Michael Deru
ASHRAE
Albuquerque, NM
June 30, 2010
Better Green House Gas Calculations for Buildings
NREL is a national laboratory of the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, operated by the Alliance for Sustainable Energy, LLC.
Why?
Source: Energy Information Administration, Emissions of Greenhouse Gases in the United States 2008
17.6%
19.2%
35.6%
27.6%
36.8%
Equals emissions from India
Calculating GHGs is Easy, right?
Step 1: Find a GHG calculatorStep 2: Plug in your energy useStep 3: Done, next project
But,
Which GHG calculator should I use?
Where do the numbers come from and what do they mean?
A survey by Texas A&M found 48 GHG calculators and large differences between them
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Emiss
ions
(m
etric
tonn
e)1 State CO2e (+ precombustion)
2 State CO2
3 NERC Subregion CO2
4 State CO2e
4 State CO2e (elec. only)
5 National CO2 (elec. only)
GHG Calculator Comparisons
Credit: Michael Deru, NREL
Potential Issues in Building GHG Calculations
• Finding and interpreting emission factors• Regional variations in electric grid• Transmission and distribution losses• Time of day variations• Life-cycle emissions• On-site fuel combustion• On-site renewable energy• Accounting for electricity exports• Accounting for energy and CO2 offsets
Where do GHG Emissions Come From?
Combustion
CO2, CH4, N20Leakage
CFC, HFC, SF6
Scope-1 Emissions
Combustion
CO2, CH4, N2O
Precombustion
CH4, CO2, N2O
Scope-2 Emissions
Leakage
SF6
Scope-3 Emissions Typically only combustion emissions are
accounted for
Credit: Michael Deru, NREL
Global Warming Potential• GWP compares the ability to trap radiant energy in the
atmosphere relative to CO2 over a defined period.
100-yearCO2 1CH4 25N2O 298SF6 22,800R11 4,750R12 10,900R22 1,810404A 3,922407A 2,107410A 2,088
Sources: IPCC 2007 and ASHRAE 2006 Handbook
Global Warming Potential• GWP compares the ability to trap radiant energy in the
atmosphere relative to CO2 over a defined period.
20-year 100-year 500-yearCO2 1 1 1CH4 72 25 7.6N2O 289 298 153SF6 16,300 22,800 32,600R11 6,730 4,750 1,620R12 11,000 10,900 5,200R22 5,160 1,810 549404A 6,010 3,922 1,328407A 4,538 2,107 655410A 4,340 2,088 653
Sources: IPCC 2007 and ASHRAE 2006 Handbook
National Electric Grid
Source: NERC - www.nerc.com/page.php?cid=1|9|119
National Electric Grid Balancing Authorities
Source: NERC - www.nerc.com/page.php?cid=1|9|119
eGRID Subregions (26)
Source: EPA - www.epa.gov/cleanenergy/energy-resources/egrid/index.html
So, what’s the best region to use?
National, NERC, eGRID, State?
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Miami Albuquerque Seatle
CO2
Emis
sion
s (lb
/MHh
)
StateeGRID subregionNERC regionNational average
Regional Variability in Emission Factors
Source: eGRID 2007v1.1, EPA
Transmission and Distribution Losses
Not well understood
Highly variable with load
eGRID estimate ~ 5.3%
Worst case estimate from an isolated plant ~ 40% loss
Transmission
Distribution
Emission Factors
CO2e emissions for delivered electricity (lb/kWh)
Eastern Western ERCOT National%
Precombustion1.74 1.31 1.84 1.67 10.2%
Source: Deru and Torcellini (2007) Source Energy and Emission Factors for Energy Use in Buildings
CO2e emissions for natural gas–
0.5 lb/kWh
–Precombustion emissions ~ 18% of total
Time of Day Variations
Average Hourly Emissions
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Emis
sion
s (lb
s CO
2/M
Wh)
Total Average of CAISOTotal Min of CAISOTotal Max of CAISO2
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CO2
Emis
sion
s (lb
s CO
2/M
Wh)
Total Average of AZNMNVTotal Min of AZNMNV2Total Max of AZNMNV
Credit: Michael Deru, Daniel Studer, Greg Brinkman - NREL
CAISO
AZNMNV
Emissions peak at night!
Marginal Hourly Emissions – CAISO
Credit: Michael Deru, Daniel Studer, Greg Brinkman - NREL
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CAISOlb
/MW
h
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CO2
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sion
s (lb
s CO
2/M
Wh)
Total Average of CAISOTotal Min of CAISOTotal Max of CAISO2
Recommendations
• Clearly define the project scope• Use eGRID subregion or larger region data • Include T&D losses• Include precombustion emissions• Don’t forget on-site combustion and refrigerant
leakage (if applicable)• Use time-of-day factors to evaluate load
shifting and renewable energy
Conclusions
• Can’t get exact GHG emissions• Hopefully, we can get close and understand
whether they are going up or down• Nation wide hourly and time of use emissions
and source energy data coming in the fall
Thank you