Towards a multi-objective optimization approach for improving energy efficiency in buildings

The energy sector worldwide faces evidently significant challenges that everyday become even more acute. Innovative technologies and energy efficiency measures are nowadays well known and widely spread, and the main issue is to identify those that will be proven to be the more effective and reliable in the long term. With such a variety of proposed measures, the decision maker has to compensate environmental, energy, financial and social factors in order to reach the best possible solution that will ensure the maximization of the energy efficiency of a building satisfying at the same time the building's final user/occupant/owner needs. This paper investigates the feasibility of the application of multi-objective optimization techniques to the problem of the improvement of the energy efficiency in buildings, so that the maximum possible number of alternative solutions and energy efficiency measures may be considered. It further shows that no optimal solution exists for this problem due to the competitiveness of the involved decision criteria. A simple example is used to identify the potential strengths and weaknesses of the proposed approach, and highlight potential problems that may arise.     

Energy efficiency in Spanish wastewater treatment plants: a non-radial DEA approach

Wastewater treatment plants (WWTPs) are energy-intensive facilities. Thus, reducing their carbon footprint is particularly important, both economically and environmentally. Knowing the real operating energy efficiency of WWTPs is the starting point for any energy-saving initiative. In this article, we applied a non-radial Data Envelopment Analysis (DEA) methodology to calculate energy efficiency indices for sampling of WWTPs located in Spain. In a second stage analysis, we examined the operating variables contributing to differences in energy efficiency among plants. It is verified that energy efficiencies of the analyzed WWTPs were quite low, with only 10% of them being efficient. We found that plant size, quantity of organic matter removed, and type of bioreactor aeration were significant variables in explaining energy efficiency differences. In contrast, age of the plant was not a determining factor in energy consumption. Lastly, we quantified the potential savings, both in economic terms and in terms of CO₂ emissions, that could be expected from an improvement in energy efficiency of WWTPs.     

European residential buildings and empirical assessment of the Hellenic building stock,energy consumption,emissions and potential energy savings

The existing building stock in European countries accounts for over 40% of final energy consumption in the European Union (EU) member states, of which residential use represents 63% of total energy consumption in the buildings sector. Consequently, an increase of building energy performance can constitute an important instrument in the efforts to alleviate the EU energy import dependency (currently at about 48%) and comply with the Kyoto Protocol to reduce carbon dioxide emissions. This is also in accordance to the European Directive (EPBD 2002/91/EC) on the energy performance of buildings, which is currently under consideration in all EU member states. This paper presents an overview of the EU residential building stock and focuses on the Hellenic buildings. It elaborates the methodology used to determine the priorities for energy conservation measures (ECMs) in Hellenic residential buildings to reduce the environmental impact from CO₂ emissions, through the implementation of a realistic and effective national action plan. A major obstacle that had to overcome was the need to make suitable assumptions for missing detailed primary data. Accordingly, a qualitative and quantitative assessment of scattered national data resulted to a realistic assessment of the existing residential building stock and energy consumption. This is the first time that this kind of aggregate data is presented on a national level. Different energy conservation scenarios and their impact on the reduction of CO₂ emissions were evaluated. Accordingly, the most effective ECMs are the insulation of external walls (33–60% energy savings), weather proofing of openings (16–21%), the installation of double-glazed windows (14–20%), the regular maintenance of central heating boilers (10–12%), and the installation of solar collectors for sanitary hot water production (50–80%).     

Thermal upgrades of existing homes in Germany: The building code, subsidies, and economic efficiency

One of the cheapest ways to reduce CO₂ emissions is thermal renovation of existing homes. Germany is a world leader in this project, with a strict building code, generous state subsidies, and an advanced renovation infrastructure. The effects of its policies are here explored in the light of progressive tightening of the building code, and the strict criteria for subsidies. Data on costs and outcomes of residential building renovations are presented from published reports on renovation projects, and cross-checked with projects investigated directly. Comparisons are made in terms of euros invested for every kilowatt hour of heating energy saved over the lifetime of the renovations, for standards ranging from 150 kWh (the lowest standard) to 15 kWh (the highest) of primary energy use per square metre of floor area per year. It is found that the lowest standard is an order of magnitude more cost-effective than the highest, in terms of both energy saved per euro invested, and return on investment over the lifetime of the renovations, regardless of fuel prices. It is argued that this throws into question Germany's policy of progressively regulating for higher renovation standards, and offering subsidies only for projects that go beyond the minimum standard.     

