The distribution of indoor airflow velocity by cross ventilation is influenced by the regional climateconditions, and the location as well as the shape of the building. In this study, CVDHI of 25 cases tochange the number and position of openings at 842 cities in Japan are calculated for the simple housemodel. The results indicate that CVDHI increases relatively in every case from the south to the north ofJapan.
To accurately estimate the natural wind driven ventilation potential of a specific low rise building in a densely shielded or built-up area under local wind conditions, it is necessary to have site wind frequency data, pressure coefficient data, details about the windward and leeward openings of the building and the data related to building design. This paper summarises the appropriate data and discusses how to obtain these in order to estimate the natural cross ventilation potential of such a low-rise building.
Cross ventilation is one of the most important techniques for maintaining a comfortable indoorenvironment in hot and mild seasons with less cooling energy. But, at present, it is difficult to designindoor environment under cross ventilation because there is insufficient knowledge to evaluate theeffect of cross ventilation quantitatively. Thus the full-scale model experiment has been done in a large wind tunnel to examine the airflow property in the cross-ventilated space.
The proposed local dynamic similarity model can select an adequate discharge coefficient to match the approaching flow angle. This is an improvement over the conventional orifice flow model where the discharge coefficient is set to a fixed value. The accuracy of predicting ventilation flow rates for an isolated cross-ventilation model is greatly improved when the discharge coefficients actually decrease with change of wind direction.
Pressure loss mechanism at the inflow opening of Cross-Ventilation is studied by detailed analysis of LES results. Manipulation of energy transfer equation through inflow openings suggests that reduction of discharge coefficient should be originated from dynamic pressure in tangential direction and should be observed as increased static pressure at the opening.
The authors recently reported the detailed experimental results on that the discharge coefficient of the openings exposed to the wind driven airflow clearly changes depending upon the windangle and consequent conditions. A full-scale building model in a wind tunnel has been used for theexperiment. In this paper, the mechanism of the change is discussed more deeply, and the predictionmethods of the discharge coefficient are tested by the new experimental results for different conditions of opening size and location.
The 40 story high-rise headquarter of the Deutsche Post AG in Bonn features an integratedcomfort and low energy concept. Contrary to common high-rise design, the building does not require a central mechanical ventilation system. Instead it is decentrally ventilated by a double faade, which decreases wind loads and allows for natural ventilation through window openings.The typical floor plan is designed to provide a cross ventilation from the double faade through officerooms to a central atrium serving as exhaust duct.
In case of cross ventilation through the large opening, it is well known that the inflow directionat the opening is not normal to the opening. Authors proposed the simplified prediction method of theinflow direction at the inlet opening and the airflow rate simultaneously. It is also well known that the use of general discharged coefficient (CD) values is not suitable for the calculation of cross ventilation rate. First reason is that the simple connection of the pressure loss coefficient of an opening ( ?? as the reciprocal of square CD) in series under-estimates the airflow rate.
It is difficult to evaluate the effect of cross ventilation quantitatively, because the indoor environment under cross ventilation is uneven and changes with the outside conditions. In this paper, the decay process of tracer gas is measured in uneven space under cross ventilation, and the property of spatial unevenness is examined by the concentration decay and velocity distribution.
Wind-driven cross-ventilation in a single-zone cubic building with two large openings is investigated using a computational fluid dynamics approach. We analyzed the driving force and the ventilation flow rate due to wind as a function of the relative location and geometry of the two ventilation openings. The aim is to understand how well the conventional simple macroscopic method predicts the ventilation flow rate and when the simple method fails. Parametric studies were completed using building envelope porosity as the primary variable of interest.
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