Field Test of Controller with Fault Detection and Diagnostics

After-market RTU controller and supply fan variable speed drive. Steps supply fan speed based upon stages of cooling/heating. Adjusts outside air damper for DCV. Provides Fault Detection and Diagnostics.

This Air Conditioning (AC) Controller field assessment measures the electrical energy and demand savings of an enhanced controller for a packaged AC unit retrofit. This controller included variable supply fan speed control, Demand Control Ventilation (DCV), and Fault Detection and Diagnostics (FDD). Approximately 65% of California’s commercial floor area is conditioned by packaged AC unitsi . The majority of existing units are constant volume systems, delivering a fixed amount of conditioned supply air to the building space. This supply air quantity is based upon the space’s maximum cooling demand. Because this demand occurs for only a few hours per year, the AC units operate at part load for the majority of the year. However, the AC unit supply fan consumes the same amount of energy regardless of the space’s cooling or heating demand. Several manufacturers have developed systems that convert constant volume AC units to variable air volume operation. These systems reduce the supply air flow when there is no call for cooling or heating from the served space. The systems can be retrofitted into existing AC units. They consist of a variable frequency drive (VFD), sensors, and controls. In this study, a retrofit controls system was added to four rooftop packaged heat pumps serving the common atrium area of an enclosed shopping mall in the metropolitan area of Loa Angeles County, California. This system reduced the AC units’ supply fan flows when there was no call for cooling or heating in the conditioned spaces. The supply fan and cooling system energy consumption was measured and recorded, and compared to baseline operation (constant volume fan). Fan energy savings were measured at each AC unit when outside air temperature was between 50 - 95°F. As outside air temperature rose, the demand for cooling increased, and fan energy savings decreased. Table 1 summarizes the supply fan energy savings for each of the tested AC units, for 5°F outside air temperature bins. These savings are compared to the same supply fans operating continuously at full speed during the AC units’ hours of operation.