Method and system for controlling an hvac system to reduce infection risk in a building

A method for controlling a fresh air intake of an Air Handling Unit (AHU) of an HVAC (Heating, Ventilating and Air Conditioning) system servicing a building space of a building, the AHU including a fresh air intake damper for admitting a fresh air ventilation air flow, a return air duct for receiving return air from the building space, a mixed air duct for mixing the fresh air ventilation air flow from the fresh air intake damper and return air from the return air duct and providing a mixed air flow to a heating and/or cooling unit of the AHU which supplies a supply air flow to the building space, the AHU including a fan for providing a motive force to move the return air, the fresh air ventilation air flow, the mixed air flow and the supply air flow through the AHU, the method comprising:

• accessing a plurality of control algorithms for controlling the fresh air intake damper of the AHU, each of the plurality of control algorithms has one or more predefined conditions, and each of the plurality of control algorithms has an assigned priority relative to the other of the plurality of control algorithms;
• determining which of the plurality of control algorithms have their one or more predefined conditions satisfied if any, and if more than one of the plurality of control algorithms have their one or more predefined conditions satisfied, selecting the control algorithm that has the highest priority relative to the other of the more than one of the plurality of control algorithms that have their one or more predefined conditions satisfied;
• controlling the fresh air intake damper of the AHU using the selected control algorithm;
• and
• repeating the determining and controlling steps over time.

A method for controlling an Air Handling Unit (AHU) of an HVAC (Heating, Ventilating and Air Conditioning) system servicing a building space of a building, the AHU including a return air duct for receiving return air from the building space, a filter for filtering pathogens from the return air, a heating and/or cooling unit for receiving and condition the return air and providing the conditioned return air to the building space as supply air, the AHU including a fan for providing a motive force to move the return air and the supply air through the AHU, the method comprising:

• determining a pathogen transmission risk function that monotonically increases over time and is dependent on a pathogen transmission risk in the building space, the pathogen transmission risk function is based at least in part on an occupancy of the building space, a pulmonary ventilation rate, a quanta generation rate and a clean air flow rate of substantially pathogen free air into the building space;
• determining an ideal monotonically increasing pathogen transmission risk curve extending from an occupied start time to an occupied end time of the building space;
• tracking the pathogen transmission risk function against the ideal monotonically increasing pathogen transmission risk curve;
• determining when the pathogen transmission risk function begins to exceed the ideal monotonically increasing pathogen transmission risk curve for at least a period of time;
• and
• in response to determining that the pathogen transmission risk function exceeds the ideal monotonically increasing pathogen transmission risk curve for at least a period of time, controlling the AHU to increase the clean air flow rate of substantially pathogen free air into the building space.