Variable Speed RTUs, Laboratory Testing, Energy Simulation, Performance Map
Commercial rooftop units (RTUs) that incorporate variable-speed components are quickly entering the marketplace; however, the design and modeling tools that calculate the energy benefits of these units cannot properly estimate performance. This is because 1) there are insufficient measured performance data of real systems that can be input into these simulations, and 2) building energy simulators are unable to properly interpret performance data. Therefore, publicly available data sets designed to encompass the entire performance map coupled with control sequence information are needed as inputs for these modeling programs to accurately estimate energy savings and promote the benefits of variable-speed RTUs. As part of the Validation and Uncertainty Characterization for Energy Simulation project funded by the U.S. Department of Energy, the National Renewable Energy Laboratory recorded and published data across the entire performance range for two commercially available RTUs: one with a two-stage compressor and variable-speed supply fan and another with a fully variable-speed compressor, supply fan, and condenser fan. This paper details 1) how the design of experiments was created and 2) the operational limitations of the two units that complicate the measurement and interpretation of the performance maps. This paper also discusses methods for improving energy simulation programs to properly interpret these data sets and integrate them into building energy simulation models.