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Industrial Fans and Application Product Lines

Summary

This chapter finishes the product-line survey with the heavier-duty and application-specific fans: plug fans, vaneaxial fans, pressure blowers, radial bladed and radial tip fans, duct fans, filtered supply fans, utility sets, air kits, paint booth exhaust fans, and dust collection fans. It closes with how laboratory exhaust fans use bypass flow and plume dilution to discharge contaminated air safely. After completing it, readers know the full range of fan families and product lines the rest of the book refers to.

Concepts Covered

This chapter covers the following 16 concepts from the learning graph:

Concept Concept Impact Score
Roof Mounted Panel Fan 1
Inline Lab Exhaust Fan 1
Plug Fan 72
Vaneaxial Fan 22
Pressure Blower 5
Radial Bladed Fan 14
Radial Tip Fan 22
Duct Fan 22
Filtered Supply Fan 1
Utility Set 22
Air Kit 2
Plume Dilution 4
Paint Booth Exhaust Fan 3
Dust Collection Fan 3
Bypass Flow 2
Lab Exhaust Total Flow 1

Prerequisites

This chapter builds on concepts from:

From the Plant Floor to the Lab Roof

Breeze waving welcome The calls that test a new engineer or rep rarely ask for "a fan." They ask for something that can live in the wall of a hot curing oven, chew through paper trim, or throw lab fumes high above a roof. By the end of this chapter you will know which product line each of those calls is really asking for, and why. Let's follow the airflow.

Chapters 4 and 5 sorted fans into families and walked through the roof, wall and building-ventilation products most people picture when they hear the word "fan." This chapter finishes the survey with the lines that show up on industrial orders and in application-specific specifications. Some are defined by how they are built, such as a plug fan that mounts through a plenum wall or a vaneaxial fan with a vane section behind its impeller. Others are defined by the job they do: dust collection, paint booth exhaust and laboratory fume exhaust. A customer may describe either the hardware ("we need a radial blade") or the problem ("our cyclone keeps plugging the fan"), and you should land on the same product.

Plug Fans: The Impeller Goes In, the Drive Stays Out

Chapter 5 described the plenum fan, an unhoused centrifugal fan that sits inside an air-filled box (the plenum) and pressurizes it, with the plenum walls doing the job a scroll housing would otherwise do. A plug fan is the industrial cousin of that idea. FanPedia describes it as an unhoused centrifugal fan "plugged" into the wall of a plenum: a mounting panel fastens to the outside of the plenum wall, the impeller sits inside, and air moves through an inlet funnel into the impeller and out into the pressurized space (FanPedia p. 5). The current Twin City Fan catalog page adds the feature that sells the design: the gusseted mounting panel separates the motor and drive components from the process air, and the fan can be installed and removed as a unit.

That separation is the key difference from a plenum fan, whose motor, shaft and bearings live in the air the impeller moves. FanPedia names the typical industrial uses directly: high-temperature ovens and OEM paint booths, where the air being recirculated is either too hot or too dirty to wash over a motor (FanPedia p. 5). The current catalog lists high-temperature construction to 1000 °F, spark resistant construction, ATEX construction, special materials and a pedestal design for floor mounting as options.

One Wall, Two Environments

Breeze thinking Think of the mounting panel as a property line: process air on one side, motor and bearings on the other. Almost every plug fan decision, from arrangement to temperature option, comes back to protecting that line.

Plug fans come in several arrangements, the standard ways the drive, bearings and impeller are put together (Chapter 11 covers arrangements in full). FanPedia's technical descriptions define seven for plug fans (pp. 170–172), and they differ on two questions: is the fan direct drive or belt driven, and does the customer's wall carry the whole fan, or does the fan stand on the foundation ("grade")? The "P" suffix marks the pedestal, grade-mounted version.

What \"P\" and \"PL\" mean in a name

Twin City Fan engineering explains: "Typically any arrangement with a 'P' or 'PL' signifies a plug fan type of arrangement. The 'P' is generally used in the arrangement nomenclature and the 'PL' is generally used in the fan model nomenclature. When used in the fan model nomenclature, it means the customer wants that type of wheel in a plug fan style arrangement (i.e. 'RBAPL'. 'BCPL' = 'BC Style Wheel', 'BFPL' = 'BF Style wheel', etc)." So BCPL is a BC style wheel built as a plug fan, and BFPL is a BF style wheel built as a plug fan. The two sources fit together: in FanPedia's arrangement codes the P marks the grade-mounted plug variants (1P, 4P, 8P, 9P), while its plug section also calls the plain 4, 8 and 9 "(Plug)", so a plug fan does not always carry a P in its arrangement code. Read a P in an arrangement code as a sign of a plug-type arrangement, and read PL at the end of a model name as "this wheel style, as a plug fan."

  • Arrangement 4: direct drive, impeller mounted on the motor shaft; compact and low maintenance because there is no fan shaft, bearings or belts. High airstream temperatures may limit its use.
  • Arrangement 8: direct drive with the motor shaft coupled to a separate fan shaft; the whole assembly hangs on the wall. It is the least common plug arrangement because of its length.
  • Arrangement 9: the most common plug arrangement, fully supported by the customer's wall, belt driven on an adjustable motor base.
  • Arrangement 1P: belt driven and mounted to grade, with the motor mounted separate from the fan, on its own base. FanPedia and the current catalogs list it only in this grade-mounted form, and use it typically on larger fans and larger-HP motors.
  • Arrangements 4P, 8P and 9P: the same three, mounted to grade. On 9P the motor rides on a pedestal with the fan. FanPedia gives two reasons to choose them: the customer's wall may not be sufficient by itself, and foundation mounting helps meet lower vibration requirements. The mounting panel is optional on the P versions.

