Ventilation Rates

The building regulations require those habitable rooms and toilets are to be vented by natural or mechanical means.

Natural Ventilation

A habitable room requires one or more ventilation openings, the total area of which must not be less than 1/20 th. of the floor area of the room, and some part of the opening must be more than 1.7 metres above floor level.

When ventilation is by mechanical means, one air change per hour must be provided to habitable rooms and three air changes per hour to bathrooms and kitchens.

Design Criteria

To design a ventilation system, the engineer has to meet two basic requirements:

1. To supply fresh air for the occupants

2. To change the air in the room sufficiently so that smells, fumes and contaminants are removed.

Ventilation Rates in CIBSE guide

The following table gives Ventilation Rates for buildings.

Table 3.1 CIBSE Guide B2 (2001) Summary of recommendations

(Extract from Table)

 

Building sector

Section

number

Recommendations

Animal husbandry

3.24.1

See Table 3.20

Assembly halls

3.3

See Table 3.6

Atria

3.4

See section 3.4.3

Broadcasting studios

3.5

6 -10ACH (but heat gain should be assessed)

Call centres

3.24.2

4 - 6 ACH (but heat gain should be assessed)

Catering (inc. commercial kitchens)

3.6

30 - 40 ACH

Cleanrooms

3.7

See Tables 3.11 and 3.12

Communal residential buildings

3.8

0.5 - 1 ACH

Computer rooms

3.9

See Table 3.13

Court rooms

3.24.3

As for typically naturally ventilated buildings

Darkrooms (photographic)

3.24.4

6 - 10 ACH (but heat gain should be assessed)

Dealing rooms

3.24.5

As offices for ventilation (but heat gain should be assessed)

Dwellings (inc. high-rise dwellings)

3.10

0.5 - 1 ACH

Factories and warehouses

3.11

See 3.11.1 for regulatory requirements

High-rise (non-domestic) buildings

3.12

4 - 6 ACH for office areas; up to 10ACH for meeting space.

Horticulture

3.24.6

30 - 50 litres/s/m2 for greenhouses (45 - 60 ACH)

Hospitals and health care buildings

3.13

See Table 3.15

Hotels

3.14

10 - 15 ACH minimum for guest rooms with en-suite bathrooms

Industrial ventilation

3.15

Sufficient to minimise airborne contamination

Laboratories

3.16

6 - 15 ACH (allowance must be made for fume cupboards)

Museums, libraries and art galleries

3.17

Depends on nature of exhibits

Offices

3.2

See Tables 3.2 and 3.3

Plant rooms

3.18

Specific regulations apply, see section 3.18

Schools and educational buildings

3.19

See Table 3.18

Shops and retail premises

3.20

5 - 8 litres/s per person

Sports centres (inc. swimming pools)

3.21

See Table 3.19

Standards rooms

3.24.7

45 - 60 ACH

Toilets

3.22

Building Regulations apply; opening windows of area 1/20th of floor area or mechanical ventilation at 6 litres/s per WC or 3 ACH minimum for non-domestic buildings; opening windows area 1/20th of floor area (1/30th in Scotland) or mechanical extract at 6 litres/s (3 ACH in Scotland) minimum for dwellings.

Transportation buildings (inc. carparks)

3.23

6 ACH for car parks (normal operation)

10 ACH (fire conditions)

 

 

The Table below gives Ventilation rates required to limit CO2 concentration where level of activity is known.

Table 3.2 CIBSE Guide B2 (2001) Ventilation rates required to limit CO2 concentration for differing activity levels

Activity

Minimum ventilation requirement

Litres /s per person

0.5% CO2 limit

0.25% CO2 limit

Seated quietly

0.8

1.8

Light work

1.3 2.6

2.8 5.6

Moderate work

2.6 3.9

N/A

Heavy work

3.9 5.3

N/A

Very heavy work

5.3 6.4

N/A

 

The following table gives fresh air rates.

Table 3.3 CIBSE Guide B2 (2001) Recommended outdoor air supply rates for sedentary occupants.

Level of Smoking

Outdoor air supply rate (litre/s per person)

No smoking

8

Some smoking

16

Heavy smoking

24

Very heavy smoking

36

The table below is an extract from Table 3.6 and gives rates for Assembly Halls and Auditoria

Design Requirements : Assembly halls and auditoria

Parameter

Design requirement

Fresh air ventilation rates

To suit occupancy levels

Air change rate

3 4 air changes per hour for displacement strategy

6 10 air changes per hour for high level mechanical strategy

 

Ventilation Calculations

The following formulae may be used:

1. For General Mechanical Ventilation

Ventilation rate (m3/h) = Air Change Rate (/h) x Room Volume (m3)

Air Change Rate (/h) comes from CIBSE Guide B2 Table 3.1

Ventilation rate (m3/s) = Ventilation rate (m3/h) / 3600

 

2. For Calculating Fresh Air Ventilation Rates

Fresh Air Rate (m3/s) = Fresh Air rate per person (l/s/p) x number of occupants

Fresh Air rate per person (l/s/p) comes from CIBSE Guide B2 Table 3.3.