Forecasting future cooling demand in London

Cooling of buildings in the UK is responsible for around 15 TWh per year of energy demand, largely powered by electricity with highly related CO₂ emissions. The Greater London Authority wished to understand the potential impact of London's growing need for cooling on UK CO₂ emissions in the period up to 2030. This paper describes a model developed to analyse the cooling requirements for London's key building stock and assess how these would be affected by change in system mix, improvements in system efficiencies, and by varying degrees of climate change.The analysis showed that, if left unchecked, the growth in active cooling systems in London could lead to a doubling of CO₂ emissions from this source by 2030. This growth will be due to increase in building stock, increase in market share of cooling systems, and climate change. The last of these is difficult to predict, but by itself could add 260,000-360,000 tonnes of CO₂ emissions by 2030. This increase can be strongly mitigated, or even offset, by improvements in system efficiency. The difference between no efficiency improvements, and an assumed 1-3% annual efficiency improvement is around 340,000 tonnes by 2030.     

Saturation, energy consumption, CO2 emission and energy efficiency from urban and rural households appliances in Mexico

Energy usage and energy efficiency are of increasing concern in Mexico, electricity generation principally depends upon fossil fuels. On one hand, the stocks of these fuels have been confirmed to be critically limited. On the other hand, in process of electricity generation by means of these fuels, a number of poisonous by-products adversely affect the conservation of natural eco-system.This paper focuses on estimation of energy consumption, energy savings, reduction of emissions of CO₂ for use of urban and rural household appliances in Mexico between 1996 and 2021.The analysis concentrates on six major energy end uses in the residential sector: refrigerators, air conditioners, washing machines, TV set, iron and heater.It is estimated that by 2021 there will be a cumulative saving of 22,605 GWh, as a result of the implementation of government programs on energy efficiency that represents a cumulative reduction of CO2 emissions of 15,087 Tg CO2.It means that Mexico can reduce in 5650 MW the generation capacity of national electricity system, which is to avoid burning 40.35 MM barrels of oil.The findings can be useful to policy makers as well as household appliances users.     

Analysis of domestic hot water energy consumption in large buildings under standard conditions in Senegal

This paper presents an investigation of the energy consumption due to domestic hot water (DHW) production in large buildings. We have studied three types of reference buildings: one office, one residence and a 3-star hotel located in Senegal. The DOE2.1E (the building energy program of the Department of Energy Version 2.1E) has been used. One of its main advantage is that it allows to take into account both energy end use categories and a great number of parameters of the building energy performance. Four climatic regions have been identified and their equivalent “standard” conditions are all defined. Those conditions are the same as the current design and operating conditions of each type of building. The DHW energy consumption is calculated and compared with the total energy generated by all end uses (lighting, cooling/ventilation, DHW, and other equipment). Before we carry out wide and systematic simulations of the three buildings energy performance, we pay special attention to check and validate the DHW part of the DOE2.1E model. There was an agreement between the recorded monthly DHW energy load on the one hand, and on the other the computed results. We end up finding results that could open new perspectives for building a strategic methodology to provide guidelines for DHW energy saving measures in large buildings in West Africa. Furthermore, it is expected that energy researchers concerned about energy and environmental efficiency would consider this study for promoting CO₂ emission reduction in relation with DHW production in large buildings.     

Optimizing CO2 emissions from heating and cooling and from the materials used in residential buildings,depending on their geometric characteristics

The objective of this research was to obtain the environmentally optimal design of a building with the following starting conditions: constant constructed surface, constant volume, square floor layout, and a variable number of floors. For this purpose, the study evaluated the impact of CO₂ emissions stemming from the energy needed to maintain the building at a constant temperature of 19 °C in winter and 25 °C in the summer. Furthermore, one of the results was the CO₂ emissions curve from the manufacturing of the materials used in the construction of the building and the building envelope.     

