Public health Drainage Sealed solution
Collaboration between a UK university and a manufacturer has led to the development of an innovative building drainage technique, write John Swaffield and Steve White
P
artnerships and collaborations between industry and academia are commonplace in high-tech industries such as aerospace. Needless to say, they are rather more rare in the public health
engineering sector. However, a 15-year partnership between Heriot Watt University (HWU) and Studor, a manufacturer of air admittance valves (AAVs), has delivered both innovative product and design methodologies, as well as a non-invasive methodology for the assessment of trap seal integrity. HWU has worked with Studor since the mid-
1990s, when together they started to develop models to characterise the action of AAV in the control and suppression of negative air pressure transients, generated by sudden increases in water discharge to vertical stack networks.
In 1999 Studor was introduced to HWU’s invention
of a variable volume containment device to control and suppress positive air pressure transients generated by the cessation of the entrained airflow path through the drainage network, and particularly down the system vertical stacks due to surcharge at stack base or at stack offsets. The device – now called a Positive Air Pressure
Figure 2: Demonstration of the +1/-1 reflection coefficients encountered at a closed and open end termination of a single pipe subject to a positive pressure pulse
10 20 30 40 50 60
-30 -20 -10 0
Closed End Open End
-1 reflection coefficient
+ve reflection from closed end
+ve reflection from open end
The multiple positive air pressure attenuator installation at the Pak Tin estate in Hong Kong cured the stack surcharge transient propagation
Attenuator (PAPATM ) – was used to much acclaim to
remedy positive air pressure transients within the Pak Tin housing complex in Hong Kong, where bathrooms on the first five floors were unusable due to the water seals being ejected by the severe transients following surcharge – the surcharge being due to both poor stack base design and indeterminate occupation levels (pictured above). PAPATM
is essentially an inflatable bag normally
evacuated by the negative pressure regime within the stack. It provides a diversionary route for an entrained airflow brought to rest suddenly by a surcharge – an application of the control and suppression approaches followed in mainstream pressure surge analysis, the most important being to ensure that the rate of change of the flow is reduced, thereby cutting the transient pressure generated. PAPATM
should also be positioned between the
source of the transient and the device to be protected. Following the development of the PAPATM
and the
earlier work on modelling AAV characteristics, HWU proposed the Active Control approach to the venting design of building drainage systems, where a traditional roof penetration was impossible. The technique relies on the AAV installation to limit negative pressure transient propagation while the PAPATM
units control the positive
transients. The HWU’s development of a simulation package, AIRNET, allowed the feasibility of such a methodology to be evaluated, and the approach has been incorporated into the drainage network installation in the O2 dome in London, (see Figure 1). Thanks to collaboration with Studor, this methodology
-1 reflection coefficient 2.55 2.6 2.65 2.7 2.75 Time, seconds 2.8 2.85 2.9
is promoted worldwide and has now been used elsewhere on buildings utilising Studor products. In 2003, poor drainage design was found to be a factor in the spread of the SARS virus within the Amoy Gardens housing complex in Hong Kong. A World Health Organisation investigation, and HWU’s own modelling, confirmed that the spread of SARS was
www.cibsejournal.com September 2010 CIBSE Journal 49
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Pressure (mm Water Gauge)
John Swaffield
Studor
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