MIXING DEVICE FOR AN AIR HANDLING UNIT AND CONTROL METHODS THEREFOR

Description

TECHNICAL FIELD

This invention relates to air handling systems. In particular, this invention relates to mixing devices configured to control distribution of airflow in air handling systems.

BACKGROUND OF THE INVENTION

Energy recovery ventilators (ERVs) improve the thermal efficiency of an air handling system by providing for the transfer of sensible and latent energy from exhaust air from an interior space to fresh air supplied to the interior space. That is, ERVs transfer energy from the exhaust air to the incoming fresh air to pre-heat or pre-cool the fresh air, as the case may be. Historically, a distinction was drawn between enthalpy recovery ventilators and heat recovery ventilators (HRVs). However it is becoming industry standard to refer to both HRVs and enthalpy recovery ventilators as ERVs, and for clarity any reference to ERV herein also includes HRVs and enthalpy recovery ventilators.

In cold climates, incoming fresh air may cause frost to form in the ERV, which can reduce performance and potentially damage the ERV. Therefore, the ERV may periodically require defrosting.

U.S. Pat. No. 7,942,193 to Caldwell discloses a defrost system for an energy recovery ventilator (ERV). The defrost system uses the interior space supply air of an integrated fan coil for defrosting a ERV core without creating negative pressure in the interior space, without need of an external fifth port from which to draw defrost air from the interior space, and without re-circulating exhaust air into the interior space. During the defrost cycle, automatically controlled dampers close off the fresh air and exhaust air inputs, and exhaust output, and circulate supply air through the heat exchange core and into the living space.

U.S. Pat. No. 8,939,826 to Zorzit and Chu discloses an apparatus for heating, ventilation and/or air conditioning of an interior space that includes a heat exchanger core and a heating/cooling device in fluid connection with the heat exchanger core. A recirculation port is arranged between a supply air chamber and an outside air chamber. A damper is adapted to move between a first position in which the damper blocks the recirculation port and a second position in which the recirculation port is unblocked. When the damper is in the second position, at least a portion of supply air is guided to flow from the supply air chamber through the outside air chamber to the heat exchanger core so as to defrost the heat exchanger core.

There remains a general desire for improved methods and systems for defrosting of ERVs. and of bypassing the ERV when it is unable to supply sufficient outdoor air to the conditioned space to satisfy ventilation or make-up-air requirements. There is also a need to block the outdoor air flow when the outdoor air is poorer quality than the current indoor air (e.g. when the outdoor air contains contaminants such as smoke, noxious odours, and/or the like).

The foregoing examples of the related art and limitations related thereto are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon a reading of the specification and a study of the drawings.

SUMMARY OF THE INVENTION

The following embodiments and aspects thereof are described and illustrated in conjunction with systems, tools and methods which are meant to be exemplary and illustrative, not limiting in scope. In various embodiments, one or more of the above-described problems have been reduced or eliminated, while other embodiments are directed to other improvements.

One aspect of the invention provides 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 comprises a mixing plenum. The mixing plenum includes 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 is 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.

In a further aspect, the mixing damper is incrementally positionable across a first range of positions between the first position and the second position.

In a further aspect, the mixing damper is incrementally positionable across a second range of positions between the second position and the third position.

In a further aspect, the mixing device includes 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.

In a still further aspect, 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.

In a yet still further aspect, the linkage comprises a mechanical linkage between the return air damper and the mixing damper.

In a yet still further aspect, the mixing damper comprises a first actuator configured to actuate the mixing damper and the linkage comprises a second actuator electronically linked to the first actuator and configured to actuate the return air damper.

In a further aspect, 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.

In a still further aspect, 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.

Another aspect of the invention provides an air handling system. The air handling system comprises 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. The ERV is operatively connected to the heat exchanger downstream of the mixing device. 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.

In a further aspect, the air handling system comprises an air filter upstream of the heat exchanger and/or upstream of the ERV.

Another aspect of the invention provides a method of mitigating frost formation in a heat recovery ventilator/energy recovery ventilator (ERV). The method comprises 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.

In a further aspect, the method comprises, 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.

Another aspect of the invention provides a method of operating an air handling device to mitigate airborne contamination in an indoor space. The air handling device comprises 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 comprises 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.

In a further aspect, the method comprises measuring a concentration of the airborne contaminant in the indoor space, and the predetermined threshold is the measured concentration in the indoor space.

In a further aspect the airborne contaminant is one or more of smoke, allergens, dust, combustion exhaust compounds, and aroma compounds.

Another aspect of the invention provides a method of operating an air handling device to provide make-up air to an indoor space. The air handling device comprises 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 comprises 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.

In addition to the exemplary aspects and embodiments described above, further aspects and embodiments will become apparent by reference to the drawings and by study of the following detailed descriptions.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments are illustrated in referenced figures of the drawings. It is intended that the embodiments and figures disclosed herein are to be considered illustrative rather than restrictive.

FIG. 1 is a schematic diagram of an air handling system according to an embodiment of the invention.

FIG. 2 is a schematic diagram of a mixing device according to an embodiment of the invention.

FIG. 3 is a perspective view of a mixing damper assembly according to an embodiment of the invention.

FIG. 4A is a schematic diagram of the FIG. 2 mixing device with a mixing damper thereof in a neutral position.

FIG. 4B is a schematic diagram of the FIG. 2 mixing device with the mixing damper thereof in a recirculation position.

FIG. 4C is a schematic diagram of the FIG. 2 mixing device with the mixing damper thereof in an example defrost position.

FIG. 4D is a schematic diagram of the FIG. 2 mixing device with the mixing damper thereof in a free cooling or free heating position.

FIG. 4E is a schematic diagram of the FIG. 2 mixing device with the mixing damper thereof in an example make-up position.

FIG. 5A is a perspective view of the FIG. 3 mixing damper assembly with a mixing damper thereof in the recirculation position.

