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PLUMBING CONNECTION Winter 2022
AVOIDING THE PITFALLS OF CLOSED-
CIRCUIT HEATING&COOLING SYSTEMS
W
hen installing an Automatic
Refill Unit correctly they are
an ideal backflow protection
device. However, when installed
incorrectly, there is every possibility
that they can become a direct cross-
connection with the possibility of
contaminating the potable water supply
(drinking water). How is that possible?
And what measures should you take as a
professional plumber?
THE AUTOMATIC REFILL UNIT
These refill units generally consist of
a non-corrosive supply tank (usually
stainless steel or polyethylene), a fill
valve for the break tank, pressure pump
and pressure switch. Other additional
pieces of equipment used in these
systems are the Expansion Tanks and
Chemical Stainless Steel Dosing Pots.
Chemical additives are added via the
dosing pot to avoid corrosion of pipes
and components. The dosing pot is a
small pressure vessel, which is installed
upon a side-stream bypass that allows
it to be isolated.
Once it is filled with the appropriate
chemical, it is sealed from the
atmosphere and then it is opened to
the mechanical or hydraulic circuit.
The chemical additive is then pumped
around the system with the aid of the
existing circulating pump.
Once the system is primed, the boiler
or chiller system then relies on the
Automatic Refill Unit for any additional
water that may be required. (See
Diagram 1.)
WHAT CAN GOWRONG?
In most cases a ‘quick-fill’ connection
is installed in the pipework so that
mains water can be initially used to fill
the system upon installation, or if the
system must be drained down. This is
usually done through a flexible hose.
Once the system is full the hose used for
the initial fill must be disconnected. It is
this type of connection that potentially
becomes the direct cross-connection,
as this hose is sometimes left
connected, and the isolation valve has
been left on, as can be seen in Images
1 and 2.
In both instances, the chemical used
to treat the chiller and boiler systems
could potentially end up back in the
drinking water system. Although the
ball valve is in the closed position in this
picture, it can easily be turned and left
on, or over time is could simply leak.
To overcome any potential backflow
situation occurring if the ‘quick-fill’ is to
be plumbed in, either with a flexible hose
or with copper, then the appropriate
additional backflow device MUST be
installed on this line.
Some systems have expansion tanks
that contain a rubber membrane that is
not approved for drinking water. Should
the system be plumbed via the ‘quick-
fill’ and a backflow situation were to
occur, then the water that has been in
contact with the non-approved rubber
could leech back into the drinking water
supply, thus being an additional source of
contamination. (See Images 3 and 4.)
In some areas of Australia, closed-circuit heating and cooling systems have been used for several years.
However, these systems can have backflow pitfalls associated with Automatic Refill Units.
Peter Damaso
,
our regular columnist from the Backflow Prevention Association of Australia (BPAA), in consultation with
fellow member
Andrew Meade
, explain why proper backflow protection is so important.
DIAGRAM 1
BACKFLOW PREVENTION -
PETER DAMASO
Image 1: The flexible connection is the
‘quick-fill’ that should be disconnected
and capped once the system is full.
DOSINGPOT
PRESSURE
RELIEFVALVE
STRAINER
SERVICE
VALVE
DETACHABLE
FLEXIBLE
HOSE
TUNDISH
DRAINTOWASTE
MAINSWATER
SUPPLYTOSYSTEM
REFILLUNIT
RETURNFROMSYSTEM
PRESSURE
RELIEFVALVE
AUTOAIR
VENT
SUPPLYTOSYSTEM
BOILEROR
CHILLER
BACKFLOW
PREVENTION
ADJUSTABLE
REDUCINGVALVE
ANDGAUGE
PUMP
CHECK
VALVE
ALTERNATIVE
LOCATIONOF
BOILEROR
CHILLER
EXPANSION
TANK