Weather Modeling - Legacy System

To represent the climatic variation across the U.S., we used The Nature Conservancy (TNC) “Ecoregions” (TNC 2001) to associate each Zip Code with an appropriate Weather City based on climate and environment, as well as linear distance.

The Nature Conservancy has created a set of GIS layers delineating EcoRegions on four different scales. The two smallest scales — the Province and the Section — were used in this analysis. These EcoRegions describe areas with relatively homogeneous environmental factors such as temperature, precipitation, humidity, vegetation, and landscape features. While not all these factors are directly related to building energy use, the predominant factors are climate-related and thus highly correlated with building energy use. On visual inspection, we also chose to use the EcoRegions because they correlate well with other climate regions used in energy analysis (e.g., the CEC climate zones) and are available nationally at a fine spatial scale. The figure below shows examples of the EcoRegions used in this analysis. See for further description of the ecoregion concept. ZIP code boundary data were obtained from the U.S. Census Bureau (2004)

Example EcoRegions in the Western U.S.


Source: . (TNC 2001).

Note that Sections (right) are subdivisions of Provinces (left).

To assign ZIP codes, we found the closest Weather City that is also within the same Ecoregion as that ZIP code. For each ZIP code, we first tried to do this matching at the Ecoregion “Section” (smallest scale) level, but if there was no matching Weather City we would then match at the Province level. If no match was possible at the Province level, we simply used the closest weather city (in geographic distance). Distances were based on ZIP code centroid to city center. Finally, the matches were reviewed and adjusted manually. In the case of California, Zip codes are mapped to utility service areas based on EIA's Form 861 Database (2002). Table File 5 of the Form 861 database lists all the counties served by individual utilities. Zip codes are then linked to counties through a county's unique FIPS code.

For use in modeling water heating energy consumption, we estimate the annual average inlet water temperature (from the domestic water system) by subtracting 2˚F from the annual average dry-bulb air temperature reported in the weather data files. Inlet water temperatures in Alaska were constrained to be greater than 32˚F. These values are listed in Appendix C.

Summary weather statistics for each weather data file were calculated using the DOE-2 weather packing routines. These summary statistics include seasonal heating and cooling degree-days, winter and summer design-day conditions, and weather-station location data. DOE-2 utilizes the full TMY2 weather tape, extracting solar gains (insolation) and other needed information for use in the annual simulation.