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NAGASAWA Yasuhiro

    Department of Architecture　Associate Professor
Last Updated :2024/04/19

Researcher Information

J-Global ID

Research Interests

  • 除湿   遮熱   測定   放射率   シミュレーション   エネルギー消費   熱環境   給湯   日射反射率   分光反射率   通気層   断熱   住宅   

Research Areas

  • Social infrastructure (civil Engineering, architecture, disaster prevention) / Construction environment and equipment

Academic & Professional Experience

  • 2014/04 - Today  Kindai UniversityFaculty of Architecture准教授
  • 2006/02 - 2014/03  Kagoshima UniversityFaculty of Engineering助教

Published Papers

  • Yasushi KONDO; Yasuhiro NAGASAWA; Wataru NARITA
    Journal of Environmental Engineering (Transactions of AIJ) Architectural Institute of Japan 88 (812) 779 - 788 1348-0685 2023/10 [Refereed]
  • Yasuhiro NAGASAWA; Nao NISHIKAWA; Yasushi KONDO
    Journal of Environmental Engineering (Transactions of AIJ) Architectural Institute of Japan 88 (810) 658 - 669 1348-0685 2023/08 [Refereed]
  • Yasuhiro NAGASAWA; Nao NISHIKAWA; Mayuko TANNO; Yasushi KONDO
    Journal of Environmental Engineering (Transactions of AIJ) Architectural Institute of Japan 88 (807) 409 - 420 1348-0685 2023/05 [Refereed]
  • Yasuhiro NAGASAWA; Yasushi KONDO
    AIJ Journal of Technology and Design Architectural Institute of Japan 29 (71) 239 - 244 1341-9463 2023/02 [Refereed]
  • Yasuhiro Nagasawa; Yasushi KONDO
    Journal of Environmental Engineering (Transactions of AIJ) Architectural Institute of Japan 87 (797) 417 - 427 1348-0685 2022/07 [Refereed]
  • Yasuhiro Nagasawa; Yasushi Kondo
    Journal of Environmental Engineering 77 (672) 55 - 64 1348-0685 2012/02 [Refereed]
     
    Computational Fluid Dynamics (hereafter, CFD) is one of the most useful techniques to predict the airflow distribution in air-conditioned and ventilated rooms. The previous studies show that the prescribed velocity method (hereafter, P. V. method) is effective to simulate complicated airflow from an air diffuser in CFD. However, the velocity distribution in the vicinity of the air diffuser as boundary conditions of coarse gird CFD using P. V. method can be affected by the airflow rate, the connecting conditions of the diffuser and supply air duct, and the buoyancy effect due to the temperature distribution. In this paper, the development of the versatile airflow data for P. V. method and the method for its application are discussed. In the first study, the unstructured fine elements CFD simulations under isothermal condition are carried out and the obtained airflow distributions of the system ceiling air diffuser are compared. The relationship between the airflow rate and the velocity near the diffuser, the influence of connecting conditions of the diffuser and air duct are confirmed by the comparison of CFD results. In the second study, the influence of the buoyancy near the diffuser is compared to the inertial force of discharged air on the basis of local Archimedes number obtained by the unstructured CFD simulations under non-isothermal condition.
  • Yasushi Kondo; Fa Zhao; Kyohei Ota; Yasuhiro Nagasawa
    Journal of Environmental Engineering 76 (667) 785 - 792 1348-0685 2011/09 [Refereed]
     
    The previous studies show that the prescribed velocity method (hereafter, P. V. method) is effective to simulate complicated airflow from an air diffuser in CFD. However P.V. method is not applied to system ceiling air diffusers which are popular in office buildings. In this paper, the unstructured fine mesh CFD is conducted to obtain the airflow data of four types of system ceiling diffuser. Then the airflow data is applied in the structured coarse mesh CFD and the short circuit rate and the normalized concentration of occupied zone are examined as ventilation effectiveness. The relationship between shape of diffuser and ventilation effectiveness is discussed on the basis of CFD results.
  • Yasushi Kondo; Atsushi Iwamae; Yasuhiro Nagasawa; Tetsuo Fujimoto; Yusuke Kikuchi; Taichi Tasaka
    Journal of Environmental Engineering 日本建築学会 75 (649) 261 - 269 1348-0685 2010/03 [Refereed]
     
