Easy-to-Install Sensor Charms Tough Buyers
Easy-to-Install Sensor Charms Tough Buyers
California-based Wattstopper won the Swedish technology procurement competition for an easy-to-install and reliable occupancy sensor for private office rooms. Wattstopper, through its European distributor and co-owner Legrand, will deliver 20 000 sensors to a buyer group consisting of some 20 large office building owners over a two-year period.
Images from test room.
In 1996, Swedish Nutek (the Swedish national energy agency before STEM took over in January 1998) announced a technology procurement competition concerning a low-cost, easy-to-install, and reliable occupancy sensor for single-person office rooms. Since electricity prices in Sweden are fairly low, it was paramount that the sensor be cheap. The price of the winning sensor under the 20 000-unit basic ordering agreement is SEK 250 (~US$ 31). The specifications also required the installation and commissioning time to be kept below 20 minutes per sensor. This corresponds to an installation cost of ~SEK 400 (~$50). However, in favorable cases, the sensors can be installed in a few minutes, which would correspond to about SEK 100 ($12.50).
Measured and verified data on the actual savings achievable with occupancy sensors are scarce. However, the buyer group has agreed to use an average 40 percent reduction in operation time in their calculations. This, they think, will yield a 5-10 year payback under the most unfavorable installation conditions.
The buyers also point out that installing sensors in their premises should yield additional "soft" benefits. More specifically, since lighting is a highly visible type of energy consumption, they hope for spin-off benefits in other areas of energy use by showing that something can be done about lighting.
RELIABILITY CRUCIAL
One problem often faced with occupancy sensors is that office staff can get irritated when the sensors switch lights off during working hours. Another problem is that sensors may be turned on inadvertently by airflow or persons passing outside the room.
To avoid such problems, the functional specifications were very strict with regard to these issues. After the technical proposals had been delivered, a few prototypes were selected for testing at the Lighting Research Center in Troy, NY. One of the tests was to assess the ability of the sensor to detect typing movements. A moveable test desk was placed in a mock-up office room. A student was hired to play the computer game "Tetris" at ten-minute intervals at various pre-determined spots in the room. Since only finger movements were to be detected, the test person had to place his or her chin in a chin rest to keep the body still. The legs were also hidden behind a curtain.
OVERALL PERFORMANCE TESTED
A passive infrared (PIR) ceiling-mounted sensor performed best when it came to detecting fine finger movements. However, Wattstopper's wall-mounted PIR sensor not only also performed very well in this respect, but was also excellent in not detecting movements outside the room. Moreover, the winning sensor was the easiest to install and thus had the best overall cost-performance ratio. Project manager Hans Isaksson does not want to rule out ceiling-mounted sensors: "Once these models have been slightly improved, they will be a very competitive option in new installations" he says.
The winning sensor will come configured to be switched on manually, and it will turn off the lights automatically if it hasnŐt sensed motion for 20 minutes. If the sensor detects motion within 30 seconds after it has turned the lights off, it will automatically turn them on again. DIP switches allow users to customize sensor operations, e.g. change the sensor time settings and allow the sensor to always turn on lights automatically when the occupant enters the room. The sensor also has a contact enabling it to be connected to HVAC controls and alarm systems.
Nils Borg
Contact: Hans Isaksson
Tel: +46 704 21 64 64
Email: hans.isaksson@kkonsult.se
More about occupancy sensors in IAEEL newsletter 3/96