Inlet vs. Outlet Damper
Inlet vs. Outlet Damper
(OP)
A very general question, but when do you use an inlet damper vs. an outlet damper?
Cheers.
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Inlet vs. Outlet Damper
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Inlet vs. Outlet DamperInlet vs. Outlet Damper(OP)
A very general question, but when do you use an inlet damper vs. an outlet damper?
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RE: Inlet vs. Outlet Damper
If you'd like, you can quote me on this... CB
RE: Inlet vs. Outlet Damper
RE: Inlet vs. Outlet Damper
RE: Inlet vs. Outlet Damper
The most important point is that an inlet damper changes the fan curve. Closing inlet damper brings the fan head-flow curve down, with the shut off head more or less unchanged. Along with this shift, the surge line also gets shifted towards the y-axis, which would mean that the fan can be safely operated with inlet damper at very low flow conditions without causing surging.
In the case of discharge damper, the fan curve remains the same, but the system curve changes. There is no change in surge line, hence risky to operate at very low flows.
The second advantage of an inlet damper control is the lower energy consumption compared to discharge damper.
Regards
Dinesh
RE: Inlet vs. Outlet Damper
I would think that an outlet damper would increase the static pressure so that the operating point on the fan curve would move to reduce flow.
Quark, that looks like a great link. I will read through when I get a chance.
RE: Inlet vs. Outlet Damper
An expensive mistake.
Rob
RE: Inlet vs. Outlet Damper
RE: Inlet vs. Outlet Damper
Outlet damper would increase static pressure at discharge, as you have pointed out. The system curve would move towards y-axis when you close the discharge damper.
Regards
Dinesh
RE: Inlet vs. Outlet Damper
Regardless, I'd recommend a VFD over inlet or discharge dampers for volume control.
RE: Inlet vs. Outlet Damper
I was curious about volume control. We have systems with fans reaching 400hp and prefer to use dampers than vfd's on these units. On smaller fans we use vfds.
RE: Inlet vs. Outlet Damper
When you use either suction or discharge dampers, the fan static head can be matched with the system resistance. The extra head is absorbed at the damper. However, when you use variable speed devices, your fan static head reduces and this will be a problem if your system resistance is predominantly static in nature (for ex. aeration, boiler draught fans etc).
RE: Inlet vs. Outlet Damper
We use these vfd's on boilers. Why are boiler draft fans static? I would expect that the resistance would be proportional to air flow so that if the fan is turned down the resistance drops as well.
I always thought that when vfd's were used the system curve moved toward the y-axis along the same static pressure curve. If this is the case then we should have no issues with turn down - which we do not seem to have.
You wouldn't happen to have any literature on vfd's for fans similar to the link for dampers you provided earlier?
RE: Inlet vs. Outlet Damper
I would still be interested in any links/reports/books about vfd's though.
Cheers.
RE: Inlet vs. Outlet Damper
The performance curve of a fan changes with both inlet dampers and VFDs. You can get better advantage with VFDs if the resistance is purely (or significantly) dynamic.
However, high stack applications require minimum static head for effective purging of the combustion system. If your flow reduction incidentally matches with the reduction in static head then you will not have any problems. Otherwise, you may have to run your fan at higher flowrates (than required) to match system resistance.
This Fans link gives you some idea about fan operation with various controls.