For STEM Types

Part One

Why deflect?

All vent registers are deflectors.

Before German immigrant Franz Kurth invented diffusers for the Anemostat Corporation of America in the 1930s, climate control meant passive convention or at best a booster fan for “octopus” furnace hot air, rising out of floor and inner wall cast iron grates. This was practical because hot air rises, and cold fell down outer wall return grates. Thick asbestos-insulated supply ducts led to heavy ornate iron wall registers that also radiated heat into the room[1]. Large building relied on steam-fed radiators more than convection[2]. Cooling was achieved by awnings on all the sun-facing windows, high ceilings, opening the windows and doors to create drafts down hallways, ice in drinks stored in ice boxes, and later, electric fans[3].

Note the louvered shutters on the back side of nearly 2’ tall cast-iron wall grate for natural aspiration of furnace air up 14” wide asbestos-insulated smooth steel duct pipes. The connection profile to the duct is massive, because without forced (electrically fanned) velocity, they relied on volume to deliver. This notoriously reverberated sound up and down the ducts, so a conversation downstairs could be heard clearly 2 floors above by sitting close to the grate.

Air conditioning, which removes humidity and heat during the summer, was first introduced to affordable houses in Dallas in the 1930s. The 200 home Stevens Park Estates, many of which were designed by quirky Charles Dilbeck, saw the Pat Boyd Company adding automatic central air conditioning in 1932. Their description was, “the air is washed and dried and delivered to the consumer in a clean, sweet, health-giving condition, all smoke, dust, and pollen having been removed and the summer temperature kept about 15 degrees below the outside atmosphere.”

To move the cold air around the room, diffusers achieve what is called “mixing ventilation.” This evens out a room’s temperature. They have angled vanes, usually of painted steel, that deflect the duct pipe air. It may help to think of them as ceiling fans in reverse. A ceiling fan has angled blades, and they move through the air to fan it out. A diffuser has angled blades, but the air moves over them to fan out.

The original Anemostat 1930s diffusers dropped down in the center of a concentric circumference, so that one blade or vane could turn air nearly 90 degrees without running into the backside of another. They also had built-in dampers, in case conditions changed in a room and the occupant wanted to adjust the air flow (no longer is it recommended to shut-off air at an outlet, but via special electrically controlled in-line duct dampers). At first they were made for train cars, but quickly were adopted for building spaces.

Here is a 1950s steel diffuser from the inventor’s home, which has drop-center turning vanes in concentric circles, and a chain to operate a spring-loaded damper.

Note the nearly 90 degree scooping curve profile, and how each ring steps up above its neighbor.

The goal is to move air around the room, making the space we occupy comfortable. If it was always nice outside, we’d do everything there. But even when we work outside, as the expression “shade tree mechanic” implies, we try to find as much comfort as we can. This is because it’s hard to be productive if our bodies are suffering: discomfort is distraction. Some associate comfort with laziness and torpor, but fact, it is of productivity.

In colder climates, central heat and air systems are oftentimes designed for the heat. As it was before the 1930s, their vent grates are on the floor, and made to be stepped on. There is no deflection. They may have no air conditioning at all, or back-up window units. Their roof pitches are steep, to shed snow off.

In hotter climates, the HVAC is mostly AC. Instead of an oil-burning furnace in a basement, convention is to have a gas burning furnace unit integrated with the air conditioning evaporator (where the cold air comes from, and humidity is condensed and removed by pipes). The vent registers are on ceilings or walls, and do deflect air. Their roof pitches are shallow, to save cost, better handle high storm winds, and allow trees to overhang and shade the roof.

In low pitch roofs, there’s no space to run ventilation to the edges of rooms, because the roofs only have inches of clearance. So hot climate homes place their vent registers nearer the center, where the attic height is greatest. The most common registers for these homes are two and three-way stamped steel, designed to blow the air away from the inner walls and out towards the extremities, including windows. But there is a major trade-off issue.

Mixing or Throwing?

The common flat registers angle their vane either near 45 degree angles, or closer to 20 degrees. A 45^o angle will certainly throw air out for a wider mix, but causes more backpressure, turbulence, and reduces duct air velocity to 70%. A 20^o angle won’t deflect air far, but you’ll get 90% of the velocity, so there is more air and it is moving faster, until it runs into a floor or wall.

In a commercial setting, or a mansion, there are complex ways the industry has tried to address this. High Induction Diffusers, often called very high (VHI for short), can include jet nozzles, and linear slot diffusers. Because air is very loud when it is constricted then expanded, these VHIs are supplied with slower air than conventionally induced diffusers. They are also more numerous – either many little constricting nozzles, or the air is released over long linear slots.

The idea is they’ll provide higher mixing, like the 45^o angle vanes of a cheap residential register. They will send the air further out into the room. But because VHIs have reduced velocity – to stay quiet – their throw distance is short[4].

To make up for this, chilled beams will send colder air (around 40^o F instead of conventional 55^o F). This can work, but adds cost and condensate. Air has to be extra dry at colder temperatures, otherwise cold water will spittle off the vent[5].

