BENSON AH150 - Minimum Space Requirements; Air Distribution System

2.10 Minimum space requirements
The minimum space requirements for single and multiple heater applications are detailed in
section 3.3
later within this manual.
2.11 Air distribution system
All materials used within the construction of the delivery and return air ducts must not represent
a fire
hazard and should be made from thermally inert materials. The selection of materials must
take account of the environment into which the heater and its air delivery system is expected to
work, it must also take account of the stresses and loadings placed upon it during its normal
working life. Where interjoist spaces are used to route ducting these must be lined with fire resistant
insulation material.
In installations
where forced recirculation is a feature, a full and unobstructed return air path to
the heater(s) must be provided, with return air grilles connected by ducting directly to the return air
inlet
on the heater. The limit for recirculation should not be greater than 85 % recirculated air to 15%
fresh air.
Where
the heater is installed within a compartment or plant room the return air and discharge air
arrangement must be such that the air circulation fan does not interfere with the operation of the
flue.
The return air intake and warm air outlet should therefore be fully ducted to and from the
heater respectively, within the compartment or plant room. If the inlet air is ducted to the outside,
then the lowest edge of the inlet air duct must be at least 500mm above the outside floor or ground
level, it must also be fitted with an access point(s) to allow for cleaning and servicing to occur. The
openings in the structure of the plant room, through which the duct work passes must be of fire
resistant material
and constructed to prevent the likelihood of any fire from spreading .
In
ducted applications the ductwork must be designed so as to give a static pressure within the
limits
stated in section 8 of this manual. It should be noted that if the static pressure is too high ,
nuisance
shut-down will occur when the heater goes out on the overheat limit thermostat, if the
static
pressure is too low, then damage can be caused to the fan motor .
Warm air outlets on ducted applications must be such that they cannot be closed or become
blocked, which again would lead to an increase in static pressure and nuisance shut-down. The
outlets
must not be sited so that warm air can be discharged onto combustible materials, if necessary,
guard rails should be used to ensure that effected areas are kept clear. Return air intakes must not be
located so
that potentially harmful or hazardous contaminated air can be drawn into the system.
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