Evaluation of BIM energy performance and CO2 emissions assessment tools: a case study in warm weather

ABSTRACT

The EU members have adopted regulations and official methods for evaluating the energy performance in buildings. Most of these methods are applied at the end of the project phase, with few opportunities to correct erroneous design decisions when the desired building energy performance is not achieved. It is demonstrated that there is no European standard for sustainability and that the decision-making process during the development of a building project is compromised by the methodologies and some concepts, as thermal inertia, are withdrawn. Currently, the industry has been developing alternative tools for evaluating energy performance and CO₂ emissions in buildings over their entire life cycle. These software programs, which belong to the BIM environment, use databases and make simplifications adapted to the stage of design when the software can be applied. The main objective of this paper is to evaluate the accuracy of this software and how the databases and simplifications influence the decision-making process in building design. Calculation examples are carried out with various tools and compared to real building performance data. The results demonstrate that, as with the official methods, the tools influence the results and therefore condition, sometimes wrongly, the decision-making process to produce better buildings.     

北京市《公共建筑节能评审标准》简介

北京市大型公共建筑单位建筑面积的全年耗电量高达100~350 kWh/(m2·a),是普通居民住宅的10~15倍,节能潜力达到30%~50%。不节能的原因之一是设计方案本身存在问题,强制性的节能设计标准没有得到执行。解决的途径是通过大型公共建筑的节能评审标准对设计方案进行节能审查和评估。所介绍的节能评审标准是对大型公共建筑能源需求、转换和消耗过程中建筑本身、能源转换和设备系统、可再生能源三个环节的多项指标给出定量的详细模拟计算结果,从而对设计方案的节能性给出全面评价,作为政府审批固定资产投资项目、鼓励和奖励节能设计的依据。     

Using Display Energy Certificates to quantify schools' energy consumption

The UK non-domestic sector accounts for 2 million buildings and 19% of national CO₂ emissions, representing a significant opportunity for emission reductions. However, substantial improvement of the stock requires a greater understanding of current energy performance characteristics. This paper explores energy consumption in English schools, using data from the Display Energy Certificates (DECs) database. DECs are a key step in understanding the non-domestic stock, incorporating national-scale statistical data, covering bottom-up details of the individual buildings. Significant variations in emissions between primary and secondary schools and academies exist, primarily caused by large differences in electricity consumption. Considering pupil numbers is shown to accentuate the differences, revealing a 47% rise in CO₂ emissions per pupil from primary to secondary schools, and a further increase between secondary schools and academies. The extent to which building characteristics, including location, heating, ventilation and air-conditioning (HVAC) and size, influence performance has also been evaluated. Location, HVAC and school density are shown to correlate with variations in energy use. Finally, a comparison of current school performance against past data reveals considerable reductions in fossil-thermal energy consumption over the last decade. However, this has been offset by a significant increase in electricity consumption, resulting in rising typical emissions across the school types.

Le secteur non domestique britannique représente 2 millions de bâtiments et 19% des émissions de CO₂ du pays, ce qui constitue une importante opportunité de réduction des émissions. Cependant, une amélioration substantielle du parc exige une plus grande compréhension des caractéristiques actuelles des performances énergétiques. Cet article examine la consommation d'énergie dans les écoles anglaises, en utilisant les données provenant de la base de données des Display Energy Certificates (DEC – Certificats de Performance Energétique à afficher). Les certificats DEC sont une étape clé pour mieux connaître le parc non domestique, intégrant des données statistiques à l'échelle nationale et couvrant en détail selon une approche ascendante les différents bâtiments. D'importantes variations des émissions entre les écoles primaires, les écoles secondaires et les académies existent, principalement dues à de grandes différences dans la consommation électrique. Il est démontré que la prise en compte du nombre d'élèves accentue les différences, révélant une hausse de 47% des émissions de CO₂ par élève entre les écoles primaires et secondaires, une hausse supplémentaire intervenant entre les écoles secondaires et les académies. A également été évalué le degré d'influence sur les performances des caractéristiques des bâtiments, au nombre desquelles l'emplacement, le chauffage, la ventilation mécanique et la climatisation (CVCA), ainsi que la taille. Il est démontré que l'emplacement, la CVCA et la densité des écoles sont en corrélation avec les variations de la consommation d'énergie. Enfin, une comparaison des performances actuelles des écoles par rapport aux données passées révèle des réductions considérables de la consommation d'énergie thermique fossile au cours de la dernière décennie. Cependant, ceci a été contrebalancé par une augmentation importante de la consommation d'électricité, qui s'est traduite par une hausse des émissions moyennes sur l'ensemble des types d'écoles.

