Development of a fault detection and diagnostic tool for use in walk-through energy audits
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abstract
2015 ASHRAE. Simple, walk-through energy audits are constrained by time and availability of tools, and thus often fail to do an indepth analysis of the control systems of the audited equipment, and detect the faults affecting the performance of these systems. Motivated by the well-documented prevalence of faults that degrade the performance of the air-conditioning systems found in these audits, this paper discusses the development of a low-cost fault detection and diagnostic tool that can increase the scope of walk-through audits. Existing HVAC fault detection tools need to be installed on the equipment for extended periods of time, and need information such as system specific models or manufacturer's map models that are not always available to the auditor on a one-day audit. The proposed automated fault detection and diagnostic device for unitary air conditioners overcomes these challenges by use of seven temperature and two pressure sensors, and by using information available on nameplates or brochures. The device detects refrigerant undercharge, refrigerant overcharge, liquid line restriction, condenser fouling, and evaporator fouling faults, and also predicts the related energy and cost savings for each fault. The sensor inputs are used to generate features that are sensitive to the fault, but less sensitive to operating conditions, so fault diagnosis can occur based on a combination of the feature values. The developed device is tested for individual and multiple faults with systems using different expansion valves. It works well for refrigerant line faults giving conservative estimates of energy and cost savings, which are usually preferred by energy auditors.
