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Cooling Mode Fault Detection and Diagnosis Method for a Residential Heat Pump.


pdf icon Cooling Mode Fault Detection and Diagnosis Method for a Residential Heat Pump. (1965 K)
Kim, M. S.; Yoon, S. H.; Payne, W. V.; Domanski, P. A.

NIST SP 1087; NIST Special Publication 1087; 98 p. October 2008.

Keywords:

heat pumps; cooling; fault detection; fault diagnosis; steady state; methodology; energy efficient; environmental effects; conservation; costs; air conditioning; verification; sensitivity

Abstract:

This research addresses the need for fault detection and diagnosis (FDD) in residential-style, air conditioner, and heat pump systems in an attempt to make these systems more trouble free and energy efficient over their entire lifetime. This work is one of the first to apply FDD techniques to a residential system with the added control element of a thermostatic expansion valve (TXV). Any control element actively seeks to perform its duties and thus obscures any faults occurring by making adjustments. This research work takes this into account and shows how FDD techniques may be applied to this type of system operating in the cooling mode. Performance characteristics of an R410A residential unitary split heat pump equipped with a TXV were investigated in the cooling mode under no-fault and faulty conditions. Six artificial faults were imposed: compressor/reversing valve leakage, improper outdoor air flow, improper indoor air flow, liquid-line restriction, refrigerant undercharge/overcharge, and presence of non-condensable gas. An automated method of steady-state detection was developed to produce consistent collection of data for all tests. The no-fault test measurements were used to develop a multivariate polynomial reference model for those system features (temperatures) that varied the most when a single fault was imposed. Outdoor air dry-bulb temperature, indoor air dry-bulb temperature, and indoor air dew-point temperature were used as the independent variables. From the no-fault reference model, feature residuals (differences between model predictions and measured values) were determined. Since the system was controlled by a TXV, the system could adapt itself to external variation much easier than a system with a fixed area expansion device. This added measure of refrigerant flow control provided by the TXV meant that the system compensated for faulty behavior more easily than a fixed area expansion device system. The distinctiveness of a fault depended on the TXV control status (fully open or fully closed), and thus the TXV affected the fault response of the selected features.