April 2007
  
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Achieving Energy Savings with Building Automation Systems

Unfortunately, just installing a BAS is often not enough to guarantee energy savings.

Kristin Kamm
 

Kristin Kamm
Sr. Associate Research
E SOURCE

Building automation systems (BASs) can be a powerful tool for commercial-building energy managers, but some managers are unsure about the prospective energy-savings benefits and first costs. A BAS might go into a building that has no existing system, replace outdated pneumatic controls, or replace an existing direct digital control system, but ultimately the energy savings will depend on how inefficiently the building was operating before installation. It’s possible, however, to make some generalizations about savings potential and costs. This can give energy managers who are considering BAS implementation a place to start—and help them work with energy providers to attain financial support.

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A BAS—also called an energy management system—controls energy-consuming equipment in a building to reduce energy use while maintaining a comfortable environment. These systems, which are present in more than half of all buildings in the U.S. larger than 100,000 square feet (ft2), may also include other features such as maintenance planning, fire- and physical-safety functions, and security services.

Some of the most common strategies that BASs employ to cut energy use include:

  • Scheduling—Scheduling turns equipment on or off depending on time of day, day of the week, day type, or other variables such as outdoor air conditions.

  • Lockouts—Lockouts ensure that equipment doesn’t turn on unless it's necessary. For example, a chiller and its associated pumps can be locked out according to calendar date, when the outdoor air falls below a certain temperature, or when building cooling requirements are below a minimum.

  • Resets—When equipment operates at greater capacity than necessary to meet building loads, it wastes energy. A BAS can ensure equipment operates at the minimum needed capacity by automatically resetting operating parameters to match current weather conditions. For example, as the outdoor air temperature decreases, the chilled water temperature can be reset to a higher value.

  • Diagnostics—Building operators who use a BAS to monitor information such as temperatures, flows, pressures, and actuator positions may use that data to determine whether equipment is operating incorrectly or inefficiently, and to troubleshoot problems. Some systems also the use the data to automatically provide maintenance bulletins.

Research studies performed over the past decade have shown a wide range of energy savings for BASs—from none at all to annual savings of more than 30 percent. Summary discussions in the literature put average energy savings at between 5 and 15 percent of overall building energy consumption1. The savings can be greater for older or poorly maintained buildings. For many of the BAS-equipped buildings at the low end of savings, the BAS may not be functioning as intended.

Jack McGowan, president of Energy Control Inc., an energy service company and system integrator, provides more information about potential energy savings. Based on his experience, commercial buildings that have built-up HVAC systems with boilers and chillers can often reduce their overall energy use by 18 to 20 percent. Commercial buildings that have unitary packaged rooftop units, such as retail establishments, often save 12 to 15 percent. In both cases, the savings break down to approximately 60 percent electricity and 40 percent gas. The baseline building used for comparison has round-the-clock operation of lights, HVAC, etc., due to a lack of scheduling or manual turn off.

Reducing energy use isn’t the only benefit. Commercial buildings that employ a BAS will also experience some demand savings. Few case-specific data are available, although a 1996 study shows BAS demand savings averaging seven percent without specific demand-limiting strategies in place2. However, significant demand reduction requires demand-limiting strategies, which are only employed by a small fraction of BAS-equipped buildings. An example of a demand-limiting strategy is to program the BAS so that when the demand on a building meter or piece of equipment (such as a chiller) approaches a predetermined setpoint, the BAS does not allow the equipment to load up any further. Another way to minimize peak demand is to program time delays between the start-up of major pieces of electrical load equipment, preventing a situation in which several pieces of equipment start up at the same time.

As for system costs, according to McGowan’s estimates a BAS that centralizes building control and information flows at a single location costs about $0.50 to $1.00 per ft2. He figures it would cost an additional $0.10 to $0.25 per ft2 to optimize performance by adding control through internet access, demand-response capability, and communication to the utility.

Reliable Controls Unfortunately, just installing a BAS is often not enough to guarantee energy savings, and many BASs save less energy than they are capable of saving. In one detailed study of 11 BAS-equipped buildings in New England, five were found to be underachievers, producing less than 55 percent of the expected savings. One site produced no savings at all.

Improving the likelihood that a BAS will achieve the expected benefits entails taking advantage of advanced control strategies that use the computer-processing power of a BAS and adopting a comprehensive approach to quality control known as commissioning. This process is now required for some buildings, such as some public institutions and buildings with Leadership in Energy and Environmental Design (LEED) certification. Commissioning includes reviews and inspections throughout the design and construction process as well as rigorous performance tests that move the system through its sequences of operation before the building is occupied.

It’s also important to ensure that the system continues to work properly over time. Recommissioning—where building operators use trending and energy consumption data to periodically verify, document, and improve a building's operation—can be conducted throughout the life of the building. This can be done in-house or by hiring a system integrator or energy service company. Recommissioning is useful for identifying broken components, recalibrating sensors, and correcting control functions that have been disabled by building operators. Energy managers can plan to implement recommissioning over the system’s entire lifetime, tie the verification timeframe to the time it takes to achieve return on investment (ROI), or else determine a time period sufficient to ensure building operators understand the system and use it properly. McGowan’s company is creating dashboards that display real-time ROI to help energy managers—as well as utilities that provide rebates for BAS installations—measure energy savings.


About the Author

Kristin Kamm is a senior research associate at E Source. E Source information services provide member organizations with unbiased, independent analysis of retail energy markets, services, and technologies. E Source clients include electric and gas utilities and other energy service providers, large corporate and institutional energy users, government agencies, energy service companies, manufacturers, consultants, research institutions, and other organizations in nearly two dozen countries worldwide.


[1] M.R. Brambley, et al., “Advanced Sensors and Controls for Building Applications: Market Assessment and Potential R&D Pathways,” prepared for the U.S. Department of Energy by Pacific Northwest National Laboratory (April 2005), p. 2.15.

[2] Wortman, D.N., E.A. Evans, F. Porter, A.M. Hatcher, “An Innovative Approach to Impact Evaluation of Energy Management System Incentive Programs,” ACEEE Summer Study on Energy Efficiency in Buildings  (August 1996), American Council for an Energy Efficient Economy, Washington, D.C.

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