Objective
Due to the lack of communications among chillers, air handling units (AHU), and terminal boxes (TB), existing Heating, Ventilation, and Air-conditioning (HVAC) load management technologies, including a) centralized control at chillers, b) cooling load control at AHU, and c) global temperature adjustment (GTA) control at TB, have a technical challenge to simultaneously provide accurate demand control at chillers and share reduced cooling load evenly among all zones in demand response events.
The goal of this project is to achieve energy cost savings through dynamically responsive HVAC demand control with minimized negative thermal comfort impacts, while also achieving strengthened resilience for the critical Department of Defense (DoD) mission functions during a power outage. Since the water loop pressure differential (WLP) indicates the energy balance between chiller cooling supply and AHU cooling load while the air duct static pressure (DSP) indicates the energy balance between AHU cooling supply and TB cooling load, this goal can be achieved through the HVAC load management approach using two cascade controls on the WLP and DSP to enable the communications among chillers, AHU, and TB. Specifically, the technical objectives of the demonstration are to:
- Evaluate the implementation, operation, and maintenance costs of the HVAC demand control approach along with energy efficiency improvements on a real-world DoD installation.
- Validate the performance, i.e., the accurate HVAC demand control and cost savings under accepted indoor thermal condition, of the approach using real-world DoD operating conditions.
- Enable direct technology transfer and commercialization making the technology available and scalable across DoD facilities.
Technology Description
The approach for HVAC load management consists of three existing HVAC load management technologies and integrates them with two cascade controls on the WLP and DSP to evenly distribute the controlled cooling supply from chillers to AHU and then from AHU to zones in a chiller demand-priority way.
- Technology I: The cascade controller on the WLP is applied to maintain the WLP setpoint by adjusting the cooling load setpoint at AHU on the load side under the controlled chiller power demand instead of adjusting the chilled water pump speed on the supply side.
- Technology II: The cascade controller on the DSP is applied to maintain the DSP setpoint by adjusting the zone temperature setpoint at TB on the load side under the adjusted AHU cooling load instead of adjusting the AHU fan speed on the supply side.
Benefits
Due to the building thermal mass and HVAC equipment response time, the HVAC demand cannot be quickly and accurately controlled in a demand response event using the popular GTA technology which often results in demand penalties across utility tariffs. With the HVAC load management approach, the HVAC demand can always be accurately controlled at the preset desired level to avoid such demand penalties while also ensuring minimized negative indoor thermal comfort.
Accurate peak demand reductions can help the DoD defer capital investments by downsizing photovoltaic system, thermal storage and microgrid systems, provide additional revenue when connected to grid, and maintain the essential mission during a power outage.