Here are the steps we use to compute an ENERGY STAR Score:
- We calculate your Actual Source EUI by dividing your Source Energy by your Gross Floor Area (GFA).
- We calculate your “Predicted” Source EUI. We start with the average Source EUI for your property type and make adjustments based on your location (for climate and weather data – using HDD and CDD) and your specific Property Use Details (such as Hours of Operation and Number of Workers). 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 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.
If your property has multiple scorable property types, then we calculate the "Predicted" Source EUI (Step 2 above) for each property type, combine these predictions based on the size of each space, calculate the efficiency ratio, and map that ratio to your 1-100 score using a look up table that is adjusted to account for the different property types.
If your property has a data center (with metered IT energy), then the same procedure above is followed, with an additional step. Stand-alone data centers are not evaluated using the EUI based model like above, but instead a PUE (power usage effectiveness) model (PUE = Total Data Center Source Energy/ IT Source Energy), where the Predicted PUE is compared with the Actual PUE. But, since this data center is only part of the property, we don’t know the Total Data Center Source Energy, and therefore we can’t calculate an Actual PUE to compare to the Predicted PUE. Instead, we use the Predicted Source Energy for the data center as we do for other property types. The Predicted Source Energy for a Data Center = Predicted PUE * IT Energy Use. This data center Predicted Source Energy is combined with the other space type’s Predicted Source Energy(s) based on the size of each space. Finally, we calculate the efficiency ratio (the ratio of your actual property Source EUI to your predicted Source EUI), and map that ratio to a combined lookup table with each property type to determine your 1-100 score.
For more information, see our general ENERGY STAR Score Technical Reference.
Or the specific document for for each property type:
- Data Center
- Hospital (General Medical and Surgical)
- K-12 School
- Medical Office
- Multifamily Housing
- Office (covers office, bank branch, financial office, and courthouse)
- Residence Hall/ Dormitory
- Retail Store (covers retail and wholesale club/supercenter)
- Senior Care Community
- Supermarket/Grocery Store
- Swimming Pool
- Warehouse (covers distribution center, non-refrigerated warehouse, and refrigerated warehouse)
- Wastewater Treatment Plant
- Worship Facility