Availability varies by product line

FanPedia describes all seven arrangements, but a given model is not built in every one. The current catalogs (April 2024) list Arrangements 1P, 9 and 9P (belt driven) and 4, 4P and 8P (direct drive) for the BEPL (Catalog 355) and BFPL (Catalog 360), and 1P, 9, 9P, 4 and 8P for the BCPL and AFPL (Catalog 350). None of the four lists a plain Arrangement 8 (whether it is offered is still an open question for Twin City Fan), and the BCPL and AFPL catalog has no 4P. Check the catalog for the line you are selecting, or confirm with Twin City Fan.

Worked example: choosing a plug fan arrangement. An OEM builds curing ovens and wants a recirculating fan mounted through the oven's side wall. The oven runs hot, the OEM wants belt drive so the fan speed can be trimmed after startup, and its engineer says the oven wall panel was never designed to carry a large motor. Work through the three questions in order:

  1. Direct or belt? The customer asked for belt drive, so the belt-driven arrangements (9, 9P and 1P) remain.
  2. Wall or grade? The wall cannot carry the full weight, so a grade-mounted version wins. With the motor riding on a pedestal beside the fan, that is Arrangement 9P (1P is the same idea with the motor on its own base).
  3. Temperature? A hot airstream would have ruled out Arrangement 4 (impeller on the motor shaft); 9P keeps the motor outside the oven, and high-temperature construction is still ordered as a separate option.

The answer is an Arrangement 9P plug fan with high-temperature construction. Twin City Fan's current plug fan lines include backward curved high-efficiency models (BEPL, BFPL) and airfoil and backward inclined models for non-HVAC duty (AFPL, BCPL); check the catalog for the sizes and limits of each.

The activity below lets you practice the same three questions on nine more jobs.

Diagram: Plug Fan Arrangement Picker

Run Plug Fan Arrangement Picker Fullscreen

Plug Fan Arrangement Picker

Type: microsim sim-id: ch06-plug-fan-arrangement-picker
Library: p5.js
Status: Specified
Bloom Level: Apply
Bloom Verb: apply
Learning Objective: The learner will apply the drive, support and temperature rules for plug fan arrangements to choose the correct arrangement (1P, 4, 4P, 8, 8P, 9 or 9P) for a described job, getting at least 7 of 9 scenarios right on the first attempt.

Prerequisites: plug fan, plenum fan, mounting panel, arrangement, direct drive, belt drive, grade (all defined in the section "Plug Fans: The Impeller Goes In, the Drive Stays Out").

Evidence of Mastery: For each of 9 scenarios the learner commits one arrangement from the seven choices. A choice is correct when it matches the "Correct" column in Content. Mastery is 7 of 9 correct on the first attempt (78%, scaled from the earlier 6 of 8). Opening the arrangement reference cards is exploration, not evidence.

Misconceptions: (1) Arrangement 4 is always the best choice because it has the fewest parts, even with a hot airstream. (2) The "P" versions are a different fan rather than the same arrangement mounted to grade. (3) Arrangement 8 is common; FanPedia calls it the least common plug arrangement. (4) Every grade-mounted belt-driven fan is 9P; 1P is the belt-driven grade version whose motor sits on its own base, separate from the fan.

Instructional Rationale: Choosing an arrangement is an Apply-level task: the learner must use three decision rules on a new job description. Committing a choice before seeing the answer produces evidence; the reason shown afterward ties each answer back to the rule that decided it.

Content:

Reference cards (available at all times):

Arrangement Drive Carried by Card text
1P Belt, motor on its own base Grade Belt driven; fan mounted to grade with the motor mounted separate from the fan. Larger fans and larger-HP motors. Mounting panel optional.
4 Direct, impeller on motor shaft Customer's wall Compact; no fan shaft, bearings or belts. High airstream temperatures may limit use.
4P Direct, impeller on motor shaft Grade Arrangement 4 mounted to grade, for walls that cannot carry the fan or lower vibration requirements. Mounting panel optional.
8 Direct, motor coupled to fan shaft Customer's wall Least common plug arrangement because of assembly length.
8P Direct, motor coupled to fan shaft Grade Arrangement 8 mounted to grade; larger fans and larger-HP motors. Mounting panel optional.
9 Belt Customer's wall Most common plug arrangement.
9P Belt Grade Arrangement 9 mounted to grade; larger fans and larger-HP motors. Mounting panel optional.

Scenarios, in fixed order:

# Scenario shown to the learner Correct Why (shown as feedback)
1 Recirculating fan for a warm (not hot) process enclosure. Customer wants no belts or fan bearings to maintain. Wall is stiff enough to carry the fan. 4 Direct drive with the impeller on the motor shaft removes belts and fan bearings, and the wall can carry it.
2 Same job as #1, but the customer's engineer says the enclosure wall cannot carry the fan by itself. 4P Same direct-drive choice, mounted to grade because the wall is not sufficient.
3 General belt-driven recirculation fan; the wall is adequate and nothing unusual is required. 9 Belt drive on a wall that can carry it is the most common plug arrangement.
4 Large belt-driven fan with a large-HP motor on the fan's own pedestal; the wall cannot carry it. 9P Belt drive plus a wall that is not sufficient points to the grade-mounted 9P.
5 Customer wants direct drive, but the airstream is hot, so the impeller should not sit on the motor shaft. The wall is adequate and there is room for a long assembly. 8 High airstream temperature may limit Arrangement 4; Arrangement 8 is the direct-drive alternative with a separate fan shaft.
6 Direct drive with the motor coupled to a fan shaft, large-HP motor, the wall is not sufficient by itself. 8P Coupled direct drive on a weak wall calls for the grade-mounted 8P.
7 Belt-driven fan with its motor on the fan's own pedestal; the wall could carry it, but the project has a strict low-vibration requirement. 9P FanPedia notes that mounting to the foundation helps meet lower vibration requirements.
8 Customer wants the most compact, lowest-maintenance plug fan possible, the airstream is near room temperature, and the wall is adequate. 4 Arrangement 4 is the compact, low-maintenance choice when temperature does not rule it out.
9 Large belt-driven fan with a large-HP motor. The wall cannot carry it, so the fan stands on grade, and the plant wants the motor on its own separate base on the floor, not on the fan's pedestal. 1P Belt driven, mounted to grade, with the motor mounted separate from the fan is Arrangement 1P. On 9P the motor rides on the fan's pedestal.

