Source Energy
Commercial buildings use different mixes of energy including electricity, natural gas, fuel oil, district steam, and many others. To evaluate energy performance for these buildings, we must express these different energy types in a single common unit. Source energy is the most equitable unit of evaluation and enables a complete assessment of energy efficiency.
Site energy may be delivered to a facility in one of two forms. Primary energy is the raw fuel that is burned to create heat and electricity, such as natural gas or fuel oil. Secondary energy is the energy product created from a raw fuel, such as electricity purchased from the grid or heat received from a district steam system. A unit of primary energy and a unit of secondary energy consumed at the site are not directly comparable because one represents a raw fuel while the other represents a converted fuel. Ultimately, buildings require heat and electricity to operate, and there are always losses associated with generating and delivering this heat and electricity. Source energy traces the heat and electricity requirements of the building back to the raw fuel input, thereby accounting for any losses and enabling a complete thermodynamic assessment.
Ultimately, the goal of the conversion to source energy is to account for the total primary fuel needed to deliver heat and electricity to the site. Generally, this means the methodology should perform the following adjustments for energy consumed on site:
Primary Energy. Account for losses that occur in the distribution, storage and dispensing of the primary fuel (e.g., natural gas, fuel oil).
Secondary Energy. Account for conversion losses at the plant in addition to losses incurred during transmission and distribution of secondary energy to the building (e.g., electricity, district steam).
The Benefits of Source Energy
· Allows for a whole-building assessment that combines all fuels
· Evaluates all buildings fairly, regardless of heating system
· Fairly evaluates electric heating in relation to natural gas and steam systems
o Identifies geothermal heating as most efficient
o Evaluates air source heat pump systems as efficient, on par with natural gas
o boilers and district steam systems
o Identifies electric resistance heating as least efficient
· Provides the equitable comparison of steam systems with natural gas-fired systems
· Fairly compares natural gas boilers with different on-site efficiency levels
Source: Energy Star - U.S. Environmental Protection Agency
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