Potterton NXR4 Installation, Operation & Maintenance Manual page 8

POTTERTON COMMERCIAL PRODUCTS DIVISION
INSTALLATION, OPERATION & MAINTENANCE MANUAL
NXR4
VENTILATION
Safe, efficient and
conventionally flued boilers is vitally dependent on the
provision of an adequate supply of fresh air to the
room in which the appliance is installed. Account must
also be taken of any other fuel burning appliance
existing or to be fitted when designing the ventilation
and combustion air systems.
IMPORTANT: The use of an extractor fan in the
same room as the boiler (or in an adjacent room in
communication) can,
adversely affect the safe operation of the boiler
and therefore must be avoided.
Further guidance on ventilation for gas appliances is
provided by BS 6644 - 1991. For oil see relevant
Standard.
FLUE
To ensure safe and satisfactory operation the chimney
system, which may be individual or common in the
case of modular boiler installations, shall be capable
of the complete evacuation of combustion products at
all times. The effective height of the chimney
terminal(s) above the boiler(s) flue outlet(s) shall
ensure sufficient buoyancy
resistance of the bends, tees and runs of the flue pipe
involved and shall terminate in a down draught free
zone. The number of bends used should be kept to a
minimum and runs of flue pipe less than 45° to the
horizontal should be avoided in order to comply with
the recommendations made in BS 6644 - 1991 and
British Gas publication IM/11 " Flues for Commercial
and Industrial Gas Fired Boilers and Air Heaters". The
third edition of the 1956 Clean Air Act Memorandum
and Building Regulations should be strictly observed
and approval obtained where applicable, combustion
chamber details are given in Section 1.
IMPORTANT: 90° square bends must not be used
on the flue system, including the boiler flue
spigot, a straight length followed by an "easy
sweep" or lobster back bend should be used.
FLUE SIZE CONSIDERATIONS
Nominal flue connection sizes are given in Table 3,
these sizes refer to the boiler flue connection spigot.
The actual size of the flue system will depend on
individual site applications.
considerations on sizing flue systems.
Horizontal Flue Runs
Horizontal flue runs are not recommended particularly
over 3m in length, where these are unavoidable
advice should be sought from a flue system specialist.
trouble free operation
in certain conditions,
to overcome
Below are general
Common Flue Systems
of Where multiple boilers are installed on a common flue
system the flue system should be designed to ensure
the correct operation of the flue on varying load
conditions. For the safe and reliable operation of the
boiler plant it is recommended that the variance in flue
draught available at each appliance under full and part
load operation is designed to a minimum.
(It is essential that the services of a flue specialist
flue system manufacturer are sought for design of
common flue systems).
For further information regarding ventilation and
flueing see Potterton Technical Bulletin No.4, current
issue or see relevant British Standard publication
BS6644 - 1991.
THE ABOVE RECOMMENDATIONS ARE FOR
GENERAL
COMMERCIAL
RESPONSIBILITY FOR FLUE SYSTEM DESIGNS
BASED ON THE ABOVE RECOMMENDATIONS.
WATER CIRCULATION SYSTEMS
The water circulation system should be indirect and
the installed in accordance with the relevant parts of
British Standards Codes of Practice CP342.2 and
BS 6644 - 1991.
The maximum and minimum design temperature
differential across the boiler should be 20°C and 10°C
and the boiler should be prevented from operating
with flow rates giving a temperature difference across
the boiler greater than 25°C based on the full boiler
output.
Boilers operating under constant flow conditions can
be more accurately controlled and are not subject to
excessive temperature stresses.
The boilers MUST NOT be fired under any
circumstances with less than the minimum water flow.
On systems with variable flow rates due to flow
reducing devices, ie. TRVs, zone valves, etc, or where
the minimum heat demand, ie. Summer domestic hot
water load, does not achieve the minimum boiler flow
rate then consideration shall be given to incorporating
a primary loop system.
It is recommended that the system is designed to give
a constant boiler flow rate. For further information on
water circulation systems see Potterton Technical
Bulletin No. 1 current issue.
SECTION 3
GUIDANCE ONLY.
DIVISION CANNOT
PAGE 7
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