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Fault Detection and Diagnostics for Air-Conditioners and Heat Pumps

Summary:

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.

Description:

Objective:  By FY2015, 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?  This project will advance measurement science and facilitate implementation of residential FDD methods by developing new adaptable FDD algorithms to capture AC and HP faulty operation. Adaptable FDD methods are required to accommodate different equipment installations and aging effects.  These 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 FY2014 project will build on project outputs delivered within the three tasks begun in prior years. Within Task 1, measurement science will be advanced by refining the NIST developed adaptable (self-training) algorithm as a key for deploying FDD in field-assembled systems. In FY2012, the cooling mode FDD algorithm was incorporated into a program that allowed user input of system data. In FY2013, we validated it against available laboratory test data. This work prompted the development of a technique by which an existing heat pump’s fault-free model was “scaled” to allow the use of the same model form for FDD on similar, untested systems. This work also revealed the need to have “real world” data that includes system cycling and noisy transients in order to develop a robust, adaptable algorithm. Our goals for FY2014 are to focus on data collection methods and “low overhead” computing techniques for correlating fault-free system performance. To this end, accelerated diurnal, cyclic psychrometric testing in the cooling and heating modes at multiple operating conditions will be performed for a residential heat pump. Extensive testing will feed development of our adaptable algorithms by providing performance data for both fault-free and faulty operation under cyclic, transient conditions. The FY2015 effort will include the development of a custom data collection module for remotely monitoring and performing FDD on residential split and commercial rooftop AC&HP systems.

The goal of Task 2 is to develop a test method for rating AC and HP commercial FDD protocols. This test method will be implemented in the Tester/Evaluator program, which will generate sets of AC and HP operating parameters and feed them to the FDD device (or protocol) being tested. The diagnostics will be post-processed by the Tester/Evaluator and evaluated according to prescribed performance metrics.

The significant elements of this complex task are development of: (1) data needed for understanding how different system configurations respond to common faults, (2) “game-proof” testing scenarios and (3) a figure of merit for FDD protocols. FY2013 saw a significant refinement of the inverse model developed for simulating fault impacts on vapor compression systems, which will be used for generating the random test sets of AC and HP operating parameters. Also, a research version of the Tester/Evaluator was developed and applied to evaluate four FDD protocols used in California in utility-sponsored AC and HP maintenance programs. Feedback from the California evaluation generated unexpected and significant refinements to the Tester/Evaluator; this unplanned yet important effort was documented in an ASHRAE HVAC&R journal paper. The focus of FY2014 will be the development of the figure of merit for FDD protocols and completion of the Tester/Evaluator for evaluating user-input FDD protocols. The FY2015 effort will center on expanding the testing capabilities to FDD methods embedded in specific ACs and HPs.

In January of 2012, ASHRAE Standard Project Committee 207P “Laboratory Method of Test of Fault Detection and Diagnostics Applied to Commercial Air-Cooled Packaged Systems” was formed to promote FDD. This committee has directly used concepts and software developed in Task 2 to formulate test methods for different types of faults. NIST personnel have actively supported the work of this committee by chairing a sub-committee on air flow faults and contributing to the development of standardized definitions for faults. The preliminary test method developed by this subcommittee was incorporated into the draft standard. Task 2 feeds directly into SPC 207P and may require the adjustment of certain milestones to accommodate the needs of this committee.

Task 3 will entail 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 heat pump 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. Monitoring of the heat pump system began in FY2013. Monitoring of the heat pump system will continue for FY2014 with the goal of cataloging fault-free performance and updating the FDD capabilities of the monitoring process.

Major Accomplishments:

Research Outcomes:

  • Heo, Payne, Domanski,  “Normalized Performance Parameters for a Residential Heat Pump in the Cooling Mode with Single Faults Imposed”

Realized Research Impacts:

  • Kim, Yoon, Payne, Domanski, “Design of a steady-state detector for fault detection and diagnosis of a residential air conditioner”, Int. Jrn. of Refrig., Vol. 31, pp. 790-99, 2009.

Impact of Standards and Tools:

  • Cooling and heating mode performance data used by commercial developers of residential FDD equipment. (FY 2011)