This report examines variable capacity technology as applied within unitary packaged rooftop air-conditioning units, an HVAC configuration commonly used in commercial buildings in the United States. The purpose of this study is to provide a resource for evaluating and potentially implementing a program for variable capacity rooftop units to promote energy efficiency, peak electrical load reduction, and/or increased flexibility (such as for demand response) in commercial space conditioning equipment. 

This study provides new information to the growing body of documented performance for VC-RTU equipment. By mapping efficiency, capacity, power draw, and air flow rates, in every operating mode, and across a range of climate conditions, this study paints a clear picture of the VC-RTU’s characteristic performance capabilities. The study also presents an application specific assessment of performance for the installation observed to better understand the system’s advantages in a particular application that posed a number of unique challenges.