Contrasting the Capabilities of Building Energy Performance

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doi:10.1016/j.bu

�CorrespondE-mail addr

Building and Environment 43 (2008) 661–673

www.elsevier.com/locate/buildenv

Contrasting the capabilities of building energy performancesimulation programs

Drury B. Crawleya,�, Jon W. Handb, Michael Kummertc, Brent T. Griffithd

aUS Department of Energy, EE-2J, 1000 Independence Avenue, SW, Washington, DC 20585 0121, USAbEnergy Systems Research Unit, University of Strathclyde, Glasgow, Scotland, UKcSolar Energy Laboratory, University of Wisconsin-Madison, Madison, WI, USA

dNational Renewable Energy Laboratory, Golden, CO, USA

Abstract

For the past 50 years, a wide variety of building energy simulation programs have been developed, enhanced and are in use throughout

the building energy community. This paper is an overview of a report, which provides up-to-date comparison of the features and

capabilities of twenty major building energy simulation programs. The comparison is based on information provided by the program

developers in the following categories: general modeling features; zone loads; building envelope and daylighting and solar; infiltration,

ventilation and multizone airflow; renewable energy systems; electrical systems and equipment; HVAC systems; HVAC equipment;

environmental emissions; economic evaluation; climate data availability, results reporting; validation; and user interface, links to other

programs, and availability.

r 2006 Elsevier Ltd. All rights reserved.

1. Introduction

Over the past 50 years, literally hundreds of buildingenergy programs have been developed, enhanced and are inuse. The core tools in the building energy field are thewhole-building energy simulation programs, which provideusers with key building performance indicators such asenergy use and demand, temperature, humidity, and costs.

During that time, a number of comparative surveys ofenergy programs have been published, including:

�
Building Design Tool Council [1,2] and Willman [3]: aprocedure for evaluating simulation tools as well as areport on ASEAM, CALPAS3, CIRA, and SERI-RES. � US Army Construction Engineering Research Labora-
tory [4]: evaluation of available microcomputer energyprograms.
� International Energy Agency Solar Heating and Cool-
ing Programme (IEA SHC) Task 8, Jorgensen [5]:survey of analysis tools; Rittelman and Admed [6]:

e front matter r 2006 Elsevier Ltd. All rights reserved.

ildenv.2006.10.027

ing author. Tel.: +1202 586 2344; fax: +1 202 586 4617.

ess: [email protected] (D.B. Crawley).

survey of design tools specifically for passive and hybridsolar low-energy buildings including summary results onmore than 230 tools.
� Matsuo [7]: a survey of available tools in Japan and
Asia.
� American Society of Heating, Refrigerating, and Air-
Conditioning Engineers [8]: bibliography on programsin the areas of heating, ventilating, air-conditioning andrefrigeration.
� Building Environmental Performance Analysis Club [9]
and UK Department of Energy [10]: comparison ofthree tools.
� Bonneville Power Administration: comparison of energy
software for the Energy Edge new commercial buildingprogram [11].
� Ahmad and Szokolay [12]: comparative study of
thermal tools used in Australia.
� Scientific Computing: a series of reviews from 1993
through 1995 in Engineered Systems Magazine [13,14].
� Kenny and Lewis [15]: survey of available tools for the
European Commission.
� Lighting Design and Application magazine [16]: survey
of lighting design software.

www.elsevier.com/locate/buildenv

dx.doi.org/10.1016/j.buildenv.2006.10.027

mailto:[email protected]

ARTICLE IN PRESSD.B. Crawley et al. / Building and Environment 43 (2008) 661–673662

�

1

Dir

con

y.g

Lomas et al. [17]: IEA SHC Task 12 empirical validationof thermal building simulation programs using testroom data.
� US Department of Energy [18]: directory of 50 building
energy tools developed by DOE.1

�
Aizlewood and Littlefair [19]: survey of the use ofdaylight prediction models. � Natural Resources Canada [20]: directory of more than
100 tools for energy auditing.
� Underwood [21]: comparison of the results from two
programs.
� Natural Resources Canada [22,23]: evaluation of
capabilities of a broad range of simulation engines.
� IEA SHC Task 21 [24]: survey of simple design tools for
daylight in buildings including simple formulas, tables,nomographs, diagrams, protractors, software tools, andscale models.
� Waltz [25]: summary of contact and other basic
information about a variety of building energy, life-cycle costing, and utility rate tools.
� ARTI 21CR [26]: survey of user requirements (archi-
tectural designers, engineering practitioners, and design/build contractors); review whole building, buildingenvelope, and HVAC component and system simulationand design tools; evaluate existing tools relative to userrequirements; and provide recommendations for furthertool development.

Yet in our study we found that no comprehensivecomparative survey of tools had been conducted in the pastten years.

This paper provides a small excerpt from a much longerreport which compares the features of twenty majorbuilding energy simulation programs: BLAST, BSim,DeST, DOE-2.1E, ECOTECT, Ener-Win, Energy Express,Energy-10, EnergyPlus, eQUEST, ESP-r, IDA ICE, IES/VES, HAP, HEED, PowerDomus, SUNREL, Tas,TRACE and TRNSYS. The developers of these programsprovided initial detailed information about their tools. Thisreport by Crawley et al. [27] includes more than five pagesof detailed references for the twenty tools.

