How long does it take to learn Sauna?
To get started with Sauna, you should work all eight of the introductory
exercises in the Sauna user manual. For most engineers, this can
be accomplished in one day. This provides the necessary background
to analyze heat sinks, boards and boxes of moderate complexity. Many of
the introductory exercise are available here.
For complex constructions, you may need to work some of the intermediate
and supplemental exercises. All in all, assume that it takes 1 to 2 days
to learn Sauna. This compares quite favorably with FEM and CFD software.
I only perform thermal analysis once in a while.
I might be involved with thermal issues for several weeks, then six months
might pass before the next thermal project. Will I
be able to use Sauna on an occasional basis?
Yes! In reality, there are very few Sauna users that do thermal
analysis on a continuous basis. Since Sauna is easy to learn,
the program is well suited for this intermittent type of use.
If the period of non-use if greater than 6 months, it's a good
idea to work one or two exercises in the manual as
a refresher course. This might take an hour or two, but the
time savings will be substantial when you start to build the
What is the difference between Sauna Standard and
Sauna Modeling System?
The differences are described here.
Remember, if you are having trouble deciding between Sauna Standard
and Sauna MS, start with Sauna Standard. This is a logical approach
because you can upgrade with full credit during the first year after
What is the numerical method used
Sauna is a thermal network (finite difference) program which uses
analogy. At the lowest level a Sauna thermal model is composed of
nodes, thermal resistors and thermal capacitors. However, users
rarely specify thermal resistances and capacitances. Instead,
a user specifies a material type and plate or board dimensions.
Sauna then creates the appropriate resistance/capacitance network
based on Sauna's library of material properties and the current
For calculating steady state temperatures, Sauna uses a sparse,
direct matrix solver which is based on Gaussian Elimination.
Transient temperature calculations are based on either an implicit
or explicit solver, depending on the model parameters
and user settings.
If you have further questions, feel free to contact Technical Support.
Can Sauna be used to find the optimum
fin spacing for a heat sink?
Yes. Fin optimization can be accomplished in two different ways.
First, there is a utility for optimizing fin spacing and thickness
within Sauna's Toolbox. Second, it's also possible to optimize fins by
performing what-if modifications of the Sauna model.
Fin spacing can be optimized for both natural and forced air
cooling. Sauna can even optimize fins for unconventional fin
orientations, such as naturally cooled horizontal baseplate
Can liquid-cooled cold plates be modeled?
Yes, although the process is a bit more complicated than for
air cooling networks. For liquid cooling applications, you
start by obtaining the pipe-to-fluid resistance with Sauna's Toolbox.
Next, you create the flow network. As the last step,
the pipe-to-fluid resistance
is handled by creating generic resistors between the plate and the
flow ambients. There is an exercise in the Sauna user manual
which describes the method.
Sauna includes a flow network feature.
Does Sauna have computational fluid dynamics (CFD) capability?
No. With the flow network capability, the user can define a flow
path (or paths) and Sauna will calculate the appropriate air
temperature increase as air moves along the flow path. However, it
is up to the user to specify all flow volumes (except for heat sinks,
see next paragraph). If the box has a
straightforward flow path, the flow volume can be readily calculated
by using the fan characteristics and box dimensions (or simply
entered for what-if studies). The Sauna user manual explains how
to perform flow calculations.
For heat sinks, Sauna can perform an integrated fan/flow
calculation. You just need to assign a fan curve to the flow
network and Sauna will handle all of the flow/pressure
calculations. Here again, however, this is handled without
More details on the differences between Sauna and CFD programs are
Can AutoCAD files be imported? Can SolidWorks files
At the present time, you cannot import data from AutoCAD, SolidWorks,
etc. Although importing CAD data seems like a great idea, there
are many practical limitations. CAD models tend to have
too much dimensional information and not enough physical data.
For example, a solids model of a molded plastic part can be
quite complicated due to draft angles, blends, etc. But in
a thermal model it isn't critical to know every dimension,
particularly for materials with low thermal conductivity. If
every detail is included, the model might take days to calculate
but the answer won't be much better than a simplified
On the other hand, CAD models frequently lack the necessary
properties such as thermal conductivity, specific heat and
emissivity. This is particularly true for circuit boards.
So, while it seems like a great thing, we're not convinced
that importing CAD models is really important. But we might
add the feature anyway, just because so many people ask for it.
We already own a finite element (FEM) program (such
as Nastran, Ansys, CosmosWorks, etc.) My boss says we should use the
FEM package for thermal analysis instead of purchasing an electronics
thermal package like Sauna. Why should we buy Sauna instead of using
our FEM package?