Provenance: Arrangement definitions from FanPedia pp. 170–172 (Technical Descriptions, Arrangements 1P, 4, 4P, 8, 8P, 9, 9P Plug; the picker offers all seven; the current BEPL, BFPL, BCPL and AFPL catalogs word 1P the same way) and p. 14 (belt-driven plug fan exploded view, Arr. 9P). Scenarios are illustrative jobs written for this chapter; the sim labels them "illustrative scenarios."

Rules: Decision order: (1) drive type from the scenario (direct or belt); (2) if direct drive and the scenario says the airstream is hot, Arrangement 4/4P is excluded and 8/8P is used; (3) if the scenario says the wall is not sufficient, or states a low-vibration requirement, use the P version; otherwise use the wall-mounted version. For belt drive on grade, a motor on its own base separate from the fan is 1P and a motor on the fan's pedestal is 9P. Exactly one arrangement is correct per scenario.

Learner Activity:

  1. The learner reads scenario 1 and selects one of the seven arrangements.
  2. The learner presses Check. The sim marks the choice correct or incorrect and shows the "Why" text, highlighting which of the three rules decided it.
  3. The learner presses Next to move to the following scenario. A checked scenario cannot be re-answered for score, but its reason stays visible when revisited.
  4. After scenario 9 the sim shows the score and lists any missed scenarios with their reasons.

Feedback: 9 scenarios, fixed order, one scored attempt each. Correct: "Correct: Arrangement . ". Incorrect: "Not quite. The answer is Arrangement . ". The correct answer is revealed immediately after each check. A running count "Correct: n of 9" is shown; the summary states that 7 of 9 is the mastery level.

Starting State: Scenario 1 is shown with no arrangement selected and the seven reference cards closed. The prompt reads "Which plug fan arrangement fits this job?"

Chapter Anchors: Seven plug fan arrangements in FanPedia (1P, 4, 4P, 8, 8P, 9, 9P), all offered by the picker; its belt-driven grade scenarios name where the motor sits (on the fan's pedestal: 9P; on its own base: 1P). The current catalogs do not list plain Arrangement 8 (see the availability note). Arrangement 9 is the most common; Arrangement 8 is the least common. The chapter's worked example lands on Arrangement 9P for a hot oven with belt drive and a weak wall.

Vaneaxial Fans and Roof Mounted Panel Fans

Chapter 5 introduced the tubeaxial fan: an axial impeller turning inside a plain tubular housing. Air leaving any axial impeller carries a swirl, because the blades push it around the axis as well as along it. A vaneaxial fan adds a section of stationary guide vanes inside the housing to straighten that airflow as it moves through the fan (FanPedia p. 7). Straightening matters because swirling air carries energy that does not show up as useful pressure in the duct; the vanes turn part of that rotational energy into static pressure. That is why the current Twin City Fan catalog describes vaneaxial fans as built for large volumes of air at moderate to high pressures, in a tubular package that uses minimal space. Current models include TCVA (cast aluminum impeller), TCVX (adjustable-pitch aluminum impeller) and TCVS (steel impeller), in direct and belt driven versions; FanPedia's exploded views show the guide vanes sitting behind the impeller in both drive types (FanPedia p. 16).

Worked example: why a vaneaxial earns its vanes. A process supply job calls for 20,000 CFM through a 36-inch round duct, with a system pressure too high for a plain tubeaxial to deliver efficiently, and there is no floor space for a housed centrifugal. First check the duct velocity. The flow area is

\[ A = \pi \left(\frac{36}{2 \times 12}\right)^2 = 7.07 \ \text{ft}^2 \]

so the average velocity is \( V = 20{,}000 / 7.07 \approx 2{,}830 \) fpm. For standard air, velocity pressure is \( VP = (V/4005)^2 \approx 0.50 \) in. wg. That is a meaningful slice of energy riding in the axial velocity alone; any swirl the impeller adds on top is energy the duct cannot use. A vaneaxial fan's vane section recovers part of that swirl as static pressure, so the same inline package reaches pressures a tubeaxial cannot. The decision follows from the job: large volume, moderate-to-high pressure, straight duct, little space. That combination is the vaneaxial's home ground. (The flow, diameter and the claim that a tubeaxial falls short are illustrative; confirm with ratings from the current catalog.)

The panel fan from Chapter 4 is an axial impeller centered in a flat, panel-shaped housing, usually wall mounted. A roof mounted panel fan uses that panel fan as its base model and adds roof accessories such as a stack cap or a hood (FanPedia p. 8). With a stack cap the air moves in a straight line up through the fan. With a hood the air moves straight through the fan and is then deflected down and outward for exhaust, or flows in the reverse direction for supply. On a drawing, the giveaway is a flat panel unit with a weatherhood or stack cap sitting on a curb, rather than the round tube of a roof mounted axial fan.

Heavy-Duty Centrifugals for Dirty Air and High Pressure

The next three product lines are all housed centrifugal fans: a scroll housing around a rotating impeller, with air entering along the shaft and leaving at a right angle to it (FanPedia p. 4). What separates them is the blade shape and the airstream each is built to survive. A particulate-laden airstream carries solids such as dust, chips, fibers or sticky material, and it destroys or clogs impellers designed for clean air. Chapter 8 treats impeller types in depth; here the goal is to recognize the product lines.

Radial Bladed Fans

A radial bladed fan has flat blades that point straight out from the hub, like the spokes of a wheel. Material striking a flat radial blade tends to slide off rather than build up, and the blades can be made from heavy plate. The current Twin City Fan catalog calls the line the "workhorse" of the industry: heavy-gauge, all-welded construction proven by years of handling dirty, abrasive, sticky or bulky particulate-laden airstreams.

