Determination of return air temperature

A method of operating a heating, ventilation, and air conditioning (HVAC) system, the method comprising, by a controller of the HVAC system:

• determining that heating or cooling mode operation is not requested;
• following determining that heating or cooling mode operation is not requested, causing the blower to provide a flow of air at a first flow rate, wherein the flow of air is provided through at least one air duct of the HVAC system and into a conditioned space;
• following causing the blower to provide the flow of air at the first flow rate, receiving, over a first period of time, measurements of the discharge air temperature from a temperature sensor positioned and configured to measure a discharge air temperature of the flow of air provided to the conditioned space;
• determining that the measured discharge air temperature satisfies predefined stability criteria associated with a change in the discharge air temperature during the first period of time being less than a threshold value;
• in response to determining that the measured discharge air temperature satisfies the predefined stability criteria, determining a first temperature offset comprising a difference between the discharge air temperature following the first period of time and an indoor temperature at a corresponding time point;
• determining a first outdoor temperature;
• and
• storing, in a memory of the controller, the first temperature offset in a lookup table such that the stored first temperature offset is associated with the first flow rate of the flow of air provided by the blower and the first outdoor temperature.

A controller of a heating, ventilation, and air conditioning (HVAC) system, the controller comprising:

• an input/output interface communicatively coupled to:
• a blower configured to provide a flow of air through at least one air duct and into a conditioned space;
• and
• a temperature sensor positioned and configured to measure a discharge air temperature of the flow of air provided to the conditioned space;
• and
• a processor coupled to the input/output interface, the processor configured to:
• determine that heating or cooling mode operation is not requested;
• following determining that heating or cooling mode operation is not requested, cause the blower to provide the flow of air at a first flow rate;
• following causing the blower to provide the flow of air at the first flow rate, receive, from the temperature sensor over a first period of time, measurements of the discharge air temperature;
• determine that the measured discharge air temperature satisfies predefined stability criteria associated with a change in the discharge air temperature during the first period of time being less than a threshold value;
• in response to determining that the measured discharge air temperature satisfies the predefined stability criteria, determine a first temperature offset comprising a difference between the discharge air temperature following the first period of time and an indoor temperature at a corresponding time point;
• determine a first outdoor temperature;
• and
• store, in a memory of the controller, the first temperature offset in a lookup table such that the stored first temperature offset is associated with the first flow rate of the flow of air provided by the blower and the first outdoor temperature.