Spinning Reserves from Controllable Packaged Through the Wall Air Conditioner (PTAC) Units

Abstract

This report summarizes the feasibility of providing spinning reserves from packaged through the wall air conditioning (PTAC) units. Spinning reserves, together with non-spinning reserves, compose the contingency reserves; the essential resources that the power system operator uses to restore the generation and load balance and maintain bulk power system reliability in the event of a major generation or transmission outage. Spinning reserves are the fastest responding and most expensive reserves. Many responsive load technologies could (and we hope will) be used to provide spinning reserve. It is also easier for many loads (including air conditioning loads) to provide the relatively shorter and less frequent interruptions required to respond to contingencies than it is for them to reduce consumption for an entire peak period. Oak Ridge National Laboratory (ORNL) is conducting research on obtaining spinning reserve from large pumping loads and from residential and small commercial thermostat controlled heating, ventilation and air conditioning (HVAC) units. The technology selected for this project, Digi-Log's retrofit PTAC controller, offers significant advantages. To evaluate the availability of spinning reserve capacity from responsive heating and air conditioning loads, ORNL obtained data from a number of units operating over a year at a motel in the TVA service territory. A total of 24 PTAC units in as many rooms were fitted with Digi-Log's supervisory control unit that could be controlled from the motel front desk. Twelve of the rooms formed the group in which the controller was controlled from the hotel front desk only. The remaining twelve rooms were controlled by the occupant and formed the uncontrolled group. This enables us to evaluate the spinning reserve capacity from PTACS that were operating normally and from those under active energy management. A second generation of the Digi-Log controller that will respond quickly enough to provide spinning reserve has been designed but not yet manufactured. Manufacture of these units is pending arrival of funds from NYSERDA. The new Digi-Log equipment will utilize satellite signals from Skytel to activate the controller from a remote site by the ISO and to respond to curtailment events. PTACs account for approximately 3% of the total commercial cooling load in the US, equivalent to an average energy consumption rate of 3,000 MW with peak consumption being significantly higher. Hence PTACs alone represent a sizable opportunity for providing spinning reserves from load. The residential buildings sector cooling and heating load averages about 33,000 MW, more than 10 times the commercial PTAC load. The buildings sector represents an even greater opportunity than the PTAC commercial sector for providing spinning reserves from load. Technology to implement load curtailment and monitor its effect already exists and can readily be further customized to meet ISO and utility needs. Further research is needed to prove the technical feasibility of PTAC units and other small loads providing spinning reserves. Aggregation, communication, control, and monitoring issues remain to be addressed. If the technical issues can be resolved however, it is likely that system operators, loads, and regulators will have significant incentives to resolve these other resources since spinning reserve from load has the potential to provide large benefits to each community.