To help explain, let’s look at an example with a property that is 75% Office, 25% Fitness Center (100,000 sq ft total). Here are the steps:
- We calculate your Actual Source EUI by dividing your Source Energy by your total Gross Floor Area (Office and Fitness Center combined).
- We calculate your “Predicted” Source EUI for your Office. We start with the average Source EUI for an Office and make adjustments based on your location (for climate and weather data – using HDD and CDD) and your specific Property Use Details (Hours of Operation, Number of Workers, etc.). For example, if you have less than the average Number of Workers, we’ll assume you needed a little less energy than average. If you had a very hot summer, we’ll assume you needed a little more energy than average.
- We assume that the predicted Source EUI for your Fitness Center is identical to the predicted Source EUI of your Office. Therefore, the predicted Source EUI for the whole building equals the Predicted Source EUI of the Office. We do this because there is no valid means of predicting the energy use for the Fitness Center. It is reasonable to assume that it could be greater than or less than the Office. EPA does not make an assumption either way, but rather assumes a constant EUI. This limitation is the reason why the other use types are limited to 25% of total floor area. The limit reduces the amount of error introduced by the energy intensity assumptions. If this 25% limit is exceeded, the property will not receive a score.
- We compare your Predicted Source EUI with your Actual Source EUI. If your actual EUI is lower (better) than your predicted EUI, then you are using less energy than we predicted and your score will be above 50. If your actual EUI is higher (worse) than your predicted EUI, then you are using more energy than predicted and your score will be below 50. The ratio of your actual source EUI to your predicted source EUI is called the efficiency ratio, which can be mapped through a lookup table to determine your 1 -100 ENERGY STAR score.
See this document for more details: ENERGY STAR Score Technical Reference