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In 2015, Bonneville Power Administration contracted with SBW to develop an Advanced Rooftop Control (ARC) savings calculator. The methodology automated in the ARC calculator was tested against work done by Bill Koran for BPA to evaluate post install savings for VFDs.

The ARC calculator requires ex post power, speed, and temperature data to perform statistical calculations of savings. Ex ante performance is extrapolated by developing fan curves to back out energy use without the advanced rooftop unit controls. These calculations were all designed to be normalized with TMY3 data to predict savings for a typical year within the BPA service region. The calculator can estimate savings for up to 7 speed settings on a control unit, or a true variable speed control. Savings can be calculated for any gas heated or heat pump rooftop units.

To use the ARC calculator, download the zipped file from the Materials section and then decompress the folder on your computer or network. Open the document labeled ARC_V1-01 which was created in Excel 2010. Instructions are provided on each sheet. Sample data files are also included in the zipped folder.

Previous Work

Starting in 2004, the RTF began conducting a series of data collection and analysis efforts to develop energy savings estimation methods for commercial-sector rooftop unit (RTU) and commercial split HVAC system O&M. The result was the RTF standard protocol for Packaged and Split System HVAC - Fan and Cooling Savings, approved on March 13, 2012.

Five phases of protocol development work included:

  1. A review of the existing research data nationwide on the energy savings that could be attributed to RTU from maintenance programs,
  2. Initial work on a simplified field energy savings measurement protocol that also included discovery of a dry bulb economizer sensor problem that led to the development of a new digital sensor that is now installed as a requirement in all PNW RTU maintenance programs,
  3. A larger scale RTU field test sponsored by the Bonneville Power Administration of a simplified measurement protocol including annual measurement of energy use and savings in a subset of units. Also completed was an RTU measurement database of more than 100 RTUs that is publicly accessible on this web page,
  4. Further review and refinement of the energy savings protocol and development of a normal annualized use and savings calculator using true power measurement and weather data as the two key input data requirements, and
  5. Completion of the protocol and Standard Protocol and Savings Calculator that was approved by the RTF on March 13, 2012.
Have questions?

Have questions? Please get in touch.

Jennifer Light
RTF Manager/Chair