Energy reducing retrofit apparatus for a constant volume HVAC system

A method comprising:

• receiving, with a controller of a heating, ventilation, and air-conditioning (HVAC) system for an indoor space, signals corresponding to whether the indoor space is less than fully occupied, the HVAC system having a cooling assembly that includes at least one of an economizer or a compressor;
• controlling, with the controller, a variable frequency drive that drives a fan motor of the HVAC system within a range of fan motor speeds to ventilate the indoor space by reducing a speed of the fan motor based on the received signals;
• and
• determining, with the controller, an energy consumption fault,
• wherein the controller determines the energy consumption fault by:
• determining an outside air temperature, a heat mode runtime, a cool mode runtime, and a ventilation mode runtime at preset intervals;
• determining an actual energy consumption of the HVAC system;
• accessing a database that stores historical data correlating time of day data and outside air temperature data with energy consumption data of the HVAC system to determine a normal energy consumption range for the HVAC system when a sufficient amount of previously sampled energy consumption data is present;
• comparing the actual energy consumption of the HVAC system with the normal energy consumption range;
• and determining that the energy consumption fault exists in response to the actual energy consumption being outside of the normal energy consumption range.

A system comprising:

• a controller configured to (i) communicate with a variable frequency drive that is configured to drive a fan motor of a heating, ventilation, and air-conditioning (HVAC) system within a range of fan motor speeds to ventilate an indoor space, the HVAC system having a cooling assembly that includes at least one of an economizer or a compressor, (ii) receive signals corresponding to whether the indoor space is less than fully occupied, (iii) control the variable frequency drive to reduce a speed of the fan motor based on the received signals, and (iv)—determine an energy consumption fault,
• wherein the controller is further configured to determine the energy consumption fault by:
• determining an outside air temperature, a heat mode runtime, a cool mode runtime, and a ventilation mode runtime at preset intervals;
• determining an actual energy consumption of the HVAC system;
• accessing a database that stores historical data correlating time of day data and outside air temperature data with energy consumption data of the HVAC system to determine a normal energy consumption range for the HVAC system when a sufficient amount of previously sampled energy consumption data is present;
• comparing the actual energy consumption of the HVAC system with the normal energy consumption range;
• and determining that the energy consumption fault exists in response to the actual energy consumption being outside of the normal energy consumption range.