One great exception is a swirl diffuser. Rather than relying on constricting air to increase its velocity, they shape a hurricane on your ceiling for cooling, and a tornado column for heating, if variable. Most are fixed, and look something like the grill of a Vornado fan, or a circle of angled vanes. Like Ventner, they rely on the preferential attachment of flows to surfaces, called the Coanda effect. The most elaborate ones have servos and electronics to control inner individual blades, which allows some preferential directional control. Air swirls out in a continuous spiral, spinning and holding close to the ceiling, mixing in air from below until either hitting a wall and dropping, or falling gently and at a more moderated and mixed temperature than the initial forced air from the plenum.

Ventner achieves what the most expensive servo-controlled swirl diffusers do: direct your air, with good throw, and good mixing. While Ventner saves customers hundreds of dollars, unfortunately it is lumped in with cheap plastic deflectors designed in the 60s, that do not direct your air, and mediocre improvements in mixing at the expense of greatly reduced throw. This keeps our profits low, but that is your delta-of-benefit to enjoy.

Ventner’s Approach

Ventner is not trying to emulate a high inducing system, but it does have a similar effect. The improved circumferential deflection of the brim is similar to the swirl diffuser’s reaching and mixing effect. The scoop’s surface attached stream extends the flow-inducing throw of a register. And by extending flow to otherwise stagnant parts of a room, it induces mixing and reduces stratification and humidity build-up. This is to help your system in the engineer’s standard way: the ASHRAE Air Diffusion Performance Index (ADPI) metric, which is “a single number rating index for a diffuser with specified supply air volume, supply air temperature, and space cooling load. It is based on the air speed and effective draft temperature of the occupied zone.”

Ventner was tested and engineered to not create back-pressure, as constricting high induction diffusers do. I measured the inches of water pressure in a test ductwork setup, and set the depth of the scoop - or the height of the rim if you prefer – to be sufficient for normal speed systems, at 2 and 3/8” inches for the common range of 80 to 150 cubic feet a minute flowing from your register, that is, with at or under 0.02 inches of water additional backpressure.

This was the first Ventner prototype (in orange) that yielded ultra-low backpressure – earlier ones had been shallower, and less efficient at all tested speeds (mostly lower than shown). Even if your system blows hard, Ventner does not compromise velocity and throw, and it doesn’t fall off.

Coanda Effect

Ventner achieves this added throw without constriction by use of the Coanda effect.

Here are the anemometer measured flows from the Ventner. Note that it works similarly at lower flows.

If you stand facing your vent on the left, and the far wall on your right, this is how the scooped airflow is moving:

If this is a ceiling vent installation, this chart is showing how the air starts 2.5” below the ceiling – fresh out of the front chute of Ventner’s scoop. Then the Coanda effect pulls the air up higher, to its happy place 1” below the ceiling, until it slows down beyond 55 inches (about 5’) and begins to drift down. In practice, I’ve found it to still flow along the surface 12’ away (see video); this test’s table ended at 80” and may have created turbulence that affected measurements upstream, i.e. pushed air up and over the end-table turbulent zone.

Ventner’s scooped beam of air also has a strong inductive effect, where the beam pulls in air to flow with it along the surface. See the data:

0” is the centerline, where the scooped air from Ventner comes out. It takes 5’ of run, but the columnated air turns into a 2’ wide sheet because it has pulled in air from 1’ out on both sides. Note the grey and light-blue lines are first to be pulled in, only needing 2 feet, because they’re closest, at 4” either side of the centerline.

Historical note: early tests included both a single loop and scoop, and concentric double scoops: imagine Ventner with a second peripheral rim. This is the more effective and economical ‘single loop’ U-shaped scoop with brim.

The brim is a secondary deflection surface. So if the register deflects air 20^o to 45^o, the brim will give space and chance to deflect further, towards 70-90^o.

Shown here is the deflection angle of a 45^o three-way steel stamped register, as visualized with dry ice fog. Depending on where it’s placed on a vent, it generally sends air out and down at a 20 degree angle, or from the air coming out of the duct’s perspective, it’s turned from headed straight down, to 70^o over into the room.

The brim is important because without it, most vents will draft down, potentially causing discomfort. And it runs in a full circumference – 360^o – so it can send all the unscooped air out further yet locally. If for example ventner is placed on a 3-way register under the center section, the brim will help both side vanes move their air further out. If this 3-way is on a wall over your bed, you will enjoy not having the AC or heat drafting down over you all year – the ventner’s brim will be billowing those side vanes further around the bed, while the central scoop sends the air across the room to fully ventilate and mix the air.

The brim is helping the vent do its job. It is not changing the vent’s purpose.
The scoop is repurposing the vent, turning it into a high induction diffuser, most similar to a directed swirl diffuser.

Ventner is primarily designed for flat steel vent registers, but it works well with concentric circular registers. For aluminum, plastic, bronze and other non-iron materials, we have the low cost fixed location Ventner with plastic hooks.

Mean Radiant Temperature (MRT)

What is “Thermal Glare?” Like high-beams on the road at night, a room with intense banks of fluorescent ceiling lights, or a screen too bright at night: glare is our perception of intense electromagnetic radiation.
It is distracting and uncomfortable.

