Performance investigation of a naturally driven building ventilation terminal.

Naturally driven ventilation terminals (wind vents) offer a way of improving comfort conditions while reducing building carbon emissions. The device sits on top of the building, trapping the air at higher velocity and delivering it into the interior of the building. The current cross-ventilated design combines the velocity, pressure, and density of air to produce wind driven ventilation. Currently there is scarce research investigating the performance of these devices in the United Kingdom (UK).This thesis provides a performance evaluation and optimisation of a commercially available building ventilation terminal (a benchmark) in the UK. A systematic review and optimisation of the device's geometrical components has been carried out using Computational Fluid Dynamics (CFD) and far-field experimentation.An extensive literature review was carried out to provide the framework for this investigation. Building on existing (developed) research techniques, the knowledge gaps identified in this subject area, were isolated and examined thoroughly.A new methodology for creating and dynamically modifying CFD models using complete wind vent geometry was devised. Using this technique the wind vent was subjected to systematic geometrical variation to establish the contribution of each component to the overall performance of the device.The research used full scale Far field experimentation to validate the CFD models of the wind vent. The Far field experimentation provided greater accuracy (0 - 0.08m/s) for this application, when compared to other validation techniques such as wind tunnel experimentation (0 - 0.15m/s).A new empirical methodology was devised for predicting the airflow through a wind vent. The empirical method was based on two dimensionless coefficients (0.44 and 0.3) found through the CFD experimentation research carried out.The investigation established the device is capable of meeting current British Standards Institute (BSI) guidelines, and is therefore suitable for UK applications. The BSI recommended 0.8L/sec of fresh air per m[2] floor area. The benchmark wind vent geometry delivered 1.1 L/sec per m[2] of floor area with an external wind speed of 1m/s (UK average was 4.5m/s).The key geometrical components (in isolation) were identified as the louver angle, distance between louvers and the number of louvers (now subject to patent number 0809311.4). Each of these geometrical variations provided an increase in performance over the benchmark case in the range of 27 - 45%. An optimum configuration of these parameters did not deliver the same increased performance range as the isolated case. However the optimised combination case increased the internal air movement rate using 50% less material than that of the benchmark geometry.