Using a fan below its minimum rated flow-rate.
Using a fan below its minimum rated flow-rate.
(OP)
Hi all,
We are are designing a test chamber for an HVAC system that is capable of operating in a volume flow range of 10 lt/s to 2000 lt/s. The plug fan that we have selected for our pressure head can only go to down to 10% of its maximum deliverable flow rate due to the design requirements of the motor electronic.
We had a discussion with our senior engineer and he came up with using holes in the fan support plate to cause the air to flow in the reverse direction. This way even though the fan will be operating at 10% or more of its maximum flow rate, the actual flow rate through the system will be quite less. It is a closed system so we cannot let the air to leave the chamber. I have attached an diagram to illustrate what I mean.
I have: Fan performance curves and system curve for system without any holes/perforations in the fan plate.
I need: The size of the perforations that will give us the required flow rate by causing reverse flow through them.
We are are designing a test chamber for an HVAC system that is capable of operating in a volume flow range of 10 lt/s to 2000 lt/s. The plug fan that we have selected for our pressure head can only go to down to 10% of its maximum deliverable flow rate due to the design requirements of the motor electronic.
We had a discussion with our senior engineer and he came up with using holes in the fan support plate to cause the air to flow in the reverse direction. This way even though the fan will be operating at 10% or more of its maximum flow rate, the actual flow rate through the system will be quite less. It is a closed system so we cannot let the air to leave the chamber. I have attached an diagram to illustrate what I mean.
I have: Fan performance curves and system curve for system without any holes/perforations in the fan plate.
I need: The size of the perforations that will give us the required flow rate by causing reverse flow through them.





RE: Using a fan below its minimum rated flow-rate.
Going for a 200:1 turndown with a single unit is just asking for trouble though...
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RE: Using a fan below its minimum rated flow-rate.
RE: Using a fan below its minimum rated flow-rate.
Peace,
Abe
RE: Using a fan below its minimum rated flow-rate.
From your description, the pressure upstream of the test device will vary depending on the flow through it, so obviously you cannot base the setting of this damper based on pressure - do you have a flow meter somewhere in the path of this air stream ?
RE: Using a fan below its minimum rated flow-rate.
RE: Using a fan below its minimum rated flow-rate.
Else consider relocating this flow device to (a) upstream of this fan - some where near where you've got the upstream arrow or (b) on the air exit from this test device - near the downstream arrow. (a) may be better, since it is not prone to errors in flow readout resulting from temp drop through the test device which will be the case with location (b).