Frequently Asked Questions
General TRNSYS Questions
TRNSYS Simulation Studio / Online Registration
TRNBuild / Building model (Type 56) / TRNSYS3D
Troubleshooting TRNSYS Simulations
Q: What is TRNSYS?
A: TRNSYS (pronounced: 'tran-sis') is a software package that has been commercially available since 1975. The software package consisits of a graphical front-end (TRNSYS Simulation Studio) to intuitively create a simulation, an interface for the detailed TRNSYS multi-zone building (TRNBuild/Type56), a Google SketchUp plugin for creating the multi-zone building envelope (TRNSYS3D), and a tool for manually editing the TRNSYS input files and creating stand-alone TRNSYS-based applications (TRNEdit/TRNSED). TRNSYS takes a modular, "black box" component approach to developing and solving simulations: the outputs of one component are sent to the inputs of another component (transient successive subsitution). TRNSYS has been used extensively but is definitely not limited to simulate solar processes and other renewable energy, high performance buildings, and electric power generation.
Q: Where may I find more information about TRNSYS Training Courses or TRNSYS related events?
A: Announcements and events will be communicated via the TRNSYS facebook page and the TRNSYS Users mailing list. Some of the TRNSYS distributors offer TRNSYS Training Courses throughout the year and host TRNSYS Workshops at the International Building Performance Simulation Association (IBPSA) conferences. Thermal Energy System Specialists usually hosts at least three courses year round in Madison, WI, USA.
Q: What standards does TRNSYS
comply to ?
A: TRNSYS has become reference
world. It is one of the
listed simulation programs in the recent European Standards on solar
systems (ENV-12977-2). The level of detail of TRNSYS' building model,
"Type 56", is compliant with the requirements of ANSI/ASHRAE Standard
140-2001. The level of detail of Type 56 also meets the general
requirements of the European Directive on the Energy Performance of
which makes TRNSYS a potential candidate for compliance with the
implementations in various EU countries. TRNSYS was not only used for the IEA Task34/43, to increase the accuracy of the ground-coupled heat transfer, but it was also the only whole building energy simulation program that was deemed as a BESTEST reference standard. TRNSYS has also been used for building simulation for numerous LEED projects.
Q: Is there an evaluation or demo version available for TRNSYS?
A: Yes, the demo version may be obtained from the Demo Version page.
Q: How do I reference TRNSYS for a publication?
A: Klein, S.A. et al, 2010, TRNSYS 17: A Transient System Simulation Program, Solar Energy Laboratory, University of Wisconsin, Madison, USA, http://sel.me.wisc.edu/trnsys.
Q: How do I purchase TRNSYS?
A: TRNSYS may be purchased from one of the official TRNSYS distributors. Please contact the respective distributor, and please note that there are exclusive distributors for the United States(TESS), France(CSTB), Germany(Transsolar), and Portugal/Spain(Aiguasol). If your company or institution is not located in one of those countries, you may purchase from any of the official TRNSYS distributors.
Q: How much does TRNSYS cost?
A: Please contact your official TRNSYS distributor for a price list or more information.
Q: I am a software reseller. Do I get a discount?
A: No discounts are applied to software resellers as the official TRNSYS distributor is responsible for the technical support of the software.
TRNSYS Simulation Studio / Online Registration
Q: What is the Online Studio Registration, and how do I implement it?
A: The TRNSYS Simulation Studio in TRNSYS version 17 requires an online registration to generate an activation key for your particular PC with TRNSYS. You only need to be online this one time to generate the activation key at your respective TRNSYS Distributor's activation website. When you open the Simulation Studio for the first time, a small window will prompt with your specific computer machine code identification number. Highlight and copy this machine ID number. Go to your respective distributor's activation website, enter the appropriate information, and generate an activation key. Highlight and copy the activation key, and paste it back in the small window of the Simulation Studio.
Q: The Online Studio Registration did not work, what should I do now?
