This is a major step forward, the first tool that provides time- and weather-resolved GHG emissions calculations. It is based on a dispatch model,* that is a model of how the grid inventory would be over time through the year 2020. Since electricity demand and consumption as well as grid performance are highly dependent on weather and time of day or week, an annual average value for GHG emissions at a location or a portion of the regional or sub-regional electric grid is not accurate.
Other commonly used and well-known GHG calculation tools use annual average emissions for a grid region or sub-region. In some countries, a national average is used. In fact, we know of no other tool that addresses the time of use and weather impacts on building energy use and associated GHG emissions. The other available tools can greatly distort the impact of a building on GHG emissions and result in very poor design and operational decisions.
The distortions can lead to mistaken result from analysis of a building's energy use either from use data or simulation models. Designers and building operators need more accurate, time and weather resolved data to make informed decisions intended to affect GHG emissions.
Design always involves trade-offs. Designers are now focused on reducing energy use. But grid-generated electricity has different carbon implications, depending on the time when it is used and the simultaneous inventory of electricity generators in the grid region or sub-region. For example,
- To understand whether load shifting by using thermal storage or increasing building envelope insulation is more effective in reducing GHG emissions, one needs to model building performance with a time- and weather-resolved model and GHG emissions data.
- Is it more effective to produce electricity on-site with solar PV or to invest the same amount in high performance glazing?
Questions like these can only be answered with a tool that considers the time of use and concurrent grid performance. Use of an annual average can distort the result of a comparison of alternative designs by as much as 60% in some grid regions in the U.S. while in other grid regions, the annual average is relatively accurate. Buildings are the largest electricity user in the U.S. (70%) and in most of the world. The potential to reduce GHG emissions in buildings is huge, largely because buildings are currently quite inefficient. Reducing electricity consumption will have a major impact on GHG emissions, and site energy use intensity, the usual metric for building energy use, is roughly only 1/3 of source energy use and the associated GHG emissions.
Addressing climate change in buildings also has huge potential to reduce the environmental impacts of buildings but also to be highly profitable to building owners. An estimate in the IPCC 2007 Nobel Prize-winning report on climate change places buildings as having the greatest potential to reduce GHG emissions and to do so largely at a negative cost to building owners. More than 80% of the estimated potential reduction in buildings' GHG emissions can be accomplished while saving money, according to .
A study by Synapse Energy Economics of Cambridge, Massachusetts quantifies the differences by hour of the day and day of the year in a study for the U.S. Environmental Protection Agency. Using grid performance data from 2005, Synapse looked at the impacts of various strategies on GHG emissions for each grid subregion. The differences among regions are dramatic as can be seen in Synapse's color plots of GHG emissions hour-by-hour for the entire year. The Synapse report,.
The Synapse report clearly illustrates that the contrast within, between and among regions is dramatic at various times of day and year. The lead on the tool's development, Amber Mahone of Energy and Environmental Economics (E3) of San Francisco, was the consultant to the Project Committee for the ASHRAE GHG emissions tool development project. The concept for the project came out of E3's work helping define a concept for ASHRAE's GHG tool development. I encouraged Mahone to write a proposal to develop a tool for California and I requested (through Martha Brook) that the California Energy Commission fund it. The funding came, and the result is available now for downloading along with a User's Manual at the E3 web site. Please check out the tool, give some feedback, and spread the word. I would also appreciate hearing your comments on the tool after you have had a chance to look it over.