Readers are reminded that the tables are based onvendor-supplied information and only a limited peer reviewhas been undertaken to verify the information supplied.Some of the descriptions within the tables employ vendorspecific jargon and thus is somewhat opaque to the broadersimulation community. One of our findings is that thesimulation community is a long way from having a clearlanguage to describe the facilities offered by tools and theentities that are used to define simulation models. As aresult the tables are not yet uniform in their treatment oftopics. Some vendors included components as separate

This report comprised the initial content of the Building Energy Tools

ectory launched in August 1996. This web-based directory now

tains information on more than 330 tools: www.energytoolsdirector-

ov

entries and others preferred a general description ofcomponent types. Clearly there is considerable scope forimprovement in both the layout of the table and in theclarity of the entries.It is our hope that this will become a living document

that will evolve over time to reflect the evolution of toolsand an evolution of the language the community uses todiscuss the facilities within tools. This task is beyond theresources of three or four authors. It requires communityinput that not only holds vendors to account for theveracity of their entries, but injects additional methodol-ogies into the task of tool comparison.The report described briefly here contains detailed tables

comparing the features and capabilities of the programs inthe following 14 categories: General Modeling Features,Zone Loads, Building Envelope and Daylighting, Infiltra-tion, Ventilation and Multizone Airflow, RenewableEnergy Systems, Electrical Systems and Equipment,HVAC Systems, HVAC Equipment, Environmental Emis-sions, Economic Evaluation, Climate Data Availability,Results Reporting, Validation, and User Interface, Linksto Other Programs, and Availability. The detailed report isavailable on the web: www.energytoolsdirectory.gov/pdfs/comparative_paper.pdf.

2. Overview of the twenty programs

2.1. Building Loads Analysis and System Thermodynamics

(BLAST) Version 3.0 Level 334, August 1998

www.bso.uiuc.edu/BLAST

The BLAST system predicts energy consumption andenergy system performance and cost in buildings. BLASTcontains three major subprograms: Space Loads Predic-tion, Air System Simulation, and Central Plant. SpaceLoads Prediction computes hourly space loads givenhourly weather data and building construction andoperation details using a radiant, convective, and con-ductive heat balance for all surfaces and a heat balance ofthe room air. This includes transmission loads, solar loads,internal heat gains, infiltration loads, and the temperaturecontrol strategy used to maintain the space temperature.BLAST can be used to investigate the energy performanceof new or retrofit building design options of almost anytype and size.

2.2. BSim Version 4.4.12.11 www.bsim.dk

BSim provides user-friendly simulation of detailed,combined hygrothermal simulations of buildings andconstructions. The package comprise several modules:SimView (graphic editor), tsbi5 (building simulation),SimLight (daylight), XSun (direct sunlight and shadow-ing), SimPV (photovoltaic power), NatVent (naturalventilation) and SimDxf (import from CAD). BSimhas been used extensively over the past twentyyears, previously under the name tsbi3. Today BSim is

http://www.energytoolsdirectory.gov/pdfs/comparative_paper.pdf

http://www.energytoolsdirectory.gov/pdfs/comparative_paper.pdf

http://www.bso.uiuc.edu/BLAST

http://www.bsim.dk

http://www.energytoolsdirectory.gov

http://www.energytoolsdirectory.gov

ARTICLE IN PRESSD.B. Crawley et al. / Building and Environment 43 (2008) 661–673 663

the most commonly used tool in Denmark, and withincreasing interest abroad, for energy design of buildingsand for moisture analysis.

2.3. Designer’s simulation toolkits (DeST) Version 2.0,

2005 www.dest.com.cn (Chinese version only)

DeST allows detailed analysis of building thermalprocesses and HVAC system performance. DeSTcomprises a number of different modules for handlingdifferent functions: Medpha (weather data), VentPlus(natural ventilation), Bshadow (external shading), Lighting(lighting), and CABD (CAD interface). BAS (buildinganalysis and simulation) performs hourly calculationsfor indoor air temperatures and cooling/heating loadsfor buildings, including complicated buildings of up to1000 rooms.

There are five versions in the DeST family: DeST-h(residences), DeST-c (commercial), DeST-e (building eva-luation), DeST-r (building ratings) and DeST-s (solarbuildings). DeST has been widely used in China for variousprestige large structures such as the State Grand Theatreand the State Swimming Centre.

2.4. DOE-2.1E Version 121, September 2003

simulationresearch.lbl.gv

DOE-2.1E predicts the hourly energy use and energycost of a building given hourly weather information, abuilding geometric and HVAC description, and utility ratestructure. DOE-2.1E has one subprogram for translationof input (BDL Processor), and four simulation subpro-grams (LOADS, SYSTEMS, PLANT and ECON).LOADS, SYSTEMS and PLANT are executed in se-quence, with the output of LOADS becoming the input ofSYSTEMS, etc. The output then becomes the input toECONOMICS. Each of the simulation subprograms alsoproduces printed reports of the results of its calculations.

DOE-2.1E has been used extensively for more thantwenty-five years for both building design studies, analysisof retrofit opportunities, and for developing and testingbuilding energy standards in the US and around the world.The private sector has adopted DOE-2.1E by creating morethan twenty interfaces that make the program easier to use.

