Document ID: EPA-HQ-OAR-2008-0664-0163
Agency: epa
Document Type: Supporting & Related Material
Title: 
Posted Date: 2011-02-22T05:00Z

MEMORANDUM

To:
Margaret Sheppard , U.S. EPA 
From:
Emily Herzog and Mark Wagner, ICF International 
Date:
April 7, 2010
Re:
Summary of HFO-1234yf Emissions Assumptions (Deliverable under EPA Contract Number EP-W-06-008 Task Order 038, Task 06)

This memorandum summarizes the proposed emissions assumptions to be used in the sensitivity analysis of the revised Assessment of the Potential Impacts of HFO-1234yf and the Associated Production of TFA on Aquatic Communities and Local Air Quality.  As previously conducted, the baseline analysis will be based on Vintaging Model emission assumptions for HFC-134a while the sensitivity analysis will be based on the findings of Papasavva et al. as described in their 2009 paper Estimated 2017 Refrigerant Emissions of 2,3,3,3-tetrafluoropropene (HFC-1234yf) in the United Stated Resulting from Automobile Air Conditioning.  The memorandum is organized as follows:
   1) Overview of Vintaging Model HFC-134a Assumptions
   2) Summary of Findings from Papasavva et al. (2009)
   3) Proposed Sensitivity Analysis Assumptions

Please contact Mark Wagner at 202-862-1155 with any questions or comments.

       
   1)      OVERVIEW OF VINTAGING MODEL HFC-134A ASSUMPTIONS
ICF used EPA's Vintaging Model to estimate potential emissions of HFO-1234yf, a new refrigerant to be used as a drop in replacement for HFC-134a in new MVAC systems.  ICF assumed that emissions of HFO-1234yf from all systems will be the same as emissions from commercially available systems.  The Vintaging Model emissions assumptions for HFC-134a from the MVAC sector are described below in table 1.

Table 1: HFC-134a MVAC Sector Assumptions[a] 
                                  Assumption

                                     Unit
Vehicle lifetime
                                      12
                                     years
Light duty vehicle (LDV) charge size
                                      555
                                   g/vehicle
Light duty truck (LDT) charge size
                                      793
                                   g/vehicle
LDV market share
                                     58[b]
                                       %
LDT market share
                                     42[b]
                                       %
Percent of fleet retired each year
                                     8[b]
                                       %
Leak rate
                                       8
                                       %
Servicing leaks (annualized)
                                      10
                                       %
End-of-life loss rate
                                     42.5
                                       %
a VM IO file_v4.4_12.16.09.xls
[b] Number varies depending on the year.  Estimated average through 2050 is shown
SUMMARY OF FINDINGS FROM PAPASAVVA ET AL. (2009)
Papasavva et al. (2009) reported on their team's research on the estimated emissions of HFO-1234yf from MVAC systems.  The general findings from Papsavva et al. (2009) are described in table 2 below.
TABLE 2: Summary of Findings from Papasavva et al. (2009)
                                  Leak Source
                                     Range
                                     Units
regular leaks
                                  13.6 - 14.1
g/vehicle/year
irregular leaks
                                      17
g/vehicle/year
service leaks
                                    40 - 70
g/vehicle/service
DIY service leaks
                                      160
g/vehicle/service
End-of-life emissions
                                  100 - 450 
g/vehicle
                                       
Papasavva et al. (2009) noted that the sum of the average annual regular and irregular emissions per vehicle represents 5.6% of total refrigerant charge, assuming a typical sedan MAC with a 550 g charge.  They also noted that on average in the U.S., a vehicle goes for a MAC service once during its 9-year lifetime, so vehicle servicing accounts for between 4.4 and 17.8 g/y of annual refrigerant emissions.  Combined with regular and irregular annual losses, Papasavva et al. (2009) estimated annual leaks to be 35 - 48.4 g/yr or 6 - 8.8% of the original charge.
Based on their findings, Papasavva et al. (2009) then estimated total HFO-1234yf emissions for the year 2017.  Papasavva et al. (2009) developed two scenarios, a low leak scenario and a high leak scenario, both of which are described in table 3 below. 

