Analyze Data to Evaluate Greenhouse Gas Emissions Profile for Buildings
Once the relevant data have been collected, the next step is to identify the biggest building energy users and their greenhouse gas (GHG) emissions contribution. Ideally would be done at the program level using actual building characteristic and performance data. However, assumptions may be established about energy performance of buildings based on general location and building type.
Ultimately, building efficiency measures need to be evaluated at the building level before implementing them, but facility energy managers can evaluate the relative impact of different GHG reduction approaches using assumptions about the building characteristics and estimates of efficiency gains.
Following the approach illustrated in Figure 1 below, an agency will be able to prioritize initial opportunities for building emissions reductions.
Table 1 below illustrates how this information can be used to support agency planning.
Table 1. Analysis of Agency Building Emissions to Prioritize Sites for Mitigation Planning
|Type of Analysis||How it Supports Planning||Calculation|
|Total emissions by program||Identifies which programs contribute the most to agency emissions, and helps agencies to prioritize where to focus efforts first.||For each fuel type consumed: Emissions = Energy consumption * Region-specific Emissions Factor|
|Total energy consumption by building type||Identifies key building types that an agency or program should focus on first. Can use default estimates for energy use intensity (EUI) by building type, such as CBECS. See the ENERGY STAR website for more information on EUI.||Energy consumption (kBtu) = Square footage of building type (SF) x Average EUI of building type (kBtu/SF). For more information, see Thermal Conversions in Portfolio Manager on the ENERGY STAR website.|
|Locations of key building types||Identifies differences in energy use and emissions due to variability in climate and electric grid emissions by region. Establishes sites that may warrant a more detailed analysis of emission reduction potential. See Table 2 in Collect Data to Evaluate Greenhouse Gas Emissions Profile for Buildings.||Weighted regional factor = eGRID emissions factor *Climate zone ratio *% Building floor space by region or site (Note: Climate zone ratio compares regional energy intensity to national average energy intensity)|
1. Evaluate Buildings Contribution by Program
Evaluate emissions contribution by Program
To prioritize building types and sites for mitigation planning start with the programs that contribute the most to their total building GHG emissions.
In the example below, Agency ABC should focus on Programs B and C first because together they represent over 80% of building emissions. Agencies would eventually evaluate all programs, but should initially focus on programs where reduction strategies may have the greatest impact.
Table 1. Agency ABC Program Data for Evaluating GHG Emissions
|Program Name||Emissions from Electricity Use||Emissions from Natural Gas Use||Emissions from Other Fuels*||Total Buildings Emissions||% of Total Emissions||Rank by % of Total Emissions|
|*Includes fuel oil, biomass, or other fuels.|
2. Estimate Greenhouse Gas Emissions by Building Type
Estimate emissions by building type
The agency should next determine which building types operated by the largest emitting programs use the most energy (Figure 1). Using total building floor area for each building type and average energy use intensities, the program can estimate total energy use for each building type. Building types are ranked within each program by the proportion of total energy they consume. The program can then focus on the building types representing at least 50% of each program's energy consumption.
The following example in Table 1 illustrates how Agency ABC's Program B would establish which building types to focus on initially. In this example, offices are estimated to make up the largest proportion of Program B's building energy consumption at 45% (see the figure below). Storage facilities should also be targeted for further analysis of GHG reduction potential because together they account for 80% of the program's emissions.
Table 1. Estimate Emissions by Building Type Example
|Program Name||Building Type||Total Building Area (Million SF)||Energy Use Intensity (kBtu/SF)1||Estimated Energy Contribution (MMBtu)2||Percent of Program's Total Energy Consumption3||Rank by Percent of Total Energy|
1 EIA's Commercial Buildings Energy Consumption Survey (CBECS) values can be used for default EUIs by building type. Alternatively, real metered data, proxy buildings, or Agency-specific values could be used instead, which would provide a more accurate estimate.
2 Estimated Energy Contribution = total building area (Million SF) x energy use intensity (kBtu/SF). Note that this estimate is not intended to be calibrated against total program energy use, but rather to estimate which building types contribute the most the a program's emissions.
3 Percent of Program's total energy consumption = Estimated Energy Contribution of Building Type ÷ total Program B energy consumption
3. Establish Building Locations for Greenhouse Gas Mitigation
Establish locations for GHG mitigation analysis
After estimating greenhouse gas (GHG) emissions by building type, building location is an important consideration due to geographic differences in heating and cooling needs and the carbon emissions intensity differences across regions of the grid.
If site-level energy use estimates are available for each of the program's key building types, the program can identify building locations with the greatest emission reduction potential by benchmarking data. Locations with the worst energy performance relative to the benchmark are likely the best candidates to evaluate first for their emissions reduction potential. For more information, see Benchmarking Building Types for Energy Intensity at the Site Level.
