Guidance on the Control of Odour and Noise from ... - Defra

More detailed description and input data are given in HVCA publication DW
171 [21] and CIBSE guide B [11] .
4. Air Changes Method: A per hour vent rate equivalent to 40 times the ventilation
volume is considered minimum for comfort under normal conditions, but rates as
high as 60-100 volumes per hour may be required where high-output equipment
is densely located. Using this method air will may be extracted via both a hood
extract and a ceiling extract.
5. Linear Extract Method: Each linear meter of active filter length is assigned a
vent rate depending on the vent canopy type.
6. Meals Method: Extract rate in litres/sec is expressed as 10-15 times the number
of meals served per hour.
7. Area Method: Area of the cooking space in m 2 is multiplied by 15-20 litres/sec to
give an approximate volume flow rate.
Table 4.1 Recommended Canopy Types
Canopy type
(see figure 4.3)
Light duty Medium duty Heavy duty Extra heavy duty
Wall mounted 0.23-0.31 (m 3 /s) 0.31-0.46
(m 3 /s)
Single Island 0.39-0.46 (m 3 /s) 0.46-0.62
(m 3 /s)
Double Island 0.23-0.31 (m 3 /s) 0.31-0.46
(m 3 /s)
Eyebrow 0.23-0.39 (m 3 /s) 0.23-0.39
(m 3 /s)
Passover/Backs
helf
4.2.3 Make-up air
0.15-0.31 (m 3 /s) 0.31-0.46
(m 3 /s)
39
0.31-0.62 (m 3 /s) >0.54 (m 3 /s)
0.46-0.93 (m 3 /s) >0.85 (m 3 /s)
0.39-0.62 (m 3 /s) >0.77 (m 3 /s)
-- --
0.46-0.62 (m 3 /s) not
recommended
In order for a kitchen extract system to function correctly the overall design must
include provision for make-up or replacement air. Air can be made up either by
natural infiltration or by using a mechanical supply. If a mechanical input system is
used, typically 85% of air will be provided mechanically and the remaining 15% by
natural means.
The Food Safety (General Food Hygiene) Regulations 1995 [20] require that
‘mechanical air flow from a contaminated area to a clean area must be avoided’.
Mechanical systems offer a greater degree of control and avoid:
• Unfiltered air entering the kitchen;