FIG. 5B is a perspective view of the FIG. 3 mixing damper assembly with the mixing damper thereof in the neutral position.

FIG. 5C is a perspective view of the FIG. 3 mixing damper assembly with the mixing damper thereof in an example make-up position.

FIG. 5D is a perspective view of the FIG. 3 mixing damper assembly with the mixing damper thereof in a free cooling position and a return damper thereof actuated.

FIG. 6 is a flowchart showing an example method of operating the FIG. 2 mixing device to mitigate frost formation in and/or defrost an ERV of the FIG. 1 air handling system.

FIG. 7 is a flowchart showing an example method of operating the FIG. 2 mixing device to prevent low quality air entering the FIG. 1 air handling system.

FIG. 8 is a flowchart showing an example method of operating the FIG. 2 mixing device to provide make-up air to the FIG. 1 air handling system by utilizing airflow readings.

FIG. 9 is a flowchart showing an example method of operating the FIG. 2 mixing device to take advantage of free heating or free cooling provided by outside air.

FIG. 10 is a flowchart showing an example method of operating the FIG. 2 mixing device in the neutral position.

FIG. 11 is a schematic diagram of an air handling system according to another embodiment of the invention.

FIG. 12 is a flowchart showing an example method of operating the FIG. 2 mixing device to provide make-up air to the FIG. 11 air handling system by utilizing pressure readings.

DETAILED DESCRIPTION OF THE INVENTION

Throughout the following description specific details are set forth in order to provide a more thorough understanding to persons skilled in the art. However, well known elements may not have been shown or described in detail to avoid unnecessarily obscuring the disclosure. Accordingly, the description and drawings are to be regarded in an illustrative, rather than a restrictive, sense.

Referring to FIG. 1, there is provided an air handling system 100 according to an embodiment of the invention. Air handling system 100 provides heating and/or cooling to an interior space (not shown), and in some embodiments may also provide other conditioning to air in the interior space, including but not limited to filtration, purification, humidification, dehumidification, and the like.

Air handling system 100 comprises a return plenum 102 which receives return air from the interior space for recirculation through air handling system 100. Air handling system 100 comprises an outside duct 104 in fluid communication with air outside of the interior space for supplying fresh outside air to the air handling system 100.

Air handling system 100 comprises a mixing device 200, according to an embodiment of the invention, in fluid communication with return plenum 102 and in fluid communication with outside duct 104. Aspects of mixing device 200 are described in further detail below.

Air handling system 100 comprises an energy recovery ventilator (ERV) 106 in fluid communication with mixing device 200. ERV 106 may be a heat recovery ventilator and/or an enthalpy recovery ventilator. There may be provided an ERV source duct 107 connecting mixing device 200 to ERV 106 to provide fluid communication between ERV 106 and mixing device 200. Air handling system 100 comprises a heat exchanger 108 in fluid communication with mixing device 200 and ERV 106. There may be provided a mixed-air duct 109 connecting mixing device 200 to heat exchanger 108. Mixed-air duct 109 may include an air handling system junction 111 downstream of mixing device 200, and there may be provided an intake duct 113 connecting ERV 106 to air handling system junction 111.

In a default operating mode, mixing device 200 is configured to direct return air from return plenum 102 to mixed-air duct 109 and to direct outside air from outside duct 104 to ERV 106. Mixing device 200 is further configured to provide selective combinations, in variable proportions, of return air flowing from return plenum 102 and outside air flowing from outside duct 104. Mixing device 200 is configured to then distribute, in varying proportions, the resultant combined air to mixed air duct 109 and ERV 106.

Air handling system 100 comprises one or more supply fans 110 in fluid communication between heat exchanger 108 and the interior space for supplying temperature-controlled (i.e. mixed air from mixed-air duct 109 that has been heated and/or cooled by heat exchanger 108) supply air to the interior space. Air handling system 100 is connected to an exhaust plenum 112 in fluid communication between the interior space and ERV 106. Exhaust plenum 112 is configured to extract stale air from the interior space (e.g. from bathrooms, laundry, kitchen, etc., not shown). Air handling system 100 comprises a discharge vent 114 in fluid communication between ERV 106 and an environment surrounding the interior space. During regular operation, ERV 106 is configured to provide sensible heat exchange and/or latent enthalpy exchange (collectively, energy exchange) between the outside air received by air handling system 100 via outside duct 104 and mixing device 200 and the exhaust air received from exhaust air plenum 112. After the energy exchange occurs, the exhaust air is discharged from ERV 106 via discharge vent 114, and the pre-heated/pre-cooled intake air flows through intake air duct 113 to air handling system junction 111, where it mixes with return air and/or combined air produced by combination of return air with outside air in mixing device 200. Resultant mixed air flows through mixed air duct 109 to heat exchanger 108.

Referring to FIGS. 2 and 3, mixing device 200 comprises a mixing plenum 202. Mixing plenum 202 comprises a return aperture 204 in fluid communication with return plenum 102, an outside aperture 206 in fluid communication with outside duct 104, an ERV aperture 208 in fluid communication with ERV 106 (via ERV source duct 107 in the embodiment shown), and a supply aperture 210 in fluid communication with heat exchanger 108 (via mixed-air duct 109 in the embodiment shown). Mixing device 200 includes a mixing damper assembly 212 positioned in mixing plenum 202. Mixing damper assembly 212 is selectively and incrementally movable between positions which partially or fully obstruct either return aperture 204 or outside aperture 206, or to a neutral position which partitions mixing plenum 202 so as to separate air flows from return plenum 102 to heat exchanger 108 and from outside duct 104 to ERV 106. “Incrementally” means that mixing damper assembly 212 is selectively positionable in a plurality of positions in a range between full obstruction of return aperture 204 and the neutral position, and in a plurality of positions in a range between the neutral position and full obstruction of outside aperture 206.

