A review of benchmarking, rating and labelling concepts within the framework of building energy certification schemes

Accepted Manuscript Title: A review of benchmarking, rating, labelling concepts within the framework of building energy certification schemes Authors: Luis P´ erez-Lombard, Jose Ortiz, Roc´ ıo Gonz´ alez, Ismael R. Maestre PII: S0378-7788(08)00220-X DOI: doi:10.1016/j.enbuild.2008.10.004 Reference: ENB 2526 To appear in: ENB Received date: 1-2-2008 Revised date: 10-10-2008 Accepted date: 13-10-2008 Please cite this article as: L. P´ erez-Lombard, J. Ortiz, R. Gonz´ alez, I.R. Maestre, A review of benchmarking, rating, labelling concepts within the framework of building energy certification schemes, Energy and Buildings (2008), doi:10.1016/j.enbuild.2008.10.004 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. Elsevier. Versión Aceptada. Licencia Creative Commons CC BY-NC-ND Page 1 of 31 Accepted Manuscript 1 A REVIEW OF BENCHMARKING, RATING AND LABELLING CONCEPTS WITHIN THE FRAMEWORK OF BUILDING ENERGY CERTIFICATION SCHEMES Abstract Energy certification schemes for buildings emerged in the early 1990s as an essential method for improving energy efficiency, minimising energy consumption and enabling greater transparency with regards to the use of energy in buildings. However, from the beginning their definition and implementation process were diffuse and, occasionally, have confused building sector stakeholders. A multiplicity of terms and concepts such as energy performance, energy efficiency, energy ratings, benchmarking, labelling, etc, have emerged with sometimes overlapping meanings. This has frequently led to misleading interpretations by regulatory bodies, energy agencies and final consumers. This paper analyses the origin and the historic development of energy certification schemes in buildings along with the definition and scope of a building energy certificate and critical aspects of its implementation. Concepts such as benchmarking tools, energy ratings and energy labelling are clarified within the wider topic of certification schemes. Finally, a seven steps process is proposed as a guide for implementing building energy certification. Keywords Energy certification, energy labelling, energy rating, energy benchmarking. Page 2 of 31 Accepted Manuscript 2 1. Introduction World energy crises, such as the 1979 oil shortage caused by the Iranian revolution or the drastic increase in the price of oil in the early 1990s due to the first Gulf War, raised governmental concerns over the supply of and access to worldwide energy resources. European nations, highly dependent on energy resources from politically unstable areas, were particularly affected. At the same time, the global contribution from the energy consumption of buildings was steadily increasing, to around 20-40% in developed countries and exceeding the other major sectors, industry and transportation [1]. It was under such circumstances that a new concept relating to energy efficiency in buildings emerged in the early 1990s as an essential method of reducing energy use and CO2emissions: energy certification for buildings. An overall objective of energy policy in buildings is to save energy consumption without compromising comfort, health and productivity levels. In other words, consuming less energy while providing equal or improved building services, that is, being more energy efficient. Regulatory bodies (Government, energy agencies, local authorities, etc.) have three basic instruments available for encouraging savings and maximising energy efficiency in buildings: regulations, auditing and certification. Building energy regulations, also referred to as building energy codes, establish minimum requirements to achieve energy efficient design in new buildings. The primary aim is saving final energy or any related parameter (primary energy, CO2 emissions or energy costs) without compromising comfort or productivity. Europe developed early building envelope regulations in the late 1970s to reduce heat transfer through envelope elements and control vapour diffusion and air permeability. This was followed by regulations or best practice recommendations on design, calculation and Page 3 of 31 Accepted Manuscript 3 maintenance of building thermal services (HVAC and DHW). Eventually, HVAC equipment was subject for the first time to minimum requirements of energy efficiency. This paper analyses energy certification in buildings and focuses on three critical issues: (1) the definition and scope of energy certification schemes, (2) building energy classification and (3) the implementation of energy certificates in buildings. 2. Definition and scope of building energy certification From the beginning this term has been imprecisely and inconsistently used. In the European Council Directive 93/76/CEE [2] to limit carbon dioxide emissions by improving energy efficiency, energy certification is presented as one of the cornerstones for achieving energy efficiency in buildings. This certification “shall consist of a description of their energy characteristics, must provide information for prospective users concerning a building's energy efficiency” and additionally, “may also include options for the improvement of these energy characteristics”. The directive was non-mandatory and also full of ambiguities (with regards to how to provide information about building energy efficiency) that resulted in low impact implementations of its requirements across Member States. This is the case of the Spanish certification schemes for dwellings, CEV [3] and for commercial buildings, CALENER [4]. Almost ten years later, the EU acknowledged the need for a new regulatory instrument and introduced directive 2002/91/EC [5] on the energy performance of buildings. Directive 2002/91 was ambitious, although lacked sufficient detail for a clear and consistent implementation across the EU members. Among other objectives it contained the requirement for a building energy performance certificate as “a certificate Page 4 of 31 Accepted Manuscript 4 recognised by the Member State... which includes the energy performance of a building calculated according to a methodology...”