ASSESSMENT OF HVAC NOISE IMPACTS FROM HALF MOON BAY CATHOLIC ELEMENTARY SCHOOL

Transcription

1 Ottawa, Ontario, Canada ASSESSMENT OF HVAC NOISE IMPACTS FROM HALF MOON BAY CATHOLIC ELEMENTARY SCHOOL Prepared for Prepared by Hugh Williamson Associates Inc. Postal Address: PO Box 74056, RPO Beechwood, Ottawa, Ontario, K1M 2H9, Canada Phone/Fax: , Web:

2 ASSESSMENT OF HVAC NOISE IMPACTS FROM HALF MOON BAY CATHOLIC ELEMENTARY SCHOOL OTTAWA CATHOLC SHOOL BOARD Table of Contents Section Table of Contents Page i 1.0 Introduction Points of Reception and Sound Level Limits Noise Sources Noise Modelling Mitigation Conclusion 9 References 10 P a g e i

3 Appendix 1 Figures Figure A1.1: Figure A1.2: Figure A1.3: Figure A1.4: Figure A1.5: Figure A1.6: Figure A1.7: Area Plan showing School and Surrounding Lots School Roof Plan showing significant HVAC Equipment Locations Acoustic Model of Half Moon Bay School and Surrounds Worst Case Points of Reception Selected for Analysis Noise Contours, Day (7 a.m. to 7 p.m.) Noise Contours, Evening (7 p.m. to 11 p.m.) Noise Contours, Night (11 p.m. to 7 a. m.) Resume: Dr. Hugh Williamson P a g e ii

4 ASSESSMENT OF HVAC NOISE IMPACTS FROM HALF MOON BAY CATHOLIC ELEMENTARY SCHOOL 1.0 Introduction The, OCSB, intends to build Half Moon Bay Catholic Elementary School, the School, on the southwest corner of the intersection of River Mist Road and des Soldats-Riendau Street, in the southern part of Ottawa, Barrhaven Ward, see Figure A1.1. As part of the approval process, the City of Ottawa has requested a study of noise impacts on surrounding residences from school HVAC equipment. This report addresses these impacts and has been prepared by Hugh Williamson Associates on behalf of OCSB. Noise impacts from the proposed HVAC equipment on the School have been assessed according to City of Ottawa Environmental Noise Control Guidelines 1, ENCG. For assessing stationary noise sources, such as HVAC equipment, the ENCG refer to guidelines from the Ontario Ministry of Environment and Climate Change, MOECC. The current MOECC noise guideline is NPC-300, hence, this assessment has been carried out according to both the City of Ottawa and MOECC noise guidelines. The noise assessment methodology is summarised below. Identify the closest points of reception for proposed residences in vicinity of the School. Determine the sound level limits at these points of reception according to City of Ottawa and MOECC guidelines 1, 2. Identify and quantify the significant HVAC noise sources at the school. These consist of roof top air conditioning units (RTU s) and exhaust fans. Calculate sound levels at the points of reception based. The noise modelling technique 3 used is one approved by the MOECC. P a g e 1

5 Compare calculated sound levels at points of reception to the sound level limits as established by the guidelines. If needed, recommend noise mitigation measures to ensure that the noise guidelines are met. Terminology Sound: Sound is an oscillation of air pressure which is detected by the ear. Sound pressure is the magnitude of the oscillations in pressure. Decibels: A measure of sound levels. Sound levels are expressed in units of decibels, db. Sound level is 10 times the logarithm of the squared ratio of the sound pressure over a reference pressure, 20 x 10-6 Pascals. Decibels are also used as a measure of the sound power of a noise source, in which case the reference sound power is Watts. Equivalent sound level, Leq, is the energy based average sound level over a period of time. Leq 1-hour is the energy based average sound level over a 1-hour period. A-weighting is an internationally standardized frequency weighting which is applied to sound measurements and approximates the variation in sensitivity of human hearing with frequency (pitch). For sound levels where A-weighting has been applied, the decibel units are written as dba. Noise is unwanted sound. Point of Reception: A point on the premises of a person where sound from other than those premises is received. 2.0 Points of Reception and Sound Level Limits As shown in Figures A1.1 the School is located in a residential area. Directions refer to Site North as defined in Figure A1.1. Points of Reception To the north of the School, across des Soldats-Riendeau Street, two storey houses are currently under construction. To the west of the School, City plans as shown in Figure A1.1 show residential properties abutting the western property line of the school. P a g e 2

