Ryozo Ooka

The University of Tokyo, Edo, Tōkyō, Japan

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Publications (161)129.35 Total impact

  • Source
    Wonjun Choi · Ryozo Ooka
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    ABSTRACT: To interpret thermal response tests (TRTs), analytical models that assume constant heat flux from the source are widely used because of their simplicity. However, in actual field conditions, the constant heat flux assumption is violated by the heat exchange between the above-ground TRT setup and outdoor environment. This results in perturbations in the temperature response and causes fluctuations in estimation and consequent estimation errors in the interpretation of TRTs. For a better design of experiments and obtaining quality data from a TRT, a systematic analysis of the disturbance factors is important. In this study, we developed an analytical model that describes the heat exchange in an above-ground TRT setup. On the basis of this model, a parametric study and sensitivity analysis were conducted in a systematic manner using disturbance-related parameters, such as test settings (heat injection rate and flow rate), above-ground connecting circuit parameters (insulation thickness, length, and radiation absorptivity), temperature of fluid, and weather conditions (solar irradiation, environmental temperature, and wind velocity). The above-ground circuit length and parameters related to radiative heat transfer showed the highest sensitivity coefficients. Based on the results, some suggestions are provided for experimenters on designing TRT setups and conducting TRTs to obtain quality data.
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    Madhavi Indraganti · Ryozo Ooka · Hom B Rijal
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    ABSTRACT: Reports on occupant behavioral adaptation to varying thermal conditions in India are limited. We analyzed the data from our thermal comfort survey of 2787 occupants in 28 office buildings (N= 6048): 13 mixed mode (MM), 14 completely air-conditioned and one naturally ventilated building in Chennai and Hyderabad. Behavioral adaptation was found to be vital for thermal comfort. Occupants adaptively used air-conditioners and or fans in MM buildings during the temperature excursions. Our logistic regression predicts 89.4% and 28.5% of air conditioners to be operating in MM buildings in Chennai and Hyderabad respectively, at 29 °C of outdoor daily mean temperature. Females, young subjects, and people with low body mass index had higher comfort temperatures than males, older people, and obese occupants respectively, with a difference of 0.3 – 1.0 K in various groups, which is significant at 95% confidence interval. In naturally ventilated environments females were comfortable at 28.5 °C and men at 27.8 °C. Females accepted the environments better. Many behavioral control actions were noted throughout the year without much seasonal shifts. Staying in airy place was the most prominent behavioral adaptation all through. This reinforces the need for elevated air movement indoors.
    Energy and Buildings 09/2015; DOI:10.1016/j.enbuild.2015.05.042 · 2.47 Impact Factor
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    9th International Conference on Urban Climate, Toulouse, France; 07/2015
  • Hideki Kikumoto · Ryozo Ooka · Yusuke Arima
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    ABSTRACT: Enhancement of very hot weather conditions in summer due to climate changes at global and local scales can increase mortality through thermal stresses. To estimate the impact of climate changes on the risks of heat disorder (HD) in Japan around the year 2030, we conducted numerical climate simulations using a global circulation model (GCM) and a regional climate model (RCM). The GCM results for the global climate change analysis were provided as initial and boundary conditions, and climate information was dynamically downscaled by the RCM. We carried out simulations of the situation in August over 10-year periods for the present (2001–2010) and near-future (2026–2035) cases. The wet-bulb globe temperature (WBGT) was used as a thermal stress index. The modeled 10-year average WBGT values for the present time agreed very well with observation data. An increase of 1.11 °C (from 24.96 °C to 26.07 °C) in average WBGT from the present to the future cases was predicted based on the data. Changes in HD incidence rates were then evaluated using the obtained results and past statistical data. The average number of people transported by ambulance per day in August was predicted to increase by 63%.
    Energy and Buildings 07/2015; DOI:10.1016/j.enbuild.2015.07.033 · 2.47 Impact Factor
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    Hideki Kikumoto · Ryozo Ooka
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    ABSTRACT: Vertical profiles of wind velocity within the urban boundary layer were measured in the Tokyo center district for seven months using a Doppler lidar system. We applied the power law to approximate the measured wind profiles and discussed their approximation accuracy. The power-law index showed a diurnal variation from 0.1 in the daytime to 0.3 in the night; the average of the power-law index is 0.206 for the all observation periods. The approximation accuracy significantly depended on wind velocity and averaging period. The power law could be a good model for high velocity conditions with long averaging time. However, the relative error of the approximation using the power law became more than 20% for cases with 10-minute average in which wind velocity was less than 5 m/s.
