Improving our CO2 calculations

by ‐ Tags: WegoWise updates

WegoWise has a great feature that lets you see the environmental impact of your energy consumption in terms of CO2 emissions. Recently, we changed how these calculations are performed, making them more precise. This all happened behind the scenes, so users saw a feature upgrade without needing to learn any new interfaces. The details behind these changes are interesting, though, and we'd like to tell you about it.

For most energy sources, there is a single value for the CO2 emission coefficient. The emissions from these fuels are generally unchanging based on geography, although they may change over time as refinement techniques become more effective. You can consult this table provided by the EPA to see how different fuels stack up. The EPA numbers are what we use at WegoWise for most of our CO2 calculations.

Until recently, WegoWise calculated CO2 emissions associated with electricity in the same way as other fuels, and used a single coefficient based on the US national average. But electricity is different from other fuels because it is generated in so many different ways. A utility company in one region may use exceptionally clean energy sources to generate its electricity, while a utility in a different region uses a terribly dirty one. If the utility company takes a large percentage of its electricity from coal, for example, the mix will be dirty and the CO2 emission coefficient will be large. On the other hand, if a utility company mostly relies on renewables (hydroelectric, wind power, solar, etc.) the CO2 emission coefficient can approach zero.

In order to better reflect the diverse reality of electricity generation, WegoWise now calculates electric CO2 emissions using regional coefficients. This can lead to significantly higher or lower CO2 production based on the location of a building.

The source of our regional emission coefficients is the EPA's eGRID project, "a comprehensive source of data on the environmental characteristics of almost all electric power generated in the United States". The EPA determined the energy mixes for electric utilities across the US and, because utility companies tend to operate in distinct geographic areas, was able to designate electricity production regions and subregions. These regions are shown in the map below:

Map of the United States divided into EGRID regions

For each subregion there is a published emission coefficient, available in this document. For example, we see that the New England region (NEWE) has a CO2 emission coefficient of 0.5214 lbs./MWh.

By combining the subregion map with the corresponding coefficients, we are able to determine the region-specific electric CO2 emission coefficient for any building in our database. We get per-province emission coefficients for Canada from a similar document, published here.

If you're a WegoWise user, you're going to want to take another look at your CO2 reports, especially for electric energy. You can see a combined report on the (brand new) summary page for your building:

CO2 card from building summary page

To see the electric-specific CO2 data you can view a more detailed report filtered by "Electricity use" and "lbs. CO2":

Building detail report showing electricity use in CO2

You can also view the specific coefficients for each region on this support page.