FanPedia shows five radial bladed impeller styles (FanPedia p. 32), each a variation on the same flat blade:

  • Paddle impeller (open type): single-thickness radial paddle blades with no plates.
  • Paddle impeller with end rings: the open design with front and back end rings added.
  • Material handling impeller (wool): the open design with a full back plate.
  • Paper handling impeller: a full back plate with gussets for extra rugged durability.
  • Air handling impeller: heavy-gauge blades welded to both a back plate and a front plate.

The current catalog's model codes follow those names: RBO and RBR (paddle impellers), RBW (back plate wool impeller), RBP (paper handling impeller), RBA (air handling impeller) and JRW (compact design).

Worked example: reading the impeller from the airstream. A paper converting plant wants to convey edge trim from a slitter line to a baler. The airstream is long, light strips of paper, the material passes through the fan, and the customer complains that the previous fan "wrapped up." Start with the family: material passing through the fan rules out the high-efficiency backward inclined and airfoil designs, which are meant for cleaner air, and points to a radial bladed fan. Then pick the impeller: FanPedia names a paper handling impeller with a full back plate and gussets, and the catalog sells it as model RBP. Nothing has been sized yet, but the line and the impeller are narrowed, which is the first job on any industrial inquiry. Confirm materials and any abrasion resistant option against the current catalog.

Radial Tip Fans

A radial tip fan splits the difference between a radial blade and a forward curved blade. FanPedia defines its impeller as a blade curved forward at the entering edge and radial at the tip of the leaving edge (FanPedia p. 31). The radial tip suits dirty, particulate-laden air, and the curved entry lets air onto the blade more smoothly. The current catalog states the payoff: with high airflows, the radial tip fan is much more efficient than a comparable radial blade fan. Twin City Fan sells radial tip fans as RTF (industrial) and HRT (industrial, high specific speed), alongside the high-efficiency HAF (airfoil) and HIB (backward curved) fans meant for high temperatures, corrosive airstreams and light particulate.

To see why that efficiency matters, recall that the power a fan draws grows with airflow and pressure and shrinks with efficiency. Fan brake horsepower is

Fan Brake Horsepower

\[ \text{BHP} = \frac{Q \times TP}{6356 \times \eta} \]

where:

  • \( Q \) is the airflow in cubic feet per minute (CFM)
  • \( TP \) is the fan total pressure in inches of water gauge (in. wg)
  • \( \eta \) is the fan total efficiency, as a decimal
  • 6356 is the unit constant that converts CFM × in. wg to horsepower

Worked example: radial blade or radial tip? A dryer exhaust carries light, dusty air at 30,000 CFM and 12 in. wg total pressure. Suppose a radial bladed selection runs at 60% total efficiency and a radial tip selection runs at 72% (illustrative efficiencies, not catalog values). Then

\[ \text{BHP}_{\text{radial blade}} = \frac{30{,}000 \times 12}{6356 \times 0.60} \approx 94.4 \]
\[ \text{BHP}_{\text{radial tip}} = \frac{30{,}000 \times 12}{6356 \times 0.72} \approx 78.7 \]

The radial tip draws about 15.7 BHP less for as long as it runs, which on a continuous process fan adds up quickly. The radial blade still wins when the airstream is bulky, sticky or abrasive enough that efficiency must give way to durability. That trade-off, efficiency at high airflow versus survival in the worst material, is the question to ask whenever a customer says "dirty air."

Ask What Passes Through the Impeller

Breeze giving a tip On any dirty-air inquiry, ask one question first: "Does the material go through the fan, or is the fan on the clean side of a filter?" Through the fan points you to radial bladed or radial tip; clean side opens up the high-efficiency backward inclined designs.

Pressure Blowers

A pressure blower is a housed centrifugal built for high pressure at relatively low airflow. FanPedia notes that pressure blowers have narrower housings and impeller widths than standard centrifugal fans (FanPedia p. 4). The current catalog adds two practical traits: performance stays stable through the operating range, and the blower can be turned down to zero flow with a discharge damper. Impeller choices include radial back plate, backward curved, open radial and shrouded types, and housings are fabricated steel, cast aluminum or cast iron (FanPedia p. 62 shows the cast versions). Typical uses are dust collection, flue gas recirculation, material handling, explosion-proof processes and wet well station exhaust. Cast aluminum pressure blowers can carry a slide gate damper for manual airflow adjustment (FanPedia p. 192).

The following table pulls the three heavy-duty lines together.

Product line Blade shape Best fit Trade-off
Radial bladed fan Flat radial blades Abrasive, sticky, bulky particulate passing through the fan Rugged, but less efficient at high airflow
Radial tip fan Curved at entry, radial at tip High airflow, dirty particulate-laden air More efficient than radial blade at high airflow; not for the bulkiest material
Pressure blower Several, in a narrow housing High pressure at relatively low airflow Small volumes; turned down with a damper

Packaged Centrifugal Product Lines

Several product lines package a centrifugal fan for a common job, from a complete outdoor unit down to bare impellers for an OEM's enclosure. Four appear on industrial orders often enough to learn by name.

Utility Sets

A utility set is a compact, belt- or direct-driven single-inlet centrifugal package for general exhaust and supply in commercial and light industrial buildings. The current Twin City Fan catalog notes it works indoors, and outdoors with a weather cover that encloses the motor and drives, with housings in lock-seam galvanized steel, welded heavy-gauge steel, aluminum or stainless steel. FanPedia ties the term to an arrangement: for Class I and II fans in sizes 122 through 365, Arrangement 10 units are commonly called ventilating sets, with the adjustable motor base mounted inside the bearing pedestal (FanPedia p. 167). That makes Arrangement 10 more compact than Arrangement 9, and it is suitable for roof or outdoor installations with the optional weather cover.

Current utility set models are grouped by impeller:

  • Backward inclined: DCV (direct drive), BCV (belt driven), BCVR (belt driven, kitchen exhaust), BCVSH (smoke and heat).
  • Airfoil: BAV (belt driven).
  • Forward curved: DDF (direct drive), FCV (utility set).

