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Section 6
Sealed and Open Vent Systems & Equipment
FIG 6.1
SAFETY VENT, EXPANSIONS, COLD FEED AND PRIMARY CIRCUIT DESCRIPTIONS
Expansion
Vessel
Optional
Filling Point
NRG ZONE
Zones
FIG 6.2
Expansion Tank
NRG ZONE
Cold Feed
with
Heat-Lock
Loop
It is always recommended to over-size a system expansion vessel to avoid later problems. The
point of connection of the expansion vessel into the system is important. The ' pressure-neutral
point' of an NRG ZONE is perfectly suitable to allow open access to any appliance connected to
the expanding system volume as the system contents heat and cool. The physical location of
the vessel can be at any convenient unused port in the NRG ZONE giving maximum flexibility, or
can be directly on the inlet side of the heating appliance.
If a system is extended, an expansion vessel of increased volume (or an additional vessel) may
be required, unless previous provision has been made for the extension. The vessel charge pressure (1.5 bar standard) should not be less than the static head pressure at the centre of the expansion vessel. For static heads greater than 15 metres, the vessel charge pressure should be
increased. As a guide, the expansion vessel is undersized if the pressure gauge indicates 2.65
bar or above when the boiler is at maximum temperature with all radiators or other zone distribution equipment in circulation. In such a case, a larger (or additional) expansion vessel is required. (Note that an appliance safety valve will commence over-pressure discharge at around 3
bar). It is also important that the discharge outlet from either safety valves or Automatic Air
Vents (AAV) should never be located directly above the NRG ZONE unit as inadvertent leakage
may go unnoticed and corrode the manifold.
When installing an 'open' system for a temperature controlled oil or gas boiler it is essential to
ensure that the appliance has an unrestricted open vent and separate cold feed. It is also good
practice to prevent heat rising in the cold feed pipe. This would warm the expansion tank contents which would evaporate and cause more fresh water to enter the system and damage the
ferrous parts. The example at FIG 6.2 shows how a heat-lock loop could be formed to prevent
that occurrence.
The cold feed and expansion pipe may be connected separately to the manifold if the expansion
pipe rises adequately above the tank. Fig 6.2 shows a 'double T' configuration from connections
'T2 & T3 on the cold feed and expansion which may
be useful by serving two functions;
FIG 6.3
NRG ZONE with Heating
Priority Configuration
1) it will create a vent for the cold feed loop &
2) it will also minimise any inadvertent
'pitching-over' of water from
the expansion to the tank.
Zones
When installing a solid fuel heating system it is essential to ensure
that the appliance has an unrestricted open vent and separate cold
feed. Possible solutions are illustrated at Fig 6.3 & Fig 6.4.
P1
NRG ZONE with DHW
Priority Configuration
An expansion header tank is located at the highest point in the system and a
cold feed connected through a 'heat-lock' loop as shown. The optional by-pass methods shown in Figs 6.3 & 6.4 connect the expansion pipe through a 'Flap type' non-return
valve on a horizontal pipe run and into the return on a the vertical rise from the heat-lock
loop. This method is useful when the height of the expansion pipe is restricted.
FIG 6.4
The optional expansion pipe to return by-pass strategy shown will minimise the
possibility of water rising in the expansion pipe and pitching-over into the tank
which is a trait commonly found in poorly configured open systems.
Both methods shown provide the pre-requisite safe primary gravity fed heat-leak circuit through the DHW cylinder. However, Option one (Fig 6.3) will make the primary
circuit heat available for heating in the NRG ZONE manifold before it heats the Hot Water cylinder. Option two; Fig (6.4) will make the primary circuit heat available for heating
hot water in the cylinder before it reaches the NRG ZONE manifold. In both instances the appliance's pump (P1) should be thermostatically controlled by a pipe thermostat fitted on the
return to the appliance to turn the pump 'ON' above 55°C. This will prevent condensation
forming in the fire-chamber which would otherwise damage the appliance.
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P1