Video shows the water bath experiment as viewed from the side
THE WATER TANK:
Megan and her team have been carrying out experiments investigating the effect of temperature differences on cross-ventilation. The experiments are performed in a large flume, with a cross-sectional area of 2 m x 1 m. Into the flume is placed a model room, which is a 0.5 m cube.
Before the start of an experiment, the water inside the model room is heated and dyed. The flume is switched on, to provide a flow past the model room, modelling the effect of wind. Two windows are opened on opposite walls of the model room, one at the front, facing the wind, and one at the back.
Recent experiments have examined the effect of temperature on cross-ventilation. Results show that the major effect of the initial temperature difference between the room and ambient is to create a two-layer stratification, reducing the effective volume of the room. New theory indicates that the temperature difference does not significantly impact the ventilation flow rate through the windows, but the change in effective room volume alters the timescale over which the room is ventilated. These results are currently being written up for publication. You can read a summary of the findings here.
Experiments performed by Megan Davies Wykes and Elkhansaa Chahour.
In the video opposite, Will explains his work recreating the London test site in the Enflo wind tunnel at the University of Surrey. Will is now building a scaled-down replica of our Cambridge test site for the next phase of wind-tunnel experiments, and he has already created a drawing of each of the 167 model buildings.
CAMBRIDGE TEST SITE:
Shiwei and the test team have now completed experiments and monitoring at our second test site, at the University of Cambridge architecture department. We chose the site because it's next to both a busy main road and also a large expanse of green space with a river. So we hope that it will help us to better understand the impact of green and blue space on pollution flows.
Working with Cambridge City Council, MAGIC monitors and temperature loggers were installed around the city. MAGIC monitors, wall temperature monitors, two ultrasonic anenometers and a temperature array were set up in the room itself.
As well as ongoing monitoring we also conducted short-term, controlled experiments to explore the impact of different window opening set-ups on natural ventilation and comfort in the room.
The photo below shows the room with our monitoring equipment carefully positioned.
Shiwei and the team are currently crunching the data, but some interesting findings are already apparent. For example, significantly lower temperatures were observed at green and blue spaces and outdoor pollutant distribution appeared to be influenced by street layout - with the street canyon effect particularly noticeable.
You can download Shiwei's latest presentation here.