Patent Description:
Server-based datacenters, sometimes known as server farms or server clusters, are a large collection of computers, often at a physically remote but network accessible location, that provide clients with expanded computing capability. The expanded computing capability typically is in the form of data storage, data processing, database management, file management, and website management.

Each computer of the system usually includes a base or case supporting a set of computer components. Depending on the application, computer components may include items such as one or more microprocessors, hard drives, solid state memory devices, routers and power supplies. More generally, there are many types of electronic equipment and/or other devices that may emit heat to the surrounding area during operation. To maintain such components at a safe operating temperature, the base or case of each computer or other heat generating device usually includes or is otherwise associated with a cooling fan that forces a current of environmentally controlled air from a front face of the computer or other device, across the components, and out through a back end of the computer or other device. In some cases, it is this current of air that defines the front and back ends of the computer or other device.

Somewhat resembling books in an open bookshelf, computers at a datacenter may be stacked in rack-like cabinets that are neatly arranged in rows separated by aisles. The aisles provide manual access to the front and back ends of the computers. The rows of computers are oriented such that each individual aisle is exposed solely to computer fronts or solely to computer backs. Thus, the front ends of computers in one row face the front ends of computers in the next row across the aisle. In the very next aisle, the back ends of computers on opposite sides of that aisle face each other. Aisles of computer fronts are generally cooler than backside aisles due to the computer components heating the current of air developed by the computers' internal cooling fans. Thus, front side cooler aisles are often called "cold aisles," and back side aisles are known as "hot aisles. " Each aisle being exposed to only computer fronts or to only computer backs creates an alternating arrangement of cold aisles and hot aisles. Similar arrangements of other types of electronic equipment or other devices that generate heat may be implemented to cool such devices during operation.

Datacenters usually run nonstop and generate a lot of heat. Consequently, a building air conditioning system is usually needed to prevent the computers from overheating. In the event of a fire, a generally inert gas system or some other type of fire suppression system automatically activates to prevent or reduce (e.g., minimize) damage.

<CIT> relates to a mobile soft duct system, which includes a soft duct that can be extended and retracted along a track to deliver an air supply to various locations.

<CIT> relates to a further system for conveying air from one location to another, having a soft duct with a passage and an air flow control device. The air flow control device can be operated to vary a cross sectional area of a portion of the passage of the soft duct.

Example cooling systems for server-based datacenters, or server farms, include air permeable inflatable air ducts installed above multiple rows of computer racks. In some examples, in the event of a fire, the air ducts deflate and collapse so as not to obstruct the flow of a fire extinguishing gas. In the embodiments covered by the claimed invention, when inflated, the air ducts have an expanded shape that inhibits adverse mixing of air between hot aisles and cold aisles. In some embodiments not covered by the claimed invention, wings extend laterally from the air duct to further reduce the mixing of hot and cold air. In some embodiments not covered by the claimed invention, a series of inflatable branch ducts extend downward from a supply air duct to reach well into cold aisles. In some embodiments covered by the claimed invention, nozzles and/or internal baffles promote radial air discharge from the supply air duct.

<FIG> and <FIG> show an example datacenter <NUM> including a building <NUM> containing a plurality of computers <NUM> in a plurality of cabinets <NUM>. The term, "computer" refers to any digital processing device, examples of which include a server, a data storage device, a hard drive, a solid state memory, etc. The term, "cabinet" refers to any structure for supporting and/or housing one or more of the plurality of computers <NUM>. Examples of a cabinet include a plurality of enclosures supporting and/or housing at least one computer, a single enclosure containing a single computer, a single enclosure housing a plurality of computers, a rack, a shelf, etc. In examples where a plurality of computers are housed or supported by or within one or more cabinets, the term, "row of computers" encompasses the associated cabinets (i.e., the racks, shelving, and/or other enclosure or support for the computers). So, in some examples, the terms, "row of computers" and "row of cabinets" can be used interchangeably. Although the teachings of this disclosure are described with respect to rows of computers, the teachings of this disclosure may apply to any other type of electronic equipment or devices that are to be cooled through forced air when arranged in one or more rows.

