System and method for controlling ventilation air of a target space

A method of operating a heating, ventilation, and air condition (HVAC) system configured to regulate a temperature of a target space, the method comprising:

• measuring a concentration of at least one gas in the target space;
• determining that the concentration of the at least one gas exceeds a gas concentration threshold;
• determining that operation of the HVAC system in a ventilation mode is indicated to reduce the concentration of the at least one gas, wherein the HVAC system operates in the ventilation mode by:
• introducing an outdoor ventilation airflow to an outdoor ventilation inlet of a duct system using a blower, wherein the outdoor ventilation inlet is in communication with the target space, wherein the duct system includes a return air inlet that communicates a return airflow from the target space to the blower;
• and
• discharging exhaust airflow in communication with the target space through an exhaust air outlet of the duct system using the blower to reduce the concentration of the at least one gas in the target space, and after determining that operation of the HVAC system in the ventilation mode is indicated, the method further comprises;
• determining a total capacity of the HVAC system, wherein the total capacity is a total thermal load (BTU/hr) that the HVAC system is configured to provide to the target space;
• determining a current capacity that the HVAC system, wherein the current capacity is a current thermal load (BTU/hr) that the HVAC system is using to regulate the temperature of the target space, wherein the current capacity is determined based at least on the temperature of the target space, a temperature of the return airflow, and a flow rate of the return airflow;
• causing the HVAC system to operate in the ventilation mode after validating that the total capacity is greater than the current capacity during operation of the HVAC system in the ventilation mode.

A controller of a heating, ventilation, and air conditioning (HVAC) system configured to regulate a temperature of a target space, the controller comprising:

• a network interface circuit communicatively coupled to:
• an air quality sensor positioned in the target space, the air quality sensor configured to sense a concentration of at least one gas in the target space;
• at least one room sensor positioned in the target space, the at least one room sensor configured to measure at least the temperature of the target space;
• a blower positioned in a duct system, the blower configured to move a return airflow in the duct system across a first heat exchanger to transfer heat between a refrigerant in the first heat exchanger and the return airflow to produce a first conditioned airflow that is communicated to the target space;
• at least one return air sensor positioned upstream of the blower in the duct system, the at least one return air sensor configured to measure a temperature of the return airflow in the duct system;
• a memory coupled to the network interface circuit, the memory operable to store a total capacity of the HVAC system, wherein the total capacity is a total thermal load (BTU/hr) that the HVAC system is configured to provide to the target space, the memory further operable to store a gas concentration threshold for the target space;
• a processor operably coupled to the network interface circuit, the processor configured to:
• receive the concentration of the at least one gas in the target space from the air quality sensor;
• determine that the concentration of the at least one gas exceeds the gas concentration threshold;
• determine that operation of the HVAC system in a ventilation mode is indicated to reduce the concentration of the at least one gas, wherein the HVAC system operates in the ventilation mode by:
• introducing outdoor ventilation airflow to an outdoor ventilation inlet of the duct system, wherein the outdoor ventilation inlet is in communication with the target space;
• and
• discharging exhaust airflow in communication with the target space through an exhaust air outlet of the duct system to reduce the concentration of the at least one gas in the target space, and after determining that operation of the HVAC system in the ventilation mode is indicated, the processor is further configured to:
• receive the temperature of the target space from the at least one room sensor;
• receive the temperature of the return airflow from the at least one return air sensor;
• receive a flow rate of the return airflow from the blower;
• determine a current capacity that the HVAC system, wherein the current capacity is a current thermal load (BTU/hr) that the HVAC system is using to regulate the temperature of the target space, wherein the current capacity is determined based at least on the temperature of the target space, the temperature of the return air, and the flow rate of the return airflow;
• and
• cause the HVAC system to operate in the ventilation mode after validating that the total capacity is greater than the current capacity during operation of the HVAC system in the ventilation mode.