ENERGY SAVING USING OCCUPANCY SENSORS

In many organisations light are needlessly left on even when there is no one in the office. Occupancy sensors work by using infra-red to detect the presence of staff and switching the lights off when not required. A typical ceiling mounted Passive Infra-red Detector (PIR) is shown below.

To make sure that the PIR detector does not plunge staff into darkness, enough of them have to be used. For example the “zone” covered by a single PIR is shown below.

If for example the office is bigger than 5 to 7 meters square, then additional PIRs have to be fitted. These can cover a bigger area as shown below.

If a long corridor has to be covered then a more directional PIR detector is required. The PIR and the zone it covers are shown below.

CASE STUDY

How an annual saving of £93 was achieved using occupancy sensors in a shipping area.

The shipping area in a warehouse has lights that consume about 800W. Typically the room is occupied around 3 hours a day when staff go in to carry out shipping. But often they are out of the room to attend to other tasks. However the lights are left on all day.

The cost to install an occupancy sensor in this room was £120. The annual savings from the lights being switched off when the room is unoccupied was 5 (hours a day) x 5 (days a week) x 52 (weeks a year) x 0.8 (kW) x 0.09 (cost per kWh) = £93