Renovate HVAC Building 2007

Question: Revised Section 01 11 00 paragraph 1.4.b states, "The Noise Criterion (NC) for the project area within the building is 35db. All new VAV and air side units shall be attenuated such that all new and interdicted ductwork and the balanced air flow shall meet the NC." Does the Government require maximum 35dB or NC35 for Room 119C? In our opinion, limiting the Contractor to straight 35dB across all frequencies is not feasible for this project. The following highlights the difference between "dB" levels and "NC" ratings: Noise Criterion (NC) were established in the U.S. for rating indoor noise like noise from air-conditioning equipment and similar. In Europe it is common to use the Noise Rating Curve - NR <http://www.engineeringtoolbox.com/nr-noise-rating-d_60.html> . The method consists of a set of criteria curves ranging 63 to 8000 Hz and a tangency rating procedure. The criteria curves defines the limits of octave band spectra that must not be exceeded to meet the occupants acceptance in the actual spaces. The NC rating can be determined by plotting the octave band levels for a given noise spectrum - the NC curves. The noise spectrum is specified as having a NC rating same as the lowest NC curve which is not exceeded by the spectrum. Answer: Noise level is acceptable 35db to 40db or acceptable levels as per office building industry standards.