Fan Law 3 addresses the relationship between airflow (CFM) and the horsepower required to achieve it, emphasizing that horsepower needs increase cubically with increases in CFM. This law highlights the importance of considering energy efficiency and motor capacity when planning changes to fan operation, ensuring that systems are not only effective but also sustainable.
Fan Law 3: Horsepower and CFM Relationship
Law: Horsepower required by the fan changes with the cube of CFM (or RPM).
Formula: HP2 = HP1 × (CFM2 ÷ CFM1)³
Practical Meaning: A slight increase in airflow requires a disproportionately larger increase in horsepower. A 10% increase in CFM results in a 33% increase in horsepower.
Field Application: Before increasing airflow, it's essential to ensure the motor can handle the increased load. An increase from 1000 CFM to 1200 CFM significantly increases the horsepower required, potentially overloading the motor.
In practice, Fan Law 3 is a critical guideline for managing the energy consumption and operational costs of HVAC systems. It cautions professionals to consider the substantial increase in power requirements when increasing airflow, thereby preventing motor overload and promoting the longevity of system components. This law is a cornerstone for sustainable HVAC management, ensuring that systems are powerful and practical in their energy use.
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