Demonstration of HVAC chiller control for power grid frequency regulation-Part 2: Discussion of results and considerations for broader deployment

Secondary frequency regulation is an electric grid ancillary service that balances the electric power system supply and demand on short time intervals. A companion article (Su and Norford 2015) developed and experimentally demonstrated a practical controller to modify chiller power demand to provide secondary frequency regulation with sufficient performance to meet market qualification requirements. This article compares experimental results to model predictions and to other sources of secondary frequency regulation. Delay time, ramp-rate limits, minimum power, and variable coefficient of performance are identified as factors that contribute to chiller power transient behavior and should be considered when predicting performance. This article additionally introduces results from a second building to assess the applicability of similar chiller control strategies for other HVAC systems. The second building produced less positive results due to communication delays associated with a modified setup and due to less favorable chiller characteristics, such as ramp-rate limitations and compressor cycling. While these constraints may be lessened with changes to chiller settings, the significant variations between the two buildings suggest that for a given site, observations are necessary in addition to design information to ascertain a chiller's suitability for providing secondary frequency regulation.