Mixing device for an air handling unit and control methods therefor

Abstract

An air handling system comprising a mixing device. The mixing device is in fluid communication with a return air plenum of the air handling system, an outside air duct, and a heat/energy recovery ventilator of the air handling system. The mixing device includes a mixing damper that is selectively and incrementally movable to partially and/or completely obstruct one of the return air plenum and the outside air duct. The mixing damper is selectively positionable in a neutral position wherein air flows from the return air plenum directly to a heat exchanger of the air handling system, and air flows from the outside air duct directly to the heat/energy recovery ventilator.

1 . A mixing device for an air handling system, the air handling system comprising a heat exchanger, a heat recovery ventilator/energy recovery ventilator (ERV), and a return air plenum, the mixing device comprising:
 a mixing plenum, the mixing plenum including:
 a return air aperture connected to the return air plenum; 
 an outside air aperture connected to the outside air duct; 
 an ERV supply aperture in fluid communication with the ERV; and 
 a supply aperture in fluid communication with the heat exchanger; and 
   a mixing damper positioned in the mixing plenum, the mixing damper actuable to move incrementally along a path comprising:
 a first position wherein the mixing damper inhibits a flow of outside air through the outside air aperture and a flow of return air from the return air plenum flows from the return air aperture to the ERV supply aperture and the supply aperture; 
 a second position wherein the mixing damper partitions the mixing plenum such that the flow of outside air flows through the mixing plenum from the outside air aperture to the ERV supply aperture and a flow of return air from the return air plenum flows through the mixing plenum from the return air aperture to the supply aperture; and 
 a third position wherein the mixing damper inhibits the flow of the return air through the return air aperture and the flow of outside air flows from the outside air aperture to the ERV aperture and the supply aperture. 
   
     
     
         2 . A mixing device according to  claim 1 , wherein the mixing damper is incrementally positionable across a first range of positions between the first position and the second position. 
     
     
         3 . A mixing device according to  claim 1 , wherein the mixing damper is incrementally positionable across a second range of positions between the second position and the third position. 
     
     
         4 . A mixing device according to  claim 1 , further comprising a return air damper located in the return plenum, wherein the return air damper is coupled to the mixing damper via a linkage, the linkage configured to, when the mixing damper is actuated to the third position, actuate the return air damper to inhibit the flow of return air through the return air plenum. 
     
     
         5 . A mixing device according to  claim 4 , wherein the linkage is configured to only begin actuating the return air damper when the mixing damper is moved from an intermediate position between the second position and the third position to the third position. 
     
     
         6 . A mixing device according to  claim 4 , wherein the linkage comprises a mechanical linkage between the return air damper and the mixing damper. 
     
     
         7 . A mixing device according to  claim 4 , the mixing damper comprising a first actuator configured to actuate the mixing damper, and wherein the linkage comprises a second actuator electronically linked to the first actuator and configured to actuate the return air damper. 
     
     
         8 . A mixing device according to  claim 1 , wherein:
 the return air aperture and the outside air aperture are located on a first wall of the mixing plenum;   the supply aperture and the ERV aperture are located on a second wall of the mixing plenum;   the second wall opposes the first wall;   the return air aperture is generally aligned with the supply aperture; and   the outside air aperture is generally aligned with the ERV aperture.   
     
     
         9 . A mixing device according to  claim 8 , wherein the mixing damper comprises:
 an axle rotatably supported adjacent the first wall between the return air aperture and the outside air aperture; and   a paddle extending radially from the axle; and   rotation of the axle pivotably moves the paddle between the first position wherein the paddle covers the outside air aperture, the second position wherein the paddle extends from the first wall to the second wall, and the third position wherein the paddle covers the return air aperture.   
     
     
         10 . An air handling system comprising:
 a mixing device according to  claim 1 ;   a heat exchanger;   a heat recovery ventilator/energy recovery ventilator (ERV);   a return air plenum;   a supply duct connecting the supply aperture to the heat exchanger; and   an intake duct connecting the ERV to the supply duct; and   wherein the ERV is configured to provide intake air to the heat exchanger via the intake duct.   
     