A: When you paste the activation key back in the small window of the Simulation Studio, make sure that you do not have any spaces before or after the activation key. Make sure that you are pasting the correct activation key and not any machine ID number. You may also need administrator privleges to implement this for version 17.0. If it still does not work, please contact your TRNSYS Distributor.
Q: What constraints should the
simulation time step comply to ?
A: The timestep should be 1/n of an
n is an integer. The reason is to make sure that an integer number of
steps will fit into one hour (many things happen at the hour:
In TRNSYS 17 the rule
is n/m where n and m both are integers. m
is forced to be smaller than 1 / (minimum time step), which is
currently set to
0.1 sec, i.e. 0.00002777777778 hours (so the denominator must be
36000). The reason is here again to make sure that we can count on
"reaching round numbers at some point inthe
simulation". Data readers, Printers and integrators etc. will warn you
their time step is not an integer multiple of the time step (and it's
recommended to keep it).
TRNBuild / Building model (Type 56) / TRNSYS3D
Q: How can I delete a GAIN from
the TYPES menu in TRNBuild
Menu ZONES, OPTIONAL DATA, GAINS; use delete button (D letter)
Q: I am using Type 56 and am
bad results depending on what START time I use. What am I
(Note: this problem is
corrected in recent TRNSYS 15 releases and all TRNSYS 16 releases: Type
generates an error message) The simulation START time must be an
multiple of the wall TIMEBASE in TRNBuild or the program WILL NOT run
correctly. For example, if the wall timebase
hours, the simulation start time must be 0.0, 0.5, 1.0, 1.5 etc., or
program will not produce correct results. In fact, it will produce
strange results. If you find this hard to believe, change the
example provided with purchase. If you change the timebase
to 0.5 and the simulation start times to 0,0.25,0.5,0.75,
and 1.0... the results
are different for all but the
0,0.5, and 1 cases.
How to calculate
solar radiation that hits an internal wall in a zone that has no
the sun beam gets there passing through another zone
TRNSYS 16 introduced the
concepts of ‘internal windows’ as well as
factors for this situation. The ‘tricks’ needed in
earlier versions are no
longer necessary !
I have a building
description using lots of windows. I would like to try a variant of the
replacing all windows of one type by another one. Do I have to change
WINDOW type everywhere in the project or is there a trick ?
You can redefine the window - type in the Window manager: open the
manager; select the window type; click on the "W4-lib" - button;
choose the new window type.
What does the default
value of the solar absorbtance
factors used in TRNBuild
These factors for the
inside (ABS-FRONT) describe the distribution of solar gains that a zone
through its windows.
default value of 0.6 is
the case for a vertical wall. Other recomended
0.1 for ceilings
Where can I get the
WINDOW program needed to introduce new windows into TrnBuild ?
The program is available for free at the following website. http://windows.lbl.gov/software/window/window.html
I want to define an
airflow from one zone (z1) to another one (z2), without a flow in the
(from z2 to z1) - i.e. define cross ventilation. Where does the air in
from and how do I define it ?
The "coupling air
flow" specified for a zone is always the flow into the zone - it CANNOT
negative. To compensate for air leaving a zone, you have to adapt the
infiltration rate of the zone (z1, in the example). You always need to
air coming into a zone (by specifying coupling flowrates,
or adapting infiltration rates). Air going out is "removed
automatically". (You have to make sure that zones do not
"implode"; "exploding" zones are no problem).
Q: I want to model a sloped window as part of a
sloped wall in type 56.
How does that work ?
You have to
- adapt the sky factor for the wall in which the window is
- define a new orientation for this orientation/slope in the TrnBuild "Project
Initialization" window, and use
it for the wall the window is in
- calculate the orientation / slope with a type 16 / 15 (solar
processor) and connect it to type 56.
Does the ESHADE
factor cut direct and diffuse radiation in the same way ?
