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

Abstract

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 includes determining when there is an elevated pathogen transmission risk in the building space. In response to determining that there is an elevated pathogen transmission risk in the building space, the AHU is controlled to adjust operation of the AHU to alleviate the elevated pathogen transmission risk.

What is claimed is: 
     
         1 . 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 the return air, a heating and/or cooling unit for receiving and condition the return air and providing the conditioned return air as supply air to the building space, 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 when the indoor air quality in the building space falls below a threshold; and   in response to determining that the indoor air quality in the building space has fallen below the threshold, controlling the AHU to adjust one or more parameters of the supply air of the AHU to increase a volume of supply air that is required to pass through the filter to satisfy a heating and/or cooling call of the building space.   
     
     
         2 . The method of  claim 1 , wherein in response to the heating and/or cooling call, the AHU operates the fan and the heating and/or cooling unit of the AHU to provide supply air to the building space that causes a temperature of the air in the building space to move toward a temperature setpoint. 
     
     
         3 . The method of  claim 2 , wherein controlling the AHU to adjust one or more parameters of the supply air to increase the volume of supply air that is required to satisfy a heating and/or cooling call of the building space includes controlling the heating and/or cooling unit of the AHU to adjust a supply air temperature of the supply air toward the temperature setpoint. 
     
     
         4 . The method of  claim 3 , wherein controlling the AHU to adjust one or more parameters of the supply air to increase the volume of supply air that is required to satisfy a heating and/or cooling call of the building space includes controlling the fan of the AHU to increase a flow rate of the supply air into the building space, which enables a larger adjustment in the supply air temperature toward the temperature setpoint while still being able to satisfy the heating and/or cooling call. 
     
     
         5 . The method of  claim 2 , wherein in response to determining that the indoor air quality in the building space has fallen below the threshold, the method comprising:
 determining an air change rate for the building space that is sufficient to increase the indoor air quality in the building space above the threshold;   determining whether the increased volume of supply air meets the determined air change rate of the building space; and   when the volume of the supply air does not meet the determined air change rate for the building space, adjusting one or more parameters of the supply air of the AHU to further increase the volume of supply air that is required to satisfy the heating and/or cooling call of the building space.   
     
     
         6 . The method of  claim 5 , wherein controlling the AHU to adjust one or more parameters of the supply air to increase the volume of supply air that is required to satisfy a heating and/or cooling call of the building space includes controlling the heating and/or cooling unit of the AHU to adjust a supply air temperature of the supply air toward the temperature setpoint. 
     
     
         7 . The method of  claim 6 , wherein when the supply air temperature of the supply air is adjusted such that the AHU can no longer satisfy the heating and/or cooling call, but the volume of the supply air still does not meet the determined air change rate for the building space, adjusting the fan of the AHU to increase a flow rate of the supply air into the building space. 
     
     
         8 . The method of  claim 1 , wherein the AHU includes a fresh air intake damper for admitting a fresh air ventilation air flow, and 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 the heating and/or cooling unit of the AHU, the method comprising:
 closing the fresh air intake damper to a minimum damper position in response to determining that the indoor air quality in the building space has fallen below the threshold.   
     
     
         9 . 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.   
     
     
         10 . The method of  claim 9 , wherein the accessing, determining, controlling and repeating steps are executed on premises. 
     
     
         11 . The method of  claim 9 , wherein the plurality of control algorithms comprise one or more of:
 an indoor air quality parameter control algorithm that is configured to keep one or more indoor air quality parameters in the building space below one or more indoor air quality thresholds;   a pathogen transmission risk control algorithm that is configured to keep a pathogen transmission risk in the building space below a pathogen transmission risk threshold;   a demand control ventilation control algorithm that is configured to maintain a balance between one or more indoor air quality parameters and energy consumption of the AHU;   an energy minimization control algorithm that is configured to minimize energy consumption of the AHU by controlling the fresh air intake damper at a minimum ventilation position; and   an economizer control algorithm that is configured to control the fresh air intake damper to achieve free heating and/or cooling when available.   
     
     
         12 . The method of  claim 9 , wherein one of the one or more predefined conditions of at least one of the plurality of control algorithms includes having a particular sensor available to the AHU. 
     
     
         13 . The method of  claim 9 , wherein one of the one or more predefined conditions of at least one of the plurality of control algorithms includes having one or more sensed values meet one or more predefined conditions. 
     
     
         14 . The method of  claim 9 , wherein one of the one or more predefined conditions of at least one of the plurality of control algorithms includes Boolean logic. 
     
     
         15 . The method of  claim 9 , further comprising receiving the assigned priority of the plurality of control algorithms from a user via a user interface to customize the assigned priorities for the building. 
     
     
         16 . The method of  claim 15 , wherein the one or more predefined conditions of the plurality of control algorithms are not available to be customized for the building via the user interface. 
     
     
         17 . 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.   
     
     
         18 . The method of  claim 17 , further comprising:
 projecting a value of the pathogen transmission risk function at the occupied end time, resulting in a projected pathogen transmission risk value;   determining when the projected pathogen transmission risk value exceeds the ideal monotonically increasing pathogen transmission risk curve at the occupied end time by at least a warning amount; and   in response to determining that the projected pathogen transmission risk value exceeds the ideal monotonically increasing pathogen transmission risk curve at the occupied end time by at least the warning amount, issuing a warning alert to a user via a user interface.   
     
     
         19 . The method of  claim 17 , wherein determining the pathogen transmission risk function, determining the ideal monotonically increasing pathogen transmission risk curve, tracking the pathogen transmission risk function, determining when the pathogen transmission risk function exceeds the ideal monotonically increasing pathogen transmission risk curve, and controlling the AHU to increase the clean air flow rate of substantially pathogen free air into the building space are executed on premises. 
     
     
         20 . The method of  claim 17  comprising:
 controlling the AHU in accordance with a programmable schedule that includes occupied time periods and unoccupied time periods, wherein the occupied start time and the occupied end time correspond to one of the occupied time periods of the programmable schedule.