There has been considerable interest in the interaction between buoyancy and wind pressure gradients on the overall structure of natural ventilation flows. Indeed, it has been shown that when wind and buoyancy forces act in opposition, it is possible that for certain wind speeds, multiple steady states may emerge, with a stable wind dominated and a stable buoyancy dominated regime being possible for identical conditions; while at lower wind speeds, the buoyancy dominated flow develops and higher wind speeds, the wind dominated flow develops.
This paper investigates the single-sided natural ventilation through a VELUX centre pivot roof window under natural weather conditions. The aim of the investigation is to develop an empirical formulation for air flow rate through a roof window based on CFD and tracer gas decay measurement methods. CFD can separate buoyancy and wind effects in the calculation of the air flow rate through a window opening, but it is difficult to isolate wind effect from buoyancy forces during measurements.
Experiments were carried out to study transition phenomena in buoyancy-induced natural ventilation in a relatively large-scale enclosure equipped with a localized heat source and two openings (upper and lower) on one of the sidewalls. The process studied is transition from the mixing to the displacement ventilation mode realized by opening the lower vent to different heights while keeping the upper vent fully open. Measurements included inside vertical temperature profiles and air velocity through the upper vent.
The air exchange in a room with different windows and window geometries is investigated. The aim is to get reliable data for the air change rate and the air exchange efficiency for natural ventilation. Before using a CFD program for the calculations experimental studies have been carried out. In order to meet different demands we distinguish between short time and continuous ventilation. The results are availabe as figures, graphs or approximate equations.
The influence of thermal effects on the dispersion of a gas in a naturally-ventilated room is investigated using CFD in conjunction with measurements. The gas dispersion inside the room, with and without thermal effects, is characterised by a statistical analysis of the CFD-predicted gas concentrations at a large number of points across the room with a view to quantifying the thermal effects. It is concluded that even small temperature differences can lead to significantly different cross flow behaviour and rates of gas concentration decay at the relatively low air change rate considered.
We investigate two different natural ventilation regimes of an auditorium or other occupied open-plan space which is equipped with pre-cooling. The room has a low-level vent and a high level vent. The occupants act as a source of heat, which if without pre-cooling, can lead to the room becoming too warm for comfort. In the first ventilation regime, a chiller is fitted to the low-level vent, and the occupants provide positive buoyancy which drives the ventilation upwards and draws fresh air through the pre-cooling system.
We describe the results of simple modelling and some laboratory experiments of the natural ventilation flows which can develop in an office building when air is supplied from a central atrium, passes through the floor-space of the building, and then vents through stacks at the perimeter of the building.
Predicting the performance of natural ventilation is difficult, especially for the large scale naturally ventilated buildings, because of the lack of accurate and efficient prediction tools. This paper presents a strategy, integrating a multi-zone model and computational fluid dynamics (CFD), to improve natural ventilation prediction and design. Large openings and atrium are broadly used in naturally ventilated buildings to promote buoyancy force and optimize air movement. How to properly deal with large openings and atrium is discussed and compared in this paper.
Natural ventilation is a more pleasant and acceptable ventilation mode, which is favorable to human physical and psychological comfort and health. In this research, experiments and analysis on the fluctuant characteristics of natural wind in outdoor environment and in different positions of indoor area are conducted. The authors analyze the physical structure of airflow fluctuations with turbulence statistical theory, chaos and fractal theory. The fluctuant characteristics of the natural wind in different built environment are found and generalized in the paper.
When designing natural ventilation for complex buildings, it is key to understand whether there is a unique solution for the flow, or if multiple flow regimes are possible. Here, we show that in a 2 storey open plan office type building, in which the floors are connected to a common atrium, two stable flow regimes may occur under identical conditions.
Login