Ryozo Ooka

The University of Tokyo, Edo, Tōkyō, Japan

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Publications (146)110.24 Total impact

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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
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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. DOI:10.1016/j.scs.2014.08.007
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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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    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 · 2.70 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: 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 · 2.70 Impact Factor
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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 · 2.70 Impact Factor
  • Eighth Asia-Pacific Conference on Wind Engineering; 01/2013
  • Eighth Asia-Pacific Conference on Wind Engineering; 01/2013
  • Journal of Environmental Engineering (Transactions of AIJ) 01/2013; 78(689):579-588. DOI:10.3130/aije.78.579
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    Isaac Lun, Ryozo Ooka, Akashi Mochida
  • Hideki Kikumoto, Ryozo Ooka
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    ABSTRACT: Large-eddy simulations (LESs) were performed on the reactive air pollutant dispersion in three types of urban street canyons that had various roof-height levels. Line sources that emit nitrogen monoxide (NO) were set on the bottom of the canyon space in each case. NO dispersed on the cavity eddy and reacted with ozone included in the free stream. The reactivity of air pollutants and the roof heights had a considerable influence on the concentrations of the pollutants inside street canyons. Deeper canyon spaces weakened the ventilation efficiency for pollutants generated inside the canyon. In contrast, variations in the roof height improved the ventilation efficiency. However, in terms of pollutants that came from outside the canyon, the concentration was the lowest for the case with the highest aspect ratio because of the effluent reactions that occurred during retention inside the canyon space. The correlation of the reactors’ concentrations was also inspected to reveal the influence of the turbulent nature of the atmosphere on the reaction rate. The correlation had a magnitude of more than 5% to 10% of the total reaction rate inside the street canyons, and it could reach 40% at the maximum in the case with an aspect ratio of 2.0.
    Journal of Wind Engineering and Industrial Aerodynamics 07/2012; s 104–106:516–522. DOI:10.1016/j.jweia.2012.03.001 · 1.70 Impact Factor
  • Hideki Kikumoto, Ryozo Ooka
    Journal of Environmental Engineering (Transactions of AIJ) 01/2012; 77(674):267-273. DOI:10.3130/aije.77.267
  • Toru Yamanaka, Ryozo Ooka
    Journal of Environmental Engineering (Transactions of AIJ) 01/2012; 77(674):303-312. DOI:10.3130/aije.77.303
  • Jongyeon Lim, Ryozo Ooka
    Journal of Environmental Engineering (Transactions of AIJ) 01/2012; 77(679):721-728. DOI:10.3130/aije.77.721
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    ABSTRACT: In general, water pumped from a well used in a groundwater heat pump (GWHP) system is discharged to the well or the other wells. However, long-term pumping and injection may cause clogging of the wells, which is a major problem encountered when injecting groundwater into a well. “Reverse circulation” has been proposed as a solution to this problem, but this only results in temporary improvement of the injection efficiency and is not a permanent solution. With the aim of reducing the environment load and conserving groundwater resources, a groundwater circulation heat pump system was developed that is well suited for long-term use. This article provides an overview of the system and the results of real-scale experiments carried out at two sites (Chiba and Nagoya, Japan). These experiments have been conducted to evaluate the heating and cooling performance of the system. The system used at the Chiba site is equipped with two submersible pumps and two wells because of the deep groundwater level (–11 m (36 ft) G.L.). However, in the system at the Nagoya site, where the groundwater level is –4 m (13 ft) G.L., a land pump and a single well (for both production and injection) are used. Results show that the coefficient of performance (COP) of the groundwater heat pump is higher than that of the air-source heat pump. Furthermore, an automatic reverse circulation system was introduced that prevents clogging of the return well. Also, the effectiveness of a packer is confirmed for preventing short circuiting of the temperature in the aquifer in the case of the single well system. Finally, it is concluded that a small pumping rate and large temperature difference are very effective for reducing pumping-energy consumption and improving the coefficient of performance.