Thermal glare, like light glare, is literally also electromagnetic radiation.
But it’s further out the spectrum, in the “infrared” bandwidth.

Hot/cold surfaces are the flares that cause the glare.
(Yes we made this term up, for normies)

Homes are where we re-charge.
To help us relax and restore us in our sanctuaries, we make the room flow.
Ventner is your paintbrush, air is the paint.

The apotheosis of Ventner is MRT amelioration with a variable speed air handler. In other words, steady treatment of thermal glare.

Left to Right, Starting Top Left: Off, with window temp of 87.6^o F.
Within 15 minutes, cool air has reached 14’ across room and chilled window spot by 6^o F.
Within 30 minutes, window spot chilled by 10.6^o F. And 45 mins, 16.2^o F.
If you read on, you’ll know what this means.






ASHRAE, the American Society of Heating, Refrigerating and Air-Conditioning Engineers, has Standard 55: Thermal Environmental Conditions for Human Occupancy[6].

Note ASHRAE have no association with Ventner, any more than Dan Fahrenheit does.


The Core Metric: Mean Radiant Temperature

While standard thermostats only read the operative air temperature, ASHRAE Standard 55 dictates that true thermal comfort relies heavily on MRT—the uniform temperature of an imaginary enclosure in which the radiant heat transfer from the human body is equal to the radiant heat transfer in the actual non-uniform enclosure.

If your walls, windows, or ceilings deviate too far from the room's air temperature, the human body immediately notices the localized heat gain or loss.

Radiant Temperature Asymmetry Limits

To prevent that "one side frozen, one side roasting" effect, Standard 55 sets strict maximum allowable differentials for radiant asymmetry. These limits are based on a threshold where no more than 5% of occupants would find the asymmetry uncomfortable[7].

The allowable ranges depend entirely on which surfaces are uneven:

Not all thermal glare (surfaces exceeding max allowable asymmetry) sources are equally bothersome. Moving on.

The Flōrum Solution.

What part of the room will you be using the most?
Let’s call that bed, table, sofa, duchesse-brisée-chaise-longue or clawed-up easy chair the “most commonly occupied area” (MCOA).

Radiant effects rise or fall exponentially, meaning if there’s a hot spot far from a MCOA, it’s not going to be strongly felt. But if it’s large and proximate to a MCOA, it deserves attention.

And note also that drywall/sheetrock stores thermal energy well – heat or AC can be off for an hour but ceiling / wall sheetrock will steadily provide comfortable radiant temperatures. Thus even absent a window or corner, there might be a stretch of ceiling, floor, or wall that can be turned into a radiant cooling (cavern) or heating (warmth of sun) effect surface.

[8]

If you’re in an older city and have exposed brick walls, they’re even better, capable of storing heat or coolth for hours.

So we use ventner to create radiant heating and cooling, without needing wires or plumbing.

 
A 50s house with circular vent. Note that, despite proximity, this vent is not appreciably reaching into the hot corner, nor into the window sill recessed area. The room below is in the comfort zone, but surfaces adjacent this kitchen table MCOA are outside the MRT range.
A ventner projecting to the wall above the window could bring these MRTs into range.

A house in Austin, TX in August. 
A common rectangular register, either 20^o or 45^o pitch vanes (top, right). Lower (purple) areas are receiving good mixing, but sliding glass doors and ceiling are pushing 90^o F (ceiling corners exceed 9^o F max MRT). At bottom left is kitchen table MCOA.
Aim ventner over right sliding door.

An example of a front door without an awning. It’s August and south-facing, radiating up to 109^o F into the living room. However, this is not a MCOA. Most likely, a couch adjacent a window elsewhere in this living room is the MCOA. At Flōrum, we’d recommend an awning outside here, and sealing strips around the door[9].
Don’t waste energy, do not use a ventner on such a door.

There is a large 3-pane living room window at left (same room as seen below). The loveseat at back, and swivel chair are MCOAs and within range of this window. The house’s roof has a low pitch, thus vent outlet is 14’ across the room from the window (can’t put ducting under 1’ attic space). Ventner is directed at far window; note close 4^o F range between 2 and 3 bullet radiant temps.

Same living room and moment in time as above; note how cool window gets within main stream of ventner, even at 14’ range (due to Coanda effect induction): about 64^o F ceiling and 67^o F window.

Compare above (taken 1:33 PM) with this, taken during the lunch hour.
Window dropped from 80^o F to 67^o F with ventilation projected by ventner. Note it’s not the heat of the day, AC had been on earlier that morning, and the surface area of this heating window is about 6’ by 5’ – it can be felt across the room.
 

And we saved the best for last.

This was taken minutes into the first real-world test of a ventner prototype.
She said “I turn my fan on because at first I’m hot, but later on I wake up cold and pull up the blankets. But this thing (ventner) runs with the AC so it keeps me cool at first but doesn’t bother me later. It’s just enough.” Cat is a rescue, named “Brigitte.”

Note many also report fans dry them out, causing dry sinuses, and muscle cramps upon waking.

Direct ventner out over your bed for a better night’s sleep.