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The purpose of this project is to evaluate the demand response (DR) potential of variable-capacity (VC) heating, ventilation, and air-conditioning (HVAC) equipment in light commercial building applications. VC HVAC systems provide enhanced energy efficiency and customer comfort benefits, but their DR capabilities have not been fully demonstrated. The study aimed to demonstrate emerging controls approaches at Southern California field sites and evaluate their response in terms of demand reduction, impact on occupant comfort, and potential to manage recovery.

The technology used in the study included variable-speed rooftop units (RTUs) and variable refrigerant flow (VRF) systems, which leverage variable-speed compressors, electronic expansion valves, and refrigerant management controls to match HVAC system output to the building's cooling and heating requirements. The study found that VC HVAC systems can provide improved DR over baseline equipment, with the VRF system reducing electrical demand by 15-25% during 1- or 2-hour DR events.

The evaluation approach included installing monitoring equipment to verify system response and performance, and developing a test matrix to evaluate the available DR functions with a range of control parameters. The study found that the VRF system responded as expected to commands sent via OpenADR 2.0b, and that the Capacity Limit control can reduce electrical demand with minimal impact on indoor temperatures.

The major findings of the study include:
- The VRF system can reduce electrical demand by 15-25% during 1- or 2-hour DR events using Capacity Limit control.
- The strategy of Pre-cooling followed by Capacity Limit control can also provide a 15% reduction in demand.
- The VRF system responds as expected to commands sent via OpenADR 2.0b.
- The variable-speed packaged RTU did not take full advantage of its variable-speed capabilities for DR and instead shut off in response to setpoint offset commands in several test events.

The project findings suggest several follow-on activities, including developing an industry standard to harmonize DR responses from variable-speed HVAC systems, and conducting additional field testing of larger VRF systems to evaluate their DR potential and possible impact on occupant comfort at scale.