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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]

Heating, Ventilation, and Air Conditioning (HVAC) systems operate at dynamic loads and may present unpredictable disturbances. Relatively minor disturbances can greatly affect the performance of certain subsystems, such as the cooling coil control valve. The operating error of the cooling coil control valve has the potential to compound with error from other subsystems and deteriorate the performance of the air handling unit (AHU). In many cases, the control systems are nonlinear and of high order, which reduces the likelihood of system stability with conventional control approaches. The objective of this paper is to experimentally evaluate the cooling coil control valve performance of cascade control by comparing it with a conventional Proportional- Integral (PI) control, on a nonlinear cooling coil control system. In the paper, the performances of both controls were compared first using a step change in reference input, i.e. supply air temperature setpoint step change and a step change in disturbance input, such as chilled water loop differential pressure (DP) step change. The primary testing criterion is the operating error, in terms of mean integral square error (mISE). System stability, settling time, and disturbance rejection are also considered in the comparison of the two control approaches. As a result, the cascade control is found to be the most effective when the valve system experiences pressure interruptions. For example, a maximum error of 0.46 °F for the cascade control and 0.95 °F for the single loop control were observed when the DP is reduced by 5 psi (27.8% of the operation value), while the mISE in the cascade control was only 5.5% of the single loop mISE. In addition, the mISE value of the cascade control is approximately 42% of the single loop mISE value for reference step change test. [ABSTRACT FROM AUTHOR]