Defining Net Zero

There is a wide variation on the definitions of net zero, however the general concept is that on an annual basis the energy consumption of a building is offset by renewable energy generation. Some definitions use site energy, or the energy as measured at the building’s utility meter. Others definitions use source energy, which is the primary energy consumed at the utility source (e.g. coal consumed at the electrical power plant). Still other definitions use the greenhouse gas emissions attributed to the energy consumed, offset by the credits in emissions generated by renewable energy sources. Finally some definitions only allow for on(site renewable energy generation.

As this project is conceptually located in Cambridge Ontario, we elected to use a variation on the carbon neutral definition used by Sustainable Waterloo, a local volunteer standard for businesses seeking to achieve carbon neutral operations. That standard is based on measured utility information as well all energy uses to operate the building. However it does allow for up to 49% of the renewable energy supply to be purchased through off(site renewable energy such as Bullfrog Green Power or other certified EcoLogo green power sources. Using this standard and limiting the energy consumption consideration to just the building’s energy use, for the purposes of this report, the following qualifications will be used to ensure a complete definition of net zero:

  • Net zero will be evaluated using the energy consumption value as calculated by an energy model over the course of one year.
  • Site energy, not source energy will be considered. Exported energy (e.g. from solar power) will offset imported energy (e.g. natural gas and/or electricity consumption) on an equivalent energy unit basis. Site energy is the consumption that is measured by the on(site utility meters. Source energy is the amount of energy provided by the utility plant, including all losses along the path of energy.
  • Following similar rules to the Sustainable Waterloo Region carbon neutral initiative (http://www.sustainablewaterloo.org/), no more than 49% of the
    building’s modelled energy consumption may be purchased in offsets. Only green power as recognized by Eco(Energy will be considered as eligible
    offsets.

Figure 1: Purchased Offsets vs. On Site Generation

With a large enough investment in both offsets and site area for renewable technologies, virtually any building can achieve a net zero designation. However, the economic feasibility of purchasing the required offsets and installing on(site renewable energy generation will be prohibitive for high energy use buildings. By focusing on strategies to reduce energy consumption before offsets and renewables are applied, significant capital cost savings can be achieved.