A comparison of winter pre-heating requirements for natural displacement and natural mixing ventilation

In winter, natural ventilation can be achieved either through mixing ventilation or upward displacement ventilation (P.F. Linden, The fluid mechanics of natural ventilation, Annual Review of Fluid Mechanics 31 (1999) pp. 201-238). We show there is a significant energy saving possible by using mixing ventilation, in the case that the internal heat gains are significant, and illustrate these savings using an idealized model, which predicts that with internal heat gains of order 0.1 kW per person, mixing ventilation uses of a fraction of order 0.2-0.4 of the heat load of displacement ventilation assuming a well-insulated building. We then describe a strategy for such mixing natural ventilation in an atrium style building in which the rooms surrounding the atrium are able to vent directly to the exterior and also through the atrium to the exterior. The results are motivated by the desire to reduce the energy burden in large public buildings such as hospitals, schools or office buildings centred on atria. We illustrate a strategy for the natural mixing ventilation in order that the rooms surrounding the atrium receive both pre-heated but also sufficiently fresh air, while the central atrium zone remains warm. We test the principles with some laboratory experiments in which a model air chamber is ventilated using both mixing and displacement ventilation, and compare the energy loads in each case. We conclude with a discussion of the potential applications of the approach within the context of open plan atria type office buildings.

Non-aqueous phase liquid behavior in the subsurface: Transportation, source zone characterization and remediation

Contaminant behaviour in soils and fractured rock is very complex, not least because of the heterogeneity of the subsurface environment. For non-aqueous phase liquids (NAPLs), a liquid density contrast and interfacial tension between the contaminant and interstitial fluid adds to the complexity of behaviour, increasing the difficulty of predicting NAPL behaviour in the subsurface. This paper outlines the need for physical model tests that can improve fundamental understanding of NAPL behaviour in the subsurface, enhance risk assessments of NAPL contaminated sites, reduce uncertainty associated with NAPL source remediation and improve current technologies for NAPL plume remediation. Four case histories are presented to illustrate physical modelling approaches that have addressed problems associated with NAPL transport, remediation and source zone characterization. © 2006 Taylor & Francis Group, London.