Rating the energy efficiency of air conditioned buildings.

BRE, working with a group of industry and property representatives, have developed a simple method for assessing the likely energy efficiency of air conditioned and mechanically ventilated buildings. For new buildings, the method uses information available at the early design stages. It therefore provides designers with a tool to assess the implications of various plant and envelope options from the beginning. It can be used as a label or target for energy efficiency and, as such, as a means of assessing buildings in both voluntary systems such as BREEAM or perhaps in Building Regulations. Using the index in reverse could provide designers with a means of targeting the size of plant and therefore plant room space. The resulting Energy Performance Index has been tested against energy use data from existing buildings, initially for air conditioned and mechanically ventilated office buildings, and works well despite its simplicity. The method applies equally to existing buildings and new building designs. It can be applied to several building sectors, such as offices, hotels and department stores to indicate likely efficiency relative to suitable benchmarks, like the Energy Efficiency Office's Energy Consumption Guide 19 for Offices.