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Energy and Buildings 36 (2004) 855–863
Analytical and comparative testing of EnergyPlus using IEA HVAC
BESTEST E100–E200 test suite
Robert H. Henningera,∗, Michael J. Wittea, Drury B. Crawleyb
aGARD Analytics Inc., 1028 Busse Highway, Park Ridge, Illinois, IL 60068, USA
bUS Department of Energy, 1000 Independence Avenue, SW, Washington, DC 20585, USA
Abstract
The EnergyPlus building energy simulation software has been tested using the IEA HVAC BESTEST E100–E200 series of tests. The
volume 1 final report for the International Energy Agency (IEA) solar heating and cooling programme task 22 building energy simulation
test and diagnostic method for heating, ventilating, and air conditioning equipment models (HVAC BESTEST) was recently published in
January 2002. HVAC BESTEST is a series of steady-state tests for a single-zone DX cooling system. Cases range from dry to wet coil,
low to high part load, and low to high temperatures. This published test suite includes three sets of analytical solutions and results from
several other simulation programs for comparison.
This test suite was initially used to test EnergyPlus beginning with beta versions prior to its official public release, and it is also applied
as an ongoing quality assurance test. The application of these tests proved to be very useful in several ways:
•revealed input model shortcomings, which resulted in new user inputs being added;
•revealed reporting errors which were fixed;
•revealed algorithmic errors which were fixed;
•revealed algorithmic shortcomings which were improved or eliminated through the use of more rigorous calculations for certain com-
ponents;
•in later versions, caught newly introduced bugs before public release of updates.
Overall, the application of this test suite has been extremely useful in debugging and verifying the DX cooling algorithms in EnergyPlus.
This paper summarizes the difficulties encountered and the benefits gained in applying the tests.
© 2004 Elsevier B.V. All rights reserved.
Keywords: EnergyPlus; Energy simulation; Software validation; HVAC system
1. Introduction
The International Energy Agency (IEA) Solar Heating and
Cooling Programme (SHC) task 22 created a set of analyti-
cal tests as well as a set of comparative results from seven
other whole building simulation programs that participated
in the IEA SHC task. Analytical tests compare a programs
results to mathematical solutions for simple cases. This is
an excellent method to use for assessing the accuracy of re-
sults since there is only one solution for the case analyzed
given the boundary conditions. Comparative tests compare a
program against itself or to other simulation programs. Both
types of testing accomplish results on two different levels,
both validation and debugging. Validation is accomplished
∗Corresponding author. Tel.: +1-847-698-5688; fax: +1-847-698-5600.
E-mail address: rhenninger@gard.com (R.H. Henninger).
when the results of the test program compare favorably with
the analytical results. Debugging is accomplished when the
results for certain cases do not compare favorably with the
analytical results and then through systematic checking it is
determined that the source of the difference is due to an in-
put error, a modeling inconsistency or flaw in the program
logic.
The EnergyPlus [1] building energy simulation software
has been tested using the tests described in International En-
ergy Agency (IEA) Solar Heating and Cooling Programme
(SHC) Task 22 Building Energy Simulation Test and Di-
agnostic Method for HVAC Equipment Models (HVAC
BESTEST), volume 1: Cases E100–E200 [2]. Final com-
parison results for all programs that participated in the IEA
SHC task are reported in an NREL report by the same name
as above but with a January 2002 publication date [3].
As stated in its Introduction, the IEA SHC task 22 HVAC
BESTEST report “documents an analytical verification and
0378-7788/$ – see front matter © 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.enbuild.2004.01.025
856 R.H. Henninger et al./Energy and Buildings 36 (2004) 855–863
comparative diagnostic procedure for testing the ability of
whole building simulation programs to model the perfor-
mance of unitary space cooling equipment that is typically
modeled using manufacturer design data presented in the
form of empirically derived performance maps. The report
also includes results from simulation programs that were
used for field trials of the test procedure.”
2. Summary of test cases
The following tests were performed as specified in the
HVAC BESTEST user’s manual (Section 1.3):
•Case E100—base case building and mechanical system;
•additional dry coil test cases (Cases E110, E120, E130
and E140);
•humid zone test cases (Cases E150, E160, E165, E170,
E180, E185, E190, E195 and E200).
2.1. Base case building and mechanical system (Case
E100)
The basic test building is a rectangular 48m2single-zone
(8 m wide×6 m long×2.7 m high) with no interior partitions
and no windows. The building is intended as a near-adiabatic
cell with cooling load driven by user specified internal gains.