In the example embodiment shown, return aperture 204 and supply aperture 210 are positioned on opposing sides of mixing plenum 202 and are generally aligned with each other. Outside aperture 206 and ERV aperture 208 are similarly positioned on opposing sides of mixing plenum 202 and are generally aligned with each other. Return aperture 204 and outside aperture 206 may be on the same side of mixing plenum 202 and supply aperture 210 and ERV aperture 208 may be on the same side of mixing plenum 202.

In the example embodiment shown, mixing damper assembly 212 comprises a damper axle 214 rotatably supported in mixing plenum 202 and a mixing damper 216 extending radially from damper axle 214. Mixing damper 216 may be generally paddle-shaped as shown. Mixing damper assembly 212 includes an actuator 218 configured to selectively and incrementally rotate damper axle 214 through at least 180 degrees of rotation. “Incrementally” means that damper axle 214 is selectively positionable at incremental angles between 0 degrees and 180 degrees. Non-limiting examples of this include that damper axle 214 may be positionable at every 10 degrees (0 degrees, 10 degrees, 20 degrees, . . . 180 degrees), at every 5 degrees (0 degrees, 5 degrees, 10 degrees, . . . 180 degrees), and/or at every 1 degree (0 degrees, 1 degree, 2 degrees, . . . 180 degrees). A non-limiting example of a suitable actuator 218 is the CMB24-3 damper actuator available from Belimo® Aircontrols (USA), Inc.

Referring to FIGS. 4A to 4E, Mixing damper assembly 212 is selectively and incrementally movable between positions which partially or fully obstruct either return aperture 204 or outside aperture 206, or a plenum space between return aperture 204 and outside aperture 206 (i.e. the neutral position).

FIG. 4A shows mixing damper 216 in the neutral position. In the neutral position, mixing damper 216 partitions mixing plenum 202 into two separate chambers, such that return air flows from return plenum 102 through return aperture 204 to supply aperture 210 and outside air flows from outside duct 104 through outside aperture 206 to ERV aperture 208 (i.e. through source duct 107). That is, cross flow from return aperture 204 to ERV aperture 208 is blocked by mixing damper 216, and cross flow from outside duct 104 to supply aperture 210 is likewise blocked by mixing damper 216. Outside air then passes through ERV 106 where energy is transferred from exhaust air flowing from exhaust plenum 112 to ERV 106. As a result of said energy transfer, outside air is converted (i.e. by being heated and/or cooled by exhaust air) into intake air. Intake air flows to and mixes with return air downstream of mixing plenum 202 and resulting mixed air flows to heat exchanger 108. Exhaust air is converted in ERV 106 (i.e. via energy transfer with outside air) to discharge air, which flows out of air handling system 100 via discharge vent 114. The neutral position may alternatively be described as a 50% position and/or as a 90° position, and is referred to herein as position 30.

FIG. 4B shows mixing damper 216 in a recirculation position, wherein mixing damper 216 substantially obstructs outside aperture 206. In the recirculation position, outside air is prevented from entering air handling system 100. If supply fan 110 is not operating, intake air flows from intake air duct 113 through supply aperture 210 into mixing plenum 202 and returns to ERV 106 through ERV aperture 208. If supply fan 110 is operating, return air flows through both supply aperture 210 and ERV aperture 208, since a flow volume of return air under normal operation tends to be greater than a flow volume of intake air. The recirculation position may alternatively be described as a 0% position and/or as a 0° position, and is referred to herein as position 10.

FIG. 4C shows mixing damper 216 in an example defrost position, the example defrost position being an intermediate angular position between neutral position 30 and recirculation position 10. Mixing damper 216 is incrementally positionable in a plurality of defrost positions between position 10 and position 30 depending upon operating requirements of air handling system 100. When in the defrost positions, mixing damper 216 partially obstructs outside aperture 204 and a flow of outside air into mixing plenum 202 is restricted. Return air enters mixing plenum 202 via return aperture 204 and a portion of return air exits mixing plenum 202 via supply aperture 210. Another portion of return air mixes with the restricted flow of outside air and flows through ERV aperture 208 to ERV 106. Normally, the volume of intake air will be greater than the restricted volume of outside air, in order that substantially all of outside air is entrained with return air to flow through ERV aperture 208, and little or no outside air flows through supply aperture 210. Mixing damper 216 may be modulated through a range of the defrost positions to control relative proportions of return air and outside air supplied to ERV 106. The defrost positions may alternatively be described as a range of positions between 0% and 50%, and/or as a range of positions between 0° and 90°, and is referred to herein as range 20. The example defrost position shown may alternatively be described as a 25% position and/or a 45° position.

FIG. 4D shows mixing damper 216 in a maximum free cooling/heating position, wherein mixing damper 216 obstructs return aperture 204. In the free cooling position, return air RA is inhibited from entering mixing plenum 202. Outside air flows through mixing plenum 202 to both ERV aperture 208 and supply aperture 210. The maximum free cooling/heating position may alternatively be described as a 100% position and/or as a 180° position, and is referred to herein as position 60.

FIG. 4E shows mixing damper 216 in an example make-up position. Mixing damper 216 is incrementally positionable in a plurality of make-up positions between position 30 and position 60 depending upon operating requirements of air handling system 100. in the make-up positions, return air aperture 204 is partially obstructed by mixing damper 216 and a flow of return air is restricted. Outside air enters mixing plenum 202 via outside air aperture 202 and a portion of outside air exits mixing plenum 202 via ERV aperture 208. Another portion of outside air mixes with the restricted flow of return air RA and flows through supply aperture 210 to heat exchanger 108. Mixing damper 216 may be modulated through a range of the make-up positions to control relative proportions of return air and outside air supplied to heat exchanger 108. The make-up positions may alternatively be described as a range of positions between 50% and 100%, and/or as a range of positions between 90° and 180°. The range of positions between 50% and 75% is referred to herein as range 40, and the range of positions between 75% and 100% is referred to herein as range 50. The example make-up position shown may alternatively be described as a 75% position and/or a 135° position. The 75% position also provides defrosting functionality under certain conditions, for example when the building requires a large volume of outside air, ERV 106 is frosting, and intake fan 136 is slowed or stopped while exhaust fan 138 continues to operate. Under these conditions, minimal outside air flows directly to ERV 106 via source duct 107. Outside air OA instead flows directly to heat exchanger 108, and substantially only exhaust air EA flows through ERV 106, thereby mitigating frost build-up.

