The diagnosis of soft faults in vapor compression cooling systemsis a crucial activity, since malfunctions may provoke heavydegradation in plant performance and increase the power consumptionfor space cooling. Among the various Faults Detection and Diagnosistechniques developed over the last two decades, thermoeconomicdiagnosis has been playing only a marginal role due to the difficultiesencountered when applying the conventional thermoeconomicapproaches to vapor compression refrigeration plants. In this paper acritical analysis on capabilities and limits of thermoeconomicdiagnosis of refrigeration systems is proposed. The reference plantassumed for this study is a 116 kWc air-condensed rooftop systemscharged with R407C as refrigerant. A reliable 1-D steady-statesimulator is used to calculate thermodynamic and performance data in“off-design” operating conditions; since the simulator has no specificcapabilities to simulate faulty systems, literature-derived results wereused to adjust the input settings for each specific fault simulated.Among the most common faults in rooftop air conditioners, fourdifferent malfunctions are examined: fouling at condenser, fouling atevaporator, refrigerant undercharge (either due to leakage or erroneouscharging during service) and extra-superheating along the suction line;the faults are imposed both individually and simultaneously. Thethermoeconomic diagnosis is performed basing on the “fuel impact”approach; the need to split physical exergy into its thermal andmechanical fractions and the presence of dissipative componentssuggested us to formulate some methodological premises, discussed indetail in the paper. The results testify that the adopted conventionalapproach is not very reliable; although some faults are properlyidentified, in fact, false fault signals and erroneous causalizationeventually resulted, due to the presence of system-level faults (i.e.faults not strictly associated with any specific plant component, likerefrigerant undercharge), the subjective assumptions made as concernsthe cost allocation of residues and some controversial aspectsconcerning the productive structure.
|Numero di pagine||12|
|Stato di pubblicazione||Published - 2012|
All Science Journal Classification (ASJC) codes
- Control and Systems Engineering
- Mechanical Engineering