For further details refer to Section 1.3.2.1 of the HVAC
BESTEST user’s manual.
The mechanical system is a simple unitary vapor com-
pression cooling system with air cooled condenser and
indoor evaporator coil, 100% convective air system, no
outside air or exhaust air, single speed, draw-through air
distribution fan, indoor and outdoor fans cycle on/off with
compressor, no cylinder unloading, no hot gas bypass,
crankcase heater and other auxiliary energy are 0.0. There is
a non-proportional-type thermostat, heat always off, cooling
on if zone air temperature >22.2◦C and heat extraction rate
is assumed to equal the maximum capacity of the equip-
ment for the hour’s environmental conditions. For further
specifications and equipment’s full-load and part load per-
formance specifications, see Section 1.3.2.2 and Tables 1–6
in the HVAC BESTEST user’s manual.
2.2. Dry zone and wet zone series (Cases E110–E200)
The 13 other cases represent a set of fundamental me-
chanical equipment tests. These cases test a program’s abil-
ity to model unitary space cooling equipment performance
under controlled load and weather conditions. Given the un-
derlying physical assumptions in the case definitions, there
is a mathematically provable and deterministic solution for
each case. The results of analytical solutions are included in
the IEA SHC/NREL report. Only the following parameters
are varied to develop the remaining test cases:
•internal sensible gains;
•internal latent gains;
•thermostat setpoint (dry-bulb);
•outdoor dry-bulb temperature.
2.3. Weather data
Four three-month long (January–March) TMY format
weather files were provided with the test suite. The only
parameter that is different for each weather file is the ambi-
ent dry-bulb temperature; all other data is the same for each
weather file. Simulations for all cases were run for a 3 month
period. The first month of the simulation period (January)
served as an initialization period. The output results reported
were for the second month of the simulation (February).
3. EnergyPlus modeling methodology and issues
With nearly any published test suite, issues and choices
arise when modeling the tests with a specific software pack-
age. These issues are summarized below.
3.1. Building envelope construction
The specification for the building envelope indicates that
the exterior walls, roof and floor are made up of one opaque
layer of insulation (R=100) with differing radiative prop-
erties for the interior surface and exterior surface (Ref.
Tables 1–4 of volume 1). To allow the surface radiative
properties to be set at different values, the exterior wall,
roof and floor had to be simulated as two insulation layers,
each with R=50.
3.2. HVAC system
For modeling of the simple unitary vapor compression
cooling system, the EnergyPlus window air conditioner
model was utilized. No other direct expansion (DX) coil
cooling system was available at the time that this work
began, but others have been added since then. The window
air conditioner model consists of three modules for which
specifications can be entered: DX cooling coil, indoor fan
and outside air mixer. The outside air quantity was set to
0.0. The DX coil model is based upon the DOE-2.1E DX
coil simulation algorithms with modifications to the coil
bypass factor calculations.
The specification calls for the unitary air conditioner to
have a draw-through indoor fan. The window air conditioner
model in early beta versions of EnergyPlus could only model
a blow-through fan configuration. In Version 1 build 05 and
later a draw-through configuration is also available. This
limitation may have affected the latent load on the cooling
coil and the compressor energy consumption in the early re-
sults (Rounds 1 and 2), but other issues were also contribut-
ing errors at that point. A draw-through fan was modeled in
Rounds 3 and 4.
R.H. Henninger et al./Energy and Buildings 36 (2004) 855–863 857
The rated coefficient of performance (COP) required as
input by the EnergyPlus DX coil model requires that the in-
put power be the combined power for the compressor and
condenser fans. As such, there are no separate input vari-
ables or output variables available for the compressor or con-
denser fan. The only output variable available for reporting
in EnergyPlus is the DX coil electricity consumption which
includes compressor plus condenser fan.
3.3. Weather data
The typical meteorological year (TMY) weather files
provided as part of the HVAC BESTEST package are not
directly usable by EnergyPlus. In order to create an En-
ergyPlus compatible weather file, the TMY file was first
converted to BLAST format using the BLAST weather
processor (WIFE). An EnergyPlus translator was then used
to convert the weather data from the BLAST format to
EnergyPlus format.
