Modelling natural ventilation

University of Bath

An exciting opportunity has arisen to join our Centre for Doctoral Training in Decarbonisation of the Built Environment (dCarb), to undertake a three-year doctoral programme in low-carbon technologies, starting in October 2015.

Project overview

First supervisor: Sukumar Natarajan
Second supervisor: Jun Zang
Industrial supervisor: Thomas Blight (Buro Happold)

This project will develop methodologies to help architects and engineers designing ventilation in buildings. At the moment, only large firms have the resources to run complex fluid dynamic software (CFD) to adequately evaluate the design to provide good ventilation. These tools are complex and computationally intensive. In most cases, however, the air flows are not complex, and could be categorised and studied to create empirical rules and calculation tables. This project will develop methodologies that sit between the simple equations found in professional guides, such as CIBSE’s or ASHRAE’s, and more complex tools, such as IES microflow or CFD.

Natural ventilation is still the most common way of maintaining good air quality and preventing overheating in British dwellings. The UK is a heating dominated climate so the need for cooling devices has historically been nonexistent. Dwellings typically have high levels of infiltration and large windows, which have been sufficient to ventilate the living spaces and get rid of moisture, CO2, odours and other elements that compromise air quality. In most cases, occupants operate their windows to obtain a comfortable environment; however, natural ventilation is a complex phenomenon and, in some cases, air flow through rooms is not sufficient to create a healthy environment.

Fluid dynamics are governed by complex mathematics that have to be solved with computationally intensive algorithms even for the simplest problems. The geometry of the buildings, the different types of openings, the internal partitions or the surroundings all have to be taken into consideration when looking at air flows in buildings. Most literature takes one of two approaches:

(1) Run complex numerical simulations using CFD, in which the model considers a great deal of the geometry of the problem but that has to be limited to particular cases (runs of the order of hours).
(2) Use a simple pressure network in which each opening contributes to the network with a “wind resistance” and each room is represented for one node at a given pressure. This approach allows a year’s simulation; however, the solutions are far from accurate as the geometrical features given by the layout of the dwelling don’t have an effect in the calculations (such as sharp corners).

This project will use CFD to cover a wide range of tests and experimentation that will allow us to characterise the effects that types of dwellings have on air flows. CFD models will be validated in real dwellings using measurements and later used as a reference point from which the study will be extended for different conditions and building topologies.

The output of this research will be a set of quasi-empirical rules that will allow designers to calculate the effects that different openings, internal layouts and other factors will have in the real ventilation achieved in the actual building. In addition, these rules could be implemented in full-year building simulation software to have a more accurate estimation of the ventilation of a given design, which will be key to addressing potential problems such as overheating and poor air quality.

Research environment

The EPSRC Centre for Doctoral Training in Decarbonisation of the Built Environment (dCarb) was launched in 2014 to address the challenge set by the UK to cut carbon emissions by 80% by 2050. The Centre carries out multidisciplinary research into the design and creation of zero-carbon technologies that will potentially transform the future of our built environment. Find out more about the Centre at http://www.bath.ac.uk/ace/pg-research/cdt-decarbonisation/

The Centre is based in the Department of Architecture & Civil Engineering at the University of Bath. The Department was ranked equal first in the UK out of 45 submissions to the Architecture, Built Environment and Planning in the 2014 Research Excellence Framework (REF). Half of its research achieved the top 4* rating, the highest percentage awarded to any submission; and an impressive 90% of research was rated as either 4* or 3* (world leading/ internationally excellent in terms of originality, significance and rigour).