This guide primarily applies to facility managers and energy managers of large existing office buildings larger than 100,000 square feet, but also includes considerations for small and medium office buildings. By presenting general project planning guidance as well as financial payback metrics for the most common energy efficiency measures, this guide provides a practical roadmap for effectively planning and implementing performance improvements for existing buildings.
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Retail buildings in the U.S. are second only to office buildings in total energy consumption and represent approximately 13% of energy use in commercial buildings nationwide. The Advanced Energy Retrofit Guide for Retail Buildings presents general project planning guidance as well as more detailed descriptions and financial payback metrics for the most important and relevant energy efficiency measures to provide a practical roadmap for effectively planning and implementing performance improvements in existing buildings. This guide is primarily designed for facility managers and energy managers of existing retail buildings of all sizes.
In 2011, the U.S. Department of Energy’s Building Technology Office (DOE’s 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). In April 2013, Carrier’s 10-ton WeatherExpert unit model was recognized by DOE to have met the RTU Challenge specifications. Carrier also committed to have its entire line of WeatherExpert models for commercial buildings compliant with integrated energy efficiency ratio (IEER) meeting the RTU Challenge requirement. This report documents the development of part-load performance curves and their use with the EnergyPlus simulation tool to estimate the potential savings from the use of WeatherExpert units compared to other standard options.
A detailed EnergyPlus model was developed for a prototypical big-box retail store. The model used the performance curves from the new model along with detailed energy management control code to estimate the energy consumption of the prototypical big-box retail store in three locations. 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 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 (2015) Federal regulations for commercial equipment standards, so it can be used as the baseline to estimate the potential for energy savings from WeatherExpert units in comparison with new RTUs that meet the minimum efficiency requirements. The third reference unit (Reference 3) represents units that meet 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.
The following conclusion can be drawn about the comparison of energy cost for WeatherExpert unit compared to the three reference units:
• Using Reference 1 as the baseline, WeatherExpert units result in about 45% lower heating, ventilation and air conditioning (HVAC) energy cost in Houston, 55% lower cost in Los Angeles, and 35% lower cost in Chicago. The percentage savings of electricity cost is more than 50% for all three locations.
• Using Reference 2 as the baseline, WeatherExpert units result in about 39% lower HVAC energy cost in Houston, 52% lower cost in Los Angeles, and 32% lower cost in Chicago. The percentage savings of electricity cost is 44%, 55%, and 57%, respectively for the three locations.
• Using Reference 3 as the baseline, WeatherExpert units result in about 25% lower HVAC energy cost in Houston, 35% lower cost in Los Angeles, and 18% lower cost in Chicago. The percentage savings of electricity cost is 29%, 38%, and 37%, respectively.
Based on the simulation results, the WeatherExpert RTU Challenge unit, if widely adopted, could lead to significant energy, cost and emission reductions. Because the cost of these units was not available and because the costs would be specific to a given installation, no attempt was made to estimate the potential payback periods associated with any of the three reference scenarios. However, if the incremental cost relative to any of the three reference cases is known, one can easily estimate a simple payback period.
In FY14, BTO funded PNNL to develop and integrate AFDD methods for both air-side and refrigerant-side fault detection and diagnostics with one of the leading advanced RTU controllers sold in the market today. The work also includes testing and validating the integrated solution in the field. If the results from the field demonstrations show reliable fault diagnostics, it will encourage utilities to provide incentives to pursue the integrated technology because it makes the retrofit controller more cost effective and could make market adoption of the retrofit controller even more attractive to building owners.
Seven AFDD algorithms were developed, deployed and tested on the RTU controller for detecting and diagnosing faults with RTU economizer and ventilation operations using sensors that are commonly installed for advanced control purposes.