2.5. ECOTECT Version 5.50, April 2005 www.ecotect.com

Ecotect is a highly visual architectural design andanalysis tool that links a comprehensive 3D modeler witha wide range of performance analysis functions coveringthermal, energy, lighting, shading, acoustics and costaspects. Whilst its modeling and analysis capabilities canhandle geometry of any size and complexity, its mainadvantage is a focus on feedback at the earliest stages ofthe building design process.

In addition to standard graph and table-based reports,analysis results can be mapped over building surfaces or

displayed directly within the spaces. This includes visuali-zation of volumetric and spatial analysis results, includingimported 3D CFD data. Real-time animation features areprovided along with interactive acoustic and solar raytracing that updates in real time with changes to buildinggeometry and material properties.

2.6. Ener-Win Version EC, June 2005 members.cox.net/

enerwin

Ener-Win, originally developed at Texas A&M Uni-versity, simulates hourly energy consumption in buildings,including annual and monthly energy consumption, peakdemand charges, peak heating and cooling loads, solarheating fraction through glazing, daylighting contribution,and a life-cycle cost analysis. Design data, tabulated byzones, also show duct sizes and electric power require-ments.The Ener-Win software is composed of several mod-

ules—an interface module, a weather data retrievalmodule, a sketching module, and an energy simulationmodule. The interface module includes a rudimentarybuilding-sketching interface. Ener-Win requires only threebasic inputs: (1) the building type, (2) the building’slocation, and (3) the building’s geometrical data.

2.7. Energy Express, Version 1.0, February 2005

www.ee.hearne.com.au

Energy Express is a design tool, created by CSIRO, forestimating energy consumption and cost at the designstage. The user interface allows fast and accurate modelcreation and manipulation. Energy Express includes adynamic multi-zone heat transfer model coupled to anintegrated HVAC model so that zone temperatures areimpacted by any HVAC shortcomings.Energy Express for Architects provides graphic geome-

try input and editing, multiple report viewing, comparisonof alternative designs and results, simplified HVAC model,and detailed online help. Energy Express for Engineersprovides those capabilities along with peak load estimating,and detailed HVAC model, graphic editing of air handlingsystem and thermal plant layouts.

2.8. Energy-10 Version 1.8, June 2005 www.nrel.gov/

buildings/energy10

Energy-10 was designed to facilitate the analysis ofbuildings early in the design process with a focus onproviding a comprehensive tool suited to the design-teamenvironment for smaller buildings. Rapid presentation ofreference and low-energy cases is the hallmarks of Energy-10. Since Energy-10 evaluates one or two thermal zones, itis most suitable for smaller, 10,000 ft2 (1000m2) or less,simpler, commercial and residential buildings.Energy-10 takes a baseline simulation and automatically

applies a number of predefined strategies ranging from

http://www.dest.com.cn

http://www.simulationresearch.lbl.gv

http://www.ecotect.com

http://members.cox.net/enerwin

http://members.cox.net/enerwin

http://www.ee.hearne.com.au

http://www.nrel.gov/buildings/energy10

http://www.nrel.gov/buildings/energy10


building envelope (insulation, glazing, shading, thermalmass, etc.) and system efficiency options (HVAC, lighting,daylighting, solar service hot water and integrated photo-voltaic electricity generation). Full life-cycle costing is anintegral part of the software.

2.9. EnergyPlus Version 1.2.2, April 2005

www.energyplus.gov

EnergyPlus is a modular, structured code based on themost popular features and capabilities of BLAST andDOE-2.1E. It is a simulation engine with input and outputof text files. Loads calculated (by a heat balance engine) ata user-specified time step (15-min default) are passed to thebuilding systems simulation module at the same time step.The EnergyPlus building systems simulation module, witha variable time step, calculates heating and cooling systemand plant and electrical system response. This integratedsolution provides more accurate space temperature predic-tion—crucial for system and plant sizing, occupantcomfort and occupant health calculations. Integratedsimulation also allows users to evaluate realistic systemcontrols, moisture adsorption and desorption in buildingelements, radiant heating and cooling systems, andinterzone air flow.

2.10. eQUEST Version 3.55, February 2005

www.doe2.com/equest

eQUEST is a easy to use building energy use analysistool which provides high quality results by combining abuilding creation wizard, an energy efficiency measure(EEM) wizard and a graphical results display module withan enhanced DOE-2.2-derived building energy use simula-tion program.

The building creation wizard walks a user through theprocess of creating a building model. Within eQUEST,DOE-2.2 performs an hourly simulation of the buildingbased on walls, windows, glass, people, plug loads, andventilation. DOE-2.2 also simulates the performance offans, pumps, chillers, boilers, and other energy-consumingdevices. eQUEST allows users to create multiple simula-tions and view the alternative results in side-by-sidegraphics. It offers energy cost estimating, daylighting andlighting system control, and automatic implementation ofenergy efficiency measures (by selecting preferred measuresfrom a list).

