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HomeMy WebLinkAboutCUP 00-46B; Pacific Bell Harding Street Building Addition; Conditional Use Permit (CUP) (11)6 L..dineering, Planning, Environmental Sciences and Management Services Encinitas, California 92024 Corporate Office: 605 Third Street &ASSOCIATES, INC. Profeasiond %wm for Complex Projects December 4, 2000 760.942.51 47 Fax 760.632.0164 P.N. 2709.01 Mr. Hector Zuniga Joseph Wong Design Architects 2359 4* Avenue, Suite 300 San Diego, CA 92101 PROJECT: Pacifc Bell-Harding $beet RE: Mechanical Equipmimt Noise Study Dear Mr. Zuniga: Dudek & Associates, Inc., has evaluated the future mechanical equipment noise associated with the Pacific Bell-Harding Street Facility located in the City of Carlsbad. In summary, the eastern portion of the project site is currently exposed to a noise level of approximately 70 dB CNEL due to Interstate 5 traffic noise. The project would install various types of outdoor mechanical equipment including three chillers and a radiator fan on the east side of the existing facility. In addition, three new air handlers and a generator would be located within the facility. To mitigate outdoor mechanical equipment noise to meet the City’s noise criteria will require construction of a minimum 14-foot high noise barrier around the mechanical equipment yard. The air handler units and generator set will require installation of sound attenuators within the equipment rooms. Several other measures are also outlined in the mitigation section of this report. With implementation of the noise abatement measures, the noise level associated with the mechanical equipment would be less than the existing noise level at the site. 1 .O BACKGROUND The Pacific Bell-Harding Street Facility is located along Harding Street in the City of Carlsbad. The site is currently utilized by Pacific Bell. Apartments are located north and south of the site. Interstate 5 0-5) is located to the east and Harding Street is located to the west. Beyond Harding Street are ballfields. As part of the project, three 100-ton capacity air-cooled chillers are proposed to located outside near the eastern boundary. The chillers would most likely be York Model YCASOl00. A remote generator radiator fan would also be located outside adjacent to the chillers. The radiator fan would most likely be Young Model HC 366VlOT46XQ-IP/2P. Two air handlers would be located on the north side of the proposed building at the second floor level and a third air handler would be located at the first floor of the existing building. The chillers and air handlers would . .. t Mr. Hector Zuniga December 4, 2000 Page 2 be capable of operating 24 hours, seven days a week. A 1000 kW Caterpillar Model 3508B emergency standby generator would be located on the north side of the proposed building at the first floor level. City of Carlsbad Noise Standards The City's noise ordinance is qualitative and does not specify noise level criteria. However, the City's Noise Element states that noise levels should not exceed a CNEL of 60 dB at residential areas. Assuming the equipment operates continuously for a 24-hour period, a maximum hourly average noise level of 53 dB would result in a CNEL of 60 dB. Therefore, because the equipment would operate continuously, the one-hour average noise level should not exceed 53 dB at the adjacent residential areas. The City has also noted that if the existing noise level exceeds 60 dB CNEL then the project should not exceed the existing noise level. Definitions of acoustical terms used in this study are provided in Attachment 1. All sound levels discussed in this report are A- weighted. 2.0 EXISTING NOISE LEVEL The primary existing noise source at the site is traffic noise along 1-5. A 24-hour noise measurement as well as five short-term (ten-minute) noise measurements were conducted at the site on November 14 and 15,2000. The noise measurements were made using a calibrated Larson-Davis Laboratories Model 700 (S.N. 2132) digital integrating sound level meter. The sound level meter is equipped with a Bruel & Kjaer Type 4176 %-inch pre-polarized condenser microphone with a pre-amplifier. When equipped with this microphone, the sound level meter meets the current American National Standards Institute (ANSI) standard for a ,Type 1 precision sound level meter. Also, a Larson-Davis Laboratories Model 700 Type 2 digital integrating sound level meter was used. The measurement sites were located along the eastern portion of the site where the proposed facility expansion would generally be located. Site A depicted on Figure I is the location of the 24-hour noise measurement. Sites 1-5 are the short-term noise measurement locations. The existing noise level associated with 1-5 ranges from approximately 69 to 72 dB CNEL at the eastern portion of the site adjacent to the proposed expansion area. The existing CNEL is also depicted on Figure I at the adjacent noise measurement locations. 