PJM©2016

Converting SEER to EER for Peak Forecasting

Itron’s Annual Energy Forecasting Meeting

Andrew Gledhill, PJM

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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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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.

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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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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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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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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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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)

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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)

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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

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