Equipment Noise Sources

Transcription

1 MECHANICAL AND ELECTRICAL* EQUIPMENT NOISE CONTROL Three elements of concern: source path receiver *the electrical part may be premature, but that s OK Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Grondzik 1 Equipment Noise Sources Chillers Pumps Cooling towers Exhaust fans Air-handling units (the fan) Fan-coil units (the fan) Air distribution components (ductwork, VAV boxes, etc.) Air delivery devices Transformers Emergency generators DWV piping Owner equipment (photocopiers, printers ) Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Grondzik 2 1

2 Equipment Noise Receivers Building visitors (short-term occupants) Building users (long-term occupants) Building residents (overnight occupants) Each group has different schedules, expectations, adaptations remember that noise is a perception Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Grondzik 3 Equipment Noise Paths form structure partitions volume the building is a potential path blogs.utexas.edu/housing/2010/03/25/dr-steven-a-moore-school-of-architecture/ Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Grondzik 4 2

3 Equipment Noise Path Groups Air-borne paths (requiring consideration of noise reduction and transmission loss) Structure-borne paths (requiring specialized isolation/attenuation) Duct-borne paths (requiring specialized attenuation) Vibration (requiring isolation) Typically structure-borne we feel we hear vibration control can be very specialized and will often involve a consultant Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Grondzik 5 Equipment (Noise Source) Locations Source may be external to building For example: cooling tower, transformer easiest condition to mitigate (can use distance, location, barrier) Source may be in a central mechanical room For example: chiller, pumps, fans, emergency generators fair condition to mitigate (can use location, barrier) Sources may be distributed throughout building and may be adjacent to occupied spaces For example: air-handlers, VAV boxes, step-down transformers iffy condition to mitigate (options are often constrained) Sources may be distributed throughout building within occupied spaces For example: diffusers, fan-coil units; unitary AC units terrible condition to mitigate (few, if any, options) Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Grondzik 6 3

4 Air-borne Noise Control Lowest-cost design solution is: smart location of equipment Away; away from critical areas (use distance) Low-cost solution: use spatial buffers Interpose less-acoustically-sensitive spaces between source and receiver (use hierarchy of spaces) Expensive* solution: wise selection of equipment Chose quiet equipment (to reduce sound power) Expensive solution: sound barriers Involves mass and money (to deliver TL) * but, the investment may improve energy efficiency and extend equipment life Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Grondzik 7 Structure-borne Noise Control Lowest cost solution is: smart location of equipment Away from critical areas For example: slab-on-grade versus mid-span on bar joists Expensive* solution: wise selection of equipment Chose quiet and/or less dynamic equipment To reduce sound power; reduce vibration Expensive solution: structural isolation Floating constructions, springs, etc. If impact noise is a particular problem Barriers Not an option in the traditional sense (a barrier is structure ) * but, may improve energy efficiency and extend replacement life Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Grondzik 8 4

5 Floating Floor wood to mitigate impact noise (for example, footsteps) Architectural Acoustics: Mehta, Johnson, Rocafort Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Grondzik 9 Floating Floor concrete Architectural Acoustics: Mehta, Johnson, Rocafort Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Grondzik 10 5

6 Duct-borne Noise Control Good solution is: smart selection of equipment Chose quiet equipment To reduce sound power and thus sound pressure level OK solution: smart location of equipment Away from critical areas But, remember that the pathway is ductwork acting as a transmission channel OK solution: add attenuation Distance, duct splits, elbows, acoustical liner, sound absorbers, active noise cancellation, etc. By inserting acceptable things into the transmission channel Not an option: using barriers You cannot block air flow with a barrier duct-borne noise control is conceptually and practically different from air-borne Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Grondzik 11 Duct-borne Noise Control Context noise sources space of concern AHU noise noise caution! supply return attenuation opportunities the return air path is often acoustically ignored not a good idea Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Grondzik 12 6

7 Duct-borne Noise Control bad layout (little opportunity for attenuation) better layout (more attenuation opportunities) -- sound enters one diffuser and exits another diffuser Architectural Acoustics: Mehta, Johnson, Rocafort Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Grondzik 13 Duct-borne Noise Control low-cost duct silencer glass-fiber pipe insulation segments in a return air duct (probably a desperate retrofit) Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Grondzik 14 7

8 Active Duct-borne Noise Control replaces a section of ductwork electronically produces a valley where there is naturally a crest Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Grondzik 15 Vibration Control Very effective solution: smart location of equipment Away from resonance-prone areas Place at least-flexible structural location (on grade, not mid-span) Effective solution: smart selection of equipment Chose equipment with less propensity for shaking and rattling To reduce source-vibration potential Effective solution: add inertia Attach equipment to a heavy mass To dissipate vibration through mechanical frustration Effective solution: install equipment on vibration isolators Pads, springs, flexible connectors, industrial balloons To interrupt transmission path Not a solution: barriers Because building elements can/will transmit vibration Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Grondzik 16 8

9 Vibration Control Options step-down transformer (in electrical closet) suspended using springs Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Grondzik 17 Vibration Control Options pads: effective for high frequencies springs: effective for low frequencies Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Grondzik 18 9

10 Vibration Control Options air springs (industrial balloons) springs and flexible connectors Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Grondzik 19 Vibration Control Options housekeeping pad inertia block housekeeping pad keeps water away from metal springs inertia block adds mass to an object that wants to move Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Grondzik 20 10

11 Bad Noise Control Specifications yet commonly seen The chiller shall not be noisy noisy is a perception, it cannot be measured by a contractor The fan noise shall not disturb people disturb is an opinion ( I say, you say) The pump will not cause vibration as above (plus if it does, it is too late to do anything) The diffuser will not exceed NC 35 NC is a sound pressure level limit, sound power is produced by a diffuser and the manufacturer should not do the design analysis required to connect cause (power) and effect (pressure) Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Grondzik 21 there are serious legal and ethical implications to punting on specs drawings and specifications are contract documents and must be enforceable Good Noise Control Specifications The chiller sound power level shall not exceed xxx Sound power will be known by the manufacturer (and thus the contractor) the designer will need to do the math to convert desired sound power to sound pressure The fan sound power level shall not exceed xxx as above; it is not appropriate to pass design work off to the contractor (it is in fact unethical) The pump sound power level and vibration spectrum shall not exceed xxx as above The diffuser sound power level shall not exceed xxx as above lack of understanding of acoustics is the biggest impediment to good specs Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Grondzik 22 11