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Tokyo University of Science (Department of Architecture, Faculty of Engineering)
Simulating Human Comfort of Heated Environment and Smoking Room

Picture 1: Professor Takashi Kurabuchi (D.Eng.)
Department of Architecture, Faculty of Engineering, Tokyo University of Science

[Vol. 1] How indoor airflow affects human comfort is still not fully understood. Professor Takashi Kurabuchi (Picture 1) has been using SC/Tetra to conduct CFD (Computational Fluid Dynamics) simulations in order to investigate indoor airflow in buildings.

The research at the Kurabuchi Laboratory, in the Department of Architecture, Faculty of Engineering at the Tokyo University of Science, involves architecture and building engineering, architectural equipment, and CFD. CFD simulations are used to study ventilation effects and human comfort. Some examples include investigations on air-conditioning energy efficiency, quanification of human comfort, and bathroom heating. Kurabuchi Laboratory studies both residential living and commercial working environment using CFD and experimental results.

When Professor Kurabuchi first started with CFD, he used his own structured mesh code. However, this meant he was the only one who understood the contents of the code. As the code needed to be modified to solve particular fluid problems, his laboratory students found challenging to customize the code. This encouraged Professor Kurabuchi to consider using commercial codes.
 

Practical Solutions Offered by CFD

Before using commercial CFD tools, Professor Kurabuchi’s research mainly studied how simulation results conformed to real phenomenon. This changed when he started considering using commercial codes. “At that time, fluid analyses results were already fairly accurate. Researchers’ interests shifted toward more practical issues. Some of these included how to use fluid analyses to improve the building environment and optimize facilities,” says Professor Kurabuchi. This encouraged him to start using commercial codes when working problems that were difficult to solve using his in-house code. Since he was using CFD to research the human sensation of warmth, Professor Kurabuchi was looking for a CFD tool, which could flexibly model the human body shape. SC/Tetra, which is equipped with a highly accurate human body thermoregulation model, was the ideal tool.
 

Analyzing the Effects of Floor Heating and Air-conditioners

One of Professor Kurabuchi's research topics compared the effects of floor heating and wall heating units. The human sensation of warmth, as well as the flow of air, is different for those two heating systems. Professor Kurabuchi conducted CFD simulations and experiments to investigate the heating mechanism of each method and assessed human comfort and energy consumption. Professor Kurabuchi used SC/Tetra for the CFD simulations.

The human sensation of warmth was different depending on the type of heating due to the difference in the impact of the convection heat transfer coefficient on the human body surface. When performing the CFD analyses, mesh elements must be flexibly adjusted to the human body geometry to accurately predict the convection heat transfer coefficient. As SC/Tetra was highly capable of controlling the mesh around human body, the analysis results were very accurate.
 

Fig 1: Comparison between fluid analysis and experiment results on a thermal manikin showing thermal conductivity. Click to enlarge.

Professor Kurabuchi undertook experiments to see how the heat transfer coefficient on a thermal manikin was altered by temperature changes. His experimental results were different from the temperature patterns identified in other engineering evaluations that used objects with simpler geometries. This was due to the increased physical details of the thermal manikin. Professor Kurabuchi accurately reproduced these details in CFD simulations and obtained results that were within the range of error of the experiments. Because of this, he found he could predict heat transfer (Fig 1). “The analysis accuracy was higher than I thought. It’s far more beneficial to use the CFD tool for investigating some phenomena that cannot be accurately represented in experiments. I think the analysis tool is becoming capable of helping us decide, for example, which (design idea) is better (based on the simulation results),” says Professor Kurabuchi.

Using CFD simulation and experiment results, Professor Kurabuchi progressed to solving engineering design problem. His challenge was to evaluate the differences in the indoor environment when using a wall heating unit compared to floor heating. He assumed the same level of warmth would be felt by human subjects in both cases. He also estimated the amount of energy required.

Fig 2: Difference between temperature distribution for thermal manikin depending on types of heating.
​Click to enlarge. ​
 

Fig 3: Analysis results of human thermal conductivity between two types of heating. Click to enlarge.

Fig 2 shows that for both cases, the average heat emission from the thermal manikin is equal, for floor heating and the wall heating unit. However, the room temperature is 3 °C higher when the wall heating unit is used. One of the reasons for this is that the wall is warmer when floor heating is used but the air is cooler. Another reason is that, although the wall heating unit supplies warm air, it feels cooler because of the presence of airflow. Circulating air that is colder than the human body surface temperature creates cooling effects. This is effective in a cooling mode, but not in a heating mode. Since there is no need to increase the air temperature with floor heating, secondary energy consumption can be kept low. Overall, Professor Kurabuchi found that radiative heating methods such as floor heating may be better than convective heating.

Fig 3 shows that values of the radiative heat transfer coefficient using floor heating compared to using a wall heating unit were equally independent of the type of body parts. However, the values of the convective heat transfer coefficient were different depending on the type of heating and type of body parts. The value of the combined heat transfer coefficient was 8 W/(m2•K) with the floor heating, and 10 W/(m2•K) with the wall heating unit. This means about 20 % of the heat is lost when the wall heating units used. In addition, floor heating does not produce a draft, which means that less heat escapes even when the temperature is relatively low. Because of the drafts produced by the wall heating unit, the difference between the human body surface temperature and the room temperature must be kept small. In terms of energy consumption, floor heating required 10 - 20 % less energy than the wall heating unit.

​​*All product and service names mentioned are registered trademarks or trademarks of their respective companies.
*Contents and specifications of products are as of April 1, 2015 and subject to change without notice. We shall not be held liable for any errors in figures and pictures, or any typographical errors in this brochure.

Institute Details

 

Tokyo University of Science
(Department of Architecture, Faculty of Engineering)
Establishment of University 1881
Establishment of Department 1962
Location Katsushika-ku,
Tokyo, Japan
Type of University Private

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