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Sauna Thermal Modeling - FAQ

History
When was Sauna first introduced?
Was the Sauna program originally developed at the University Of Michigan?

Learning Sauna
What technical background is required to become a Sauna user?
How long does it take to learn Sauna?
Will I be able to use Sauna on an occasional basis?

Product Features
What is the difference between Sauna Standard and Sauna Modeling System?
What is the numerical method used by Sauna?
Can Sauna model and optimize PCB thermal vias?
Can Sauna be used to find the optimum fin spacing for a heat sink?
Can liquid-cooled cold plates be modeled?
Does Sauna have computational fluid dynamics (CFD) capability?
Can AutoCAD files be imported? Can SolidWorks files be imported?
Why should we buy Sauna instead of using our FEM package?
How does Sauna compare with finite element modeling (FEM, FEA) software?
How does Sauna compare with computational fluid dynamics (CFD) software?

Pricing And Terms
Is Sauna leased or sold as a perpetual license?
Is there a guarantee?

Technical Support
Does the purchase price include technical support?
How do I know that technical support is of good quality?

Misc Questions
Do I need a powerful PC to run Sauna?
Can the evaluation package be used for real design problems?
I am looking to install a sauna in my house, how big a heater will I need?


History

When was Sauna first introduced?

Development of Sauna began in July 1987. The first release was sold to Motorola in October 1989. Sauna has been in commercial release for over 25 years. There are very few thermal software packages that have this record of longevity.

Was the Sauna program originally developed at the University Of Michigan?

No. Sauna was 100% developed by Thermal Solutions. We are located a few miles from the University Of Michigan but there are no connections with the university.


Learning Sauna

What technical background is required to become a Sauna user?

The target user is an electrical or mechanical engineer working in the electronics industry. It is helpful if the engineer has completed a heat transfer class in college, but this is not a requirement. There is no need to have experience with finite element analysis or computational fluid dynamics. Since Sauna uses the intuitive thermal resistance network method, it is easily understood by almost all engineers.

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 model.


Product Features

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 purchase.

What is the numerical method used by Sauna?

Sauna is a thermal network (finite difference) program which uses the thermal/electric 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 modeling setup.

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.

I need to know how many thermal vias will be required beneath a surface mount component. Can Sauna model and optimize PCB thermal vias?

Yes. The method is described in the introductory board exercise which is available here. As a general trend, companies use more vias than actually required.

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 heat sinks.

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 CFD.

More details on the differences between Sauna and CFD programs are given here.

Can AutoCAD files be imported? Can SolidWorks files be imported?

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 model.

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 program.

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 license?

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.

Is there a guarantee?

Sauna is sold with a 60 day moneyback guarantee. If you are not satisfied, for any reason, simply return the product for a refund. In 25 years, only two Sauna packages have been returned for a refund.


Technical Support

Does the purchase price include technical support?

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.

How do I know that technical support is of good quality?

You should perform a test. Call 734-761-1956 and ask a question. Or send an email. After contacting Thermal Solutions, try the same test with some other engineering software suppliers. Then ask yourself which company provides the best technical support.


Misc Questions

Do I need a powerful PC to run Sauna?

No. You should be able to run Sauna on any contemporary Windows computer. More details are given here.

Can the evaluation package be used for real design problems?

No. You can create any model you want, but you will only be able to calculate temperatures for the models created in the tutorials.

I am looking to install a sauna in my house, how big a heater will I need?

You are at the wrong website! This website is for thermal modeling software. Go to www.google.com and perform a search.

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