Unvented Systems - Hamworthy Sherborne Series Installation, Commissioning And Service Manual

8.10 Controls
8.10.1.1 Temperature Controls
The temperature of the water outflow can be set between 65
and 90°C on high efficiency boilers and 30 and 90°C on
condensing boilers. - see Figure 8.10. A temperature limiter,
(hand reset limit thermostat) is also fitted to the boiler and is
set at 100°C.
NOTE! To accommodate modular boiler installations, the
limit thermostat is adjustable up to a maximum of 110°C.
The minimum difference between control thermostat and
temperature limiter must never be less than 10°C.
8.10.2 Water Flow Controls
Any external mixing valve/shunt pump or similar controls
should ALWAYS ENSURE that the minimum water flow
rate as shown in Figure 2.2. is maintained. If there is any
doubt relating to site flow conditions it is suggested that a
flow switch is fitted. The flow switch should be connected
such that the boiler will shut down if insufficient flow occurs.
8.10.3 Frost Protection
If the Hamworthy boiler sequencer with an outside tempera-
ture sensor is not used, consideration should be given to
fitting a frost thermostat set at approximately 4°C.

8.11 Unvented Systems

See Figure 1.1. for typical layout of an Unvented
(Pressurised) Hot Water System. For system design refer to
BS 7074 Part 2.
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 (metres).
2) System volume - if it is not known a general rule of thumb
of 10 litres/kW of installed boiler power can be used.
3) Maximum flow temperature (°C).
4) Maximum system hot working pressure, generally given
in bar gauge.
From the above information Hamworthy Heating can size
the pressurisation unit and also the expansion vessel re-
quired.
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, for information.
See also BS 6880: Part 1 for design considerations.
8.12.1 Boiler Control Schemes
8.12.2 Single Boiler Installations
For single boiler installations the Sherborne range of boilers
HAMWORTHY HEATING LTD
can be operated in fully modulating mode, controlled from a
simple time-clock or BMS system via a remote stop/start
loop. – see Figure 8.12.
8.12.3 Modular Boiler Installations
For modular installations of the Sherborne range of boilers,
Hamworthy Heating can supply an optional Milton fully
modulating boiler sequencer control system.
This system comprises of a wall mounted Master control
which communicates with the boilers, water temperature
sensor, room sensor (optional) and outside temperature
sensor (optional), and optionally can control separate do-
mestic hot water and heating zones. The Milton incorporates
diagnostic and data logging capabilities. For further informa-
tion, contact Hamworthy Heating for details.
Alternatively, the Sherborne boilers can be set to a high/low
mode of operation for sequence control, via the remote stop/
start control loop and a high/low control loop, by a non HHL
control system. – see Figure 8.12.
In order to enable remote fully modulating boiler control by a
non-HHL control system Hamworthy Heating can also sup-
ply an optional Sequencing Interface Module fitted within
each boiler's control panel. This interface module will control
the boiler firing rate based on the level of a 0-10V analogue
signal from the external control system. A 0-10V output from
the external control system will be required for each boiler.
Where a modular installation comprises of a combination of
condensing and high efficiency Sherborne boilers, the con-
densing boilers should always lead the firing sequence.
9.0 ELECTRICAL CONNECTIONS
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 cable.
(Size 0.75mm
for 230 volts, 50 Hz. Boiler fuse rating is 1 A. External fuses
should be 6 A. for all boilers.
Figure 8.10 Controls Housing showing
Temperature Controls
14
SHERBORNE
2
csa). Boilers are normally supplied suitable
Route site wiring
through plastic
trunking into
controls housing
Temperature
Limit Thermostat
/ Reset Switch
75
70
80
65
85
°C
90
On/Off Knob
- Push to Activate
500001103/E