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Secondary circulation
If secondary circulation is required it is recommended
that it be connected to the cylinder as shown (see Fig.
8).
The secondary return pipe should be in 15mm pipe
`
and incorporate a check valve to prevent backflow.
A suitable WRAS approved circulation pump will
`
be required.
On large systems, due to the increase in system
`
water content, it may be necessary to fit an
additional expansion vessel to the secondary
circuit. This should be done if the capacity of
the secondary circuit exceeds 10 litres. It is
recommended that a swept Tee is fitted to direct
water flow to the cylinder to improve performance.
Pipe capacity (copper):
15mm O.D. = 0.13 l/m (10 litres = 77m)
22mm O.D. = 0.38 l/m (10 litres = 26m)
28mm O.D. = 0.55 l/m (10 litres = 18m)
Note: Plastic pipe capacities may be reduced due to
Figure 8: Secondary circulation schematic (direct)
To Hot
Outlets
thicker wall sections.
Cold Water
Inlet
Swept Tee
Secondary
Circulation Pump
Secondary
Return
Check Valve
In direct electric installations where a secondary
circulation is required particular attention should be
paid by the installer to maintain the returning water
temperature (guidelines state that a minimum of 55°C
return temperature is advisable). Factors such as,
but not limited to, secondary circulation flow rates,
minimising heat loss of all secondary circuit pipework
and timed operation during periods of high demand
are critical to the correct operation and longevity of the
heating element(s) and thermostats.
Secondary circulation is not recommended for
direct electric units using off-peak tariffs where the
secondary circulation is not controlled in conjunction
with the heat source as performance can be affected.
15
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