Worked example: matching three requests to utility set models. A contractor sends three line items for the same building. Item one is a rooftop kitchen exhaust fan; the catalog's kitchen exhaust utility set is BCVR, and the outdoor location means the weather cover goes on the order. Item two is a fan that must run during a fire to remove smoke and heat; that points to BCVSH, the smoke and heat version, and to the UL listings shown for the line (UL 705, UL 762 and UL smoke and heat). Item three is a small indoor general exhaust fan where the customer wants no belts to service; a direct drive model, DCV (backward inclined) or DDF (forward curved), fits. Notice what you did: you used the application to choose within one product line before anyone opened a performance table. Sizing comes later, with the methods in Chapter 26.

Duct Fans

A duct fan is a double-inlet scroll fan mounted inside an enclosure: air is drawn through both inlets of the fan and discharged at a right angle to the fan shaft (FanPedia p. 4). The enclosed unit is installed as a package in the duct system, the network of ducts that carries air to and from the fan.

Worked example: what the second inlet buys you. A double-width, double-inlet (DWDI) wheel behaves roughly like two single-width, single-inlet (SWSI) wheels of the same diameter placed back to back. At the same speed and pressure it moves roughly twice the air. If a SWSI wheel of a given diameter moves about 4,000 CFM at 1 in. wg, the DWDI version of that diameter would move on the order of 8,000 CFM at the same pressure and speed (illustrative numbers). That is a large volume from a compact wheel, which is what fits inside an enclosure. When you see a drawing with a scroll housing inside a rectangular box and inlets on both sides of the wheel, read it as a duct fan, not a utility set (single inlet) or a square inline fan (straight-through tube).

Filtered Supply Fans and Air Kits

A filtered supply fan delivers filtered outside air into a building. FanPedia describes filtered configurations as roof mounted units with forward curved or backward inclined impellers that pull outside air through filters and move it downward into the building (FanPedia p. 4). The current catalog describes them as belt driven centrifugal fans that supply make-up air to buildings such as manufacturing plants, warehouses and auditoriums, replacing air lost through industrial processes, fume hood exhaust or general ventilation. Models include BCRFS (single side intake) and LPSF (louvered penthouse). On a site, look for a roof unit with a filter section and a supply opening pointing down into the curb.

An air kit is a fan sold without a housing, as a component for someone else's enclosure. The current Twin City Fan catalog describes air kits as forward curved impellers in a double-width, double-inlet arrangement. The forward curved design allows a low operating speed and economically sized shafting. Air kits provide reliable, quiet operation in ovens and plenums where it is not desirable to have the fan bearings in the airstream, and they move large volumes (up to 100,000 CFM) at static pressures up to 6 in. wg in a compact design. Air kits are supplied as a single fan kit (one impeller centered in the plenum) or a twin fan kit (two impellers on a common shaft, spaced so the restriction is the same at all four inlets). FanPedia shows the air kit as an Arrangement 3 assembly whose enclosure and insulation are provided by others in the field, and notes that air kits need support supplied by Twin City Fan or others rather than a pedestal (FanPedia pp. 83, 115).

An Air Kit Is Not a Finished Fan

Breeze with a warning A common trap is quoting an air kit as if the housing, supports and insulation come with it. FanPedia is explicit that the enclosure and insulation are provided by others, so write the scope split on the quote and confirm who supplies the supports before the order is released.

Application Fans: Paint Booths and Dust Collectors

The next two product lines are named for the job, not the hardware. Each one draws on fan types you already know, and the skill is recognizing which construction features the job demands.

A paint booth exhaust fan removes fumes and overspray from a spray booth. The current Twin City Fan application page sets out the requirements: airflow must be precise, with velocity low enough to keep a consistent flow into and out of the booth but high enough to carry fumes and overspray out of the work area. The impeller must be easy to clean and service, and efficiency and noise also matter. Twin City Fan answers the cleaning need with swingout construction on centrifugal fans, and clamshell or swingout construction on axial fans. FanPedia describes swingout fans as having the whole impeller, shaft and bearing assembly mounted on a large door that swings open, and clamshell fans as opening to give complete access to the fan interior without removing ductwork (FanPedia p. 123). The commonly used fans include the TCBS paint booth exhaust tubeaxial fan, TCVA vaneaxial fans, plug and plenum fans, and single-width airfoil and backward inclined centrifugals.

A dust collection fan is the fan that moves air through a dust collector. The current application page states the split that matters: backward inclined fans are used on the clean side of a filter, and radial bladed fans are used for cyclone applications, where the dust-laden air reaches the fan. Twin City Fan also builds top-mounted and side-mounted units, and lists radial tip fans (HRT, RTF) and pressure blowers among the fans commonly used on collectors. The position of the fan relative to the filter is the first fact to pin down, because it decides between a high-efficiency clean-air fan and a rugged dirty-air fan.

Application What the job demands Typical answer
Paint booth exhaust Precise velocity, easy impeller cleaning, efficiency, low noise Swingout or clamshell construction; tubeaxial, vaneaxial, plug, plenum or SWSI centrifugal
Dust collector, clean side of filter Efficient air moving after the dust is removed Backward inclined centrifugal
Dust collector, cyclone (dirty side) Dust-laden air through the fan Radial bladed fan

Laboratory Exhaust: Dilute, Then Throw It High

Chapter 4 introduced the laboratory fume exhaust fan, and Chapter 5 explained entrained flow, the outside air a lab fan's nozzle or windband pulls into the exhaust jet. This section completes that picture with the inline product line and the flow bookkeeping behind every lab exhaust selection.

An inline lab exhaust fan is a lab exhaust fan built on a tubular inline centrifugal or mixed flow fan: the housing is a tube and air moves straight through the fan with a rotating impeller (FanPedia p. 6). Current Twin City Fan inline models include the induced-flow, mixed flow TVIFE (direct drive) and QIFE (belt driven), and the venturi nozzle QFE (mixed flow) and TFE (inline centrifugal). The housed centrifugal versions, BAIFE and BCIFE, use scroll housings instead. FanPedia shows isolation dampers, bypass dampers and actuators on both groups (FanPedia p. 138).

