This Design Clinic shows three different ways you can save energy in an existing corridor without compromising on the quality of the lighting, using products from Ex-Or. We are not altering the light distribution (like some LED tubes do), or lowering the CRI or using super cool light sources. Instead, we are using simple controls that can be retrofitted in to an existing installation – you will have to do a bit of rewiring though.
I’m not the only person whose mind goes a bit blank when confronted with terms like multiple universes, nodes, interoperability and protocols. The secret is to keep things really simple. Start with a small area and then work your way up.
Whenever you install controls, you save energy. This, in itself, is a good thing to do. In most cases, you can also save money. This is an added benefit but the actual amount you save depends on the location, design, how the space is used, combination of controls, dimmability of the light source and so on.
If you are a heavy user of electricity, you can often save extra money by reducing energy at peak times. Some supermarkets save on their maximum demand tariff by reducing the air-conditioning, or cooling to the chiller cabinets, just for short periods of time.
Our corridor is 3m wide and 2.8m high. It is lit to 200 lx using dimmable LED downlights with a dished opal diffuser. There are offices on one side and windows on the other.
The same luminaires are used throughout. Only the type of control used has been changed. In fact, it is possible to combine all three controls to get maximum savings.
One final point that needs to be mentioned is ease of setup. With some other suppliers, commissioning can be a total pain and may even require an outside specialist to be brought in. Ex-Or has devoted a lot of effort developing its QuickSet Pro handheld setup controller.
This is an example of daylight harvesting and is one of the easiest control options to understand. Quite simply, when the daylight is providing sufficient illumination in the corridor, the luminaires are dimmed or switched off.
In essence, a photocell sensor in the corridor detects the illumination level and dims the luminaires as required. Strictly speaking, the sensor is actually reading the luminance of the floor. I.e. how much light is reflected back off the floor and in to the p-cell. The amount obviously varies not only on the illumination level, but also the colour/reflectance of the floor and so these sensors are often commissioned at installation so that they respond to the correct amount of light. Ex-Or offers a sensor which can actually be calibrated to a specific lux level.
The settings will change depending on whether the windows face N, S, E or W.
However, there are several refinements. The first is that people don’t like seeing the light output of a luminaire changing rapidly. This is especially true in offices. You need to ensure that the fade up and down is done slowly. Daylight can vary quite quickly and so Ex-Or include what they call a ‘passing cloud timer’.
Depending on the window layout, it is worth considering whether all the luminaires should be in the same group. For example, some windows may be over-shadowed or of a different size.
Lastly, watch out for shadows. I worked in an office where each luminaire had a p-cell sensor and, at a certain time of day, one of the luminaires switched to 100 per cent output because a strong shadow fell directly under the sensor.
- Control type: Daylight harvesting
- Arrangement: Usually one per line of luminaires.
- Energy saving: Typically, a stand-alone daylight harvesting system will save 10 per cent
Controls can sometimes be difficult to illustrate in a static picture (after all, if the lights were switched off because no-one was there, you would see a black page!) This second option uses PIR controls so that the luminaires only operate when people are using the corridor.
Since there is no daylight, the luminaires are at 100 per cent output. A useful feature is that instead of completely switching off when the corridor is empty, the lighting can be dimmed to 10 per cent output, thus saving most of the energy but still providing some security.
Not all PIR detectors are the same and this unit incorporates a lens mask whereby you can “aim” the detector so it doesn’t trigger unnecessarily. This is particularly useful in open plan offices where you can create a virtual corridor which only triggers when people are passing through. For long corridors, it is worth grouping the luminaires so that they don’t all trigger long before people get there.
If you have ever done a LENI calculation, you will know that it includes a figure for the quiescent power load of the sensors. This is also known as the parasitic load. The Ex-Or unit used here has a particularly low rating at just 150mW.
- Control type: PIR
- Arrangement: Can be used individually or control a group of luminaires
- Energy saving: Varies enormously but can be as much as 25% or even more
If you have to work late at the office, it can be a bit spooky after dark if you are the only one there. If it is a large, open plan office, a properly designed scheme can dim the remoter areas without totally switching them off. The more sophisticated PIR sensors have a dual function of being an absence detector by day and a presence detector by night.
The Ex-Or unit has micro and macro movement detection such that small movements are detected in a reduced zone and larger movement over a wider area.
However, when you are finished work, you may be entering a dark corridor and this is where the “corridor hold” or “pseudo occupancy” function is useful. This links the corridor lighting to the offices so that there is a low level of illumination, say 10% or 20% output, all the time that the offices are occupied. This gives staff a much greater feeling of security because they can see a clearly illuminated route all the way from their workstation to the end of the corridor.
The illustration shows that the first two offices are occupied and the corridor lights are dimmed to 10 per cent. When staff enter the corridor, the lights switch to 100% output. When the corridor is once again empty, timers will then reduce the illumination in the corridor to its default level.
- Control type: Corridor hold
- Arrangement: Linked to office lighting
- Energy saving: Savings compared with having the corridor lights on and increased security compared with corridor totally off