Occupancy sensors for the home
Occupancy sensors for the home
Occupancy sensors - or presence detectors - offer good options for minimizing energy use in residential lighting applications while meeting the requirements for safety and convenience.
In many places in and around houses, lighting is only necessary when someone passes by or has to be there for a short while. Such places include access paths to the house, near entrance doors, hallways, corridors, stairwells, cellars, toilets, bathrooms, closets, and garages. The light usually remains on much longer than necessary in those places, often for the sake of convenience or because someone forgets to turn the light off. Exterior lighting usually remains on permanently during the dark hours in order to provide burglary prevention.
Passive infrared and ultrasonic occupancy sensors signal moving objects within a certain range and under certain conditions. After detection the light is turned on, and after a certain length of time (usually set - within certain limits - by the user) it is automatically turned off again.
An occupancy sensor not only limits the use of energy, but is usually also very easy to use, because nobody has to use the switch. This also has implications for disabled and elderly people. The use of a occupancy sensor can also deter unwanted guests because they are suddenly showered in light.
PRODUCT TYPES
Ultrasonic sensors can, in principle, only be used inside. But since these sensors only are manufactured for commercial applications, they will be left aside here.
Passive infrared (PIR) occupancy sensors are available in various versions, both for built-in and wall-mounted fittings, in standard or more advanced versions and for applications inside and outside. The customer can also choose between sensors that switch on one fixture or a group of fixtures, or he or she can opt for detectors that can work in groups. The latter option is particularly interesting for large rooms and around the house or for a large part of it.
For outdoor applications it is usually also advisable to make sure that the detector only reacts within a certain area, to prevent the light from being turned on by any passer-by. Many detectors are available that enable the user to delimit the detection area rather precisely. Often, fixtures with built-in occupancy sensors do not have this option.
In cases where lighting is only needed for very brief moments, compact and other fluorescent lamps are usually not suitable for use with PIR sensors. This is because it takes a while before the lamp reaches full light output, especially in a cold environment.
SYSTEMS INTEGRATION
Recently occupancy sensors were introduced that can be connected to an advanced lighting switch and control system of either programmable or non-programmable type. This makes it possible to, for example, receive a warning in certain rooms if movements in other rooms or areas around the house have been detected.
Such advanced systems require that the standard luminaires be adapted or extended. Unfortunately, it is often difficult or impossible to conceal sensors and wiring units if the house has not been constructed with the wiring for additional controls in mind.
Automatic twilight switches and occupancy sensors are also used in combination, both together in the same fixture or as separate units. The advantage of the combination is that the sensor does not turn on the lights when there is enough surrounding light, even if it detects motion.
SENSOR ENERGY CONSUMPTION
All the above-mentioned switching systems are intended to save energy as well as to offer more convenience. To determine the amount of savings, one must, however, take the energy consumption of the detectors themselves into account.
Nearly all presence detectors and automatic twilight switches continuously use energy as a result of their own losses during standby. This means that they consume energy 24 hours a day. In general, the energy consumption is approx. 1W or less for presence detectors and 0.1-5W for automatic twilight switches, depending on the type and version. In almost all applications occupancy sensors in residential environments will save more energy than they consume. (See also IAEEL No. 3/96)
Rienk Visser
The author belongs to the firm Technical Management in Amersfoort, The Netherlands.
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