The purpose of all this hardware is plume dilution: mixing fresh outside air into the contaminated exhaust so it leaves the stack at a lower concentration, then discharging it at high velocity so the plume rises up and away from the building. The current catalog explains the stakes: lab fumes can be hazardous in concentrated form, and the exhaust must not return into the building or the surrounding areas where people may be present. Two streams of outside air do the diluting (FanPedia pp. 4, 6):

  • Bypass flow is fresh outside air drawn in through a bypass air plenum at the fan inlet, controlled by bypass dampers. It enters before the impeller, so it passes through the fan. In common practice the bypass damper also opens as fume hood sashes close, keeping the fan's flow and stack velocity steady while the lab's exhaust varies.
  • Entrained flow is outside air pulled into the jet at the nozzle or windband after the air leaves the fan. It never passes through the impeller.

Three Streams, One Plume

Breeze thinking Notice where each stream joins: contaminated air and bypass air go through the impeller together, and entrained air joins only after the fan. Once you place each stream on that path, every lab exhaust number on a submittal falls into place.

Putting the streams together gives the lab exhaust total flow: the full volume leaving the stack as a plume. FanPedia's lab exhaust diagrams label the parts as contaminated air, bypass flow, fan flow, entrained flow and total flow (FanPedia pp. 4, 6). The relationships are:

Lab Exhaust Fan Flow and Total Flow

\[ Q_{\text{fan}} = Q_{\text{contaminated}} + Q_{\text{bypass}} \]
\[ Q_{\text{total}} = Q_{\text{fan}} + Q_{\text{entrained}} \]

where:

  • \( Q_{\text{contaminated}} \) is the contaminated air drawn from the fume hoods, in CFM
  • \( Q_{\text{bypass}} \) is the fresh air drawn through the bypass air plenum, in CFM
  • \( Q_{\text{fan}} \) is the fan flow, the air that actually passes through the impeller, in CFM
  • \( Q_{\text{entrained}} \) is the outside air entrained at the nozzle or windband, in CFM
  • \( Q_{\text{total}} \) is the lab exhaust total flow leaving the stack, in CFM

Worked example. A lab's fume hoods exhaust 8,000 CFM of contaminated air. The bypass damper admits 2,000 CFM, so the fan flow is 10,000 CFM. If the fan's nozzle entrains another 10,000 CFM (an illustrative value; real entrainment comes from the manufacturer's rating for the selected fan and nozzle), the total flow is 20,000 CFM. Contaminated air is then \( 8{,}000 / 20{,}000 = 40\% \) of the plume. At night, when sashes close and the hoods exhaust only 5,000 CFM, the bypass damper opens to 5,000 CFM and the fan flow stays at 10,000 CFM; with the same 10,000 CFM entrained, the contaminated share falls to 25%.

Don't Size the Fan to the Total Flow

Breeze with a warning The impeller only moves the fan flow; the entrained air is extra volume that the nozzle adds outside the fan. Select the fan on contaminated plus bypass flow, and report total flow separately as the plume volume.

The calculator below lets you practice that bookkeeping before you meet it on a real submittal.

Diagram: Lab Exhaust Flow Calculator

Run Lab Exhaust Flow Calculator Fullscreen

Lab Exhaust Flow Calculator

Type: microsim sim-id: ch06-lab-exhaust-flow-calculator
Library: p5.js
Status: Specified
Bloom Level: Apply
Bloom Verb: calculate
Learning Objective: The learner will calculate the fan flow, the lab exhaust total flow and the contaminated share of the plume from given contaminated, bypass and entrained flows, matching the model values exactly on at least 3 of 3 challenges.

Prerequisites: contaminated air, bypass flow, bypass air plenum, entrained flow, fan flow, lab exhaust total flow, plume dilution (all defined in the section "Laboratory Exhaust: Dilute, Then Throw It High").

Evidence of Mastery: For each of 3 challenges the learner types the fan flow and the total flow in CFM, then the contaminated share in percent, before the stack diagram fills in. Flows are correct when they equal the model values exactly; the share is correct within ±1 percentage point. Mastery is 3 of 3 challenges with all three values correct. Free exploration with the inputs afterward is not evidence.

Misconceptions: (1) Entrained air passes through the fan, so the fan must be sized for total flow. (2) Bypass air is wasted air that does not help dilution. (3) When fume hood exhaust drops, the fan flow must drop too.

Instructional Rationale: The flow relationships are a small Apply-level calculation; committing numbers before the answer appears gives checkable evidence, and the stack diagram that fills in afterward shows where each stream joins, which confronts misconception (1).

Content:

The diagram shows a lab exhaust fan with four labeled streams: contaminated air entering from the fume hood duct, bypass flow entering through the bypass air plenum before the fan, fan flow through the impeller, entrained flow joining at the nozzle or windband after the fan, and total flow leaving the stack. After each check the diagram shows the value on each stream.

Adjustable quantities (exploration mode):

Quantity Min Max Step Default Unit
Contaminated air 0 20,000 500 8,000 CFM
Bypass flow 0 10,000 500 2,000 CFM
Entrained flow 0 30,000 500 10,000 CFM

Challenges, in fixed order:

# Contaminated Bypass Entrained Fan flow Total flow Contaminated share Feedback when wrong
1 6,000 0 9,000 6,000 15,000 40% With no bypass, fan flow equals contaminated flow; entrained air is added after the fan: 6,000 + 9,000 = 15,000 CFM.
2 5,000 5,000 10,000 10,000 20,000 25% Bypass air goes through the fan: 5,000 + 5,000 = 10,000 CFM fan flow, then 10,000 + 10,000 = 20,000 CFM total.
3 12,000 3,000 15,000 15,000 30,000 40% Fan flow is 12,000 + 3,000 = 15,000 CFM; total is 15,000 + 15,000 = 30,000 CFM; share is 12,000 / 30,000 = 40%.

