Building-grid integration, ancillary services, grid-interactive control
Real-time power supply and demand balances are critical to ensure stable power frequency and quality power services. However, the growing integration of renewable energy increasingly challenges the power infrastructure because most of the renewable resources, e.g., solar and wind energy, are intermittent and difficult to predict. To meet the stringent power frequency requirements, more fast reacting frequency regulation resources are being brought online among which grid-level batteries are the dominant ones. Although batteries can provide fast and high quality regulation services, they suffer from high initial cost, high environmental impact and round-trip efficiency loss. When providing fast frequency regulation services, battery life span could be significantly reduced, leading to even higher cost per unit of frequency regulation service. Buildings consume more than 73% of the electricity in the US, offering significant regulation reserves for the power grid. Variable-speed air-conditioning systems are taking an increasing share of the market due to the higher efficiency requirements imposed by federal agencies. In addition to efficiency benefits, variable-speed cooling/heating systems are also perfectly suited for providing ancillary services as these units can modulate their power continuously over a wide range. Compared to batteries, HVAC systems have several advantages when providing frequency regulation services: 1) in theory, they do not incur any round-trip efficiency loss; 2) the time response of an AC unit could be faster than a battery (especially compared to energy batteries with slower ramping rates and relatively larger capacities); 3) the existing regulation capacity of HVAC systems is huge and the implementation cost is much lower; 4) the environmental impact of using HVAC systems for regulation services is lower than for battery systems. This paper presents lab test results of a variable-speed heat pump for providing ancillary services. Regulation performances for both the traditional (slow) and dynamic (fast) regulation services are reported. The tested performance scores were above 0.97 and the regulation performance even beats the average battery regulation performance. Preliminary economic analysis was also performed using historical PJM prices. It was shown that the credit received for providing ancillary services could easily offset 50% of the HVAC energy cost under the tested conditions.