    14th International Conference on Wind Engineering, Porto Alegre, Brazil; 06/2015
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    Wonjun Choi · Ryozo Ooka
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    ABSTRACT: Effective ground thermal conductivity and borehole thermal resistance, which are key parameters in the design of borehole heat exchangers (BHEs), are often determined on the basis of in-situ thermal response tests (TRTs). However, many disturbance factors can affect the accuracy of a TRT, e.g., voltage fluctuations from the power grid and oscillating external environments where a TRT rig is installed. Interpretation of TRT data is often done using the infinite line source (ILS) model, combined with the sequential plot method, because it is not only simple but also provides additional information about the estimation behavior and convergence. However, estimation behavior using the sequential method tends to fluctuate over time because the constant heat flux assumption is always violated as a result of the disturbance factors. As an alternative, a temporal superposition applied analytical model can be used in a recursive curve fitting manner, but this method cannot provide the additional information that sequential method can. In this study, as a solution for interpreting disturbed TRT data and to utilize additional information from the sequential plot method, we proposed an alternative method using a temporal superposition applied ILS model combined with the quasi-Newton optimization method. To verify the effectiveness, the proposed method was applied to in-situ TRTs and the results were compared with those from the conventional method in terms of the estimation stability and convergence speed. The results showed that, compared to the conventional sequential method using the ILS model, the proposed method yielded standard deviations for the effective thermal conductivity and borehole thermal resistance that were at least six times and four times lower, respectively. Moreover, the proposed method was able to achieve about four times faster convergence speeds.
    Applied Energy 06/2015; 148:476-488. DOI:10.1016/j.apenergy.2015.03.097 · 5.61 Impact Factor
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    ABSTRACT: As in many other countries in the world, Japan has witnessed an increased focus on low-energy buildings. For testing different engineering solutions for energy-efficient buildings, a low-energy building was built at the University of Tokyo as an experimental pilot project. In this building, a radiant heating/cooling ceiling panel system is used. However, no standard exists for the in situ performance evaluation of radiant heating/cooling ceiling systems; furthermore, no published database is available for comparison. Thus, this study aims to not only clarify the system performance but also to share our experience and our results for them to serve as a reference for other similar projects. Here, the system performance in relation to its heating/cooling capacity and thermal comfort has been evaluated. The heat transfer coefficient from water to room was 3.7 W/(m(2) K) and 4.8 W/(m(2) K) for heating and cooling cases, respectively. The upward heat flux from the panels was found to be as large as 30-40% of the water heating/cooling capacity; this would translate into heat loss in certain operating modes. Several proposals for reducing the upward heat flux were discussed. The measurements also showed that a category B thermal environment was obtained using the radiant ceiling heating/cooling system.
    Energy and Buildings 01/2015; 86. DOI:10.1016/j.enbuild.2014.09.070 · 2.47 Impact Factor
  • Hang YIN · Ryozo OOKA · Masanori SHUKUYA
    Journal of Environmental Engineering (Transactions of AIJ) 01/2015; 80(711):425-432. DOI:10.3130/aije.80.425
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    ABSTRACT: In this paper, we dynamically downscaled GCM (Global ClimateModel) in August for present (2001-2010) and near future (2026-2035). We confirmed bias of the obtained weather data and corrected the weather data with observations to reduce the bias of both RCM and GCM. We then selected the average monthly weather data which represent typical weather conditions for ten years among the results of downscaled GCM and made prototypes of current and near future standard weather data. We conducted building energy simulation using the prototypeof current standard weather data and confirmed the availability of the weather data for building energy simulations. In addition, we conducted future building energy simulation to access the impact of climate change on energy consumption of a two-story detached house in Tokyo. Under this conditions, total sensible heat load in August increased 26% and latent heat load increase 10%.