Provenance: Stream names and the order in which streams join come from FanPedia pp. 4 and 6 (lab exhaust diagrams: bypass flow, entrained flow, fan flow, contaminated air, total flow) and p. 138 (bypass dampers). All flow values are illustrative; the sim labels them "illustrative values." In a real fan, entrained flow depends on the fan flow and the nozzle design and comes from the manufacturer's rating; the sim states this on screen and treats entrained flow as an independent input for practice.

Rules: Fan flow = contaminated + bypass (CFM). Total flow = fan flow + entrained (CFM). Contaminated share = contaminated / total × 100, rounded to the nearest whole percent. If total flow is 0, the share is shown as "not defined" and no plume is drawn. All inputs sit on the 500 CFM step grid.

Learner Activity:

  1. The learner reads challenge 1's three given flows and types fan flow, total flow and contaminated share.
  2. The learner presses Check. Each value is marked correct or incorrect. If all three are right, the stack diagram fills in every stream with its value and the feedback text appears. If not, each wrong value gets a hint line, the diagram stays without values, and the learner tries again; after the second attempt the diagram fills in and the model values are shown.
  3. The learner presses Next for challenges 2 and 3.
  4. After challenge 3, exploration mode unlocks: the learner changes the three inputs and the diagram updates all streams and the share at once. The first time the learner lowers contaminated air while raising bypass by the same amount, the sim points out that fan flow stayed constant.

Feedback: 3 challenges, fixed order, two attempts each. Correct: "Correct: fan flow CFM, total flow CFM, contaminated share %." Hint after a first wrong attempt: each value is marked correct or incorrect, and each wrong value gets one rule or slip line, never a model value or a worked sum: entrained air counted in the fan flow ("Fan flow: entrained air joins after the fan."), bypass air left out ("Fan flow: bypass air passes through the fan too." / "Total flow: count the bypass air too."), entrained air left out of the total ("Total flow: count the entrained air too."), share divided by the fan flow ("Share: divide by the total flow, not the fan flow."), share typed as a fraction ("Share: give it as a percent, not a fraction."), otherwise the rule for that value. The stack diagram stays without values until the challenge resolves. After the final attempt: the "Feedback when wrong" text for that challenge with the model values, and the challenge counts as missed. A running count "Challenges correct: n of 3" is shown.

Starting State: Challenge 1 is shown with empty answer boxes and the stack diagram showing stream labels but no values. The prompt reads "How much air passes through the fan, and how much leaves the stack?"

Chapter Anchors: The chapter's worked example uses 8,000 CFM contaminated, 2,000 CFM bypass, 10,000 CFM fan flow, 10,000 CFM entrained, 20,000 CFM total and a 40% contaminated share; at night, 5,000 CFM contaminated and 5,000 CFM bypass give a 25% share. The chapter states that the fan is sized on contaminated plus bypass flow.

Matching the Job to the Product Line

With this chapter, the product-line survey that began in Chapter 4 is complete. On a real inquiry you rarely get the product name; you get a job. The activity below asks you to recommend a product line from a job description using the features covered in this chapter.

Diagram: Industrial Product Line Matcher

Run Industrial Product Line Matcher Fullscreen

Industrial Product Line Matcher

Type: microsim sim-id: ch06-industrial-product-line-matcher
Library: p5.js
Status: Specified
Bloom Level: Evaluate
Bloom Verb: recommend
Learning Objective: The learner will recommend the product line that best fits each of 13 industrial job descriptions, justifying the choice by the deciding feature, with at least 10 of 13 correct on the first attempt.

Prerequisites: plug fan, vaneaxial fan, roof mounted panel fan, radial bladed fan, radial tip fan, pressure blower, utility set, duct fan, filtered supply fan, air kit, paint booth exhaust fan, dust collection fan, inline lab exhaust fan (all defined in this chapter).

Evidence of Mastery: For each job the learner picks one of the 13 product lines and then one deciding feature from three offered. A recommendation is correct when the product line matches the "Correct line" column; the deciding feature is correct when it matches the "Deciding feature" column. Mastery is 10 of 13 product lines correct on the first attempt. The feature choice is scored separately and reported, but does not count toward mastery.

Misconceptions: (1) Any dirty-air job takes a radial bladed fan, even when the fan sits on the clean side of a filter. (2) An air kit is a complete fan with housing and supports. (3) Pressure blowers are chosen for large airflow. (4) Plug fans and plenum fans are the same thing.

Instructional Rationale: Recommending a line from a job description is how the skill is used on real inquiries; asking for the deciding feature makes the learner judge which requirement controls the choice instead of matching keywords.

Content:

Product lines offered (same list for every job): Plug fan; Vaneaxial fan; Roof mounted panel fan; Radial bladed fan; Radial tip fan; Pressure blower; Utility set; Duct fan; Filtered supply fan; Air kit; Paint booth exhaust fan; Dust collection fan; Inline lab exhaust fan.

Jobs, shown in shuffled order:

