Ryozo Ooka

The University of Tokyo, Edo, Tōkyō, Japan

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Publications (116)61.56 Total impact

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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.
    Sustainable Cities and Society. 08/2014;
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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; · 2.43 Impact Factor
  • Energy and Buildings 01/2014; 76:102–108. · 2.68 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 01/2014; 75:447–455. · 2.68 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. · 2.43 Impact Factor
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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. · 1.34 Impact Factor
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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. · 0.59 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. · 3.40 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; 31:244-272. · 3.40 Impact Factor
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    ABSTRACT: We investigated the influence of meteorological factors that affect ozone in summer using both measurement analysis and numerical simulation. The results show that there is a close relationship between changes in meteorological conditions and variations in ozone concentrations over the central Kanto area. In summer, up to 84% of long-term variations in peak ozone concentrations may be accounted for by changes in the seasonally averaged daily maximum temperatures and seasonally averaged wind speeds. The ozone episodes in the Kanto region are dominated by three major patterns, of which Patterns I and II are regular summertime pressure patterns with a 26% and 16% frequency of occurrence, respectively. A detailed process analysis of ozone formation under urban heat island (UHI) at two areas in the Kanto region – urban and rural area – indicates that ozone formation is mainly controlled by chemistry, dry deposition, vertical transport, and horizontal transport processes. The groundlevel ozone concentrations are enhanced mainly by the vertical mixing of ozone-rich air from aloft, whereas dry deposition process mainly depletes ozone. Horizontal transport and chemistry processes play opposite roles in the net change of ozone concentration between the two areas. The results of numerical simulations also indicate that the sea breeze has significant effects on the ozone accumulation and distribution in the Kanto area. The high ozone was first observed in urban area and then was transported to the rural area by sea breeze. At rural area, the highest ozone concentrations were found in late afternoon, about two hours later in comparison with the urban area.
    Energy Policy - ENERG POLICY. 01/2011; 4:138-150.
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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 01/2011; 23(2):236-46. · 1.77 Impact Factor
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    ABSTRACT: The summer climate around the Tokyo metropolitan area has been analysed on an urban scale, and the regional characteristics of the thermal energy balance of a bayside business district in the centre of Tokyo (Otemachi) have been compared with an inland residential district (Nerima), using a mesoscale meteorological model incorporating an urban canopy model. From the results of the analysis, the mechanism of diurnal change in air temperature and absolute humidity in these areas is quantitatively demonstrated, with a focus on the thermal energy balance. Moreover, effective countermeasures against urban heat-islands are considered from the viewpoint of each region’s thermal energy balance characteristics. In addition to thermal energy outflux by turbulent diffusion, advection by sea-breezes from Tokyo Bay discharges sensible heat in Otemachi. This mitigates temperature increases during the day. On the other hand, because all sea-breezes must first cross the centre of Tokyo, it has less of a cooling effect in Nerima. As a result, the air temperature during the day in Nerima is higher than that in Otemachi. KeywordsHeat-island phenomenon-Meteorological mesoscale model-Thermal energy balance analysis-Urban canopy model
    Boundary-Layer Meteorology 01/2011; 138(1):77-97. · 2.29 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.
    Lancet. 01/2011; 43(2):677-685.
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    ABSTRACT: The present study explains the application of a numerical simulation to investigate the thermal environment of a new riverside residential development in summer. The case study area consists of more than one hundred two-story detached houses built next to a river near Tokyo, Japan. According to the meteorological data, prevailing wind directions are at an angle to the northbound river flow affecting the microclimate of the study area in terms of surface temperature of land and buildings, air temperature and wind distribution at pedestrian height. These factors have been estimated using the stepwise CFD (computational fluid dynamics) simulation of radiation, conduction and convection. This method leads to an improvement of outdoor thermal environment by manipulating the site design and layout planning scenarios. The effect of river, permeable pavements and green space on thermal environment is examined by the site design options. Likewise, the impact of building arrangement is evaluated using alternative layout planning scenarios. In total, five scenarios have been simulated for the proposed sustainable development as explained in the paper. Above simulations provided an insight into the mitigation effects of each countermeasure. It is also shown that the management of inflow paths and the creation of wind paths for the interior of the site have the potentials to improve the outdoor thermal environment of riverside residential development. Keywordsprevailing wind-thermal environment-layout planning-site design-riverside development-CFD