    Journal of Environmental Engineering (Transactions of AIJ) 01/2015; 80(710):371-379. DOI:10.3130/aije.80.371
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    ABSTRACT: A distinct feature of Wuhan is that almost a quarter of the total area of this city is covered with water, leading to its unique hot and humid climate characteristics in summer. However, according to records, water area in built-up zone of Wuhan has been reduced by 130.5 km2 from 1965 to 2008, while the annual average air temperature has been increased by more than 3℃. To investigate the quantitative connection between the water area reduction and air temperature increase, three scenarios were simulated in a summer; to evaluate the impact of water reduction on the local thermal environment in different water areas; and to study the impact of water reduction on the urban heat island (UHI) phenomenon. Meso-scale meteorological models of Weather Research and Forecasting model were applied in this study for quantitative assessment and prediction. With the predictions, this study reveals that the decreased water area could affect air temperature, wind velocity and wind flow direction, energy balance and the UHI intensity. The simulations show that areas with significant wind velocity, wind direction and air temperature differences are distributed among the downwind zones. Moreover, the areas with high UHI intensity are wider and farther from the boundary of urban areas because of the reduction of water areas.
    Indoor and Built Environment 08/2014; DOI:10.1177/1420326X14546774 · 1.72 Impact Factor
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    ABSTRACT: Energy simulations are often used to evaluate the indoor thermal environment and energy consumption of buildings. In such simulations, it is common to use regional weather data that are typically based on current or past weather conditions. However, most buildings have a lifespan of several decades, during which climate can change gradually. Therefore, the design of energy conservation systems and energy simulations should incorporate climate change predictions to ensure that buildings are adaptable to future climatic conditions. The present study aims to construct future (i.e., 2030s) standard weather data for use in architectural design using numerical meteorological models. For this purpose, we adopted a dynamical downscaling method, used global climate model (GCM) data as the initial and boundary conditions for input into a regional climate model (RCM), and physically downscaled the data using the RCM. We constructed a prototype of the future (i.e., 2031–2035) standard weather data based on version 4 of the Model for Interdisciplinary Research on Climate (MIROC) and the Weather Research and Forecasting (WRF) model. The results confirm that the weather data generated via the dynamical downscaling method can predict local climate. Subsequently, we simulated building thermal load consumption using regional climate data. By comparing the results for the present (2007) and future (2034), we estimated the impact of climate change on the energy performance of a detached house. In particular, the sensible heat load for the house was predicted to increase by 15% under the conditions considered.
    08/2014; 14:404-413. DOI:10.1016/j.scs.2014.08.007
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    Hideki Kikumoto · Ryozo Ooka
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    ABSTRACT: The filtering operation in the large-eddy simulation (LES) makes it difficult to predict high-concentration events. In this study, LES with models of concentration variance at the subgrid-scale (SGS) was carried out for a dispersing plume from a point source within an urban canyon. To predict high-concentration events considering the SGS variance, the distributions of concentration at the SGS were expressed through probability functions. The SGS variance affected 99-percentile value of concentration by about 30% at a location near the source. However, dispersion at small scale proceeded rapidly, and the SGS effect reduced with the increasing distance from the source.
    CWE2014, Hamburg, Germany; 06/2014
  • Janghoo Seo · Ryozo Ooka · Jeong Tai Kim · Yujin Nam
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    ABSTRACT: The purpose of this study is to propose an optimal design method for the HVAC system in apartment using a genetic algorithm and to examine the possibility for the energy conservation of a designed HVAC system. The energy demand for cooling and heating in apartment house is determined by using TRNSYS. By a modified genetic algorithm called multi-island genetic algorithm, the optimal running pattern of HVAC systems is decided to minimize the energy consumption. An optimal design method for the HVAC system of the apartment house was proposed using both genetic algorithm and data of cooling/heating demand load simulated by TRNSYS. It has been confirmed that energy for equipment systems in apartment house can be saved by using operation plan of HVAC systems. The results show that this proposed method is significantly capable of determining optimal system design for saving energy in apartment house. We will perform the design of HVAC system considering an initial cost, a running cost and emission of CO2, and so on in the future.