. This second approach to an energy certification definition perpetuated two unresolved issues: how to define and how to measure building energy efficiency. It also introduced a new term energy performance referring to building energy use. In this context, European energy performance indicators (EPI) and American energy-intensity indicators [6] or energy use intensities (EUI), are equivalent since both are ratios of energy use input to energy service output (site energy per square meter, CO2emissions per home, etc.). The new European standard EN 15217 [7] is an attempt to describe methods for expressing energy efficiency and certification of buildings. Energy Performance Certificates are redefined within the development of a certification scheme (Figure 1) which must contain at least: • An overall energy performance index (EPI) stated in terms of energy consumption, carbon dioxide emissions or energy cost, per unit of conditioned area to allow the comparison between buildings. • An overall minimum efficiency requirement to be established by the legislation as a limit of the energy performance index (EPIMAX). The standard recommends its correlation with other parameters (such as climate and building type) or a self-reference method. • A label based in the A to G bands to achieve a suitable grading of buildings. A key issue is the definition of the scale that should make reference, at least, to the building energy regulations (Rr), the existing building stock (Rs) and the zero-energy building (R0). Page 5 of 31 Accepted Manuscript 5 • Energy consumption by the main building components, such us building envelope and services, together with recommendations of energy efficiency measures for building owners’ consideration. The scope of the certification is therefore extended not only to the energy performance of the building but also to include a minimum requirement and a label or class that allows users to compare and assess prospective buildings. The certificate must contain, amongst other information, a classification of the building energy efficiency based on an energy label. 3. Building energy classification The term building energy classification encompasses any procedure that allows the determination of the quality of a building (in terms of energy use) in comparison with others. Several similar terms have been used which has caused some confusion within the industry. This section attempts to clarify the concepts of benchmarking, rating and labelling in the context of building energy classification. 3.1. Benchmarking process Originally, the word benchmark was used exclusively in topography to precisely define a reference point in terrain or geological analysis. In the 1970s, some companies developed benchmarking tools to allow comparison of key production parameters and thus to check whether improved processes enhanced their performance. In the 1990s, the term building energy benchmarking started to be used to refer to the comparison of energy use in buildings of similar characteristics. Basically it consists of a comparison of the EPI of a building with a sample of similar buildings. A common EPI used for many building types is annual energy use per unit Page 6 of 31 Accepted Manuscript 6 area but others such as energy per worker or energy per bed may also be used. Energy services companies use the EPI as a starting point in energy audits and assess saving opportunities by comparing with existing references (benchmarks) of average (typical), above average (good) and excellent (best) practice. At the design stage, energy performance indices for different designs are of great use when choosing suitable technologies, particularly if benchmarks for similar buildings are available. Last but not least, governments should consider benchmarking in the early conception, development and implementation of energy efficiency policies within the building sector. The benchmarking process consists of four stages [8]. First, it is necessary to hold or develop a database with information on the energy performance of a significant number of buildings. This information should be categorised, at least, by building type and size. Second is gathering the relevant information for the evaluation of the EPI for the actual building. Third, a comparative analysis of the building energy performance against the samples held in the database gives a quantification of the quality of the building in terms of energy use. Finally, energy efficiency measures that are feasible from both technical and economical perspectives should be recommended (Figure 2). The energy consumption of the actual building can be predicted via a computersimulation-method or measured on site (Table 1). Energy simulation offers detailed information and a wide variety of outputs, however, it may require a great number of inputs, skilled users and a significant amount of time to gather and input the necessary