6 To the east of the School, across River Mist Road are some houses plus an open park. To the south of the School, development has yet to be planned. To be conservative it has been assumed that two storey residential development will occur on the land adjacent to the School in this direction. For a residence, the guidelines call for two types of points of reception per property. A plane of window point of reception. For two storey residences, these points of reception are taken to be 4.5 m above ground, the approximate height of 2 nd storey windows. In the acoustic model, these points of reception are designated POR1_W, POR2_W, etc., see Figure A1.4. An outdoor point of reception. These points of reception represent noise impacts on outdoor areas of the property and are taken to be 1.5 m above ground, the approximate height of a standing person s ears. In the acoustic model, these points of reception are designated POR1_O, POR2_O, etc., see Figure A1.4. As shown in Figure A1.4, seven surrounding residences were chosen for detailed analysis. These seven residences represent cases of worst impact compared to nearby residences. That is, other nearby residences will receive the same or less noise impact than the seven residences chosen for detailed analysis. Form a review of site plan elevations, and a visit to the site, it was determined that the land surrounding the School is essentially flat and open. Sound Level Limits Sound level limits as specified in the City of Ottawa and MOECC guidelines 1, 2, depend on the acoustical classification of the area as Class 1, 2, 3 or 4. Class 1 area 'an area with an acoustical environment typical of a major population centre, where the background sound level is dominated by the activities of people, usually road traffic, often referred to as urban hum. Class 2 area 'an area with an acoustical environment that has qualities representative of both Class 1 and Class 3 areas: sound levels characteristic of Class 1 during daytime (07:00 to 19:00 or to 23:00 hours); and, low evening and night background sound level defined by natural environment and infrequent human activity starting as early as 19:00 hours (19:00 or 23:00 to 07:00 hours). Class 3 area 'a rural area with an acoustical environment that is dominated by natural sounds having little or no road traffic, such as: a small community; agricultural area; a rural resort area such as a cottage or resort area; or, a wilderness area. ' P a g e 3

7 Class 4 area an area or specific site that would otherwise be defined as Class 1 or 2 and which: is an area intended for development with new noise sensitive land use(s) that are not yet built; is in proximity to existing, lawfully established stationary source(s); and, has formal confirmation from the land use planning authority with the Class 4 area classification which is determined during the land use planning process. Additionally, areas with existing noise sensitive land use(s) cannot be classified as Class 4 areas. (At this time, Class 4 has not been adopted by the City of Ottawa.) As a residential part of the City of Ottawa, well away from major roads, the land in the vicinity of the School is a Class 2 Area according to the guidelines 1, 2. The applicable outdoor sound limit at a point of reception, expressed in terms of the 1-hour equivalent sound level, L eq, is the higher of the applicable exclusion limit value given in Tables 1 and 2, or the background sound level for that point of reception. Background sound level means the sound level that is present in the environment, produced by noise sources other than the source under assessment, expressed as the 1- hour equivalent sound level, L eq. Road traffic noise is an example of background sound. As this is a relatively quiet residential area, the limits shown in Tables 1 and 2 below are taken as the sound level limits for the purpose of this assessment. Note that the limits vary with time of day: Day, Evening, or Night, and that the limits also vary for outdoor and plane of window points of reception. Table 1: Exclusion Limit Values for One-Hour Equivalent Sound Level (Leq, dba) at Outdoor Points of Reception Time of Day Class 1 Area Class 2 Area Class 3 Area Class 4 Area Day: 07:00 19: Evening: 19:00 23: Table 2: Exclusion Limit Values for One-Hour Equivalent Sound Level (Leq, dba) at Plane of Window of Noise Sensitive Spaces Time of Day Class 1 Area Class 2 Area Class 3 Area Class 4 Area Day: 07:00 19: Evening: 19:00 23: Night: 23:00 07: P a g e 4