Your company will save money in the long run with Sauna. There are
basically 3 costs associated with a software package: (a) the
purchase price, (b) the training cost and (c) the modeling cost. If
you already own the FEM package, the (a) purchase price will be zero,
of course. The (b) training cost may also be zero if the thermal
modeler is experienced with finite element work. However, if an
engineer is not familiar with the FEM method, there will be a long
startup time for FEM. Sauna, on the other hand, uses the intuitive
thermal resistor network method so it can be easily learned
by any mechanical or electrical engineer (or even civil/chemical
engineers and physical science persons). Finally, and most
importantly, there is (c) the modeling cost. As described here, the FEM programs really only deal with a part of
the overall thermal problems. So a model which might take an hour or
two with Sauna could take days with the FEM program. This will cost
your company money.
It's important to realize that an engineering man-week now costs
$3,000 or more. So Sauna will pay off quickly when compared with an
FEM program. Nearly all Sauna customers are also owners of an FEM
software package. But these companies use Sauna for thermal problems
because it is so much more efficient.
How does Sauna compare with finite element modeling
(FEM, FEA) software?
The finite element method (FEM), also known as finite element
analysis (FEA), was developed to analyze deflection and stress
in solid mechanical structures. Once the finite element
mesh has been created, it's also possible to solve for heat
flows and temperatures within the solid material.
However there are three distinct modes of heat transfer: conduction,
convection and radiation. FEM programs really only deal with the
conduction part of the problem. For the convection part of the
problem, it's usually up to the user to enter a convection
coefficient and, in general, only simple convection to the room is
allowed. For thermal radiation, most FEM packages only include
simple black body radiation to the room environment and there is no
ability for walls of a box to radiate to each other. The result
will be lengthy model creation time and incomplete models.
For the most part, FEM packages are not competitive with Sauna.
Nearly all Sauna users also own an FEM package, but the FEM
packages are reserved for purely mechanical problems.
How does Sauna compare with computational fluid
dynamics (CFD) software?
Computation fluid dynamic (CFD) software is a numerical
simulation of the Navier-Stokes equation of fluid motion. This
method is computationally intensive and only became practical within
the last 15 years. The two most popular electronics CFD packages
are ANSYS Icepak and Mentor Graphics FloTHERM.
CFD's primary advantage is the ability to predict flow. If you want
to model a box with 3 fans, and you don't know where the air is
going, then you may wish to consider the CFD approach. With Sauna,
the user must specify the flow rate (Sauna handles all other
aspects of the problem). If the flow path is simple so that flow
volume is readily calculated (details provided in the Sauna user manual),
or for natural cooling, Sauna can be very effective and accurate.
But there are situations where CFD software is useful.
You should be aware of the drawbacks of CFD:
1. CFD programs focus on air flow and convection. CFD programs
are not always effective at handling the conduction and radiation parts
of the problem. For example, a potential purchaser needs to investigate
the way that multilayer circuit boards are modeled and whether the CFD program
has the ability to model radiation networks in complex boxes.
These are very important features for an electronics thermal modeling
2. Details are important in CFD analysis. For example, it's
important in CFD simulations to correctly specify surface roughness
and vent drag coefficients. Sometimes these values must be measured
experimentally. You can't just create a model and assume that
predicted results are on target.
3. CFD analysis is computationally intensive. It's very difficult
to perform duty cycle analysis because the computing time can be
quite significant. What-if analysis is harder because of the
time required for each iteration.
4. CFD software takes time to learn and requires a skilled user.
Since CFD starts with the Navier Stokes equation, it's important
to have a solid background in both heat transfer and viscous fluid
flow. In addition to the proper background, you can expect to
invest at least a week learning the software.
5. CFD software is expensive. Actually, very expensive.
So CFD is not a "silver bullet" method which excels in all
aspects of thermal modeling. When it comes to ease of use,
cost-effectiveness, radiation modeling and duty cycle capabilities,
Sauna is superior. It really is a question of different programs
for different needs. Many Sauna customers own both Sauna
and a CFD program.
Pricing And Terms
Is Sauna leased or sold as a perpetual
Perpetual license, you own the software. There are no mandatory
annual fees. You have the option of purchasing annual comprehensive
support, includes software enhancements, but this is not required.
As described here, lifetime basic technical
support is included in the purchase price.
Does the purchase price include technical
As described here, Sauna Standard includes
comprehensive support (includes software updates) for 6 months, while
the comprehensive support period for Sauna Modeling System is 1 year.
During the comprehensive support period, any questions about thermal
modeling will be answered. When appropriate, technical support will
also review user models to check for proper modeling technique and to
locate obvious flaws. Please be aware that Technical Support does
not provide a "checking" service. The responsibility for "checking"
always resides with the user.
After the initial period, a one year support package can be purchased,
which would include software updates. If this is declined, then
lifetime basic technical support is provided. Basic support means
that Thermal Solutions will respond to phone calls and brief emails
about the operation of Sauna. Questions will not be answered about
modeling assumptions and other thermal issues. Models cannot be
emailed for review and no software updates will be provided.