Potterton Derwent Compact Plus Installation, Operation & Maintenance Manual page 8

SECTION 3
PAGE 6
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 in certain conditions adversely
effect the safe operation of the boiler and therefore
must be avoided.
Further guidance on ventilation for gas appliances is
provided by BS 6644: 1991 and BS 5440 1989 Part
2.
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 to overcome the
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 the Building Regulations should
be strictly observed and approval obtained where
applicable, combustion chamber details are given in
Section 1.
The flue system must be designed to work
specifically to remove the products of combustion.
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 technical
data Table 3, these sizes refer to the boiler flue
connection spigot.
The actual size of the flue system will depend on
individual site applications. Below are general
considerations on sizing flue systems. These notes
INSTALLATION, OPERATION AND MAINTENANCE MANUAL
trouble free operation
POTTERTON COMMERCIAL PRODUCTS DIVISION
DERWENT COMPACT PLUS - CONDENSING
are for guidance only and Potterton Commercial
Division cannot accept responsibility for any flue
of system designs.
Horizontal Flue Runs
Horizontal
particularly over 3m in length, where these are
unavoidable, advice should be sought from a flue
system specialist.
Common Flue Systems
Where multiple boilers are installed on a common
flue system then the flue system should be designed
to ensure the correct operation of the flue on varying
load conditions. In particular that the appliance flue
draught is within the operating parameter under full
load and partial load conditions. For 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 specialist flue
system manufacturer are sought for the 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
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 20°C based
on the full boiler output. Boilers operating under
constant flow conditions can be more accurately
controlled and
temperature stresses.
flue runs are not
GUIDANCE ONLY.
DIVISION CANNOT
are not subject
recommended
POTTERTON
ACCEPT
to excessive