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Computational Fluid Dynamics Simulations of Personalised Ventilation

Gilkeson, Natalie Ariana (2018) Computational Fluid Dynamics Simulations of Personalised Ventilation. PhD thesis, University of Leeds.

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Abstract

Personalised ventilation (PV) systems create a micro- climate around individuals in indoor environments, and they have the potential to improve personal comfort, indoor air quality and productivity of building occupants. The focus of the research undertaken in this Ph.D was to determine whether the use of PV strategies can enhance thermal comfort and air quality compared to a traditional displacement ventilation technique. The studies were simulation based and considered multiple configurations, with the methods validated against a benchmark test case. Computational Fluid Dynamics (CFD) simulations modelled the deployment of clean air to a seated computational thermal manikin (CTM) in a mechanically ventilated chamber. The effects of radiation were accounted for using the Discrete Ordinates (DO) model which enhanced the prediction of thermal properties in the domain. High-fidelity CFD simulations were computed on meshes of 5.4 million cells for single CTM cases and up to 9.4 million cells for two CTMs. Solutions were generated using the transition SST turbulence model which accounted for the range of Reynolds numbers from laminar to turbulent, in every single flow field. Results showed that PV jet temperature and its proximity to a CTM face influences airflow patterns which in turn impacts the levels of thermal comfort and indoor air quality seen. It is important to use realistically shaped CTMs in conjunction with the heat flux thermal boundary condition if details of the flow and thermal comfort is important. In contrast, where details of the flow field in small spaces are unimportant, a simplified CTM in the form of an upright cylinder is suitable, simplifying the modelling process. A PV jet with no thermal mass in the domain can give an indication of where best to place the PV nozzle, for a given set of conditions. For simulations using realistic CTM shapes, there exists a strong interaction between the PV jet, the convective boundary layer around the CTM and the thermal plume. If the PV jet is placed too far away from the CTM (outside of the zone of flow establishment), air quality can be impaired and may lead to worse air quality than room ventilation alone. Extending the work to two CTMs in a room highlighted the fact that both thermal plumes tended to move towards each other with the strength of attraction greater when the CTMs were in closer proximity. This mutual plume attraction phenomenon set up two large recirculation currents in the room which were somewhat different to the single CTM flow fields. Overall, a significant conclusion from this research is that PV systems can be very effective for improving air quality and thermal comfort if used appropriately, however they can also prove to be detrimental to the overall indoor environment when poorly placed.

Item Type: Thesis (PhD)
Academic Units: The University of Leeds > Faculty of Engineering (Leeds) > School of Civil Engineering (Leeds)
Depositing User: Dr N A Gilkeson
Date Deposited: 29 Oct 2018 12:05
Last Modified: 10 Oct 2019 08:41
URI: http://etheses.whiterose.ac.uk/id/eprint/21947

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