Cooling Mode Fault Detection and Diagnosis Method for a Residential Heat Pump.
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.
Building and Fire Research Laboratory
National Institute of Standards and Technology
Gaithersburg, MD 20899