7
Water circulation system
In a combined central heating and domestic hot water
system, the hot water storage vessel must be of the indirect
cylinder type. The hot water storage vessel should be
insulated with not less than 75mm thick mineral fibre or its
equivalent.
Cisterns and pipework should not be situated in areas which
may be exposed by freezing conditions and should be
insulated.
Draining taps must be located in accessible positions which
permit the draining of the whole system, including the heat
storage vessel.
The appliance boiler section should be connected to cistern
water supply, subject to a maximum head of 3 bar (30m),
minimum of .1 bar (1m).
The heating system must be designed (and adjusted if
necessary) to give temperature differential across the boiler
at full output of 10-14ºC.When horizontal runs are used the
pipes should rise upwards in the direction away from the
appliance.
Circulating Pump
It is recommended that the selected pump be sized to suit
the boiler pressure loss (see
Fig. 1.3
) and therefore adequate
to give the required temperature differential between the
flow and return.
The pump should be able to meet the requirements of the
system design and fitted in a readily accessible position.
Isolating Valves
Isolating valves (preferably of the keyless type) must be fitted
to the inlet and outlet of the circulating pump to facilitate
service and replacement of pump without draining the
system.
Inhibitor
A corrosion inhibitor
MUST
be added to the heating system
to protect the heat exchanger and pipework. Inhibitor must
also be replaced if the system is drained after installation. As
a precaution the heating system
MUST
also be flushed out
prior to the addition of the inhibitor to ensure any flux, debris
is removed.
300
600
900
1200
1500
Fig. 1.3
Pressure Loss Curve
Sealed System Requirements See
on page 24 and on
page 25