Session 6 Paper 1, CIBSE ASHRAE Technical Symposium, Imperial College, London, UK
18th and 19th April 2012
To truly understand how a building uses energy you need to know something about the building itself and about how it is used. In current parlance, that requires both an Asset and an Operational energy rating. An asset rating models the theoretical, as designed, energy efficiency of a particular building, based on the intrinsic performance potential of the building envelope (the fabric) and its services (such as heating, ventilation and lighting).The higher the numeric rating, the worse the building is, and the greater the opportunity to reduce carbon emissions by improving the building itself. However, the asset rating provides no information about how the building is operated in practice.
The operational rating records the actual energy use from a building over the course of a year, and benchmarks it against buildings of similar type. Factors other than building quality, such as unregulated loads (e.g. IT, plug-in appliances) or building user behaviour also create emissions, which are reflected in the operational rating.
There is significant confusion in the non-domestic property market between the two different building energy ratings currently in use. Property owners mistrust asset ratings because they don't map directly onto measured fuel bills.
As a result of a UNDP funded project for the Republic of Mauritius, BRE's Building Energy Modelling team has identified a possible solution which has been developed as an audit tool to underpin the Mauritian Energy Audit Management Scheme (EAMs). This tool – the Mauritian Building Energy Audit Tool (MBEAT) – captures and quantifies the degree of Energy Management within the building by the use of a spreadsheet tool. The data from this tool and the meter readings are then input into a version of iSBEM that has been adapted for this process and for the Mauritian building stock and climate.
This paper discussed the underlying principles of how the tools were designed and how they bridge the gap between the two ratings to provide a more complete picture of how energy is used in a building.