    In order to save energy consumption for air-conditioning of buildings throughout those lifecycle, thermal performance of insulation materials applied in buildings should be kept in required value. On the other hand, there are many factors of ageing of insulation materials such as ambient temperature, vibration and moisture etc. In the previous paper, main factors of thermal performance change were discussed and several experimental results were shown. This paper examines the influences of moisture on thermal performance of various insulations based on three kinds of experiment. In first experiment, the relationship between equilibrium moisture content and thermal conductivity of fiber insulations is obtained. Second experiment is on the influence of gaseous moisture on fiber insulations and the results show that the dimension change of fiber insulations is small even in very humid condition. Third experiment is on the reversibility of thermal conductivity after the internal dew condensation process and the dry process, and the results show that many insulation materials have reversibility except for several plastic insulation foams.
  • Yasushi Kondo; Atsushi Iwamae; Yasuhiro Nagasawa; Tetsuo Fujimoto; Yusuke Kikuchi; Taichi Tasaka
    Journal of Environmental Engineering 日本建築学会 74 (643) 1049 - 1057 1348-0685 2009/09 [Refereed]
     
    Thermal performance of insulation materials decreases with the passage of time. Such ageing of insulations should be considered in the design stage of buildings to keep insulation performance within the required one throughout the lifecycle of buildings. Firstly this paper focused various factors that affect performances of insulations. The main factors for fiber insulations are moisture vibration and microbe. The main factor for plastic insulation foams is ambient temperature that accelerates the diffusion of blowing agent. Secondly real performances of sold new insulations and scraped old ones were measured and compared the required value by Japanese standard. Performances of some insulations were lower than standard values and performance change was detected. Finally this paper discussed the influence of vibration on performance for fiber insulations based on the experimental data. The changes of insulation depth and thermal resistances were observed after the vibration test.
  • YOSHIMURA Jun-ichi; ITO Kazuhide; NAGASAWA Yasuhiro; KIM Taeyeon; HAYASHI Tetsuo
    Transactions of the Society of Heating, Air-Conditioning and Sanitary Engineers of Japan 社団法人空気調和・衛生工学会 34 (144) 53 - 62 0385-275X 2009/03 [Refereed]
     
    CFD code is used routinely to predict air movement and temperature distributions in indoor environment. Especially commercial CFD software is applied against complex geometry and multi-physics phenomenon. In this paper, we discuss the aspects related to numerical errors on choice of turbulence modeling and computational grid concerning the application of commercial CFD code. This paper consists of three examinations, comparison of (1) five different mesh designs, (2) different turbulence model, (3) different commercial CFD code. Finally, recommendations are given for execution of suitable CFD calculations.
  • Yasushi Kondo; Yasuhiro Nagasawa; Tetsuo Fujimoto; Taichi Tasaka
    Journal of Environmental Engineering 一般社団法人日本建築学会 73 (634) 1361 - 1368 1348-0685 2008/12 [Refereed]
     
    The insulation materials are used to improve thermal performance of buildings and their performance should be kept in required value during building life time, however long term change of thermal conductivity is observed for most of insulation materials. It is well known that the thermal conductivity of insulation foams increases with time due to the emission of the blowing agents from the insulation foams and the transfer of the air into them. In this paper, the aging of thermal conductivity in various insulation foams is discussed with measured data and numerical analysis. Two kinds of accelerated test are conducted and the aging characteristics of various foams are examined. The estimation equations of thermal conductivity change of insulation foams are shown and applied to the measured materials. The effective diffusion coefficient of the blowing agents is obtained by comparing the simulation results and the measured value.
  • KONDO Yasushi; NAGASAWA Yasuhiro; OGASAWARA Takeshi; MURAKAMI Shuzo
    Journal of environmental engineering 一般社団法人日本建築学会 71 (606) 23 - 30 1348-0685 2006/08 [Refereed]
     
