Effective Tracking of Building Energy Use: Improving the Commercial Buildings and Residential Energy Consumption Surveys (2012)

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Commercial Buildings Energy Consumption Survey Program History and Design

The primary purpose of the Commercial Buildings Energy Consumption Survey (CBECS) is to provide comprehensive information about commercial-sector energy use in the United States, and it does this by collecting data from a national sample of commercial buildings. Both the scope of the survey and the approach to data collection have evolved over the years, driven mostly by practical considerations. Table 3-1 summarizes the history of the survey, which started out with a design that aimed to represent all nonresidential buildings in the four census regions and has moved to a more focused approach that includes only buildings that are predominantly commercial in nature (50 percent or more of the floor space) and excludes certain commercial buildings that are difficult to survey and that do not represent a large proportion of commercial energy use.

The smallest level of geographic detail for which the CBECS data are available is the census division, which is a relatively large geographic area, covering many different climates and, therefore, different energy consumption characteristics. For example, the Mountain West division includes eight states, from New Mexico to Montana (see Appendix C). This limits the analysis that can be conducted at the subnational level using data from the CBECS.

In addition to the energy consumption and expenditure data, the CBECS also collects various details about building characteristics, such as a building’s physical structure, activities performed, equipment used, and energy source. Typically, the CBECS is administered in two data collection

TABLE 3-1 CBECS Data Collection Years and Survey Characteristics

TABLE 3-1 Continued

SOURCE: U.S. Energy Information Administration (http://www.cia.gov/cmcu/cbccs/contents.html ([December 2011]).

stages: a building characteristics survey and an energy suppliers survey. During the first stage of the data collection, interviewers visit the buildings selected into the sample and ask a representative, such as the building’s owner, manager, or other knowledgeable person, to complete the survey. During the second stage of the data collection, the energy suppliers (e.g. utilities) of the buildings for which inadequate information was provided in the first stage are contacted to obtain usage and expenditure data for those buildings from the supplier’s records. This usually happens if the building respondent is not able to report energy usage and cost information or if the information provided falls outside the range of “likely” energy consumption, determined based on regression models that take into account responses from previous years. In a typical CBECS, the energy suppliers for about half of the buildings in the sample need to be contacted (Michaels, 2010). Unlike the building survey responses, the suppliers’ responses are mandatory under the Federal Energy Administration Act. Box 3-1 shows the topics included

on the 2003 CBECS building questionnaire. For more information on the CBECS data collection instruments, including the shopping mall protocols and energy supplier surveys, see http://www.eia.gov/emeu/cbecs/forms.html [December 2011].

The basic unit of data collection and analysis for the CBECS is the building. The U.S. Energy Information Administration (EIA) originally considered using establishments instead of buildings as the energy-consuming unit that would best explain energy use in the commercial sector, but this approach was abandoned during the initial planning of the survey program for two reasons: (1) energy use in the service industry (which many commercial buildings belong to) is more closely associated with the characteristics of a building than with the characteristics of the establishments that occupy the building (for example, an office building is different from a warehouse, regardless of the profile of the companies that may be sharing the space within the same building); and (2) if several establishments share space in the same building, energy data are more likely to be available at the building level than at the establishment level (French, 2007). It has always been recognized, however, that no matter what unit of data collection is used, there will always be cases in which energy data are not available for the level of the data collection unit and there may also be differences by energy type within the same data collection unit.

Exceptions to the building-level energy-supply model can and do cause coverage problems, for example, in cases where tenants in a shopping mall receive their power individually or cases where energy is delivered to an entity larger than a building, such as a college campus. This led EIA to experiment with slightly different data collection procedures for shopping malls and college campuses and to customize questionnaires for establishments within a mall as well as for a mall manager who can provide information about the building overall.

Today the CBECS is the only national survey of the characteristics and energy use of commercial buildings in the United States, which presents a particularly difficult challenge for EIA. Without another nationwide source of information about the stock of commercial buildings in the United States, there is no comprehensive list of buildings that could help in the construction of a sampling frame for the CBECS. Thus EIA periodically builds a new area probability sampling frame for the CBECS. Full area frame listings have been created twice, in 1986 and 2003.

By definition, field listings are resource intensive, but relying on sources that are not comprehensive to update the sampling frame leads to coverage

problems. As a result, the CBECS sample design has undergone numerous revisions over the years, as EIA has attempted to address both the cost and the coverage issues. Generally speaking, most rounds of the CBECS have relied on a combination of an area frame and a list frame, merging existing lists of commercial buildings from a variety of sources and adding them at the second stage of the area frame sample.

The area frame is based on field listings of commercial buildings within specified geographic areas. Over the years, the sample typically included between 100 and 130 counties or groups of counties, which served as primary sampling units (PSUs). Within the PSUs smaller geographic areas were randomly selected, and then all commercial buildings within these areas were listed and stratified. In the final step a sample of buildings was randomly selected from each stratum. The sampling frame is updated from one data collection to the next in order to account for changes, such as new construction. The updates are typically based on information from local sources or databases of commercial projects, and new construction is usually sampled at a higher rate to enable EIA to produce estimates for this subpopulation.

Given the variations in building size and in the intensity of energy use among commercial buildings, the sampling rates for large buildings that use large amounts of energy must be higher than would be feasible to accomplish through the area-probability sampling alone. To assure that these types of buildings are adequately represented in the sample, the area frame is supplemented with a list frame of special buildings, such as very large buildings, hospitals, and government buildings. The two frames are then matched, and duplicates are eliminated.

Over the years, EIA has considered a variety of lists to use as the primary source for the sampling frame, including tax records, mail delivery points, insurance lists, customer information from utilities, Federal Emergency Management Agency records, and aerial and satellite photographs (French, 2007). Some of these alternatives have been evaluated empirically, while others have not. One feasibility study, which was conducted in 1981 in the service areas of Seattle Power and Light Company and Portland Electric, was performed to evaluate the use of electric utility customer information in building a sampling frame. The study concluded that differences between the way that records are kept at different utilities and the utilities’ varying degree of motivation to respond to an energy survey would represent significant challenges (French, 2007).

For the last round of the CBECS in 2007, EIA’s data collection contractor, the National Opinion Research Center (NORC), proposed a new

sample-updating approach that was expected to be cost efficient. After supplementation with lists of buildings that were over 200,000 square feet in size, including federal buildings, colleges, hospitals, and airports, the 2003 area frame was updated using a commercial version of the U.S. Postal Service (USPS) delivery sequence file (DSF), purchased from a vendor licensed by USPS. The DSF is the USPS’s list of all delivery points in the United States. To use the DSF for updating, the list had to be matched to the addresses in the second-stage area frame and the duplicates removed. NORC reported that the removing of duplicates turned out to be a major challenge, in part because of imprecise address records. The use of this new approach to update the survey frame, along with implementation errors made by the contractor, ultimately led to the data quality problems that prevented EIA from being able to release the 2007 CBECS data (U.S. Energy Information Administration, 2011e).

The CBECS was initially conducted in the form of in-person interviews, using paper and pencil. Since 1995, however, it has been conducted using computer-assisted personal interviewing. The 1999 data collection was an exception because, in an effort to control costs, it was done by computer-assisted telephone interviewing. This was made possible by re-interviewing the sample from the 1995 CBECS. The supplier survey has always been conducted by mail.