4. Results of testing during initial EnergyPlus
development
HVAC BESTEST was first modeled using a beta version
of EnergyPlus. This section discusses issues which arose
during this phase of testing. Four separate rounds of official
results were submitted to the IEA SHC HVAC BESTEST
Fig. 1. Indoor fan power results for early versions of EnergyPlus.
group.Each round of tests is discussedbelow. Figs. 1–6 show
selected results illustrating the issues which arose during
this testing.
4.1. Round 1—EnergyPlus Beta 5 build 007
During the first round of simulations several potential
software errors were identified in EnergyPlus Beta Version
5-07:
•fan electrical power and fan heat were consistently low
compared to the analytical results for all tests;
•the reported cooling coil loads were consistently too high
and apparently had not been adjusted for the fraction of
the time step that the equipment operated, however, the
DX coil electricity consumption and actual load delivered
to the space were being adjusted appropriately for cycling
time;
•for the dry coil cases, the reported sensible coil load was
slightly higher than the reported total coil load. Latent
load was not available as an output variable, but was cal-
culated by subtracting the sensible from the total. This
error caused small negative latent loads to be calculated
for the dry coil cases;
•zone relative humidity was higher for many tests com-
pared to the analytical results, especially for the tests with
wet coils. This difference was probably due to simulat-
ing a blow-through configuration rather than the required
draw-through configuration.
858 R.H. Henninger et al./Energy and Buildings 36 (2004) 855–863
Fig. 2. Compressor plus outdoor fan electricity consumption results for early versions of EnergyPlus.
Fig. 3. Sensible cooling coil load results for early versions of EnergyPlus.
R.H. Henninger et al./Energy and Buildings 36 (2004) 855–863 859
Fig. 4. Latent cooling coil load results for early versions of EnergyPlus.
Fig. 5. Indoor dry-bulb temperature for early versions of EnergyPlus.
Software change requests were posted. Once a new ver-
sion became available, the tests were rerun.
4.2. Round 2—EnergyPlus Beta 5 build 014
EnergyPlus Beta 5–14 included changes to fix the fol-
lowing problems which were identified in HVAC BESTEST
Round 1:
•reporting of cooling coil loads were corrected to account
for run time during cycling operation;
•the methods of calculating sensible heat ratio (SHR) and
coil bypass factor were modified to eliminate the problem
where the dry coil cases reported sensible coil loads which
were slightly higher than the reported total coil loads.
This error was causing small negative latent loads to be
calculated for the dry coil cases.
During the second round of simulations with Energy-
Plus Beta 5–14 the cooling coil error identified during the
first round of simulations was corrected to account for cy-
cling during each time step, and this brought the evaporator
860 R.H. Henninger et al./Energy and Buildings 36 (2004) 855–863
Fig. 6. Indoor humidity ratio results for early versions of EnergyPlus.
coil loads closer to the range of results for the other pro-
grams; but the loads were still higher than they should
be. Another potential error was therefore identified which
may have been masked by the coil problem identified in
Round 1:
•although there was excellent agreement for zone total
cooling load, the evaporator cooling coil load was larger
than the zone cooling load plus fan heat;
•also, the mean indoor dry-bulb for Case E200 moved from
26.7 to 27.1C;
•the other problems identified in Round 1 still remained
(low fan power, poor agreement in zone humidity ratio).
4.3. Round 3—EnergyPlus, Version 1.0.0.011
The suite of HVAC BESTEST cases were simulated again
using EnergyPlus, Version 1.0.0.011 (the first public release
of Version 1.0, April 2001), which included the following
changes, made since Round 2:
•modified method for calculating coil outlet conditions;
•changed to use of double precision throughout all of En-
ergyPlus (this change was prompted by various issues not
related to HVAC BESTEST);
•added two output variables for tracking fan and compres-
sor run time;
•added an output variable for coil latent load;
•added draw-through fan option to window air conditioner
model;
•the name of the DX coil object was changed from
COIL:DX:DOE2 to COIL:DX:BF-Empirical to better
represent its algorithmic basis.
In addition, the following input file changes were made:
•changed from blow-through fan to draw-through config-
uration;
•updated the DX coil object name to COIL:DX:BF-
Empirical.
The following changes in results were observed:
•indoor fan power consumption and fan heat decreased sig-
nificantly from Round 2, moving farther below the ana-
lytical results;
•space cooling electricity consumption changed slightly
from Round 2 and moved closer to the analytical
results;
•mean indoor humidity ratio decreased compared to Round
2, moving farther away from the analytical results for most
of the dry coil cases and moving closer to the analytical
results for the wet coil cases;
•mean indoor dry-bulb for Case E200 moved further out
of range to 27.5C (the setpoint for this case is 26.7C).
