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PJM©2016
Converting SEER to EER for Peak Forecasting
Itron’s Annual Energy Forecasting Meeting
Andrew Gledhill, PJM
www.pjm.com
PJM©20162
Agenda
• PJM Adoption of End-Use Modeling Practices
• SEER vs EER: Why the Efficiency Term Used Matters
• Converting SEER to EER
• Results in PJM
• References
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PJM©20163
Breakdown in Accuracy
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• PJM’s original methodology used
economics as a primary driver.
• As the elasticity of load to
economics weakened, so did
model performance.
• Investigated new variables to
help explain the growing
disconnect.
PJM©20164
Equipment Indexes
• Create equipment variables across three usage categories:
Heating, Cooling, and Other.
– (1) Develop Residential and Commercial sector indexes
– (2) Weight sector indexes and combine into single variables
• Each index is a weighted average across equipment types of
saturation normalized for efficiency
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PJM©20165
Cooling Equipment Index
• Within the Residential Component of Cooling, there are four
types: Central Air Conditioners, Air-Source Heat Pumps,
Geothermal Heat Pumps, Room Air Conditioners
– The latter two use the Energy Efficiency Ratio (EER) to measure
efficiency, whereas the former use the Seasonal Energy Efficiency
Ratio (SEER)
• While investigating PJM’s proposed model changes, Navigant
indicated that the use of SEER might be an issue and provided
guidance to correct the problem.
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PJM©20166
SEER vs EER: Why does it matter?
• PJM’s goal is to forecast load under system peak conditions, not
average conditions. This is at odds with the purpose of the SEER
measure:
– SEER measures seasonal average performance
– EER measures performance at a single outside temperature of 95
degrees
• If there’s a significant difference, then it could lead to a bias
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PJM©20167
SEER vs EER
• A typical 13 SEER unit has
an EER of 11 (a 0.85 ratio)
• A typical 18 SEER unit has
an EER rating of 13 (a 0.72
ratio)
• Improvements in average
performance don’t
necessarily translate to
peak period performance at
the same rate.
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PJM©20168
SEER vs EER Conversion
• Different relationships used
before and after 2006
• In each case, median units
are considered. Data is fit
with a second order
polynomial to account for
declining EER to SEER
ratio
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PJM©20169
SEER to EER Conversion Framework
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Stock of
Cooling UnitsNew Cooling
Units
Retiring Cooling
Units
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SEER to EER Conversion: Determine the moving parts
• Total Units (given)
– Function of number of households and the saturation rate
• Retired Units
– Retire units from the total at a rate according to their average
lifetime (19 years in the case of central A/C units)
• New Units
– Equal to growth in total units plus retired units
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PJM©201611
SEER to EER Conversion: Establish SEER of cooling units
• SEER of all units (given)
– Changes over time are a function of:
• Efficiency of total units in prior period (given)
• Efficiency of retiring units exiting from the prior period
– Assume to be average
• Efficiency of new units coming in from the prior period
– Can be inferred algebraically from the below identity
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Avg_SEERt x Total_Unitst = (Avg_SEERt-1 x Total_Unitst-1) –
(Avg_SEERt-1 x Retired_Unitst-1) + (Avg_New_SEERt-1 x New_Unitst-1)
PJM©201612
SEER to EER Conversion: Translating SEER to EER
• Transform SEER of new units into EER using conversion
equations
• Translation is then done using a recursive process
– Establish base year EER (1995) using SEER-EER conversion
equations
– EER values can then be calculated going forward using the
formula:
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Avg_EERt x Total_Unitst = (Avg_EERt-1 x Total_Unitst-1) - (Avg_EERt-1 x
Retired_Unitst-1) + (Avg_New_EERt-1 x New_Unitst-1)
PJM©201613
Impact on Efficiency
• In our model, EER-based
measures produce slightly
more accurate results in our
historical testing.
• The five-year forecasted
annualized growth rate of
SEER is 0.9% versus 0.6%
for EER
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PJM©201614
Impact on PJM Load
• Increases forecasted load by
0.5-0.6% at the outset of the
forecast, and by just under
one percent 15 years from
now.
• In PJM, this amounts to
approximately 800-1500
MW
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PJM©201615
References
• Air-Conditioning, Heating, and Refrigeration Institute
– https://www.ahridirectory.org/ahridirectory/pages/home.aspx
• U.S. DOE Technical Documentation (pre-2006 EER-to-SEER)
– http://www.regulations.gov/#!documentDetail;D=EERE-2006-STD-
0089-0371 (Chapter 4; Table 4.27)
• PJM Load Analysis Subcommittee
– http://www.pjm.com/committees-and-groups/subcommittees/las.aspx
• PJM Load Forecasting Model Whitepaper
– http://www.pjm.com/~/media/planning/res-adeq/load-forecast/2016-
load-forecast-whitepaper.ashx
www.pjm.com
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