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 % 19.2% 35.6% 27.6% 36.8% Equals emissions from India

Calculating GHGs is Easy, right? Step 1: Find a GHG calculator Step 2: Plug in your energy use Step 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

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 CO 2 offsets

Where do GHG Emissions Come From? Combustion CO 2, CH 4, N 2 0 Leakage CFC, HFC, SF 6 Scope-1 Emissions Combustion CO 2, CH 4, N 2 O Precombustion CH 4, CO 2, N 2 O Scope-2 Emissions Leakage SF 6 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 CO 2 over a defined period. Sources: IPCC 2007 and ASHRAE 2006 Handbook

Global Warming Potential GWP compares the ability to trap radiant energy in the atmosphere relative to CO 2 over a defined period. Sources: IPCC 2007 and ASHRAE 2006 Handbook

National Electric Grid Source: NERC -

National Electric Grid Balancing Authorities Source: NERC -

eGRID Subregions (26) Source: EPA - So, what’s the best region to use? National, NERC, eGRID, State?

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) EasternWesternERCOTNational % Precombustion % Source: Deru and Torcellini (2007) Source Energy and Emission Factors for Energy Use in Buildings CO 2e emissions for natural gas –0.5 lb/kWh –Precombustion emissions ~ 18% of total

Time of Day Variations

Average Hourly Emissions 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 lb/MWh

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