indicateurs de référence, parc immobilier, émissions de CO₂, Certificats de Performance Energétique (DEC), consommation d'énergie, écoles     

Improved benchmarking comparability for energy consumption in schools

The method behind the UK Display Energy Certificate (DEC) improves the comparability of benchmarking by accounting for variations in weather and occupancy. To improve the comparability further, the incorporation of other features that are intrinsic to buildings (e.g. built form and building services) deserve exploration. This study investigates the impact of these features and explores ways to improve further comparability in benchmarking the energy performance of schools. Statistical analyses of approximately 7700 schools were performed, followed by analyses of causal factors in 465 schools in greater detail using artificial neural networks (ANNs), each designed to understand and identify the factors that have significant impact on the pattern of energy use of schools. Changes in the pattern of energy use of schools have occurred over the past four years. This fact highlights issues associated with static benchmarks. A significant difference in energy performance between primary and secondary schools meant that it was necessary to re-examine the way non-domestic buildings are classified. Factors were identified as having significant impact on the pattern of energy use. The characteristics raise new possibilities for developing sector-specific methods and improving comparability.     

Model-predictive control for non-domestic buildings: a critical review and prospects

Model-predictive control (MPC) has recently excited much interest as a new control paradigm for non-domestic buildings. Since it is based on the notion of optimization, MPC is, in principle, well placed to deliver significant energy savings and reductions in CO₂ emissions compared with existing rule-based control systems. The prospects for buildings MPC are critically reviewed, in particular, the central role of the predictive mathematical model that lies at its heart. The emphasis is on practical implementation rather than control-theoretic aspects, and covers the role of occupants as well as the form of the predictive model. The most appropriate structure for such a model is still an open question, which is considered alongside the development of the initial model, and the process of updating the model during the building's operational life. The importance of sensor placement is highlighted alongside the possibility of updating the model with occupants’ comfort perception. It is concluded that there is an urgent need for research on the automated creation and updating of predictive models if MPC is to become an economically viable control method for non-domestic buildings. More evidence through operating full-scale buildings with MPC is required to demonstrate the viability of this method.     

Evaluating the potential impact of global warming on the UAE residential buildings – A contribution to reduce the CO2 emissions

There is significant evidence that the world is warming. The International Panel of Climate Change stated that there would be a steady increase in the ambient temperature during the end of the 21st century. This increase will impact the built environment, particularly the requirements of energy used for air-conditioning buildings. This paper discusses issues related to the potential impact of global warming on air-conditioning energy use in the hot climate of the United Arab Emirates. Al-Ain city was chosen for this study. Simulation studies and energy analysis were employed to investigate the energy consumption of buildings and the most effective measures to cope with this impact under different climate scenarios. The paper focuses on residential buildings and concludes that global warming is likely to increase the energy used for cooling buildings by 23.5% if Al-Ain city warms by 5.9 °C. The net CO₂ emissions could increase at around 5.4% over the next few decades. The simulation results show that the energy design measures such as thermal insulation and thermal mass are important to cope with global warming, while window area and glazing system are beneficial and sensitive to climate change, whereas the shading devices are moderate as a building CO₂ emissions saver and insensitive to global warming.     

