Energy Implications of Retrofitting Retail Sector Rooftop Units with Stepped-Speed and Variable-Speed Functionality

Abstract

NOTICEThis report was prepared as an account of work sponsored by an agency of the United States government. Neither the United States government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States government or any agency thereof. (Felts et al. 2000). Thus, RTU supply fans may provide air at rates that are much higher than those needed to meet most thermal loads, wasting the energy needed to move and heat or cool the excess air.To address this issue, some U.S. retailers have started to upgrade existing RTUs, retrofitting their constant-speed motors with stepped-or variable-speed functionality. Such retrofits may be more cost effective than replacing an entire RTU, particularly if the unit is in the middle of its lifespan. Other U.S. retailers, however, are uncomfortable pursuing this measure, as there is a lack of supporting data detailing the climate zone-specific energy savings potential associated with this upgrade. Building and portfolio energy managers have thus been unable to present a compelling business case for RTU fan motor upgrades.This study uses whole-building energy simulation to estimate the energy impact of stepped-and variable-speed RTU fan motor retrofits in the retail environment, across 16 locations in all 15 U.S. climate zones. The results allow retailers to estimate the building-level energy savings associated with this retrofit measure. This is a critical step in enabling retailers to determine whether a compelling business case can be made. Development ProcessEnergyPlus Version 6.0 (DOE 2010) was used to evaluate the whole-building energy savings associated with stepped-and variable-speed RTU fan motor retrofits as follows:1. Two prototype big-box retail EnergyPlus models were created: one with refrigeration systems and one without.2. Each prototype model was replicated across 16 locations, which encompassed all 15 U.S. climate zones, as defined by DOE (2005).3. Standard 90. 1-20041- (ASHRAE 2004a) was applied to the building envelope to create climate-specific baseline models.4. Custom sizing and control logic was used to modify a subset of the baseline models with stepped-and variable-speed RTU fan motor controls.5. EnergyPlus was used to simulate the energy performance of all models to determine the energy savings associated with these retrofits.v Results Table ES-1 through Table ES-3 present an overview of the simulation results 1 . Annual whole...

End-Use Savings Shapes Measure Documentation: Advanced Rooftop Unit Control

“…Meanwhile, Studer et al (2012) performed a modeling analysis of implementing VFDs or stepped-speed fans in RTUs serving retail buildings, and presented aggregate energy savings as a fraction of whole-building (electric and gas) energy use, finding savings of 0.7 to 8.4% depending on climate zone and the presence or absence of refrigerated cases in the building (Studer, 2012). Studer et al found a range of 29% to 55% fan energy savings with the steppedspeed fans and 44% to 57% savings with the fully variable speed fans in modeled buildings with refrigeration, and 31%-63% and 50%-72%, respectively, in modeled buildings without refrigeration (Studer, 2012). Refrigeration was modeled as being present in grocery areas of bigbox retail stores.…”

Performance Evaluation of Three RTU Energy Efficiency Technologies

“…Further detail is provided in Section 4. Assumptions regarding economizer type and heating efficiency were taken from previous research done at the National Renewable Energy Laboratory (NREL) (Studer et al 2012).…”

RM12-2703 Advanced Rooftop Unit Control Retrofit Kit Field Demonstration: Hawaii and Guam Energy Improvement Technology Demonstration Project

“…This demonstration focused on ARC retrofit impacts on (1) annual energy savings and ROI; (2) thermal comfort; and (3) demand response. Independent modeling studies (Studer 2012;Wang 2011) and other DOE and utility field demonstrations (Wang 2013;BPA 2013;Snohomish 2013; Appendix C) have shown significant energy savings potential and aggressive paybacks for ARC retrofits. Yet none of the demonstrations were in a hot-humid climate (ASHRAE climate zone 1A), and to date no studies have analyzed the impacts on interior thermal comfort and demand response.…”