooling load and electrical lighting requirements, which definitely benefits our environmental and economic aspects. [Copyright &y& Elsevier]

Abstract: This paper presents a simplified energy performance assessment method for existing buildings in cooling season, which is based on energy bill disaggregation and energy performance analysis. This method requests very limited building energy data and can effectively assess the energy performance at building and system levels, and disaggregate the whole-building consumption into consumptions of three groups of end-uses. This method is based on two basic energy balance principles, i.e., the electricity consumption balances at building level and the cooling energy balances between demand side and supply side of HVAC systems. An optimization algorithm is developed to establish best possible cooling energy balances by minimizing the balance residuals and therefore to disaggregate the energy consumption of different users. The performance of the proposed method was validated in two existing buildings in Hong Kong and Beijing. The results, including the disaggregated energy consumptions and the key energy performance indicators of HVAC system, agreed well with the “measured” data in mechanical cooling months. [Copyright &y& Elsevier]

Abstract: Proper design, reliable control and health of variable–air–volume (VAV) terminals are essential for reliable operation and energy efficiency of VAV air-conditioning systems. This paper presents an online fault diagnosis tool for pressure-independent VAV terminals and its implementation. The fault diagnosis tool is developed using a robust fault detection and diagnosis strategy for VAV terminals. Cumulative sum (CUSUM) control chart with estimated process parameters is utilized to detect faults in VAV terminals. A rule-based fault classifier is designed and utilized to find the sources of faults in VAV terminals. The fault diagnosis tool relies only upon the sensor data and control signals that are commonly available in building management control systems (BMCS). The fault diagnosis tool can be installed in BMCS to online read the operating data of all VAV terminals in a building through local area network and diagnose faults of VAV terminals in the building. The fault diagnosis tool has been validated in a large-scale office building located in Hong Kong and can effectively find all faults occurring in VAV terminals. [Copyright &y& Elsevier]

[Display omitted] • The communal areas can have different levels of energy performance in the 15 types of public residential buildings under study. • Spatial design features can evidently affect the energy consumption in the communal areas. • The ability to harvest daylight serves as a key determinant of energy efficiency. • Both econometric and machine learning techniques are proved to be effective to generate reliable findings. In this paper, we construct a unique database for 1228 residential buildings in Hong Kong to investigate how the spatial features of these residential buildings affect the electricity consumption in the communal area. We choose Hong Kong for this analysis as the city owns a large number of standard-type residential buildings managed by the public institution, which could be affected strongly by environmental policies. Both the machine learning method, based on the Least Absolute Shrinkage and Selection Operator (LASSO), and econometric regressions are adopted to analyse the data. We first utilize the machine learning LASSO technique to identify the most relevant factors for the subsequent econometric analysis. Our results show that the electricity demand for relatively low consumption building types, such as Twin Tower, is 6% lower than that of the high consumption building types. Newly constructed buildings usually belong to the medium consumption types, with the estimated monthly electricity consumption per apartment in communal areas to be around 50.2 kWh on average in 2020. These findings shed light on the nexus between spatial features and energy use for complex buildings, potentially contributing to the better crafting of energy-saving policy and the improvement of residential building programmes. [ABSTRACT FROM AUTHOR]

Considering the significant consumption of energy in existing building stocks, effective retrofitting has great potential for reducing such consumption and promoting sustainability in existing buildings. This study aims to develop a sustainable retrofit decision-making mechanism for high-rise buildings in Hong Kong, China, by uncovering the optimum set of retrofit solutions based on the local climatic conditions, building features and cost. Based on a prototype building in Hong Kong, the study employed the net present value (NPV) to unveil the most suitable solutions to maximise the energy efficiency of existing buildings and minimise their retrofit costs, integrating the energy simulation. This study revealed that it is desirable to adopt an optimal set of measures for achieving a 40% energy improvement since the energy conservation can be as much as 82 (kWh/m2)/year with the optimal NPV of more than US$3300 over a 20 year life span. However, the cooling system, building energy management system and thickness of wall insulation are the most influential factors to the optimum NPV and energy conservation in Hong Kong. The identified optimal set of cost-effective retrofit measures can be effectively implemented for sustainable retrofit projects in the existing building, and the developed methodological framework can be suitably adapted for sustainable building retrofit projects in different climatic zones. The decision-making model is validated by the process of calculating energy consumption, selecting practical retrofit measures and analysing retrofit benefits when taking the local building standards into account. [ABSTRACT FROM AUTHOR]

