Condition monitoring of high efficiency heating, ventilation and air conditioning systems

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Jiang, Chen
Habetler, Thomas G.
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The objective of the proposed research is to increase energy efficiency in HVAC (Heating, Ventilation and Air conditioning) systems. Energy consumption has increased rapidly in recent decades. This has elevated concerns of a future energy crisis, and heavy negative environmental impacts. An air handler, or air handling unit, is a device used to condition and circulate air as part of a HVAC system. The operation of air handlers account, on average, for 40% of an industrial site’s total energy consumption. The air handler in the HVAC system has electrical and mechanical components that can experience problems from time to time. Airflow blockage and a failure of a blower motor are two of the most common problems in air handlers. Airflow blockage is detected utilizing a current-based condition monitoring method, which analyzes the static pressure of the fan blade, load torque, and the fan motor speeds. For most air handlers, the unbalanced load of the blower wheel is created by unevenly distributed contaminants on the blades. The traditional current-based condition monitoring method is conducted on a brushless DC, or BLDC, fan motor, followed by a stray flux spectrum analysis, which increases reliability in detecting an unbalanced load condition. Static eccentricity and dynamic eccentricity are two of the main faults commonly found in the rotor of a BLDC motor. An improved method for detecting static eccentricity is proposed based on a comparison between the positive sequence current and negative sequence current. Finally, a current-based nonintrusive condition monitoring method is established for refrigerant level detection. A thermal model of a compressor is analyzed under insufficient refrigerant level conditions to explore the mathematical relationship between refrigerant level and stator winding resistance. An undercharged detection algorithm is proposed with a detailed analysis of temperature threshold settings. This algorithm can be easily implemented on the original HVAC system to increase the system’s reliability and efficiency, and to reduce the labor cost of refrigerant level detection.
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