Referring to FIGS. 5A to 5D, in some embodiments mixing damper assembly 212 includes a return damper 220 positioned and pivotably supported in return plenum 102. Return air damper 220 is coupled to damper axle 214 by a linkage 222. Linkage 222 is configured to actuate (pivot) return air damper 220 over only a portion of a range of motion of damper axle 214 and mixing damper 216. For example, moving mixing damper 216 over range 20 and range 40 may not cause linkage 222 to actuate return damper 220, as shown in FIGS. 5A, 5B, and 5C. Moving mixing damper 216 over range 50, as shown in FIG. 5D, may cause linkage 222 to actuate return damper 220 to progressively obstruct return air plenum 102. When mixing damper 216 is at position 60, return damper 220 fully obstructs return plenum 102. Return damper 220 may thus assist in obstructing the comparatively large return air volume from entering mixing plenum 202. Return damper 220 may also assist in obstructing outside air from flowing into return plenum 102 and entering the interior space directly.

Referring back to FIG. 1, air handling system 100 may comprise a supply filter 116 positioned upstream of heat exchanger 108. “Upstream” refers to a component preceding another component in a direction of fluid flow, while “downstream” refers to a component following another component in a direction of fluid flow. Air handling system 100 may comprise an outside filter 118 positioned upstream of ERV 106 and downstream of mixing device 200. Air handling system 100 may comprise an exhaust filter 120 positioned upstream of ERV 106 and downstream of exhaust plenum 112.

Air handling system 100 comprises a controller 122 in operative connection with actuator 218. Air handling system 100 comprises a return temperature sensor 124 located in return air plenum 102 and an outside temperature sensor 126 located in outside air duct 104. Temperature sensors 124, 126 are in operative connection with controller 122. Controller 122 is configured to control actuator 218 to move mixing damper 216 in response to temperatures measured by temperature sensors 124, 126. In some embodiments, return damper 220 is actuated by a separate actuating motor (not shown) and controller 122 is configured to actuate the actuating motor of return damper 220 separately or in conjunction with actuator 218 and mixing damper 216. That is, in some embodiments, linkage 222 comprises an electronic relationship between return damper 220 and mixing damper 216 rather than a mechanical linkage connecting return damper 220 and mixing damper 216 as shown in FIG. 3. Actuating return damper 220 independently of mixing damper 216 may assist in certain functions, including but not limited to providing make-up air to air handling system 100 when supply fan 110 is operating at low speeds.

FIG. 6 shows an example method 1000 of controlling mixing damper 216 to prevent and/or mitigate frost buildup in ERV 106. At step 1002, return temperature sensor 124 measures a return air temperature T_RA and outside temperature sensor 126 measures an outside air temperature T_OA. At step 1004, controller 122 compares return air temperature T_RA to a return temperature threshold THR_R (e.g. 5° C.) and outside air temperature T_OA to return air temperature T_RA. When return air temperature T_RA is colder than return temperature threshold THR_R, and outside air temperature T_OA is colder than return air temperature T_RA, there is potential for components of air handling system 100 to begin freezing, in particular ERV 106. To mitigate this potential for freezing, at step 1006 controller 122 actuates mixing damper 216 to position 10, thereby reducing a volume of outside air entering air handling system 100 to zero. Otherwise, at step 1008 controller 122 compares outside air temperature T_OA to if an outside temperature THR_O. If outside air temperature T_OA is less than outside temperature threshold THR_O, there may be potential for frost/ice to form in ERV 106. Accordingly, if return air temperature T_RA is greater than return temperature threshold THR_R and outside air temperature T_OA is less than outside temperature threshold THR_O, at step 1010 controller 122 controls actuator 208 to move mixing damper 216 to a defrost position (i.e. in range 20), thereby diverting a portion of warmer return air to ERV 106 so as to prevent and/or mitigate frost/ice formation in ERV 106. The warmer return air will then bring ERV 106 up to return air temperature T_RA, which may promote melting of frost/ice in ERV 106.

Referring back to FIG. 1, air handling system 100 may comprise an ERV source temperature sensor 128 positioned in ERV source duct 107. ERV source temperature sensor 128 is in operative connection with controller 122 and is configured to directly measure a temperature of source air entering ERV 106 from mixing device 200. If the source air temperature is less than a predetermined threshold (for example, 0° C.) this may cause frost/ice formation in ERV 106, and controller 122 will actuate mixing damper 216 to a defrost position in range 20 to mitigate said frost formation.

Air handling system 100 may comprise an air quality sensor 130 positioned downstream of outside duct 104. In some embodiments, air quality sensor 130 is positioned upstream of mixing device 200, for example proximate to outside aperture 206. In some embodiments, air quality sensor 130 is positioned in mixing plenum 202. In some embodiments, air quality sensor 130 is positioned downstream of mixing device 200 (e.g. in ERV source duct 107). In the embodiment shown, air quality sensor 130 is positioned in ERV 106 and after outside filter 118. Air quality sensor 130 is configured to detect the presence of airborne contaminants such as smoke, pollen, spores, dust, vehicle exhaust, noxious odours caused by undesirable aroma compounds, and/or the like. Air quality sensor 130 is in operative communication with controller 122.