    HVAC&R RESEARCH 08/2011; 17(4):556-565. DOI:10.1080/10789669.2011.594777 · 0.75 Impact Factor
  • Yujin Nam, Ryozo Ooka
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    ABSTRACT: It is necessary for optimum design of GSHP systems to estimate accurately thermal properties of the designed ground and predict the heat extraction rate from the ground. Generally, experimental analysis has been used for the feasibility of system introduction such as thermal response test, pumping test or cone penetrating test, but it causes to increase estimation cost before the introduction, equivalent to tens of thousands of dollars in Japan. On the other hand, the heat exchange rate and the effect of the system on underground environment can be predicted by using numerical simulation. In this research, in order to estimate the effect of the ground thermal properties on system performance, numerical simulation has been conducted through the sensitivity analysis with the developed simulation tool. Furthermore, the method to develop an energy potential for GSHP system has been suggested and its application for Tokyo 23 ward area has been conducted with GIS data.
    Energy and Buildings 02/2011; 43(2):677-685. DOI:10.1016/j.enbuild.2010.11.011 · 2.47 Impact Factor
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    ABSTRACT: We assessed the ability of the MM5/CMAQ model to predict ozone (O3) air quality over the Kanto area and to investigate the factors that affect simulation of O3. We find that the coupled MM5/CMAQ model is a useful tool for the analysis of urban environmental problems. The simulation results were compared with observational data and were found to accurately replicate most of the important observed characteristics. The initial and boundary conditions were found to have a significant effect on simulated O3 concentrations. The results show that on hot and dry days with high O3 concentration, the CMAQ model provides a poor simulation of O3 maxima when using initial and boundary conditions derived from the CMAQ default data. The simulation of peak O3 concentrations is improved with the JCAP initial and boundary conditions. On mild days, the default CMAQ initial and boundary conditions provide a more realistic simulation. Meteorological conditions also have a strong impact on the simulated distribution and accumulation of O3 concentrations in this area. Low O3 concentrations are simulated during mild weather conditions, and high concentrations are predicted during hot and dry weather. By investigating the effects of different meteorological conditions on each model process, we find that advection and diffusion differ the most between the two meteorological regimes. Thus, differences in the winds that govern the transport of O3 and its precursors are likely the most important meteorological drivers of ozone concentration over the central Kanto area.
    Journal of Environmental Sciences 02/2011; 23(2):236-46. DOI:10.1016/S1001-0742(10)60398-1 · 1.92 Impact Factor
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    ABSTRACT: Urban land surface schemes have been developed to model the distinct features of the urban surface and the associated energy exchange processes. These models have been developed for a range of purposes and make different assumptions related to the inclusion and representation of the relevant processes. Here, the first results of Phase 2 from an international comparison project to evaluate 32 urban land surface schemes are presented. This is the first large-scale systematic evaluation of these models. In four stages, participants were given increasingly detailed information about an urban site for which urban fluxes were directly observed. At each stage, each group returned their models' calculated surface energy balance fluxes. Wide variations are evident in the performance of the models for individual fluxes. No individual model performs best for all fluxes. Providing additional information about the surface generally results in better performance. However, there is clear evidence that poor choice of parameter values can cause a large drop in performance for models that otherwise perform well. As many models do not perform well across all fluxes, there is need for caution in their application, and users should be aware of the implications for applications and decision making. Copyright © 2010 Royal Meteorological Society
    International Journal of Climatology 01/2011; 31(2):244 - 272. DOI:10.1002/joc.2227 · 3.40 Impact Factor

Publication Stats

815 Citations
110.24 Total Impact Points

Institutions

  • 1997–2014
    • The University of Tokyo
      • • Department of Human and Social Systems
      • • Institute of Industrial Science
      Edo, Tōkyō, Japan
  • 2004
    • Keio University
      • Faculty of Science and Technology
      Edo, Tōkyō, Japan
  • 1999
    • Fukui University
      Hukui, Fukui, Japan