Analysis of HVAC system oversizing in commercial buildings through field measurements

•We investigate the over-sizing issue of RTUs in 12 retail stores in different climates.•We propose an improved N-analysis method to improve the credibility of the results.•Different dead-band temperatures are used to self-validate the findings.•Five over-sizing levels, over-sizing capacity, and energy penalty are presented.•The results can be utilized to assist system design and optimize real operation.

This study analyzes the oversizing issues of HVAC equipment in commercial buildings based on the data from long-time field measurements. Specifically, retail stores are selected as the typical commercial buildings to evaluate the status of equipment oversizing and its effect on energy consumption. Rooftop units (RTUs) in 12 retail stores located in different climatic regions are analyzed in terms of the oversizing status in both cooling and heating mode. The proposed method utilizes three parameters, namely cycling number (N), run time fraction (RTF), and maximum cycling number (Nmax) to jointly determine the performance of a RTU based on the annual design condition. The accuracy of the methodology is evaluated by self-validation in terms of uncertainty and compared with previous studies. The results can be used to evaluate the oversizing level of RTUs and quantify the average energy penalty of sample buildings. Designers can also use the findings as a reference to evaluate building load design. More importantly, the analytical process presented in this article can be automated and applied in the smart building management system for the advanced soft repair of an oversizing issue with RTUs.