FIG. 7 shows an example method 1100 of controlling mixing device 200 to mitigate airborne contaminant infiltration to the interior space. At step 1102, air quality sensor 130 measures an outdoor air quality OAQ, after filtration by outside filter 118 where outside filter 118 is included in air handling system 100. For example, air quality sensor may provide a measurement of concentration of fine inhalable particulate matter, PM_2.5, in micrograms/cubic metre. At step 1104, controller 122 compares the measured outdoor air quality OAQ to a predetermined threshold THR_Q. If the measured outdoor air quality is below threshold THR_Q (e.g. the concentration of inhalable particulate matter exceeds a predetermined threshold), then at step 1106 controller 122 actuates mixing damper to position 10, thereby substantially preventing outdoor air OA (with measured contaminants) from entering air handling system 100 and the interior space.

Referring back to FIG. 1, air handling system 100 comprises an exhaust airflow sensor 132 positioned in exhaust plenum 112 and an outside airflow sensor 134 positioned in outside duct 104. ERV 106 comprises an ERV intake fan 136 in fluid communication between mixing device 200 and heat exchanger 108 and an ERV discharge fan 138 in fluid communication between exhaust plenum 112 and discharge vent 114. In some embodiments, air handling system includes an intake airflow sensor 146 positioned downstream of ERV intake fan 136.

FIG. 8 shows an example method 1200 of controlling mixing device 200 to provide make-up air to air handling system 100, based on air flow in air handling system 100. Initially, mixing damper 216 is in neutral position 30 and both intake fan 136 and discharge fan 138 are operating. Under these conditions, an outside airflow rate F_OA in outside duct 104 and an intake airflow rate F_IA in intake air duct 113 will be the same. At step 1202, outside airflow sensor 134 measures the outside airflow rate F_OA (which is equivalent to intake airflow rate F_IA) and exhaust airflow sensor 132 measures an exhaust airflow rate FEA over time at specific fan speeds of intake fan 136 and discharge fan 138. In some embodiments, intake airflow sensor 146 directly measures intake airflow rate F_IA. At step 1203, controller 122 receives and stores this current data, and calculates averages using previously stored data to develop a relationship between the flow rates and fan speeds. At step 1204, controller 122 monitors intake airflow rate F_IA (directly or via outside airflow rate F_OA) while holding fan speeds of intake fan 136 and discharge fan 138 steady. If intake air flow rate F_IA/outside airflow rate F_OA has increased at the current speed of intake fan 136, and exhaust airflow rate FEA has decreased at the current speed of discharge fan 138, this may be indicative of a decrease in building pressure relative to the outdoors necessitating that make-up air be provided to air handling system 100 to maintain building pressure. Accordingly, at step 1206, controller 122 actuates mixing damper 216 to a position in range 40 or range 50, thereby diverting a portion of outside airflow volume directly to heat exchanger 108 and supply fan 110.

Referring back to FIG. 1, in some embodiments air handling system 100 comprises a return humidity sensor 150 positioned in return plenum 102 and an outside humidity sensor 152 positioned in outside duct 104. Humidity sensors 150, 152 are operatively connected to controller 122.

FIG. 9 shows an example method 1300 of controlling mixing device 200 to provide free cooling or free heating to the interior space cooled or heated by air handling system 100. At step 1302, return temperature sensor 124 measures return air temperature T_RA, outside temperature sensor 126 measures outside air temperature T_OA, return humidity sensor 150 measures a return air humidity Ø_RA, and outside humidity sensor 152 measures an outside air humidity Ø_OA. At step 1304, controller 122 calculates a return air enthalpy H_RA from return air temperature T_RA and return air humidity Ø_RA and an outside air enthalpy H_OA from outside air temperature T_OA and outside air humidity Ø_OA.

If air handling system 100 is operating in a cooling mode, at step 1306 controller 122 compares the return air enthalpy H_RA to a cooling target mixed air enthalpy H_MAC and to the outside air enthalpy H_OA. If the cooling target mixed air enthalpy H_MAC is less than the return air enthalpy H_RA and the outside air enthalpy is less H_OA than the return air enthalpy H_RA, then at step 1310 controller 122 assesses whether a target supply airflow F_SA of supply fan 110 exceeds a maximum permitted airflow F_OA,max of outside duct 104. If the target supply airflow F_SA is less than maximum permitted airflow F_OA,max, then at step 1312 controller actuates mixing damper 216 to a position in range 50, which reduces or blocks the return airflow so as to cool the mixed air flowing to heat exchanger 108. If target supply airflow F_SA is greater than F_OA,max, then at step 1314 controller 122 actuates mixing damper 216 to range 40 to facilitate mixing of the outside airflow with the return airflow. Air handling system 100 thereby takes advantage of cooling provided by outside air without having to expend significant further energy to cool the mixed air (via heat exchanger 108) flowing to supply fan 110.

If air handling system 100 is operating in a heating mode, at step 1308 controller 122 compares the return air enthalpy H_RA to a heating target mixed air enthalpy H_MAH and to the outside air enthalpy H_OA. If the heating target mixed air enthalpy H_MAH is greater than the return air enthalpy H_RA and the outside air enthalpy is greater H_OA than the return air enthalpy H_RA, then controller 122 moves to step 1310 and assesses whether a target supply airflow F_SA of supply fan 110 exceeds a maximum permitted airflow F_OA,max of outside duct 104. If the target supply airflow F_SA is less than maximum permitted airflow F_OA,max, then controller 122 moves to step 1312 and actuates mixing damper 216 to a position in range 50, which reduces or blocks the return airflow so as to heat the mixed air flowing to heat exchanger 108. If target supply airflow F_SA is greater than F_OA,max, then at step 1314 controller 122 actuates mixing damper 216 to range 40 to facilitate mixing of the outside airflow with the return airflow. Air handling system 100 thereby takes advantage of heating provided by outside air without having to expend significant further energy to heat (via heat exchanger 108) the mixed air flowing to supply fan 110.

