How Altitude Effects Blower Efficiency and Sizing

One of the most critical factors in blower selection is the altitude of the installation site. As elevation increases, air density decreases. While this change may not be noticeable to humans, it has a significant impact on blower performance. Reduced air density alters the blower’s performance curve, meaning adjustments must be made to ensure the unit can still deliver the required pressure and airflow under actual operating conditions.

Understanding Altitude: What if a blower is running at Extreme Elevation.

At higher elevations, typically anything above 250 ft, the blower performance curve begins to shift due to changes in air density. As air density decreases, the blower requires less effort to maintain a given rotational speed. However, this comes with a drawback: although the volumetric airflow (CFM) remains constant, the mass flow rate decreases because less air mass is being moved per unit volume compared to sea level conditions. Additionally, the pressure capability of the blower is affected by this reduction in density. This relationship can be expressed using the following equation.

In equation 1 the P is pressure and ρ is density. So as  becomes less this causes  to become less. So in order to maintain the pressure that you would want at sea level (sea) you would have to lower the flowrate so the pressure can increase to the pressure you wanted.

Best Practices for High Elevation Operation

The following are some of the best practices to do when operating a blower at high altitudes. 

• Oversize the blower: altitude causes the air to be thinner and therefore you will need more airflow for higher pressure.
• Derate motors: cooling is less effective in the thin air.
• Plan for cooling: make sure there is sufficient air flow over the motor.
• Account for temperature: Hot ambient air at altitude further reduces density compounding performance loss.
  

Conclusion

As air density decreases with altitude, it is essential to account for changes in blower performance to ensure reliable operation. At Optimal, we evaluate each blower selection against the customer’s specific requirements, including the elevation of their installation site, to confirm that the equipment will perform as intended. This ensures that every customer receives the best blower for their application and operating environment. Contact us today to discuss your needs, and we’ll help you select the right blower solution for your altitude and application.