Greenheck Fan 129 manual Motor Horsepower, Belt Drive, Applications, Fan Model

Introduction to FAN SELECTION

Motor Horsepower
The motor horsepower for direct drive fans is	If this is the case, we will need a 1/2 hp motor
always sized by Greenheck and does not require	because our fan will have to run at almost
further consideration. For belt drive models,	810 rpm (refer to performance box - 2052 cfm at
the catalog identifies which horsepower is	0.625 in. Ps). Therefore, choosing a 1/2 hp motor
recommended. However, there are times when it	in this case is exercising good judgement.
is wise to bump the horsepower one size. For	The complete model designation for this
example, the hp recommended for the GB-180
	application is GB-180-5.
at 810 rpm (2375 cfm @ .5” Ps) is 1/3 hp.
Although a 1/3 hp motor is recommended, it is	Note: The GB-180-5 has an rpm range of 700-940.
	This means that if the static pressure is less than
not necessarily a good motor selection for this
	estimated, say 0.25 in. Ps, the fan can be slowed down
application. Our static pressure of 0.5 in. was only
	to accommodate this condition.
an estimate. It may actually turn out to be .625 in.
Belt Drive
One advantage of choosing a belt drive over a direct
drive is that it is capable of adjusting the fan rpm,
which enables the fan to move more air if necessary.
Motor pulleys are adjusted by loosening the set			Belt
screw and turning the top half of the pulley (see
illustrations at right). This causes the pulley diameter	Opening	the pulley decreases		fan	rpm.
to change, which results in changing the fan rpm.	Closing the pulley increases			fan	rpm.
Applications	The information that follows will help walk you
Ventilating a building simply replaces stale or foul	through this type of problem and enable you to
	select the right fan for the job.
air with clean, fresh air. Although the ventilation
process is required for many different applications,
the airflow fundamentals never change:	Fan Model
Undesired air out, fresh air in
	Fans all perform the basic function of moving air
The key variables that do change depending on	from one space to another. But the great diversity of
	fan applications creates the need for manufacturers
applications are the fan model and the air volume
	to develop many different models. Each model has
flow rate (cfm). Other considerations include the
	benefits for certain applications, providing the most
resistance to airflow (static pressure or Ps) and
	economical means of performing the air movement
sound produced by the fan (Sones).
	function. The trick for most users is sorting through
Occasionally, a customer will require a fan to perform
	all of the models available to find one that is
a particular function, yet does not know which model	suitable for their needs.
to use or even what cfm is necessary. In this case,
some fan specification work must be done.

Fan specification is usually not a precise science and can be done confidently when the fan application is understood.

Based on the application, four parameters need to be determined. They are:

Fan Model

Cubic Feet per Minute (cfm)

Static Pressure (Ps)

Loudness limit (sones)

Propeller vs. Centrifugal Wheel

Propeller fans provide an economical method to move large air volumes (5,000+ cfm) at low static pressures (0.50 in. or less). Motors are typically mounted in the airstream which limits applications to relatively clean air at maximum temperatures of 110°F.

Centrifugal fans are more efficient at higher static pressures and are quieter than propeller fans. Many centrifugal fan models are designed with motors mounted out of the airstream to ventilate contaminated and high temperature air.

130F A N F U N D A M E N T A L S