Naoshi Kakitsuba * Meijo University, JAPAN

Transcription

1 1C.7 ANALYSES OF ENVIRONMENTAL FACTORS AFFECTING CHANGE IN MICROCLIMATE Naoshi Kakitsuba * Meijo University, JAPAN 1. INTRODUCTION Microclimate in Japan has been extensively studied by meteorologists (for example, Yoshino, 1955,1975) and engineers (for example, Hoyano et al. 1997, Mitsuya et al., 21). Considering these studies, Kakistuba et al. (23) carried out consecutive observation on microclimates in the housing estate called Nisshin Kaguyama Housing Estate located east of Nagoya city, JAPAN for eight years to estimate effect of development on microclimate. Dramatic change in microclimate was then reported while the housing estate had been under developement. One of the results indicated that a cool or a hot spot appeared periodically on the specific locations. Since this result was an unfathomable, the present study was designed to analyze an underlying mechanism of spot formation. Ambient temperature (Ta), relative humidity, wind velocity, wind direction, solar irradiation on multiple locations in the housing estate were observed. In addition, effect of the heat absorbed to the ground surface and the surroundings on change in local Ta was evaluated. 2. MEASUREMENTS 2.1 Relationship between local wind and Ta in the housing estate An entire area map of the housing estate called Nissin Kaguyama Housing estate was shown in Fig.1. There are three apartment complexes. Since cool and hot spots were often observed around the complexes, multiple locations were selected as indicated in Fig.2 (a), Fig.2 (b) and Fig.2 (c). White circles and black circles indicate the locations for continuous observation and locations for a 15-min observation using mobile equipment, respectively. Black circles were located on the concentric circle of which diameter was 1 m as a center of each white circle. Both batteries allowed for measuring Ta, relative humidity, wind velocity (V), wind direction, solar irradiation. Observation was carried out in summer and winter. Complex 2 Complex 1 Complex 3 Fig. 1. Area map of Nisshin Kaguyama Housing Estate Fig. 2 (a). Observation locations in the Complex Effect of ground surface temperature on Microclimate Fig. 3 indicates observation locations on the campus of Meijo University in Nagoya city. Using the mobile battery described earlier, climatic factors on two locations were simultaneously monitored in summer and winter. In addition, the ground surface temperature (Tss) was measured with an infrared * Corresponding author address: Naoshi Kakitsuba, Meijo Univ., Dept. of Environ. Science and Tech., Fac. of Science and Tech., Shiogamaguchi 1-51, Tenpaku-ku, Nagoya-City, Aichi Prefecture, JAPAN; naoshi@meijo-u.ac.jp Fig. 2(b). Observation locations in the Complex 2

2 Fig. 2(c). Observation locations in the Complex 3 thermometer (Thermo-Shot F3, NEC Avio Technology Co. Ltd) while Ta was measured. 2.3 Effect of the heat absorbed from solar irradiation to the surroundings on microclimate Kajita et al. (26) reported that cool air was defusing in summer from the edge of the large urban forestry park called Higashiyama Zoo and Botanical Gardens in Nagoya city as described in Fig. 4. In the present study, the same park was the subject to estimate effect of the heat absorbed from solar irradiation to the ground and the surroundings on microclimate development, particularly change in Ta. Three reference locations A, B and C were first selected for continuous observation and 4 locations at 5 m intervals for each reference location were then selected. Using the mobile battery, climatic factors at 12 different locations were monitored in summer. In addition, Tss and surface temperature (Ts) of the surroundings on each location were measured with the infrared thermometer. 3. RESULTS AND DISCUSSION 3.1 Relationship between local wind and Ta in the housing estate Considering that Ta generally changes with time and altitude, all the Ta values observed were corrected based on change in Ta at the continuous observation, i.e., the reference Ta value. A temperature difference ( Ta) was then calculated as a result of subtracting the reference Ta value from the corrected Ta value. A wind velocity difference ( V) was also calculated as a result of subtracting the reference V value from the V value observed with the mobile equipment. The results are indicated in Fig. 5 and Fig. 6. It was demonstrated that Ta were inversely correlated with V (r=.6) in summer whereas Ta were directly correlated with V (r=.86) in winter. Since seasonal change in wind direction was often observed at a few locations, it was confirmed that V and wind direction were the contributory factors, particularly on seasonal spot formation. Fig.3. Observation locations on the Meijo University Campus Reference location A Reference Higashiyama Zoo and Botanical Gardens location Reference location C Fig.4. Observation locations in the proximity of the large urban forestry park called Higashiyama Zoo and Botanical Gardens in Nagoya city 3.2 Effect of ground surface temperature on Microclimate Air temperature differences ( Ta) between location 1 (loan surface) and location 2 (concrete surface) are indicated in Fig. 7 and Fig. 8, together with change in solar irradiation. The Ta over the loan surface was 1 o C lower than that over the concrete

