Effect of damper and heat source on wind catcher natural ventilation performance
Introduction
Wind catchers/towers systems were employed in buildings in the Middle East for many centuries and they are known by different names in different parts of the region [1], [2], [3]. They were constructed, traditionally, from wood-reinforced masonry with openings at height above the building roof ranging from 2 to 20 m. With taller towers capturing winds at higher speeds and with less dust [1], [4], [5]. Their application in the hot arid region of the Middle East is to provide for natural ventilation/passive cooling and hence thermal comfort, exploiting, particularly, night-time ventilation strategy. They can be beautiful objects, feasible architectural feature additions to buildings and are inherently durable [6], [7], [8].
In the modern design of wind catchers, the two ventilation principles of wind tower and passive stack are combined in one design around a stack that is divided into two halves or four quadrants with the division running the full length of the stack [9], [10]. As the wind direction changes so do the functions of each of the halves or the quadrants in the wind catcher. This renders the wind catcher as being operational whichever way the wind is blowing. As there are no free parts to the wind catchers, their maintenance is very small [11]. It has the benefit of taking air supplied at roof level, which is often cleaner than air supplied at ground level, particularly where the building is adjacent to a road in urban areas. The wind catcher systems come in various configurations to suit various building type and requirements such as the incorporation of solar panel (solar chimney) and light pipes to boost stack effect [12], [13]. Recently, the wind catcher systems are increasingly being installed in buildings around the UK. In most of these modern installations, the wind catchers terminate at the ceiling level with four quadrants acting as supply/extract for the air. Some of these buildings have had great attentions in the recent years, such as the Queen's building at Demonfort University, the Inland Revenue building in Nottingham, a shopping mall building, Solihull, the Jubilee Campus at Nottingham University and the BRE office of the future [3]. There are inherent control problems with applying natural ventilation techniques in building including wind catchers. The air flow through wind catchers/towers is controlled by a mechanism of dampers and egg crate grilles at ceiling level. These volume control dampers are controlled either manually or automatically via actuators. In this paper wind tunnel, smoke visualisation tests and CFD modelling were conducted to investigate the effect of installation of dampers and egg crate grille on a commercial wind catcher together with the influence of heat source inside rooms on the air flow.
Section snippets
Wind tunnel experimental set-up and measurement procedures
The experimental investigation was carried out using an open working section wind tunnel located at the laboratories of the Building Services Research and Information Association (BSRIA), Crowthorne. BSRIA's wind tunnel was designed for the testing of natural ventilation devices. The wind tunnel consists of three main sections; one circular section with 1.250 m diameter and two octagonal shaped sections (2 m × 2 m) connected together with a total length of 17.550 m approximately. The open working
CFD simulation set-up
The CFD commercial code used for the modelling of the wind catcher was CFX Windows environment [16]. This CFD code was used to evaluate the pressure coefficients distributions and air flow around and through the wind catcher to the room. A geometrical representation of the wind tunnel testing set-up was produced in CFX. Rigorous efforts were exerted to simulate the louvers as they are in the full scale model. The dampers and egg crate grilles were simulating by creating a plane of resistance
Results and discussion
The test results showed variation in the measured pressure coefficients with wind speed especially at wind speeds in the range 0.5–2 m/s due to the low values of measured pressure. In case 1 experimental investigation was carried out to assess the value of Cp when the louvers were open or blocked. Variations in the measured Cp's were observed, particularly at the middle of louvers. Less variation were recorded for the Cp's measured at the top of the louvers. The use of open or blocked (solid)
Conclusions
Wind tunnelling and CFD modelling were used to study the effect of dampers and heat sources on the performance of a wind catcher for natural ventilation purposes in buildings. Wind tunnel and smoke visualisations tests and CFX CFD code were used in this investigation. The experimental testing in the wind tunnel was carried out for square sections wind catcher (500 mm × 500 mm and a height of 1.5 m). The wind catcher was connected to a test room in open section wind tunnel at BSRIA. The tests were
Acknowledgment
The author would like to acknowledge the support of BSRIA, Ansys CFX and Monodraught Ltd. in carrying out this investigation.
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