Plumbing Connection 2-2015

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3 8 PLUMBING CONNECTION WINTER 2015
and feed off the bacteria. Legionella take advantage of these
larger organisms. Once ingested, they live inside and breed,
bursting free when the larger organism dies.
“That’s one of the reasons why legionella is quite difficult
to treat,” Steve says. “In spite of the high sterilisation
temperatures used during thermal disinfection routines, the
biofilm offers the legionella bacteria a degree of protection
from the thermal shock.”
Given legionella and pseudomonas’ ability to spread
quickly, become multi-drug resistant, and kill the elderly
and ill, it’s important that bacteria control is addressed in
hospitals and aged care facilities. As mentioned earlier, a
multi-pronged attack is needed, covering the following four
areas:
∫ Keep hot water hot
∫ Keep cold water cold
∫ Keep it moving
∫ Keep it clean
KEEP HOT WATER HOT
“The first parameter to consider is storage temperature –
this needs to be maintained above the 60°C range to ensure
the hot water storage vessels and calorifiers can’t become
a breeding ground for legionella,” says Antonio, an hydraulic
project engineer from Wood & Grieve Engineers.
This temperature requirement includes water in storage
and in circulation. Antonio gives the example of poor design
work in hospitals where the hot water pipes have long dead
legs and reticulation doesn’t pass close enough to isolated
fixtures. These flaws can increase the surface area of the
hot water and the time water spends in the line, cooling it to
a dangerous temperature.
For many years, internal water systems in Australia
have not been designed with these factors in mind. Peter
explains, “In Australia, we’ve had things like warm water
systems installed which will deliberately send warm water
through the whole system, on the basis that you had to
maintain the temperature at one point – in the basement
– and you didn’t have to maintain it anywhere else. Which
is great, but then you’ve created an entire legionella risk
through your whole system.”
Once these ‘warm water systems’ are addressed, the
mixing of hot and cold water needs to be taken as close to
the source as possible. One way of doing so is to employ
thermostatic mixing valves (TMVs). By mixing the hot water
at the point of use, TMVs ensure the water can be kept hot
for as long as possible, without the risk of scalding.
KEEP COLDWATER COLD
On the flipside, it’s important to keep cold water cold –
below 20°C. As with keeping hot water hot, a step towards
achieving this is keeping cold and hot water separate; there
is, however, an additional problem. The increasing use and
Order.
Chaos.
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