Thermostat with demand controlled indoor air quality

1 . A heating, ventilation, or air conditioning (HVAC) system for a building, the HVAC system comprising:

an environmental sensor configured to provide an indoor air quality (IAQ) value indicative of a concentration of at least one of a pollutant or a pathogen in a space in the building; and

a controller positioned in the space, the controller comprising a processing circuit comprising one or more memory devices coupled to one or more processors, the one or more memory devices configured to store instructions thereon that, when executed by the one or more processors, cause the one or more processors to:

receive the IAQ value from the environmental sensor;

determine if the IAQ value in the space is above an IAQ setpoint for the space;

determine an occupancy status for the space;

calculate a purge duration of a pre-occupancy purge mode or a post-occupancy purge mode based on an air exchange rate of the space and a number of air changes; and

control HVAC equipment to ventilate the space with outdoor air at a flowrate in response to determining that the IAQ value is above the IAQ setpoint, such that the flowrate when the occupancy status of the space is unoccupied is less than the flowrate when the occupancy status of the space is occupied except during execution of the pre-occupancy purge mode or the post-occupancy purge mode.

2 . The HVAC system of claim 1 , wherein the controller is configured to abstain from ventilating the space with the outdoor air if a quality of outdoor air is poorer than the IAQ value.

3 . The HVAC system of claim 1 , wherein the one or more memory devices are further configured to store instructions thereon that, when executed by the one or more processors, cause the one or more processors to determine the occupancy status for the space based on an occupancy schedule.

4 . The HVAC system of claim 1 , wherein the one or more memory devices are further configured to store instructions thereon that, when executed by the one or more processors, cause the one or more processors to determine the occupancy status for the space based on occupancy data from an occupant sensor positioned in the space.

5 . The HVAC system of claim 1 , the one or more memory devices are further configured to store instructions thereon that, when executed by the one or more processors, cause the one or more processors to:

determine if the IAQ value is above a critical threshold, the critical threshold greater than the IAQ setpoint; and

provide an alarm to a user of the space in response to determining the IAQ value is above the critical threshold.

6 . The HVAC system of claim 1 , further comprising an outdoor environmental sensor, the one or more memory devices are further configured to store instructions thereon that, when executed by the one or more processors, cause the one or more processors to:

receive outdoor air data indicative of at least one of temperature, pressure, or humidity of an outdoor air outside the building from the outdoor environmental sensor;

determine, based on the outdoor air data, an outdoor air quality of the outdoor air; and

control the HVAC equipment to ventilate the space based on a delta between the IAQ value and the outdoor air quality meeting a predetermined threshold.

7 . The HVAC system of claim 6 , the one or more memory devices are further configured to store instructions thereon that, when executed by the one or more processors, cause the one or more processors to:

select either a ventilate mode or a normal mode based on the outdoor air quality; and

control the HVAC equipment to ventilate the space based on the IAQ value, the outdoor air quality, and the selected mode,

wherein the HVAC equipment provides outdoor air to the space in response to selecting the ventilate mode, and

wherein the HVAC equipment provides return air from within the building to the space in response to selecting a normal mode.

8 . The HVAC system of claim 1 , the one or more memory devices are further configured to store instructions thereon that, when executed by the one or more processors, cause the one or more processors to not ventilate the space in response to a determination that the IAQ value is below the IAQ setpoint.

9 . The HVAC system of claim 1 , the one or more memory devices are further configured to store instructions thereon that, when executed by the one or more processors, cause the one or more processors to:

receive an occupancy schedule indicating at least one of a first occupied period or a last unoccupied period for the space in the building for a schedule period;

receive a user input indicating the space should be purged based on occupancy;

select, based on the user input, a purge mode, wherein the purge mode includes at least one of the pre-occupancy purge mode or the post-occupancy purge mode;

control the HVAC equipment to ventilate the space for the purge duration prior to the beginning of the first occupied period in response to selecting the pre-occupancy purge mode; and

control the HVAC equipment to ventilate the space for the purge duration at the beginning of the last unoccupied period in response to selecting the post-occupancy purge mode.

10 . The HVAC system of claim 1 , the HVAC equipment comprising;

an airside economizer communicably coupled to the controller and comprising:

a first air intake configured to receive return air from within the building;

a second air intake configured to receive outdoor air from outside the building; and

an air discharge configured to provide discharge air to the building;

wherein the one or more memory devices are further configured to store instructions thereon that, when executed by the one or more processors, cause the one or more processors to control the HVAC equipment to ventilate the space by modulating the position of a damper in the airside economizer to control an amount of an outdoor air received in the space, wherein the position of the damper is based on a rate of change of temperature of the space and a minimum damper position.