    The diffusion of the blowing agents in the building insulation foams and the transfer of the air into the insulation foams cause the decrease of the thermal insulation performance. In order to evaluate the protection effectiveness of global warming for the long term, it is important to estimate the aging of the thermal conductivity in the building insulation foams. In this paper, the aging of thermal conductivity in building insulation foams using fluorocarbons or hydrocarbons as the blowing agents was discussed with measured data and numerical analysis. The equations to estimate the thermal conductivity in insulation foams were expressed and the measured data of the thermal conductivity in polyurethane foam and polystyrene foam were represented. The several numerical simulations using these equations were conducted. The calculated thermal conductivity was compared to the measured value and the calculated results showed the good agreement with the measured data. The decay of the partial pressure of the blowing agents was calculated with numerical simulation and the thermal conductivity in the insulation foams increased because the partial pressure within the insulation foams was decreased and the total pressure became the atmospheric pressure.
  • KONDO Yasushi; ABE Yukiko; NAGASAWA Yasuhiro
    Journal of environmental engineering 一般社団法人日本建築学会 71 (601) 29 - 34 1348-0685 2006/03 [Refereed]
     
    Problems in indoor air quality (IAQ) are considered to cause "Sick House Syndrome" in Japan. As such, the building standard was revised to improve IAQ in rooms in Japan in 2003. It is also very important to ventilate indoor spaces efficiently to reduce energy and CO_2 consumption. Ventilation efficiency indexes have been proposed as a means to evaluate the efficiency of ventilation systems and these indexes have been taken into account in ventilation design. This paper proposes the effective ventilated volume as a ventilation efficiency index and gives a definition for the equation of the effective ventilated volume based on the volume integral with a weighting function. The meaning of the effective ventilated volume depends on the selected weighting function, therefore different forms of the weighting function are examined. Three functions are chosen to express the effective ventilated volume for a volume in a well-ventilated zone compared to that in a perfect mixing condition. The weighting functions are described with the local age of air, and the volume of the zone is either neglected or reduced in evaluating the effective ventilated volume when the local age of air is larger than the nominal time constant, i.e. the age of air under the perfect mixing condition. 2-D case studies on the effective ventilated volume based on computation fluid dynamics (CFD) are demonstrated.
  • Kondo Yasushi; Nagasawa Yasuhiro; Ohki Taisuke; Abe Yukiko; Xu Guohai
    Transactions of the Society of Heating,Air-conditioning and Sanitary Engineers of Japan The Society of Heating, Air-Conditioning & Sanitary Engineers of Japan 30 (102) 17 - 23 0385-275X 2005 [Refereed]
     