A: ESHADE reduces
both direct and diffuse
radiation in the same way.
coefficients are defined by a radiative
convective part; in TrnBuild,
the convective part can
be entered. How to input the radiative
All surfaces are assumed to be black for long wave radiative
exchange and radiative
internal gains for surfaces
inside the zone. This is a good approximation for most real world cases
(exceptions would be huge mirrors or stainless steel panels at inside
or windows with low-E coatings towards the zone). It is not possible to
this assumption easily in type 56. A possible workaround would be to
additional wall gains, but it is usually not worth the effort. All
surfaces are assumed to be grey (E=0.9) for longwave
radiation exchange with the sky. The values of longwave
for windows are taken from the
Is it possible
to use different values for Absorption and Emissivity
in type 56 ?
The longwave absorption
for opaque walls are assumed to be equal (E=A=1 inside the zone).
Question: How to input latent heat for persons,
given in Watt, in TRNBuild ?
They can be entered
under ‘Other Gains’, under ‘abs.
Humidity’. To convert from Watt to kg/hr, use
the enthalpy of evaporation constant (2454 kJ/ kg h). E.g., 44 W latent
=> 44 W / 2454 kJ / kg h = 44 / 2454 * 3.6 kJ / kJ * kg / h =
0.06455 kg / h
Q: What is alpha-calculation (in the BUI) ?
These are coefficients
for the automatic heat transfer in type 56 like you
could do externally with TYPE
80 in previous versions of TRNSYS (15 and earlier).
Troubleshooting TRNSYS Simulations
Q: How to optimize my
for speed ?
A: You can
optimize the 'TRNSYS side' and the 'programming' (FORTRAN, C,...) side. Common tricks for the
TRNSYS side include:
GLOBAL cards carfully
...) - the usual precission
vs. speed tradeoff
component parameters carefully (minimum number of nodes necessary,
is usually most efficient.
component order (components which do not compute a lot (printers, onlline, ...)
at the end, ...)
programming environment (e.g., FORTRAN compiler), make sure you
use the 'Release' build (not the debug build) and check 'Optimize for
the settings (e.g. FORTRAN/Optimisations category). Make sure to apply
ALL modules (modifiy
settings for all modules,
rebuild all modules). Be careful, however: some unstable third-party
not support optimization (e.g. Range Check error in type 140). In this
you can 'locally' deactivate optimization for this type only.
Q: I have a TRNSYS ERROR 25 when using equations, although the unit used
equation appears in the deck
A: This problem may be caused when copying
equation models between
projects, renaming models, or transfering
between projects AFTER the equations have been defined in the equation
Delete the equation causing the problem and redefine it.
data generator does not account for extreme situations, like very hot
days. What can I do to check my building against problems on such days ?
A: The program Meteonorm, a program for
generating weather data, can be used for this. It is available from www.meteonorm.com and from some TRNSYS
can I run TRNSYS (perhaps from another program or batch file) and avoid
to click 'Continue' or 'Yes' at the end of each simulation?
A: From the command line, the "/N" switch is
used to tell
TRNExe.EXE that you don't want the dialog box at the end of the
example, to run the input file called C:\Trnsys17\Examples\SDHW\SDHW.dck such that no dialog box
at the end of the simulation, the following command line statement
"C:\Trnsys17\Exe\TRNExe.exe" "C:\Trnsys17\Examples\SDHW\SDHW.dck" /n
Furthermore, the "/h" switch is also available if you need TRNSYS to
run completely in the background (without even creating a Window). The
switch implies /n and is only applicable to simulations that do not use
online plotter (Type 65):
"C:\Trnsys17\Exe\TRNExe.exe" "C:\Trnsys17\Examples\SDHW\SDHW.dck" /h
Q: I want to distribute my TRNSYS simulation in TRNSED format to others.
What do I
have to send to the client?
