Serious energy savings can be achieved by retrofitting existing packaged rooftop air handler units (RTUs) with advanced control strategies, according to a recent multiyear project conducted by the U.S. Department of Energy. The report on the project, “Advanced Rooftop Control (ARC) Retrofit: Field-Test Results,” points out that not using advanced controls for RTUs is a big missed opportunity.
A detailed simulation analysis in FY11 showed that RTU retrofits led to significant energy (between 24 and 35 percent) and cost savings (38 percent) from fan, cooling and heating energy consumption. The simulation analysis was followed by an extensive field test of a retrofittable advanced RTU controller, the Catalyst product manufactured by TransformativeWave. The recommended advanced control package included multispeed fan control, integrated economizer controls and demand-controlled ventilation (DCV).
To get a sense of the huge swath of opportunity that RTUs represent, consider these compelling stats: “Packaged rooftop units (RTUs) are used in 46% (2.1 million) of all commercial buildings, serving over 60% (39 billion square feet) of the commercial building floor space in the U.S. (EIA 2003). The site cooling energy consumption associated with RTUs is about 160 trillion BTUs annually. Packaged heat pumps account for an additional 70 trillion BTUs annually. The source energy consumption of these units is over 1,000 trillion BTUs.”
With such big numbers at play, just a small improvement in part-load operation of these units can lead to enormous overall reductions of energy use and carbon emissions. The in-depth analysis of the more than 60 units in the report included four different building types and four climate locations. Results showed building type, unit runtime and supply-fan motor size were significant contributors to the energy savings potential. Here are five key tips from the report to help maximize energy savings of RTU retrofits.