Letting a Fan Breathe Through Its Sides A Ring Shaped Bypass Intake That Adds Thrust Without Adding Power

This application covers the shape of a ducted fan housing, specifically a continuous ring shaped gap cut around the outside of the shroud partway down its length. Air pulled through the fan by the blade creates a low pressure zone inside the housing, and that low pressure drags a second stream of ambient air in through the ring shaped gap and down a separate channel, where it joins the main flow and adds to it. It was filed by Airius IP Holdings, LLC, the intellectual property arm of the Colorado company that makes destratification fans for warehouses, gyms and other tall buildings, and names Raymond B. Avedon as the sole inventor. The application is a divisional of Australian application 2020257205.

The Problem

Start with the word that explains why this class of fan exists at all. Warm air is less dense than cool air, so in any tall enclosed space it floats to the top and stays there. In a warehouse with a ten metre ceiling in winter, the air at head height can be uncomfortably cold while the air at the roof line is many degrees warmer, and the heating system keeps running because the thermostat sits down at the bottom. That layering is thermal stratification, and stirring it back into a single uniform temperature is thermal destratification. A destratification fan is mounted at or near the ceiling and throws a narrow column of air straight down to the floor, where it spreads and rolls back up, turning over the whole volume of the room. Doing that instead of heating the roof space is where the energy savings come from.

The specification states the problem in one flat sentence in its background. Air moving devices “require power to rotate a blade to generate a thrust with the moving air,” and existing solutions “have high power requirements for a given thrust and/or generate a low thrust for a give power input.” That is the entire stated prior art discussion. The document does not cite competing fan designs, does not name a competitor and does not quantify how bad existing fans are. It simply asserts that more thrust per watt would be desirable and then describes a housing shape intended to deliver it.

That sparseness is worth flagging, because it means the reader has to judge the invention on the mechanism rather than on a comparison. The specification does offer one number for the claimed benefit, and it appears in paragraph 67: the relationships between the bypass dimensions “may allow for 5% or more, 7% or more, 10% or more, 15% or more, or 20% or more thrust as compared to an air moving device that did not have the bypass intake features described herein.” There is no test data behind that figure. No worked example, no measured airflow, no power draw table. It is an assertion in the body of the specification, and the article should not dress it up as anything more.

What This Invention Does

Claim 1 is an apparatus claim, and it is entirely about geometry. It recites an air moving device with a housing extending axially, an upper portion and a lower portion, and an impeller assembly supported by the housing that rotates a blade so that air enters through the upper portion and leaves through the lower portion.

The upper portion has a primary inlet and two concentric walls: an upper inner sidewall running down from the inlet to a lower inner edge, and an upper outer sidewall sitting radially outside it and running down to a lower outer edge. The inner wall defines the upper region of the primary flow path, and that region has a first width. The lower portion has its own outer sidewall running from an upper edge down to the primary outlet, and it defines the lower region of the primary flow path, which has a second width that is greater than the first width. So the duct narrows at the top and then steps out wider at the bottom.

The last element of the claim is the invention. A secondary flow path runs from an annular secondary inlet on the outside of the housing to an annular inner outlet that opens into the primary flow path. The annular secondary inlet is the gap between the lower outer edge of the upper outer sidewall and the upper edge of the lower outer sidewall, in other words a continuous slot all the way around the housing where the two shells overlap but do not meet. The annular inner outlet sits between the lower outer sidewall and the lower inner edge of the upper inner sidewall, which is to say the bypass air is delivered into the main stream at exactly the point where the duct steps out to its wider diameter.

The mechanism is an ejector. The specification explains it in paragraph 60: because the second width is greater than the first, “the expanded cross-sectional area due to the increased width W2 thus creates a low pressure zone that pulls in air through the secondary flow path.” Paragraph 69 sets out what that buys you. The secondary air arrives with a velocity component pointing in the same direction as the primary flow, so it is additive, and “the mixing of air from the primary and secondary flow paths creates more thrust for a given power input.” The blade does not work harder. It just gets more air to work with, by dragging the extra air in through the slot rather than through the blade.

The dimensions are all relative rather than absolute, which is normal for an apparatus claim but does make the document harder to read. The upper width W1 is stated as 4 to 12 inches, the lower width W2 as 5 to 13 inches, with W2 typically about 1 inch greater than W1, or 3 to 20 per cent greater. The height of the annular slot, D2, is given as 1.25 inches in the worked geometry, with a listed range from 0.25 inches to 3 inches. Claim 20 requires that D2 be at least 70 per cent of D5, the radial width of the bypass channel, and claim 21 pins it at 80 per cent. Claims 18 and 19 govern how far down the housing the slot sits: the distance from the primary inlet to the top of the slot must be at least 80 per cent of the slot height, and in claim 19 greater than it. Claim 22 adds a constraint tying the slot position and height to the length of the inner wall, D1 plus D2 being less than 1.1 times D3, so that the bypass air is delivered at or just above the bottom lip of the nozzle rather than below it.

Claim 9 is a much broader second independent claim covering the same idea stripped of the two shell construction: an annular housing, an impeller, and a secondary flow path from an annular secondary inlet to an inner outlet located adjacent the primary flow path. Claim 30 is a third, framed around a cowling and a lower sidewall. Anyone assessing the scope of this filing should read claim 9 first, because it is the one with the fewest limitations.

