This post will outline some of the easiest ways to save energy
using KNX lighting control. In the post, I will lay out a few common options
that you should consider adding to your building automation system design.
I'm assuming that you are not completely novice at this, and have installed LED downlights and flood lights, T5 tubes and CFL wall lights, as opposed to the power-sapping "old school" incandescent and halogen bulbs.
Interestingly, the real power consumption of a CFL is more than double what is written on the package, because the power factor angle is conveniently not taken into account when providing the reading, but that's a story for another blog post.
Presence detectors
Presence detectors are devices that work in the same way as
the PIR (also known as an “eye”) from conventional alarm systems, except that
they are a lot more sensitive. A good brand of KNX Presence detector like the ones from ABB will also have
built in lux meters (light intensity meters), so that the lights will not be
turned on unnecessarily if there is enough natural light in the room.
Presence detectors send a “switch on” message onto the KNX
bus whenever movement is detected in the room. Then, if no movement is detected
for an amount of time (you can choose this time), it will send a “switch off”
message onto the bus so that the lights can be turned off.
It is important to use good quality presence detectors that
can detect small movements , otherwise (I have seen this in a building – it is
funny to watch) the people in the room will be left in the dark if they sit
still for too long, and they will need to wave their arms to turn the lights on
again.
The energy saving from presence detectors comes primarily from our
lazy nature as human beings. When going into a room, and leaving it again,
people are often lazy to switch off the light again. The result is that a
massive percentage amount of the total energy for that room will be wasted.
Presence detectors also make the use of a building more easy
and functional. I work in an office building where all lighting is automated
(ok, I was the person who did the automation, so maybe I am biased)
Nonetheless, when I go to another office building that is not
automated, it is suddenly strange for me to turn on the lights manually. I
think to myself “why doesn’t the building know I am here”?
I also use presence detectors to turn off the air
conditioners when nobody is present in the room. If you work in an office, and
have ever left the air conditioner on overnight accidentally, and needed to sit
in a “fridge” the next morning, you will know what I am talking about.
Brightness control
Most rooms in a building allow a considerable amount of
natural light into a room.
The maximum available natural
light is next to the window, but the natural light decreases further
into the room.
It stands to reason that if a luminary (light fitting) next
to the window is at full brightness, then that electricity is being wasted.
However, as the distance of the fittings from the window increases, so the
brightness of the lights must also be increased.
Another advantage of dimming a fluorescent tube, is that the
life of the tube is significantly increased as opposed to being left at 100% brightness.
This saves on the cost of maintenance, as well as of the tubes themselves.
KNX dimmers which cater for brightness control can be used
to effectively light a room to the required brightness without wasting any
power on unnecessary light. They will also require a lux meter to determine the
light level in the room at the time.
If your dimmer does not support this function, then a cost
effective way of achieving this goal is to use a scene to switch on the lights
instead of simply an on/off signal.
For example, if you have 8 light ballasts in a room, create
8 Group addresses for that room (one for each ballast), and set the operation
of the light switch to send a scene when pressed.
Then you can define the brightness for each ballast
(increase the percentage for each ballast further from the window). Please
remember to still allow “all on/off” for night operation.
Using the above simple techniques, you can really minimize
the running cost of your building associated with lighting.
Be sure to see my next blog to see how to save energy using
HVAC.
