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Fig. 32-8 Family of Fan Performance Curves. Source: Babcock and Wilcox efficiency. Figure 32-7 shows a typical base performance test curve that relates several performance characteristics to airflow rate. For a given fan, performance values can be changed by varying the operating speed (rpm) to yield a family of curves. Figure 32-8 shows a family of fan performance curves over an operating range of 860 to 1,160 rpm. The curves show static pressure and shaft hp versus flow output.

Fan capacity must often be controlled to meet varying system airflow requirements. The impact on performance of alternative control methods can be determined using the fan laws. Following is a discussion of various methods of control, along with an illustration of power requirement versus flow under varying load conditions.

• Outlet damper control is a throttling method that decreases air volume at constant speed by adding some resistance to the system. The maximum turndown rate is determined by the leakage rate at the fully closed position, although, in some cases, fan operation may be unstable under very low load. As shown in Figure

Fig. 32-9 Power Savings Potential with Outlet Damper Control.

Source: Buffalo Forge, The Howden Fan Company

32-9, some power reduction accompanies the capacity reduction as the damper position is changed from wide-open to 3/4 to 1/2 to 1/4 open. Note that this is only true if the basic power characteristic of the fan is of the type shown which has a positive performance slope. In some cases, particularly with axial-flow and propeller fans, the fan's power characteristic will have a negative slope over part of the range and there will be a

Renewable Energy Eco Friendly

Renewable Energy Eco Friendly

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable.

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