Short answer: Below are the Site-to-Source conversion factors, which are the multipliers to convert Site energy into Source energy for each fuel type.
Longer answer: Commercial buildings all use different mixes of energy including electricity, natural gas, fuel oil, district steam, etc. In order to evaluate energy performance of these buildings, we have to express all of the different energy types in a single common unit. Source energy is the most equitable unit of evaluation, because it includes the energy “losses” associated with generating and delivering the fuel.
Site energy, the amount of heat and electricity consumed by a building as reflected in utility bills, does not include the “losses.” 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, fuel oil, or coal.
- 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 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 the losses and enabling a complete energy assessment.