In general, except for fan power, fan heat, and humid-
ity ratio, the overall EnergyPlus, Version 1.0.0.011 results
compared much better to the HVAC BESTEST analytical
results.
R.H. Henninger et al./Energy and Buildings 36 (2004) 855–863 861
4.4. Round 4—EnergyPlus, Version 1.0.0.023
The suite of HVAC BESTEST cases was simulated again
using EnergyPlus, Version 1.0.0.023 (a maintenance release,
June 2001), which included both input file and source code
changes from Version 1.0.0.011.
Input file changes for Round 4:
•the equipment performance curves were refit from scratch
using data from Tables 1–6c of the HVAC BESTEST
specification. Previously, the curve coefficients had been
taken from DOE-2 input files developed by another mod-
eler. The energy input ratio (EIR) curve required for the
EnergyPlus DX coil model is based on compressor in-
put power plus outdoor condenser fan power, but the EIR
curve fit done for DOE-2 applied only to the compressor
input power;
•relaxed the min/max limits of the performance curve
independent variables (cooling coil entering wet bulb
and condenser entering dry-bulb) to allow extrapolation
of cooling capacity as a function or temperature (Cool-
CapFT) and EIR as a function of temperature (EIRFT)
outside the bounds of the equipment performance data
given in the specification;
•the BESTEST cycling degradation factor (CDF) curve
was determined based on net total capacities of the unit
while the EnergyPlus DX coil model requires that the part
load curve be expressed on the basis of gross sensible
capacities. A new CDF curve was developed which was
intended to be on a gross capacity basis, but a later review
of this curve showed an error in the derivation. Further re-
view showed that there is really little difference between
net part load and gross part load, so the revised curve
was then removed and the original CDF curve was used;
•the CDF curve (part load curve) was applied to the
indoor fan operation where previously there was no
input available for this. This change also required
using the FAN:SIMPLE:ONOFF object instead of
FAN:SIMPLE:CONSTVOLUME which had been used
previously;
•added 1 week of infiltration to the beginning of the Case
E120 run period to prevent over drying of the zone during
the simulation warm-up period (see the results discussion
below for more details).
Relevant source code changes from Version 1.0.0.011 to
1.0.0.023:
•standard air conditions for converting volume flow to mass
flow in the indoor fan calculations were changed. HVAC
BESTEST specifies that the volume flow rate is for dry air
at 20 C. EnergyPlus was using a dry-bulb of 25C at the ini-
tial outdoor barometric pressure with a humidity ratio of
0.014kg/kg, although the EnergyPlus documentation in-
dicated 21C and 101, 325Pa was being used. EnergyPlus
now calculates the initial air mass flow based on dry air at
20C at the standard barometric pressure for the specified
altitude, and the documentation reflects this change;
•the specific heat for air throughout the air-side HVAC
simulation was changed from a dry cpbasis to a moist cp
basis. Previously, a mixture of dry and moist cphad been
used for various HVAC calculations;
•the heat of vaporization (hfg) for converting a zone latent
load into a load in the HVAC system was changed;
•a new input field was added to FAN:SIMPLE:ONOFF
to allow a CDF curve (part load curve) to be applied
to the indoor fan operation where previously part load
adjustments could only be applied to the compressor and
outdoor fan;
•changed the moisture initialization to use the initial out-
door humidity ratio to initialize all HVAC air nodes.
The following changes in results were observed:
•the sensible and latent coil loads improved and now track
very close to the analytical results;
•the mean indoor temperature for Case E200 improved and
now, along with rest of the cases, matches exactly with
the analytical results;
•the mean indoor humidity ratio tracks the analytical val-
ues better, especially for the wet coil cases. For Case
E120, however, the EnergyPlus humidity ratio (0.0038)
was much less than the analytical value (0.0079). Intro-
ducing infiltration for the first week of January only and
then turning infiltration off, eliminates this problem and
gives a mean indoor humidity ratio for the month of Febru-
ary of 0.0081. Even though all nodes are initialized to the
outdoor humidity ratio at the beginning of the simulation,
conditions during the simulation warm-up days over dry
the zone for this case. Without the infiltration during the
first week, there is no source of moisture to overcome the
over drying and establish the desired equilibrium;
•indoor fan power consumption and fan heat match ana-
lytical results in most cases or are slightly less than ana-
lytical results;
•COP results changed but are still mixed. One problem may
have to do with the basis of the CDF curve in BESTEST
versus what EnergyPlus requires. The BESTEST CDF
curve was determined based on net total capacities of the
unit while the EnergyPlus DX coil model requires that the
part load curve be expressed on the basis of gross sensible
capacities.
