Automated Demand Response Agent (DR Agent)
Many utilities around the country have or are considering implementing dynamic electrical pricing programs that use time-of-use electrical rates. Time-of-use electrical rates vary based on the demand for electricity. Critical peak pricing (CPP), also referred to as critical peak days or event days, is an electrical rate where utilities charge an increased price above normal pricing for peak hours on the CPP day. CPP times coincide with peak demand on the utility; these events are generally called between 5 to 15 times per year and occur when the electrical demand is high and the supply is low. When a CPP event occurs, these customers can reduce their electrical consumption and receive a utility incentive. Most CPP events occur during the summer season on very hot days. For this purpose the initial implementation of the DR agent addresses CPP events where the RTU would normally be cooling. Later, implementation of a sequence to handle CPP events for heating, during the winter season will be added. Also, this implementation of the DR agent is specific to the CPP, but it can be easily modified to work with other incentive signals (real-time pricing, day head, etc.).
The main goal of the building owner/operator is to minimize the electricity consumption during the peak periods on a CPP day. To accomplish that goal, the DR agent performs three distinct functions:
Step 1 – Pre-Cooling: Prior to the CPP event period, the cooling and heating set points are reset lower to allow for pre-cooling. This step allows the RTU to cool the building below its normal cooling set point while the electrical rates are still low (compared to the during the peak CPP event times). The cooling set point is typically lowered between 3 and 5oF below the normal. Rather than change the set point to a value that is 3 to 5oF below the normal at once, the set point gradually lowered over a period of time.
Step 2 – Event: During the CPP event the cooling set point is raised, the damper is commanded to a position that is slightly below the normal minimum, the fan speed is slightly reduced (if the unit has a variable frequency drive), and the second stage cooling differential (time delay between stage one and stage two cooling) is increased, if the unit has multiple stages. These steps will reduce the electrical consumption during the event. The pre-cooling actions taken in step one will allow the temperature to slowly float up to the CPP cooling temperature set point and reduce occupant discomfort during the attempt to shed load.
Step 3 – Post-Event: The DR agent will begin to return the RTU to normal operations by changing the cooling and heating set points to their normal values. Again, rather than changing the set point in one step, the set point is changed gradually over a period of time to avoid the "rebound" effect.
DR agents are currently running on two demonstration sites in western Washington and northern California. Coming soon are the results from the past events.