Many programs, however, will not know building energy use by building type and location. In these cases, identify sites with the largest amount of floor space for the key building types and focus initial emission reduction assessments on those buildings.
To illustrate, Agency ABC looks at floor space for office buildings across four sites as shown in Table 1 to help prioritize sites for mitigation analysis.
Table 1. Program B Example Establish Priority Locations for Mitigation Analysis
|Site Name||Building Type||Floor Area (KSF)||Percent of Total Program Square Footage by Building Type (%)|
|Site 1 (Duluth)||Offices||1,100||11%|
|Site 2 (Seattle)||Offices||4,500||45%|
|Site 3 (Chicago)||Offices||2,200||22%|
|Site 4 (Miami)||Offices||2,200||22%|
In this example, Site 2, Site 3, and Site 4 should be evaluated further for potential reductions because combined, the office space square footage comprises over 80% of Program B's office space.
4. Rank Sites by Building Type and Location for Greenhouse Gas Mitigation
Once the sites with the greatest opportunity for efficiency gains have been identified, they can be ranked based on their location. Location is important because the carbon intensity of the electric grid varies by region and the heating and cooling demand of buildings varies by climate zone. Using eGRID emission factors and energy intensity ratios for different climate regions, an energy manager can quickly compare locations based on their carbon and energy intensity.
To illustrate, Program B has facilities in Chicago and Miami, each with the same proportion of office space (22%) as shown in Table 1. Considering the carbon and energy intensity of those locations (see "eGRID-Climate Weight"), office buildings at the Chicago site should be prioritized over Miami for GHG mitigation measures.
Table 1. Example: Program B Office Location Evaluation
|Site Name||Percent of Total Program Square Footage by Building Type (%)||eGRID||Climate Region||eGRID-Climate Weight3||Location Rank|
|Region||Emission Factor Ratio||Climate Zone1||Zone Ratio2|
|Site 2 (Seattle)||45%||NWPP||0.39||3||1.1||0.19||2|
|Site 3 (Chicago)||22%||SRMW||0.81||2||1.1||0.20||1|
|Site 4 (Miami)||22%||SRVC||0.51||5||0.8||0.09||3|
1 See Details of U.S. Climate Zones on the U.S. Energy Information Administration's website for more information.
2 For more information see CBECS Energy Intensities.
3 eGRID Climate Weight = Emissions Factor Ratio * Climate Region Zone Ratio * % Building Size
Agencies can map their sites to eGRID regions using eGRIDweb and to climate zones using the U.S. Climate Zones for 2003 Map. The eGRID emission factor ratios and climate zone ratios in Tables 2 and 3 can help the energy manager determine which sites have the highest eGRID-Climate weighting.
Table 2. Emissions Factor Ratio Values
|eGRID1 subregion acronym||eGRID subregion name||Emission Factor (MTCO2e/MWh)|
|NYUP||NPCC Upstate NY||0.31|
|NEWE||NPCC New England||0.38|
|SRMV||SERC Mississippi Valley||0.46|
|AKGD||ASCC Alaska Grid||0.58|
|NYLI||NPCC Long Island||0.65|
|SRTV||SERC Tennessee Valley||0.70|
Table 3. CBECS Zone Ratio
|Climate Zone2||Zone Description||CBECS Zone Ratio|
|Zone 1||< 2,000 CDD and > 7,000 HDD||1.04|
|Zone 2||< 2,000 CDD and 5,500-7,000 HDD||1.13|
|Zone 3||< 2,000 CDD and 4,000-5,499 HDD||1.10|
|Zone 4||< 2,000 CDD and < 4,000 HDD||0.86|
|Zone 5||>=2,000 CDD and < 4,000 HDD||0.84|
Each program can use the rankings by building type and location to determine which sites to evaluate for GHG emission reduction strategies. Programs should consider both rankings when deciding which sites to engage first.
As illustrated in Table 4 below, Program B would engage Sites 2 and 3 first for assessments of GHG strategies because they have the lowest overall scores. Site 4 may still need to be assessed to meet Federal agency targets.
Table 4. Program B Summary of
|Site Name||Building Type||Building Type Rank||Location Rank1||Overall Score – Low is better2|
|Site 3 (Chicago)||Office||1||1||1|
|Site 2 (Seattle)||Office||1||2||2|
|Site 4 (Miami)||Office||1||3||3|
1Location rank accounts for the proportion of the site's square footage by each building type, thus the location rank may be different for building types at the same site.
2Overall score = Building rank * Location rank
After analyzing data to evaluate an emissions profile, the next step is to GHG mitigation planning for buildings.
- Step 1
Assess Agency Size Changes
- Step 2
Evaluate Emissions Profile
- Step 3
Evaluate Reduction Strategies
- Step 4
Estimate Implementation Costs
- Step 5
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