Exchange Flows

The primary aim of the research is to enhance our understanding and predictive capability of the natural ventilation of modern buildings. Specifically, the focus will be on 'exchange' flows. This terminology encompasses a spectrum of different situations when across a given ventilation opening there is simultaneously a flow into the room from the exterior and a flow out of the room to the exterior. Exchange flow occurs when there is, for example, a single high-level vent in a warm room - for example, via a sash window opening or bespoke vent. Whilst simplified descriptions of this particular situation have been developed, the picture is considerably more complex when there are multiple high-level vents (whether horizontal or vertically oriented). For example, with two horizontal vents the flow may exchange through both vents for a period before switching to a mode in which the flow is in through one vent and out through the other -- and then reverting back to exchange flow and so on. One of the challenges will be to develop an understanding of this cycling between different modes of flow, including the implications for low-energy ventilation design. Numerous other aspects of exchange flows will be examined, including the influence of vent orientation on the rate of exchange, on the cyclic behaviour and internal temperature distribution. Moreover, an additional key focus will be on 'unbalanced' exchange flows, namely, those which occur when, in addition to the upper vent, a lower vent is opened. The approach adopted to study these flows will be small-scale physical modelling and complementary theoretical modelling.