data, all of which can make the process expensive. Measured consumptions can be obtained from energy bills or monitoring. Energy bills give easy access to energy consumption by energy source, although it is difficult to establish a split by end-uses. Energy monitoring based on sub-metering can also be expensive but offers profuse Page 7 of 31 Accepted Manuscript 7 performance information of great use to auditors and building maintenance. In summary, energy use of new and existing buildings may be obtained at different levels of accuracy and cost. In any case, there are always discrepancies between predicted and measured energy use. Some sources of error are natural uncertainties like the differences between real weather and typical simulation climate data. Others, like the use of default data for internal loads may be reduced by adjusting the building model to the existing building real conditions. The influence of occupant behaviour on energy performance is considerable. Variables like number of people and activity, thermostat setpoints, equipment usage, natural ventilation, hot water demand, etc. are strongly dependent on the occupants or owner and can result in large variations in energy use, even for the same climate and building type. Database information availability is a different issue. Gathering energy information to populate a database with a representative sample of the building stock is not only expensive but also technically complex. It is not surprising that only a few nations have undertaken this task to date. Usually, information is collected on site from building owners, tenants, facility managers, etc. An outstanding example is the US Energy Information Administration (EIA) database and the later surveys for both the residential sector (RECS [9]) and commercial buildings (CBECS [10]). A different approach to database generation is the application of building energy simulation to a variety of building types for a range of energy parameters (parametric benchmarking). Careful selection of building types and calculation methods is critical to the validity of the database. Another added constraint is the need to customise building envelopes and HVAC sizing for each climate and system type. An advantage is the Page 8 of 31 Accepted Manuscript 8 possibility of covering a wide range of building energy consumption characteristics with a suitable selection and variation of the energy parameters. Additionally, energy simulation provides a wider range of energy outputs for future comparisons. Finally, any benchmarking program that combines the use of measured energy consumption for actual buildings with a database based on simulation must be calibrated to ensure the comparative analysis is consistent. At the moment, most benchmarking programs are based on measured energy use of existing buildings. The core of the benchmarking process is the comparative analysis. First, the degree of similarity between buildings to be compared must be specified. Every parameter not easily influenced by the design process and with a potential significant impact on building energy use must be similar in the comparison process. The minimum degree of similarity is two: same climate and building type. Within the building type, it is common to use subtypes to avoid the comparison of buildings with different shape or mixes of activities. For example, individual detached houses consume significantly more energy than flats in the same weather, and if compared within the same building type (e.g. dwellings) would have their energy quality artificially degraded. A subset of comparable buildings could be obtained by filtering the database against similarity parameters. This is called the comparison scenario. Energy intensity frequency distribution curves for that scenario enables determination of a percentile ranking, percentage of buildings with better (or worse) energy performance. Programs such as Energy Star [11] score from 1 to 100, based on models and normalization methods of statistical analysis applied to the EIA database. To obtain a certificate (Energy Star Label) the building must achieve a minimum of 75 points, equivalent to belonging to the quartile of better energy efficiency. Other tools such us Cal-Arch [12] Page 15 of 31 Accepted Manuscript 15 make the certificate expensive and have possible repercussions on building purchase or rental prices, on the experience and training required from professionals and manufacturers, or on the ability of the government to control and inspect the certification process. Thus, credibility and success of the certification scheme are strongly dependent on the second step of building energy certification implementation: development of an energy calculation tool. 4.3. How should the limit for energy efficiency be set? Building regulations should answer this question setting the minimum overall requirement for the energy performance index (EPI < EPIr). Again, there are two different approaches: fixed and customized limits. Energy efficiency of different building types is not comparable in terms of the energy performance index, since they provide different services. A hospital is not less efficient than a dwelling despite having an EPI more than five times bigger on average. Thus the limit value should be discriminated at least by building type. Climate dependence of the overall requirement causes controversy. Some authors [29] defend an unique threshold value for every climate because of heating/cooling compensation and an excessive cost for little environmental