# Job description Correct line Deciding feature (correct) Distractor features Why (shown as feedback)
1 Recirculate hot air in an industrial oven; the fan mounts through the oven wall and the motor and bearings must stay outside the process air. Plug fan Mounting panel separates drive from process air Double inlet wheel; Vane section A plug fan mounts through the plenum wall with motor and drive outside the process air.
2 Convey long paper trim strips from a slitter to a baler; the material passes through the fan. Radial bladed fan Rugged radial blades for bulky material High efficiency at high airflow; Narrow housing for high pressure Bulky material through the fan calls for the radial bladed "workhorse," such as the paper handling impeller.
3 Exhaust a high airflow of light, dusty air where power cost matters and material does not build up badly. Radial tip fan More efficient than radial blade at high airflow Full back plate with gussets; Swingout door Radial tip handles particulate-laden air and is much more efficient than a radial blade at high airflow.
4 Supply high pressure at a relatively low airflow to a process, with turndown to zero flow through a discharge damper. Pressure blower High pressure at relatively low volume Large volume at moderate pressure; Filter section Pressure blowers use narrow housings for high pressure at relatively low volume and turn down with a damper.
5 Move a large volume at moderate to high pressure in a straight duct run with almost no floor space. Vaneaxial fan Guide vanes straighten the airflow Scroll housing in an enclosure; Weather cover The vaneaxial's vane section recovers swirl, giving moderate to high pressure in a compact tube.
6 Roof exhaust built on a wall-type panel fan, fitted with a stack cap so air leaves straight up. Roof mounted panel fan Panel fan base with stack cap or hood Tubular housing with nozzle; Double inlet wheel A roof mounted panel fan is a panel fan base with roof accessories such as a stack cap.
7 General exhaust for a light-industrial building, installed outdoors, compact belt-driven Arrangement 10 package with a weather cover. Utility set Arrangement 10 ventilating set Bypass air plenum; Clamshell construction Arrangement 10 units in the ventilating-set size range are utility sets, suitable outdoors with a weather cover.
8 Double-inlet scroll fan supplied already mounted inside an enclosure for a ceiling equipment space. Duct fan Double inlet scroll housing inside an enclosure Radial tip blades; Forward curved kit without housing A duct fan is a double-inlet scroll housing mounted inside an enclosure.
9 Roof unit that pulls outside air through filters and supplies it down into a warehouse as make-up air. Filtered supply fan Filters outside air before it enters the building Plume discharge; Swingout door Filtered supply fans pull outside air through filters and move it downward into the building.
10 Oven builder wants forward curved double-inlet impellers on a shaft to install in its own insulated enclosure, with bearings out of the airstream. Air kit Impellers supplied for an enclosure built by others Gusseted mounting panel; Narrow housing An air kit supplies the forward curved DWDI impellers and shaft; the enclosure and insulation are provided by others.
11 Exhaust overspray from an automotive spray booth; the impeller must be cleaned often. Paint booth exhaust fan Swingout or clamshell access for cleaning Bypass dampers; High pressure at low volume Paint booth exhaust needs precise velocity and easy cleaning, provided by swingout and clamshell construction.
12 Fan on the clean side of a cartridge dust collector's filter, side-mounted on the collector. Dust collection fan Clean-side backward inclined fan Radial paddle impeller; Vane section On the clean side of the filter the dust is already removed, so a backward inclined dust collection fan fits.
13 Exhaust a bank of fume hoods through a tubular mixed flow fan that dilutes the exhaust and throws a high plume. Inline lab exhaust fan Tubular lab fan with bypass and entrained dilution Scroll housing in an enclosure; Weather cover over drives Inline lab exhaust fans are tubular mixed flow or inline centrifugal fans that dilute and discharge the plume high.

Provenance: Product line definitions from this chapter, which draws on FanPedia pp. 4–8, 31–32, 62, 83, 115, 123, 138, 167 and 171–172, and on the current tcf.com product and application pages for plug fans, axial fans, radial bladed fans, radial tip and high efficiency fans, pressure blowers, utility sets, centrifugal filtered supply fans, air kits, laboratory and fume exhaust fans, spray booth exhaust and dust collectors. Job descriptions are illustrative; the sim labels them "illustrative jobs."

Rules: Exactly one product line is correct per job. The three feature options per job are the correct feature and the two distractors listed, shown in shuffled order. The product line is scored first; the feature question appears after the line is checked.

Learner Activity:

  1. The learner reads a job and selects one of the 13 product lines.
  2. The learner presses Check. The line is marked correct or incorrect and the "Why" text is shown.
  3. The learner then picks the deciding feature from three options and presses Check; the feature is marked correct or incorrect.
  4. The learner presses Next. After 13 jobs, the sim shows both scores and lists the missed jobs with their "Why" text.

Feedback: 13 jobs, shuffled order, one scored attempt per job for the line and one for the feature. Correct line: "Correct: . ". Incorrect line: "The better fit is . ". Correct feature: "Right: decides this job." Incorrect feature: "The deciding feature is ." Answers are revealed after each check. Scores "Lines correct: n of 13" and "Features correct: n of 13" are shown; the summary states that 10 of 13 lines is the mastery level.

Starting State: The first shuffled job is shown with no line selected. The prompt reads "Which product line would you recommend for this job?"

Chapter Anchors: 13 product lines, as named in this chapter's sections. The chapter states that backward inclined fans serve the clean side of a filter and radial bladed fans serve cyclone applications, that radial tip fans are more efficient than radial blade fans at high airflow, and that air kit enclosures and insulation are provided by others.

Key Takeaways

  • A plug fan mounts through a plenum wall, keeping motor and drive out of the process air; Arrangement 9 is most common, and P versions mount to grade.
  • A vaneaxial fan uses guide vanes to straighten swirl for moderate to high pressure in a compact tube; a roof mounted panel fan is a panel fan with a stack cap or hood.
  • Radial bladed fans survive abrasive, sticky or bulky material; radial tip fans handle dirty air more efficiently at high airflow; pressure blowers give high pressure at relatively low volume.
  • Utility sets are packaged Arrangement 10 ventilating sets; duct fans are double-inlet scroll fans in an enclosure; filtered supply fans filter outside make-up air; air kits are forward curved DWDI impellers for enclosures built by others.
  • Paint booth exhaust fans need precise velocity and easy cleaning; dust collection fans depend on fan position: backward inclined on the clean side, radial bladed for cyclones.
  • Inline lab exhaust fans achieve plume dilution with bypass flow and entrained flow. Fan flow is contaminated plus bypass; lab exhaust total flow adds entrained flow.

The Product-Line Map Is Complete

Breeze celebrating You can now take an industrial job description, from a hot oven wall to a dusty cyclone to a lab roof, and name the product line built for it along with the feature that decides it. Every later chapter on impellers, arrangements and construction builds on that map.

See Annotated References