Controlling energy costs in public spaces is clearly a cornerstone requirement for the move to a sustainable environment. There are numerous opportunities for energy cost containment in this arena including the use of renewable energy plants, development of green buildings and more energy efficient use of HVAC systems. The key to energy optimization is the ability to know, in real time, what the occupancy state of a facility or public space is in relation to the energy use. To accomplish this, it is necessary to implement a monitoring and control process for determining occupancy levels across various spaces, from individual rooms to building floors and multiple building sites.

I have been fortunate enough to have been involved in the early prototype stage of an occupancy tracking project that aimed to accomplish this via the installation and monitoring of office space. The goal of this project was not focused on environmental control, but rather, the determination and assessment of office space utilization. The purpose here, was to provide historical usage pattern information to companies trying to effectively allocate and use expensive office real estate. As such, these monitoring installations were temporary in nature and were not focused on real-time data acquisition.

The technical implementation however, was similar enough to real-time monitoring to allow for a useful comparison with environmental control. There are only a few major components that are required to implement a successful occupancy monitoring system. There are also a few significant technical challenges, and more than a few 'social' challenges with occupancy sensing.

The components of an occupancy sensing system are: a set of sensing devices capable of transmitting meaningful data packets in fairly short intervals; a data aggregation device to collect and store the data (at least temporarily); and a monitoring and control application that can both monitor the state of the system and provide control information to HVAC and lighting systems in response to the incoming data. In addition, it is usually desirable to have an analysis component – some sort of business intelligence system – that can provide usage pattern analysis for further refinement of the system.

All of these components exist and are fairly mature technologies. The challenge from a technical point of view is getting all of the pieces talking. Sensors need to be accurate in the ability to distinguish real occupancy from noise and also broadcast results frequently enough to maintain a good response from the environmental control units. Interval ranges can be from a few seconds to as long as ten minutes, depending on the amount of real-time responsiveness desired. Most systems like this are wireless unless they are built in during the construction phase. Wired installations can be prohibitively expensive and problematic to upgrade. Wireless devices on the other hand, can be installed retroactively in an existing facility and upgraded more frequently. Cost is a factor. If the facility or campus is large, the number of devices can be large. Sensing technologies based on infrared or vibration typically have a limited range but are much less expensive per unit than other options (video, sonic, etc).