Measuring Building Occupancy The movement toward a better integrated, inclusive, and accurate occupant measuring system is something to consider.

Paul Ehrlich, Ira Goldschmidt & Angela Lewis Building Intelligence Group As published   July Issue - Column

There are many potential benefits to knowing not only how many people are in a building, but ideally were they are located.  Why would we want to know?  Well with better information on occupancy we could:

• Demand Controlled Ventilation:  Under ASHRAE 62 ventilation levels for the ventilation portion for occupants (the People Outdoor Air Rate or Rp) can be adjusted based on occupancy.  The general way to do this is to measure and control based on CO2 levels.  While this works well, CO2 sensing is expensive to install and properly maintain.  Good data on occupancy can be used as an alternative to utilizing CO2.  When areas are not at all occupied then the ventilation requirement for the area outdoor air rate (Ra) can also moved to zero.
  

• Occupancy Control:  Being able to see when an area is occupied could be a valuable tool for turning off lights and as well as HVAC.
  

• Building Utilization:  Good data about occupancy can be a valuable tool to show how a building is actually utilized. Imagine being able to see how many people are in an office area and when, or how classrooms are actually utilized.  This information may help owners make decisions about space planning and better utilization.
  

• Security:  Accurate people counts can be invaluable for security. Accurate measurements can be used for security as well as for emergency evacuation and safety.

On past projects we have used several proxies for occupancy including the use of CO2, manual operator input, and data from card access systems.  While all of these are good proxies none is highly accurate.  For example not all building occupants use their cards to enter an building and in many buildings occupants do not use their cards when exiting the building. 

[an error occurred while processing this directive] There are now a series of new technologies becoming available for people counting. Some of these are coming from security systems, and others have evolved from retailing.  Retailing?  Yes, it turns out that retailers needed an accurate way to measure how long customers have been standing in line so that they can decide if they should open another register.  This same technology can be readily used across a commercial building and integrated in as part of an intelligent building.  The technologies include infrared sensors, cameras, and thermal imagers.  When looking at a solution some considerations include cost, flexibility, support and of course the ability to deal with the issue of occupant privacy.

The movement toward a better integrated, inclusive, and accurate occupant measuring system is something to consider.  While these systems add to project cost and complexity, they offer benefits and could reduce the need for existing tools including occupancy and CO2 sensors. 

About the Authors

Paul and Ira first worked together on a series of ASHRAE projects including the BACnet committee and Guideline 13 – Specifying DDC Controls. The formation of Building Intelligence Group provided them the ability to work together professionally providing assistance to owners with the planning, design and development of Intelligent Building Systems. Building Intelligence Group provides services for clients worldwide including leading Universities, Corporations, and Developers. More information can be found at www.buildingintelligencegroup.com  We also invite you to contact us directly at Paul@buildingintelligencegroup.com or ira@buildingintelligencegroup.com

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