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Understanding blowers

   Becuase of the widespread application of air blowers, it becomes very important to have efficient & effective use of blowers.

    Tremendous variety and specification of blower makes it difficult for engineer to understand, evaluate & determine the effectiveness and efficiency of particular blower installed in application.

Here we present you with process of evaluating the performance of existing blower, check for the scope of energy saving and cost reduction.
  1.     COLLECT THE DATA of technical specification of existing blower. Existing blower technical specification can be collected by looking into the blower manual, manufacturers name plate, correspondence with the manufacturer. Collect the information about flow, pressure, rated speed, efficiency, BHP Consumption at operating, trial test certificate & Charecterstic Curve (performance curve).

    Many times during the working, specifications of blower is changed by changing the fan speed or impeller etc. (This may be done becuase of change in process requirement or using the blower for some different application) So it is recommended to actualy carry out complete performance test of the blower and determine the performance based on performace test. This will eliminate any possibilites of mistake arising for misleading / wrong information about particular blower. To understand about blower testing and performance curve read article


Now that you know the rating and operating curve of blower, you need to find out exact operating point. For this you will need static pressure readings at inlet and exit of the blower. (you have to take out tapings for fixing the U-Tube manometer immediately before inlet & after exit of blower). The Static Pressure of blower is equal to sum of inlet & outlet static pressure readings. Take the current readings at the operating point.

Now you can find out the air flow at operating point using
a. Value of Static Pressure & Current at operating point &
b. tracking it for correspoinding flow on Operating Characterstic Curve.

  1. PREPARE LAYOUT DRAWING OF COMPLETE DUCTING SYSTEM showing duct length, duct sizes, elbows (bends), blower position, dampers, filters, equipments, etc.
Using the data of air flow at operating point theoroticaly calculate the total static pressure in the system. It may help to read our article HOW TO CALCULATE STATIC PRESSURE
It may happen that there is 10 to 15% diffrence between actual static pressure drop measured and theoroticaly calculated static pressure drop. This is acceptable (& is normaly adjusted in factor of safety). The exercise give you idea about how the pressure drop is added across the system.

Pressure Drop acting on the blower is the resistance to air flow offered by the restriction in flow area. More the restriction in flow area, more will be the pressure drop. Air blowers are designed to overcome this resistance to air flow (pressure drop) by developing equal amount of Static Pressure in the generated air. More Static pressure means more work done by blower hence more power requirement.

There are two inverse cost implications while designing the blower system
 a. We can reduce the initial cost by reducing duct sizes. This will add pressure drop hence running cost will increase.
 b. We can reduce the running cost of blower by  increasing the duct sizes. This will increase the initial cost of system.

Now that you know the pressure drop of your systems ask yourself following
a. What can you do to reduce the pressure drop of system?
b. Can you increase the duct sizes?
c. What will be the static pressure drop if you increase the duct size?
d. What will be the cost of changing the duct size?
e. What will be cost of renovating/ replacing blower to match new operating condition
f. What wil be energy saving in 5years (decide time period based on duct life)
g. How much days/ months/ years will be require to recover the cost of changing duct.

 Working on above questiongs will give you good idea about the prospects of energy cost reduction in your blower system.


    a. After doing exercises from point 1 to point 4 you will be in position of information about efficiency of your blower at operating point. 

  b. Consult with blower manufacturers about what better efficiency they can provide for the same operating point.

  c. What is the cost of new (more efficient blower)

 d. What is the energy saving from new blower.

 e. Calculate how many years will be required  to recover the cost of new blowers by the energy saving provided by new blower.

 If you are getting good return than you can decide for replacing the blower imediately.

Or you can wait for the existing blower to worn out and then be replaced by more efficient one based on above given information.


  1. Blower flow output capacity is way above the requirement. You are reducing the air flow by using manual butterfly damper. When you control the flow through damper you are adding resistance to reduce the air flow. For air blowers any resistance added to reduce the air flow is loss of energy.
  2. Purpose of ducting is to transport the air from the blower to the actual point of application. Essentialy ducting is transport channel. It is important to keep the ducting path as minimum as possible and avoid bends. (minimum length & minimum no. of bends is desirable). Also the more the cross section area, lesser will be the resistance (pressure drop) to air flow. Many times wrong ducting layout and duct cross section adds to unnecessare resistance to air flow. Energy required to overcome this unnecessary resistance to air flow is loss of energy.
  3. Many times air blowers are not working at there operating points. Lets say A amount of air flow is requied @ X inch of pressure drop. Now Air Blower working is designed for B amount of air flow @ Y inch of pressure drop. This means that blower in operation is not working at its designed operating conditions. As per rough estimate If the change is within 10% there is not much change is efficiency of blower. However any greater shift from designed point of blower will reduce the efficiency of blower tremendously adding to the inefficiency and energy loss.
  4. It is also improtant to know the actual efficiency of air blower. Normaly the data is provided by the blower manufacturer. If the data is not provided that engineer needs to calculate actual efficiency of blower. Compare the efficiency with actual efficiency provided by other blower manufcturers. Sometimes the variation in efficiency gives high savings in energy and it becomes profitable to replace the old inefficient blower with high efficiency blower.

Blower Applications
Blower Selection
Preventive Maintenance
Energy Saving / Cost Reduction