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.

Building Energy Simulation Test 

for Existing Homes (BESTEST-EX)

Ron Judkoff 

Joel Neymark

Ben Polly

 Updated: December 2011

NREL/PR-5500-53701
2

Goals of NREL Analysis Accuracy R&D

• Provide industry with the tools and technical 

information needed to improve the accuracy 

and consistency of analysis methods

• Reduce the risks associated with purchasing, 

financing, and selling energy efficiency upgrades

• Enhance software and input collection methods 

considering impacts on accuracy, cost, and time 

of energy assessments
3

BESTEST-EX Goals

• Test software predictions of retrofit energy 

savings in existing homes

• Ensure building physics calculations and 

utility bill calibration procedures perform up 

to a minimum standard

• Quantify impact of uncertainties in input 

audit data and occupant behavior
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What is BESTEST-EX?

The current test suite:

• Compares audit software predictions to state-of-theart detailed simulation program results (EnergyPlus, 

SUNREL, DOE2.1E)

• Evaluates limitations of audit software

• Tests basic building physics algorithms and calibration 

methods associated with audit software

• Specifies audit software inputs for an existing home 

and several retrofit measures

• Tests include retrofit measures applicable to two 

climates: one cold and one hot
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How does it work?

• Audit software completes two types of test 

cases: “Building Physics” and “Utility Bill 

Calibration”

• Test suite prescribes the building simulations to 

be performed

• Audit software developers create models 

according to specifications, run their software 

programs, and submit simulation results

• Simulation results are compared with reference 

results
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“Building Physics” Cases
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“Building Physics” Cases

The following retrofit measures are included in 

the current test suite:

o Air Sealing

o Attic Insulation

o Wall Insulation

o Programmable Thermostat

o Low-e Double-Pane Windows

o Reflective (Cool) Roof

o Exterior Shading

o Combined Measures
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-25

0

25

50

75

100

125

150

base-case air_seal attic_ins. wall_ins. setback windows sol_abs shading combined

Gas Usage or Savings (million Btu) 

Case

Annual Gas Usage or Savings

Buildings Physics Heating Tests

E+

SUNREL

DOE2.1E

“Building Physics” Reference Results

Usage

Savings

Blue and green range bars are 

examples of acceptance ranges 

based on statistical and 

economic threshold criteria, 

respectively. 
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“Utility Bill Calibration” Cases
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Limitations

• BESTEST-EX is a repeatable procedure that tests how 

well audit software predictions compare to the 

current state of the art in building energy simulation. 

There is no direct truth standard. However, reference 

software have been subjected to validation testing, 

including comparisons with empirical data

• Interim Test Procedure does not specify how the 

calibration must be performed for the “Utility Bill 

Calibration” cases

• The set of cases in the Interim Test Procedure is a 

subset of possible retrofit scenarios applied in a 

subset of U.S. climate zones
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Potential Future Work

• BESTEST-EX is multi-generational

• Refinements to existing cases and additional 

cases, as needed

• Additional cases: mechanical equipment 

replacement, duct sealing, etc.

• Compare pre-retrofit consumption and retrofit 

energy savings results to empirical data: revise 

test cases based on empirical data comparison, 

as needed

• Submit test suite for inclusion in maintained 

standards, such as ASHRAE 140
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Acknowledgements

Working Group of software developers and 

other stakeholders fully engaged and 

participative.

• Software Developers: AEC (RemRate), Apogee 

(EnergyInsights), CSG (HomeCheck), FSEC (EnergyGauge), ICF 

(BEACON HEA), ORNL (NEAT), PSD (TREAT)

• Others: CEC, EPA, Earth Advantage, LBNL, NYSERDA, 

Navigant, RESNET, TAMU

• DOE (David Lee, Eric Werling, Sam Rashkin)

• Former DOE (Terry Logee, Ed Pollock, Lew Pratsch)

• Former NREL (Marcus Bianchi)