Tadahisa Katayama

Study of the effect of green areas on the thermal environment in an urban area

Abstract This paper gives details of investigation results of the relationship between meteorological elements and green distribution in an urban area. The meteorological elements were measured in large and small areas of Kumamoto City. In the large area, the measurements of air temperature were carried out by moving observation using five automobiles. In the small area, the measurements of dry-bulb temperature, wet-bulb temperature, globe temperature, wind direction and velocity were carried out on foot. The land-cover condition and surface temperature were estimated using remote-sensing data from an airplane. From the results of these investigations, it became clear that air temperature distribution in an urban area is closely related to the distribution of green covering and even a small green area of about 60 m × 40 m indicates the cooling effect.

Full-scale measurements and wind tunnel tests on cross-ventilation

Abstract This paper describes the full-scale measurements and the wind tunnel model tests on cross-ventilation induced by the natural wind and the similarity between them. The full-scale measurements were conducted in a group of apartment houses under the condition that the direction of the approaching wind to the objective site was almost constant. The air flow speed around the objective buildings and the indoor air flow speed caused by the cross-ventilation are measured in the full-scale measurements. The wind tunnel tests consist of two kinds of experiments. One is the experiments on the air flow around buildings and the wind pressure on building surfaces as the source power of the cross-ventilation. The other is the experiments on the distribution of indoor air flow. Each of these experiments needs each experiment model. Their results are compared with the full-scale measurements.

Field surveys on cooling effects of vegetation in an urban area

Abstract 1. 1. Three kinds of field survey on different scales were carried out in Fukuoka City in summer to examine the relationship between the quantity of vegetation and air temperature. 2. 2. The field of the largerst scale measurement is across the city. 3. 3. Several parks and shrines of various sizes in the city were selected as other measurement areas. 4. 4. The most detailed measurements are carried out in a park with an area of 1.25 ha located in a down town area of the city. 5. 5. Though the amount of vegetation is expressed in a unique way in each survey, it is clearly found that the greener it is, the lower is the air temperature.

Numerical simulation of air flow in an urban area with regularly aligned blocks

Numerical simulation of air flow distribution in a built-up area is an effective way to analyze and predict the urban thermal environment. A cyclic boundary conditions method for the numerical simulation of air flow around a block is used to model the unlimited spread of a built-up area. An equation for the calculation of the pressure difference between the windward and the leeward boundaries is proposed. Another simulation model which has 10 blocks aligned with the wind direction is used for comparison. The inflow boundary conditions are given by a wind tunnel test. The cyclic boundary conditions produced stable calculation results. The simulation results of the cyclic boundary conditions model are similar to those of the 10-block model in the cavity space. There is, however, a little difference between the results of these two models, and between them and the wind tunnel test in the higher area above the cavity and at the crossing point of the streets.

Wind tunnel tests of wind pressure on regularly aligned buildings

Abstract Model experiments are carried out in order to make the characteristics of wind pressure on groups of buildings clear. The wind pressure is thought to be a natural ventilation force and the model buildings are assumed to be apartment buildings. The approaching flow of the wind tunnel tests simulates the wind over a built-up area. The main parameter of the layout of buildings is the building volume ratio. A staggered grid layout is compared with a normal grid layout. The effect of the wind direction is also examined. The results of the experiments are presented as the wind pressure coefficient difference between windward and leeward. The relations between the average wind pressure coefficient in a model and various layouts of buildings are mainly discussed. The distributions of the wind pressure coefficient in model buildings are also presented in this paper.

Investigation and numerical simulation of the wind effects on thermal comfort in a house

Abstract Full-scale measurement of indoor thermal factors and numerical simulation of indoor air flow are presented in this paper. The measurement was carried out in summer in two dwelling units of an apartment building; one was ventilated naturally through opening windows and the other was unventilated. Indoor thermal conditions of these two houses were estimated by the predicted mean vote and compared to find that the thermal conditions in the ventilated house ranged in the comfort zone while it was in the hot zone in the unventilated house, which depended upon the indoor air flow speed. Numerical simulation of indoor and outdoor air flow of a single unit house was carried out to predict the air flow speed by natural ventilation through opening windows. Multi-mesh system and k-a 2-equation model were applied for the indoor and the outdoor turbulent air flow for which the scales were greatly different.

Cooling effects of a river and sea breeze on the thermal environment in a built-up area

Abstract Two kinds of field observation are carried out to examine the cooling effects of a river and a sea breeze on the thermal environment in a built-up area in summer. One is the measurements along a river and an avenue which go in the direction of the sea-land breeze. The other is the measurements along a street nearly perpendicular to the river. The wind speed above the river is larger than that above the street when the sea breeze blows, while the air temperature above the river is clearly lower than that above the avenue. The air temperature difference between them falls less downstream of the sea breeze. The air temperature in the space between buildings is the highest in the street and that at the cross point is the next; the wind direction is close to that of the sea breeze. Even if the paths are rather narrow, the ventilation effect by the sea breeze is clearly recognized.

A comparison of field surveys on the thermal environment in urban areas surroundings a large pond: when filled and when drained

Abstract This paper describes the thermal effect of a pond with an area of 127 000 m2 on the surrounding built-up area. Two surveys were conducted and compared, when water filled the pond and after the pond was drained. Moreover, two similar surveys were carried out in the extended area. In the water-filled case, the air temperature distribution demonstrated that a clear cool island was caused by the pond. In the afternoon, it was most prominent with a temperature differential of about three degrees between the center of the pond and the far outside streets, and it extended about a few hundred meters leewards. In the water-drained case, a cool island, caused by the wet bed including water pools left in the leeward half of the pond due to incomplete drainage, diminished with half the differential.

Observations of heat flux in an urban area with a large pond by kytoons

Abstract There are few studies on the thermal environment in urban areas, considering the convective heat flux by natural wind and covering materials on the ground surface. In this paper, the heat flux is calculated from the profiles of the wind speed and the air temperature, which are simultaneously observed by kytoons at three points in an urban area with a large pond, to examine the difference between the built-up area and the water surface, and to make clear the relation between the convective heat transfer and the wind speed.

An experimental study on the effect of humidity on thermal sensations of people in summer

Abstract 1. 1. The authors propose humidity reduction instead of lowering room temperature in order to reduce cooling syndrome. 2. 2. They conducted experiments with subjects in the rooms, one with controlling humidity to about 40% r.h. and another without humidity control. Air-conditioning system with humidity control has a greater promise in making a comfortable environment, even at the temperature as high as 30°C, in comparison with conventional means using temperature control alone. 3. 3. Relationship of actual mean votes on temperature sensation and comfort sensation with PMV and SET, respectively, suggests that Japanese people might be more sensitive to humidity than Westerners and so different methods from those used in the western countries should be required for human thermal environmental studies with respect to the hot humid summer in Japan.