A: In TRNSYS 17, the "TRNSED/Create
Distributable" command in
the TRNEdit environment will place all the TRNSYS files needed in the
destination folder. You then need to add all the input files, pictures,
required by your application. We recommend that you test your
application on a
different machine or after renaming your Trnsys17 directory to make
are not using some files from the TRNSYS installation.
Q: Does TRNSYS 17
take advantage of 64-bit computer architecture?
A: The current TRNSYS version does not take
direct advantage of features
that are specific to 64-bit computer architecture. However, TRNSYS will
a 64-bit machine as far as the Developers are aware. To take advantage
64 bit architecture, one first needs a 64 bit FORTRAN compiler. There
several around so if you get TRNSYS to compile with one of these
(giving up the Type65 online plotter and on external DLLs not compiled
64-bit compiler), then TRNSYS will take advantage of the 64 bit
potentially run faster (see remark at the end).
The current FORTRAN compiler that the
Developers use is the Intel Visual
FORTRAN compiler. Intel specifically addresses 64 bit architecture
The Intel site information is focused on
address space size (how much
memory you can manage), which is the main motivation to use 64 rather
bit processors - not so much the potential gains in execution speed
even be reduced due to the systematic use of longer words). If it is
speed that you are after then multiprocessors are better at gaining
speed ( IVF supports
Q: When using a type 53, my
crashes at execution time.
Check that the external
data file for chiller
performances does not contain
any zero data points; type 53 doesn't accept them. This is a workaround
should be fixed in future versions.
connect type 34 to type 56 ?
Answer: To distinguish
between the reduction of
direct and diffuse radiation by wingwalls
overhangs ESHADE should not be used ;
instead use Type
define a new orientation for the
shaded window in TrnBuild
(e.g. SWINDOW, for a window
facing south); this will create 3 new inputs to type 56:
ITSWINDOW - Incident Radiation for orientation SWINDOW
b) IBSWINDOW – Incident Beam Radiation for orientation SWINDOW
c) AISWINDOW – Angle of Incidence for orientation SWINDOW
use type 34 output 1 for a) and 2 for
use type 16 (or 109) output to compute c)
type 34 precedes type 56 in the simulation order
How do I fix the strange comdlg32.ocx error when I try to open the Ground Temperature Display Viewer?
1) Downloaded the comdlg32.ocx file from the link below: http://www.bioinformatics.org/snp-tools-excel/comdlg32.ocx
2) Move the downloaded file to the C:\\Windows\System32 folder
3) Go to Start -> All Programs -> Accessories -> right click "Command Prompt" and select "Run as administrator"
4) In the command prompt window that opens, type "REGSVR32 C:\Windows\System32\comdlg32.ocx" (without the quotes)
5) Check for a pop-up message saying "DllRegisterServer in C:\WINDOWS\System32\comdlg32.ocx succeeded.", which should appear if it installed correctly.
6) Restart Windows and try opening the viewer again.
Q: I wrote a new type, recompiled
TRNSYS and executed a project using my type; but it looks like it never
Note that in TRNSYS 16,
you should create a DLL, using the File/Export As…
command from your Proforma. This makes the process of creating a new
you create your own
workspace or modified the generated source code, this error can occur
The type in question
uses a return statement that does not return the value 1 to the calling
The generated DLL does
not contain the type, and no DLL containing the type is found in the UserLib directory. In this case,
you get an error message
when trying to compile the type or when running the simulation.
15 and earlier : Please
check carefully about these
errors when using the old make tool in IISiBat. The tool always says,
TRNSYS executable is up to date" at the end of the process. This,
does not mean that there were no errors during compiling / linking
! A frequent source of
problems are file time
stamps. In particular during the very first compilation of a new
get confused if no *.obj
file exists yet. Make sure the .obj
file has been
created. Check the time stamps to make sure it was created from *your*
Certain parameters of
the TYPECHECK function can also cause this problem. Try to comment your
this subroutine if you have it, recompile and link the DLL to check if
a problem with your type.
4. The generated DLL does
not export the type