Setting a stormwater standard
by Vincent Ciccarello
A
revolutionary stormwater roof drainage system is one step closer to
having an Australian Standard, thanks to a combined PhD and Honours
research project.
Siphonic drainage, a pump-free system of removing stormwater under pressure, has been used very successfully for a number of years now at many international and Australian buildings including Sydney’s Olympic Stadium and the Hong Kong, Adelaide and Sydney airport terminals. In Adelaide, the IKEA building and the new SA Water Headquarters in Victoria Square both have siphonic roofwater systems.
But, considering the concept was devised in the 1970s, the wider take-up of this system - which has enormous potential in harvesting stormwater - has been relatively slow.
According
to Terry Lucke, PhD candidate and lecturer in UniSA’s School of
Natural and Built Environments, there are a number of reasons for
this – one is the absence of an Australian Siphonic Standard, and
another is uncertainty as to how the systems perform when operating
under very low pressures.
"Siphonic systems on tall buildings can develop extremely low pressures which can cause water to vaporise," Lucke said.
With Bachelor of Civil Engineering Honours students Derek Langman and Kai Keller, and with the support of Australian industry leader Syfon Systems, Lucke has recently completed a pilot study into the effects and design implications of vaporisation in siphonic systems.
"The current standards advise not to use downpipes longer than 8m, simply because there hasn’t been sufficient research to determine how the pipes are going to react," Lucke said.
"We know that when the water vapour reaches a boiling state that you have a lot of pressure on the outside of the pipe; and if the pipe wall isn’t strong enough, it basically crushes.
"Our
testing looked at what happens in the downpipe when you go beyond
10m in length."
The pilot study involved introducing small amounts of air at strategic points into an elaborate test rig of clear Perspex pipes to control the vaporisation process. The results so far have been promising.
"One of the significant results we found is that the introduction of a lot of air, significantly reduced the flow rate," Derek Langman said.
"But it was possible just to inject some air at certain places which would reduce the danger of low pressures, while the flow would remain relatively close to maximum."
Kai Keller added that there were other performance issues associated with water vaporisation.
"It also affects the way the pipes are primed with water, and some of the vibrations it can cause," Keller said.
"We have found that there is a maximum flow rate that the system will take, and pretty much a minimum one. We’ve got a better idea now about what goes on inside the pipes."
Lucke said the results will be presented to Syfon Systems and, eventually to the Australian Standard for Siphonic Roof Drainage Systems committee chaired by Director of UniSA’s SA Water Centre for Water Management and Reuse and Lucke’s supervisor, Professor Simon Beecham.
"However, until we complete the research, it’s an unknown quantity. The Australian Standard is still being drafted and this research will feed directly into the new Standard," Lucke said.
For Langman and Keller, the experience has opened their eyes to the possibility of postgraduate research in the future.
"We think it’s been fantastic to get some hands-on practical work as part of an Honours project," Langman said.
"It hasn’t just been a token project but really valuable research and we feel we’ve played an important part in that.
"Having seen what’s involved, how it can be hands-on and really practical and have real, significant advantages, it’s definitely put the thought in my head about further study by research – if not for now, then later down the track."