16.01.2013 Views

Handbook of air conditioning and refrigeration / Shan K

Handbook of air conditioning and refrigeration / Shan K

Handbook of air conditioning and refrigeration / Shan K

SHOW MORE
SHOW LESS

You also want an ePaper? Increase the reach of your titles

YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.

19.28 CHAPTER NINETEEN<br />

Octave b<strong>and</strong> center frequency, Hz<br />

125 250 500 1000 2000 4000<br />

Lrad,r, dB 57.5 53 49.5 45.5 40.5 36.5<br />

Ceiling plenum effect, dB � 5 � 9 � 10 � 12 � 14 � 15<br />

Room effect, dB � 9 � 9.5 � 11 � 11.5 � 12.5 � 13.5<br />

Total sound pressure level, dB 43.5 34.5 28.5 22 14 8<br />

3. For path 2, the discharge sound power level <strong>of</strong> the VAV box changes from the free field L w,dis<br />

to the reverberant field L dis,r <strong>and</strong> the duct-borne fan noise at the terminal unit L w,f. Their combination<br />

is as follows:<br />

Octave b<strong>and</strong> center frequency, Hz<br />

125 250 500 1000 2000 4000<br />

Ldis,r, dB 60 58.5 46 46.5 53.5 51<br />

Fan noise Lw,f,dB 65 63 61 52 46 45<br />

Ldis,r � Lw,f, dB 66.5 64.5 61.5 53.5 54.5 52<br />

The sound pressure level in the occupied zone due to the combination L dis,r � L w,f transmitted along<br />

sound path 2 can be estimated by subtracting the transmission loss <strong>of</strong> the flexible duct wall, the<br />

plenum ceiling effect, <strong>and</strong> the room effect from L dis,r � L w, f.<br />

Octave b<strong>and</strong> center frequency, Hz<br />

125 250 500 1000 2000 4000<br />

Ldis,r � Lw,f, dB 66.5 64.5 61.5 53.5 54.5 52<br />

Flexible, TLout, dB � 8 � 11 � 14 � 17 � 20 � 25<br />

Ceiling-plenum, dB � 5 � 9 � 10 � 12 � 14 � 15<br />

Room effect, dB � 9 � 9.5 � 11 � 11.5 � 12.5 � 13.5<br />

Sound pressure level, dB 44.5 35 26.5 13 8 � 0<br />

4. For path 4, there are two flexible ducts <strong>and</strong> slot diffusers connected to the terminal unit; therefore,<br />

the branch power division is 3 dB. The sound pressure level in the occupied zone due to ductborne<br />

noise transmitted along sound path 4 can be evaluated by subtracting the branch power<br />

division L w,b, the insertion loss <strong>of</strong> the flexible duct IL flex, <strong>and</strong> the room effect from the combination<br />

L dis,r � L w,f .<br />

Octave b<strong>and</strong> center frequency, Hz<br />

125 250 500 1000 2000 4000<br />

Ldis,r � Lw,f, dB 66.5 64.5 61.5 53.5 54.5 52<br />

Lw,b,dB � 3 � 3 � 3 � 3 � 3 � 3<br />

ILflex, dB � 2.5 � 4 � 7 � 11 � 10 � 8<br />

Room effect, dB � 9 � 9.5 � 11 � 11.5 � 12.5 � 13.5<br />

Sound pressure level, dB 52 48 40.5 28 29 27.5<br />

5. For path 5, change the sound power level <strong>of</strong> the slot diffuser from free field L w,s to reverberant<br />

field L s,r.

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!