In the illustrated example, the cabinets <NUM> are arranged in a plurality of rows <NUM> to create a first row of computers 18a (a first row of cabinets) and a second row of computers 18b (a second row of cabinets). The plurality of rows of computers <NUM> also creates an alternating arrangement of a plurality of cold aisles <NUM> (e.g., a first aisle 20a) and a plurality of hot aisles <NUM> (e.g., a second aisle 22a and a third aisle 22b). In some examples, there may be only a single hot aisle and a single cold aisle. As used herein, the term "aisle" refers to the space between adjacent rows of computers <NUM> as well as the space adjacent the outer side of an outer row of the plurality of rows <NUM>. Thus, in some examples, there may be only a single row of computers <NUM> that defines hot and cold aisles on either side without adjacent rows on either side of the single row of computers <NUM>. The terms, "hot" and "cold" in reference to an aisle merely means that the average air temperature of the hot aisle is greater than that of the cold aisle. The terms, "hot aisle" and "cold aisle" do not suggest that either aisle is at any particular absolute temperature. At least one computer <NUM> and/or at least one row of cabinets <NUM> define an air passageway <NUM> between a cold aisle 20a and one or more hot aisles 22a, 22b. One or more internal fans <NUM> within the air passageway <NUM> creates a current of air <NUM> (e.g., a first current of air 26a from the cold aisle 20a (the first aisle) to the first hot aisle 22a (the second aisle) and/or a second current of air 26b from the cold aisle 20a to the second hot aisle 22b (the third aisle) for cooling the internal components of the computers <NUM>. The cabinets <NUM> have a top surface <NUM> that is below and spaced apart from an overhead surface <NUM> of the building <NUM> to create a gap <NUM> between the top surface <NUM> and the overhead surface <NUM>.

In the illustrated example, the datacenter <NUM> also includes a fire suppression system <NUM>. In some examples, the fire suppression system <NUM> includes one or more pressurized tanks <NUM> of a fire extinguishing fluid <NUM> (<FIG>) such as halon, halocarbons, carbon dioxide or an inert gas. In the event of a fire-related incident (e.g., fire, heat, smoke, manually triggered fire alarm, etc.), a sensor <NUM> detects and responds to the incident by sending a signal <NUM> that opens a valve <NUM>, which releases the fire extinguishing fluid <NUM> from the tanks <NUM> to displace the oxygen surrounding the rows of computers <NUM>.

<FIG> show a cooling system <NUM> according to an embodiment of the invention, for efficiently extracting heat generated by the computers <NUM> during normal operation without interfering with the fire suppression system <NUM> during a fire <NUM> (<FIG>). In this embodiment, the cooling system <NUM> includes an air filter <NUM>, a known cooling coil <NUM> (e.g., a water, glycol, or refrigerant cooled heat exchanger), a blower system <NUM>, a supply air manifold <NUM>, at least one branch air duct <NUM>, at least one supply air duct <NUM>, at least one return air register <NUM>, and a return air manifold <NUM>. The term, "blower system" refers to one or more blowers <NUM> powered by at least one motor <NUM>. The supply air duct <NUM> is inflatable by virtue of its tubular wall <NUM> (e.g., 70a and 70b) being made of a pliable material (e.g. air permeable sheet, air impermeable sheet, nonmetallic sheet, coated fabric, uncoated fabric, and various combinations thereof). The term, "pliable" refers to a material that can be crumpled and later straightened without appreciable damage to the material. The term, "inflatable" as it relates to an air duct means that the duct's internal volume expands with internal air pressure and tends to collapse when the pressure is removed.

During normal operation, as shown in <FIG> and <FIG>, the blower <NUM> draws air <NUM> from the return air manifold <NUM>, through the filter <NUM>, and through the cooling coil <NUM>. The blower <NUM> then discharges the filtered cool air through the supply air manifold <NUM>, through the branch air ducts <NUM> and into an axial end <NUM> of each supply air duct <NUM>. In the illustrated embodiment, the discharge pressure of blower <NUM> inflates or fully expands each supply air duct <NUM>. The supply air duct <NUM> in its expanded state, as shown in the examples of <FIG> and <FIG>, creates an obstruction that substantially fills or blocks gap <NUM> between the top surface <NUM> and the overhead surface <NUM>. In some embodiments, the supply air duct <NUM> spans the entire gap <NUM> so as to be in contact with both the top surface <NUM> and the overhead surface <NUM> when inflated. The supply air duct <NUM> blocking the gap <NUM> reduces (e.g., minimizes) the mixing of cold and warm air between the cold aisle 20a and the hot aisle 22a.

