EPIC Documentation
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Units in EPIC
Units describe data. When we compare 2 kilograms to 2 square feet, the units help us to understand which is a measure of mass and which of area. In EPIC, where data are used both to calculate and present the result of carbon reduction measures, the interpretation of units is essential to the evaluation and comparison of carbon reduction strategies. EPIC uses a set of units specific to the tool's objectives. The units included in EPIC, and the consequences of their inclusion, are described below.

Area Units

  • Square feet. As the geographic scope of EPIC is currently limited to the United States, area is described in square feet and emissions evaluated on a per square foot basis. In much of the literature on carbon emissions from buildings, however, emissions are compared on a per square meter basis. To compare results from EPIC to results on a per square meter basis, unit conversion is necessary.

Time Units

  • Years. EPIC evaluates emissions on an annual basis. The choice of an annual basis means that EPIC cannot describe intra-annual variations in carbon emissions from electricity, such as seasonal or daily variations. This approach is standard practice, but precludes inclusion of important carbon reduction measures such as demand response or battery storage in EPIC.
Energy and Power
  • kBtu/sf/yr. This unit describes Energy Use Intensity (EUI), the quantity of energy required by a building per square foot per year. 1 kBtu is equivalent to 1,000 British thermal units and 293 Watt-hours. In EPIC, energy use is measured at the project site (site EUI) and not at the generation source.
  • kW. The nameplate capacity of a solar array is described in kilowatts (kW), a unit of power.

Carbon Emissions

  • Metric tons of CO2-equivalent. Following conventions across the literature, carbon emissions are described in metric units. One metric ton is equal to 1000 kilograms and 2,204 pounds. EPIC measures emissions of "carbon dioxide equivalents," using emission factors published by the IPCC to include emissions of extremely potent greenhouse gases (such as methane and nitrous oxide) based on their comparability to carbon dioxide emissions.
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