FAN PERFORMANCE

The first two sections of this guide contain information needed to select the right fan for the particular application. The information in this section is useful once the fan has been selected and installed on the job.

The fan curves and system resistance curves below will help to solve fan performance problems that may be encountered in a variety of applications.

Fan Dynamics

A fan is simply an air pump. The rate at which a fan can “pump” air depends on the pressure the fan must overcome. This principle also relates to water pumps. A water pump is able to deliver more water through a

2 in. diameter hose than a 1 in. diameter hose because the 1 in. hose creates more resistance to flow.

For a fan, every flow rate (CFM-Cubic Feet per Minute) corresponds to a specific resistance to flow (Ps-Static Pressure). The series of cfm, Ps points for a fan at a constant rpm is called a fan curve. A fan curve at 700 rpm is shown below.

At 0.25 in. Ps, this fan will deliver 1000 cfm. If the pressure increases, cfm decreases. If the pressure decreases, cfm will increase.

At 700 rpm, the operating point will slide along the fan curve as static pressure changes, but it will never lie off the curve. In order for a fan to perform at a point off the curve, the rpm must be changed.

The figure below illustrates how rpm affects the fan curve. Notice that the general shape of the curves are the same. Changing rpm simply moves the curve outward or inward.

Fan Curve

 

Varying Fan Curve

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

System Dynamics

For a given flow rate (cfm), an air distribution system produces a resistance to airflow (Ps). This resistance is the sum of all static pressure losses as the air flows through the system. Resistance producing elements include ductwork, dampers, grills, coils, etc.

A fan is simply the device that creates the pressure differential to move air through the system.

The greater the pressure differential created by the fan, the greater the volume of air moved through the system. Again, this is the same principle that relates to water pumps. The main difference in our case is that the fan is pumping air.

Tests have established a relationship between cfm and Ps. This relationship is parabolic and takes the form of the following equation:

Ps = K x (cfm)2

Where K is the constant that reflects the “steepness” of the parabola. This equation literally states that Ps varies as the square of the cfm.

For example, whenever the cfm doubles, the Ps will increase 4 times. The figures on the next page graphically illustrate this concept.

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Greenheck Fan 240XP-CUb manual Fan Dynamics, Fan Curve Varying Fan Curve
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240XP-CUb specifications

The Greenheck Fan 240XP-CUb is a premium addition to the commercial and industrial ventilation market, delivering exceptional performance and reliability. Designed for a variety of applications, the 240XP-CUb combines cutting-edge technology with robust construction to ensure efficient airflow management.

One of the standout features of the 240XP-CUb is its energy efficiency. This model is engineered to minimize energy consumption while maximizing airflow, thanks to advanced motor technology and aerodynamically optimized fan blades. The fan operates with a sound level that is comfortably low, making it an ideal choice for environments where noise reduction is critical, such as schools, hospitals, and office buildings.

The 240XP-CUb is equipped with a high-efficiency, permanent split capacitor (PSC) motor that enhances its overall performance. This type of motor reduces energy costs while providing consistent operation, ensuring longevity and durability. With variable speed options, the fan can be tailored to suit specific application requirements, allowing for better control over airflow and energy use.

In terms of construction, the Greenheck Fan 240XP-CUb is built to last. It features a heavy-duty galvanized steel housing that is resistant to corrosion and can withstand the rigors of commercial use. This ensures that the fan remains reliable in various environments, from manufacturing facilities to food processing plants. The design also includes an easy-access panel for maintenance, further enhancing the unit's user-friendly nature.

Another significant aspect of the 240XP-CUb is its versatility. It can be installed in a range of configurations, including horizontal and vertical orientations, making it suitable for different spaces and applications. Furthermore, it supports a variety of accessories and options that allow for customization, such as inlet guards, dampers, and different mounting configurations.

The Greenheck Fan 240XP-CUb adheres to the latest regulatory standards for efficiency and emissions, making it an environmentally friendly choice for businesses looking to reduce their carbon footprint. With its combination of performance, efficiency, and durability, the 240XP-CUb stands out as a top-tier solution for anyone in need of reliable ventilation solutions. Whether for new installations or retrofits, this fan is designed to meet the demands of modern HVAC systems, ensuring a comfortable and healthy environment.
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