HAMWORTHY HEATING LTD
WARMWELL
500001091/F
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 1.1 (p2) for typical layout of a
pressurised (Un-vented) 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.
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.
8.8
Minimum Water Flow Rates
Minimum water flow rates are shown in Figure 2.2
(p4). 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
Water Pressure Drop
The waterside hydraulic resistance (Pressure drop)
is shown in Figure 2.2 (p4).
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.
8.10
Control Schemes
8.10.1
Temperature Controls
An electronic control thermostat using a 10k
Ω
NTC
thermistor temperature sensor is incorporated within
the boiler controls. A potentiometer is used to adjust
the control thermostat set point between the range
25 to 95°C. The potentiometer also acts as the
boiler on/off switch via a push and release action.
An additional potentiometer (fitted to the boiler main
control PCB) provides a temperature offset below
the main control set point for high/low control
switching, which can be adjusted up to 10°C below
the main set point (5°C recommended).
If the boiler is required to run in condensing mode the
return temperature should be between 30-45
°
C. The
control thermostat should therefore be set at 45-55
°
C.
This will be dependent on boiler water flow-rate and
hence
∆
T achieved.
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 95°C.
A standard electro-mechanical temperature limiter,
(hand reset limit thermostat) is also fitted to the boiler
and must be set at 100°C.
NOTE!
To meet the requirements of the EN
standard the temperature limiter’s maximum setting
should be 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 2.2 (p4) is maintained.
Figure 8.10.1 Temperature Controls and Boiler
On/Off Switch
°C
Temperature
Limit Thermostat
/ Reset Switch
On/Off Knob
Push to activate
25
30
75
90
95
80
85
40
35
45 50
65
60
70
55
12
Содержание Warmwell 120
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