3 surface in summer. On the other hand, no difference was observed in winter. In association with change in solar irradiation, Tss of concrete surface was 2 o C higher than that of the loan surface in summer while its difference became half in winter. So, Tss higher than some threshold value may induce a significant Ta which may be related to spot formation in the specific period in a day. 3.3 Effect of the heat absorbed from solar irradiation to the surroundings on microclimate As an example, Ta between the Nagoya-city Obserbatory and the local observation is indicated in Fig.9. The results demonstrated that cool air diffused further from the edge of the Park in the morning as compared with afternoon and the evening. As an example, Tss and Ts of the surroundings on Location 1 is shown in Fig.1. Both Tss and Ts in the morning were lower than those in afternoon and the evening. Therefore, effect of the heat absorbed to the ground and the surroundings, i.e., cumulated heat from solar irradiation, on change in Ta becomes greater in afternoon and the evening in summer which may be related to spot formation in the specific period in a day as well. Tmeperature difference ( o C) Appartment complex 1 Appartment complex 2 Appartment complex 3 y=-.33x+.5 r= Wind velocity difference (m/s) Fig.5 Relationship between Ta and V in summer Tmeperature difference ( o C) Appartment complex 1 Appartment complex 2 Appartment complex 3 y =.58x r = Wind velocity difference (m/s) Fig.6 Relationship between Ta and V in winter Ambient temperature ( o C) loan surface concrete surface irradiation :47 12:55 13:3 13:11 13:19 13:27 13:35 13:43 13:51 Fig.7 Changes in Ta over the loan surface and the concrete surface and change in solar irradiation in summer Ambine ttemperature ( o C) loan surface concrete surface Irradiation 12 12:5 13:6 13:22 13:38 13: Fig.8 Changes in Ta over the loan surface and the concrete surface and change in solar irradiation in winter Temperature differences between Nagoya Meteorological Observatory and the locations ( o C) Reference location 11:~12: 13:~14: 15:~16: Location 1 Location 2 Location 3 Location 4 Fig.9 An example of distribution of Ta between Nagoya Meteorological Observatory and locations 1 to 4 observed in summer 4. CONCLUSION The underlying mechanism of periodical observation on cool and hot spots were investigated. As a result, the state of wind flow through the houses was found to be the influential factor on change in microclimate, particularly seasonal spot Irradiation (W/m 2 ) Irradiation (W/m 2 )

4 formation. Cumulated heat from solar irradiation, which is dependent on its magnitude and duration, to the ground and the planimetric features surrounding a location is also found to be the influential factor on change in microclimate, particularly spot formation in the specific period in a day. According to the results from the present study, wind temperature, which may be defined as air temperature while wind is blowing, appears to be strongly related to wind velocity and surface temperature of the ground and the surroundings. These surface temperatures are then dependent on the magnitude of solar irradiation. This relation of cause and effect may be the main reason of cool or hot spot formation. On this basis, hot spot formation was described in Fig. 11. Average surface temperature at five different directions ( o C) the ground West side North side East side South side 2 11: 13: 15: Fig.1 An example of change in Tss and Ts of 5 different directions of the surrounding on Location 1 REFERENCES Kajita et al., 26: Observation on Cool island phenomena in urban district and forestry hills in Nagoya city. Proc. of Tokai Branch of Architectural Inst. of Japan, (Written in Japanese) Kakitsuba, N., Ishibashi, R., Ishibashi, S., 23: A field survay of microclimate in the housing estate under developent Results from 1994 to 1998 survays. Japanese. J. of Biometeorology, 4(2): (Abstract in English) Kakitsuba, N., Ishibashi, R., Ishibashi, S., 25: An Investigation on environmental factors affecting microclimate in the housing estate. Japanese J. of Biometeorology, 4(2): (Abstract in English) Hoyano et al., 1997: Consideration on relationship between space formation, materials and dry heat flux from the surrounding surfaces in the apartment housings. J. of Architectural Inst. of Japan, 52: (Abstract in English) Mitsuya et al., 21: Analyses on urban climate in various residential densities In the case of Maebashi city. Proc. of Architectural Inst. of Japan, (Written in Japanese) Yoshino, M., 1955: Wind distribution in the Tokyo Metropolitan area. Weather, 2(8): (Abstract in English) Yoshino, M (1975) Climate in a small area, University of Tokyo press, Tokyo, 549 Yoshino, M (28) Wind over the world and Japan, Seizan-do (Written in Japanese) No (e.g. morning or cloudy) Surface temperature of the surroundings is not so high relative to Ta No Ground surface (concrete, loan etc.) and duration of exposure to irradiation Yes Local Ta is slightly higher than the reference Ta* (possibly hot spot) Has the heat by irradiation been absorbed to the surface for long? Does wind flow in and out smoothly? Yes (e.g. afternoon) Surface temperature of the surroundings is very high relative to Ta Density and height of houses surrounding a location Influential factors Local Ta is almost equal to the reference Ta* (not hot spot) * The reference Ta is defined as Ta on an open field with no irradiation Influential factors Does wind flow in and out smoothly? Yes Local Ta is slightly higher than the reference Ta* (possibly hot spot) Ta is markedly higher than the reference Ta* (definitely hot spot) Fig. 11 Flowchart of hot spot formation No

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