Metering Sound in HVAC
Metering Sound in HVAC
(OP)
I work in a position as a construction inspector (new construction) for the government. Last week I encountered a problem of louder than normal HVAC supply/return registers in several offices. To confirm my suspicions that this noise was above acceptable standards, I purchased a sound meter.
The readings received within these spaces ranged from 68 to 75db. My meter was set at "low range" (35-90db), "A" frequency weighting, for general sound level measurement, and "slow" for normal measurements.
Using these same settings,. one of our people checked a fire alarm and his reading was 83db..
My question:
How is it, that the HVAC noise had such high readings, and yet, it was not near as offensive to the ears as the fire alarm, and this alarm, reading only 10db above the HVAC, was extremely offensive to the ears?
This fact led my supervisor to question my readings. (which I double-checked)
Thank you for any rational explanation that I may give these people..
Tom Fitz
The readings received within these spaces ranged from 68 to 75db. My meter was set at "low range" (35-90db), "A" frequency weighting, for general sound level measurement, and "slow" for normal measurements.
Using these same settings,. one of our people checked a fire alarm and his reading was 83db..
My question:
How is it, that the HVAC noise had such high readings, and yet, it was not near as offensive to the ears as the fire alarm, and this alarm, reading only 10db above the HVAC, was extremely offensive to the ears?
This fact led my supervisor to question my readings. (which I double-checked)
Thank you for any rational explanation that I may give these people..
Tom Fitz





RE: Metering Sound in HVAC
Bear in mind that a fire alarm is usually a highly tonal noise where as HVAC noise is broadband atonal noise. The ear reacts to these sounds in different ways and the brain perceives different levels of loudness even if the energy content of the 2 sounds is the same.
M
RE: Metering Sound in HVAC
(http://www.omega.com/ppt/pptsc.asp?ref=HHSL&Nav=teml12)
here's the info:
Omega Sound Level Meter MODEL#HHSL-1
Standard Applied: IEC 651 Type 2
Portability and Simplicity
AC and DC Output
A and C Frequency Weighting Characteristics
Slow and Fast Time Frequency Weighting Characteristics
Maximum Hold Function
Range: Lo: 35 to 90 dB, Hi: 75 to 130 dB
Under and Over Range Indication
Resolution: 0.1 dB
Accuracy: ±1.5 dB (ref 94 dB@1kHz)
Dynamic Range: 55 dB
Frequency Range: 31.5 to 8000 Hz
Valox Housing to Withstand Accidental Drops
Frequency Weighting: A, C
Time Weighting: Slow & Fast
Impedance: 600 Ohms
Maximum Hold: Decay <1 dB/3min
Electret condenser microphone
It's not the very cheapest,.. but not the very best either.
RE: Metering Sound in HVAC
Having said all of that, 75 dBA would be higher than normal for an office, even worse for a conference room. A normal person would not be very productive in that environment. Then again.... we are talking about a Government office...
:)
Fire alarms are only meant to be used during an emergency. I would want it as loud as possilbe since people have a tendency to keep on working during a fire alarm.
C. Hugh
RE: Metering Sound in HVAC
RE: Metering Sound in HVAC
http://www.hvac-toolbox.com/35.html
RE: Metering Sound in HVAC
However, for HVAC installations, is there any standard type meter that should be used used by QAR's (quality assurance representatives) to assure that the sound level meets required standards?
If so,.. could someone point me in a general direction or recommend a particular meter?
BTW... I'm purchasing this myself since the government is not providing one.. so go easy on me!
This is not a requirement for my job,. but in spite of what some people think of federal employees,.. some of us do want to give the tax payers quality work!
Thanks again for any assistance..
Tom Fitz
RE: Metering Sound in HVAC
Two important points:
First, the decibel measurement system is on a log scale, so 10 dB difference is a huge difference'
Second, as mentioned above a fire alarm is highly tonal, and is intended to be annoying, while HVAC noise is most likely a very broad-band noise akin to white noise.
I'd suggest you get a basic text on noise and acoustics, and that you spend a few hours familiarizing yourself with the basic concepts before you spend a great deal more time measuring sound levels.
Best regards,
Robert
RE: Metering Sound in HVAC
Unfortunately, with 17 buildings going up in one project,..several others in 2 other projects, a lack of personnel to handle the QA duties, and volumes of specs and drawings to read when I do get home,.. it is difficult and frustrating. I only wish there were 48 hours in the day!
For the time being, I was hoping to accurately measure the HVAC noise levels with a meter that would be used in this particular area.. Judging from responses I have received,.. I am under the impression that the sound meter I bought(specs listed above)is not suitable.
TomFitz
RE: Metering Sound in HVAC
IEC179 : Precision Sound Level Meters (1965 and 1973)
ISO R 3745-1977 : Determination of sound power levels of noise sources- Precision methods for anechic and semi-anechoic rooms (Also 3744)
ISO3741-1975 : Determination of sound power levels of noise sources- Precision methods for broadband sources in reverberation rooms
RE: Metering Sound in HVAC
First, the results you got appear awfully high to me. The noise limits used in Norway for HVAC is 40dBA.
Second, you got many answers which are a bit to complicated for your application. Your meter is good enough. Measure the sound level in the middel of the room or close to the place the person is sitting, depending what seems most relevant to you. Wait till the level is stable, like a variation within 1dB, and that's it. Just compare with the value I gave you, 40dBA. Above this, especially above 45dBA, you'll get complain from the users, garanteed.
It's a bit groove measurements, it's just a survey, but it'll tell all you need to know: whether there's a problem or not.
OkdB
RE: Metering Sound in HVAC
M
RE: Metering Sound in HVAC
This area of Acoustical Engineering is away over my head and for the present, just needed to know that I was going in the correct direction and have the correct meter.
And yes indeed,.. the rooms are very noisy. But I was taking my readings from directly beneath the registers..
Steping back to the middle of the room,.. it has reduced the dBA approx. 6 to 8 dBA.. Still, it is very loud.
According to the "NEBB"(National Environmental Balancing Bureau)here in the states, I should be looking for 35 to 50 dBA in general office space.
Thanks again to everyone for your input..
The more I learn,... the more I find out how much I don't know! (and the more I need to study)..
TomFitz