In this example, each supply air duct <NUM> has an air permeable sidewall 70a facing the cold aisle 20a and a substantially impermeable opposite sidewall 70b facing the hot aisle 22a. The sidewall 70a is made permeable by any suitable means, examples of which include porosity in the material of the tubular wall 70a, perforations in the tubular wall 70a, and/or the sidewall 70a having one or more nozzles <NUM> (<FIG>). In examples where only the sidewall 70a is air permeable, air discharged from the blower <NUM> flows lengthwise <NUM> (<FIG>) through the supply air duct <NUM>, radially outward through the sidewall 70a, and downward into the cold aisle 20a. From the cold aisle 20a, the cool air flows through the computers <NUM> via an air passageway <NUM> (through the computers <NUM> and/or through the cabinets <NUM>), into the hot aisle 22a, and downward toward the return register <NUM>. The register <NUM> conveys the air from the hot aisle 22a into the return manifold <NUM>, which returns the air back to the filter <NUM> for recirculation.

In some examples, in the event of a fire <NUM> or a fire-related incident (e.g., flame, smoke, heat, manually triggered fire alarm, etc.), the sensor <NUM> responds by sending the signal <NUM> to activate the fire suppression system <NUM>, as described earlier, and also sends a signal <NUM> that de-energizes the motor <NUM> and, thus, stops the blower <NUM>. Stopping the blower <NUM> depressurizes the supply air duct <NUM>, which causes the supply air duct <NUM> to collapse to its deflated state, as shown in <FIG> and <FIG>. In the deflated state, the collapsed supply air duct <NUM> opens or substantially unblocks the gap <NUM> so that the fire extinguishing fluid <NUM> in a gaseous state can readily disperse over, around and through the multiple rows of computers <NUM>.

In some embodiments, the cooling system <NUM> includes means for preventing a collapsed supply air duct <NUM> from drooping excessively over the sides of the cabinets <NUM> and/or the computers <NUM>. In the embodiment covered by the claimed invention shown in <FIG> an internal restraint <NUM> (e.g., a string, a strap, a cable, a chain, a horizontal sheet, an elastic cord, a tie rod, etc.) limits the radially outward movement of the sidewalls 70a and 70b as the supply air ducts <NUM> deflate. <FIG> shows the supply air duct <NUM> in its inflated state, and <FIG> shows the supply air duct <NUM> in its deflated state. In some examples, a pair of taut internal or external restraints (e.g., cables) running parallel to the supply air duct <NUM> extend along the entire length of the sidewalls 70a and 70b. In the embodiment covered by the claimed invention, the supply air duct <NUM> rests upon the top surface <NUM> such that the weight of the supply air duct is supported by the top surface <NUM>. In some embodiments, the supply air duct <NUM> is secured to the top surface <NUM> to prevent the supply air duct <NUM> from sliding off the edge of the top surface <NUM> of the cabinets <NUM>. In some embodiments not covered by the claimed invention, a bottom <NUM> of the supply air duct <NUM> rests upon a basket (not shown) rather than directly on the top surface <NUM> of the cabinets <NUM>, wherein the basket is wider than the top surface <NUM> of the cabinets <NUM>.

<FIG> and <FIG> show an example cooling system <NUM> not covered by the claimed invention with a supply air duct <NUM> installed lengthwise (i.e., duct <NUM> is elongate in a direction parallel to the aisles) over the first cold aisle 20a, between the rows of computer 18a and 18b. In some examples, the supply air duct <NUM> has a pliable tubular wall <NUM> that renders the duct <NUM> inflatable, so the duct <NUM> has selectively an inflated state (<FIG>) and a deflated state (<FIG>). In the illustrated example, the supply air duct <NUM> has an air permeable lower section <NUM> for delivering cool supply air into the cold aisle 20a.

To prevent or reduce mixing of air between cold and hot aisles, the supply air duct <NUM> has an air impermeable upper section <NUM> and at least one wing <NUM> (e.g., a first wing 96a and a second wing 96b) extending from the supply air duct <NUM> toward an adjacent row of computers <NUM>. In the illustrated example, the first wing 96a extends laterally from the supply air duct <NUM> to a first top surface <NUM> of the first row of computers 18a (and/or its associated cabinet <NUM>), and the second wing 96b extends to a second top surface <NUM> of the second row of computers 18b (and/or its associated cabinet <NUM>). In some examples, the wings <NUM> extend lengthwise substantially the full length of the rows of computer <NUM> and are made of a pliable sheet of material held taut by having distal edges 98a, 98b fastened to the cabinets <NUM> of the computer rows <NUM>.