Table 3: Emission Estimates of HFO-1234yf in 2017
                                  Assumption
Low Leak Scenario
High Leak Scenario
                                     Units
Vehicle lifetime
                                       9
                                       9
years
Number of services
                                       1
                                       1
Services/lifetime
Percent of fleet serviced per year
                                      10
                                      15
%
Percent of vehicles serviced by a DIYer
                                       0
                                      25
%
Percent of fleet retired
                                       5
                                      10
%
Regular leaks
                                     13.6
                                13.6  -  15[a]
g/vehicle/year
Irregular leaks
                                      17
                                      17
g/vehicle/year
Professional servicing leaks
                                      40
                                      40
g/vehicle/service
DIY servicing leaks
                                      160
                                      160
g/vehicle/service
End-of-life emissions
                                      100
                                      450
g/vehicle
Total Emissions
                                     11.4
                                     24.7
thousand MT
a Assumes older vehicles have a leak rate that is 10% higher
PROPOSED SENSITIVITY ANALYSIS ASSUMPTIONS
To accommodate for the findings of Papasavva et al. (2009), ICF will additionally run the HFO-1234yf emissions scenarios in the Vintaging Model (VM) using revised annual leak rate assumptions.  No changes will be made to the estimated vehicle fleet, the charge sizes of either LDV or LDT, or percent of fleet retired each year.  Additionally, no changes will be made to the end-of-life emission assumptions since the loss rate assumed in the VM (42.5%) falls within the range estimated by Papasavva et al. (2009) (100  -  450 g/vehicle or 18  -  81%).  
As stated above, Papasavva et al. (2009) estimated annual regular, irregular, and servicing leaks to be 35 - 48.4 g/yr or 6 - 8.8% of the original charge.  Therefore, ICF proposes to use the following annual leak rate assumptions for the sensitivity analysis, as summarized in table 4 below.  Leak rate assumptions for the baseline scenario are also provided for comparison.

Table 4: Proposed Refrigerant Loss Assumptions for Baseline and Sensitivity Analysis
                                  Assumption
                 Emission Rate as a Percentage of Charge Size
                  Equivalent Emission Rate[b] (g/vehicle/yr)
                                       
                                  Baseline[a]
                             Sensitivity Analysis
                                  Baseline[a]
                             Sensitivity Analysis
Leak rate
                                      8%
                                     5.6%
                                      44
                                     30.8
Servicing leaks (annualized)
                                      10%
                                     3.2%
                                      55
                                     17.6
  Subtotal, annual leaks
                                      18%
                                     8.8%
                                      99
                                     48.4
End-of-life loss rate
                                     42.5%
                                     42.5%
                                      234
                                      234
[a] HFC-134a MVAC assumptions
[b] Assuming an average charge of 550 g/vehicle.

   2)      CHANGES IN EMISSION ESTIMATES
ICF has updated the Vintaging Model since 2009 to include the most up-to-date projects of growth and trends in transitions to alternatives in all industrial sectors.  The baseline values will be calculated using the updated version of the Vintaging Model.  Depending on the year and scenario, these values may be higher or lower than those used in ICF's 2009 analysis.  The comparison below shows how emission values will be affected by these changes.  Overall, changes were relatively small, being less than 6% different from the earlier analysis. 
Table 5:  Comparison of Emissions using Vintaging Model Outputs (in Metric Tons)
                        2009 Analysis vs. 2010 Analysis
Scenarios
                                     2020
                                     2030
                                     2040
                                     2050
Scenario 1- MVAC  (2009)[a]
                                     6,244
                                    28,327
                                    33,196
                                    36,478
Scenario 1- MVAC (2010)[b]
                                     6,244
                                    28,327
                                    33,093
                                    35,851
% change
                                     0.0%
                                     0.0%
                                     -0.3%
                                     -1.7%
                                       
Scenario 2 - All Ref/AC (2009)[a]
                                    10,345
                                    42,800
                                    55,349
                                    64,324
Scenario 2  -  All Ref/AC (2010)[b]
                                    10,501
                                    43,296
                                    55,070
                                    60,616
% change
                                     1.5%
                                     1.2%
                                     -0.5%
                                     -5.8%
   [a] ICF projected emissions of HFO-1234yf using special scenarios designed specifically for the August 4, 2009 analysis and run on the U.S. EPA Vintaging Model, Version VM IO File v4.1 5-19-09.   
   [b] ICF projected emissions of HFO-1234yf using special scenarios designed specifically for the sensitivity analysis and run on the U.S. EPA Vintaging Model, Version VM IO File v4.4_12-16-09.   

Specific changes to the Vintaging Model between May 2009 and December 2009 include the following:
   1. Historic sales figures of light-duty motor vehicles were updated based on more recent data from Ward's Automotive.  The updated data showed drops in new vehicle sales over the last few years.
   2. Project sales growth rates for new vehicles through 2030 were estimated based on the Energy Information Administration's report, An Updated Reference Case Reflecting Provisions of the American Recovery and Reinvestment Act as found in EIA's Annual Energy Outlook.  For the May 2009 version of the Vintaging Model, projections were estimated using a constant compound growth rate
   3. Average refrigerant charge sizes for light-duty motor vehicles were updated based on more recent information from Ward's Automotive and from Mobile AC Society (MACS) Worldwide's Air Conditioning Specifications Domestic and Import Cars, APVs, Vans and Light Trucks: 1990 through 1998 and A/C & Cooling System Specifications: 1996-2007.  The average charge size for a light-duty truck went down from 910 g to 793 g per truck.  The average charge size for other light-duty vehicles such as cars and vans went down from 690 g to 555 g per vehicle.
   The first two of these changes resulted in reductions in the estimated number of cars and vans, but not trucks, in 2020 from 253 million in the May 2009 version of the Vintaging Model to 190 million in the December 2009 version.