2.11. ESP-r Version 10.1, February 2005

www.esru.strath.ac.uk/Programs/ESP-r.htm

ESP is a general purpose, multi-domain—buildingthermal, inter-zone air flow, intra-zone air movement,HVAC systems and electrical power flow—simulationenvironment which has been under development formore than 25 years. It follows the pattern of ‘simulationfollows description’ where additional technical domain

solvers are invoked as the building and system descriptionevolves. Users control the complexity of the geometric,environmental control and operations to match therequirements of particular projects. It supports anexplicit energy balance in each zone and at each surface.ESP-r is distributed under a GPL license. The web sitealso includes an extensive publications list, examplemodels, source code, tutorials and resources fordevelopers.

2.12. Hourly analysis program (HAP) Version 4.20a,

February 2004 www.commercial.carrier.com

HAP provides two tools in one package: sizingcommercial HVAC systems and simulating hourly buildingenergy performance to derive annual energy use and energycosts. Input data and results from system design calcula-tions can be used directly in energy studies.HAP is designed for the practicing engineer, to facilitate

the efficient day-to-day work of estimating loads, designingsystems and evaluating energy performance. Tabular andgraphical output reports provide both summaries of anddetailed information about building, system and equipmentperformance.HAP is suitable for a wide range of new design and

retrofit applications. It provides extensive featuresfor configuring and controlling air-side HVAC systemsand terminal equipment. Part-load performance modelsare provided for split DX units, packaged DX units,heat pumps, chillers and cooling towers. Hydronic loopscan be simulated with primary-only and primary/second-ary configurations, using constant speed or variable speedpumps.

2.13. HEED Version 1.2, January 2005 www.aud.ucla.edu/

heed

The objective of HEED is to combine a single-zonesimulation engine with an user-friendly interface. It isintended for use at the very beginning of the design process,when most of the decisions are made that ultimately impactthe energy performance of envelope-dominated buildings.HEED requires just four project inputs: floor area,

number of stories, location (zip code), and building type.An expert system uses this information to design two basecase buildings: scheme 1 meets California’s Title 24 EnergyCode, and a scheme 2 which is 30% more energy efficient.HEED automatically manages up to 9 schemes for up to 25different projects.HEED’s strengths are ease of use, simplicity of input

data, a wide array of graphic output displays, computa-tional speed, and the ability to quickly compare multipledesign alternatives. Context specific Help, Advice, and aFAQ file are included. A full Spanish language version isalso included. HEED is free, and can be downloaded fromwww.aud.ucla.edu/heed.

http://www.energyplus.gov

http://www.doe2.com/equest

http://www.esru.strath.ac.uk/Programs/ESP-r.htm

http://www.commercial.carrier.com

http://www.aud.ucla.edu/heed




2.14. IDA indoor climate and energy (IDA ICE) Version

3.0, build 15, April 2005 www.equa.se/ice

IDA ICE is based on a general simulation platform formodular systems, IDA simulation environment. Physicalsystems from several domains are in IDA described usingsymbolic equations, stated in either or both of thesimulation languages Neutral Model Format (NMF) orModelica. IDA ICE offers separated but integrated userinterfaces to different user categories:

�
Wizard interfaces lead the user through the steps ofbuilding a model for a specific type of study. TheInternet browser based IDA Room wizard calculatescooling and heating load. � Standard interface for users to formulate a simulation
model using domain specific concepts and objects, suchas zones, radiators and windows.
� Advanced level interface—where the user is able
to browse and edit the mathematical model of thesystem.
� NMF and/or Modelica programming—for developers.
2.15. IES /Virtual EnvironmentS (IES /VES) Version

5.2, December 2004 www.iesve.com

The IES /VES is an integrated suite of applicationslinked by a common user interface and a single integrateddata model. /Virtual EnvironmentS modules include:

�
ModelIT—geometry creation and editing � ApacheCalc—loads analysis � ApacheSim—thermal � MacroFlo—natural ventilation � Apache HVAC—component-based HVAC � SunCast—shading visualisation and analysis � MicroFlo—3D computational fluid dynamics � FlucsPro/Radiance—lighting design � DEFT—model optimisation � LifeCycle—life-cycle energy and cost analysis � Simulex—building evacuation
The program provides an environment for the detailedevaluation of building and system designs, allowingthem to be optimized with regard to comfort criteria andenergy use.

2.16. PowerDomus Version 1.5, September 2005

www.pucpr.br/lst

PowerDomus is a whole-building simulation tool foranalysis of both thermal comfort and energy use. It hasbeen developed to model coupled heat and moisturetransfer in buildings when subjected to any kind of climateconditions, i.e., considering both vapor diffusion andcapillary migration. Its models predict temperature and

moisture content profiles within multi-layer walls forany time step and temperature and relative humidity foreach zone.PowerDomus allows users to visualize the sun path and

inter-buildings shading effects and provides reports withgraphical results of zone temperature and relative humid-ity, PMV and PPD, thermal loads statistics, temperatureand moisture content within user-selectable walls/roofs,surface vapor fluxes and daily integrated moisture sorp-tion/desorption capacity.

2.17. SUNREL Version 1.14, November 2004

www.nrel.gov/buildings/sunrel

SUNREL is an hourly building energy simulationprogram that aids in the design of small energy-efficientbuildings where the loads are dominated by the dynamicinteractions between the building’s envelope, its environ-ment, and its occupants.SUNREL has a simplified multizone nodal airflow

algorithm that can be used to calculate infiltrationand natural ventilation. Windows can be modeled by oneof two methods. Users can enter exact optical interactionsof windows with identical layers of clear or tinted glassand no coatings on the layers. Thermal propertiesare modeled with a fixed U-value and fixed surfacecoefficients. For the second method, a user importsdata from Window 4 or 5. SUNREL only models idea-lized HVAC equipment. The equipment and loadscalculations are solved simultaneously, and the equip-ment capacities can be set to unlimited. Fans move aschedulable fixed amount of air between zones or fromoutside.

