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Waseda University
Using CFD to Predict and Evaluate Human Body Thermal Comfort

 

One basic application of Computation Fluid Dynamics (CFD) is to simulate air flow in building spaces. The outputs from CFD can be used to ensure that air flow rate, velocities, and patterns meet environmental standards for human comfort. Taking a step further, CFD has recently been used to predict and evaluate thermal comfort using thermo-regulation models of the human body.

Shin-ichi Tanabe
Professor, Department of Architecture
FASHRAE, Ph.D.
Waseda University

Basic JOS Human Body Model


  The human body model in JOS is divided into seventeen segments, each having an inner and outer layer. In the latest version of the software released in 2012, the head segment has four layers, which improves modeling accuracy. In addition to the segments, arterial and intravenous blood transports are calculated. Basal metabolism, thermal conductance, and heat capacity are specified as well. When the external environment causes the body temperature to exceed a specified threshold, blood transport in the skin is increased to release more heat from the body. If the temperature remains high, sweat is produced. The amount and distribution of sweat can be an output from the simulation. The JOS model developed by Prof. Tanabe is unique because it contains a large number of segments and results in increased accuracy for calculating time dependent changes in body temperature.

  The practical aspects of using JOS in CFD software like SC/Tetra can be cumbersome. 3D geometry data of a human body must be created, and boundary condition information must be specified for each body segment. Fortunately, human body mesh models from scanned bodies are already included in SC/Tetra for three different postures, standing, seated, and seated on the floor. SC/Tetra can also accommodate new additional human body specifications and boundary information.

Figure 3. Spot cooling

How JOS has evolved


  The most difficult aspect of developing an accurate human body thermoregulation model is obtaining accurate material properties. This is where the JOS model in SC/Tetra has harnessed Prof. Tanabe's research findings. Because human organs and tissues are alive (unlike building materials), it is almost impossible to measure their material properties. Many other aspects of human bodies are also technically challenging to quantify. These include the heat capacities and thermal conductivities of skin and body fat, the amount of blood transport, and how nerves react to thermal conditions. In the past, the only way to acquire material property information was to consult past research. If the input data was not accurate, however (which was frequently the case), the simulation results were erroneous.

  In contrast, by leveraging the experimental research conducted by Prof. Tanabe and marrying these results with the JOS model in SC/Tetra, the JOS model already contains significant "know-how". One example is the system for controlling body temperature. In the human body, sweating, increased/decreased blood transport, and material properties are all variables that control the body temperature. No significant body of medical research can provide input values for these critical phenomena. However, the JOS model uses empirical data obtained from Prof. Tanabe's experiments with human subjects to match simulation results with reality.


  The latest version of SC/Tetra contains many improvements to the JOS model in response to customer requests. Major improvements have been made for face temperature control and sweating in warm environments. The face was not cooling as quickly as it should when exposed to a cool breeze such as air from an air conditioning system. Previously, the face was represented by two temperature layers, and the surface temperature was very close to the deep portion, which did not respond to temperature changes as quickly. Increasing the face model to include four layers enabled temperatures to change more easily.

  Sweating conditions have been modified to account for conditions in hot, high humidity environments. Previously, the model was designed to be used in "dry" air. However, a considerable number of applications have been for high-humidity environments such as saunas and shower rooms. In a "dry" environment most of the sweat evaporates. In highhumidity applications, a portion of the sweat remains in the liquid phase and rolls down the skin. The new model enables simulations in "wet" environments.


Future Improvements


  Prof. Tanabe expects continued support from Cradle to make the SC/Tetra even more capable in the future, not only for JOS applications but also other architectural applications. Two areas of interest for architectural applications is smoothly coupling the air flow and/or thermal conditions with structural analysis or lighting in the surroundings. If we can easily review many designs with regard to these aspects and maintain the reputation for high accuracy by SC/Tetra and scSTREAM (Cradle's general purpose, structured grid CFD software), that is going to be very helpful.

  Prof. Tanabe also aims to improve the JOS model even more. For example, one area of improvement is clothing. Although the current model considers clothing, it does not reproduce the shape of the clothing perfectly, nor are there gaps between the clothing and the skin as there should be. In addition, clothing is porous, permitting air through the material. This is a difficult phenomenon to replicate in a CFD simulation. Prof. Tanabe re-emphasized his commitment to continue improving the JOS model. I will update the model every time we obtain new empirical data for human bodies. Improving the model is a continual process.

*All product and service names mentioned are registered trademarks or trademarks of their respective companies.
*Contents and specifications of products are as of January 31, 2013 and subject to change without notice. We shall not be held liable for any errors in figures and pictures, or any typographical errors.

Institute Details


Department of Architecture, Waseda University
Shin-ichi Tanabe Laboratory

Shin-ichi Tanabe
Professor (Doctor of Engineering),
Department of Architecture, Waseda University
Main Research
Architectural Environmental Engineering
History
1999

Launch of Laboratory 

(First established in 1989 at Ochanomizu University)

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