In some examples, the supply air duct <NUM> is installed at each cold aisle, so when the blower <NUM> is activated during normal operation, a first supply current of air <NUM> flows sequentially from the second aisle 22a (the first hot aisle), through the return register <NUM>, through the return air manifold <NUM>, through the filter <NUM>, through the cooling coil <NUM>, through the blower <NUM>, through the supply air manifold <NUM>, lengthwise through the first supply air duct <NUM>, and downward from the first supply air duct <NUM> into the first aisle 20a (the cold aisle). Further, in the illustrated example, a second supply current of air <NUM> flows sequentially from the third aisle 22b (the second hot aisle), through the return register <NUM>, through the return air manifold <NUM>, through the filter <NUM>, through the cooling coil <NUM>, through the blower <NUM>, through the supply air manifold <NUM>, lengthwise through the supply air duct <NUM>, and downward from the supply air duct <NUM> into the first aisle 20a (the cold aisle). The relatively cool air in the first aisle 20a supplies a first current of air 26a flowing through the first row of computers 18a to the second aisle 22a and further supplies a second current of air 26b flowing through the second row of computers 18b to the third aisle 22b.

In the event of a fire-related incident, the sensor <NUM> deactivates the blower <NUM> in some examples, which causes the supply air duct <NUM> to collapse to its deflated state, as shown in <FIG>. In the deflated state, the collapsed supply air duct <NUM> opens or unblocks the gap <NUM> to facilitate the dispersion of the fire extinguishing fluid <NUM>.

<FIG> and <FIG> show an example cooling system <NUM> not covered by the claimed invention that is similar to the system <NUM> of <FIG> and <FIG>. With the cooling system <NUM>, however, the supply air duct <NUM> is elevated to place the wings <NUM> above and spaced apart from the computer rows <NUM>. The vertical spacing further facilitates the dispersion of the fire extinguishing fluid <NUM> when needed while reducing the amount of warm air above the supply air duct <NUM> (e.g., above the wings <NUM>) from being entrained by the cooler air dispersed from the bottom of the supply air duct <NUM> (e.g., below the wings <NUM>) into the cold aisle. <FIG> shows the supply air duct <NUM> in its inflated state, and <FIG> shows the supply air duct <NUM> in its deflated state. In some examples, the wing <NUM> extends lengthwise substantially the full length of the rows of computer <NUM> and is made of a pliable sheet of material. The supply air duct <NUM> can be supported and the wings <NUM> can be held taut by any suitable means, such as by a taut cable, a track, struts, and/or combinations thereof.

<FIG> show an example cooling system <NUM> not covered by the claimed invention that provides a more concentrated discharge of cool supply air directly in the cold aisles <NUM>, thereby reducing (e.g., minimizing) the mixing of cool air with warmer air in the hot aisles <NUM>. In the illustrated example, a supply air duct <NUM> with a plurality of branch air ducts <NUM> are installed in each cold aisle <NUM>. <FIG> show at least one of the air ducts in an inflated state, and <FIG> shows at least one of them in a deflated state. The supply air duct <NUM> is elevated with an upper section <NUM> that is higher than the top surface <NUM> of the rows of computer <NUM> to provide head clearance for personnel in the area and to facilitate the dispersion of the fire extinguishing fluid <NUM> when needed.

To ensure that the branch air ducts <NUM> inject cool air well into the cold aisle <NUM>, a lowermost distal point <NUM> of the branch air duct <NUM> extends lower than the top surface <NUM> of the computer rows <NUM>, and the distal point <NUM> lies within a certain row length <NUM> of the row of computers <NUM>. That is, the distal point <NUM> is positioned within a length of the cold aisle <NUM> defined by ends of the row of computers <NUM>. he branch air ducts <NUM> include an air permeable tubular wall <NUM> made of a pliable material so that personnel working in the aisle can simply shove branch air ducts aside to gain unobstructed access to the computers <NUM>.

