Selecting Fans/Blowers for Ventilation Systems: Calculating Pressure Gain/Loss

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SUMMARY

The discussion focuses on the selection process for fans and blowers in ventilation systems, emphasizing the calculation of pressure gain and loss. Key factors include determining the required CFM based on AC/Hr and room volume, and understanding duct sizing and FPM, typically around 500 ft/min. The challenge lies in accurately calculating the pressure gain from the fan or blower, which is often derived from the pressure loss in ducting. The conversation highlights the necessity of applying impulse conservation and Newton's laws to derive the required pressure gain.

PREREQUISITES
  • Understanding of CFM (Cubic Feet per Minute) calculations
  • Familiarity with duct sizing principles and airflow velocity (FPM)
  • Knowledge of pressure loss calculations for ducting and fittings
  • Basic principles of physics, specifically impulse conservation and Newton's laws
NEXT STEPS
  • Research fan performance curves and how to interpret them for pressure gain calculations
  • Learn about duct design software tools for accurate pressure loss assessments
  • Explore advanced airflow modeling techniques using Computational Fluid Dynamics (CFD)
  • Study the impact of different fan types on system performance and efficiency
USEFUL FOR

Engineers, HVAC professionals, and anyone involved in designing or optimizing ventilation systems will benefit from this discussion.

rah32d
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I looked, but didn't see any post on this topic. This is in regards to the selection process for fans/blowers in ventilation systems, which I am still new to.

From AC/Hr and the room volume we know the required CFM we need to supply to the space, and we can determine the size of ducts and FPM while adhering to basic rules of thumb (i.e. inlet FPM ~ 500 ft/min). My problem arises when calculating the pressure loss/gain through the system. Determining the loss/gain for ducting and fitting is simple enough, but how do we determine the pressure gained from the fan/blower?

From what I've seen there are only vague graphs of pressure values in relation to air capacity, which seem unique to each fan. Is the only way to calculate the required pressure gain from the fan to back calculate after I've determined the loss from the supply ducting?
 
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just apply impulse conservation/ Newton action and reaction law...
from:
force x time_it_is_applied = variation_of_speed x mass_of_accelerated_body
results:
Force = air speed x mass flow of the fan.
 

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