“Best Practices” Strategies for HVAC Equipment

1. “Best Practices” Strategies for HVAC Equipment

2. Best PracticesAcoustic Design • Answer the 5 questions • Use 3 to 5 dBA safety factor • Cursory review on every project; in depth review when warranted • Assess site ambient noise levels • Evaluate airborne and structure-borne transmission • System problems require system solutions

3. Best PracticesSpecifications • Design specs preferred over performance specs • Evaluate objective and subjective criteria • Indoor criteria: NC, RC, NCB, RC Mark II • Outdoor criteria: Zoning and ordinance criteria • Place in Division 15 with equipment • Specify single source • Specify turnkey where installation critical • Require submission for approval as “or equal” 10 days before bid date

4. Do’s & Don’ts For: • Outdoor Chillers • Indoor Chillers • Pumps • Cooling Towers • Vibration Isolation • AHU Duct Silencers • Curb Mounted RTU • Room Diffusers • VAV Boxes

5. Best PracticesOutdoor Chillers • Thickened slab for rooftop • Avoid steel coil springs for screw chiller isolation • Attenuate compressor tones with sound blankets • Special consideration for remote evap piping • Evaluate building and property line noise • Optimize aerodynamic performance to achieve total system pressure loss of .25” to .35” w.g. • Use molded neoprene flexes • Flexible conduit power-up

6. Treating Compressor Circuits

7. Treating Air Intakes

8. Treating Condenser Discharge

9. Enclosure Treatments

10. Best Practices Indoor Chillers • Thickened slabs and walls • Locate chiller over columns when above grade • Avoid steel coil springs for screw chiller isolation • Attenuate compressor tones with sound blankets • Use molded neoprene flexes • Flexible conduit power-up

11. Treating Compressor Circuits

12. Enclosure Treatments

14. Best Practices Pumps • Neoprene isolators for slab on grade installations • Inertia bases with steel coil springs for above grade mechanical rooms • Inertia base mass to equal 1 ½ times pump total weight • Support suction and discharge elbows on isolation base • Use molded neoprene flexes • Acoustic treatment rarely needed

16. Best Practices Cooling Towers • Avoid point isolation • Properly position continuous spring rails • Best isolation is restrained spring isolators with dunnage beams • Use molded neoprene flexes • Silencer banks for air inlet attenuation • Acoustical barrier walls for radiated noise

19. Rooftop Curb Mounted AHU Best Practices • Integral vibration/seismic curb • Lock down internal isolation • Add mass inside curbs • Seal (acoustic) duct drops • Dissipate supply breakout noise above deck • Plenum style acoustic curbs

21. In-Curb Treatment

22. Integrated Sound Attenuators

23. External Acoustic Duct Lagging 7 - 9 dB reduction in first 3 octave bands

24. Rooftop Unit Condenser Section Treatments

25. Best Practices VAV Boxes • Lined discharge 10’ to 15’ or XLP silencer • First take-off minimum 4’ from discharge • Minimum 3 diameters straight inlet • Maximum velocity 1000 FPM • External wraps for casing radiated noise

26. Best PracticesVibration Isolation • Follow ASHRAE guidelines for static deflection • Verify deflections in field • Avoid suspended piping in mechanical rooms below noise sensitive space • Use bases to pick up cantilevered equipment loads • Inspect for proper adjustment of isolator lockdowns and snubbers • Follow IBC for seismic anchorage requirements

29. Best Practices AHU Duct Silencers • Avoid high pressure drop models • Evaluate self generated noise • Apply ∆p correction factors • Stay 3 equivalent duct diameters away from fittings • Maximum ∆p 0.3” w.g.

30. Best Practices Ductwork • Limit high aspect ratios • Select duct gauges and add stiffeners to control ductwork “oilcanning” • Follow SMACNA & ASHRAE duct design guidelines to control regenerated noise • Isolate ductwork in mechanical room and at wall & riser penetrations • Locate silencer 2 to 3 equivalent duct diameters from fittings • Consider self generated noise when selecting silencers • Always flex ductwork at equipment connections

31. Room Diffusers Best Practices • Select diffusers for 6 to 8 NC points below room target NC • Long radius 90° flexes to diffusers add 1 to 3 NC points • “Kinked” flexes add 7 to 9 NC points • Balancing dampers should be located three equivalent duct diameters away from diffusers and fittings • Open plenum return grilles may require lined elbow

33. Comments, Questions or Concerns