5. Results of testing with subsequent releases of
EnergyPlus
IEA SHC task 22 has completed their activities and fi-
nal results are recorded in a report authored and released
by NREL in January 2002 [3]. Since the completion of
that study, further capabilities and improvements have been
added to EnergyPlus with new releases occurring in June
2002 (Version 1.0.1), August 2002 (Version 1.0.2) and
862 R.H. Henninger et al./Energy and Buildings 36 (2004) 855–863
Fig. 7. Latent cooling coil load results for later versions of EnergyPlus. Note the increase in latent load in Version 1.0.2.008 which was later corrected
in Version 1.0.3.01.
December 2002 (Version 1.0.3). The results for the HVAC
BESTEST series with the three new releases of EnergyPlus
along with the analytical results and results for the last test
series reported in the IEA HVAC BESTEST final report
(Versions 1–23) are presented in a report located on the En-
ergyPlus web site [4]. Although some minor changes took
place in Version 1.0.2 and were later reversed in Version
1.0.3, the results for Version 1.0.3 build 19 are identical
to those for Versions 1–23. Pertinent changes implemented
subsequent to Versions 1–23 were:
•reformatted and changed the hfg psychrometric function
to conform with ASHRAE equations;
•added hgpsychrometric function as per ASHRAE equa-
tions and now use this for latent gain conversion to hu-
midity ratio.
Fig. 7 shows the latent cooling coil loads for Energy-
Plus release Versions 1.0.0.023, 1.0.1.012, 1.0.2.008, and
1.0.3.019.
6. Conclusions
EnergyPlus, Version 1.0.0.023 and subsequent versions
up through the most recent release, EnergyPlus Version
1.0.3.019, were used to model a range of HVAC equipment
load specifications as specified in International Energy
Agency Solar Heating and Cooling Programme Building
Energy Simulation Test and Diagnostic Method for HVAC
Equipment Models (HVAC BESTEST). The ability of En-
ergyPlus to predict zone loads, cooling coil loads, cooling
equipment energy consumption and resulting zone envi-
ronment was tested using a test suite of 14 cases which
included varying internal loads and outdoor conditions.
The results predicted by EnergyPlus for 14 different cases
were compared to results from seven other whole building
energy simulation programs that participated in an Inter-
national Energy Agency (IEA) Solar Heating and Cool-
ing Programme task which concluded in January 2002.
Comparisons were also made with the results from three
analytical solutions. EnergyPlus results generally agreed
to within 1% of the analytical results except for the mean
zone humidity ratio which agreed to within 3% for high
SHR cases but was within 0.20% for low SHR cases.
For more detailed results and discussion, see the Ener-
gyPlus testing report for HVAC BESTEST E100–E200
[4].
The HVAC BESTEST suite is a very valuable testing tool
which provides excellent benchmarks for testing HVAC sys-
tem and equipment algorithms versus the results of other
international building simulation programs. As discussed
above, HVAC BESTEST allowed the developers of Energy-
Plus to identify errors in algorithms and improve simulation
accuracy.
R.H. Henninger et al./Energy and Buildings 36 (2004) 855–863 863
Acknowledgements
This work was supported by the Assistant Secretary for
Energy Efficiency and Renewable Energy, Office of Building
Technologies of the US Department of Energy.
References
[1] EnergyPlus, 2003. http://www.energyplus.gov.
[2] J. Neymark, R. Judkoff, International Energy Agency Solar Heating
and Cooling Programme Task 22 Building Energy Simulation Test and
Diagnostic Method for HVAC Equipment Models (HVAC BESTEST),
National Renewable Energy Laboratory, Golden, CO, October
2001.
[3] J. Neymark, R. Judkoff, International Energy Agency So-
lar Heating and Cooling Programme Task 22 Building En-
ergy Simulation Test and Diagnostic Method for HVAC Equip-
ment Models (HVAC BESTEST), National Renewable En-
ergy Laboratory, Golden, CO, NREL/TP-550-30152, January
2002.
[4] R.H. Henninger, M.J. Witte, EnergyPlus Testing with HVAC
BESTEST. Part 1. Tests E100 to E200, EnergyPlus, Ver-
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