    Energy and Buildings 06/2014; 76:102–108. DOI:10.1016/j.enbuild.2014.02.034 · 2.47 Impact Factor
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    Rongling Li · Ryozo Ooka · Masanori Shukuya
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    ABSTRACT: This study presents exergetic characteristics of both ground source heat pump systems (GSHPs) and air source heat pump systems (ASHPs) based on the concepts of “cool exergy” and “warm exergy”. Quantitative example followed by theoretical analysis shows that GSHPs consume less exergy than ASHPs do. This is because firstly “cool exergy” is obtained from the ground in GSHPs, whereas no “cool exergy” is extracted from the environment by the ASHPs. Secondly, temperature difference between refrigerant via cooling water and ground in GSHPs is smaller than that between refrigerant and air in ASHPs. In the GSHP, cool exergy flows into the cooling water from the ground and then enters the indoor air through the refrigerant cycle. In the ASHP, the refrigerant cycle separates the electricity input of the compressor into “cool exergy” and “warm exergy.” The “cool exergy” enters the indoor air and the “warm exergy” is exhausted to the ambient environment. The analysis also shows that compressor requires largest exergy input among the total exergy inputs, and the exergy consumption in the refrigerant cycle is the highest. Thus, the improvement of the compressor performance to reduce its electricity consumption was confirmed to be of vital in minimizing unnecessary exergy consumption.
    Energy and Buildings 06/2014; 75:447–455. DOI:10.1016/j.enbuild.2014.02.019 · 2.47 Impact Factor
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    ABSTRACT: Abstract The current Indian indoor comfort standards do not reflect the country’s great cultural and climatic diversity. There have been very few reports on the actual environments in Indian offices in the last three decades. We conducted a thermal comfort field study in 28 naturally ventilated (NV) and air-conditioned (AC) offices in Chennai and Hyderabad for fourteen months, and collected 6048 responses from 2787 individuals. Warm humid and composite climates are experienced in these cities, and these two climates cover about 80% area of the country. This paper proposes an adaptive thermal comfort model for South India based on this data. Mean comfort temperature was found to be 28.0 °C in NV mode, and 26.4 °C in AC mode on all data. Chennai had slightly higher comfort temperature. We found an adaptive relationship between the prevailing outdoor temperature and the comfortable indoor temperatures. Most of the environments in NV mode and about half in AC mode were warmer than the current Indian Standard upper limit (26 °C). In most cases, the air speed was below 0.20 m/s. Most of the subjects used fans. Air speeds of 1 m/s increased the comfort temperature by 2.7 K in both the modes. Logistic regression predicted 87% and 50% fan usage at 29 °C in NV and AC modes respectively. Several factors prevented further thermal adaptation. We can potentially improve comfort and reduce air-conditioning by providing higher air speeds with energy-efficient fans. Such strategies may be vital given the scale of the scarcity of power.
    Building and Environment 01/2014; DOI:10.1016/j.buildenv.2014.01.002 · 3.34 Impact Factor
  • Toru Yamanaka · Ryozo Ooka
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    ABSTRACT: Moisture transportation by local circulation is examined during calm summer days at Kanto plain using meso-scale numerical model, in order to clarify an urban effect on the distribution of water vapor in the urban boundary layer. The numerical results show that the vertical velocity at sea breeze head is enhanced when sea breeze and thermal convection are combined in urban area near Tokyo. Because the combined updraft strongly lifts surrounding surface humid air, precipitable water vapor is increased around the urban area. CAPE indicates a little bit of decrease in atmospheric stability in the urban area on calm summer days.
