BENSON OUH 2 100, Installation And Operating Manual, Page: 11 / 44

1.11 Air supply
Consideration must be given to the provision of air for the
purposes of combustion and ventilation of the heated space,
plant room or enclosure where heaters are to be installed.
It is a requirement that the area where the air heater is located
must have a permanent air vent of negligible resistance direct
to the outside air.
Such air vents must be positioned so as not to become
blocked or fl ooded, nor should they be placed so as to
introduce undesirable matter (e.g. fl ammable, volatile, or
aggressive chemicals/compounds or potentially hazardous or
harmful substances) either direct from the outside, or through
their proximity to an adjacent extraction system.
Note:
It is strongly recommended that BS6230 is referred to for
further information concerning ventilation requirements
Where mechanical ventilation is used it is a requirement that
the inlet is of the mechanical type, and the outlet is either
mechanical or natural.
1.11.1 Heaters installed within the heated space.
Where heaters are installed within the space to be heated (i.e.
not a plant room or enclosure) then:
Combustion air or heater related ventilation air will not be
required if -
• The design air change rate of the heated space is 0.5
air changes per hour or greater
or
• The design air change rate may be satisfi ed by natural
infi ltration or by mechanical ventilation
Combustion and General ventilation will be required if -
• The design air change rate of the heated space is less
than 0.5 air changes per hour
or
• Where the heated space has an air change rate of less
than 0.5 air changes per hour then it will be necessary to
provide either natural ventilation openings to the heated
space (section 1.11.1.1. refers) or the mechanical ventilation
of the heated space (section 1.11.1.2. refers)
1.11.1.1 Natural Ventilation Openings to the Heated Space.
If the heated space design air change rate is less than 0.5
air changes per hour then provision for low level natural
ventilation openings will only be necessary.
The minimum free area of the low level natural ventilation
opening shall be:
• 2cm2 for each kW of rated heat input
The low level natural ventilation opening should be situated
on an external wall and be within 1000 mm of fl oor level.
The following table provides specifi c data for each heater
model as -
Minimum Free Area of ventilation
opening
Model
High Level cm² Low Level cm²
40
None 88
60
None 128
70
None 166
90
None 192
100
None 230
1.11.1.2 Mechanical Ventilation to the Heated Space.
In the event that the heated space has a design air change of
less than 0.5 air changes per hour and that installer prefers to
mechanically ventilate the heated space rather than provide
ventilation openings then:-
• The heated space needs to be mechanically ventilated
so that the design air change is 0.5 air changes or greater.
• It is a requirement that the mechanical ventilation shall
be of the ‘input’ type with either natural or mechanical
extraction.
• Systems of mechanical extraction with a natural inlet
shall not be used.
It is necessary to provide an automatic means to safely inhibit
heater(s) operation should mechanical air supply fail for any
reason.
1.11.2. Heaters Installed within a Plant Room or Enclosure.
A plant room means a room housing the heater plant and
probably other items of building service plant and would
generally have generous space for maintenance.
An enclosure is where the heater is installed within a
compartment or confi ned area where space is limited.
Where heaters are installed within a plant room or enclosure then
provision for both combustion air and air for general ventilation
will be required by means of high
and
low level ventilation