benefit, while others propose an increasing EPI limit with increasing climate severity [30]. Other parameters for achieving discrimination could be building shape, energy source and ventilation rates. Therefore, in the fixed limit option, the threshold value is dependent upon the parameters whose impact is to be reduced or neutralized: ...)climate,type,building(fEPIr(4) Page 16 of 31 Accepted Manuscript 16 A customised limit may be obtained by the self-reference (also called notional building) approach, where EPIris set by a reference building having at least same location, geometry and pattern of use but different envelope and systems. The difference between the standards and calculation tool languages might be a source of problems. The rules to model the reference building must be written in the calculation tool terminology while regulations use a normative language. Thus, certification and energy code developers must have experience in both fields to assure the consistency and effectiveness of the certification scheme. 4.4. To what should the building energy efficiency be compared? Once the EPI of the building has been calculated, a sample of buildings to be compared to must be found. Thus, the fourth step in the implementation process is the definition of the comparison scenario. The key question is whether the EPI of a wide number of buildings is available. For the affirmative answer, the comparison is feasible and a certain degree of similarity between buildings to be compared must be set. Minimum degree of similarity would be two, climate and building type, but other parameters like energy sources or building shape may be considered. A subset of comparable buildings must be obtained by filtering the database against similarity parameters. Alternatively, when there are no buildings to be compared to, the solution is the selfreference approach where the actual building is compared with a reference building derived from the actual building according to rules laid down in the energy code. Page 17 of 31 Accepted Manuscript 17 4.5. How should building energy efficiency be labelled? The next step is to classify the building energy performance related to the comparison scenario by assigning an energy label. First, a label index (LI) should be defined. If a sample for comparison is available, LI would be defined as the ratio of the EPI of the building to the EPI average value of the sample (equation 1). In the self-reference approach, label index shows the saving percentage in relation to the reference building performance (equation 3). Second, we must set the limits between classes (definition of the scale) on the label index frequency curve if the comparison scenario is available or depending on the saving percentages ahead the reference building for the self-reference approach. Among others, two criteria should be considered for the scale definition: scale sensitivity, the ability to improve the energy label of a given building, and scale credibility, buildings with better labels should save energy. 4.6. What energy efficiency improvements should be recommended? Building energy certification schemes should produce a list of recommended measures to encourage building designers, owners, operators and users to improve the energy performance of their buildings. For new buildings at design stage, engineers should work in parallel with architects to adjust design parameters to reduce energy consumption. An early stage model of the building could be enough for the evaluation of energy efficiency measures with the energy calculation tool in order to check how far and cost-effective an improved label would be. Energy analyst knowledge and experience are necessary to suggest those measures of greater impact on savings and labels. Intelligent tools capable to automatically explore different options and even to select an optimum are part of the Page 18 of 31 Accepted Manuscript 18 coming future, meanwhile a results based analysis tool to guide the user in the improvement process could be of great help. 4.7. What information should the energy certificate include? Obviously, building energy certification final report must include at least the energy label and the EPI. In order to assess what other information should be included we suggest three categories of energy information according to its final use: (1) administrative data such as building address, date, certifier name, etc. are necessary to identify both building and certifier, (2) energy variables to be controlled and inspected (glass shading coefficient, boiler efficiency, etc.) by competent bodies and (3) information gathered by the energy agencies to populate their building database (building type, total area, conditioned area, HVAC system type, energy sources, etc.). 