Key Features

• A continuous slot instead of a sealed shroud. The annular secondary inlet is the gap left where the upper shell overlaps the lower shell without touching it, so ambient air can enter the housing all the way around its circumference rather than only at the top.
• A step change in duct diameter as the pump. The lower region of the primary flow path is wider than the upper region, and the specification relies on that expansion to create the low pressure region at the inner outlet that pulls the bypass air in. No extra moving part is involved.
• Delivery point tied to the nozzle lip. Claim 22 requires that the sum of the distances D1 and D2 be less than 1.1 times D3, which keeps the mixing region at or near the lower end of the bypass channel rather than letting the secondary inlet drop below the inner wall.
• Longitudinal ribs and stator vanes as one part. Dependent claims 5 to 7 add ribs bridging the two upper walls along the bypass channel and stator vanes in the primary path. Paragraph 75 notes the rib and the vane may be one continuous part running to the bottom of the housing, which straightens the swirl out of the flow and produces the columnar discharge these fans depend on.
• A minimum distance between inlet and blade. Claim 25 requires the uppermost part of the blade to sit at least 2 inches below the primary inlet, giving the incoming air a settling length before it reaches the impeller.
• Housing height as the throw control. Paragraph 70 treats the overall height H as the design handle for how far the column of air carries. Increase H for a longer throw, decrease it for a shorter and more widely dispersed cone. Claims 27 to 29 tie H to the inlet width W1 at 75 per cent, 100 per cent and 125 per cent thresholds.

Who Is Behind It

Airius IP Holdings, LLC is the patent holding entity for Airius Fans, a Colorado business whose product is exactly the thing this claim describes: a compact ducted fan hung from a ceiling that pushes a column of air to the floor. The company’s own history page traces its origins to Avedon Engineering, founded in 1963 as a custom injection moulding business in the western United States, and records that Ray Avedon began developing the first Airius fan, the Air Pear, in the early 2000s as moulding work moved offshore. Airius LLC was founded in 2004. The sole named inventor on this application, Raymond B. Avedon, is that founder.

Unusually for a patent article, you can check the claim against the seller’s own marketing. Airius lists “Side Intake Bypass” among its patented technologies and describes it in plain terms as a secondary inlet that entrains additional air into the primary flow path to maximise air volume at the discharge. The company attributes that feature to US patent 11,598,539, which shares this specification’s title, abstract and assignee. So this is not a speculative filing. It is Australian protection for a feature already shipping in the product line. The same page credits the earlier multi vane stator and Venturi nozzle work to US 7,381,129, which is one of roughly a dozen “Columnar Air Moving Devices, Systems and Methods” patents incorporated by reference in the body of this specification. The Australian market is served by Airius Air Solutions, which sells the same Air Pear, Q and Retail series.

A caution for anyone searching: the domain airius.com does not belong to this company. It resolves to an unrelated cybersecurity and compliance consultancy also trading as Airius, LLC. The fan business is at airiusfans.com.

On priority, this specification is explicit where many are silent. Paragraph 1 claims the benefit of two United States provisional applications, 62/835,314 filed 17 April 2019 and 62/876,514 filed 19 July 2019, both titled “Air Moving Device With Bypass Intake.” The parent Australian application 2020257205 corresponds to international application PCT/US2020/028354, published as WO 2020/214729, whose header appears on every page of this document. The priority country is therefore the United States.

Why It Matters

Destratification fans are a small category with a straightforward economic argument behind them. Heating a tall building means heating air that immediately rises out of reach, and any device that turns the room over and puts the warm air back where people are standing pays for itself in reduced heating load. That argument depends on the fan being cheap to run. A destratification fan in a distribution centre may run continuously through the colder months, so its own electricity consumption is subtracted directly from the saving it creates. A claimed 5 to 20 per cent gain in thrust for the same power input is not a dramatic figure, but on a continuously running load across a fleet of fans it is the kind of number that decides a specification.

The engineering interest is that the gain is claimed to come from a hole. There is no second motor, no variable geometry, no control system. The housing is a two piece injection moulding, and the invention is the decision to leave a gap where the two pieces meet and to size that gap against the duct dimensions. For a company founded on custom injection moulding, that is a natural place to look for an advantage, and it explains why so much of the claim set is taken up with ratios between lengths that are really mould tool parameters. The same logic drives commercial ducted fan and ejector design more generally, where entrained secondary flow is a standard way to raise mass flow without raising shaft power.

Two honest caveats. First, the specification asserts that the expanded lower duct creates a low pressure zone, and although a fast jet entraining slower surrounding air is a well established effect, an expanding duct considered on its own normally acts as a diffuser and recovers pressure. The document does not present computational or measured evidence for the pressure field it describes, so the reader is taking the mechanism on the applicant’s word plus the fact that the feature is in a shipping product. Second, the drafting in this specification is loose in places. Paragraph 73 says “the distance D1 is greater than the distance D2,” then that D2 may equal D1, then that D2 may be greater than D1, all within five lines, and elsewhere the text contains plain typographical errors including “a give power input,” “amitted form the device” and a sentence beginning “In some embodiments, may be 0.25 inches” with the subject missing. None of that affects the claims, which are clean, but it does mean the body text should be read for intent rather than as a precise engineering document.

Related Concepts

• Convection – the buoyancy driven rise of warm air that produces the temperature layering these fans exist to break up.
• Entrainment – the general engineering term for one moving fluid stream dragging another along with it, which is what the bypass intake relies on.
• Venturi effect – the pressure drop in a constricted or accelerated flow that Airius credits in its nozzle design and that underlies the ejector principle here.
• Axial fan design – the fan family the impeller assembly belongs to, where thrust is produced parallel to the shaft.
• Jet – the columnar stream of air the device discharges toward the floor, whose reach the specification calls the throw.

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AU 2026202175 was published in the Australian Official Journal of Patents on 9 April 2026 and is open for public inspection. Patent applications represent inventions that are sought to be protected and do not necessarily reflect commercially available products.