HAMWORTHY HEATING LTD. PUREWELL PERMANENT IGNITION 500001090/B
7
insulated. Insulation exposed to the weather should
be rendered waterproof.
3)
Draining taps must be located in accessible
positions, which permit the draining of the whole
system, including the boiler and hot water storage
vessel.
4)
Each boiler has one Rc2 BS21 flow and one Rc2
BS21 return tapping. Flow and return headers
should connect boilers but sufficient length of
connecting pipe should be allowed to clear the
casing before connecting into the headers. The
headers should be connected to the system in a
"reverse return" arrangement (the water flow in each
header is in the same direction) to ensure equal flow
in each module. Figure No. 8 shows typical layout.
8.2 Pressure Relief Valve (Safety Valve)
Each boiler, or in the case of a modular installations,
each bank of boilers, must be fitted with a pressure
relief valve to
BS 6759 Part 1
and sized as shown in
BS 6644
.
BS 6644
provides comprehensive information for the
selection and location of safety valves and attention
is drawn to the higher capacity requirements of
safety valves for pressurised hot water systems.
8.3 Open Vent and Cold Feed Pipe
(See
BS 6644
for further information.)
Every boiler or group of boilers should have an open
vent pipe and cold feed pipe installed between the
boiler and the first water isolating valve. The
minimum bore (mm) of these pipes per installation is
as follows: -
Boiler Output
Feed
Vent
< 60kW
19
25
60kW - 150kW
25
32
150kW - 300kW
32
38
300kW - 600kW
38
50
The vent pipe must rise continually, must not be
valved except by a design which when closed for
maintenance ensures the boiler is open to
atmosphere. The pipe shall be protected against
freezing where this might occur.
8.4 Altitude Gauge (Water Pressure Gauge)
Every boiler or group of boilers should be provided
with a gauge complete with isolating cock. See
Figure No. 8 for typical position.
8.5 Thermometer
See Figure No. 8 for typical position.
A thermometer complete with pocket should be fitted
in the pipework to indicate water flow temperature.
8.6 Drain Valves
Each boiler should have a 15mm NB drain valve (not
H.H.L. supply) fitted to drain the boiler only. The
heating system in total should have drain valves as
recommended by
BS 6644
. See Figure No. 8 for
recommended positions.
8.7 Circulating Pump
One or more circulating pumps will be required to
circulate water around the boilers and heating
system. Figure No. 1 shows the hydraulic resistance
of the boiler. The pump should be sited to facilitate
servicing. It is important to note that when Purewell
boilers are used to replace boilers on an existing
system, the pumps should be checked for
performance against the new boiler waterside
pressure drop to ensure that the minimum flow rate
can be obtained. It is also important that the existing
system be flushed through twice to remove any
loose matter, which may have accumulated. If in any
doubt regarding the cleanliness of the system, a
coarse filter should be fitted in the return pipework to
the boilers.
8.8 Minimum Water Flow Rates
Minimum water flow rates are shown in Figure No. 2.
These flow rates must be maintained through the
boiler at all times whilst the boiler is firing. If the flow
rate is allowed to fall below the minimum, the boiler
heat exchanger could fail due to the resultant scale
formation. Particular attention should be paid to the
restriction of external flow circuits during periods of
low heat demand.
8.9 Waterside Pressure Drop
The waterside hydraulic resistance (Pressure drop)
is shown in Figure Nos.1 & 2.
NOTE:
If boilers are run off time clock control, a
pump overrun (not H.H.L. supply) should be fitted
which must run for a minimum of 5 minutes on shut-
down of the last boiler.
8.10 Control Schemes
8.10.1 Temperature Controls
An adjustable control thermostat is supplied for each
boiler and should be set to operate within the range
65-90°C for standard applications.
If a higher water temperature is required, and
providing sufficient head on the water system is
available, the thermostat may be adjusted to operate
up to 120°C –
see Note
. A temperature limiter,
(hand reset limit thermostat) is also fitted to the boiler
and is normally set at 100°C with a maximum setting
of 110°C. The minimum difference between control
thermostat and temperature limiter
MUST NOT
be
less than 10°C.
