Portfolio Manager Technical Reference: Climate and Weather
The climate of the area where your property is located and the annual fluctuations you experience in weather conditions can affect how much energy you need to operate your buildings. Portfolio Manager includes metrics designed to incorporate these effects and help you understand your energy performance. These procedures rely on temperature data collected by weather monitoring stations and published by the National Climatic Data Center (NCDC), which is part of the National Oceanic and Atmospheric Administration (NOAA). To discuss how we use this data, it is helpful to introduce two concepts:
- Climate. Refers to regional variations in average weather conditions. For example, Florida has a warmer climate than Maine.
- Weather. Refers to annual variations at a single location over time. For example, this year we had a very hot summer.
In Portfolio Manager, there are two key metrics that account for these effects:
- Weather Normalized Energy. Weather normalized energy is the energy your building would have used under average conditions (also referred to as climate normals). The weather in a given year may be much hotter or colder than your building’s normal climate; weather normalized energy accounts for this difference. Note that the adjustment is for weather only, but not climate. That is, the metric evaluates your building over time, but does not account for differences between your building and other locations that have different average (normal) climates. Weather normalized energy is not available for new building design projects because they have not yet experienced years with different weather. Figure 1, below, illustrates the locations of weather stations in the U.S. and Canada that EPA uses in weather normalizaton.
- ENERGY STAR Score. The 1 - 100 ENERGY STAR score is a percentile ranking, which compares your building to its peers. The ENERGY STAR score accounts for both climate and weather. To provide a score, a regression equation is used to predict the energy your building is expected to use given its climate, weather, and business activity. Buildings that use less energy than this prediction score better and vice versa. The regression equation used for your prediction is based on a national analysis that includes buildings in all locations with different climates. Because of this national representation, regression coefficients on terms like Cooling Degree Days (CDD) and Heating Degree Days (HDD) incorporate the differences among these climates. To predict energy for your building in any given year, we will incorporate your actual experienced weather data for that year. Your building is predicted to use more energy in a very hot year, for example. In the case of a new building design, the ENERGY STAR score will use the average normal climate conditions to compute the energy prediction, as no actual weather has been experienced.
Figure 1 – Weather Stations in the U.S. and Canada