Ex. E <br /> HVAC Distance Error Calculations <br />Factory Measured Data SSA Discrepancy <br />Distance Level Predicted <br />5 feet 72 dBA 72 0 <br />10 68 66 -2 <br />20 63 60 -3 <br />30 61 56.4 -3.6 <br />40 58 54 -4 <br />50 57 52 -5 <br />60 56 50.4 -5.6 <br />le <br />distance <br />-6.3 52.5 -5.5 <br />90 53.3 47 <br />-7.7 46.5 -5.5 <br />180 48.7 41 <br />-8.0 45.5 -5.5 <br />200 48 40 <br />41.6 -5.6 <br /> 44.8 36 -8.8 <br />The SSA formula used is 72 20 Log d/5 based on simple noise model. The actual formula is <br />68 15.4 log d/10 based on actual measurements in the field by the factory. As seen in the table <br />above the discrepancy between factory measured and SSA calculated grows with distance. <br />Beyond some distance the nearfield configuration of the air conditioning units becomes small <br />compared to the distance away and the sound level drop off with distance should convert back to <br />the idealized 6 dB per doubling of distance, which was used by SSA. <br />Using this very conservative adjustment for distances beyond that measured by the factory, SSA <br />is shown to be predicting noise impacts that are at least 5.5 dB under-estimated. <br />(d) Hush Kit Correction <br />To adjust for the excessive loudness of the air conditioning units, SSA proposes that the air <br />The factory does not supply octave noise ratings for the hush kit but it does state that the ELNB <br />uation. In order to <br />allow some <br />hush kit a noise suppressing value of -5 dB. <br />Reference for hush kit: <br />http://www.marvair.com/pdfs/ComPac1_10_06.pdf <br />External Low Noise Blower (ELNB) ComPac® I and ComPac® II A/C A field <br />installed kit that consists of a condenser air hood, a centrifugal blower, controls and a <br />up to 6 <br />compressor jacket to reduce the sound level by dbA of Marvair ComPac air <br />conditioners. Available for models AVP30-60. <br />6 <br />