During normal operation, as shown in the illustrated examples of <FIG>, a main current of air <NUM> flows sequentially from the second aisle 22a (the first hot aisle), through the return air register <NUM>, through the return air manifold <NUM>, through the filter <NUM>, through the cooling coil <NUM>, through the blower <NUM>, through the supply air manifold <NUM>, into the supply air duct <NUM>, lengthwise through the supply air duct <NUM>, downward from the supply air duct <NUM> through the branch air ducts <NUM>, and outward from the branch air ducts <NUM> into the first aisle 20a (the cold aisle). The main current of air <NUM> in the first aisle 20a supplies a first current of air 26a through the first row of computers 18a and a second current of air 26b through the second row of computers 18b.

<FIG> show an example cooling system <NUM> not covered by the claimed invention that has an air duct <NUM> (e.g., air duct 130a and 130b) atop each row of computers <NUM>, wherein the air duct <NUM> has a longitudinal internal web <NUM> (e.g., first web 132a in the first air duct 130a and second web 132b in the second air duct 130b) that separates each air duct <NUM> into a supply chamber <NUM> (e.g., 134a and 134b) and a return chamber <NUM> (e.g., 136a and 136b). The air duct <NUM> has a pliable tubular wall <NUM> that is air permeable to pass air from the hot aisle 22a into the return chamber <NUM> and to release air from the supply chamber <NUM> to the cold aisle 20a. The blower <NUM> and the internal fans <NUM> drive the movement of air. To reduce the likelihood of the negative pressure in the return chamber <NUM> causing the air duct's pliable tubular wall to collapse, the air duct <NUM> includes some form of framework <NUM> that holds the air duct <NUM> in an expanded shape. Examples of the framework <NUM> include a plurality of rigid hoops, a longitudinal tensioning device, and combinations thereof.

In the illustrated example, the first row of computers 18a is between the first aisle 20a (the cold aisle) and the second aisle 22a (the first hot aisle), and the second row of computers 18b is between the first aisle 20a (the cold aisle) and the third aisle 22b (the second hot aisle). In this example, the cooling system <NUM> includes the first air duct 130a atop the first row of computers 18a, the second air duct 130b atop the second row of computers 18b, the first web 132a dividing the first air duct 130a into a first return chamber 136a and a first supply chamber 134a, the second web 132b dividing second the air duct 130b into a second return chamber 136b and a second supply chamber 134b, the blower system <NUM>, a first fan 25a for urging a first current of air 26a through the first row of computers 18a, and a second fan 25b for urging a second current of air 26b through the second row of computers 18b.

During normal operation of the example cooling system <NUM>, the blower system <NUM> draws air from the second aisle 22a (the first hot aisle) into the first return chamber 136a, the blower system <NUM> urges air from the first return chamber 136a into the first supply chamber 134a via a network of air ducts <NUM>, and the blower system <NUM> urges air from the first supply chamber 134a into the first aisle 20a (the cold aisle). Similarly, in the illustrated example, the blower system <NUM> draws air from the third aisle 22b (the second hot aisle) into the second return chamber 136b, the blower system <NUM> urges air from the second return chamber 136b into the second supply chamber 134b via the air ducts <NUM>, and the blower system <NUM> urges air from the second supply chamber 134b into the first aisle 20a (the cold aisle).

<FIG> show an embodiment covered by the claimed invention wherein an example adjustable or fixed-position nozzle <NUM> can be used to direct a main current of air <NUM> discharged from the nozzle. Further, the example nozzle <NUM> can also be used for inducing surrounding air currents <NUM> to flow in the same general direction as the main current of air <NUM>. In some examples, the surrounding air currents <NUM> are from the air released through the air permeable sidewall of a pliable air duct in the area surrounding the nozzle <NUM>. The nozzle <NUM> and the principle of inducing and directing surrounding air currents can be applied to any of the air duct examples shown in <FIG>.

<FIG> show embodiments covered by the claimed invention wherein example internal baffles <NUM>, <NUM> can be used to reduce negative effects that might otherwise result due to the dynamic air pressure of unrestricted air rushing axially through a supply air duct <NUM>, <NUM>. For instance, without the baffles <NUM>, <NUM>, air released through the air permeable sidewall of the ducts <NUM>, <NUM> might tend to follow the axial longitudinal direction of the air flowing lengthwise through the duct rather than discharging from the duct in an often more desirable radial direction (perpendicular to the duct's length). In the illustrated example, the internal baffles <NUM>, <NUM> interrupt the axial or longitudinal velocity of the air entering axial at the end <NUM> of the corresponding supply air ducts <NUM>, <NUM>. The internal baffles <NUM>, <NUM> may be applied to any of the air duct examples shown in <FIG>.