11 . A method for operating a heating, ventilation, or air conditioning (HVAC) system for a building, the method comprising:

measuring an indoor air quality (IAQ) value indicative of a concentration of at least one of a pollutant or a pathogen in a space in the building;

determining if the IAQ value in the space is above a IAQ setpoint for the space;

determining an occupancy status for the space;

calculating a purge duration of a pre-occupancy purge mode or a post-occupancy purge mode based on an air exchange rate of the space and a number of air changes; and

controlling HVAC equipment in the HVAC system to ventilate the space with outdoor air at a flowrate in response to determining that the IAQ value is both (i) above the IAQ setpoint and (ii) above an outdoor air quality value by at least a threshold value, such that the flowrate when the occupancy status of the space is unoccupied is less than the flowrate when the occupancy status of the space is occupied except during execution of the pre-occupancy purge mode or the post-occupancy purge mode.

12 . The method of claim 11 , further comprising determining the occupancy status of the space based on an occupancy schedule.

13 . The method of claim 11 , further comprising determining the occupancy status of the space based on occupancy data from an occupant sensor positioned in the space.

14 . The method of claim 11 , further comprising:

determining if the IAQ value in the space is above a critical threshold, the critical threshold greater than the IAQ setpoint; and

providing an alarm to a user of the space in response to determining the IAQ value is above the critical threshold.

15 . The method of claim 11 , further comprising:

measuring outdoor air data indicative of at least one of a temperature, pressure, or humidity of an outdoor air outside the building;

determining, based on the outdoor air data, an outdoor air quality of the outdoor air; and

controlling the HVAC equipment to ventilate the space based on a delta between the IAQ value and the outdoor air quality meeting a predetermined threshold.

16 . The method of claim 15 , further comprising

selecting either a ventilate a ventilate mode or a normal mode based on the outdoor air quality; and

controlling the HVAC equipment to ventilate the space based on the IAQ value, the outdoor air quality, and the selected mode,

wherein the HVAC equipment provides outdoor air to the space in response to selecting the ventilate mode, and

wherein the HVAC equipment provides return air from within the building to the space in response to selecting a normal mode.

17 . The method of claim 11 , further comprising not ventilating the space based on a determination the IAQ value is below the IAQ setpoint.

18 . The method of claim 11 , further comprising:

receiving an occupancy schedule indicating at least one of a first occupied period or a last unoccupied period for the space in the building for a schedule period;

receiving a user input indicating the space should be purged based on occupancy;

selecting, based on the user input, at least one of the pre-occupancy purge mode or the post-occupancy purge mode;

controlling the HVAC equipment to ventilate the space for the purge duration prior to the beginning of the first occupied period in response to selecting the pre-occupancy purge mode; and

controlling the HVAC equipment to ventilate the space for the purge duration at the beginning of the last unoccupied period in response to selecting the post-occupancy purge mode.

19 . The method of claim 11 , further comprising:

controlling the HVAC equipment to ventilate the space by modulating a position of a damper in an airside economizer to control the amount of an outdoor air received in the space, wherein the position of the damper is based on a rate of change of temperature of the space and a minimum damper position, the airside economizer comprising:

a first air intake configured to receive return air from within a building;

a second air intake configured to receive outdoor air from outside the building; and

an air discharge configured to provide discharge air to the building.

20 . A heating, ventilation, or air conditioning (HVAC) system for a building, the HVAC system comprising:

an environmental sensor configured to provide an indoor air quality (IAQ) value indicative of a concentration of at least one of a pollutant or a pathogen in a space in the building; and

a controller positioned in the space, the controller comprising a processing circuit comprising one or more memory devices coupled to one or more processors, the one or more memory devices configured to store instructions thereon that, when executed by the one or more processors, cause the one or more processors to:

receive the IAQ value from the environmental sensor;

determine if the IAQ value in the space is above an IAQ setpoint for the space;

determine an occupancy status for the space during an occupancy period;

receive a user input indicating the space should be purged based on the occupancy status;

calculate a purge duration of at least one of a pre-occupancy purge mode or a post-occupancy purge mode based on an air exchange rate of the space and a number of air changes; and

control HVAC equipment to ventilate the space with outdoor air for the purge duration during a pre-occupancy or post-occupancy period in response to determining that the IAQ value is above the IAQ setpoint, such that the HVAC equipment ventilates the space at a flowrate that is less during the occupancy period than during the pre-occupancy or post-occupancy period except during the purge duration of the pre-occupancy purge mode or the post-occupancy purge mode.