MECHANICAL VENTILATION AND EQUIPMENT
Mechanical ventilation systems for controlling conditions in individual zones can move a constant or variable supply of conditioned air to handle all or some of the heating and cooling loads. They are classified as all-air, air-water, and all-water systems. All-air systems include single-duct, dual-duct and multizone. The systems can be designed to operate at Constant Air Volume (CAV) or Variable Air Volume (VAV). Air-water and all-water systems are categorized as two-, threeand four-pipe. The Air Handling Unit (AHU) is the main air conditioning and treatment equipment. A typical AHU consists of a single volume unit with a supply fan, heating coil, cooling coil, humidifier where necessary, filters, mixed air economizer dampers, and sound attenuator. The air distribution is a key element for the successful operation of central systems to deliver the air to the conditioned spaces in an efficient way, satisfying the indoor environmental conditions as economically as possible. The air is then distributed by the ductwork and is delivered by the air-diffusion outlets. Proper circulation and exhaust must satisfy the indoor environmental quality. Mechanical ventilation systems provide great flexibility for controlling the indoor conditions, if properly designed, installed, commissioned, operated, and maintained. Proper controls can optimize their use, enhance flexibility, and improve energy efficiency. On the other hand, poor design, installation, and performance can lead to serious Indoor Air Quality (IAQ) problems, and cause thermal and acoustical discomfort, with a high energy cost.
Diagnostics for Outdoor Air Ventilation and Economizers
Today, most problems with building systems are detected as a result of occupant complaints or alarms provided by building automation systems. Building operators often respond by checking space temperatures or adjusting setpoints (or thermostat settings). The root causes of operation problems not diagnosed, so problems reoccur and the operator responds by making another adjustment. The BACnet TM standard will contribute to easier implementation by providing a standard mechanism for communication between diagnostic software and devices.
Fault diagnosis and temperature sensor recovery for an air-handling unit
The presence of faults and the influence they have on system operation is a real concern in the heating, ventilating, and air-conditioning (HVAC) community. A fault can be defined as an inadmissible or unacceptable property of a system or a component. Unless corrected, faults can lead to increased energy use, shorter equipment life, and uncomfortable and/or unhealthy conditions for building occupants. This paper describes the use of a two-stage artificial neural network for fault diagnosis in a simulated air-handling unit. The stage one neural network is trained to identify the subsystem in which a fault occurs. The stage two neural network is trained to diagnose the specific cause of a fault at the subsystem level. Regression equations for the supply and mixed-air temperatures are obtained from simulation data and are used to compute input parameters to the neutral networks. Simulation results are presented that demonstrate that, after a successful diagnosis of a supply air temperature sensor fault, the recovered estimate of the supply air temperature obtained from the regression equation can be used in a feedback control loop to bring the supply air temperature back to the setpoint value. Results are also presented that illustrate the evolution of the diagnosismore » of the two-stage artificial neural network from normal operation to various fault modes of operation.« less