    The cold air supply system, in which temperature difference between the supply and the return air is higher than usual system, has been applied to the office buildings. It is because that the cold air supply system can save energy for air transport and space for air ducts and the ice storage system by using nighttime electricity can be used for the heat source. The cold air supply system has been mainly studied by experiments and field measurements. Few Computational Fluid Dynamics (hereafter CFD) simulations was applied to that system because it was difficult to reproduced the complex airflow around the air diffuser in the CFD simulation. However the Prescribed Velocity Method (hereafter P.V. method) can simulate the airflow around the air diffuser with coarse grids system. In the previous paper, it was reported that CFD simulation using P.V. method showed good agreement with experimental results for Ceiling Air Diffuser. In this paper, measurements were carried out under non-isothermal conditions in the test room. The applicability of the isothermal airflow data to a non-isothermal CFD simulation was examined using local Archimedes number. M.I. Grimilyn et al. proposed that the buoyancy effect is not significant if the local Archimedes number at the box surface is lower than 0.1. The local Archimedes number was very small at virtual box surfaces and the isothermal airflow data can be applied to the non-isothermal simulation as the boundary condition. CFD simulations using the unstructured grid system were conducted to obtain airflow data around the high diffusion type ceiling air diffuser as boundary conditions of coarse grid CFD. In addition, the coarse grid CFD with P.V. method using the airflow data around the diffuser was compared to the result of the unstructured CFD simulations under isothermal conditions. The result of the coarse grid CFD with P.V. method showed good agreement with the one simulated using unstructured grid system. Furthermore, measurements were compared to the non-isothermal coarse grid CFD using P.V. method with the isothermal airflow data around the diffuser. The air and temperature distributions of CFD and experiment were similar except for the certain parts of the test room.
  • KONDO Yasushi; NAGASAWA Yasuhiro; MURAKAMI Shuzo
    Journal of environmental engineering 一般社団法人日本建築学会 69 (582) 99 - 106 1881-817X 2004/08 [Refereed]
     
    The amount of fluorocarbons involved in building insulation foams as blowing agents is discussed with numerical analysis and measured data in this paper. The diffusion process of fluorocarbons in insulation foams can be expressed as a simple one dimensional diffusion equation. Effective diffusivity and initial concentration of CFCs and HCFCs are necessary to calculate the decrease of concentration with the analytical solution of the diffusion equation. The initial concentration can be obtained from the information of manufactures. In order to study the effective diffusivity, the calculated concentration of CFCs and HCFCs is compared to the measured data. Many samples were collected in various areas in Japan and their CFCs and HCFCs concentrations were measured by the gas chromatography method. The emission rate of CFCs and HCFCs was estimated by the analytical solutions with the effective diffusivity and initial concentration and the database of remained volume for various ages and areas is obtained in this paper. The total amount of CFCs and HCFCs can be estimated with this database and another database of the building insulation stock that will be discussed in Part 2.
  • NAGASAWA Yasuhiro; KONDO Yasushi
    Journal of Environmental Engineering (Transactions of AIJ) Architectural Institute of Japan 69 (585) 27 - 34 1348-0685 2004 [Refereed]
     
    In the previous papers, the P. V. Method (Prescribed Velocity Method : P. V. Nielsen et al. : 1980) was applied to the coarse grid CFD simulations with the isothermal and non-isothermal airflow data obtained by the experiments. The simulated results showed good agreement with the experimental ones. If the effect of the buoyancy is smaller than that of the kinetic energy around the ceiling air diffuser, the airflow data obtained under isothermal condition can give the boundary condition for the coarse grid non-isothermal CFD using the simplified modeling method. The possibility of the application of the isothermal airflow data to the non-isothermal CFD simulation was examined in this paper. The eftect of the buoyancy in the vicinity of the ceiling air diffuser was compared to that of the kinetic energy by calculating local Archimedes number. When the virtual box around the air diffuser was small, the local Archimedes number at the box surface were much lower than 0.1 and the buoyancy effect was not significant. The CFD simulation using the P. V. method with the small virtual box based on the isothermal airflow data was carried out and compared to the experiment. The CFD can reproduce the distributions of the airflow and temperature obtained by the experiment. Therefore it was concluded in this paper that the isothermal airflow data can be applied to the non-isothermal CFD simulation under the certain conditions.
  • NAGASAWA Yasuhiro; KONDO Yasushi
    Journal of Environmental Engineering (Transactions of AIJ) Architectural Institute of Japan 69 (579) 15 - 20 1348-0685 2004 [Refereed]
     
