Shigeki Nishizawa

Wind Pressure and Air Flow in a Full-Scale Building Model under Cross Ventilation

Abstract The observation of wind pressure acting on the wall and floor of a full-scale building model under cross ventilation was carried out. The measurement of air flow was also undertaken, and the existing prediction theory of the air flow rate, namely the orifice flow equation, including the discharge coefficient, was evaluated for its accuracy. At the same time, a method of predicting the discharge coefficient has been proposed and tested. In conclusion, a tentative relationship between the discharge coefficient and the difference of wind pressure coefficient across the opening has been developed. In addition, the background concerning the difficulty of using the orifice flow equation has been described.

A Wind Tunnel Full-Scale Building Model Comparison between Experimental and CFD Results Based on the Standard k-ε Turbulence Representation

Abstract To evaluate the property of cross ventilation quantitatively, it is important that the calculated air flow field is compared with measurement. In this paper, the air flow field in the wind tunnel of the Building Research Institute of Japan (BRI) was calculated by CFD analysis using the standard k-ε model, and the adequacy of the calculation was examined by comparison with measured values. Results showed that: • The calculated air flow field was generally in good agreement with the measured field;• The distribution of the wind pressure coefficient was similar between measurement and calculation;• The calculated value of wind pressure coefficient was lower than measurement;• The turbulent kinetic energy was not significantly overestimated;• The differential pressure between openings showed a good relation to measurement;• The calculated indoor air flow, inside a simple building model enclosed in the wind tunnel, was strongly influenced by external conditions.

Study of the Airflow Structure in Cross-Ventilated Rooms based on a Full-Scale Model Experiment

Abstract Cross ventilation to reduce cooling energy is one of the most important techniques for maintaining a comfortable indoor environment in hot and mild seasons. However, at present, it is difficult to design the indoor environment under cross ventilation because there is insufficient knowledge to evaluate the effect of cross ventilation quantitatively. To develop an understanding of the flow characteristics a full-scale model experiment was performed in a large wind tunnel to examine airflow properties in a cross-ventilated space. The purpose of this paper is to clarify the airflow structure in the cross-ventilated room in relation to wind direction. The key factors determining the airflow structure in the space were found to be: the main current region, rebounding and changing flow direction, deflected flow, surface flow and circulating flow. It was observed that the main air current tends to travel in a straight line until it collides with obstacles. On collision, the flow changes direction and deflected flows are formed over and/or under the main current. When there is enough space alongside the main current region, a circulating flow is formed in each room. The room mean velocity was found to be dependent on the path of the air current. When the main current is well defined, a relatively low value of mean velocity is observed. When the main current is divided, the room containing the inflow opening has a relatively high velocity.

Estimation of Cooling Energy Reduction by Utilizing Cross-Ventilation in Detached Houses, within the Japanese newly introduced Energy Regulation - Evaluating Energy Consumption for Different Uses

Abstract The reduction of carbon dioxide emission due to energy consumption in the household sector is an urgent task, worldwide. As a measure to respond to the task, a new regulation has just been enforced since April 2009, in Japan. This regulation evaluates the energy performance of detached houses by estimating the primary energy consumption for different uses, namely, heating, cooling, ventilation, domestic hot water and lighting. Especially in mild or hot climates, it has been frequently claimed by practitioners that the regulation, which is heavily focused on insulation performance, is not enough and broader aspects should be equally evaluated. The effectiveness of cross ventilation in reducing cooling energy is one of these aspects. However, there have been difficulties to overcome in predicting the effectiveness of cross ventilation on cooling energy reduction. Among such difficulties are the decrease of the discharge coefficient of openings with inclined airflow, variation of the wind pressure coefficient depending on surrounding conditions, etc., occupants’ window opening behaviour and actual energy efficiency of air conditioners depending on their output and outdoor conditions. By referring to the results from experiments and observations on cross ventilation and air conditioners, the authors have proposed a solution for the Japanese new energy regulation on how to predict cooling energy consumption, taking the above factors into consideration. Even though there are still problems to be solved, the solution by the authors, shown in this paper, can be a guidepost to a more reasonable evaluation of the energy performance for cooling in buildings, as well as to a more reasonable design practice for windows and openings on the partition walls.

Measurement of Natural Ventilation Rate in a Japanese Residential Building

Abstract It is difficult to design a naturally ventilated indoor environment because there is insufficient knowledge to evaluate the effect of the natural ventilation space quantitatively. Especially, natural ventilation rate is not yet fully understood. In this paper, the properties of natural ventilation with large openings are examined mainly from the results of measuring ventilation rate. This measurement analysis shows that the resistance of the interior doors is large and the ventilation rate is almost caused by air exchange through a single opening when the interior doors are closed (single-sided ventilation). By contrast a high ventilation rate is observed when the interior doors are opened (giving cross ventilation). This paper also identifies which factors influence the ventilation rate through the large openings.

Verification of the Effect of Cross-Ventilation on Energy Conservation by Simulating Occupant Behaviour

Abstract Recently, natural ventilation, which is a traditional cooling method in Japan, has become considered as the key method for cooling energy conservation. The results of experiments are presented to measure the indoor thermal environment and cooling power consumption in an experimental dwelling by simulating occupants’ life-style including thermal control with natural ventilation and air conditioning. Based on the experimental results the cooling power consumption from July to September has been estimated. The results show that natural ventilation is an effective technique for saving cooling energy consumption. They also suggest that temperature parameters (the upper limit of room temperature, without using an air conditioner, and the preset temperature of an air conditioner) are very important to estimate the cooling energy saving effect with or without using natural ventilation.

Mixing Property and the Heat Exhaust Effect under Cross Ventilation in a Full-Scale Experimental Model

Abstract Cross ventilation is one of the most important techniques for achieving energy conservation and for maintaining a comfortable indoor environment in hot summer periods. However it is difficult to evaluate the effect of cross ventilation quantitatively and to undertake design based on a quantitative evaluation. This is because the indoor environment is uneven and changes according to the outside conditions. It is difficult to predict the ventilation rate under cross ventilation due to the variation in wind. Hence it is still difficult to estimate indoor comfort conditions given by cross ventilation. In this paper full-scale model cross ventilation experiments are described and the properties of airflow in and around the full-scale model (velocity field, pressure distribution on surface, visualized flow pattern, heat transfer coefficient distribution, discharge coefficient of openings and so on) have been examined. The mixing property and heat exhaust effect of cross ventilation are discussed. Tracer gas concentration decay measurements were made in the model to determine the spatial unevenness of mixing property, the air change index and the velocity distribution. It is shown that the different mixing properties are formed according to the airflow pattern. The heat exhaust effect, was determined by using plasterboard that was set on the floor for heat storage. The temperature of the air and surface was measured, and exhaust heat by cross ventilation was calculated. The relation between temperature reduction and the flow path was examined, and the total exhaust heat by cross ventilation was compared to the total convective heat transfer from the plasterboard. These experiments showed that ventilation rate is the most important factor in determining the amount of exhaust heat and the room mean age of air. However the airflow path has an influence in the exhaust heat and mixing property in the cross ventilated space.