Indoor air quality: Economizer control and air mixing in variable air volume systems

This work studied various aspects of the operation of an economizer sub-system in a variable air volume (VAV), heating, ventilating, and air conditioning (HVAC) system. All these studies were directed towards meeting ASHRAE Standard 62-1989 that stipulated the supply of a minimum amount of outside air (OA) required to provide adequate indoor air quality (IAQ).; The volume flow of outside, return and exhaust air is predominantly controlled by the modulation of control dampers within the economizer portion of a VAV system. The first part of this dissertation studied the validity of using Computational Fluid Dynamic (CFD) techniques to simulate control damper operation and consequently define control characteristics of various dampers.; In order to efficiently control the amount of ventilation air in a VAV system, velocity measurements taken at the outside air intake were found necessary to avoid severe control loop interactions. Therefore, the errors associated with placing velocity measuring instrumentation at a duct intake for common duct configurations were studied using CFD simulations. Several velocity anemometers were then tested in a wind tunnel. Results from the experiments led to the identification of suitable velocity measuring instrumentation that could be used for outside air velocity measurement.; Inadequate mixing of outside and return air often result in stratified air that leads to poor IAQ performance and consequently an increase in overall operational costs. The prohibitive costs of laboratory experimentation has presently limited the study of mixing in different mixing plenum, damper and duct configurations. CFD simulations were used to study the mixing efficiencies of commonly used duct configurations.