    In the previous paper, measurements were carried out in a test room in which a complex ceiling air diffuser was installed, and coarse arid CFD was conducted using the Box method (P. V. Nielsen et al.; 1978, 1992) and the Prescribed Velocity Method (P. V. Nielsen et al; 1980) based on the boundary airflow data obtained by the experiment. The results of the CFD using these methods showed good agreement with the measured value. In this paper, CFD simulation using the unstructured fine elements system was applied to obtained airflow data around a air diffuser as boundary conditions of coarse grid CFD. The unstructured CFD simulation reproduced the measured airflow distribution in the room and gave the boundary conditions for complex air diffuser with much less effort than by the experiment. It was also confirmed that coarse grid CFD using P. V Method with boundary airflow data obtained by the unstructured CFD gave good results.
  • Abe Yukiko; Kondo Yasushi; Nagasawa Yasuhiro
    Transactions of the Society of Heating,Air-conditioning and Sanitary Engineers of Japan The Society of Heating, Air-Conditioning & Sanitary Engineers of Japan 29 (94) 11 - 16 0385-275X 2004 [Refereed]
     
    The ventilation system in indoor ice skating arenas is usually planned for spectators. However, it was confirmed experimentally that players in arenas are much more sensitive to air contaminant than spectators in seats. In this paper, air quality in an ice arena was measured. The air in the arena was polluted by the exhausted gas from ice surface smoother vehicles and it was stagnant due to the cold air stratification in the lower part of the arena. The ventilation system of the arena was modeled and the distributions of air and pollutant concentration are simulated with Computational Fluid Dynamics (hereafter CFD). In CFD result, the cold stratification was reproduced and the concentration was found very high in the lower area. Several CFD case studies were conducted to develop effective ventilation system. CFD simulation shows that the pollutant concentration in the arena can be reduced when the supply outlets and the exhaust inlet for ventilation system are designed appropriately.
  • NAGASAWA Yasuhiro; KONDO Yasushi; HARIMOTO Kazuyoshi
    Journal of Architecture and Planning (Transactions of AIJ) Architectural Institute of Japan 68 (565) 47 - 54 1340-4210 2003 [Refereed]
     
    In the previous paper, Part 1, the full scale experiment of airflow distribution in a room was carried out under isothermal condition. With the airflow data obtained by the measurement, the BOX method and the P. V. method (the prescribed velocity method) were applied to the CFD simulation. The simulated results showed good agreement with the experimental ones not only around the diffuser but also the other part of the room. This paper presents the full scale experiment and the application of the coarse grid CFD simulation using the P. V. method under non-isothermal condition. In the full scale experiments, the detail of the airflow and temperature distributions around a complex air diffuser installed at the ceiling were obtained. The coarse grid CFD simulation with the P. V. method based on the airflow distribution around the diffuser obtained by the measurement was carried out. The results of this simulation reproduced the complex airflow distributions that were observed in the measurements, such as the attached air jet horizontally along the ceiling, the vertical downward free jet and the induced flow near the diffuser. The simulated temperature distributions of the room air and the wall surfaces also agreed with thc measured ones.
  • KONDO Yasushi; NAGASAWA Yasuhiro; HARIMORO Kazuyoshi; MORIYA Kenji
    Journal of Architecture and Planning (Transactions of AIJ) Architectural Institute of Japan 67 (557) 65 - 72 1340-4210 2002 [Refereed]
     
