[Vol. 2] 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.
Having used the simulation tool to accurately evaluate human comfort and the amount of energy consumption, Professor Kurabuchi sought further challenges. The heat transfer coefficient on the human body surface is most influential when a person is unclothed. For the elderly, many accidents occur in the bathroom. In Japan where hot baths are commonplace, drowning is the most common cause of accidental household deaths. The capillary veins contract when the room temperature is cold. This increases the resistance imposed on heart and intensifies blood pressure. An elderly person taking a hot bath under these conditions faces a significant risk of a heart attack, subsequent fall, into the bath tub, and subsequent drowning. To reduce this risk, the air temperature in the bathroom should be warm and warm baths are preferable instead of hot baths. In spite of this, the layout of many traditional Japanese houses locates the bathroom outside the insulated sections of the home. Professor Kurabuchi investigated ideal level of bathroom heating to ensure adequate human comfort.
Professor Kurabuchi simulated the following types of heating: a ceiling mounted heater with a blower that induces convection heating, a carbon heater that creates radiation heating, and an indirect flow heater, that blows air from the side (Fig 4). The indirect flow heater was Professor Kurabuchi's idea.
The simulation results show that radiative heat loss is greater than convective heat loss for a person in a bathroom where the walls of the bathroom are not well insulated. This means that a heating method that improves radiation heating should be used.
The convection heater that blows warm air from the ceiling is commonly used in Japanese houses, but it increases the convective heat transfer. The carbon heater, which is usually mounted high on the wall for safety, only warms the local area around the heater. This creates a high degree of overall thermal discomfort. The temperatures near the floor where the human subject's feet are remain considerably lower for both types of heating. The human body feels colder when it experiences high radiation heat loss. Increasing the wall temperature in the bathroom interior will help minimize the sensation of coldness.。
Professor Kurabuchi proposed the indirect flow heater as an alternative to the traditional methods. The indirect flow heater has the potential to address the problems identified with the two other heating systems. The indirect heating method uses a metallic deflection panel that is attached to the front of a convective heater to redirect the airflow. The panel keeps the air from directly hitting the human body. In addition heat is transferred by radiation from the heated panel to the human subject. The deflection panel was attached to the wall about three feet off the ground. This is at the lower side of a person who is standing. The radiation view factor is highest at this height.
Professor Kurabuchi analyzed the temperature distributions on the human body surface for the three different heating methods. He assumed the amount of heat loss is always at the same level (Fig 5). The analytical results show that the carbon heater and the indirect flow heating were both energy efficient in terms of secondary energy consumption. The variance in sensible heat loss between different body parts was the lowest using the indirect heating method. The indirect heating method achieved both the highest human comfort levels and was the most energy-efficient.
Unlike the extensive fluid/thermal research often performed on commercial and industrial products, few detailed investigations have been performed on airflow in buildings, especially on indoor airflow that involved moving objects. To accurately model indoor airflow, engineers must consider the movement of people and opening and closing of doors. Contaminant control may also be necessary for smoking rooms and bathrooms. Despite these requirements, no significant body of airflow research involving opening and closing doors and movement of people has been performed.
Assistant Professor, Dr. Sihwan Lee from the Kurabuchi Laboratory (Picture 2) has investigated how the airflow in a designated smoking room changes when the door opens and closes. He used SC/Tetra to determine whether simulation could accurately represent the airflow by comparing calculated results to experimental results. Although Dr. Lee could not perfectly reproduce the real-time characteristics of turbulence, he identified the correct trends for the ensemble average flow characteristics when compared to flow visualization results from the experiments.
Dr. Lee conducted further investigations to determine the factors that can lead to air leakage from the room. He confirmed that opening and closing the door, as well as human movements, significantly affected the amount of leakage.
The amount of leakage from the room may vary depending on how the leakage is measured and the kind of door that is used, such as sliding doors or swinging doors. In Dr. Lee's simulations, the amount of leakage was much less with sliding doors, and the people movement did not affect the leakage thorough the sliding door as much as expected. Dr. Lee wants to evaluate how the shape of the door and the use of air curtains can influence the leakage. He is also interested in exploring how the leakage mechanism may change depending on the surroundings, such as restaurants.
Different CFD tools can have different strengths. Because of this, the Kurabuchi Laboratory uses many tools and selects the most appropriate one for case being studied. “Software Cradle responds fast to our inquiries. Their engineers are thorough with the support. They give very detailed answers to the questions from our students,” says Professor Kurabuchi.
Intending to extend his students’ interests in CFD through classwork, Professor Kurabuchi gives them regular simulation assignments. These can consist of using structured mesh tools to model and analyze a situation they encounter in their daily lives. “One student analyzed the airflow in a restaurant where he works part-time. Another student analyzed the airflow in our classroom. I think they enjoy going through the analysis processes. They especially like visualizing the invisible air and animating the flow,” says Professor Kurabuchi. The students in the Kurabuchi Laboratory will use SC/Tetra when they perform analyses for research.
Professor Kurabuchi comments: “The processing capability of SC/Tetra is remarkable when dealing with heat transfer of the human body and moving mesh elements. I hope that further development will be made on this, as other CFD tools are not capable of processing to this extent.” The wide range of possible airflow research topics Professor Kurabuchi is considering includes investigation of a walking human, bathroom environments, and the effects of a mist-generating system that is installed at the Kagurazaka campus every summer. “Recent research has focused on understanding the mechanisms of new phenomena. I think that having diverse a range of functions will be helpful for such analyses,” says Professor Kurabuchi.
Professor Kurabuchi says: “Analysis tools can be far more accurate than experiments in some cases. They It can also be useful for multi-dimensional angled evaluations. For example, it is difficult to conduct experiments and make measurements for transient phenomena in a smoking room. But if we can validate an analytical simulation draw a comparison with for a testable case, and if a certain level of accuracy is ensured, we can use the CFD tool to evaluate other various ideas with confidencewithout problems. I’m expecting to see more of this research approach,” says Professor Kurabuchi. SC/Tetra is indispensable to the Kurabuchi Laboratory and will be used to evaluate the comfort levels throughout a diverse range of of residential environments in diverse fields.
|Establishment of University||1881|
|Establishment of Department||1962|
|Type of University||Private|
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