Climate Appropriate Innovations for Variable Refrigerant Flow Systems: Integrated Indirect Evaporative Cooling Adaptive Controls and Advanced Refrigerants

This project demonstrated the application of a hybrid space conditioning system that integrates variable refrigerant flow with indirect evaporative cooling as a more energy-efficient alternative to the rooftop units prevalent in small- to medium-sized commercial buildings throughout California. While variable refrigerant flow has been demonstrated as an energy-efficient space conditioning technology, one of its inherent challenges is limited ventilation capacity. This hybrid configuration uses indirect evaporative cooling as a dedicated outside air system to satisfy ventilation requirements, eliminate outside air loads during cooling, and reduce heating loads as an air-air heat exchanger.

Field demonstrations at three California sites sought to validate energy savings relative to modeled baseline performance, as well as peak load reduction, demand responsiveness, and maintained or enhanced occupant comfort.

A key advancement of this project was the development of an integrated system controller that optimizes operation of the combined variable refrigerant flow and indirect evaporative cooling configuration through zonal occupancy sensing and learned building behavior. Control sequence algorithms were based on governing logic informed by adaptive capabilities and response to inputs such as ambient weather conditions, humidity control, occupancy, and occupant comfort preferences.

This project also advanced modeling of variable refrigerant flow, indirect evaporated cooling, and hybrid variable refrigerant flow-indirect evaporative cooling systems by adding associated modules to the EnergyPlus building simulation software. This modeling work, which was calibrated with results from the field demonstrations, has developed and refined EnergyPlus for future modeling of these emerging space conditioning technologies and configurations.

Finally, this project featured laboratory testing of three leading natural refrigerants – propane, carbon dioxide, and ammonia – as sustainable, low global warming potential alternatives to traditional refrigerants. Novel heat pump and chiller equipment featuring these natural refrigerants were tested in three different laboratories, demonstrating energy-efficient performance coupled with low global warming potential.