The Problems:

•	Tobacco Smoke
•	Body Odours
•	Heat and fumes from office equipment
•	Solar heat gain

Solutions:

OFFICES: Air change rate per hour 6 minimum

Smokey, airless offices increase fatigue with consequent loss of concentration, efficiency and encourage the spread of infections. As occupants are sedentary, draughts from open windows are a nuisance; the windows are kept closed and mechanical ventilation is a necessity.

Single Offices
Ensure that the unit is sited as high as possible and opposite to the main source of air replacement (usually the door), but try to avoid placing the unit right behind the occupant - this may create a draught. If the door is normally closed, fit air replacement grilles in or near the door. An air intake facility is useful for warmer periods. Site the controller within easy reach of the occupant.

Larger Offices
These are treated in the same way as small offices, except that more units are required and air replacement has to be treated with greater care. The use of a number of units at high level enables a well distributed airflow to be achieved; fit air replacement louvres at high level to deflect incoming air to ceiling upwards.

Controllers can either be centralised, or individuals can be given control over their own microenvironment.

INTERNAL OFFICES: Air change rate per hour 6 minimum.

These areas may be ventilated by means of units mounted in the wall or ceiling, and ducted via adjoining areas or ceiling voids to atmosphere. Where noise or fumes exist, a further ducted input system may be required. Where dust is a problem, suitable filters can be incorporated.

PHOTOCOPIER ROOMS/MACHINE OFFICES: Air change rate per hour 15 minimum

These areas are generally complicated by a heat problem and persistent dust and fumes which can present health hazards. Local "spot" extract ventilation will prevent pollution becoming widespread. Ensure that the scheme complies with local authority by-laws and fire regulations.

SANITARY ACCOMMODATION - W.C. areas should be ventilated at 3 ACH or 6 l/s/WC to meet Document F1 requirements. These figures should be regarded as a minimum. Where toilet suites occur, care must be taken to avoid cross talk especially via ductwork. Special provision should be made for disabled W.C.'s: a minimum of 10 ACH should be allowed.

Size and Number of Ventilation Units

Calculate the volume of the room (height x width x length) and multiply by ACH. This equals the minimum volume required per hour. In busy offices, the rate should be increased to 10 air changes per hour and where a solar heat gain problem exists, 15 air changes per hour minimum. Choose the size and number of units from the output table to ensure that this minimum volume is achieved.

Axial fans	Output Range
150 mm ø	225 - 285 m³/h
190 mm ø	325 - 425 m³/h
230 mm ø	510 - 710 m³/h
300 mm ø	1190 - 1560 m³/h