HAMWORTHY HEATING LTD. PUREWELL AUTOMATIC IGNITION 500001035/G
8
8.9
Water 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 100
°
C. A
temperature limiter, (hand reset limit thermostat) is also
fitted to the boiler and is normally set at 100
°
C. The
minimum difference between control thermostat and
temperature limiter
MUST NOT
be less than 10
°
C.
8.10.2
Water Flow Controls
Any external mixing valves or similar controls should
ALWAYS
ensure that the minimum water flow rate shown
in Figure No. 2 is maintained.
8.10.3
Frost Protection
Consideration should be given to fitting a frost thermostat
set at approximately 4
°
C
8.11
Unvented Pressurised Systems
See Figure No. 8 for typical layout of a pressurised (Un-
vented) Hot Water System.
In order to correctly size a pressurisation unit for any
heating system certain parameters are required. These
are: -
1) Static height of highest component in system.
2) System volume - if not known a general rule of thumb
of 10 litres/kW installed boiler power can be used.
3) Maximum flow temperature, i.e. most systems run at
82
°
C.
4) Maximum system hot working pressure, generally given
in barg.
From the above information Hamworthy Heating can size
the pressure unit and also the expansion vessel required.
Care must be taken in sizing expansion vessels to ensure
maximum acceptance factors are not exceeded. Normally
manufacturers of vessels impose a limit of 0.5. This value
must not be exceeded at any time during the operation
of the boiler: this includes the over pressure condition
should a safety valve lift.
Consideration should also be given to sizing of the safety
valve(s) in the system. See
BS 6759
: Part 1 (
ISO 4126
)
for information.
See also
BS 6880
: Part 1 for design considerations.
8.12 Modular Boiler Control Schemes
For Modular applications Hamworthy Heating can supply
a unique boiler management control system called the
‘Marshall’. This system comprises: a master control unit,
which houses the main interface processor and,
dependent on the number of boilers, a slave unit for each
of the other boilers. Each unit plugs into the previous
one by a low voltage signal wire. All the sensors are
connected to the last ‘slave’ by a single cable, which is
simple to attach. Both master and slave(s) are
incorporated into the control fascia for ease of
application. For further information contact Hamworthy
Heating for details.
9.0 ELECTRICAL SUPPLY
WARNING: THIS APPLIANCE MUST BE EARTHED.
Wiring external to the boiler must be installed in
accordance with the IEE Regulations and any local
regulations, which apply. Wiring must be completed in
heat resistant 3-core cable. (Size 1.0mm
2
csa). Boilers
are normally supplied suitable for 230 volts, 50Hz.
Fascia fuse rating is 2A. External fuses should be 6A
for all single boiler sizes.
The method of connection to the mains electricity supply
must facilitate complete electrical isolation of the single
boiler/battery with a contact separation of at least 3mm
in all poles.
This appliance must be isolated from the mains
electricity supply in the event of electric arc welding
being carried out on any connecting pipework.
A mains isolator must be provided adjacent to the boiler
in a readily accessible position. The supply should only
serve the boiler.
NOTE!
Volt free contact electrical
supplies must also be isolated when fitted (see note on
fascia). Further details regarding connection to the
electricity supply are given in
BS EN 60335, Part 1 or
BS 3456, Part 201
. The power supply should not be
switched by a time clock, especially if a single header
pump kit is utilised. The Purewell boiler has a remote
stop/start loop which can be used to operate the boiler(s)
under a timed regime. This remote loop requires a volt
free contact for operation. Power is supplied by the boiler
for this circuit to function. The voltage will therefore be
the same as the boiler’s power supply. Refer to Figure
No. 10 for typical site wiring connections. See
BS 6644
for further information. Do not modify this circuit in any
way. See Figure No. 12 for note re: External wiring.
