1.3.4 Ventilation Requirements for AHU's
Refer to tables detailed on next page for calculated free
areas of ventilation grilles.
Refer to Index 1 for Air inlet/exhaust ue and ventilation
sketches
1.3.4.1 Type B ued installations.
Where AHU's are installed within the heated space (ie
not in a plant room) and having a building design air
change rate of greater than 0.5/h, additional provision for
ventilation is not required.
If the building design air change rate is less than 0.5/h,
additional provision for natural or mechanical ventilation
is required.
These being:
Natural Ventilation: Grilles having a free area of at least
2cm² per kW of rated heat input shall be provided at low
level i.e. below the level of the heater ue connection.
or
Mechanical Ventilation: Must ensure that the space air
change rate is at least 0.5/h, must be of the ‘input’ type and
interlocked to ensure the heaters cannot work if the input
system is not working.
1.3.4.2 Type B ued installations.
Where AHU's are installed in a plant room (ie not within
the heated space)
having combustion air drawn directly
from the room and connected to a ue that evacuates the
products of combustion directly from the room additional
provision for natural or mechanical ventilation is required.
These being:
Natural Ventilation:
There must be permanent air vents communicating
directly with the outside air, at high level and at low level.
For Plant Rooms
Low level (inlet) 4cm²/kw of total rated net heat input
High level (outlet) 2cm²/kw of total rated net heat input
Mechanical Ventilation: The minimum ow rate of
ventilation shall be 4.14m³/h per kilowatt of total rated heat
input.
1.3.4.3 Type C ued installations.
Where AHU's are Installed within the heated space (ie
not in a plant room)
having combustion air ducted to the
appliance and combustion products ducted to the outside
air, NO additional provision for the supply of either
combustion air or for combustion products dilution or
additional provision for the supply of air is necessary.
1.3.4.4 Type C ued installations.
Where AHU's are installed in a plant room (ie not within
the heated space)
having combustion air ducted to the
appliance and combustion products ducted to the outside,
air vents shall be provided and be permanently open.
To room or internal space
Low level (inlet) 10cm²/kw of total rated net heat input
High level (outlet) 10cm²/kw of total rated net heat input
Direct to outside air
Low level (inlet) 5cm²/kw of total rated net heat input
High level (outlet) 5cm²/kw of total rated net heat input.
1.3.5 Burner/Controls Enclosure
Where the ue system is a Type C12 or C32 the burner and
controls enclosure, whether it is part of the unit the module
is tted in or an enclosure in its own right, must meet the
requirement of BS EN1020 Clause 6.1.1.24 i.e. the air leakage
rate from the enclosure shall not exceed 0.5m³/h per kW of
heat input, with a maximum of 25 m³/h.
With the ue connected the terminal is sealed, any access
door is closed and the gas inlet is isolated. Air is passed
into the appliance via a ow meter and the air ow rate is
noted when the pressure inside the enclosure is steady at
0,5mbar above the atmospheric pressure.
NOTE A convenient method of testing the
appliance is to enclose the terminal in a plastic
bag into which an air entry pipe and tube
connected to a pressure gauge can be tted.