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Non-Intrusive Electric Load Monitoring Still Promises Tantalizing Diagnostic Potential

Dr. Michael R. Brambley has more than 30 years of academic and research experience related to energy.  He has spent the last 22 years at the U.S. Department of Energy's Pacific Northwest National Laboratory (PNNL) focused on improving energy efficiency in buildings.  At PNNL, Dr. Brambley has served in a wide variety of roles including principal investigator, project and program manager, technical group leader, department chief scientist, and research contributor.  Most of his work over the past 15 years has focused on improving the operating efficiency of buildings and other energy systems, including air conditioning.

In September 2009, PNNL published a short study by Dr. Brambley with a long title: "A Novel, Low-Cost, Reduced-Sensor Approach for Providing Smart Remote Monitoring and Diagnostics for Packaged Air Conditioners and Heat Pumps."  It begins by noting a basic conundrum: "Operation Faults are common in packaged heating, ventilation, and air conditioning (HVAC) equipment...commonly used for space conditioning space conditioning of commercial buildings with less than about 50,000 square feet and many larger buildings with three floors or less....Remote diagnostic monitoring systems have been developed, bu they are expensive and, as a result, have not achieved significant penetration into the market.  Both hardware and installation costs are too high."

Noting that, "Smart monitoring and diagnostic systems (SDMSs) built for field testing...ina a follow-on to the current project had an estimated cost of approximately &1,000 per SDMS unit," plus, "an installation cost of another $200 to $1,000," Brambley conludes, "a much more lower-cost monitoring and diagnostic system is required to serve this market effectively."

His proposed solution?  "Basic non-intrusive electric load monitoring (NIELM) techniques can be used to extract information about the electricity use and efficiency of individual components of the heating, ventilation, and air conditioning unit from measurement of power supplied to an individual HVAC unit.  By using very few sensors, the capital cost and time/cost required for installation will be minimized, creating a monitoring and diagnostic system with a cost an order of magnitude lower than previous systems developed by the research team..."

Brambley details the original idea as developed by George Hart at MIT in the 1980s, and its evolution into various diagnostics systems.  "We hypothesize that much smaller sampling periods of tens of seconds to a couple minutes might be used to distinguish the on-off events of packaged unit compressors and fans to quantify...electric energy consumption."  He contends, "This together with measurements of outdoor-air temperature (and possibly return-air or supply-air temperature) should be sufficient to detect," six different faults on larger packaged air conditioning or heat pump systems.

What could make a NIELM system powerful and affordable is that it takes these limited power samples from the air conditioner or heat pump only when starting.  Key steps needed to convert the concept into workable technology are, "Adaptation of algorithms from previous work and development of some new algorithms for using NIELM to extract on-off times, power draw, energy use, cycling frequency of packaged unit compressors, and fans from the power connection to the unit ans implementation of them in software," followed by, "Development of a very low-cost hardware package with the necessary processing, data storage and communication capabilities for implementing the NIELM and fault detection algorithms."

In conclusion, Brambley opines, "The changes possible from successfully developing and implementing the NIELM-based technology...will help transform how packaged HVAC equipment is operated and maintained, increasing its operating efficiency and decreasing the energy used for space conditioning the 90 percent of commercial buildings and the 55 percent of commercial floor area that these units serve."  The savings could be still greater, he notes, if the technology were built right into the packaged units.

The promise that Dr. Brambley notes in this intriguing study is real enough, but so too are the barriers that have yet to be overcome to make NIELM-based technology a diagnostic game-changer.  Perhaps someday they will fulfill that great promise.

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