Hisashi Kotani

Natural ventilation of light well in high-rise apartment building

Abstract Light wells in the centers of high-rise apartment buildings in Japan are called ‘Voids’. Gas water-heaters built into Voids discharge exhaust gas so a large enough opening has to be designed at the bottom of a Void to keep the indoor air quality (IAQ) acceptable. In order to secure the IAQ in the Void from contamination, a simple calculation method of the ventilation rate induced by wind force and thermal buoyancy through openings at the bottom, along with heat sources such as water-heaters, is presented. The accuracy of this calculation method was examined by wind tunnel testing. As a result, it turned out that the simple calculation methods introduced in this study were valid for predicting the vertical temperature distribution and ventilation rates in Voids.

Stream Tube based Analysis of Problems in Prediction of Cross-Ventilation Rate

Abstract The airflow rate of a building ventilated by wind is usually predicted by using the wind pressure coefficients obtained for a sealed building and discharge coefficients based on measuring the airflow characteristics through an opening in a sealed chamber (chamber method). This can result in the underestimation of wind driven flow through large openings located on opposite sides of a room. In this paper, the discharge coefficient, based on the chamber method, and the actual condition of cross-ventilation are calculated and compared with each other by means of stream tube analysis. The driving pressure based on wind pressure coefficients obtained from a sealed building are also compared with those based on pressures inside the stream tube of the actual flow field representing a porous rather than sealed building. A building model of dimensions 120 mm (width)×120 mm (height)×180 mm (length) was used for the analyses. The size of openings, expressed as the porosity (opening area divided by façade area), was 11.6 %, 20.7 % and 46.5 %. These models were analyzed by CFD simulation and the stream tubes caught by the opening were determined. From the analysis the errors in discharge coefficient and wind pressure coefficient were identified. Finally, the flow rate based on these discharge coefficients and driving pressures were calculated and compared. It is shown that the effect of the underestimation of the discharge coefficients by the chamber method is significant for all cases of porosity studied in this paper. Moreover, it is shown that the use of wind pressure coefficients is not appropriate for the case of extremely large openings.

Natural, Wind-Forced Ventilation caused by Turbulence in a Room with a Single Opening

Abstract Even if there is only one opening within a room and there is no temperature difference between the inside and outside, the room will be ventilated by the external natural wind. Two kinds of theoretical approach have been tried before to evaluate the mechanisms driving this flow: one is pulsation theory and the other is mixing layer theory. In this paper, these theories are reviewed and the validity of each is examined by means of a wind tunnel test. Results showed that the pulsation theory was not applicable to all wind directions. An experimental equation was derived from wind tunnel tests on a small building model incorporating a single circular opening. In addition, other approaches using CFD and PIV to determine the airflow inside the single opening precisely were tried and the dominant frequency of the velocity fluctuation was examined.

Wind Driven Flow Through Openings - Analysis of the Stream Tube

Abstract Wind approaching a building provided with openings on the windward and leeward sides has a choice, either it flows through the openings or flows around and above the building. This choice gives rise to a dominant stream tube containing the fluid flowing through the openings. In this paper the stream tube is analysed based on wind tunnel measurements and CFD simulation. A house model with dimensions 120 mm (Width)×120 mm (Height)×180 mm (Length) was provided with rectangular openings of equal size located opposite each other. The end walls were thin giving rise to a sharp edged opening. The size of the openings expressed as the porosity (opening area divided by the façade area) was 1.3 %, 5.2 %, 11.6 %, 20.7 % and 46.5 %. In the wind tunnel, velocity including velocity fluctuations and pressure were measured along the centre line through the openings. In the CFD prediction it was possible to visualize the stream tube by the method of “flying particles”. This made it possible to explore the change in shape of the stream tube and to calculate the cross-sections of the stream tube at different positions and to know the total pressure distribution within the stream tube cross section. Finally, the discharge coefficient based on stream tube analysis was compared to that from a conventional chamber method.

Environmental assessment of light well in high-rise apartment building

Abstract A growing number of high-rise apartment buildings each with a light well in the center of them are designed in accordance with the structural design and planning for the last 10 years in Japan. This light well is defined as an intermediate space between outdoor and indoor. The questionnaire surveys to four apartment buildings that have different sizes of the light well were conducted to make clear the occupants’ evaluation about the actual environmental conditions. As a result, the environment of light well is almost clearly satisfied except for some matters.