    Computational Fluid Dynamics (CFD) is one of the most useful techniques to predict the air distribution in air-conditioned and ventilated rooms. The supply airflow such as free jet, wall jet and combined flow of these jets has a great influence on the air distribution in rooms. Most of supply air diffusers have complex geometry, however, the shape of diffuser is usually oversimplified in CFD with coarse grids system. The results of such simulation may give incorrect prediction due to the poor modeling of diffusers. Even if the complex geometry of air diffuser can be described in detail, huge computer capacity and very long calculation time were required. In this paper, several modeling methods to simplify the boundary condition around air diffusers, such as BOX Method (P.V. Nielsen; 1976,1992) and P.V. Method (Prescribed Velocity Method, P.V. Nielsen et al.; 1980), are compared. These modelings require the distribution of air velocity, turbulence properties, temperature and concentrations around the diffuser beforehand. These data as the boundary condition for CFD with coarse grids can be obtained from the experimental measurement or the unstructured CFD simulation with fine meshes. In this paper, the full scale experiment was carried out at isothermal condition, and the airflow data around complex air diffuser installed at ceiling was obtained. With the basis of the flow data around the diffuser by the measurement, BOX Method and P.V. Method were applied to the air diffuser. The results of coarse grids CFD showed the good agreement not only around diffusers but in other part of rooms with the measurement.
  • KONDO Yasushi; NAGASAWA Yasuhiro; FUJIMURA Jun-ichi
    Journal of Architecture and Planning (Transactions of AIJ) Architectural Institute of Japan 65 (534) 57 - 62 1340-4210 2000 [Refereed]
     
    This paper describes the simulation method of the indoor humidity and temperature distributions that is important to study the wet area in rooms. (1) Buoyancy Effect of Humidity Ratio The air density depends not only on temperature but on mass concentration such as humidity, therefore the buoyancy effect of humidity may be appeared in some spaces where the spatial distribution of humidity is very large. The treatment method of this effect into the k-ε turbulence model was discussed in this paper. (2) Near Wall Mass Transfer In order to study the airflow and humidity distributions near wall region, the two-dimensional cavity flows was simulated based on the Low-Reynolds number k-ε model.
  • Kondo Yasushi; Nagasawa Yasuhiro; Irimajiri Maiko
    Transactions of the Society of Heating,Air-conditioning and Sanitary Engineers of Japan The Society of Heating, Air-Conditioning & Sanitary Engineers of Japan 25 (78) 15 - 24 0385-275X 2000 [Refereed]
     
    The cooling load of buildings is largely influenced by the heat gained from solar radiation. Therefore, the reduction of solar heat gain is very effective to decrease the energy consumption of buildings. In this paper, the effects of the solar reflectivity of the roof and the outer walls on the indoor temperature and the cooling load are studied with experiments and numerical simulations. When the reflectivity of the building roof was raised up to about 85% with the high reflective paint, the experimental data showed that the indoor temperature decreased remarkably. The air-conditioning annual loads of various types of buildings, such as gymnasiums, storage spaces, offices, factories and residential houses, were calculated. Especially in hot region, such as Okinawa and Kyusyu, the cooling load is greatly reduced with the high reflective paint. On the other hand, the heating load increased when the high reflective paint was applied, in cool regions, such as Hokkaido, the total annul load becomes rather large. In the point of view about urban climate, the reduction of solar heat gain is very important to restrain the heat island phenomenon. In this paper the urban temperature was simulated with a one-dimensional heat budget model of an urban area, and the effects of high reflective paint (high albedo paint) was evaluated when the paint was applied to 20% of total building roof area on the urban ground surface. In this paper the efficiency of high reflective paint was also evaluated experimentally and numerically when it was applied to vending machines installed out-of-doors.

Conference Activities & Talks

MISC

Research Grants & Projects

  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2006 -2007 
    Author : AKASAKA Hiroshi; NIMIYA Hideyo; MATSUMOTO Shin-ichi; ITAMI Kiyoshi; KAZUHIRO Soga; NAGASAWA Yasuhiro
     
    (1) Measurements on the surface solar reflectance and surface emissivity were carried out. As the result, both of the solar reflectance of the lace curtains and various paints, and the emissivity of various materials such as aluminum sheets with and without plastic coating, several kinds of water vapor barrier, wood and wall cloth were obtained. (2) The outline of the simulation program named REEST (Residential Environment and Energy Simulation Tool) was framed up and the specification of REEST was written. (3) The computer program named Shadewall calculating heat transfer of vented walls and roofs was included in REEST. (4) The computer program named WindEye calculating heat transfer of windows, and the simulations of the solar battery and the unsteady state room humidity change were tried to be included in REEST.

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