3.0 NOISE ASSESSMENT To determine the noise level associated with the chillers and associated chiller pumps, air i :1 I SOURCE JWDA INC. Pacific Bell - Harding Street Project - Mechanical Equipment Noise Study Noise Measurement location & Existing CNEL Mr. Hector Zuniga December 4, 2000 Page 4 handlers, generator, and outdoor radiator fan, manufacturer's noise level measurement data for the equipment was used. The sound power level generated by the York 100-ton aircooled chiller is 97 dB. The Pace air handlers generate sound power levels ranging from 98 to 11 1 dB. The Young radiator fan would generate a noise level of approximately 65 dB at a distance of 25 feet from the unit. The closest residential property boundary is located approximately 40 feet south from the nearest proposed chiller. Without mitigation measures, the CNEL would be approximately 79 dB at the southern property line, 76 dB at northern property line, and 70 dB at the eastern property line. The calculations assume that two chillers and the radiator fan would operate continuously for a 24-hour period. The third chiller would only be used if one of the other two chillers fails to operate. The existing noise levels at the adjacent residential property boundaries exceed the City's 60 dB CNEL noise criteria due to traffic noise from 1-5. Thus, the applicable noise level limit for the project is the existing noise level. As previously indicated in Figure 1, the existing noise level ranges from approximately 69 to 72 dB CNEL at the site. The noise level associated with the outdoor mechanical equipment would exceed the existing noise level at the northern and southern property lines. The proposed air handlers and emergency generator would be located on the north side of the site, within mechanical equipment rooms, approximately 12 feet north from the closest residential property boundary. Without mitigation measures, the noise level associated with the air handlers as well as with the stand-by generator would exceed 90 dB CNEL. This noise level would exceed the City's noise criteria. The calculations assume that equipment would operate continuously for 24-hours. 4.0 MITIGATION With implementation of the proposed mitigation measures noted below, the project would generate noise levels that are less than the existing noise level at the adjacent property boundaries at the project site (i.e., 69 to 72 dB CNEL). M1. Construct a minimum 14-foot high masonry sound wall around the chillers and radiator fan. An eight-foot high sound wall should be constructed around the chiller pumps as depicted in Figure 2. There should be no gaps or holes in the barriers. M2. The access door to the mechanical equipment yard should be a steel door filled with insulating materials and have full perimeter sound gaskets. , - n a I BUILDINGCOVERAQE 18,313 SITE AREA 38,970 SITE PLAN (EXISTING AND PROPOSED ADDinoN) aus*m mnl SCALE 1’ - 40’ e,’ LEGEND 1 1 1 1 Noise Barrier @ Noire Barrier Height SOURCE JWOA INC. Pacific Bell - Harding Street Project I Mechanical Equipment Noise Study FIGURE Noise Barrier Heights & locations Mr. Hector Zuniga December 4, 2000 Page 6 M3. M4. M5. M6. M7. The air handler in the first floor room should have seven-foot long sound attenuator placed inside the room at the louver opening. The sound attenuator should be Industrial Acoustics Company Model 7s or equivalent. The air handlers in the second floor room should have five-foot long sound attenuators placed inside at the louver openings. The sound attenuators should be Industrial Acoustics Company Model 5s or equivalent. The generator room should have a five-foot long sound attenuator placed inside the room at the louver wall opening. The sound attenuator should be Industrial Acoustics Company Model 5s or equivalent. A super critical grade muffler should be installed on the generator. The muffler should be GT Exhaust Systems Model 201-6100 or equivalent. Install a sound-rated door with a Sound Transmission Class (STC) 45 or greater rating for the exterior access door to the generator room. Install minimum two-inch thick, semi-rigid fiberglass sound absorbing material on at least 50 percent of the generator room interior wall and ceiling surfaces (Owens-Coming Type 703 plain or equivalent). With implementation of the proposed mitigation measures the noise level associated with the mechanical equipment would range up to approximately 62 dB CNEL at the southern property boundary, 66 dB CNEL at the northern property boundary and 56 dB CNEL at the eastern property boundary assuming 24-hour operation of all the equipment. These noise levels are less than the existing noise level at the adjacent property boundaries. This concludes our noise assessment. If you have any questions please call me. Very truly yours, Dudek & Associates, Inc. Mike Komula Acoustician ATTACHMENT 1 DEFINITIONS fi Definition Ambient Noise Level A-Weighted Sound Level Decibel, dB The composite of noise from all sources near and far. The normal or existing level of environmental noise at a given location. The sound pressure level in decibels as measured on a sound level meter using the A-weighted filter network. The A-weighting filter de- emphasizes the very low and very high frequency components of the sound in a manner similar to the frequency response of the human ear and correlates well with subjective reactions to noise. A unit for measuring sound pressure level and is equal to 10 times the logarithm to the base 10 of the ratio of the measured sound pressure squared to a reference pressure, which is 20 micropascals . Equivalent Continuous Sound Level, Le, The sound level corresponding to a steady state sound level containing the same total energy as a varying signal over a given sample period. L is designed to average all of the loud and quiet sound levels occurring over a time period. "! Maximum A-weighted Sound Level, The greatest sound level measured on a sound level (LmJ meter during a designated time interval or event using fast time-averaging and A- weighting.