The rapid growth of energy consumption in buildings has become an alarming threat to the climate. Various building-level energy saving measures have been studied and adopted to achieve energy efficiency. However, high-rise public residential buildings in subtropical climate as an important contributor to building-level energy consumption have received insufficient attention of research. The aim of this paper is to analyse the energy use of high-rise residential buildings in subtropical climate and examine the impacts of different energy saving measures for developing strategies for achieving very low-energy high-rise buildings. A typical high-rise (40-storey) public residential building in Hong Kong was selected as the case building, which has the energy use intensity of 106.6 kWh/m2 for the total building area and of 153.8 kWh/m2 for the area inside the residential units. The energy model of the case building developed using EnergyPlus software was carefully calibrated using metered energy use data and expert consultations adopting a systematic approach. Sensitivity analyses were then conducted using the parametric analysis tool jEPlus to quantify the impacts of different energy saving measures on energy use intensity reduction. It was found the measures in relation to human behaviours have the largest impact, followed by building service system efficiency and renewable energy. Building form and building envelope have the modest impact. The findings enhance the knowledge of subtropical high-rise public residential buildings' energy performance, and the developed and calibrated energy model could be used to explore more strategic energy saving measures in the long term. The quantified impacts of the measures should inform design decisions of low-energy housing production in high-rise sectors. • A 40-storey building is examined with energy use 153.8 kWh/m2 for residential area. • Energy model uses EnergyPlus software with sensitivity analyses tool jEPlus. • Behaviours have largest impact on energy use, then building services and renewables. • Building form and envelope have the modest impact on energy use reduction. • Systemic strategies are suggested for very low-energy high-rise residential buildings. [ABSTRACT FROM AUTHOR]

Sustainable development issues are currently the driving forces of many building projects. The building façade is critical for the architectural expression and has a large affect upon large parts of the building’s environmental performance. This study investigates the advantages of using multidimensional computer aided modeling and simulation to produce a sustainable façade design. A first step towards green building design is to establish a list of parameters which can then be used as design criteria, e.g. environmental performance, thermal visual and acoustic comfort, etc. Computer simulation and an analysis of recent projects in Hong Kong can help to determine the performance according to these design parameters whilst environmental impacts due to energy consumption are considered to be an important design parameter, it is also important for comfort criteria to be considered. [ABSTRACT FROM AUTHOR]

In Hong Kong, buildings consume 90% of the electricity generated and over 60% of the city's carbon emissions are attributable to generating power for buildings. In 2018, Hong Kong residential sector consumed 41,965 TJ (26%) of total electricity generated, with private housing accounting for 52% and public housing taking in 26%, making them the two major contributors of greenhouse gas emissions. Furthermore, air conditioning was the major source consuming 38% of the electricity generated for the residential building segment. Strategizing building energy efficiency measures to reduce the cooling energy consumption of the residential building sector can thus have far-reaching benefits. This study proposes a hybrid simulation strategy that integrates artificial intelligence techniques with a building energy simulation tool (EnergyPlus™) to predict the annual cooling energy consumption of residential buildings in Hong Kong. The proposed method predicts long-term thermal energy demand (annual cooling energy consumption) based on short-term (hourly) simulated data. The hybrid simulation model can analyze the impacts of building materials, construction solutions, and indoor–outdoor temperature variations on the cooling energy consumed in apartments. The results indicate that using low thermal conductivity building materials for windows and external walls can reduce the annual cooling energy consumption by 8.19%, and decreasing the window-to-wall ratio from 80% to 40% can give annual cooling energy savings of up to 18%. Moreover, significant net annual cooling energy savings of 13.65% can be achieved by changing the indoor set-point temperature from 24 °C to 26 °C. The proposed model will serve as a reference for building energy efficiency practitioners to identify key relationships between building physical characteristics and operational strategies to minimize cooling energy demand at a minimal time in comparison to traditional energy estimation methods. [ABSTRACT FROM AUTHOR]