UV Noise

[UDP10]

About two years ago, our office installed two unit ventilators in a large conference room of a school. The unit vents replaced old heating only unit vents but were increased in size to accomodate new ventilation requirements and add cooling. We warned the owner of the potential noise issue, wrote letters, even took them to another site to listen some units... of course, now it's too loud.

So, to correct the problem, we put in some extra thick filters (more pd, less airflow), remove the pencil proof grates, and put a vsd on the motor. The VSD worked like a charm, except when the motor drops below low speed, it hums likes crazy. It's not at one frequency, it's at all of them.
My next step, I guess, is to replace the motors with a larger motor or three phase motor that could accomodate the drive...

I'm running out of ideas. Has anyone encountered any fixes for loud unit vents (other than not putting fans in the space?)

 

[johnp]

Hi UDP10,
I would suggest you check your noise level at different speeds. If you are ventilating, why would you want to drop below low speed.

If you really want to have some guidance, talk to a noise control engineer. There are a number of things which could be done (it shouldn't cost all that much for a site inspection, and some verbal advice to help you along). Where is the noise coming from? Can you isolate the dominant source, and block the sound level vibrations from that? What frequencies are you trying to cut down?

Regards - Sgt John.Rz

http://www.latviantourists.com.au

Johnp.Rz

http://www.mets.net.au

 

[gerhardl]

Resonance causes? Increase or decrease number of /strengthening /dampening mechanical fasteners in the system?

 

[lilliput1]

Lock out the low speed causing resonance.