Abstract
HVAC systems in the commercial building sector consume about 3.4 quads of energy annually. Of all the HVAC systems, packaged rooftop air-conditioning units (RTUs) provide cooling and heating for over 60 percent of the commercial building floorspace (about 90 billion ft2) in the U.S. and they are a significant source of energy consumption and peak demand. All HVAC systems suffer from faults that impact thermal comfort and increase energy consumption. There are several commercially available Automated Fault Detection and Diagnostic (AFDD) tools on the market that can detect and diagnose faults, and if those faults are corrected, can save significant national energy. However, there are multiple market barriers for these tools including lack of independent verification of their performance in the field in terms of their technical capabilities, ease of use and installation. Therefore, the overall objective of this study was to establish the technical and economic feasibility of Automated Fault Detection and Diagnosis (AFDD) Tools and Technologies for retro-commissioning and continuous commissioning of HVAC systems based on independent field testing at ten sites. The project tasks included site selection, AFDD product selection for evaluation, the development of measurement and verification plan, installation of AFDD tools and independent monitoring systems at field sites, baseline testing and evaluation of AFDD tools, retro-commissioning and continuous commissioning of AFDD tools, market understanding/barrier study and the overall process evaluation. Education and outreach, and utility engagement in the project were an integral part of the project. In this study nine commercial AFDD tools consisting of one pure hardware tool, three combinational tools, and five software tools were installed on nine RTUs sourced from participating commercial building owners in Connecticut. These RTUs are also instrumented with an Independent Monitoring System (IMS) to measure and verify the faults detected by the tool and the performance of the system itself. In total the IMS features 27 sensors including temperature, relative humidity, refrigerant pressure, RMS power, and airflow instruments for each site. These sensors are instrumented on each vapor compression cooling stage (refrigerant-side), and within air section in the RTU including the return, supply, mixed, and outdoor air sections. With the use of Yuill’s and Katipaumla’s FDD methods, the IMS behaves as an FDD tool itself and can determine various faults on the evaporator, economizer, condenser, compressor, and some controls. With the use of REFPROP connected with CoolProp, both the vapor compression and air-side psychrometric calculations yield Energy Efficiency Ratios (EERs) that measure and verify system performance with nameplate RTU specifications. Furthermore, data from the IMS are sent to a central server and likewise processed through automated scripts in R to Clean, Organize, Process, and Generate visual reports for further inferencing and analysis by experts. When considering the data from the study, it is evident that most of the HVAC systems within the study either did not experience significant fault modes or a low EER that would require major retro-commissioning activities. In conjunction with the unfortunate and untimely novel coronavirus, there was a significant reduction in energy use for most of the buildings under observation. This required an extension of the study into the final 2021 cooling season, because local, state and federal governments in 2020 imposed restrictions for public health and safety, which in effect reduced occupancy in building and cooling loads for non-essential businesses. Despite the pandemic, all of the FDD tools were extensively analyzed.
Submitted Version
Published Version
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