Energy reducing retrofit method and apparatus for a constant volume hvac system

A method reducing energy consumption comprising retrofitting a preexisting single zone constant volume HVAC system that provides heating, cooling, or ventilation to an indoor space within a single zone of a building, wherein the indoor space has at least partial occupancy, and the heating, cooling, or ventilation is controlled and operable from a range of not operating to a maximum operation based on preset conditions or on occupancy command, and wherein the preexisting HVAC system comprises a fan, a fan motor associated with the fan, a thermostatic device that references temperature of the indoor space, heating or cooling equipment having equipment control terminations, and an economizer comprising at least one outside air damper and one return air damper with an associated damper actuator, the method comprising:

• providing a programmable logic controller to receive input from the thermostatic device and send instructions to the fan motor to actuate the fan to ventilate the indoor space (ventilation mode), and the heating or cooling equipment to send heat (heating mode) or cooling (cooling mode) to the indoor space, and the system economizer to actuate the damper actuator (economizer mode);
• operably connecting the programmable logic controller to the equipment control terminations;
• providing a variable frequency drive (VFD), controlled by the programmable logic controller, and operably connecting the VFD to the fan motor;
• providing an occupancy sensor to determine occupancy levels within the indoor space and sending the sensed occupancy level to the programmable logic controller for at least the ventilation mode and the heating and/or cooling mode;
• providing an input sensor and an output sensor to sense respective outside air condition and return economizer air and that the sensors communicate their sensed conditions to the programmable logic controller;
• operating the fan motor at a reduced speed during the ventilation mode when the occupancy level requires less than maximum operation in the ventilation mode;
• operating the fan motor at a reduced speed during the heating and/or cooling mode;
• and
• operating the HVAC system in the ventilation mode the heating and/or cooling mode and the economizer mode, wherein all said modes are controlled by the programmable logic controller.

An efficiency enhancing controller (EEC) for enhancing energy efficiency in an indoor space of a building having an occupancy that is served by a single zone, constant volume HVAC system, the EEC comprising:

• a programmable logic controller adaptable for a single zone constant volume HVAC system to receive input signals from sensors and a thermostatic device and send control heating, cooling, and ventilation instructions or an occupancy command to:
• a fan assembly of the constant volume HVAC system to ventilate an indoor space in a building, and
• a heating assembly that can send heat to the indoor space, and
• a cooling assembly that can send cooling to the indoor space;
• and
• a variable frequency drive (VFD) that receives signals from the programmable logic controller and can control the frequency of a fan motor of the fan assembly,
• wherein the programmable logic controller has the capability to reduce the fan motor speed via the VFD when the sensors indicate that the indoor space is less than fully occupied.