We have recently had very interesting results in trying to benchmark energy performance of a Retail Centre seeking a Green Star - Existing Building rating. Some findings below.
- Using a kWh/m2/annum benchmark that is based on Gross Lettable Area (GLA) can yield vastly skewed results! This is because the GLA as a percentage of overall area (GFA) can vary hugely between centres. For some, only 50% of their building area is GLA.
- Energy benchmarks based on GFA are hard to come by. Here is a great publication by Caroline Martin however which has benchmarks based on GFA derived from a large sample size in Cape Town, South Africa. http://www.erc.uct.ac.za/sites/default/files/image_tool/images/119/Papers-2013/13Martin-lowcost_national_energy_benchmarks.pdf
We found that using a GFA based benchmark instead of GLA gave us far better and fairer results! The GBCSA approved it for our Green Star rating, but you would need to check with them for yours.
Happy benchmarking!