8 3.0 Noise Sources Detailed design of Half Moon Bay School has yet to be completed, especially in relation to the selection of HVAC equipment. However, Half Moon Bay School as proposed will be almost identical to the recently completed Avalon Catholic Elementary School on Esprit Drive, Ottawa. Hence, HVAC noise sources for Half Moon Bay School are based on the sizes of the HVAC equipment in Avalon School. Nine roof top HVAC units, RTU s, are proposed for Half Moon Bay School. The cooling capacities of these RTU s, based on data from Avalon School, are given in Tables 3. There will also number of exhaust fans of various sizes. Based on Avalon School, only three of these fans will have capacities of greater than 1000 cubic feet per minute, cfm, and only fans with these capacities are considered to be significant noise sources in this study. Tables 3 and 4 lists these exhaust fans, F-1, F-2, etc. The locations of the RTU s and exhaust fans on the roof to Half Moon Bay School are shown in Figure A1.2. Most of Half Moon Bay School is essentially single storey with a height of the roof parapet at 4.8 m for most of the building. The gymnasium has a higher roof, parapet 7.6 m, and, there is a tower near the main school entrance with parapet height 10.1 m. The heights of noise sources, above the main roof parapet, see Table 3, have been based on sizes of equipment at Avalon School. Maximum sound power levels for the RTU s and fans are listed in Tables 3 and 4. Noise from the RTU s was found to be a critical factor in achieving noise compliance at nearby points of reception. The maximum sound powers for the RTU s in Tables 3 and 4 are based on data for AAON RN RTU s reduced by 3 db in order to achieve compliance. It was found that other potential suppliers of RTU s of the needed cooling capacities could meet the maximum sound power levels given in Tables 3 and 4. P a g e 5

9 Table 3: Outdoor Sound Power and Heights of HVAC Noise Sources Name and Capacity Height a Maximum Outdoor Sound Power b PWL (m) (dba) RTU-1, 6.4 Tons RTU-2, 15.1 Tons RTU-3, 13.3 Tons RTU-4, 13.6 Tons RTU-5, 7 Tons RTU-6, 12.6 Tons RTU-7, 8.2 Tons RTU-8, 11.9 Tons RTU-9, 14.3 Tons F-1, 1125 cfm F-2, 1075 cfm F-3, 1175 cfm Notes: a. Height above the parapet of lower roof. b. Outdoor Sound Power data for the RTU s (in dba units re Watts) are based on manufacturer s data for AAON RN units which were used at Avalon School, adjusted down by 3 db. Table 4: Maximum Outdoor Sound Power of HVAC Equipment by Octave Bands Name Octave Spectrum (Hz/dB a ) A RTU's 1, 5 & 7 b RTU's 2, 3, 4, 6, 8, & 9 b F-1, 1125 cfm F-2, 1075 cfm F-3, 1175 cfm Notes: a. Octave band sound power levels in db or dba units re Watts b. Outdoor Sound Power data for the RTU s are based on manufacturer s data for AAON RN units which were used at Avalon School, adjusted down by 3 db. P a g e 6

10 The following assumptions have been made in order to assess worst case impacts on the surrounding points of reception from the HVAC equipment. RTU s operate: o 100 % of the time during the day, 7 a.m. to 7 p.m. o 50% of the time during the evening, 7 p.m. to 11 p.m. o 33% of the time during the night, 11 p.m. to 7 a.m. Exhaust fans operate: o 100 % of the time during the day, 7 a.m. to 7 p.m. o 50% of the time during the evening, 7 p.m. to 11 p.m. o Fans do not operate during the night, 11 p.m. to 7 a.m. These assumptions are intended to represent a period of maximum cooling load for the school during the warmest months. P a g e 7

11 4.0 Noise Modelling Sound levels have been calculated using a sound propagation methodology 3 which is favoured by the City of Ottawa and MOECC. The school, noise sources and surrounding area have been modelled using the software Cadna-A, version , which is based on the ISO methodology 3. The methodology provides a conservative (i.e. high) estimate of the noise level at a receptor taking into account adverse wind and meteorological conditions. The estimation method includes the following: Distance attenuation is based on spherical spreading. Atmospheric attenuation. Ground attenuations, as appropriate. Barrier attenuation, as appropriate. Figure A1.3 shows an isometric view of the acoustic model, including the noise sources, surrounding residences, variations in roof heights and locations of noise sources. The results of noise modelling, with the mitigation set out in 5.0, are shown graphically using sound level contours in Figures A1.5, A1.6 and A1.7 for day, evening and night periods. Calculated sound levels at each of the points of reception are given in Table 5. Table 5: Results and Compliance Table (with mitigation as set out in 5.0) Point of Calculated Limit OK* Calculated Limit OK* Calculated Limit OK* Reception Day Day Evening Evening Night Night (dba) (dba) (dba) (dba) (dba) (dba) POR1_W yes yes yes POR1_O yes yes 42 - n.a. POR2_W yes yes yes POR2_O yes yes n.a. POR3_W yes yes yes POR3_O yes yes n.a. POR4_W yes yes yes POR4_O yes yes n.a. POR5_W yes yes yes POR5_O yes yes n.a. POR6_W yes yes yes POR6_O yes yes n.a. POR7_W yes yes yes POR7_O yes yes n.a. * OK, yes when in compliance, n.a. when not applicable P a g e 8

