Abstract: Systems and methods are provided and include a variable frequency drive configured to drive a fan motor of an HVAC system to ventilate an indoor space, the HVAC system having a cooling assembly that includes at least one of an economizer and a compressor. A controller is configured to communicate with the variable frequency drive, receive at least one signal from an occupancy sensing device, determine whether the indoor space is less than fully occupied based on the at least one signal, and control the variable frequency drive to reduce a speed of the fan motor in response to determining that the indoor space is less than fully occupied.

Abstract: An energy-reducing method and apparatus for retrofitting a single zone, constant volume HVAC system, with or without an economizer, that provides heating, cooling, and ventilation to occupants within a building space. The present invention includes the introduction of a programmable logic controller and variable frequency drive (VFD) that takes control of the existing fan, heating, cooling, and optional economizer operation. The reduction of the fan speed in the ventilation mode when the 100% operation is not needed saves significant energy of the existing constant volume HVAC system where the fan motor is designed to run 100% of the time.

Abstract: Systems and methods include a controller that compares an indoor temperature with a dead-band range having a heating setpoint and a cooling setpoint and that operates an HVAC system in an economizer mode to cool an indoor building space by introducing outside air to the indoor building space, prior to a call for cooling being received, in response to the indoor temperature being within the dead-band range and increasing.