    Journal of Environmental Engineering (Transactions of AIJ) 01/2014; 79(698):339-348. DOI:10.3130/aije.79.339
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    ABSTRACT: Climate change phenomena such as global warming and urban heat island effects cause serious problems for the development of building technology. Therefore, it is imperative that architects and designers consider the effects of climate change on long-term building performance. At present, energy simulations are often used to evaluate the indoor thermal environment and energy consumption of buildings. In these simulations, it is common to use regional weather data that are usually based on current or past weather conditions. However, most buildings have a lifespan of several decades, during which climate can gradually change. Therefore, the design of energy conservation systems such as ventilative cooling strategies and energy simulations should incorporate climate change predictions in order to ensure that buildings are adaptable to future climatic conditions. As a result, future weather scenarios are very important for simulating building performance. The purpose of this study is to construct future standard weather data using numerical meteorological models, for use in architectural designs. At present, the climatic data used for this purpose are obtained from a Global Climate Model (GCM). Although a GCM can predict long-term global warming, its coarse grid resolution (~100 km) cannot describe the details of local phenomena. Therefore, we employ a downscaling method. We input GCM data into a Regional Climate Model (RCM) as initial and boundary conditions, and physically downscale the data using the RCM. RCM uses nested regional climate modeling and can analyze the local climate at fine grid resolutions (~1 km). The climatic scenarios obtained via this method are expected to accurately predict local phenomena such as the urban heat island effect. The results confirm that the weather data generated via the dynamical downscaling method can predict local climate. We subsequently constructed a prototype of the future standard weather data based on the Model for Interdisciplinary Research On Climate (MIROC) and the Weather Research and Forecasting (WRF) Model, and simulated building energy consumption using regional climate data. By comparing present and future energy simulations, we estimated the impact of climate change on the energy performance of a building. KEYWORDS Climate change / Future Standard Weather Data / Building Energy Simulation / Dynamical Downscaling
    AIVC Conference 2013, Athens, Greece; 09/2013
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    Madhavi Indraganti · Ryozo Ooka · Hom B. Rijal
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    ABSTRACT: India's building energy consumption is increasing rapidly. The subcontinent does not have custom made thermal comfort standards. There is little research in this field in the last 26 years. This leaves a lot to be investigated.We conducted a thermal comfort field study in 25 office buildings in Chennai and Hyderabad for seven months during the summer and south west monsoon seasons in 2012 and collected 2612 datasets from 1658 subjects. The comfort temperature in naturally ventilated (AC off) (NV) mode was 27.6 °C and 28.1 °C in Chennai and Hyderabad respectively. In air conditioned (AC) mode, it was 27.0 °C and 26.1 °C in these two cities. These departed from the limits in the Indian National Building Code. Chennai recorded significantly higher indoor air speeds and thus higher comfort temperature. In 71% cases the air speed was less than 0.15 m/s, underscoring the need for improvement. A majority always sensed the air movement low and desired increased air speeds, despite voting comfortable.Both the States grappled with daily outages throughout the survey period. All the buildings, excepting two were forced to run without the AC at least for 2 h daily, while none were prepared well for this. Several design and non-design factors seriously impeded environmental adaptation in buildings, limiting the adaptive operation of windows and fans. Consequentially, thermal acceptability was generally low (62.5%). This calls for architect's serious attention towards environmental and thermal adaptation in buildings, in the era of power paucity and prudent consumption.
    Building and Environment 07/2013; 65:195–214. DOI:10.1016/j.buildenv.2013.04.007 · 3.34 Impact Factor
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    Madhavi Indraganti · Ryozo Ooka · Hom B. Rijal
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    ABSTRACT: Post Fukushima disaster, the energy consumption perspective in Japan has changed. It initiated unprecedented exercises towards energy saving and produced interesting results. These included the ‘setsuden (energy saving)’ campaigns, which promoted the minimum indoor temperature setting of 28 °C in summer. However, there is no scientific basis for this recommendation. Japan does not have adaptive comfort standards and the ASHRAE standard-55 does not include the data from the land of the rising sun. In this context, we conducted a thermal comfort field study in four office buildings in Tokyo for three months in summer 2012. We measured all the four environmental and the two personal variables. Through a paper based field survey, we interviewed 435 occupants who returned 2402 questionnaires.The occupants' comfort temperature was found to be 27.2 °C. Thermal acceptability was very high at 89% even when 26% of the environments were outside the three central categories of the thermal sensation scale. PMV always significantly overestimated the sensation owing to a wide range of adaptations by the subjects. The indoor air speeds were low, indicating a need for ceiling fans. In 50% of the environments the indoor temperature was more than the 28 °C limit. As the buildings were designed for AC mode, running them in NV mode posed challenges. This study calls for elaborate field studies in offices in Japan for the development of custom made adaptive comfort standards.
    Building and Environment 03/2013; 61:114–132. DOI:10.1016/j.buildenv.2012.12.008 · 3.34 Impact Factor
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    Hideki Kikumoto · Ryozo Ooka · Satoru Iizuka
    Eighth Asia-Pacific Conference on Wind Engineering; 01/2013