A holistic microclimate model

FAQ ENVI-met

Basic Questions

It is easy to install, does it work right of the box?

Yes and No. On one hand, ENVI-met is a “normal” Windows program, on the other hand, it has system requirements that other programs don't have. You might experience trouble you don't have with other programs just because of bad resource management. Also, ENVI-met constantly reads from and writes to the memory. Just one wrong value (e.g. a temperature of -9999 degree) can kill the whole simulation run. In other pieces of software you might only realize a short non-logical behavior…

ENVI-met will grab all the CPU power it can get. But it does not force Windows to give him all the CPU power, so you can switch to other applications if you have enough memory. ENVI-met reacts only from time to time in WINDOWS messages, so the program might appear as “frozen” although it is still working fine.

Theoretically yes, but it will be probably much slower compared to a generic PC (although a lot of progress has been done in virtualisation in the last time..). Better make a dual boot on the Mac if you plan to run ENVI-met on your own machine. For the real number crunching, you might also consider Cloud Computing

This feature is not implemented at the moment. If you cancel your simulation, you have to start from the beginning.

Starting with Version 4.3 (Winter1718 Release) the SCIENCE and BUSINESS Versions are able to run parallel code on many CPUs.

By default, as a microscale model, ENVI-met is not designed to simulate very large areas such as an entire city. You need to pick selected or typical areas and simulate those as case studies. Starting with V4.3, you might also simulate a (very) large area, but you need a (very) strong computer and a lot of memory.

ENVI-met is a pure physical model. It was designed for high-resolution simulations, but the model physics will also work for much larger spaces and coarser grid resolutions. Hence, ENVI-met might also be used for mesoscale applications if the features of the domain can be represented within the digital domain concept used in ENVI-met (e.g. there are no mixed landuse options in ENVI-met).

In a commercial environment (that is any environment that aims to earn money, public or private) you need the BUSINESS license of ENVI-met to work.

The price list and the feature of the different versions are listed on our download page. If you are interested, please drop us a mail under license[at]envi-met.com.

There is a large number of documents, online help and video tutorials on our web page and it is growing constantly. In addition there is our online forum, but remember that this is not an online hotline. Some question might be answered, others not because they are too complex. Also this is intended as an exchange forum between users.

In addition, the following licenses come with different individual support:

  • BUSINESS: Up to 4 hours of direct support, contact info(at)envi-met.com
  • SCIENCE: Up to 1 hours of direct support for the registered researcher or technical staff of the research institute. NOT for students working with the licenses - here we expect that you contact your professor or course instructor for help. Also contact info(at)envi-met.com and include your registration e-mail
  • STUDENT: Sorry, no direct support.

Simulation Trouble Questions

I get a “Floating point error” or a “Division by zero” error. This is probably due to some programming bug, isn't it?

It might be. But most probably it is an issue of numerical stability that causes these problems. There are billions of operations executed in ENVI-met each minute and every user (including us) wishes, it would be more. Almost any of the variables calculated depend on other variables in space and time. Hence, it might happen that one variable runs wild and hold an unrealistic values. If you are lucky, this error will be corrected by some other systems dynamics, but it may also be that case that a variable unexpectedly went e.g. to zero and is used for a division in the next operation. This must trigger an error. But this does not mean that the program has a programming error, but the dataset got broken. Checking the validity of data before every operation is not possible as the would increase the calculation into infinite. We have introduced heaps of “intelligent” routines into ENVI-met to auto-correct the most common problems. But, it is still a sophisticated numerical tool and these runtime errors belong to numerical modeling like woodchip to carpenters…

There is no general solution why a model is not running correctly. In most cases you have to try different things to get a stable simulation if there are problems occurring. However, here are some things to check, if your configuration does not work:

  • If ENVI-met crashes at the beginning, check the log output on the screen. Probably some files are missing or. Use the “Check Model” option to generate a check output.
  • Check if your input files and database files are ok and hold realistic values.
  • Is WINDOWS working properly ? ENVI-met allocates huge areas of memory for data storing. If a program has “gone wild” or WINDOWS has had some serious problems before or during the model run, it might have happened that the stored data are destroyed. Don't run ENVI-met if you are low on memory. Make sure that ENVI-met runs in your physical memory NOT in swapped memory !

This can always happen to such a complex numerical like ENVI-met. We have invested a lot of time to increase the internal intelligence of ENVI-met. The recent version can handle a lot of trouble situations by itself and find a solution to ensure a proper model run. However, sometimes things simply don't work, and here are some clues what to do:

  • Don't be sad or frustrated! Remember that you are working with a complex numerical model.
  • Move complex buildings away from the model border
  • Try to clean up your model and only keep important structures. But these structures then must make sense. Example: A narrow path between buildings might be close to the models resolution. If you think, this path is important, include it in your model and make it a free path, even if it might be broader or larger in the model than it actually is. If it is not important, delete it. There is no sense in keeping some mess of grids just because the algorithm or map adjustment suggests it.
  • Extend the vertical extension of the model
  • Decrease the time step if the model gets unstable in the normal calculation loop.
  • Consider simplifying your model. It's not the real world either, so you can adjust some very complex corners to an easier configuration

WINDOWS and computer specific questions

Although it looks messy, it is correct. ENVI-met does not react on any WINDOWS messages such as “Redraw yourself” during the simulation in order to save time. It restores the window from time to time.

ENVI-met up to and including 4.2 only uses one thread for the simulation (see next 2 FAQ's). Hence, if your system has more than one CPU core, ENVI-met only uses one of the CPU cores. Although this single core is used a 100%, the overall usage is only 50% (or 25% if you have 4 cores, and so on) if the other cores are without tasks. ENVI-met 4.3 and newer support parallel computing in the PRO/SCIENCE editions.

Yes, if you have enough memory and enough CPU cores free. If you use ENVI-met in parallel mode, you may need to adjust the CPU loading (see docu of V4.3) So if you have 4 cores, you can theoretically run 3 ENVI-mets in single-core mode. Allow each ENVI-met a free memeory of 3 GB to be used.

Version 4.3 comes as a hybrid system for both 32Bit and 64Bit Systems. On a 64Bit WINDOWS installation, the 64Bit Versions of ENVI-met and LEONARDO will be started. The other applications are 32Bit still. In the near future, ENVI-met will only be developed further for 64Bit WINDOWS.

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