2.18. Tas Version 9.0.7, May 2005 www.edsl.net

Tas is a suite of software products, which simulate thedynamic thermal performance of buildings and theirsystems. The main module is Tas Building Designer, whichperforms dynamic building simulation with integratednatural and forced airflow. It has a 3D graphics-basedgeometry input that includes a CAD link. Tas Systems is aHVAC systems/controls simulator, which may be directlycoupled with the building simulator. It performs automaticairflow and plant sizing and total energy demand. The thirdmodule, Tas Ambiens, is a robust and simple to use 2DCFD package which produces a cross section of microclimate variation in a space.Tas combines dynamic thermal simulation of the

building structure with natural ventilation calculations,which include advanced control functions on apertureopening and the ability to simulate complex mixedmode systems. The software has heating and cooling plantsizing procedures, which include optimum start. Tashas 20 years of commercial use in the UK and aroundthe world.

http://www.equa.se/ice

http://www.iesve.com

http://www.pucpr.br/lst

http://www.nrel.gov/buildings/sunrel

http://www.edsl.net


2.19. TRACE 700 Version 4.1.10, November 2004

www.tranecds.com

TRACE is divided into four distinct calculation phases:Design, System, Equipment and Economics. During theDesign Phase the program first calculates building heatgains for conduction through building surfaces as well asheat gains from people, lights, and appliances and impactof ventilation and infiltration. Finally, the program sizes allcoils and air handlers based on these maximum loads.

During the System Phase, the dynamic response of thebuilding is simulated for an 8760-h (or reduced) year bycombining room load profiles with the characteristics ofthe selected airside system to predict the load imposed onthe equipment. The Equipment Phase uses the hourly coilloads from the System Phase to determine how the cooling,heating, and air moving equipment will consume energy.The Economic Phase combines economic input supplied bythe user with the energy usage from the Equipment Phaseto calculate each alternative’s utility cost, installed cost,maintenance cost and life cycle cost.

2.20. TRNSYS Version 16.0.37, February 2005

sel.me.wisc.edu/trnsys

TRNSYS is a transient system simulation program witha modular structure that implements a component-basedapproach. TRNSYS components (referred to as ‘‘Types’’)may be as simple as a pump or pipe, or as complex as amulti-zone building model.

The components are configured and assembled using afully integrated visual interface known as the TRNSYSSimulation Studio, while building input data is enteredthrough a dedicated visual interface (TRNBuild). Thesimulation engine then solves the system of algebraic anddifferential equations that represent the whole energysystem. In building simulations, all HVAC-system compo-nents are solved simultaneously with the building envelopethermal balance and the air network at each time step. Inaddition to a detailed multizone building model, theTRNSYS library includes components for solar thermaland photovoltaic systems, low energy buildings and HVACsystems, renewable energy systems, cogeneration, fuelcells, etc.

The modular nature of TRNSYS facilitates the additionof new mathematical models to the program. Newcomponents can be developed in any programminglanguage and modules implemented using other software(e.g. Matlab/Simulink, Excel/VBA, and EES) can also bedirectly embedded in a simulation. TRNSYS can generateredistributable applications that allow non-expert users torun simulations and parametric studies.

3. Comparison among the tools

Readers of the report who have specific simulation tasksor technologies in mind should be able to quickly identify

likely candidate tools. The web sites and detailed referencesand footnotes included in the report would then allow apotential user to confirm that the programs indeed have thecapabilities.From our experience, many users are relying on a single

simulation tool when they might be more productivehaving a suite of tools from which to choose. Early designdecisions may not require a detailed simulation program todeal with massing or other early design problems. Weencourage users to consider adopting a suite of tools, whichwould support the range of simulation, needs they usuallysee in their practice.Because the 14 tables comprise 30 pages with more than

250 footnotes in the full comparison report, this paperprovides only a glimpse of the wealth of information in thetables. In this paper, we present portions of Tables 2, 3,and 11, a summary of Tables 5, 7 and 8, as well as thecomplete Table 4 to demonstrate the variety of approachesand solutions represented by these programs. For examplein Table 2, note that almost all the programs deal withinternal thermal mass; yet most tools only perform designsizing calculations using dry bulb temperature. Thefollowing provides brief observations about each of the14 tables from the full report (Tables 1–5).

3.1. Table 1: general modeling features

This table provides an overview of how the various toolsapproach the solution of the buildings and systemsdescribed in a user’s model, the frequency of the solution,the geometric elements which zones can be composed andexchange supported with other CAD and simulation tools.The table indicates that the majority of tools support thesimultaneous solution of building and environmentalsystems. Increasingly tools allow users to study perfor-mance at finer increments than one hour, especially forenvironmental systems. In the vendors’ view there issupport for a full geometric description. Certainly geo-metric detail differs between the tools and users will wantto check the vendors’ web sites for specifics. A few toolssupport exchange data with other simulation tools so thatsecond numerical opinions can be acquired without havingto re-enter all model details.

