June 22, 2020

Devil is in the Details: Deciphering CBECS for Building Energy Consumption

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Many building energy audits utilize U.S. Energy Information Administration’s (EIA) Commercial Buildings Energy Consumption Survey (CBECS) data in some capacity to assist in the assessment of energy consumption without a firm understanding of the data and its limitations. Unfortunately, this lack of understanding can lead to erroneous results when estimating both energy consumption and cost savings for a building. For example, when relying on building end-use (e.g., space heating, cooling, ventilation, DHW heating, etc.) energy consumption data in CBECS without adjustments for typical weather conditions where the building is actually located can lead to flawed energy consumption savings and therefore mistaken energy cost savings. This has been a significant contributor to building owners lack of confidence in the projected energy savings identified in energy audits.

For this reason, having a thorough understanding of CBECS data and its limitations is important for technically-sound energy savings analysis.

What is CBECS?

CBECS is a national sample survey that collects information on the stock of U.S. commercial buildings, including their energy-related building characteristics and energy consumption data. The definition of commercial buildings in CBECS includes “all buildings in which at least half of the floorspace is used for a purpose that is not residential, industrial, or agricultural.” By this definition, CBECS includes building types that might not traditionally be considered commercial, such as schools, hospitals, correctional institutions, and buildings used for religious worship, in addition to traditional commercial buildings such as retail stores, restaurants, warehouses, and office buildings.

The specific building types covered in CBECS include:

• Office
• Food Service (such as restaurants and fast food)
• Food Sales (such as grocery and convenience stores)
• Lodging (such as hotels and motels)
• Service (such as dry cleaners, car washes, barber shops, etc.)
• Warehouse and Storage (refrigerated and non-refrigerated)
• Education (elementary, high schools, colleges and universities)
• Healthcare
• Inpatient (hospitals)
• Outpatient (clinics)
• Public Assembly (such as convention centers, libraries, etc.)
• Public Order and Safety (such as police and fire stations)
• Religious Worship
• Vacant
• Other.

The first CBECS was conducted in 1979; the tenth CBECS was fielded starting in April 2013 to provide data for calendar year 2012. The next CBECS collected data for calendar year 2018; however, energy consumption data are not expected to be released until late 2021 at the earliest. Access the CBECS database here.

What building energy data are included in CBECS?

The detailed tables for the calendar year 2012 CBECS include:

• Building characteristics tables, such as the number of buildings of each property type, the amount of floor space, and structural and energy-related characteristics; and
• Energy consumption and expenditures tables, such as whole building total energy consumption data by major energy sources (electricity and fuel) and building end-use energy consumption estimates.

The energy end-use consumption tables provide estimates of the amount of electricity, natural gas, fuel oil, and district heat used for ten major end-uses:

• Space heating
• Cooling
• Ventilation
• Domestic Hot Water (DHW) Heating
• Lighting
• Cooking
• Refrigeration
• Computers (including servers)
• Office Equipment
• Other.

CBECS can serve as an excellent resource to obtain insight into the energy consumption associated with major building end-uses as a function of property type.

What areas of the country are included in CBECS?

The CBECS data cover the following relatively large U.S. regions:

• Northeast
  • New England (CT, ME, MA, NH, RI, VT)
  • Middle Atlantic (NJ, NY, PA)
• Midwest
  • East North Central (IL, IN, MI, OH, WI)
  • West North Central (IA, KS, MN, MO, NE, ND, SD)
• South
  • South Atlantic (DE, DC, FL, GA, MD, NC, SC, VA, WV)
  • East South Central (AL, KY, MI, TN)
  • West South Central (AR, LA, OK, TX)
• West
  • Mountain (AZ, CO, ID, MT, NV, NM, UT, WY)
  • Pacific (AK, CA, HI, OR, WA)

What climate zones are included in CBECS?

The 2012 CBECS classifies buildings according to climate regions created by the Building America program, sponsored by the U.S. Department of Energy’s (DOE) Office of Energy Efficiency and Renewable Energy (EERE). Building America defines eight major climate regions which CBECS collapses into five super-regions:

>> Hot-Humid

A hot-humid climate is generally defined as a region that receives more than 20 in. of annual precipitation and where one or both of the following occur:

• A 67°F or higher wet bulb temperature for 3,000 or more hours during the warmest six consecutive months of the year; or
• A 73°F or higher wet bulb temperature for 1,500 or more hours during the warmest six consecutive months of the year.

>> Mixed-Humid

A mixed-humid climate is generally defined as a region that:

• Receives more than 20 in. of annual precipitation;
• Has approximately 5,400 Heating Degree Days (HDDs, 65°F basis) or fewer; and
• Located where the average monthly outdoor temperature drops below 45°F during the winter months.

>> Hot-Dry/Mixed Dry

A hot-dry climate is generally defined as a region that receives less than 20 in. of annual precipitation and where the monthly average outdoor temperature remains above 45°F throughout the year. A mixed-dry climate is generally defined as a region that receives less than 20 in. of annual precipitation, has approximately 5,400 HDDs or less, and where the average monthly outdoor temperature drops below 45°F during the winter months.

