We have recently started a long term feasibility study which involves using occupancy sensing technologies.  Such technologies have been used in the past to control lights.  However, our approach is fairly unique in that we will also control individual space heating, ventilating and air conditioning based on occupancy.

The rationale behind this is that even though a building may be substantially occupied for more than 12 hours a day, individual offices and classrooms may be empty for extended periods of time.  Office occupants go to lunch, meetings, teach class, etc.  Conference rooms stand empty.

Classrooms may go unused for one or more time slots.  When such spaces are unoccupied, substantial energy savings can be realized by not only turning off lights, but also automatically eliminating ventilation and allowing space temperatures to drift a degree or two.

Our preliminary estimate based on real occupancy data yields an annual savings of $70 - $90 per typical 120 square foot office.  Given equipment installation costs of $180 - $200, a simple payback of between 2-3 years should be achievable.

The figure above shows the components involved.  One key element is our generic room controller (“nanostat”).  These devices already control space conditioning and ventilation in many buildings, typically by adjusting the air terminal unit and reheat coil valves shown.  The only additional components required are an occupancy sensor and a digital output interface to the lighting circuit. 

After no occupancy is detected for a specified period of time (5-10 minutes), a typical control strategy would be to turn off the lights and shut the air terminal unit and reheat coil valves completely.  If the room temperature drifts more than a degree or two, heating or cooling would be applied as necessary.  As soon as occupancy is again detected, the lights are turned on and normal heating, cooling and ventilation control behavior is again restored.  

We are currently testing occupancy sensors from several manufacturers which employ passive infrared, ultrasonic, acoustic and combination technologies.  Data is being evaluated from several office, classroom, and conference room installations at Avery Hall.  Depending on the overall savings potential, this technology may be installed in new buildings and remodels.  In addition, retrofits of existing buildings may be initiated.