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

0

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1

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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sion

s (lb

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2/M

Wh)

Total Average of CAISOTotal Min of CAISOTotal Max of CAISO2

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CO2

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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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133

967

710

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5316

9120

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6727

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8137

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CAISOlb

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CO2

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sion

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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