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Controls Help Demand Response On Campus

August 10, 2007
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This presents a series of exciting challenges and opportunities. With the spread of demand response (DR) programs and new energy conservation technologies, the building owner is now confronted with a series of questions. How do I configure my building systems to take full advantage of DR? How do I size the amount of DR I can provide to the wholesale market? Does my building control system provide any DR functionality?

These questions are particularly applicable to large buildings and campuses of buildings with complex mechanical systems where significant demand reductions may be possible. When vast amounts of real-time data derived from the ongoing commissioning of a building’s systems are analyzed and correlated with real-time energy consumption data, a number of strategies can be employed to optimize the building and payments from electricity markets. By correlating control system data with data from networked switchgear and meters (Figure 1), more granular control over these systems becomes possible.

Many techniques are currently used to temporarily reduce the electrical load of buildings, including turning off subsystems (lighting, heating, cooling, fans), adjusting temperature setpoints in building spaces, employing energy storage systems (ice or chilled water storage, etc.), and dispatching back-up or emergency generation units. In conjunction with new business practices enabled by technologies such as Cimetrics’ Infometrics, ongoing commissioning service, mechanical, electrical, and control systems behavior can be studied in order to select and optimize the sheddable load in buildings without compromising mission critical activities. The analysis of actual building performance during DR events over time can lead to improvement of the buildings’ response to such events.

Various industry groups are creating standards to facilitate the continued growth of DR. For example, ASHRAE’s BACnet committee recently developed a standard load control object to facilitate the consistent deployment of building-utility interfaces across portfolios of buildings (a load control object is defined in ANSI/ASHRAE Addendum E to ANSI/ASHRAE Standard 135-2004).

BACnet’s load control object is designed to provide a general high-level interface for controlling the total electric consumption of a building system or subsystem. Energy management applications can issue a BACnet request to a load control object such as “reduce demand to 90% of baseline for 180 minutes, starting at 3 p.m.,” after the object reports its status.

Multiple load control objects can be used in a facility or campus to control different loads. It is important to note that the definition of the load control object does not specify how to reduce electricity or how to measure load control compliance, leaving those decisions to the facilities engineering staff.

Whatever load reduction strategy is selected, the building control system will require configuration and/or programming in order to implement the chosen strategy. The load control object is an important building block for automated DR systems because it standardizes one communication interface between energy management systems and electrical loads in facilities that have sophisticated building control systems.

As the smart utility grid begins taking shape, building owners have new opportunities to participate in energy markets. Innovative products and services are helping building owners to take advantage of these opportunities today. GIB

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