Takao Sawachi

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.

Wind Pressure Coefficients for Different Building Configurations with and without an Adjacent Building

Abstract The design protocol for wind-driven cross ventilation in buildings should include two processes, namely the determination of required ventilation rate to reduce the room temperature and the prediction of the ventilation rate resulting from the arrangement of openings and wind pressure on those. Computer fluid dynamic techniques (CFD) have the potential to be a useful tool in such calculations but another more practical way is the airflow network model combined with the wind pressure coefficient (Cp) values for buildings with different shapes and surrounding conditions. The authors have conducted a series of wind tunnel experiments using scale building models to obtain the wind pressure coefficient distribution on the building envelope and have developed a database to be used as input data for network simulation programs. In the estimation of Cp, one of the challenging problems is the effect of surrounding obstacles such as adjacent buildings. There are some works that take this effect into consideration, by making corrections to the wind pressure coefficients of an isolated building. Firstly, this paper applies such correction knowledge and secondly, tries to draw some general rules, which can be applied when estimating the wind pressure coefficients for a building which is surrounded by adjacent buildings.

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.

Study on the Numerical Predictive Accuracy of Wind Pressure Distribution and Air Flow Characteristics—Part 1 Optimization of Turbulence Models for Practical Use; Part 2 Prediction Accuracy of Wind Pressure Distribution of Various Shaped Buildings

Abstract To evaluate wind pressure distribution on a building by using CFD (computational fluid dynamics), it has been general practice to use k-ϵ models. However, it is known that the use of the standard k-ϵ model has disadvantages such as overestimation of wind pressure coefficient and turbulent kinetic energy on the windward surface where wind impinges on the building. To overcome these problems, various modifications of the k-ϵ model have been proposed. In the present study, a number of modified k-ϵ models and a k-ω model were applied for the estimation of wind pressure distribution on a parallelepiped shaped building. The characteristics of each of these turbulence models were confirmed using a wind tunnel model. The results suggest that a modified k-ϵ model incorporating Durbins limiter (model parameter α=0.5) showed satisfactory results for the estimation of wind pressure distribution. In the overall evaluation, the modified k-ϵ models (incorporating Durbins limiter (α=0.65), RNG model (renormalization group theory) and Quadratic model provided good results. Part one of the study was performed on an object of extremely simple shape, and questions may arise if this is applied on an actual building. In this respect, Part 2 of the paper covers a similar evaluation on a complicated shaped object. For this case, it was found that a RNG model provides high reproduction accuracy just as in the case of the object with simple shape. Also, a problem with the model incorporating Durbins limiter (α=0.65) was found when considering the object with a complicated shape. Consequently, a modified model incorporating Durbins limiter with a higher value for a shows better results when compared to the RNG model.

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.

PROGRESS OF WOOD DECAY AND VERIFICATION OF PREDICTION MODEL UNDER ISOTHERMAL CONDITIONS

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ANALYSIS ON ENERGY CONSUMPTION FOR COMMON USE SPACE OF APARTMENT HOUSES CONSIDERING THEIR ATTRIBUTES

This study aims to found the basic data for promoting energy conservation policies by assessing the energy consumption in common space of apartment block. We investigated the actual electricity consumption in common use space of apartment houses. The data of electricity usage in common use space was collected from 1,345 apartment blocks (623,022 houses). We classified the apartment blocks by 1) year when administration had started, 2) number of floors, 3) number of houses, 4) water supply method and 5) number of elevators, in order to analyze the influences of those attributes on the electricity consumption. As a result, it became clear that the specific energy consumption of the apartment block differs significantly in the range from 42 kWh/year/house to 2,272 kWh/year/house, depending upon the abovementioned attributes.

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.