Exhaust demand control system and methods
Methods and apparatus for an exhaust demand control system for measuring one or more contaminants at one or more exhaust locations within one or a plurality of exhaust ducts or plenums served by an exhaust fan system. Example systems and methods can include sensing the one or more contaminants within the one or more exhaust duct locations using a multipoint air sampling system having one or more sensors and comparing contaminant concentration measurements from the one or more of said exhaust duct or plenum locations against an action level to create a fan setback signal.
1. An exhaust demand control system for measuring one or more contaminants at one or more locations within one or a plurality of exhaust ducts or plenums served by an exhaust fan system having one or more exhaust fans, comprising systems configured to:
sense the one or more contaminants within the one or more locations using a multipoint air sampling system having one or more sensors to determine concentration measurements;
compare the contaminant concentration measurements from the one or more locations against an action level to create a fan setback signal which controls a setback state of the exhaust fan system;
prevent the exhaust fan system from instability by controlling an operation of the one or more exhaust fans according to a sequence delay provided by control logic of the control system where the sequence delay is enabled when the contaminant concentration measurements from the one or more locations exceeds the action level, wherein the sequence delay in part determines a minimum time that the fan setback signal is disabled;
ensure sensor accuracy and reliability by enabling a flow device to provide a sensor flushing function to the one or more sensors, the sensor flushing function being activated for a period of time designated by the sequence delay when contaminant levels above the action level are detected by the one or more sensors, wherein the sensing of the one or more contaminants within the one or more locations is discontinued while the sensor flushing function is activated; and
incorporate one or more setback override functions to limit when the exhaust fan system is set back.
2. The exhaust demand control system of claim 1 , wherein the exhaust fan system includes one or more high plume fans.
3. The exhaust demand control system of claim 1 , wherein at least a portion of the one or more exhaust ducts includes one or more exhaust risers.
4. The exhaust demand control system of claim 1 which, as an added measure to ensure sensor accuracy and reliability, further includes providing a dilution sampling function which reduces the one or more sensors from exposure to exhaust contaminants.
5. The exhaust demand control system of claim 1 , wherein the multipoint air sampling system comprises a networked air sampling system.
6. The exhaust demand control system of claim 1 , wherein the one or more sensors comprises a Photoionization Detector (PID) sensor.
7. The exhaust demand control system of claim 1 further including a tubing flushing function for each tube which connects between the multipoint air sampling system and the one or more locations, wherein the tubing flushing function is configured to activate when contaminant levels above the action level are detected by the multipoint air sampling system; the tubing flushing function being dependent upon a negative pressure associated with each location to which one end of each of the tubes connects and a flow path from atmosphere which is introduced to the other end of each of the tubes through the multipoint air sampling system so that flow of ambient air through each of the tubes removes compounds accumulated within the tubing.
8. The exhaust demand control system of claim 1 , wherein the flow device which is enabled to provide a sensor flushing function is a solenoid valve.
9. The exhaust demand control system of claim 1 , wherein the one or more setback override functions comprises an occupancy signal.
10. A method of performing exhaust demand control using a system for measuring one or more contaminants at one or more locations within one or a plurality of exhaust ducts or plenums served by an exhaust fan system having one or more exhaust fans, the method comprising:
sensing the one or more contaminants within the one or more locations using a multipoint air sampling system having one or more sensors to determine concentration measurements;
comparing contaminant concentration measurements from the one or more locations against an action level to create a fan setback signal which controls a setback state of the exhaust fan system;
preventing the exhaust fan system from instability by controlling an operation of the one or more exhaust fans according to a sequence delay provided by control logic of the control system where the sequence delay is enabled when the contaminant concentration measurements from the one or more locations exceeds the action level, wherein the sequence delay in part determines a minimum time that the fan setback signal is disabled;
ensuring sensor accuracy and reliability by enabling a flow device to provide a sensor flushing function to the one or more sensors, the sensor flushing function being activated for a period of time designated by the sequence delay when contaminant levels above the action level are detected by the one or more sensors, wherein the sensing of the one or more contaminants within the one or more locations is discontinued while the sensor flushing function is activated; and
incorporating one or more setback override functions to limit when the exhaust fan system is set back.
11. The method of claim 10 , wherein the exhaust fan system includes one or more high plume fans.
12. The method of claim 10 , wherein at least a portion of the one or more exhaust ducts includes one or more exhaust risers.
13. The method of claim 10 , wherein the multipoint air sampling system comprises a networked air sampling system.
14. The method of claim 10 which, as an added measure to ensure sensor accuracy and reliability, further includes providing a dilution sampling function which reduces the one or more sensors from exposure to exhaust contaminants.
15. The method of claim 10 , wherein the one or more sensors comprises a Photoionization Detector (PID) sensor.
16. The method of claim 10 , wherein the exhaust demand control function incorporates clean exhaust minimum ACH logic.
17. The method of claim 10 further including a tubing flushing function for each tube which connects between the multipoint air sampling system and the one or more locations, wherein the tubing flushing function is configured to activate when contaminant levels above the action level are detected by the multipoint air sampling system; the tubing flushing function being dependent upon a negative pressure associated with each location to which one end of each of the tubes connects and a flow path from atmosphere which is introduced to the other end of each of the tubes through the multipoint air sampling system so that flow of ambient air through each of the tubes removes compounds accumulated within the tubing.
18. The method of claim 10 , wherein the sequence delay is adaptive.
19. The method of claim 10 , wherein the one or more setback override functions comprises an occupancy signal.
20. The method of claim 10 , wherein the exhaust demand control function incorporates clean exhaust minimum ACH logic.