United States Department of Energy Study

Advanced Rooftop Control (ARC) Retrofit: Field-Test Results

This multi-year research study was initiated to find solutions to improve packaged heating and cooling equipment operating efficiency in the field. Pacific Northwest National Laboratory (PNNL), with funding from the U.S. Department of Energy’s (DOE’s) Building Technologies Office (BTO) and Bonneville Power Administration (BPA) conducted this research, development and demonstration (RD&D) study.

Packaged heating and cooling equipment with constant speed supply fans is designed to provide ventilation at the design rate at all times when the fan is operating and when the building is occupied as required by building code. Although there are a number of hours during the day when a building may not be fully occupied or the need for ventilation is lower than designed, the ventilation rate cannot be adjusted easily with a constant speed fan. Therefore, modulating the supply fan in conjunction with demand controlled ventilation (DCV) will not only reduce the heating/cooling energy but also reduce the fan energy.

The objective of this multi-year RD&D project was to determine the magnitude of energy savings achievable by retrofitting existing packaged rooftop air units (RTUs) with advanced control strategies not ordinarily used for RTUs. First, in FY11, through detailed simulation analysis, it was shown that significant energy (between 24% and 35%) and cost savings (38%) from fan, cooling and heating energy consumption could be realized when RTUs with gas furnaces are retrofitted with advanced control packages (combining multi-speed fan control, integrated economizer controls and DCV). The simulation analysis also showed significant savings for heat pumps (between 20% and 60%). The simulation analysis was followed by an extensive field test of a retrofittable advanced RTU controller.

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