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

In summary, the conversation discussed the selection process for fans/blowers in ventilation systems, specifically in terms of CFM, duct and fitting sizes, and pressure loss/gain. The issue of determining the pressure gain from the fan was also brought up, with the suggestion to apply impulse conservation and Newton's action and reaction law to calculate it. However, it was noted that this method may require back calculating after determining the loss from the supply ducting. Overall, there is a lack of concrete data and graphs for pressure values in relation to air capacity for each fan.
  • #1
rah32d
1
0
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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  • #2
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.
 

What is the purpose of selecting fans/blowers for ventilation systems?

The purpose of selecting fans/blowers for ventilation systems is to ensure that the system is properly designed and capable of providing adequate air flow and pressure to effectively ventilate the designated space. This includes calculating the pressure gain and loss throughout the system to determine the appropriate fan/blower size and power requirements.

What factors should be considered when selecting fans/blowers for ventilation systems?

When selecting fans/blowers for ventilation systems, factors such as the size and layout of the space, the desired air flow rate, the type of ventilation system (e.g. ducted or non-ducted), and any obstructions or resistance in the air flow path should be taken into account. Climate conditions and any specific ventilation requirements for the space (e.g. air quality standards) should also be considered.

How is pressure gain/loss calculated in a ventilation system?

Pressure gain/loss in a ventilation system is calculated by considering the resistance to air flow at various points in the system, such as through ducts, filters, and other components. Each component will have a pressure drop associated with it, and these values are added together to determine the total pressure gain/loss throughout the system. This calculation is typically performed using the Bernoulli equation or other specialized software.

What is the ideal fan/blower size for a ventilation system?

The ideal fan/blower size for a ventilation system will depend on the specific requirements and constraints of the system, as well as the calculations for pressure gain/loss. It is important to choose a fan/blower that is capable of providing the necessary air flow and pressure to meet the desired ventilation goals, while also considering energy efficiency and noise levels.

Are there any safety considerations when selecting fans/blowers for ventilation systems?

Yes, safety considerations should be taken into account when selecting fans/blowers for ventilation systems. This includes ensuring that the fan/blower is properly installed and secured to prevent any hazards, and that it is suitable for the designated environment (e.g. explosion-proof fans for potentially hazardous areas). Regular maintenance and monitoring should also be performed to ensure safe operation of the ventilation system.

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