FIG. 10 shows an example method 1400 of operating air handling system 100 with mixing damper assembly 200. At step 1402, controller 122 determines if conditions for moving mixing damper 216 to position 10 are met (e.g. unacceptable outdoor air quality measurements and/or temperatures which threaten freezing of air handling system 100). If so, at step 1404, controller 122 actuates mixing damper 216 to position 10. At step 1406, controller 122 deactivates ERV exhaust fan 138, and at step 1408 controller 122 activates supply fan 110 and ERV intake fan 136, thereby circulating warmer return air into ERV 106.

If conditions for moving mixing damper to position 10 are not met, then at step 1410 controller 122 determines if conditions for moving mixing damper 216 to a position in range 50 are met (e.g. as shown in FIG. 9). If so, at step 1412 controller 122 actuates mixing damper 216 into range 50 (and may modulate mixing damper across various positions within range 50). At step 1414, controller 122 deactivates ERV intake fan 136 and activates supply fan 110 and ERV Exhaust fan 138. Air handling system 100 thereby is provided with fresh outside make-up air to replace exhausted air within the space being heated/cooled and may also take advantage of free heating/cooling provided by that fresh air so as to reduce energy consumption of heat exchanger 108.

If conditions for moving mixing damper 216 to position 10 or range 50 are not met, then at step 1418 controller 122 determines if conditions for range 40 are met (e.g. as shown in FIG. 9). If so, at step 1420 controller 122 actuates mixing damper 216 into range 40 (and may modulate mixing damper across various positions within range 40). At step 1422, controller 122 decreases fan speed of ERV intake fan 136 and at step 1424, controller 122 activates supply fan 110 and ERV exhaust fan 138. Air handling system 100 thereby provides make-up air to the space being heated/cooled and increases the building pressure.

If conditions for moving mixing damper 216 to position 10, range 50, or range 40 are not met, then at step 1426 controller 122 determines if conditions for range 20 are met (e.g. as shown in FIG. 6). If so, at step 1428 controller 122 actuates mixing damper to a position in range 20 (and may modulate mixing damper across various positions within range 20). At step 1430, controller 122 increases the fan speed of ERV intake fan 136 to the maximum allowable, and at step 1432 controller 122 activates supply fan 110 and ERV exhaust fan 138. Air handling system 100 thereby diverts a portion of return air volume to ERV 106 to facilitate defrosting of ERV 106.

If none of the conditions for moving mixing damper to position 10, range 20, range 40, or range 50 are met, then at step 1434 controller 122 actuates mixing damper 216 to position 30 and at step 1436, controller 122 operates fans 110, 136, 138 according to normal operating parameters.

Controller 122 may comprise a user interface 160. User interface 160 may comprise a display device (not shown) and an input device (not shown). The display device may for example be a screen and the input device may for example be a keypad, or the display device and input device may be combined as a touchscreen, for example. User interface 160 may be a software application on a computer, tablet, smartphone, and/or the like. User interface 160 may be configured to display operating parameters of air handling system 100, including but not limited to, a measured temperature of the interior space, a temperature set point for the interior space, return air temperature T_RA, and outside air temperature T_OA. User interface 160 may be configured to allow a user to manually control controller 122. For example, user interface 160 may allow the user to command controller 122 to move mixing damper 216 to, for example, the free cooling position.

FIG. 11 shows an air handling system 100.1 according to another embodiment of the invention. Like parts have like numbers and functioning as air handling system 100 shown in FIG. 1 with the addition of decimal extension “0.1.” Air handling system 100.1 further comprises a return pressure sensor 162 in operative communication with return air plenum 102.1 and configured to measure a return air pressure P_RA, an outside pressure sensor 164 in operative communication with outside duct 104.1 and configured to measure an outside air pressure P_OA, a supply pressure sensor 166 in operative communication with a supply duct 115 connected to supply fan 110.1 and configured to measure a supply air pressure P_SA, and an exhaust pressure sensor 168 in operative communication with exhaust plenum 112.1 and configured to measure an exhaust air pressure P_EA. In some embodiments, air handling system 100.1 includes an exhaust temperature sensor 170 in operative communication with exhaust plenum 112.1 and configured to measure an exhaust air temperature T_EA. Pressure sensors 162, 164, 166, 168 and temperature sensor 170 are all in communication with controller 122.

Air handling system 100.1 may be operated according to any of the methods shown in FIGS. 6 to 10. In addition, air handling system 100.1 may be operated according to methods that utilize data from pressure sensors 162, 164, 166, and 168.

FIG. 12 shows an example method 1500 of controlling mixing device 200 to provide make-up air to air handling system 100.1, based on pressures measured in air handling system 100.1. At step 1502, outside pressure sensor 164 and return pressure sensor 162 measure outside air pressure P_OA and return air pressure P_RA, respectively, and communicates those pressures to controller 122.1 At step 1504, controller 122.1 calculates ambient inside pressure and outside pressure based on measured outside air pressure P_OA and return air pressure P_RA, measured flow rates F_OA, F_RA, in outside duct 104.1 and return air plenum 102.1 and the characteristic flow coefficients of the outside duct 104.1 and return plenum 102.1. At step 1506, controller 122.1 calculates a pressure differential between ambient outside pressure and ambient inside pressure, and compares the pressure differential to a predetermined pressure differential threshold. Generally, controller 122.1 is configured to operate air handling system 100.1 to hold the ambient inside pressure at a negative differential to the ambient outside pressure, so that dampers associated with direct exhaust devices (e.g. bathroom fans, clothes dryers, kitchen vent hoods, and/or the like) remain closed. In the embodiment shown, the differential threshold is 15 Pa. That is, it is desirable that the ambient inside pressure is 15 Pa less than the ambient outside pressure. If the pressure differential exceeds the differential threshold, then, provided that ERV 106.1 is not at risk of freezing, controller 122.1 will modulate ERV intake fan 136.1 up to maximum speed. If that is not successful at reducing the pressure differential, then at step 1508, controller 122 will modulate mixing damper 216 from position 30 to position 60, i.e. to close return air plenum 102.1, so as to provide make-up air to air-handling system 100.1 via outside duct 104.1. In some embodiments, if supply fan 110.1 is operating at low speeds, such that airflow in return plenum 102.1 is also low, return damper 220 may be modulated to close return plenum 102.1 while mixing damper 216 remains open (e.g. in range 40 or 50). Doing so may assist in providing further make-up air flow to the space serviced by air handling system 100.1, and also may assist in preventing backflow into return plenum 102.1, which could result in unfiltered and unheated/uncooled outside air entering the space.

