Fault Detection and Diagnosis for Air-Conditioners and Heat Pumps

Fault detection and diagnostic (FDD) methods are receiving increasing consideration for application in space-conditioning equipment.  It is anticipated that utility rebate programs and building energy regulations will promote the use of FDD methods as cost-effective energy efficiency measures leading to increased market acceptance of FDD methods.  This project will accelerate market penetration of air conditioner and heat pump FDD technology by developing effective FDD algorithms and by formulating a standard procedure for rating different commercial FDD products based on their potential to avoid performance degradation and increased energy consumption on an annual basis.

Objective:  By FY2013, develop FDD methods to ensure air conditioners (ACs) and heat pumps (HPs) perform as designed throughout their lifetime and develop a testing and rating methodology to assess relative merits of different commercial FDD products thus saving energy, reducing refrigerant emissions, and providing reliable comfort. 

What is the new technical idea?  EL will advance measurement science and facilitate implementation of residential FDD methods by examining AC and HP faulty operation and developing new adaptable FDD algorithms.  The adaptable FDD methods are required to accommodate different equipment installations and aging effects.  The developed FDD methods will not only be applicable to residential heat pumps, but also to other systems that operate on the vapor-compression principle.  Generalization of these techniques and application of the statistical methods engrained within the FDD algorithms will give U.S. industry opportunities for innovation and will promote faster introduction of this technology into the marketplace.

FDD devices, like any other products marketed based on functionality, must have their figure of merit determined to promote market competition and product improvement.  Two figures of merit will be developed for FDD modules:  the first, "energetic" metric will capture potential energy savings as a result of detecting/correcting various faults detected by the system, and the second metric will capture the FDD device's ability to avoid false alarms.  The main product of the project will be an AC/HP tester/evaluator.  During a test of a commercial FDD method (e.g., an algorithm embedded in a heat pump's control unit), the AC/HP tester/evaluator will output a set of heat pump parameters that potentially could be used by the FDD module, and based on these parameters, the module will make a diagnosis regarding the "health" of the heat pump.  Calculation of the "energetic" metric will include weather data to weight the robustness of the FDD device's diagnostic capabilities over an entire year. 

What is the research plan?  The FY2012 project will entail three tasks. Within Task 1, an adaptable (self training) method will be developed for our FDD algorithms, which will be the key for deploying FDD in field-assembled systems.  The literature will be examined to determine the different approaches to "adaptive" learning, and manufacturers will be consulted to provide information on the way their aged systems perform.  Within the adaptive scheme, the FDD system will be able to refine its fault-free reference model and to adjust statistically determined fault thresholds.  This effort will involve computer modeling, data mining, and algorithm development along with some testing to fill in any data gaps.

Within Task 2, the effort to develop a test method for rating AC and HP commercial FDD products will continue. After developing a performance data library for no-fault and faulty operation with extended data analysis in FY2011, in FY2012 the project will proceed to inverse modeling of no-fault and faulty ACs and HPs; six different faults will be considered. Simultaneously, operating scenarios will be developed for fault-free and faulty operations, and they will be later implemented in the FDD tester/evaluator (prototype software tool) together with the simulation model (FY2013).  For each operating scenario, the output from the AC/HP tester/evaluator will include indoor and outdoor operating conditions and AC and HP features.  The tested FDD product will return its diagnostic information to the FDD tester/evaluator.  Testing and validation of the FDD tester/evaluator will involve laboratory and commercially available FDD algorithms (FY2013).

In FY 2012, Task 2 will also include the development of a standardized format for information exchange between the FDD tester/evaluator and the tested commercial FDD product.  Interaction with original equipment manufacturers through professional organizations and direct contacts throughout the duration of this project will seek to standardize FDD diagnostic information within the U.S. industry.  The rating algorithm developed for the FDD tester/evaluator will use weather data to produce a figure of merit reflecting energy savings through the cooling and heating seasons.  It is expected that the FDD tester/evaluator will also be used as a tool for developing new FDD methods.

Task 3 will entail the efforts to ensure proper operation of the high-efficiency, air-source heat pump selected for the EL Net-Zero Energy Residential Test Facility (NZERTF). This novel, variable-speed heat pump has unique operational modes that can provide cooling/heating load matching with humidity control, including dedicated dehumidification.  It will be one of the top energy users in the home and must operate properly for the home to reach its goal of net-zero energy.  Within Task 3, a new FDD method will be developed for the heat pump based on manufacturer's performance data, publically available FDD algorithms developed for variable-speed equipment, and NIST's previously developed Steady-State Detector.  This FDD method will be installed in the NZERTF monitoring system.  Also developed and installed will be a scheme to map the NZERTF heat pump's heating and cooling performance for an entire year which will enable a better, more detailed FDD method for this system.

Recent Results: 

Outputs:  

Yoon SH, Payne WV, Domanski PA., 2011.  Residential heat pump heating performance with single faults imposed.  Applied Thermal Engineering, 31(2011), 765-71.

Kim M, Yoon SH, Payne WV, Domanski PA., 2010.  Development of the reference model for a residential heat pump system for cooling mode fault detection and diagnosis.  Journal of Mechanical Science and Technology, 24(7)(2010), 1481-89.

Kim M, Payne WV, Domanski PA, Hermes CJL, Yoon SH., 2008.  Performance of a residential heat pump operating in the cooling mode with single faults imposed.  Applied Thermal Engineering, 29(4), 770-78.

Outcomes: 

Cooling and heating mode, fault-applied performance data given to the HVAC&R industry and academia. 

Impacts: 

Cooling and heating mode performance data have been used by at least one commercial developer of HVAC FDD equipment to develop products for the residential and small commercial market. 

Standards and Codes:  The advancements in FDD technology and potential energy savings have prompted state regulators in California to include energy conservation credits in Title 24 for rooftop air conditioners and heat pumps. Federal regulators (DOE, EPA) are considering including FDD technology in energy conservation codes as well.  These regulators have expressed the need for a standard procedure for testing and rating different commercial FDD products, as being developed within this project, as a way to enhance the effectiveness of FDD regulations.  In FY2010 and 2011, members of the NIST HVAC&R Equipment Performance Group were invited and participated in activities related to energy conservation code development in California. These activities will continue.  We also participate in ASHRAE Technical Committees 7.5 and 8.11 where discussions about future FDD-related standards have started.