Part-Load Performance Characterization and Energy Savings Potential of the RTU Challenge Unit: Daikin Rebel.

摘要

In 2011, the U.S. Department of Energy's Building Technology Office (DOEs BTO), with help from the Better Buildings Alliance (BBA) members, developed a specification (RTU Challenge) for high performance rooftop air-conditioning units with capacity ranges between 10 and 20 tons (DOE 2013). Daikins Rebel was the first rooftop unit system recognized by DOE in May 2012 as meeting the RTU Challenge specifications. This report documents the development of part-load performance curves and there use with the EnergyPlus simulation tool to estimate the potential savings from the use of Rebel units compared to other standard options. The conventional direct-expansion cooling model in EnergyPlus and its performance curve equations are not appropriate to use to capture the Rebels performance; therefore, performance curves suitable for the Rebel unit were developed. The data for the performance curves were collected through a series of laboratory tests. A detailed Energy Plus model was developed for a prototypical big-box retail store. The model used the new performance curves along with detailed energy management control code to estimate the energy consumption of the prototypical big-box retail store in three locations (Houston, Log Angeles and Chicago). The energy consumption by the big-box store was then compared to a store that used three different reference units. The first reference unit (Reference 1) represents existing rooftop units (RTUs) in the field, so it can be considered as the baseline to estimate potential energy savings from other RTU replacement options. The second reference unit (Reference 2) represents RTUs in the market that just meet the current (2013) Federal regulations for commercial equipment standards. So, it can be used as the baseline to estimate the potential for energy savings from Rebel units in comparison with new RTUs that meet the minimum efficiency requirements. The third reference unit (Reference 3) represents the latest ASHRAE 90.1-2010 requirements. For RTUs with cooling capacity greater than 11,000 Btu/h, ASHRAE 90.1-2010 (ASHRAE 2010) requires two-speed fan control or variable-speed fan control.