     
         11 . An air handling system comprising:
 a return air plenum;   an outside air duct;   a mixing device operatively connected to the return air plenum and to the outside air duct, the mixing device comprising a mixing plenum and a damper mechanism;   a heat recovery ventilator/energy recovery ventilator (ERV) operatively connected to the mixing device downstream of the return air plenum and the outside air duct;   a heat exchanger operatively connected to the mixing device downstream of the return air plenum and the outside air duct; and   one or more supply fans operatively connected to the heat exchanger and configured to supply air to a space;   wherein:
 the ERV is operatively connected to the heat exchanger downstream of the mixing device; and 
 the damper mechanism is positionable:
 in a neutral position partitioning the mixing plenum into a first chamber connecting the return air plenum to the heat exchanger and a second chamber connecting the outside air duct to the ERV; 
 incrementally between the neutral position and a defrost position wherein the damper mechanism blocks the outside air duct and the ERV is connected via the mixing plenum to the return air duct; and 
 incrementally between the neutral position and a free cooling position wherein the damper mechanism blocks the return air plenum and the outside air duct is connected via the mixing plenum to the heat exchanger. 
 
   
     
     
         12 . An air handling unit according to  claim 11 , further comprising an air filter upstream of the heat exchanger. 
     
     
         13 . An air handling unit according to  claim 11 , further comprising an air filter upstream of the ERV. 
     
     
         14 . A method of mitigating frost formation in a heat recovery ventilator/energy recovery ventilator (ERV), the method comprising:
 connecting a fresh air intake duct of the ERV to a mixing device, the mixing device including:
 a mixing plenum connected to a return air plenum and to an outside air duct; and 
 a mixing damper positioned in the mixing plenum and actuable to move incrementally between a position obstructing the return air plenum and a position obstructing the outside air duct; 
   measuring an outside air temperature in the outside air duct;   measuring a return air temperature in the return air plenum; and   in response to the outside air temperature being less than a first predetermined threshold temperature and the return air temperature being greater than a second predetermined threshold temperature, moving the mixing damper to a position partially obstructing the outside air duct so as to restrict a flow of outside air to the ERV and increase a flow of return air to the ERV.   
     
     
         15 . The method of  claim 14 , further comprising, in response to the return air temperature being less than the second predetermined threshold temperature and the return air temperature being greater than the outside air temperature, moving the mixing damper to a position fully obstructing the outside air duct so as to prevent the flow of outside air to the ERV. 
     
     
         16 . A method of operating an air handling device to mitigate airborne contamination in an indoor space, the air handling device comprising an outside air duct, a mixing device in fluid communication with the outside air duct and including a mixing damper selectively and incrementally movable to obstruct the outside air duct, and a heat recovery ventilator/energy recovery ventilator (ERV) in fluid communication with the mixing device and with the indoor space, the method comprising:
 measuring a concentration of airborne contaminant at one or more of upstream of the mixing device, downstream of the mixing device, and in the mixing device;   comparing the measured concentration of the airborne contaminant to a predetermined threshold; and   in response to the measured concentration of the airborne contaminant exceeding the predetermined threshold, operating the mixing damper to obstruct the outside air duct.   
     
     
         17 . The method according to  claim 16 , further comprising measuring a concentration of the airborne contaminant in the indoor space, and wherein the predetermined threshold is the measured concentration in the indoor space. 
     
     
         18 . The method according to  claim 16 , wherein the airborne contaminant is one or more of smoke, allergens, dust, combustion exhaust compounds, and aroma compounds. 
     
     
         19 . A method of operating an air handling device to provide make-up air to an indoor space, the air handling device comprising a return plenum in fluid communication with the indoor space, an outside duct in fluid communication with outside air, a mixing device in fluid communication with the return plenum and the outside duct and including a mixing damper selectively and incrementally positionable to obstruct the return plenum and the outside duct, and a supply fan in fluid communication with the mixing device and the indoor space, the method comprising:
 measuring a return plenum pressure and a return airflow rate in the return plenum;   measuring an outside duct pressure and an outside airflow rate in the outside duct;   calculating an inside pressure based on the return plenum pressure, the return airflow rate, and a characteristic flow coefficient of the return plenum;   calculating an outside pressure based on the outside duct pressure, the outside airflow rate, and a characteristic flow coefficient of the outside duct; and   in response to a difference between the inside pressure and the outside pressure exceeding a predetermined threshold, moving the mixing damper to obstruct the return plenum.