3.2. Table 2: zone loads

This table provides an overview of tool support forsolving the thermophysical state of rooms: whether there isa heat balance underlying the calculations, how conductionand convection within rooms are solved, and the extent towhich thermal comfort can be assessed. The majority ofvendors claim a heat balance approach although few ofthese report energy balance (see Table 12). This tableindicates considerable variation in facilities on offer. Eighttools claim no support for thermal comfort. Of those thatdo, Fanger’s PMV and PPD indices and mean radianttemperature are used by a majority of tools that calculate

http://www.tranecds.com

http://www.sel.me.wisc.edu/trnsys*

ARTIC

LEIN

PRES

S

Table 1

Zone loads (11 of the 21 rows from Table 2 of the report)

BLAST BSim DeST DOE-

2.1E

ECOTECT Ener-

Win

Energy

Express

Energy-

10

EnergyPlus eQUEST ESP-r IDA

ICE

IES /VES

HAP HEED PowerDomus SUNREL Tas TRACE TRNSYS

Interior surface

convection

� Dependent on

temperature

X X P X X X X X X X X X

� Dependent on air

flow

X X P X X X X E

� Dependent on

surface heat

coefficient from

CFD

E E X

� User-defined

coefficients

(constants,

equations or

correlations)

X X X X X E R X X X X X X

Internal thermal mass X X X X X X X X X X X X X X X X X X X

Automatic design day

calculations for

sizing

� Dry bulb

temperature

X X X X X X X X X X X X X X P X X

� Dew point

temperature or

relative humidity

X X X X X X X X X X X

� User-specified

minimum and

maximum

X X X X X X X X X X X X

� User-specified

steady-state,

steady-periodic or

fully dynamic

design conditions

X X X X X X X

X feature or capability available and in common use; P feature or capability partially implemented; O optional feature or capability; R optional feature or capability for research use; E feature or

capability requires domain expertise; I feature or capability with difficult to obtain input.

D.B

.C

raw

leyet

al.

/B

uild

ing

an

dE

nviro

nm

ent

43

(2

00

8)

66

1–

67

3667

ARTIC

LEIN

PRES

S

Table 2

Building envelope, daylighting and solar (9 of the 52 rows from Table 3 in the report)


2.1E

ECOTECT Ener-

Win

Energy

Express

Energy-

10


ICE

IES /VES


Outside surface

convection algorithm

� BLAST/TARP X X X

� DOE-2 X X X X

� MoWiTT X X X

� ASHRAE simple X X X X X X X X

� Ito, Kimura, and

Oka correlation

X X

� User-selectable X X X X X X X X X

Inside radiation view

factors

X X X X X X P X

Radiation-to-air

component separate

from detailed

convection (exterior)

X X X X X X X X X P X

Solar gain and

daylighting

calculations account

for inter-reflections

from external building

components and other

buildings

P X X X X P X



D.B

.C

raw

leyet

al.

/B

uild

ing

an

dE

nviro

nm

ent

43

(2

00

8)

66

1–

67

3668

ARTIC

LEIN

PRES

S

Table 3

Infiltration, ventilation, room air and multizone airflow


2.1E

ECOTECT Ener-

Win

Energy

Express

Energy-

10


ICE

IES /VES


Single zone infiltration X X X X X X X X X X X X X X X X X X X X

Automatic calculation

of wind pressure

coefficients

X P P X X X

Natural ventilation

(pressure, buoyancy

driven)

X P X P X X X X X X O

Multizone airflow (via

pressure network

model)

X P X X X X X X O

Hybrid natural and

mechanical ventilation

X P X I X X X X O

Control window

opening based on

zone or external

conditions

X X X X X P X O

Displacement

ventilation

X X X X X O

Mix of flow networks

and CFD domains

X E

Contaminants,

mycotoxins (mold

growth)

P R P



D.B

.C

raw

leyet

al.

/B

uild

ing

an

dE

nviro

nm

ent

43

(2

00

8)

66

1–

67

3669

ARTIC

LEIN

PRES

S

Table 4

HVAC systems/components and renewable energy systems [summary from report Tables 5, 7 and 8 (9 pages)]


2.1E

ECOTECT Ener-

Win

Energy

Express

Energy-

10


ICE

IES /VES


Renewable Energy

Systems (12 identified,

X+O)

1 2 2 1 4 0 0 2 4 2 7 1 3 0 0 1 2 2 0 12

Idealized HVAC

systems

X X X X X X X X X X

User-configurable

HVAC systems

X X P X X X X X X X R X X X

Pre-configured systems

(among 34 identified,

X+O)

14 14 20 16 0 16 5 7 28 24 23 32 28 28 10 8 1 23 26 20

Discrete HVAC

components (98

identified, X+O)

51 24 34 39 0 24 8 15 66 61 40 52 38 43 7 15 3 26 63 82



Table 5

Economic evaluation (energy costs portion of Table 11 of the report)


2.1E

ECOTECT Ener-

Win

Energy

Express

Energy-

10


ICE

IES /VES


Simple energy and

demand charges

X X X X X X X X X X X X X X X X X X

Complex energy tariffs

including fixed

charges, block

charges,

demand charges,

ratchets

X X X X X X X X X P X E

Scheduled variation in

all rate components

X X X X X X X X X P X X X

User selectable billing

dates

X X X X P X E



D.B

.C

raw

leyet

al.

