Rightsizing: using simulation tools to solve the problem of oversizing

Designers oversize HVAC systems for various reasons, and some reasons are more justifiable than others. In oversizing the system, the designers are essentially asking the building owner to incur the financial penal-ties of oversizing throughout the life of the HVAC sys-tem in favor of the theoretical benefit of perfect oc-cupant comfort during the combination of all possible extreme conditions. The initial and ongoing financial penalties associated with oversizing are often not com-municated to the client and neither are the potential comfort trade-offs of rightsizing.This paper presents the results of a study on the “right-sizing” of the rooftop HVAC systems. The study in-volves a survey and intensive interviews with HVAC designers regarding the design process to identify the factors that can lead to oversizing. The study also car-ried out extensive measurements on the performance of rooftop units (RTUs) under the peak cooling day de-sign condition. The measurements were used to iden-tify the signature of oversizing, and estimated penalty of oversizing in terms of energy consumption and peak electricity demand. This paper focuses on the results of the simulation exercise carried out as part of the study. The goal of the simulation work for the study was to extend the measured penalty estimate across the whole cooling season.