Blower Fan Performance Curve

Ratings found in centrifugal fan performance tables and curves are based on standard air scfm.

Box fan outdoor. The performance of a centrifugal fan axial fan or blower is often given as a series of pressure efficiency and shaft power characteristic curves plotted against air flow rate for specified values of speed air density and fan dimensions. The fans actual operating point on this curve will depend on the system resistance. Fans have a specific ratio of up to 111 blowers from 111 to 120 and compressors have more than 120.

The fan curve is a graphic presentation of fan performance. When your system curve intersects the cfm vs sp curve this is indicative of that fans performance when applied to your actual system. Fans operating point at a is flow q1 against pressure p1.

In general a blower can produce a higher pressure ratio. A blower curve shows the characteristics of the blower through its entire operating range. This is the bhp that the fan will require to produce the desired cfm and pressure at the given fan speed.

To review in this example the desired performance is 8000 cfm at 8 inches wg sp. It is one of the most useful tools available during the fan selection process. Draw a vertical line up from the point where the system curve intersects the cfm vs sp curve to where it crosses the cfm vs bhp curve for the fan.

The fan performance chart shows performance curves for a series of fan speeds at fan speed n1 the fan will operate along the n1 performance curve as shown in figure 57. The system curve looks kind of like the reverse of the cfm vs sp curve. Per the american society of mechanical engineers asme the specific ratio the ratio of the discharge pressure over the suction pressure is used for defining fans blowers and compressors.

A fan curve is a way to graphically understand the performance of a particular fan. What is a blower performance curve. 0 01 02 03 04 05 06 07 02 4 6 8 10 12 14 16 18 cfm x 100 pressure 0 005 01 015 02 025 03 brake horse power typical fan performance curve.

What is a fan curve. The performance curve of a roots blower a type of positive displacement blower equipped with 2 or 3 lobes popularized by roots now part of howden roots is a key design data for properly chosing a blower for a new line or for assessing or troubleshooting an existing line. However operating a blower above its maximum pressure continuously will severely limit its lifespan.

While multi rating tables are convenient see page 12 performance curves offer additional information such as how much reserve pressure head exists between the design pressure and the peak static pressure the maximum power the fan might draw and the efficiency of operation. A fan performance curve is essentially a graphical representation of exactly what a fan can. For this reason manufacturers include the pressure limit where a blower can safely operate for long periods of time.