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4.
WATER SYSTEM
Reference should be made to BS.6644, BS.6880
and CP.342 for detailed recommendations on
heating water circulation systems.
notes are given as guidance:
4.1
Pipework
The heating system should be thoroughly cleaned
prior to the installation of the boiler(s). If there is
any doubt regarding the cleanliness of an existing
system, the inclusion of a coarse filter in the return
pipe to the boiler(s) should be considered.
In
the
case
of
multiple
irrespective of the type of system, it is important that
the system design provides an even flow of water
(of not less than the minimum rate specified)
through each of the boilers in question. This can be
achieved by connecting the boilers using the
'reverse return' method, providing an even flow
through each boiler, and ensuring that the pressure
drop across any number of boilers is never greater
than that for a single boiler plus losses for the
adjacent pipework and fittings.
The system should be designed to operate with a
temperature drop of between 11 deg. C and 20 deg.
C.
The design and minimum water flow rates, with the
corresponding waterside pressure drop values, are
given in the following table 3:
TABLE 3. Water Flow Rates and Pressure Drops.
BOILER
MODEL
FLOW RATE
LILLIPUT
l/m
HE65
86.3
HE90
113.5
HAMWORTHY HEATING LTD
The following
boiler
installations,
DESIGN FLOW RATE
(11 deg. C temp. rise)
PRESS. DROP
UKgal/m
m/bar
19.0
23.8
25.0
34.5
LILLIPUT HE
4.2
Pumps
The pressure drop through both the boiler and the
heating installation should be taken into account
when selecting the circulating pump for the system.
In the case of open-vented systems, it is essential
that the pump does not 'pump over' (i.e. push water
out of the open vent pipe) during normal operation.
Some installations may require the use of a shunt
pump to maintain the temperature drop between
boiler flow and return within the recommended
range, and to provide an 'overrun' facility to
dissipate residual heat and avoid nuisance shut
down of the boiler(s) by the overheat thermostat.
Circulating
pumps
accessible position and be fitted with two isolating
valves to allow removal/replacement.
4.3
Open Vent Pipe
An open-vented system must have an open vent
pipe, sized in accordance with BS.6644, running
directly from the flow pipe adjacent to the boiler(s),
rising continuously by the shortest route, to
discharge into the feed and expansion tank above
the overflow level.
No valve should be fitted in the open vent pipe,
except on multiple boiler installations where any
isolating valve fitted between the boiler and the
open vent pipe should be a 3-way valve - venting
the boiler to atmosphere through the third port when
isolating the open vent pipe from the boiler.
MINIMUM FLOW RATE
(20 deg. C temp. rise)
FLOW RATE
in.wg
l/m
UKgal/m
9.6
47.7
13.9
62.5
7
should
be
located
PRESS. DROP
mbar
10.5
7.3
13.8
10.5
500001047/F
in
an
in.wg
2.9
4.2
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