BENSON VRBD 250 - Page 11

the design air change rate of that heated
space is less than 0.5 air changes per hour,
then provision for low level natural ventilation
openings only will be necessary.
The minimum free area of the low level
natural ventilation opening shall be
 2 cm
2
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 floor level for natural gas
and ideally at floor level for lpg gas
installations but in any event no higher than
250 mm.
The table below provides specific data for
each heater model as -
2.4.1.2 Mechanical Ventilation to the
Heated Space
In the event that the heater(s) are to be
installed without the positive connection of
combustion ductwork within a heated space
and where that heated space has a design
air change of less than 0.5 air changes per
hour and that the 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
per hour 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
2.4.2 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 confined area where
space is limited
Where heaters are installed within a plant
room or enclosure then provision for both
combustion air and / or air for general
ventilation will be required by means of high
MODEL
Minimum Free Area Of
Ventilation Opening
High Level Low Level
cm
2
cm
2
250 394 394
330 527 527
410 656 656
490 787 787
MODEL
Minimum Free Area Of
Ventilation Opening
High Level Low Level
cm
2
cm
2
250 158 316
330 211 422
410 263 525
490 315 630