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SAVING ENERGY WITH AN OFFSET

HOW THE USE OF DAYLIGHT BY CONSTANT LIGHTING CONTROL CAN BE IMPROVED EVEN FURTHER

The energy-efficient use of natural daylight has a role to play not only in architecture, but also in demand-driven building automation. Implementing an additional offset in constant lighting control provides additional potential for savings.

Use energy only when it is really needed: that is the principle behind demand-driven building automation. In terms of light control, presence and daylight dependent constant light control implements this premise particularly well through its energy-efficient use of daylight — although this can be improved even further using a simple concept.

Central perspectives, parallel perspectives and colour perspectives — just like in art, things in buildings can also often be seen from completely different points of view. One example of this is the use of daylight, which has become very important in architecture today. Daylight systems direct diffuse, natural daylight into the depths of buildings to help people in that building feel better and work more healthily. To achieve this, the architect calculates the ratio between the strength of indoor and outdoor lighting, also known as the daylight quotient.

THE PRESENCE DETECTOR — A PARTNER TO ARCHITECTS AND PLANNERS

However, the architect is not just interested in the biological effect of daylight. The optimal use of daylight also reduces energy costs: the more that daylight is used in the building, the less artificial light is required. In this age of energy transition, this concept will become just as important as daylight-dependent constant lighting control with a presence detector. After all, this also achieves the energy-efficient use of daylight. Simply from a different perspective.

The use of daylight by constant lighting control involves dimming lighting to take account of the amount of daylight coming into the building. It works as a sort of congenial partner to the architect. While the architect directs daylight into the building, the presence detector checks how successfully this process is working. The architect uses the daylight quotient as a basis for calculations, and the presence detector is guided by the nominal level of brightness to ensure safe lighting which meets all applicable standards. These two perspectives share a common goal — greater energy efficiency to reduce energy costs and global CO2 emissions.

A SIMPLE SOLUTION TO ENSURE MAXIMUM USE OF DAYLIGHT: OFFSET WITH JUST ONE REGULATING PRESENCE DETECTOR

The presence detector achieves constant lighting control using an integral light sensor. This also means that at least one detector is always required to control the light in a specific room zone. On the one hand, of course it would be ideal to do this in as many zones as possible to optimise the use of daylight. However on the other hand, it makes little sense to increase the number of detectors simply to achieve this.

So what do we do? This is the question that automation experts were also faced with — and they found a simple but effective solution: an offset between multiple lighting groups controlled by a presence detector. In other words, an offset that improves the use of daylight even if there is only one detector installed in a room. A first example of how it works is provided by the DUO DALI presence detectors in the COMPACT series from ESYLUX, which control two light channels in broadcast mode.

DUO DALI FOR TWO LIGHT CHANNELS

Classrooms are a typical application for DUO DALI presence detectors. These rooms generally have windows on only one side, which creates the perfect conditions for an offset. This is because the lighting required in the zone near the windows differs massively from the zone further away. The two zones are therefore each allocated to a different light channel of the DUO DALI (Fig. 1).

After installation, the detector is immediately ready for use with the default settings. To enable both light channels to be controlled through the offset, however, an adjustment has to be made using the remote control or the ESY-App. This requires a fixed offset between channel 2, the zone away from the windows, and channel 1, the window side. The optimal size of the offset depends on the actual room situation, but in many cases it is 30 %, which is why this value has been used here as an example.

Fig. 1: As this planning example shows, lights further away from windows and those nearer to the windows in a classroom are each assigned to a different light channel of the DUO DALI.

DIFFERENT LIGHTING NEAR THE WINDOWS AND FURTHER AWAY

The following now occurs when the lights are used: As the daylight entering the classroom increases during the morning, the detector initially dims only the lights near the window. The zone away from the window still needs 100 % light output. When the light output from the lights near the window falls to 70 %, the offset of 30 % has been reached. The detector then starts to dim the lights away from the window. Once the daylight is sufficient in both zones, it switches all the lights off.

If it gets darker outside again due to the weather or the time of day, this sequence is reversed. The detector first increases the light output from the lights away from the window while the offset delays the same process for those near the window. Only when the lights away from the window have reached 100 % and the daylight continues to fade does the detector finally also set the lights near the window to full light output. The offset therefore improves energy efficiency through the earlier reduction or delayed increase in light output from the lights near the window as the daylight fades or brightens.

DOUBLE OFFSET OF THE APC PRESENCE DETECTOR

The DUO DALI with offset variant and simple 2-channel broadcast mode has repeatedly proven its worth, making it one of the most popular products with ESYLUX customers over the years. However, anybody requiring a more flexible form of light control can now find a different solution: the APC presence detector for the updated DALI-2 standard, which can control up to 16 groups — and operates using an enhanced offset concept.

Difference number one: APC presence detectors not only enable the use of a single offset between two lighting groups, but can also provide a double offset. This is best demonstrated using a dimming curve (Fig. 2). As it shows, an upper offset can be set between group 2 and group 1 as well as a lower offset between group 2 and group 1. This double offset creates greater flexibility for the design process. Above all, it further increases energy savings.

Fig. 2: The double offset of the APC presence detectors extends the scope for design and further improves overall energy efficiency.

MORE LIGHTING GROUPS = MORE OFFSETS

Another difference is that APC presence detectors allow even more lighting groups to be formed within a room than when using the DUO DALI, all of which can then be controlled by a single presence detector. This also has an effect on the offset concept of the APC detectors: additional double offsets can be set for each newly added group. Figure 3 shows an example: the same room, but now with 3 lighting groups. In addition to group 2 by the window and group 1 further away, there is now group 3 near the door.

In the example, a double offset relative to group 1 is set for both the window group and for the door group. A negative offset for the window group, a positive one for the door group. As the level of daylight increases, the window group is dimmed earlier than group 1, while the door group is dimmed later than group 1. In a room with windows on just one side, this creates a depth graduation that adjusts the lighting even better to the daylight on one side of the room and therefore provides an even greater increase in energy efficiency.

Fig. 3: To adjust the lighting in a room to the incidental daylight even more efficiently, APC presence detectors make it possible to add more groups with an offset.

DUO-DALI-Präsenzmelder und APC-Präsenzmelder für DALI-2 zeigen so auf unterschiedliche Weise, wie sich durch einfache Offsets die Tageslichtnutzung der Konstantlichtregelung weiter verbessern lässt. Und das bei nur einem Melder und damit nur einem Lichtsensor im Raum. Es ist ein einfaches, aber wirksames Konzept, das die Energieeffizienz zusätzlich verbessert, dennoch eine normgerechte Ausleuchtung aller Zonen gewährleistet – und sich insbesondere bei den APC-Präsenzmeldern mit ihren vielfachen Gruppen übrigens ohne Weiteres auch für Räume mit mehreren Fensterseiten einsetzen lässt.

A particularly clear presentation of the functions of the DUO DALI presence detector can be found in the configuration video on our YouTube channel. A tutorial for APC presence detectors can also be viewed there.