/B

uild

ing

an

dE

nviro

nm

ent

43

(2

00

8)

66

1–

67

3670


comfort. The table indicates that there is a sub-set of toolssupporting additional inside surface convection options.Most tools claim support for internal thermal mass, but thespecifics are not yet included in the table. Users would needto check the vendors’ web sites for further detail.

3.3. Table 3: building envelope and daylighting

This table provides an overview of tool treatmentof solar radiation outside a building as well as itsdistribution within and between zones. The table alsocovers outside surface convection, how interactions withthe sky and ground are treated. Not stated in the table areassumptions that tools deal with the sun and that sunlightentering a room is accounted for. Inclusion in the table ismostly for additional facilities. The table indicates thatmost vendors view lighting control as worthy of supportbut few tools yet accept the full complexity of blinds ortranslucent fac-ade elements. As expected, most vendorssupport only 1D conduction. But users are often con-fronted by restrictions in solar and visible radiationtreatment that can be traced to the age of the underlyingcomputational methods.

3.4. Table 4: infiltration, ventilation and multizone airflow

This table provides an overview of how air movement,either from the outside or between rooms or in conjunctionwith environmental systems are treated. All tools claim toprovide at least a single zone infiltration model, somewhatfewer claim to deal with natural ventilation and fewer still,support airflow via a pressure network model. As expected,tool vendors associated with the manufacture of systemcomponents tend not to support much in the way of non-mechanical design options. Interestingly, a number ofvendors now offer support for displacement ventilation.None of the tables include items related to indoor airquality yet even though this has certainly been an issue thathas been raised in various international conferences andresearch journals. Clearly this table will expand in futureversions, but for now readers should look for furtherinformation from the vendor sites.

3.5. Table 5: renewable energy systems

This brief table provides an overview of renewableenergy systems. The table is based on entries suggested byvendors and is not yet complete in terms of its coverage ofsuch designs, what is required of the user to define suchdesigns or the performance indicators that are reported. Witha few exceptions, vendors have few facilities for suchassessments.

3.6. Table 6: electrical systems and equipment

This table provides an overview of how electrical systemsand equipment are treated in each tool. The majority of

tools claim support for building power loads. Yet most ofthese loads are simply scheduled inputs. As with renewableenergy systems, support for electrical engineers is sparse.There appears to be increasing support for basic cogenera-tion facilities, but readers should check with vendors to seewhat the specifics are.

3.7. Table 7: HVAC systems

This table provides an overview of HVAC systems, withadditional sections for demand-controlled ventilation, CO2

control and sizing. Readers should also consult Table 8,which has sections for other environmental control systemsand components. At the beginning of the table is anindicator as to whether HVAC systems are composed fromdiscrete components (implying that the user has somefreedom in the design of the system) or that there aresystem templates provided. It is notable that some toolsnow claim to support CO2 sensor control of HVACsystems. Automatic sizing is offered by quite a few tools.Most tools offer a range of zonal and room air distributiondevices. However, without further investigations it wouldbe difficult for a reader to confirm whether a particularvendors offering is appropriate or what aspects of HVACperformance are assessed.

3.8. Table 8: HVAC equipment

This table provides an overview of the HVAC compo-nents as well as components used in central plant as well ascomponents associated with domestic hot water. This tableis diverse because it reflects the diversity that vendorscurrently support. Such diversity requires the user scan thefull table for items of interest. For example, almost all toolssupport various types of pumps while few claim to haveheat exchangers in the early sub-section—but mostmention heat exchangers in a later section on air-to-airenergy recovery. DX coils seem to be included in multiplesub-sections. It remains for a later version of the report tobegin the substantial task of confirming the equivalence oflike-named entities and imposing an overall structure.Table 7 and 8 in their current form mask even morediversity: even if two vendors offer component X, each ofthem has likely taken a different approach to implementa-tion, ranging from curve fits to entities that take intoaccount the underlying physics. We urge readers not tocount the boxes ticked, but to dig deeper to confirmwhether what is on offer actually is appropriate for use in aparticular simulation project and we would be mostinterested in updating the table to reflect additionalinformation.

3.9. Table 9: environmental emissions

This table gives an overview of the emissions associatedwith the energy use of buildings and environment controlsystems. Users of most tools are able to get reports on


major greenhouse gases. There are other environmentalimpacts that are available to support national standards.This table does not address how difficult it is to gather andsupport the underlying data requirements for environmen-tal emissions.

3.10. Table 10: economic evaluation

This brief table provides a few hints as to vendor supportfor energy cost analysis and life-cycle cost analysis.Support is, at best, mixed and would appear to be sensitiveto region-specific standards and laws. Probably there is nosuch thing as a life-cycle cost definition that would beagreed upon by every tool vendor that offers the facility.Clearly there is scope for this table to expand so as tohighlight the diversity of vendor support.

3.11. Table 11: climate data availability

This table gives a summary of climatic data relatedissues. There is still a cacophony of climate file types andmany tools support a range of formats. One trend over thelast few years is the growth in the number of locationssupported by the EPW file format as well as the number oftools that use this format. It will be interesting to see ifsome tool-specific formats disappear in preference to thisemerging standard.