12 5.0 Mitigation It was found that the sound power of the roof top air conditioning units, RTU s, was critical to achieving compliance. To achieve compliance, the sound powers of the RTU s must not exceed the levels given in Table 6. Table 6: Noise Mitigation, Maximum Outdoor Sound Power of RTU s Name Octave Spectrum (Hz/dB a ) A RTU's 1, 5 & RTU's 2, 3, 4, 6, 8, & Note: a. Octave band sound power levels in db or dba units re Watts 6.0 Conclusions A noise impact assessment has been conducted in relation to HVAC equipment on the proposed using the City of Ottawa Environmental Noise Control Guidelines 1 and the relevant MOECC noise guideline NPC Noise impacts are considered at residences surrounding the proposed school. It has been found that compliance with noise guidelines will be achieved provided the mitigation measures set out in section 5.0 (limitations to the sound powers of roof top air conditioning units) are implemented. Hugh Williamson, Ph.D., P.Eng. Member, Canadian Acoustical Society Member, American Society of Heating, Ventilating, Air-conditioning Engineers, ASHRAE P a g e 9

13 References 1. City of Ottawa, Environmental Noise Control Guidelines, Ministry of Environment and Climate Change, Document NPC-300, Environmental Noise Guideline, Stationary and Transportation Sources Approval and Planning, August International Standards Organization, Acoustics - Attenuation of Sound during Propagation Outdoors, Part 2: General Method of Calculation, ISO : 1996(E). P a g e 10

14 Appendix 1 Figures Contents: Figure A1.1: Figure A1.2: Figure A1.3: Figure A1.4: Figure A1.5: Figure A1.6: Figure A1.7: Area Plan showing School and Surrounding Lots School Roof Plan showing significant HVAC Equipment Locations Acoustic Model of Half Moon Bay School and Surrounds Worst Case Points of Reception Selected for Analysis Noise Contours, Day (7 a.m. to 7 p.m.) Noise Contours, Evening (7 p.m. to 11 p.m.) Noise Contours, Night (11 p.m. to 7 a. m.) P a g e 11

15 Assessment of Half Moon Bay School Figure A1.1: Area Plan showing School and Surrounding Lots Not Subdivided Assumed Residential Des Soldats-Riendeau Street AHU-1 AHU-2 F-1 AHU-9 F-2 AHU-7 AHU-6 AHU-8 F-3 AHU-5 AHU-3 AHU-4 River Mist Road Park Site North P a g e 12

16 Assessment of Half Moon Bay School Figure A1.2: School Roof Plan showing significant HVAC Equipment Locations Noise Sources (+) RTU- 1 to 9: Roof Top A/C Units F- 1 to 3: Exhaust fans (>1000 cfm) Gymnasium (high roof) RTU-2 RTU-1 F-1 RTU-9 F-2 RTU-7 RTU-6 RTU-8 F-3 RTU-5 RTU-3 RTU-4 Tower (high roof) Site North P a g e 13

17 Half Moon Bay School Figure A1.3: Acoustic Model of Half Moon Bay School and Surrounds Half Moon Bay School Roof Top HVAC Units Nearby Houses River Mist Road Isometric view from southeast P a g e 14

18 Assessment of Half Moon Bay School Figure A1.4: Worst Case Points of Reception Selected for Analysis POR4_W POR5_W POR5_O POR4_O Des Soldats-Riendeau Street POR6_W POR6_O RTU-1 RTU-2 POR3_O POR3_W F-1 RTU-9 F-2 RTU-7 RTU-6 RTU-8 F-3 RTU-5 RTU-3 POR2_W RTU-4 POR2_O POR7_W River Mist Road POR7_O POR1_O POR = Point of Reception PORx_W: plane of window POR, height 4.5 m PORx_O: Outdoor POR, height 1.5 m POR1_W Site North P a g e 15

