Abstract
Heating, ventilation, and air-conditioning (HVAC) systems in commercial buildings have proven to be a great asset for providing secondary frequency regulation (FR) service to the power grid. However, how the provision of FR service affects the HVAC system performance is still largely unknown. This paper investigates how a HVAC system performance and its associated controls are impacted during and after a FR service. We exploit a dynamic Modelica-based medium office building model as a virtual testbed with the Air Handling Unit (AHU) fans providing the FR service for the assessment. The virtual testbed adopts state-of-the-art HVAC control sequences and an experimentally validated frequency regulation control scheme. The comprehensive study of 832 case studies considers several scenarios, consisting of different regulation capacities (demand levels), standardized FR test signals, and building load profiles in 16 U.S, climate zones. The holistic assessment includes the interaction between the FR and the HVAC baseline controls, the impact of FR on the occupant’s thermal comfort, and, more importantly, the energy efficiency.The results show that FR has little or no impact on the HVAC operation and occupant thermal comfort while the building is providing the service if an appropriate regulation capacity is pre-determined. However, if the regulation capacity is overestimated, the quality of the FR service provided by the HVAC system and the HVAC energy efficiency will be affected due to the equipment operating constraints. In addition, the AHU supply air temperature fluctuates, and the controller cannot maintain the desired setpoint as the FR magnitude is increased. After the FR service time, the system takes a certain period to return to normal operation. The rebound period extends with the increase in the FR magnitude. For this case study, there exists a control conflict between the FR control and the existing HVAC control (from ASHRAE Guideline 36-2018) during high load conditions, causing the fan speed to saturate. The increased fan electricity consumption caused by this control conflict will offset the potential revenue a building can earn from offering the FR service. In addition, the rebound power usage could have a negative effect on the grid.
Published Version
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