Using Display Energy Certificates to quantify public sector office energy consumption

The influence of internal and external characteristics on energy use in the public sector office stock in England and Wales is explored using a database of 2600 Display Energy Certificates (DECs) combined with other sources of disaggregated office information. The DEC office benchmarks are shown to match the median fossil thermal and electrical consumptions well. Analyses of heating, ventilation and air-conditioning (HVAC), size, occupancy density, building age, location and rateable value are considered. While newer offices are shown to have lower typical fossil-thermal consumption than older offices, this is counterbalanced by higher electrical consumption, resulting in higher typical CO₂ emissions. This has implications for the UK's emissions reduction targets for 2050, indicating that while building regulations that focus on thermal performance have been successful, a focus on electrical consumption (both regulated and unregulated) is key. The results are also compared with existing benchmarks for all UK offices, splitting the sample into four generic types, and compared with a similar smaller study of private offices. This indicates that public offices typically used less energy than the general benchmarks had previously predicted, particularly for prestige offices.     

Optimising the installation costs of renewable energy technologies in buildings: A Linear Programming approach

This paper demonstrates how Linear Programming (LP) can be applied to assist in the choice of renewable energy technologies for use in buildings to meet CO₂ emissions reduction targets. Since there are many possibilities for combining different renewable technologies, the capital costs associated with the installation of one or more renewables can vary widely. In terms of capital investment the preferred solution will be the one at least cost, and LP provides an effective way to find this minimum through the so-called “objective function”. This project has used “lp_solve”, a free-source Mixed Integer Linear Programming solver that has been embedded in a Microsoft Excel application called Carbon emissions And Renewables for Building OPtimisation Toolkit (CARB-OPT) developed by RES Ltd in collaboration with London South Bank University (Renewable Environmental Services Ltd. (RES) is the environmental consultancy of Long and Partners Engineering Group. RES is currently involved in a Knowledge Transfer Partnerships (KTP) project in conjunction with the Faculty of Engineering, Science and the Building Environment (ESBE) at London South Bank University). This paper reports the application of this LP optimisation process for an office building case study with four alternative combinations of renewables. The process showed the technology mix that would lead to the smallest investment needed to comply with UK Building Regulations requirements and regional planning targets. In addition, the process offers a robust methodology to test the impact that the key assumptions may have upon the optimum solution.     

Benchmarking the energy efficiency of government buildings with data envelopment analysis

Constructing an indicator to measure the effectiveness of energy management is important for energy agencies and authorities. This paper uses multiple linear regression method and data envelopment analysis to examine the effectiveness of energy management. First, the regression method using environmental factors is used to calculate the predicted energy usage intensity of each evaluated building. Data envelopment analysis is then employed to calculate overall energy efficiency, using the predicted energy usage intensity as output and the observed energy usage intensity as input. Data envelopment analysis can be further applied to measure the overall energy efficiency in details by examining environmental factors and management factors. Finally, the energy consumption of buildings can be measured to evaluate the effectiveness of energy management. Buildings examined as a case study in this paper are government office buildings in Taiwan. The results show that most of the buildings evaluated to report a higher predicted energy usage intensity have successfully used efficient energy management methods in energy saving.     

The development of reference values for energy certification of buildings in Lithuania

The paper deals with the experience in the field of arrangement of the building certification system in Lithuania. The arranged document provides the energy consumption in a building to estimate according to the calculation results, including heat losses through the building envelope elements, due to the ventilation, air infiltration and domestic hot water. The reference U-values for the building elements representing the best 50% of the building stock are derived. The changes in the energy consumption and reference values in regard with building renovation development are discussed.     

Comparative study between a ceramic evaporative cooler (CEC) and an air-source heat pump applied to a dwelling in Spain

The study described in this paper aims to evaluate comparatively the interest of an implementation of a ceramic evaporative cooler (CEC) compared to the use of a conventional device such as an air-source heat pump. This comparison is presented in three closely related ways: energy consumption, environmental impact and economic costs. This analysis is based on the hypothetical cooling of a specific room in a dwelling in six Spanish cities, each characterised by a different climate. The behaviour of the CEC in each climate is determined experimentally, reproducing the typical air conditions by an air-treatment unit. The total cooling demand in each city during the summer months is obtained from the data of the thermal load evolution in the room, provided by thermal load calculation software.