5. Conclusions The implementation of the new European building energy certification scheme is a complex task facing seven critical issues: (1) definition of the energy performance index, (2) development of an energy performance calculation tool, (3) setting a threshold value for the performance index, (4) definition of the comparison scenario, (5) definition of the scale for energy labelling, (6) identification of potential energy efficiency measures and (7) gathering energy information in the certification process. Therefore, energy labelling is only one step in the implementation process. The words energy rating should only be used for the assessment of the energy performance, both for new and existing buildings, in standard or actual conditions. Energy benchmarking tools provide a comparative appraisal of the energy performance of an existing building within a comparison scenario. Assigning classes or labels Page 19 of 31 Accepted Manuscript 19 implies a step forward: defining a scale based on a labelling index. The definition of the scale is more a political issue than a technical one, with the overall aim of reducing the energy consumption. The success of building energy certification schemes will almost certainly depend on: (1) the ability to obtain better labels cost-effectively, (2) the credibility achieved by real energy savings and (3) the degree of commitment to the global environmental crisis of the building sector stakeholders. Page 20 of 31 Accepted Manuscript 20 References [1] Pérez-Lombard, L. et al. A review on buildings energy consumption information. Energy and Buildings 2008; 40(3):394-398. [2] Council Directive 93/76/CEE of 13 September 1993 to limit carbon dioxide emissions by improving energy efficiency (SAVE). [3] Calificacion Energetica de Viviendas: Fundamentos Técnicos y Manual del Usuario. Madrid. 1999. [4] CALENER (Calificación Energética de edificios). Versión 2.02. Desarrollado por el Grupo de Termotecnia, E.S. Ingenieros de Sevilla. 2003. [5] Directive 2002/91/EC of the European Parliament and of the Council of 16 December 2002 on the energy performance of buildings. [6] Energy Information Administration (EIA). Measuring energy efficiency in the United States Economy: A Beginning. DOE/EIA-0555(95)/2. Washington D.C.: Department of Energy. 1995. [7] EN 15217. Energy performance of buildings - Methods for expressing energy performance and for energy certification of buildings. 2007. [8] Matson, N.E. and Piete, M.A. Review of California and National Methods for Energy Performance Benchmarking of Commercial Buildings, Ernest Orlando Lawrence Berkeley National Laboratory, 2005. [9] Energy Information Administration. Residential Energy Consumption Survey (RECS). U.S. Department of Energy, 2001. [10] Energy Information Administration. Commercial Buildings Energy Consumption Survey (CBECS). U.S. Department of Energy, 2003. Page 21 of 31 Accepted Manuscript 21 [11] Environmental Protection Agency and the U.S. Department of Energy. ENERGY STAR program. [12] California Energy Commission. CAL-ARCH (California Energy benchmarking tool). [13] Carbon Trust/Action Energy. Energy Consumption Guide 19, Energy use in offices. 2003. [14] Santamouris, M. et al. Energy performance of residential buildings: a practical guide for energy rating and efficiency. James & James Earthscan, 2005. [15] EUROPROSPER. European Programme for occupant satisfaction, productivity and environmental rating of buildings: certification of existing building energy performance. <http://www.europrosper.org/> [16] EPLabel. A programme to deliver energy certificates based on measured energy consumption for display in Public buildings across Europe within a harmonising framework. <http://www.eplabel.org> [17] ENPER-EXIST. Applying the EPBD to improve the Energy Performance Requirements to Existing Buildings. Building stock knowledge. <http://www.enper-exist.org> [18] U.S. Green Building Council. LEED-NC. Green Building rating system for new construction & major renovations. Version 2.2. 2005. [19] Stein, J. R. and Meier, A. Accuracy of home energy rating systems, Energy 2000; 25(4):339-354. [20] Míguez, J.L. et al.. Review of the energy rating of dwellings in the European Union as a mechanism for sustainable energy. Renewable and Sustainable Energy Reviews 2006; 10(1):24-45. Page 22 of 31 Accepted Manuscript 22 [21] EN 15603. Energy performance of buildings – Overall energy use and definition of ratings. 2008. [22] Meier, A., Olofsson, T. et al. What Is an Energy Efficient Building? ENTAC 2002, National Conference of Technology in the Built Environment, Foz do Iguaçu, Brazil. 2002. [23] Council Directive 92/75/EEC of 22 September 1992 on the indication by labelling and standard product information of the consumption of energy and other resources by household appliances. [24] Real Decreto 47/2007, de 19 de enero, por el que se aprueba el Procedimiento básico para la certificación de eficiencia energética de edificios de nueva construcción. [25] BREEAM, BRE Environmental Assessment Method. <http://www.breeam.org/>. [26] ANSI/ASHRAE/IESNA 90.1-2004. Energy Standard for Buildings Except Low-Rise Residential Buildings. 2004. [27] European Commission. Directorate-General of Energy and Tranport. Green paper on Energy efficiency. How to do more with less? Office for Official Publications of the European Communities, 2005. [28] Roulet, C.-A. et al. ORME: A multicriteria rating methodology for buildings. Building and Environment 2002; 37(6):579-586. [29] García-Casals, X. Analysis of building energy regulation and certification in Europe: Their role, limitations and differences. Energy and Buildings 2005; 38(5):381-392. Page 23 of 31 Accepted Manuscript 23 [30] Sánchez, F. et al. A new methodology towards determining building performance under modified outdoor conditions. Building and Environment 2006; 41(9):1231-1238. Page 24 of 31 Accepted Manuscript 24 Figure 1. Scope of the new European building energy certification scheme. Figure 2. Building energy benchmarking process. Figure 3. Labelling scale and cumulative frequency curve of labelling index (LI). Figure 4. Comparison of energy scales (CEN and CALENER labels and BREEAM and LEED-NC credit points) of different certifications schemes in terms of saving percentage ahead certain reference. Page 31 of 31 Accepted Manuscript Figure