CFD optimization of return air ratio and use of upper room UVGI in combined HVAC and heat recovery system

Abstract

Several strategies and techniques have been recently developed to decrease energy consumption in heating, ventilation, and air-conditioning (HVAC) systems. One method is to recirculate a fraction of return air and make use of the remaining part (exhaust) to preheat fresh air in order to reduce the heating load. However, limitations must be imposed to the return fraction to maintain acceptable indoor air quality (IAQ).The aim of this paper is to develop a computational fluid dynamics (CFD) model to predict the dispersion of CO2 and airborne bacteria in all-air HVAC systems with aforementioned heat recovery system for known return air ratios as well as the disinfection of indoor air by upper room Ultraviolet Germicidal Irradiation (UVGI).The developed model can be put to practical use for estimating the maximum allowable return that minimizes energy cost of the integrated system while maintaining acceptable IAQ. It can also be used to predict the minimum required UV output to eliminate any excess in bacteria count in the breathing zone without the need for additional fresh air intake at the supply.