    Building Simulation 01/2010; 3(1):51-61. · 0.65 Impact Factor
  • Yujin Nam, Ryozo Ooka, Yoshiro Shiba
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    ABSTRACT: To achieve high heat pump efficiency, groundwater heat pump (GWHP) system uses groundwater, which is relatively stable AT temperature compared with outdoor air, as a heat source. However, it is difficult to meet annual heating and cooling loads using only groundwater as a heat source. In order to optimize the operation method of GWHP systems, it is necessary to develop a system utilizing both groundwater and air sources according to the building load conditions. Furthermore, during intermediate seasons (such as spring and autumn) with reduced heating and cooling loads, GWHP system is less efficient than air source heat pump (ASHP) system according to temperature conditions. In order to more efficiently use GWHP systems, it is necessary to develop a system which utilizes both groundwater and air sources according to temperature conditions and building loads. This research has developed a GWHP system that employs a hybrid heat pump system with groundwater wells using dual groundwater and air heat sources. In this paper, the annual performance of the developed system has been calculated, and several case studies have been conducted on the effect of introduction location, refrigerant and pumping rate. Furthermore, the coefficient of system performance and the effects on underground environments have been evaluated by real-scale experiment using two wells.
    Energy and Buildings - ENERG BLDG. 01/2010; 42(6):909-916.
  • Genku KAYO, Ryozo OOKA
    Journal of Environmental Engineering (Transactions of AIJ) 01/2010; 75(649):297-303.
  • Suckho Hwang, Ryozo Ooka, Yujin Nam
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    ABSTRACT: Technology directed at geothermal energy, one of our renewable energy sources, to heat and air-condition buildings has become very attractive in recent years following the significant developments in ground-source heat pump (GSHP) systems. In general, although the energy efficiency of GSHP systems is far superior to conventional air-source heat pump (ASHP) systems, GSHP system is still expensive. Therefore, GSHP system employs the foundation pile of buildings as heat exchanger is introduced in order to reduce the initial cost. When designing a GSHP system (especially in case of the energy pile system), it is necessary to accurately predict the heat extraction and injection rates of the heat exchanger. The thermal and hydraulic properties of the ground are very important to accurately predict heat transfer between the ground heat exchanger and the ground. In particular, those are the most important design parameters because energy pile system is installed only a few tens of meters deep. In this paper, an estimation method is suggested in order to determine the thermal and hydraulic properties of the ground for design the heat exchanger of energy pile system base on geotechnical investigation for the design the building's foundations. The use of results from generally applied geotechnical site investigation methods to estimate ground thermal and hydraulic properties was evaluated.
    Renewable Energy. 01/2010;
  • Journal of Environmental Engineering (Transactions of AIJ) 01/2010; 75(648):205-211.
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    ABSTRACT: Recently, due to global warming and the heat-island effect, more and more people are exposed to the dangers of heat disorders. A hot thermal environment can be evaluated using various indices, such as new Standard Effective Temperature (SET∗) using the 2-Node Model (2 NM), Wet Bulb Globe Temperature (WBGT), Predicted Heat Strain (PHS) model, and so on. The authors aim to develop a safety evaluation approach for hot environments. Subject experiments are performed in a laboratory to comprehend the physiological response of the human body. The results are compared with the computed values from the 2 NM and PHS models, and improved the sweating model in 2 NM in order to take into account the relationship with metabolic rate. A demonstration is provided of using the new sweating model for evaluating thermal safety in a hot environment.
    Building and Environment. 01/2010;

Publication Stats

372 Citations
61.56 Total Impact Points

Institutions

  • 1997–2014
    • The University of Tokyo
      • • Department of Human and Social Systems
      • • Institute of Industrial Science
      Edo, Tōkyō, Japan
  • 2010
    • Yonsei University
      Sŏul, Seoul, South Korea
  • 2009
    • Nomura Research Institute, Ltd.
      Edo, Tōkyō, Japan
  • 2008–2009
    • Huazhong University of Science and Technology
      • School of Architecture and Urban Planning
      Wu-han-shih, Hubei, China
  • 2003
    • National Institute for Environmental Studies
      Tsukuba, Ibaraki, Japan