Flow Visualization and Inflow Direction Measurement at a Cross-Ventilated Large Opening

Abstract In the case of cross ventilation through a large opening, it is well known that the inflow direction at the opening is not normal to the opening. A simplified prediction method for simultaneously predicting the inflow direction at the inlet opening and the airflow rate is presented. It is also well known that the use of general discharge coefficient values (CD) is not suitable for the calculation of cross ventilation rate. The first reason is that the simple connection of the pressure loss coefficient of an opening (ζ as the reciprocal of square CD) in series, under-estimates the airflow rate. Secondly, CD varies according to the wind direction and the use of normal values over-estimates the airflow rate. Therefore, the proposed method uses the total pressure loss coefficient of the room (ξ) instead of ζ (or CD). Flow visualization was conducted under various conditions using a simple room model and showed the basic flow characteristics at the inlet opening. Wind tunnel tests using a three-storey apartment building model with a movable test room were conducted to investigate the inflow direction and the airflow rate. The combination of room positions and external wind directions results in various inflow directions at the inlet opening.

Review of Cross-Ventilation Research Papers - from the Working Group for Natural Ventilation and Cross-Ventilation of the Architectural Institute of Japan

Abstract A working group for natural ventilation and cross-ventilation at the Architectural Institute of Japan (AIJ) was established in 2005 by researchers and designers with an interest in this topic. One of the tasks of the working group is to review and classify related research papers. This paper introduces the activities of the working group and presents some results of the review work. As examples of the review work, this paper concentrates on the area cross-ventilation rate and the interference coefficient concept of the cross-ventilation phenomenon that solves the problem of the remaining dynamic pressure inside a room.

Design, Development of a Solar Chimney with Built-in Latent Heat Storage Material for Natural Ventilation

A prototype of a solar chimney with a built-in latent heat storage system for prolonging ventilation system operation until evening/night or even 24 hours was designed and developed. Sodium Sulfate Decahydrate “Na2SO4.10H2O” (melting point 32°C, latent heat of fusion 126 kJ/kg) was used as a Phase Change Material (PCM) for latent heat storage. Experiments have been carried out with the air gap of 0.20 m and 45 degree inclination angle of solar chimney. Results showed that integration of PCM storage inside the solar chimney is positive and supplies a constant airflow rate of 155 m3/h in evening and night periods. Description of the fabricated prototype solar chimney with PCM storage, thermal analysis to predict the air flow rate, and temperatures of the component of the system with experimental results are presented.

Effects of ceiling induction diffusers on indoor environmental quality of sickroom under the cooling air supply condition

ABSTRACT A series of experiments were carried out in a full-scaled model room to verify the characteristics of the air-conditioning system with ceiling induction diffusers. By the step-up tracer gas method and decay method, 10 cases with three varying parameters (the positions of exhausts, the heights of the exhaust ports and the states of the curtains around the beds) were designed to examine the influence on the indoor environment. It can be found that the exhaust ports had obvious influence on the normalised concentration distributions. The curtains made the indoor temperature higher than that of in without curtains and prevent the contaminant escaping out when in patients breathed. In terms of the local mean age of air, the ventilation efficiency presented an optimum result on a specific position of the exhaust port. However, there was minor influence on the air age caused by the height of the exhaust ports.

C&C efficiency of canopy hood exposed to horizontal air stream in commercial kitchen calculated by CFD analysis

ABSTRACT As one of the commercial kitchen ventilation researches, the mechanism of capture phenomenon and containment one of a canopy hood has to be investigated. Several experiments intended to change the Capture and Containment (C&C) efficiency of combustion gas and cooking effluence were conducted under the conditions of different suction wind velocity at the bottom of a hood, sometimes called face velocity, which is caused by the different hood size. The overall C&C efficiency was analyzed by means of computational fluid dynamics (CFD). The C&C efficiency from the experiment and CFD analysis showed good agreement, and it was assumed that the disturbing ambient airflow around the hood can influence on the C&C efficiency. Therefore the kitchen space was assumed which includes the disturbing airflow over the counter between a dining hall and a kitchen. As a result, the C&C efficiency of the larger hood decreased more under the disturbing airflow.