Additional Description

Examples of mixing devices, air handling devices comprising such mixing devices, and methods for use of such mixing devices have been described. The following clauses are offered as further description.

• 1. A mixing device for an air handling system, the mixing device comprising a mixing plenum, the mixing plenum including a return air aperture connected to a return air plenum of the air handling system; an outside air aperture connected to an outside air duct a heat recovery ventilator/energy recovery ventilator (ERV) aperture in fluid communication with an ERV of the air handling system; and a supply aperture in fluid communication with a heat exchanger of the air handling system; and a mixing damper positioned in the mixing plenum, the mixing damper actuable to move incrementally along a path between three positions 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 coil 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 clause 1, wherein the mixing damper is positionable across a first range of positions between the first position and the second position.
• 3. A mixing device according to clause 1 or clause 2, wherein the mixing damper is positionable across a second range of positions between the second position and the third position.
• 4. A mixing device according to any one of clauses 1 to 3 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 clause 4, wherein the linkage is configured to only begin actuating the return air damper when the mixing damper is moved from an intermediate position in the second range of positions to the third position.
• 6. An air handling system comprising a mixing device according to any one of clauses 1 to 4, the air handling system further comprising 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.
• 7. A mixing device according to any one of clauses 1 to 6, 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.
• 8. A mixing device according to clause 7, 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.
• 9. An air handling system comprising a mixing device operatively connected to a return air plenum and to an 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 dividing the mixing plenum into a first duct connecting the return air plenum to the heat exchanger and a second duct 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.
• 10. An air handling unit according to clause 9, comprising an air filter upstream of the heat exchanger.
• 11. An air handling unit according to clause 9 or clause 10, comprising an air filter upstream of the ERV.
• 12. An air handling system for providing heated and/or cooled air to an interior space, the air handling system comprising an outside duct configured to receive outside air; a return plenum configured to receive return air from the interior space; a mixing device in fluid communication with the outside duct and the return plenum; a heat exchanger connected to the mixing device via a mixed-air duct; and a supply fan in fluid communication with the heat exchanger and configured to provide air heated and/or cooled by the heat exchanger to the interior space; wherein the mixing device comprises a mixing plenum; an outside aperture providing fluid communication between the outside duct and the mixing plenum; a return aperture providing fluid communication between the return plenum and the mixing plenum; a supply aperture providing fluid communication between the mixing plenum and the mixed-air duct; and a damper mechanism, the damper mechanism selectively moveable to a plurality of positions in a range between a first position obstructing the outside aperture and a second position obstructing the return aperture.
• 13. An air handling system according to clause 12, the air handling system comprising one or more exhaust fans in fluid communication with the interior space; an exhaust plenum in fluid communication with the one or more exhaust fans; a heat recovery ventilator/energy recovery ventilator (ERV) in fluid communication with the exhaust plenum; an ERV source duct connecting the ERV to the mixing plenum; and an intake duct connecting the ERV to the mixed-air duct; and wherein the damper mechanism is selectively positionable in an intermediate position to partition the mixing plenum such that return air flows to the mixed-air duct and outside air flows to the ERV source duct.
• 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 comprising 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 clause 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 mitigating frost formation in a heat recovery ventilator/energy recovery ventilator (ERV), the method further comprising connecting a fresh air intake duct of the ERV to a mixing device, the mixing device comprising 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; connecting an exhaust plenum for a space being heated/cooled to the ERV; connecting a supply duct for a heat exchanger to the mixing plenum, the heat exchanger connected to one or more supply fans for supplying heated/cooled air to the space; moving the mixing damper incrementally to a position at least partially obstructing the return air plenum so as to direct outside make-up air to the heat exchanger; and activating an exhaust fan of the ERV and deactivating an intake fan of the ERV so that only exhaust air from the exhaust plenum flows through the ERV.
• 17. 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.
• 18. The method according to clause 17, 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.
• 19. The method according to clause 18 or clause 19, wherein the airborne contaminant is one or more of smoke, allergens, dust, combustion exhaust compounds, and aroma compounds.
• 20. The method according to any one of clauses 18 to 20, wherein the air handling system includes a filter upstream of the ERV and measuring the concentration of the airborne contaminant comprises measuring downstream of the filter.
• 21. 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.
• 22. The method according to clause 21, wherein the air handling device further comprises a heat recovery ventilator/energy recovery ventilator (ERV) downstream of the mixing device and upstream of the supply fan, and wherein the method further comprises, prior to moving the mixing damper, increasing a fan speed of an intake fan of the ERV.
• 23. The method according to clause 21 or clause 22, wherein the mixing device further comprises a return damper configured to selectively obstruct the return plenum, and wherein the method further comprises, in response to a fan speed of the supply fan being less than a predetermined threshold, operating the return damper to obstruct the return plenum.

