Ventilation for Buildings
Researchers: Dan Toy, Professor Andy Woods
Background
Buildings need ventilation to remove stale air and replace it with fresh air. The way we currently ventilate buildings is very energy intensive.
There are various factors that make ventilation important, for instance managing infection dispersal of airborne diseases, how carbon dioxide levels impact people’s ability to concentrate, and the comfort of temperature levels for building occupants.
The difficulty lies in the fact that different factors sit in tension, for example for reducing the spread of Covid through the air, opening all the windows is optimal, but this sits in tension with levels of comfort in terms of room temperature. Striking a balance between health, comfort, and energy efficiency is a complex challenge.
Our Work
Our research focuses on understanding and optimising room ventilation, with the ultimate goal of identifying general principles that apply across different building designs and could inform practical design rules for efficient ventilation systems.
‘Mixing ventilation’ is the most common ventilation system, which pumps in fresh air and extracts stale air from the ceiling, however we focus on ‘displacement ventilation’, a more efficient system where fresh air is pumped in at a low level and extracted at a high level. This system takes advantage of the tendency of thermal energy to rise, reducing energy usage by leveraging the properties of the heat produced in the room to do the work.
We use analogue models to simulate real-world ventilation scenarios, typically using a tank as a model room, and salt and water to model density differences.
A laboratory experiment illustrating the transient flow resulting from a change in the heating rate (Bower et al. 2008)
Illustration of mixing of a pulse of cold air produced by turbulent gusts of wind in a naturally ventilated model building (Mott and Woods 2012)
Using these smaller, contained models is very helpful in allowing us to conceptualise an entire room space, and we use dye to very visibly demonstrate the fluid mechanics at play. We then use these experiments to inform our modelling.
Implications
Our research highlights significant potential for energy savings and health improvements through optimising ventilation systems. We have developed a fundamental understanding of the fluid mechanics of ventilation systems.
Future Directions
While these experiments provide valuable insights, the critical challenge is bridging the gap between theoretical models and real-world applications. The next step would be to consider how these findings can translate into practical guidelines for architects and engineers.
A crucial challenge is creating a system that takes into account the changing conditions over a whole year to find the best answer that balances seasonal variation; inherent complexity lies in the fact that ideal ventilation solutions are markedly different in the summer months compared to the winter months.