The AHU anomaly function detects common hard and soft faults related to a building's air handling unit(s).

Large commercial buildings commonly rely on air handling units (AHUs) to supply, exhaust, recirculate, and condition indoor air. These units, typically located on the roof, are an integral component in a building's heating, ventilation, and air condition (HVAC) system, and contain a number of moving mechanical components such as dampers, valves, and fans. However, with such complex arrays of actuators and sensors, all working in harmony to maintain a healthy and desirable indoor climate, it is not uncommon for faults to arise. These faults can occur from broken or deteriorating components and sensors within the AHUs, or can even be the result of a conflict in the controller logic. If left unaddressed, which they often are, these faults can result in anomalous and suboptimal operation of the AHUs, leading to excessive energy consumption or even undesirable indoor climates.

The AHU anomaly function identifies common AHU-level system hard and soft faults. Common hard faults include stuck (open/closed) outdoor air dampers which regulate the intake of outdoor air through the AHU, and stuck (open/closed) heating and cooling coil valves which regulate the flow of steam and chilled water through the AHUs heating and cooling coils, respectively. The three common soft faults pertain to inappropriate or suboptimal economizer, supply air temperature reset, or mode of operations logic settings. More information about these common faults, what triggers them, and how to address them is found in the outputs page.

To help identify faults, three sets of visuals are generated. The first visual models the observed supply air temperature as a function of outdoor air; the warmest, coldest, and average zone air temperature are also modeled for comparison. The second visual is a split-range AHU controller diagram per ASHRAE Guideline 36 which plots AHU damper and valve positions as a function of outdoor air temperature. The third visual is a set of four to six simplified AHU schematics depicting the common combination of damper and valve positions and air temperatures within the AHU. More information about these visuals and how to interpret them is found in the outputs page.