a.
The method of filling, refilling, topping up or
flushing sealed primary hot water circuits from the
mains via a temporary hose connection is only
allowed if acceptable to the local water authority.
b.
Antifreeze fluid, corrosion and scale inhibitor fluids
suitable for use with boilers having aluminium
heat exchangers may be used in the central
heating system.
General
1.
The installation must comply with national and local
regulations.
2.
Design the system for flow temperatures up to 80
o
C.
3.
The system components must be suitable for an
operating pressure of 3 bar and a maximum temperature
of 110°C.
The following components are incorporated within the
appliance:
a.
Circulating pump.
b.
PRV, with a non-adjustable preset lift pressure of 3
bar.
c.
Pressure gauge, covering a range of 0 to 4 bar.
d.
An 8 litre expansion vessel, with an initial charge
pressure of 0.75 bar.
4.
Makeup Water
One of the following provisions must be made for
replacing system water loss:
a.
Manually filled vessel
The vessel must:
• Have a visible water level
• Be mounted at least 150 mm above the system’s
highest point
• Connect through a non-return valve to the
system
• Be at least 150 mm below the makeup vessel on
the return side of the radiators
b.
System prepressurisation.
The efficiency of the expansion vessel will be
reduced in a pressurised system; a larger vessel
or smaller system volume may be necessary. If
the vessel’s capacity is not sufficient, an additional
vessel must be installed on the return to the
boiler.
If the system is not pressurised, the cold water
capacity must not exceed 143 litres.
Guidance on vessel sizing is given in Table 4.
1.15 SYSTEM REQUIREMENTS - CENTRAL HEATING
PRV setting
bar 3.0
Vessel charge pressure
bar
0.5 to 0.75
System pre-charge pressure
bar
None
1.0
System volume
Expansion vessel
(litres)
volume (litres)
25
1.6 1.8
50
3.1 3.7
75
4.7 5.5
100
6.3 7.4
125
7.8 9.2
150
9.4 11.0
175
10.9 12.9
190
11.9 14.0
200
12.5 14.7
250
15.6 18.4
300
18.8 22.1
For other system volumes
multiply by the factor across
0.063 0.074
5. Filling
The system may be filled by the following method:
Where the mains pressure is excessive, a pressure
reducing valve must be used to facilitate filling.
a.
Thoroughly flush out the whole system with cold
water.
b.
Fill and vent the system until the pressure gauge
registers 1 bar and examine for leaks.
Refer to Section
2.18
c.
Check the operation of the PRV by raising the water
pressure until the valve lifts. This should occur within
0.3 bar of the preset lift pressure.
d.
Check no escape of water occurs except at the
discharge point
e.
Release water from the system until the
minimum system design pressure is reached;
1.0 bar if the system is to be pre-pressurised.
Water Flow Rate and Pressure Loss
Max CH Output
kW
24.2
Water Flow Rate
l/min
17.3
(gal/min) (3.8)
Temperature Differential
o
C 20
Head available for System
m.w.g.
3.4
(ft.w.g.) (11.1)
12
Installation and Servicing
Section 1 - General
Table 4 Vessel Sizing
