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‘Ultimate’ Power and Control Must Go Beyond HVAC

Aug. 2, 2011
Our HVAC control system or building automation system (BAS) enables us to control half or less of a building’s energy use and cost. To obtain ultimate control, the scope of a building’s control system needs to be increased.

Fans of the Star Wars series know that “The Force” is the source of a Jedi Knight’s ultimate power and control. But is this science fiction concept obtainable in the world of building automation? It can be, but only if multiple systems are addressed, as only a portion of the necessary power and control for building operations is provided via HVAC control systems.

The following diagram shows a breakdown of energy use by system in a typical building.

Given this profile, our HVAC control system or building automation system (BAS) enables us to control half or less of a building’s energy use and cost. Ultimate control? Hardly.

To obtain ultimate control, the scope of a building’s control system needs to be increased. A good starting point is the lighting system. In our example, the lighting system energy use is estimated conservatively at 30 percent. However, in some cases, lighting usage can exceed 50 percent of the load. By gaining better control of this usage, better control of a building’s total energy use can be obtained.

In evaluating lighting systems, on-off control merely is the starting point. Many additional options of lighting controls should be considered. True building control should include HVAC system control with granular temperature control as well as lighting and plug-load control.

In order to obtain total building control, wall switches for lighting fixtures need to be eliminated to allow the control systems to take over. A graphical user interface (GUI) provides this level of control.

Full dimmable lighting is a step in ultimate power and control of building energy use. This can be broken down into the following areas of control: task tuning, occupancy control, and daylight control.

Most building spaces are designed to provide 30 percent to 50 percent more light than most users or tasks require. This is based on the fact that most spaces are designed for 70 foot candles (FC) when 30 foot candles (FC) will suffice. Matching the task to the lighting level is called task tuning, and would minimize this overage.

In addition to over-lighting spaces, 30 percent of a building’s space often has lights left on when the spaces are not occupied. Occupancy control can reduce this wasted energy.

Other building areas to examine are perimeter spaces and offices, which typically account for 10 percent to 20 percent of a building’s floor plan. Daylight control using photocells can be sustainable using natural light, further reducing the building’s energy use.

Through better lighting control, lighting energy use can be reduced by 30 percent to 75 percent, which can be achieved as follows:

•Task tuning 30 percent to 50 percent

• Occupancy control 30 percent

• Daylight control 10 percent to 20 percent

This may sound unattainable, but we already have the engineering and technology available to achieve this level of control. When I go to work and use my key fob to access the building, the control system knows who I am and opens the doors to my office and turns on my lights. It also knows the level of light I like, so it identifies the amount of natural light available at that time of day and sets the light fixture percentage to maintain that desired level of light. If I leave my office, the lights turn off automatically. What is more, this usage can be accessed and monitored by any laptop or PDA.

Through implementing task tuning, occupancy control, and daylight control, my lights operate at 25 percent of their original power level, which is a 75 percent reduction in lighting-energy use. This type of lighting control is called a digital addressable lighting interface (DALI). It is similar to the HVAC protocols BACnet and LON. A good system integrator is capable of enabling these systems to talk to each other.

With HVAC and lighting under control, appliances and plugs should be addressed. Using the above standards and web interfaces, simple on/off relays can be installed on the plugs or plug strips to control these loads. There are even cost-effective products on the market that have integral occupancy sensors and can be remotely controlled.

Finally, building and sub-metering that provides hourly (minimum) and real-time (can be next day) data with trending and graphing capabilities is an absolute must. Without it, optimization of system operations cannot be achieved.

Ultimate power and control is within reach. May The Force be with you as you strive to achieve it!

Christopher Larry P.E., C.E.M., C.E.P., C.I.P.E, LEED AP, is director of energy engineering for Teng Solutions, Richmond, VA. He has spent more than 20 years working to minimize the building industry’s energy and environmental footprint through refining building design, building modeling, performance optimization, and intelligent controls. He has held numerous positions within the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE), including chairman of the Chapter Technology Transfer Committee and chairman for Technical, Energy and Governmental Activities. He is past president of the Association of Energy Engineers (AEE) and instructs the certified energy manager training course for AEE. He is the current chairman for the Building Intelligent Quotient (BIQ) within the Continental Automated Buildings Association (CABA) and also is a member of the Zero Energy Consortium.