HAMWORTHY HEATING LTD
7
SHAFTESBURY HE
500001049/N
8.5 Thermometer
See Figure 16.1 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 ¾” NB drain valve fitted (not
HHL supply), to drain the boiler only. A plugged Rc ¾”
connection is provided for a drain valve at the bottom of
the front boiler section. The heating system in total
should have drain valves as recommended by
BS
6644
. See Figure 16.1 for recommended positions.
8.7 Circulating Pump
One or more circulating pumps will be required to
circulate water around the boilers and heating system.
The pump should be sited to facilitate servicing. 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.
NOTE:
If boilers are run off time clock control, a pump
overrun (not HHL supply) should be fitted which must
run for a minimum of 5 minutes on shut-down of the last
boiler.
8.8 Minimum Water Flow Rates
Minimum water flow rates are shown in Figure 3.1.
These flow rates should be maintained through the
boiler at all times whilst the boiler is firing. If the
water 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
Control Schemes
8.9.1 Temperature Controls
An adjustable control thermostat is supplied with each
boiler and should be set to operate within the range 65-
90°C for standard applications. A temperature limiter,
(hand reset limit thermostat) is also fitted to the boiler
and must be set at 100°C.
NOTE!
The minimum difference between control
thermostat and temperature limiter
must never
be less
than 10°C.
8.0 WATER CIRCULATION SYSTEM
8.1 General
Recommendations for the water circulation system are
given in
BS 6644
and
CP 342
. The following notes are
of particular importance:-
1)
In a combined central heating and hot water system,
the hot water storage vessel must be of the indirect
cylinder or calorifier type. The hot water storage vessel
should be insulated preferably with not less than 75mm
(3 in) thick mineral fibre, or its thermal equivalent.
2)
Circulating pipework not forming part of the useful
heating surface should be insulated to help prevent heat
loss and possible freezing, particularly where pipes are
run through roof spaces and ventilated cavities.
Cisterns situated in areas, which may be exposed to
freezing conditions, should also be insulated. Insulation
exposed to the weather should be rendered waterproof.
3)
Drain valves 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 4” N.B. Flanged flow and return
connections located on the rear section of the boiler.
Mating flanges are supplied suitable for welding to 4”
NB pipe.
5)
Multiple boilers should be connected by flow and
return headers. 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.
8.2 Pressure Relief Valve (Safety Valve)
The most important single safety device fitted to a boiler
is its safety valve and each boiler, or in the case of a
modular installation, each bank of boilers, must be fitted
with a pressure relief valve to
BS 759
or
BS 6759
Part 1
(
ISO 4126
) 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 are detailed in
Figure 8.3.
The vent pipe must rise continually, must not be valved
except by a design which when closed for maintenance
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 valve. See
Figure 16.1 for typical position.
Boiler Output
Feed
Vent
60kW - 150kW
25
32
150kW – 300kW
32
38
300kW – 600kW
38
50
Figure 8.3. Cold Feed and Vent Pipe Sizes (mm)
