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Grid-interactive efficient buildings (GEBs) require quick and accurate manipulation of flexible electrical loads. Heating, ventilating, and air conditioning (HVAC) loads are particularly well suited for demand flexibility control by utilizing thermal mass in building structures. The HVAC load and its responding zone temperature (ZT) can be optimized by model predictive control (MPC) to minimize the operation cost with the indoor comfort constraint. However, due to the lack of reliable and affordable energy meters, the current HVAC demand control is implemented using ZT feedback control with the responding ZT optimized by MPC as the setpoint and the HVAC load as the response. Unfortunately, the building thermal mass makes the actual HVAC load significantly different than the optimized HVAC load, which is the on-demand setpoint, with potential demand penalty. Low-cost virtual flow meter technology makes the cooling load measurement at air handling units (AHUs) available, thus energy feedback control can be applied to actively control the cooling load of AHUs at its on-demand setpoint. The objective of the paper is to preliminarily investigate the demand flexibility control performance of the energy feedback control at AHUs. First, the energy feedback control at AHUs is introduced. Then, the performance of a single zone AHU is simulated and compared between the ZT feedback control and energy feedback control. Finally, a field experiment is conducted on a 7-ton single duct variable air volume AHU with these two different controls. Experimental results show that the cooling load with the current ZT feedback control drops to the on-demand setpoint after 25 minutes. On the other hand, the energy feedback control can reduce the cooling load to the on-demand setpoint in less than 3 minutes. Therefore, the active energy feedback control can significantly advance the current ZT feedback control by quickly and accurately controlling the cooling load at AHUs to avoid the demand penalty. [ABSTRACT FROM AUTHOR]

Variable frequency drives (VFDs) supply induction motors the pulse width modulation (PWM) power at variable frequency and voltage. In addition to the energy consumption by VFDs, the harmonics in the PWM power may generate additional motor power loss. An experiment was conducted on a VFD-motor drive system to investigate the VFD efficiency and additional motor power loss at the rated frequency. The experimental results show that the PWM power does not generate significant additional motor power loss and the VFD energy efficiency is 95.5% at the rated frequency for the studied drive system. [ABSTRACT FROM AUTHOR]

Variable frequency drives (VFDs) completely change the power conditions and efficiency of connected motors. Due to insufficient data, energy simulation programs, such as EnergyPlus, directly use manufacturer efficiency data by ignoring VFD impacts. The paper is to validate an approach to convert manufacture efficiency data to actual motor efficiency with VFDs using the equivalent circuit method. First the motor circuit parameters are estimated based on manufacturer data; and then applied to simulate the motor efficiency with VFDs, which is validated by the measured efficiency. The result shows the approach can effectively calculate the motor efficiency with VFDs using manufacture data. [ABSTRACT FROM AUTHOR]