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Proper measurement technique: HVAC Noise?

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John Hiemburg:
Hello all,


I'm having an *issue* with the installer of a few large evap coolers in our building. They were purchased based on the promise "74 dB(A) at 1 meter".


They sound like a jet taking off and have no low setting - so tomorrow I will measure and document.


I've got access to a basic handheld SPL meter that does fast/slow, A/C, average. To get usable, meaningful results, do I need to do anything other than stand 1 meter away and point it at the offending device?


Thanks for your help,

Brian Jojade:
As you are learning, 74 dB(A) at 1 meter is quite loud for general noise.

Steve-White:
If the spec of 74dba is inside the building, near the output duct of the cooler you are not going to be happy.

74dba is in the vicinity of the noise level that a 7500W 420cc gasoline electricity generator has when measured from 10' away on a concrete driveway.

That's way more noise than I would want in any kind of working environment.

Maybe you can put some insulated ducting on them to mute the noise level without a loss in capacity.  A curved labyrinth type of setup.

Dave Garoutte:
Doesn't that stuff usually go on the roof?

John Hiemburg:

--- Quote from: Dave Garoutte on January 06, 2022, 01:02:40 PM ---Doesn't that stuff usually go on the roof?

--- End quote ---


The units themselves are on the roof - ducted inside. The spec does not specify where that noise level is: At the unit or the duct end - I would imagine at the unit itself. Right now we're closer to 80-82 dBa at the end of the duct.


As usual: one gets an education when they post on PSW. Now we'll have to find out the best "fix".


The units as installed don't have a speed control, if we could get them down to 1/2 speed that would be great, the contractor is going to investigate 3rd party motor speed control. As they are 3-phase motors, I am told this is a little more complicated (far outside my experience).

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