>> Cold/Very Cold

A cold climate is generally defined as a region with approximately 5,400 HDDs or more and fewer than approximately 9,000 HDDs. A very cold climate is generally defined as a region with approximately 9,000 HDDs or more and fewer than approximately 12,600 HDDs.

>> Marine

A marine climate is generally defined as a region that meets the following criteria:

• A mean temperature of coldest month between 27°F and 65°F;
• A warmest month mean of less than 72°F;
• At least four months with mean temperatures more than 50°F; and
• A dry season in summer. The month with the heaviest precipitation in the cold season has at least three times as much precipitation as the month with the least precipitation in the rest of the year. The cold season is October through March in the Northern Hemisphere and April through September in the Southern Hemisphere.

Unfortunately, under these definitions there can be considerable weather variability within any climate zone.

What specific energy consumption data are in CBECS?

Energy consumption data in the 2012 CBECS are contained in Tables E1 through E11. The key energy consumption metric is the Energy Use Intensity (EUI) in units of kBtu/SF for calendar year 2012, where SF is the building square footage enclosed by the exterior walls of a building, both finished and unfinished, including indoor parking facilities, basements, hallways, lobbies, stairways, and elevator shafts. This area is not the same as the floor area used in EPA’s ENERGY STAR Portfolio Manager which excludes indoor parking area. A building’s total floor area is not the same as total rentable or leasable space, a fact that many energy audits fail to recognize.

Median EUI data are provided in CBECS by property type for:

• Total building EUI regardless of location or climate zone
• Electricity EUI regardless of location or climate zone
• Fuel (such as natural gas or oil) EUI regardless of location or climate zone.

A significant shortcoming is that the data for each property type are not provided by the climate zone where the building is located. There can be no question that the energy consumption of an office building located in Miami will be considerably different than the same type and size office building located in Chicago.

How does CBECS deal with mixed-use buildings?

In order to be included in the CBECS, a building has to be used principally for some commercial purpose: that is, more than 50% of the building’s floorspace must be devoted to activities that are not residential, manufacturing, industrial, or agricultural. The primary use or principal building activity is considered the activity or function occupying the most floorspace in the building.

If no individual property type accounts for more than 50% of the floor area, then the building is designated as Mixed Use. For such properties, the EUI for each use must be determined. The total building EUI would then be calculated by multiplying the EUI for each use by the ratio of its floor area to the total building floor area and summing these components together.

Challenges Faced by Project Developers and Energy Efficiency Professionals in Using CBECS Data

There are numerous challenges a project developer and energy efficiency professional face when using CBECS data in support of building energy audits. These include:

1. While energy audits routinely collect whole building energy consumption data, e.g., electricity and fuel, they often are unable to collect sufficient data regarding how energy is used within each building end-use, e.g., lighting, space heating, cooling, etc.
   More experienced energy auditors can analyze monthly building electricity and fuel use to gain insight into potential energy consumption of a limited number of major end-uses. For example, if a building located in the U.S. northeast has two principal energy sources, e.g., electricity and natural gas, monthly electricity data can be analyzed and electricity use in the summer months compared with electricity use in the winter months. Such analysis can provide an estimate of average electricity use for cooling assuming air conditioning is only needed in the summer months. Monthly natural gas data can also be analyzed and use in the summer months compared to use in the winter months. This can provide an estimate of average gas use for space heating and DWH heating (assuming natural gas is not used elsewhere in the building). However, such data analysis will not provide insight into other major building energy consumption end-uses such as lighting or ventilation.
   Unfortunately, the ability to undertake such analysis using monthly energy use data depends on what the building energy sources relied upon are and where the building is located (to take the impact of local climate into consideration). If a building is located where it uses electricity for both heating and cooling such as with a heat pump system, analyzing monthly electricity use data will provide little valuable insight.
2. CBECS building end-use energy consumption data have often been used directly in energy audits (percentage of total building energy consumption associated with each end-use). Unfortunately, while median building end-use energy consumptions are available in CBECS for the different property types (office, retail, lodging, etc.), they are not available by property type and climate zone (or building location). By not taking climate into consideration, end-use energy consumption may be grossly inaccurate. CBECS does identify end-use energy consumption by climate zone and geographic (census) region, but not by building type.
3. CBECS data are for calendar year 2012. Projecting energy savings is traditionally based upon typical or average weather conditions. Hence, the percentages of whole building energy consumption associated with each building end-use as calculated from 2012 CBECS data may or may not be representative of the “weather-normalized” end-use percentages. For example, if 2012 had an abnormally cold winter, the space heating energy use in 2012 would likely be higher than normal. Hence, both lack of a weather adjustment and climate zone adjustment could produce misleading results.
4. Multifamily type properties are not included in CBECS (however, they are included in EIA’s RECS, Residential Energy Consumption Survey).

Fortunately, a new generation of software, data and predictive analytic solutions are emerging specifically designed to empower project developers and energy efficiency professionals to better meet these challenges. Such new solutions can enhance the raw CBECS data to overcome many of its limitations and give property owners greater confidence in the energy savings projections. 

To learn more about how energy efficiency professionals are successfully meeting these challenges with SRS’s latest innovation: The Energy Performance Improvement Calculator (EPIC^TM), visit SRSworx.com.