IESD-Fiala model


The original IESD-FIALA model was developed in 1998 by Dr Dusan Fiala to predict human thermal responses and the associated thermal sensation in a wide range of environments. The model enables thermal influences on human beings to be analysed for transient and heterogeneous conditions with respect to both environmental influences and varying activity levels. The corresponding computer program of the IESD-FIALA model was written in PASCAL, and compiled to run on Microsoft DOS/WINDOWS® platforms (including Windows XP and Vista).

Detailed human model

Diagram of the passive system

Computer simulation of the human thermoregulatory system has been a valuable research tool contributing to a deeper understanding of the principles of human thermoregulation. Besides physiological research, there is a growing interest to predict human physiological and comfort responses also in other disciplines of science and technology.

A mathematical model of human thermoregulation and thermal comfort has been developed at IESD, De Montfort University Leicester, based on more than ten year’s research work. The multi-node, dynamic model incorporates two interacting systems of thermoregulation: the controlling, active system and the controlled passive system.

The passive system (Fiala et al. 1999) is a multi-segmental, multi-layered representation of the human body with spatial subdivisions which includes a detailed representation of the anatomic, thermophysical and thermophysiological properties of the human body. The model accounts for phenomena of human heat transfer that occur inside the body (blood circulation, metabolic heat-generation, -conduction, and -accumulation) and at its surface (free and forced surface convection, long- and shortwave radiation, skin moisture -evaporation, -diffusion, and -accumulation).

Diagram of the active system

The active system model (Fiala et al. 2001) simulates responses of the human thermoregulatory system, i.e. suppression (vasoconstriction) and elevation (vasodilatation) of the cutaneous blood flow, sweat moisture excretion and changes in the metabolic heat production by shivering thermogenesis. The active system was developed by means of regression analysis using measured responses obtained from steady and transient exposures to cold stress, cold, moderate, warm and hot stress conditions, and exercise intensities between 0.8 - 10 met.

The simulation system incorporates a dynamic thermal comfort model which predicts human perceptual responses from physiological states of the body. The comfort model has been derived by regression analysis using measured thermal sensation votes obtained from over 2000 male and female subjects.

Asymetrical radiation

The thermoregulatory and comfort models have been validated extensively against independent experimental data and showed good agreement with measured regulatory responses, mean and local skin temperatures, internal temperatures and thermal sensation responses for the whole spectrum of environmental conditions investigated and for different personal circumstances (Fiala et al. 2001, 2003).

Scientists and engineers can use the model to study responses of (unacclimatized) humans to a wide range of boundary conditions. The IESD-Fiala model provides a basis for a detailed analysis of the transient and complex inhomogeneous environments found in cars, buildings and other man-made spaces and for the analysis of outdoor weather conditions.

The model has found applications, e.g. in medical engineering to predict temperature and regulatory responses of anaesthetised patients, in the car industry to predict passengers' responses to the transient and asymmetric boundary conditions found inside car cabins, in meteorology to quantify human physiological and comfort responses to outdoor weather conditions, some military applications, and the thermal comfort analysis of buildings and individual built components.

How to get it

Please contact me for login details if you haven't got one. Otherwise download the model here:

Download IESD-Fiala model (login is required)

As an alternative, I am considering to release a Java version (jFiala) of the Fiala model. jFiala was a porting of the original IESD-Fiala model so that it can run on multiple platforms. Over the years, improvements have been added to make it a better framework for customizing/developing human thermal models. The drawback, however, is that jFiala is no longer guaranteed to produce same results as the original IESD-Fiala model. We are in the process of validating jFiala. A comprehensive comparison between jFiala and IESD-Fiala will be provided in due course.

Some of the new features of jFiala are:

  • Exposing model parameters of human body for developing individual models
  • Exposing thermal regulatory models and parameters for calibrating the active system
  • Revised solver iteration control to improve numerical stability
  • Additional pre-conditioning settings to allow core temperature and mean skin temperature being set at the start of the experiment
  • Improved output options and format

I am planning to release this version as soon as I can.

Further readings

Fiala D., K.J. Lomas, and M. Stohrer (1999) A computer model of human thermoregulation for a wide range of environmental conditions: The passive system. Journal of Applied Physiology, Vol. 87 (5), pp. 1957-1972.

Fiala D., K.J. Lomas, and M. Stohrer (2001) Computer prediction of human thermoregulatory and temperature responses to a wide range of environmental conditions. International Journal of Biometeorology, Vol. 45, pp. 143-159.

Fiala D., K.J. Lomas, and M. Stohrer (2003) First Principles Modelling of Thermal Sensation Responses in Steady State and Transient Boundary Conditions. ASHRAE Transactions, Vol. 109 (1), pp.179-186.

You are welcome to leave any questions/comments here.


