DDC offers the best sustainable solutions to existing and new buildings to save energy and save cost and allowing a measurable return on investment. These measures typically focus on: AHU Plug Fan Retrofit Upgrade. Chiller EC Fan Retrofit. IT Cooling EC Fan Retrofit. Optimization of lighting management systems. Building management systems. Replacing traditional bag filters with Electrostatic filters. Installation of Variable Frequency Drive (VFD) to adjust the speed of an HVAC fan or pump motor. Installation of capacitors banks to store electrical energy.