Center for the Built Environment

The operational carbon emissions intensity of the electricity used in a building is commonly treated as a fixed value but grid carbon emissions factors have temporal and geographical variations, which makes building operating emissions dependent on when and where electricity is used. Grid electricity carbon characteristics can be quantified by either average or marginal emission rates, leading to an increasing debate about which metric provides more accurate results for determining the effect of various decarbonization strategies. We advocate for the use of the marginal operating emissions rate (MOER) to evaluate the impacts of demand-side management because it considers the generating plants' dispatch order and is able to reflect the change in emissions induced by demand management. In this study, we examined the benefits of emission-based load-shifting strategies by first analyzing the annual temporal variations of the Northern California grid region and developed a virtual chiller load shift strategy similar to demand response but interacting with the grid MOER signal. We then assessed its effect on the case study building by calculating the avoided emissions on a seasonal and annual basis through a numerical simulation. As a result, we found that for the Northern California region, shifting load is most effective during the spring season with 18% avoided carbon emissions when the grid has more renewable supply. However, the simulated annual result shows 2% avoided carbon emissions indicating the seasonal characteristics of the proposed strategy and the limitation of considering load shift strategy as the single solution to decarbonize.