The most efficient lighting design is when the lighting is switched off, so how do sensors to provide efficient control?
The best way is to maximise the use of natural daylight with dimming ballasts installed in the light fittings. Once occupancy is detected, the sensor measures the natural light, compares this against the pre-determined light level and turns the fitting on to the required level.
Sensors are now available which can set three different lighting bands/zones for the same area, such as for school classrooms. For example, one zone for the area near the windows, another for the internal area and a third for the presentation/teacher area.
The lights are controlled on one occupancy control but switches can provide automatic and semi-automatic function, in this example, near the entrance and next to the presentation area and different light levels to ensure an overall balance.
The other development is controlling the lights and heating/ventilation with one sensor, so reducing wasted light, but also used to only have extractor fans on in a washroom, for example, when occupied. The run on times can be set individually and fan costs can also be reduced, with the timer controlled models.
For the more sophisticated building management systems, sensors with built-in thermostats, such as the PD2N-LTMS-DE from automation lighting control specialist B.E.G.
This detects the three most important values of a room: temperature, the light level on the ceiling which transmits the measured values to two 0 to 10V interfaces and, thirdly, movement, which is reported via a switch contact. This information then can be used for closed (proprietary) BUS-systems (e.g. LON or SPS) and DALI-systems.
The type of light fittings has changed, with LEDs now seen as the holy grail of efficiency. However, care must be taken to ensure that this efficiency is matched with occupancy control. Sensor control will extend the lifespan but must be able to cope with the large in-rush currents. This is why it is crucial that the sensors are fitted with reputable relays, such as the schrack relays, used by B.E.G.
To gain the most from the investment, the less detectors used and the greater the amount of lights that can be switched, the better. However, again attention must be made to ensure that there is the correct coverage.
The German manufacturer has developed sensors with built-in microphones that react on occupancy with the delay time reset on sound as well as movement. This means, for example, in a washroom there is no need to install a sensor over each cubicle; one centrally mounted sensor will provide the correct detection.
The other way to reduce energy costs is to install sensors with bigger detection patterns. Standard detectors provide 10m detection (4m seated, 6m walking towards and 10m walking across), but sensors such as the company’s PD4 range provide 24m coverage (6.4m seated, 8m walking towards and 24m walking across). There are also corridor variants, with one sensor switching a 40m corridor.
The market has been demanding smaller, more discrete sensors and with higher IP protection. The new Pico sensor by B.E.G. provides IP65 but is the size of half a Smarties sweet tube. This discrete sensor is particularly suitable for installation in wet rooms and showers, where it is used to control the lights and ventilation.
For the time being, standalone systems offer the fastest return on investment, sometimes in less than one year. However, as energy prices continue to rise, the usage of occupancy detectors to control air conditioning, heating and for generating occupancy data, open protocol bus systems, like KNX sensors, will become more and more viable.
Due to the higher installation costs, they are most associated with new builds, such as with the new Co-Operative headquarters in Manchester, which had the PD9 KNX sensors installed. Where there is a need for greater efficiency, control and monitoring, the demand for these systems will rise.
Figure 1; The PD4 sensor range more than double coverage, increasing it to 24m.
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