HVAC Fans
Corpus sync: neutrality remakes, note hygiene, datasheet relocation, transformer-split cross-refs
Showing changes from Rev 5
to Rev 6
in HVAC Fans.
---
title: HVAC Fans
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### The fan construction, materials, and bearing arrangement shall suit the airstream it handles.
−### Clean, dry, ambient-temperature supply and general exhaust air is the default service and permits standard steel construction with a standard motor. {note}
```datasheet
…9 unchanged lines
default: "Clean, dry, ambient supply or general exhaust (standard)"
```
+### Clean, dry, ambient-temperature supply and general exhaust air is the default service and permits standard steel construction with a standard motor. {note}
### Airstreams that are corrosive, high-temperature, grease-laden, moisture-laden, or that may contain flammable or combustible material change the material, finish, bearing, motor enclosure, and spark-resistance requirements and shall be identified for each fan.
…3 unchanged lines
### Fan air performance is certified at standard air density (0.075 lb/ft³, sea level, 70°F). {note}
+### Where the fan operates at elevated altitude or handles air at a temperature far from standard, the brake horsepower and the as-installed pressure shall be corrected for the actual air density.
+
```datasheet
label: Air Density Correction Basis
…5 unchanged lines
```
−### Where the fan operates at elevated altitude or handles air at a temperature far from standard, the brake horsepower and the as-installed pressure shall be corrected for the actual air density.
−
### The motor shall be sized for the highest-density (coldest, lowest-altitude) condition the fan will start and run against, because density-corrected brake horsepower rises as air gets denser.
…5 unchanged lines
### The fan type shall suit the pressure, airflow, available space, sound limit, and airstream of each application.
−### Centrifugal fans develop higher pressure efficiently and are the default for ducted supply and return systems and for higher-resistance exhaust; axial fans move large volumes at low to moderate pressure in a compact, in-duct envelope; propeller fans move large volumes against very low pressure and are used for panel and wall ventilation; inline cabinet and tubular fans package a centrifugal or mixed-flow impeller in a straight-through housing for ceiling-space duct runs; and roof and wall power ventilators and ceiling exhaust fans are pre-engineered exhaust packages. {note}
```datasheet
…14 unchanged lines
default: "Centrifugal, housed (scroll) — ducted supply/return, higher pressure"
```
+### Centrifugal fans develop higher pressure efficiently and are the default for ducted supply and return systems and for higher-resistance exhaust; axial fans move large volumes at low to moderate pressure in a compact, in-duct envelope; propeller fans move large volumes against very low pressure and are used for panel and wall ventilation; inline cabinet and tubular fans package a centrifugal or mixed-flow impeller in a straight-through housing for ceiling-space duct runs; and roof and wall power ventilators and ceiling exhaust fans are pre-engineered exhaust packages. {note}
## Centrifugal Impeller (Wheel) Type {toc}
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### Airfoil (AF) blades are the most efficient and quietest and are the default for clean air, but the hollow blade can fill with dirt or condensate; backward-inclined and backward-curved (BI/BC) blades give nearly the efficiency of airfoil with greater tolerance of moist or lightly contaminated air; forward-curved (FC) blades are compact and quiet at low pressure and are typical of small packaged and cabinet fans but are inefficient and unstable at high pressure; and radial and radial-tip blades resist material buildup and are used for dirty or material-handling exhaust at the cost of efficiency. {note}
+### The centrifugal impeller (wheel) type shall be specified for each fan, selected to suit the air cleanliness, efficiency, and pressure demands of its service.
+
```datasheet
label: Centrifugal Impeller Type
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### Direct-drive fans (impeller mounted on the motor shaft, AMCA Arrangement 4, or a close-coupled coupling) eliminate the belt, sheaves, and belt maintenance, run quieter, and are the default for small and medium fans and for any fan whose airflow is set by a variable-frequency drive or an EC motor rather than by a sheave. {note}
+### The drive type shall be specified for each fan, stating whether it is direct drive or belt drive.
+
```datasheet
label: Drive Type
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### Fans shall be furnished with the integral accessories required for their service and location.
−### Common accessories include inlet and outlet flanges or duct collars, a flexible connection at the duct, an integral or factory-mounted disconnect switch, a motorized or gravity backdraft damper, an inlet/outlet guard or bird/insect screen on open inlets, drain connections on housings subject to condensate or washdown, and weatherhoods on exterior intakes. {note}
```datasheet
…13 unchanged lines
default: "Flexible duct connection at fan"
```
+### Common accessories include inlet and outlet flanges or duct collars, a flexible connection at the duct, an integral or factory-mounted disconnect switch, a motorized or gravity backdraft damper, an inlet/outlet guard or bird/insect screen on open inlets, drain connections on housings subject to condensate or washdown, and weatherhoods on exterior intakes. {note}
### The accessory schedule shall identify the accessories furnished with each fan so that field-furnished items (for example, a damper furnished under the ductwork scope) are not duplicated or omitted.
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# Installation {toc}
−## General {toc}
+## Fans shall be installed level, plumb, and aligned in accordance with this standard, the contract drawings, the manufacturer's instructions, and NFPA 90A.
−### Fans shall be installed level, plumb, and aligned in accordance with this standard, the contract drawings, the manufacturer's instructions, and NFPA 90A.
+## Adequate clearance shall be maintained for belt and sheave service, bearing lubrication, motor removal, and impeller access.
−### Adequate clearance shall be maintained for belt and sheave service, bearing lubrication, motor removal, and impeller access.
+## The fan shall be supported entirely on its isolators or curb so that no load is carried by the connected ductwork, and the flexible connections shall be installed so they do not transmit force into the fan.
−### The fan shall be supported entirely on its isolators or curb so that no load is carried by the connected ductwork, and the flexible connections shall be installed so they do not transmit force into the fan.
−
## Inlet and Outlet System Effect {toc}
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## Spare-part identification (fan tag, belt size and quantity, bearing part numbers) shall be listed in the closeout documents.