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Abstract
Rooftop packaged air-conditioning units (RTUs) have been intensively utilized in commercial buildings for providing space heating and cooling. They serve over 60% of the commercial building floor space in the U.S. Inefficient routine operations of multiple RTUs result in waste energy consumption. Specifically, oversizing is an inherent issue practically caused by overdesign of mechanical engineers. With field test studies, oversizing can be up to 100% leading to much energy penalty.
Although there are locally advanced control technologies utilized to improve the overall efficiency performance of RTUs, they are invasive approaches to interrupt normal operations and require experienced service teams for preventative maintenance causing high first cost installation and service costs with returning on investment (ROI) being more than 3-5 years depending on the type of a building.
To reduce ROI and permanently reduce inherent oversizing issue without intervention of an original system, the report proposes a non-invasive methodology for reducing energy penalty caused by non-optimal design. The technique will use adaptive control strategies to minimize the fault impact until the receipt of actual physical repair or to ultimately eliminate the fault without any further physical intervention. Control algorithms are systematically developed to mainly reduce oversizing effect utilizing simplified instantaneous building load. With the control algorithm implemented and tested by a building simulation platform, the oversizing effect is decreased at least 30% and can be reached to 60%. With the decrease of the oversizing effect and energy penalty without original system interference, the improved results lead to: 1) compressor energy savings between 15 and 30% and fan energy savings between 30 and 55% and 2) improved indoor relative humidity resulting in more energy savings for commercial supermarket applications.
The proposed method will be further applied to: 1) temporarily minimize the fault impact caused by faulty operations and improper commissioning such as over-circulation and outdoor damper leakage and 2) temporarily disabled severe faults including fail compressor, fail heater and some control-related faults meanwhile the overall performance of a system is in acceptable thresholds until these faults are physically fixed and ready to use normally.