3.12. Table 12: results reporting

At the end of the day, simulation use is only usefulif users can get access to indicators of performance. Thetable indicates a considerable diversity in the data thatsimulation tools generate as well as the format of thereports. In general, users can create reports based onperformance indicators that they choose. A few toolsprovide in-built facilities to graph and carry out statisticaloperations. Most tools assume considerable proficiencywith third party graphing and spreadsheet applications. Itis interesting to note that simulation tools are among themost disk filling of applications, yet no tool vendor makesany claims about writing to enterprise class databaseformats.

3.13. Table 13: validation

This table gives an indication of the steps that vendorshave taken to test software. In some cases the validation isagainst an analytical standard, in others validation iscomparison between tools. Some show conformance to aparticular national or international standard. The foot-notes and references for the validation exercises are,perhaps among the primary findings of this report.Although vendors would not accidentally tick a box inerror, readers are advised to check the references given forthe specifics of the validation work.

3.14. Table 14: user interface, links to other programs, and

availability

This table takes a different format from the others andallows brief discussions of aspects of each tool that did notfit into the other tables and footnotes. The authorsrecommend this table to the reader because it highlightsissues that could be critical in their understanding ofsimulation tools.

4. Conclusions

As we began working on the report, we found that evenamong the ‘mature’ tools, there was not a commonlanguage to describe what the tools could do. There wasmuch ambiguity, which will continue to require additionalwork to resolve in the future.While the tables in the report may indicate a tool has a

capability, we note that there are many nuances of‘capability’ that the developers found difficult to commu-nicate. For example, there are several levels of resolution—one tool may do a simplified solution while another mayhave multiple approaches for that feature.The tables attempt to clarify this by providing more

depth than a simple X (has capability): they include P(partially implemented), O (optional), R (research use), E(expert use), or I (difficult to obtain input data). Extensiveexplanatory footnotes are also provided. In many tables,many tools allow user-specified correlations, solutionmethods, or convergence criteria.This report does not attempt to deal with whether the

tools would support analysis over the lifetime of theproject—from design through construction into operationand maintenance.From our experience, many users are relying on a single

simulation tool when they might be more productivehaving a suite of tools from which to choose. Early designdecisions may not require a detailed simulation program todeal with massing or other early design problems. Weencourage users to consider adopting a suite of tools, whichwould support the range of simulation needs they usuallysee in their practice.We also found that there was a relatively new level of

attention and interest in publishing validation results.Several program developers also indicated that they plan tomake the simulation inputs available to users for downloadin the near future.There is also the issue of trust: Do the tools really

perform the capabilities indicated? What level of effort andknowledge is required by the user? How detailed is themodel behind a tick in the table? For open source tools,everyone can check the model and adapt it. For the othertools, only very detailed BESTEST-like procedures cangive the answer. We may need a way for users to providefeedback and ratings for these in the future.Where do we see the next generation of this report? First,

we envision this report as a community resource which will


be regularly updated and expanded as the tools (and thesimulation field) mature and grow. Ultimately, we see adynamic web-based community resource with direct linksfor each tool to example input files for each capability aswell as the suite of validation inputs. In some sense this isalready beginning—the authors’ organizations have begunmaking their input files for IEA BESTEST easily available.

Acknowledgments

This paper could not have happened without thecooperation and help of the many people who providedinformation on tools they use or developed: Kim Wittchenof SBI for BSim. The EnergyPlus development team (LindaK. Lawrie, Curtis O. Pedersen, Walter F. Buhl, Michael J.Witte, Richard K. Strand, Richard J. Liesen, Yu JoeHuang, Robert H. Henninger, Jason Glazer, Daniel E.Fisher, Don B. Shirey, III, Robert J. Hitchcock, Brent T.Griffith, Peter G. Ellis, Lixing Gu, and Rahul Chillar) forDOE-2.1E, BLAST, and EnergyPlus. Professor Jiang Yi,Zhang Xiaoliang, and Yan Da of Tsinghua Univesity forDeST. Professor Andrew Marsh and Caroline Raines ofCardiff University and Square One Research for ECO-TECT. Larry Degelman of Texas A&M University forEner-Win. Steve Moller and Angelo Delsante of CSIROfor Energy Express. Norm Weaver of Interweaver Con-sulting for Energy-10. Mark Hydeman, Steve Taylor, andJeff Stein of Taylor Engineering for an early critical reviewand for information on eQUEST. Nick Kelly and IanMacdonald at University of Strathclyde for thought-provoking review, which significantly broadened the scopeof the comparisons. Jim Pegues and Carrier Corporationfor HAP. Professor Murray Milne of UCLA for HEED.Per Sahlin of Equa for IDA ICE. Don McLean, CraigWheatley, Eric Roberts, and Martin Gough for IES/VES. Professor Nathan Mendes of Pontifical CatholicUniversity of Parana for PowerDomus. Michael Deru ofNREL for SUNREL. Alan Jones and Ian Highton ofEDSL for Tas. Justin Wieman of the Trane Company andLarry Scheir of SEI Associates for TRACE. The TRNSYSdevelopers team at TRANSSOLAR, CSTB and TESS.

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Documents

Contrasting the Capabilities of Building Energy Performance