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 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 FY2013 project will continue the three tasks begun in FY2011.  Within Task 1, measurement science will be advanced using 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 Visual Basic Windows Environment program that allowed users to input time series data for single-speed residential sized air conditioners.  In FY2013, we will refine the algorithm and validate against available databases.  The developed FDD algorithm will be adaptable for use on single-speed air conditioners and rooftop units and will promote market implementation of FDD tools.  

The goal of Task 2 is to develop a test method for rating AC and HP commercial FDD products.  This test method will be implemented in a “Tester/Evaluator” program, where the function of the Tester will be to generate and feed the evaluated FDD device with a set of AC and HP operating parameters, and the function of the Evaluator will be to post-process the test results according to prescribed performance metrics.  In FY2012, an air conditioner air flow and refrigerant charge testing protocol applied on a large scale in California was evaluated. A technical paper summarizing eye-opening findings regarding ineffectiveness of current air conditioner service practices has been submitted to the ASHRAE HVAC&R Journal.  Also in FY2012, inverse models of fault and faulty ACs and HPs were developed for generating operating scenarios for testing FDD products.  

A new development important to this task is the creation, in January of 2012, of ASHRAE Standard Project Committee 207P “Laboratory Method of Test of Fault Detection and Diagnostics Applied to Commercial Air-Cooled Packaged Systems”.  Discussions within the committee have already highlighted the need for a standard test method to evaluate FDD protocols and hardware; therefore, the results of Task 2 will feed directly into SPC 207P and may require the adjustment of certain milestones to accommodate the needs of this committee.  While the goal of this task still requires a considerable amount of analytical effort and discussions between the stakeholders, the effort in FY2013 will gradually shift towards testing, validating, and upgrading of different elements of software, which will be included in the Tester/Evaluator.  Among the FY2013 analytical work, the most arduous challenge will be the development of the figure of merit and rating algorithm using weather data and assumed fault prevalence profile.  The extensive research required for Task 2 is being conducted in collaboration with academia through partial support of two Ph.D. dissertations.  

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 begun in FY2012 will continue for FY2013 with the goal of cataloging fault-free performance and updating the FDD capabilities of the monitoring process.  This will require use of our Visual Basic Windows Environment FDD program and further extension of its capabilities to accommodate the performance of this variable capacity, high efficiency system. 

Recent Results: 

Outputs: 

Technical paper was submitted to the ASHRAE HVAC&R Journal.  NIST developed data was used to evaluate a widely applied air flow and refrigerant charge screening program used in California (2012).  

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 provided to the HVAC&R industry and academia (2011). 

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.

Cooling and heating mode performance data have been used by ASHRAE SPC 207P (Laboratory Method of Test of Fault Detection and Diagnostics Applied to Commercial Air-Cooled Packaged Systems), the committee charged with formulating an ASHRAE standard on testing FDD devices/algorithms.

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 incentive programs (DOE) are encouraging the use of FDD technology. Code developers (ICC, IECC) are considering including FDD technology in energy conservation codes as well.  These groups 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 FY2011, members of the NIST HVAC&R Equipment Performance Group were invited and participated in activities related to energy conservation code development in California.  In FY2012, two members of the NIST HVAC&R group joined ASHRAE Standards Project Committee 207P to develop “Laboratory Method of Test of Fault Detection and Diagnostics Applied to Commercial Air-Cooled Packaged Systems”.  We also continue to participate in ASHRAE Technical Committees 7.5 (Smart Building Systems) and 8.11 (Unitary and Room Air Conditioners and Heat Pumps) where discussions about future FDD-related standards have started.