Marjanovic-Halburd, Ljiljana; Korolija, Ivan; Liddiard, Rob; Wright, Andrew; (2008) Operational Rating vs Asset Rating vs Detailed Simulation. In: 5th International Conference on Improving Energy Efficiency in Commercial Buildings - IEECB'08. The European Council for an Energy Efficient Economy: Frankfurt, Germany.

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Abstract

It is widely acknowledged that carbon dioxide emission is one of the primary causes of global warming. The Kyoto protocol, to which the European Union (EU) is a signatory, has an objective to reduce emissions of six key greenhouses gasses. This objective is unlikely to be met without the introduction of more primary legislation. Throughout the EU, the building stock is responsible for around 45% of all carbon emissions and this sector is clearly a primary target for legislative actions. This has led to the introduction of the Energy Performance of Building Directive (EPBD). The EPBD requires several different measures to achieve prudent and rational use of energy resources and to reduce the environmental impact of the energy use in buildings. The three main components for implementation of the Directive are: calculation methodology, energy certificate and inspections of boilers and air-conditioning. This paper is concerned with energy certificates of buildings. The principal categories for the energy certificate scheme are Asset rating, based on calculated energy use and Operational rating, based on metered energy. The Asset rating is determined by modelling the building under a defined set of standard conditions of occupancy, climate, environment and use. Asset rating includes energy use of heating, cooling, hot water, ventilation and lighting for non-domestic buildings. It will apply to both new and existing buildings. In the case of existing buildings, the calculation methodology for Asset rating will have to take into account that design data is unlikely to be available in existing buildings. In contrast, the Operational rating, will be based on metered energy. The metered energy consumption includes energy uses for all purposes. These intrinsic differences opened a debate about if these two ratings are at all comparable, and if so under which circumstances. This paper, as part of the UK research project “Carbon reduction in buildings”, investigates the issues surrounding the application of Asset rating on existing buildings and its compatibility with Operational Rating, but also with detailed simulation software. The case study is a typical narrow plan office building hosting University estate built in early 1970 with treated floor area of 1280m2 on 4 flours. The methodology used for the Asset rating is UK national calculation methodology SBEM, while the detailed simulation program used is DesignBuilder. In absence of a UK national methodology for Operation rating, EPLabel software has been applied, although the building energy consumption has been compared with UK design guide for office buildings. The significant differences in results (for gas 207kWh/m2 vs 276kWh/m2 vs 164kWh/m2) suggest that great care and understanding must in employed while producing and interpreting building energy certification.

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