In the embodiment shown in <FIG>, the supply air duct <NUM> includes an air permeable pliable outer wall <NUM> and the internal baffle <NUM> that is horizontally elongate. In this embodiment, the internal baffle <NUM> is tubular (e.g., conical or cylindrical). In the illustrated embodiment, the internal baffle <NUM> separates an interior space of the supply air duct <NUM> into an inner upstream chamber <NUM> and an outer downstream chamber <NUM>. A supply current of air <NUM> flows sequentially from the second aisle 22a (a hot aisle) through a cooling system, lengthwise through the upstream chamber <NUM>, radially outward through the internal baffle <NUM>, through the downstream chamber <NUM>, radially outward through an air permeable pliable outer wall <NUM> of the supply air duct <NUM>, and downward from the supply air duct <NUM> into the first aisle 20a (a cold aisle). The air may then pass through the row of computers 18a and into second aisle 22a (the hot aisle). In some examples, the cooling system includes the return register <NUM>, the blower system <NUM>, and suitable ductwork to return the air back to the upstream chamber <NUM> at the axial end <NUM> of the supply air duct <NUM> to repeat the circuit.

In the embodiment shown in <FIG>, the supply air duct <NUM> includes an air permeable pliable outer wall <NUM> and the internal baffle <NUM> that is horizontally elongate. In this example, the internal baffle <NUM> is generally planar. In the illustrated examples, the internal baffle <NUM> separates an interior space of supply air duct <NUM> into an inner upstream chamber <NUM> and an outer downstream chamber <NUM>. A supply current of air <NUM> flows sequentially from the second aisle 22a (a hot aisle) through a cooling system, lengthwise through the upstream chamber <NUM>, radially outward through the internal baffle <NUM>, through the downstream chamber <NUM>, radially outward through an air permeable pliable outer wall <NUM> of the supply air duct <NUM>, and downward from the supply air duct <NUM> into the first aisle 20a (cold aisle). The air may then pass through the row of computers 18a and into second aisle 22a (the hot aisle). In some examples, the cooling system includes the return register <NUM>, the blower system <NUM>, and suitable ductwork to return the air back to the upstream chamber <NUM> at the axial end <NUM> to repeat the circuit.

Claim 1:
A cooling system (<NUM>) for a datacenter, wherein the datacenter includes a plurality of computers (<NUM>), arranged in a row within a building, the row of computers (<NUM>) disposed between a first aisle (<NUM>) and a second aisle (<NUM>), the row of computers (<NUM>) defining an air passageway (<NUM>, <NUM>) between the first aisle (<NUM>) and the second aisle (<NUM>), the row of computers (<NUM>) associated with a top surface (<NUM>) that is below and spaced apart from an overhead surface (<NUM>) of the building (<NUM>) to define a gap (<NUM>) between the top surface (<NUM>) associated with the row of computers (<NUM>) and the overhead surface (<NUM>) of the building (<NUM>), the cooling system (<NUM>) comprising:
a blower system (<NUM>); and
an inflatable air duct (<NUM>, <NUM>, <NUM>),
wherein the blower system (<NUM>) is configured to be connected in fluid communication with the inflatable air duct (<NUM>, <NUM>, <NUM>);
characterized in that
the blower system (<NUM>) is configured to cause a current of air to flow sequentially lengthwise through the inflatable air duct (<NUM>, <NUM>, <NUM>), downward from the inflatable air duct (<NUM>, <NUM>, <NUM>) into the first aisle (<NUM>), and through the row of computers (<NUM>) to the second aisle (<NUM>);
the inflatable air duct (<NUM>, <NUM>, <NUM>) is configured to be disposed within the gap (<NUM>), lengthwise along the row of computers (<NUM>) and rests upon the top surface (<NUM>) associated with the rows of computers (<NUM>) such that a weight of the inflatable air duct (<NUM>, <NUM>, <NUM>) is supported by the top surface; and
the inflatable air duct (<NUM>, <NUM>, <NUM>) selectively has an inflated state and a deflated state, the inflatable air duct (<NUM>, <NUM>, <NUM>) filling more of the gap (<NUM>) when the inflatable air duct (<NUM>, <NUM>, <NUM>) is in the inflated state than when the inflatable air duct (<NUM>, <NUM>, <NUM>) is in the deflated state.