Strategy 3

STRATEGY 3
Installation of Occupancy Sensors in rooms with intermittent occupation
Contents Introduction Working Principle Sensor Types Sensor Settings Sensor Installation Energy Savings Equipment References

1. Introduction

The rooms where lamps are unnecessarily left switched on for long periods of the day are typically the:

Drying rooms
Changing rooms
Canteen
Toilets
Office kitchen
Meeting rooms

Occupancy sensors should be installed in these areas in order to assure that the light is switched of during periods where the space is not occupied.

The system consists of a motion detector, an electronic control unit, and a controllable switch (relay).

In most occupant sensor systems, the motion detector and controller are housed in one package. The power supply and relay comprise another integral unit. In wall box-type sensors, components are integrated into one compact package, designed to fit into an existing switch box.

Occupant sensors can also be connected to low-voltage relay and building automation systems.

Passive infrared sensors (PIR) are triggered by the movement of a heat-emitting body through their field of view. PIR sensors cannot "see" through opaque walls, partitions, or windows so occupants must be in direct line-of-site of the sensor.

Ultrasonic sensors emit an inaudible sound pattern that is disrupted by any moving object altering the signal returning to the sensor (Doppler shift). They are best suited for spaces where line-of-sight view to the occupant is not always available. This type of sensor detects very minor motion better than most infrared sensors.

Dual technology occupancy sensors use both passive infrared and ultrasonic technologies for less risk of false triggering (lights coming on when the space is unoccupied). Combining the technologies requires a more reliable, yet slightly larger and more expensive device.

We suggest for installation of occupancy sensors in construction villages, the use of PIR sensors is sufficient, as a detection of minor motions only would lead to unnecessarily switching of lights.

Most PIR sensors are sensitive to hand movement up to a distance of about 3m, arm and upper torso movement up to 6m and full body movement up to 12m. [1]

§ SENS -- sensitivity sets how far away and how small a movement will trigger the light.

§ TIME -- the length of time the light remains on after the last detected movement

Passive infra-red sensors used in toilets, changing rooms, drying rooms and office kitchen can be set to provide at least 5 minutes of light once activated. In canteen and meeting rooms lights should probably remain on longer after a detected movement.

Passive infra-red sensors could be retro-fitted to the existing lights or mounted to the wall.

Wall-box type PIR occupancy sensors are easy to install. These are best suited for small, enclosed spaces where the sensor replaces the light switch on the wall and no extra wiring is required. In the case of the construction village under investigation these would be best suited for the use in all toilets, meeting rooms and office kitchens.

Occupancy sensor placement is very important to the successful implementation of the control design intent. The layout of space has to be considered by selecting and mounting an occupancy sensor. The optimum mounting location will depend on the shape of the room, the expected location of occupants and potential obstacles such as the lockers in the drying room.

We, therefore, recommend the installation of ceiling mounted sensors in canteen, changing and drying rooms.

Occupancy sensors must be located to ensure that they will not detect movement outside of the desired coverage area, through an open doorway, for example.

According to the US EPA the following energy savings can be realised using occupancy sensors:

Typical values of energy savings for various occupancy areas [1]

Using PIR sensors for intermittent occupied areas of the construction village it is estimated that lights are switched off:

a) at least 80% of the time in toilets, drying room, changing rooms and office kitchen

These estimations take into account the occupancy pattern of the different areas studied at the construction site we have visited.

Occupancy sensors cost in between £10 and £50 dependent on the area they can cover and the maximum time delay available.

For the toilets on construction sites wall mounted PIR sensors are sufficient.

In canteen and changing room it will be better to install ceiling mounted sensors, as these are more suitable for large rooms.

(1) Tsangrassoulis A et al, SynthLight Handbook- Integration of electrical lighting-daylighting, February 2004

§ SENS -- sensitivity sets how far away and how small a movement will trigger the light.

§ TIME -- the length of time the light remains on after the last detected movement

Passive infra-red sensors used in toilets, changing rooms, drying rooms and office kitchen can be set to provide at least 5 minutes of light once activated. In canteen and meeting rooms lights should probably remain on longer after a detected movement.

Typical values of energy savings for various occupancy areas [1]

These estimations take into account the occupancy pattern of the different areas studied at the construction site we have visited.