Greenheck Fan 240XP-CUb System Resistance Curve Sample problem, Varying System Resistance Curve

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System Resistance Curve

Sample problem:

If a system is designed to move 1000 cfm at a resistance of 0.25 in. Ps, what static pressure would the fan have to overcome to produce 2000 cfm of airflow?

Solution:

Since static pressure varies as the square of cfm, we can solve for the new Ps (Ps2 ) with the following equation:

Ps2 = Ps1 x ( cfmcfm12 )2 = 0.25 in. x ( 10002000cfmcfm )2 = 1.0 in.

Referring to the figure above, this results in sliding up the system resistance curve from Point A to Point B.

For this system, it is impossible to move 2000 cfm at only 0.25 in. Ps. For any given system, every cfm requires a unique Ps. This series of cfm/Ps points forms a system resistance curve such as the one above. Once the system resistance curve is defined, changing the fan rpm will change the cfm and Ps simultaneously, which results in sliding along the system resistance curve.

Varying System Resistance Curve

Note: Physically changing the system will alter the system resistance. For example, closing a damper from 100% open to only 50% open will add resistance and increase the “steepness” of the system resistance curve. The same effect occurs as filters become dirty. The figure above illustrates this point.

Curve A defines a system that requires 0.5 in. Ps to move 1000 cfm. Curve B requires 0.75 in. Ps to move the same amount of air. This is typical of how a system reacts to increased resistance.

In this section, there are three key points to emphasize:

1.As airflow through a system changes, so does the static pressure.

2.For a steady-state system, operating points must lie on the curve defining that system’s cfm/Ps characteristics.

3.As the system’s resistive elements change, the steepness of the system resistance curve changes.

Combining Fan and System Dynamics

The previous two sections introduced fan curves and system resistance curves. This section will show how these relate to each other to provide an understanding of the way the fan-system operates as a complete entity.

Remember that a fan curve is the series of points at which the fan can operate at a constant rpm. Likewise, a system resistance curve is the series of points at which the system can operate. The operating point (cfm, Ps) for the fan-system combination is where these these two curves intersect.

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Contents Fan Selection Application-Based Selection Performance Theory Selecting the Right FAN for the JOB Table of Contents Belt Drive Direct Drive Suffix Motor hp TermsFan rpm Belt Drive Selection CFMDirect Drive Selection AccessoriesMotor Information Belt Drive Only Model RSF and BCF Selection CFM Static Pressure / Capacity ModelCompetitor Model Number Deciphering Hints AcmePropeller vs. Centrifugal Wheel Basic OverviewFan Model Direct Drive vs Belt DriveCommercial Kitchen Ventilation Supply Fan SizingExhaust Nfpa ConsiderationsGeneral Commercial Ventilation Typical Commercial Ventilation Installations Model RBU General Industrial VentilationModel SB Model RB Model RbumoModel SWB High Static Pressure VentilationModel BSQ Determining CFM cfm Suggested Air Changes for Proper VentilationDetermining Static Pressure Ps DuctworkPreliminary Selections Stability ConsiderationsSuggested Limits for Room Loudness DBAInstallation Fan Dynamics Fan Curve Varying Fan CurveSystem Resistance Curve Sample problem Varying System Resistance CurveOperating Point Varying Operating PointsFan Laws

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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