Pasala Sudhir Kumar, 2010/09/17 09:41

Dear sir,

I was trying to send the User Agreement Form for use of the IESD-Fiala model to your mail yizhang@dmu.ac.uk.

I am unable to send the mail due to following failure as given by the gmail server.

Technical details of permanent failure: Google tried to deliver your message, but it was rejected by the recipient domain. We recommend contacting the other email provider for further information about the cause of this error. The error that the other server returned was: 554 554 5.7.1 Dr.yizhang@dmu.ac.uk: Recipient address rejected: Access denied (state 14).

What can I do sir, regards Sudhir

Yi Zhang, 2010/12/06 18:43, 2012/03/03 10:24

Dear Sudhir,

You can try email again, and make sure that 'yizhang@dmu.ac.uk' is the address.



Peter Van Ransbeeck, 2013/04/05 18:22

Dear Yi

I also would like to try your jFiala software.

Thanks in advance for making a copy available.

Best regards


Mike Waggoner, 2013/04/20 15:10
I'd love to see a java version of the Fiala model.  If you'd like an assistance with this, I'd be interested in helping.
Jeremiah Crossett, 2013/05/25 21:31

I would like to explore your jFiala software if you could send a copy.

Ming Fu, 2013/07/04 14:37

Dear Yi,

I am Ming Fu, a PhD candidate in Institute of Public Safety Research (IPSR), Department of Physics Engineering, Tsinghua University. I share you with my research scope. At first, I need to develop a model for heat and mass transfer within protective clothing. Combining the clothing model and the human physiological model, thermal comfort and heat stress of human body with protective clothing will be evaluated, giving some suggestion for working during hot condition.

I think your jFiala software wuould be helpful and gives me some ideas about my research. I would like to try your jFiala software.

Thank you for sending me a copy by email.


Ming Fu

Tsung-lin Liu, 2013/11/20 01:05

Dear Dr. Yi,

Can you send your jFiala software for me? I would like to try your jFiala software. In addition, I have sent the “user agreement form” to your email. Thank for your help.

Best regards, Tsunglin

Ahmed, 2014/12/14 16:36

Dear Dr. Yi Zhang I am PhD student in Baghdad university, my research field is to improve thermal comfort and enrgy saving indoors. I have read more and more papers that used IESD-Fiala model to improve the simulation and I am intresting to use this model in my research. Could you pleas help me and send a jFiala software on my email (en_ahmed82@yahoo.com). With my best regards Ahmed

Güven Fidan, 2016/03/22 17:49

Hi Mr. Zhang,

I am a master student in Turkey. In my thesis, I've examined indoor thermal comfort by CFD methodology. This semester I am going to complete it. And than for my phd study I want to focus on thermoregulation system beside stationary cfd results.

To start thermoregulation operating modeling I want to investigate IESD-Fiala model after download from your website. If it is posibble, I wait your answer.

Thanks in advance

Dmitry, 2016/07/31 17:50

Hello Mr. Zhang

My master dissertation called “Modeling of thermal balance and forecast human thermal feelings”. So, I need IESD-Fiala model to verify my CFD model of human. If it is posible, I want you to give me this model.

Thank you for your time!

M Awais, 2016/11/24 10:09

Hello Dr. Zhang

I am doing PhD on thermalphysiological wear comfort of human. I want to use your IESD-Fiala model for some simmulation. If you allow me to use this model, please sent me detail for login to download IESD-Fiala model.

Thank you and regards

Sebastian Gatz, 2017/02/22 17:13

Hello Dr. Zhang,

I am an architecture student from Denmark, I am working on a 3d-printable exoskeleton-design and I would love to use your IESD-Fiala model to investigate the human's potential thermal comfort related to different iterations of the design.

Thank you for your time

Valentin Melnikov, 2017/03/21 08:37

Dear Dr. Zhang,

I am a researcher in Nanyang Technological University doing research in outdoor thermal comfort. Could you please give an access to Fiala's model?

Lorenzo Belussi, 2017/11/15 15:43

Dear Dr. Zhang. I am a researcher at the Construction Technologies Institute of the Italian National Research Council (ITC-CNR). Could you give me an access to Fiala's model? Thank you very much

Cristina CHICHIREZ, 2018/06/03 17:18

Good evening, Zhang !

My name is Cristina. I am a Romanian bioclimatologist. I would to try Fiala model, but I need password to download.

Please give me the authentification data for download.

Thank you so much.

Best regards, Cristina.

Cristina CHICHIREZ, 2018/06/12 10:52

Dear Dr. Zhang!

I am Cristina Chichirez, a bioclimatologist at University of Bucharest. Did you receive my e-mails? I would to give me the login data for download IESD-Fiala model.

Thank you so much.