19 Assessment of Half Moon Bay School Figure A1.5: Noise Contours, Day (7 a.m. to 7 p.m.) (4.5 m above ground, 2 nd storey window height) POR4_W POR5_W POR5_O POR4_O POR6_W POR6_O RTU-1 RTU-2 POR3_O POR3_W F-1 RTU-9 F-2 RTU-7 RTU-6 RTU-8 F-3 RTU-5 RTU-3 POR2_W RTU-4 POR2_O POR7_W POR7_O POR1_O POR1_W > 35.0 db > 40.0 db > 45.0 db > 50.0 db > 55.0 db > 60.0 db > 65.0 db > 70.0 db > 75.0 db > 80.0 db > 85.0 db P a g e 16

20 Assessment of Half Moon Bay School Figure A1.6: Noise Contours, Evening (7 p.m. to 11 p.m.) (4.5 m above ground, 2 nd storey window height) POR4_W POR5_W POR5_O POR4_O POR6_W POR6_O RTU-1 RTU-2 POR3_O POR3_W F-1 RTU-9 F-2 RTU-7 RTU-6 RTU-8 F-3 RTU-5 RTU-3 POR2_W RTU-4 POR2_O POR7_W POR7_O POR1_O POR1_W > 35.0 db > 40.0 db > 45.0 db > 50.0 db > 55.0 db > 60.0 db > 65.0 db > 70.0 db > 75.0 db > 80.0 db > 85.0 db P a g e 17

21 Assessment of Half Moon Bay School Figure A1.7: Noise Contours, Night (11 p.m. to 7 a. m.) (4.5 m above ground, 2 nd storey window height) POR4_W POR5_W POR5_O POR4_O POR6_W POR6_O RTU-1 RTU-2 POR3_O POR3_W F-1 RTU-9 F-2 RTU-7 RTU-6 RTU-8 F-3 RTU-5 RTU-3 POR2_W RTU-4 POR2_O POR7_W POR7_O POR1_O POR1_W > 35.0 db > 40.0 db > 45.0 db > 50.0 db > 55.0 db > 60.0 db > 65.0 db > 70.0 db > 75.0 db > 80.0 db > 85.0 db P a g e 18

22 Ottawa, Ontario, Canada RESUMÉ: Dr. HUGH WILLIAMSON, P.Eng. QUALIFICATIONS: Ph.D. Mechanical Engineering, University of New South Wales, 1972 B.Sc. Mechanical Engineering, (with Distinction), University of Alberta, 1967 Member, Professional Engineers, Ontario Member, Canadian Acoustical Association Member, American Society of Heating, Refrigeration and Air-conditioning Engineers KEY COMPETENCIES: Environmental noise and vibration assessments, Environmental Compliance Approval (ECA). Noise assessment for land use planning Architectural and building acoustics, acoustics of office spaces, meeting rooms, auditoriums and studios, noise and vibration control of building mechanical services. Industrial noise and vibration assessment and control. Transportation noise and vibration. PROFESSIONAL EXPERIENCE: Hugh Williamson is a professional engineer with many years of experience in the measurement, analysis and control of noise and vibration. Hugh Williamson Associates was incorporated in 1997 and provides consulting services in architectural, building, industrial, transportation and environmental acoustics and vibration. Clients include architects, engineering firms, industrial firms and government departments. Prior to establishing Hugh Williamson Associates, his career included extensive periods in industry as well as university level research and teaching. He is a former Director of the Acoustics and Vibration Unit at the Australian Defence Force Academy. He has published over 50 engineering and scientific papers and has been an invited speaker on noise and vibration at national and international conferences. He has more than 20 years of experience as a consultant. CLIENT LIST: Hugh Williamson Associates provides consulting services to large and small clients including: National Research Council, National Capital Commission, J. L. Richards & Associates, Barry Padolsky Associates, HOK Urbana Architects, Genivar, Nasittuq Corporation, PWGSC, R. W. Tomlinson, Geo. Tackaberry Construction and Miller Paving. Postal Address: PO Box 74056, RPO Beechwood, Ottawa, Ontario, K1M 2H9, Canada Phone/Fax: (613) , hugh@hwacoustics.ca,