Trees, displacement ventilation and the use of thermal mass all played their part in giving the Green Building of the Year Award to the Ministry of Defence. Ewen Rose gets under the skin of the winning building.
In order to improve the indoor air quality a change in the ventilation system is often one of the actions. The mean ventilation effectiveness or contaminant removal effectiveness is then often presented as a measure. Great care should however be taken when evaluating a system using these parameters. Measurements have shown that in displacement ventilation the mean ventilation effectiveness can fluctuate very much for the same air flow, the same cooling load, the same inlet - outlet devices and the same height of the tracer gas supply.
Computational fluid dynamics may be used to predict the details of airflow in rooms served by displacement ventilation systems, provided a suitable turbulence model can be found. Since buoyant plumes are central to the displacement ventilation strategy, four turbulence models - three eddy-viscosity models (the 'standard' k-s model, a modified k-s model, and an RNG k-s model) and the Reynolds stress model - were applied to simulate airflow in a turbulent buoyant plume.
The use of air-conditioning is known to be an energy-intensive solution to the problem of providing thermally comfortable conditions in buildings. This has led to the adoption of new techniques, such as displacement ventilation and chilled ceiling systems as a means for providing the cooling requirements. In addition, benefits are gained in terms of indoor air quality and comfort. However, there is a lack of information about the effect that chilled ceiling has on displacement air flow, and the corresponding implications for occupant thermal comfort.
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