Building Energy Benchmark Calculator

Energy Use Intensity normalises whole-building consumption by floor area so that buildings of different sizes can be compared. Every fuel must first be converted to a common thermal unit: electricity at 3.412 kBtu per kWh and natural gas at roughly 100 kBtu per therm, since a therm is defined as 100,000 Btu. Dividing the sum by gross floor area gives site EUI in kBtu per square foot per year. Source EUI restates the same consumption as primary energy by applying source-to-site multipliers of about 2.80 for grid electricity and 1.05 for natural gas, reflecting that a conventional thermal power plant converts only around a third of fuel energy into delivered electricity once transmission losses are included. Interpretation depends entirely on building type, because operating requirements differ by an order of magnitude. Typical US median site EUIs are near 30 for warehouses, 60 for schools, 85 for offices, 95 for hotels, 200 for restaurants and 250 for hospitals, the last two driven by continuous operation and heavy ventilation and cooking loads. Carbon is a separate calculation: natural gas emits about 53 kg of CO2 per thousand cubic feet burned on site, while electricity ranges from roughly 0.2 kg per kWh on hydro or nuclear heavy grids to near 1.0 kg per kWh on coal heavy grids, against a US average near 0.42. The main limitation of a raw EUI is that it is unnormalised: it does not correct for climate severity, occupancy density or operating hours, all of which a formal ENERGY STAR score adjusts for through regression.

ENERGY STAR began in 1992 as a US Environmental Protection Agency voluntary labelling program for computers and monitors, and was extended to buildings later in the decade. Portfolio Manager, the online benchmarking platform behind the modern building score, was launched in 1999, and offices were the first commercial building type eligible to earn the label. The 1 to 100 scale is anchored so that 50 represents median performance among comparable buildings, and 75 is the certification threshold, meaning top quartile performance. The statistical backbone is the Commercial Buildings Energy Consumption Survey, run by the US Energy Information Administration since 1979 and repeated at multi-year intervals. It supplies the national sample from which the regression models predicting expected energy use by building type, climate, hours and occupancy are estimated. Mandatory benchmarking followed voluntary tools: New York City adopted Local Law 84 in 2009 requiring annual benchmarking and disclosure for large buildings, a model copied by dozens of US cities. The next step moved from disclosure to enforceable limits. New York City Local Law 97, enacted in 2019, sets declining carbon intensity caps for buildings above 25,000 square feet beginning in 2024 and tightening in 2030, with penalties assessed per metric ton of exceedance, while ASHRAE Standard 100 provides the corresponding technical framework for energy efficiency in existing buildings.