Interpretation of Terms

Unless the context clearly requires otherwise, throughout the description and the claims:

• • “comprise”, “comprising”, and the like are to be construed in an inclusive sense, as opposed to an exclusive or exhaustive sense; that is to say, in the sense of “including, but not limited to”;
  • “connected”, “coupled”, or any variant thereof, means any connection or coupling, either direct or indirect, between two or more elements; the coupling or connection between the elements can be physical, logical, or a combination thereof;
  • “herein”, “above”, “below”, and words of similar import, when used to describe this specification, shall refer to this specification as a whole, and not to any particular portions of this specification;
  • “or”, in reference to a list of two or more items, covers all of the following interpretations of the word: any of the items in the list, all of the items in the list, and any combination of the items in the list;
  • the singular forms “a”, “an”, and “the” also include the meaning of any appropriate plural forms. These terms (“a”, “an”, and “the”) mean one or more unless stated otherwise;
  • “and/or” is used to indicate one or both stated cases may occur, for example A and/or B includes both (A and B) and (A or B);
  • “approximately” when applied to a numerical value means the numerical value ±10%;
  • where a feature is described as being “optional” or “optionally” present or described as being present “in some embodiments” it is intended that the present disclosure encompasses embodiments where that feature is present and other embodiments where that feature is not necessarily present and other embodiments where that feature is excluded. Further, where any combination of features is described in this application this statement is intended to serve as antecedent basis for the use of exclusive terminology such as “solely,” “only” and the like in relation to the combination of features as well as the use of “negative” limitation(s)” to exclude the presence of other features; and
  • “first” and “second” are used for descriptive purposes and cannot be understood as indicating or implying relative importance or indicating the number of indicated technical features.

Words that indicate directions such as “vertical”, “transverse”, “horizontal”, “upward”, “downward”, “forward”, “backward”, “inward”, “outward”, “left”, “right”, “front”, “back”, “top”, “bottom”, “below”, “above”, “under”, and the like, used in this description and any accompanying claims (where present), depend on the specific orientation of the apparatus described and illustrated. The subject matter described herein may assume various alternative orientations. Accordingly, these directional terms are not strictly defined and should not be interpreted narrowly.

Where a range for a value is stated, the stated range includes all sub-ranges of the range. It is intended that the statement of a range supports the value being at an endpoint of the range as well as at any intervening value to the tenth of the unit of the lower limit of the range, as well as any subrange or sets of sub ranges of the range unless the context clearly dictates otherwise or any portion(s) of the stated range is specifically excluded. Where the stated range includes one or both endpoints of the range, ranges excluding either or both of those included endpoints are also included in the invention.

Certain numerical values described herein are preceded by “about”. In this context, “about” provides literal support for the exact numerical value that it precedes, the exact numerical value ±5%, as well as all other numerical values that are near to or approximately equal to that numerical value. Unless otherwise indicated a particular numerical value is included in “about” a specifically recited numerical value where the particular numerical value provides the substantial equivalent of the specifically recited numerical value in the context in which the specifically recited numerical value is presented. For example, a statement that something has the numerical value of “about 10” is to be interpreted as: the set of statements:

• • in some embodiments the numerical value is 10;
  • in some embodiments the numerical value is in the range of 9.5 to 10.5; and if from the context the person of ordinary skill in the art would understand that values within a certain range are substantially equivalent to 10 because the values with the range would be understood to provide substantially the same result as the value 10 then “about 10” also includes:
  • in some embodiments the numerical value is in the range of C to D where C and D are respectively lower and upper endpoints of the range that encompasses all of those values that provide a substantial equivalent to the value 10

Specific examples of systems, methods and apparatus have been described herein for purposes of illustration. These are only examples. The technology provided herein can be applied to systems other than the example systems described above. Many alterations, modifications, additions, omissions, and permutations are possible within the practice of this invention. This invention includes variations on described embodiments that would be apparent to the skilled addressee, including variations obtained by: replacing features, elements and/or acts with equivalent features, elements and/or acts; mixing and matching of features, elements and/or acts from different embodiments; combining features, elements and/or acts from embodiments as described herein with features, elements and/or acts of other technology; and/or omitting combining features, elements and/or acts from described embodiments.

As will be apparent to those of skill in the art upon reading this disclosure, each of the individual embodiments described and illustrated herein has discrete components and features which may be readily separated from or combined with the features of any other described embodiment(s) without departing from the scope of the present invention.

Any aspects described above in reference to apparatus may also apply to methods and vice versa.

Any recited method can be carried out in the order of events recited or in any other order which is logically possible. For example, while processes or blocks are presented in a given order, alternative examples may perform routines having steps, or employ systems having blocks, in a different order, and some processes or blocks may be deleted, moved, added, subdivided, combined, and/or modified to provide alternatives or subcombinations. Each of these processes or blocks may be implemented in a variety of different ways. Also, while processes or blocks are at times shown as being performed in series, these processes or blocks may instead be performed in parallel, simultaneously or at different times.

Various features are described herein as being present in “some embodiments”. Such features are not mandatory and may not be present in all embodiments. Embodiments of the invention may include zero, any one or any combination of two or more of such features. All possible combinations of such features are contemplated by this disclosure even where such features are shown in different drawings and/or described in different sections or paragraphs. This is limited only to the extent that certain ones of such features are incompatible with other ones of such features in the sense that it would be impossible for a person of ordinary skill in the art to construct a practical embodiment that combines such incompatible features. Consequently, the description that “some embodiments” possess feature A and “some embodiments” possess feature B should be interpreted as an express indication that the inventors also contemplate embodiments which combine features A and B (unless the description states otherwise or features A and B are fundamentally incompatible). This is the case even if features A and B are illustrated in different drawings and/or mentioned in different paragraphs, sections or sentences.

While a number of exemplary aspects and embodiments have been discussed above, those of skill in the art will recognize certain modifications, permutations, additions and sub-combinations thereof. It is therefore intended that the following appended claims and claims hereafter introduced are interpreted to include all such modifications, permutations, additions and sub-combinations as are consistent with the broadest interpretation of the specification as a whole.