BENSON 30 - Air Supply Requirements

Doc No. 20-45-159 Page 8 of 60
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.
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 satised by natural
in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 oor level for
natural gas but no higher than 250 mm.
The following table provides specic data for each heater
model as -
Minimum Free Area of ventilation
opening
Model High Level cm² Low Level cm²
30 None 64
40 None 97
60 None 127
85 None 193
120 None 257
135 None 291
180 None 386
205 None 460
235 None 515
300 None 623
375 None 847
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.
1.12.2. 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 con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