University of Cambridge > Talks.cam > Fluids Group Seminar (CUED) > Unbalanced exchange flow and the natural ventilation of buildings

Unbalanced exchange flow and the natural ventilation of buildings

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  • UserNick Wise, CUED
  • ClockFriday 19 November 2021, 12:30-13:30
  • HouseCUED, LR3A.

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The natural ventilation of buildings at night is an essential part of a low-energy ventilation and cooling strategy, allowing excess heat to be purged and replaced with cooler night air. Instrumental to the success of such ventilation schemes is the ability to predict flow patterns and flow rates, based on the size and location of ventilation openings. A common choice is to position openings at high and low level in the building fabric with the intention of setting up a buoyancy-driven displacement flow, where warm air exhausts through the high-level opening and cool air enters through the low-level opening. However, we show that displacement flow cannot be maintained throughout a purge. Instead, the flow pattern must transition to ‘unbalanced exchange flow’, whereby the inflow of cool air at low level is maintained but there is now simultaneous inflow and outflow of warm and cool air at the high-level opening. This change in flow pattern alters the internal distribution of heat and the resulting flow rates and purging times. We develop a theoretical model that captures and predicts this behaviour, successfully predicting the transition and subsequent flow rates, then consider the implications for the design of natural ventilation systems.

This talk is part of the Fluids Group Seminar (CUED) series.

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