Air Compressor Noise Reduction Solution

Screw compressor operating noise breaks down into three categories: intake aerodynamic noise, discharge pulsation noise, and housing vibration radiated noise.

This judgment will probably offend some suppliers. But the facts are the facts. The principle of an acoustic enclosure is sound. Wrapping the noise source does reduce noise propagation. The problem is the unique nature of air compressors as equipment.

Screw compressors generate enormous heat. Over 80% of input power converts to heat. A 75 kW unit at full load continuously produces over 60 kW of heat. That heating output is like sixty 1,000-watt space heaters running at once. This heat has to be exhausted promptly. Otherwise oil temperature spikes. Unit trips on high-temperature protection.

Acoustic enclosure wraps the unit. Wraps the heat in with it.

Only one way to resolve this conflict: an attenuated ventilation system. Intake gets sound-attenuating louvers. Exhaust gets attenuated bends. Duct cross-section calculated based on heat output. Add exhaust fans for forced ventilation if needed. This system is complex to design, expensive to build. Two to three times the cost of a basic enclosure.

Reason is simple: price competition. Buyers compare total price only. Don't evaluate whether the ventilation design is adequate. Higher-priced proposals get eliminated. Lower price wins. How's the low price achieved? Cut the ventilation system cost. Punch a couple holes for vents. Whether the airflow is sufficient, don't care. Whether there's sound attenuation, don't care.

What happens after these products are installed is highly consistent: first three months, great results. Machine room is noticeably quieter. Summer arrives. High-temperature alarms start coming frequently. Maintenance checks the entire unit, finds nothing wrong with the machine itself. Eventually pinpoints: enclosure ventilation is insufficient. Solution is usually removing some side panels. Panels come off, temperature is normal, noise is back. Tens of thousands of dollars invested for a half-dismantled box.

Ingersoll Rand offers factory-installed quiet enclosures on some models. These factory solutions are entirely different from aftermarket products. Factory quiet enclosures have ventilation systems co-developed with the unit. Airflow, air resistance, and noise attenuation are calculated and matched during the design phase. Tested with the complete unit before shipping. Aftermarket enclosure suppliers can't get the unit's detailed thermal engineering data. Design has to estimate. How accurate the estimate is depends on experience and luck.

Atlas Copco takes a different approach. GA series high-end models incorporate noise reduction into the unit's internal structure. Intake system, exhaust system, housing vibration isolation all have targeted design. The unit's noise spec is inherently low. No external enclosure needed. This approach solves the problem at the root. No conflict between noise reduction and cooling. Downside is unit price is high. Lower-end market can't afford it.

Among domestic brands, Baosi has a few low-noise models with a similar design approach. Internal noise reduction is fairly well done. Price is a tier below imported brands. Kaishan's mid-to-high-end models have decent internal vibration isolation. Low-end models, to control cost, have thinner shells and simplified vibration isolation. Noise specs are much worse.

Back to acoustic enclosures. Are there reliable aftermarket enclosure suppliers on the market?

Yes. Not many. Xinlei has been in this niche for many years. Can produce a complete attenuated ventilation design. Quote is also high. A 75 kW unit enclosure with ventilation system can quote at one-third the unit's price. A lot of project budgets can't cover that.

Enclosure panel configuration is another variable. Outer steel plate thickness determines the floor for sound insulation. 1.2 mm vs. 0.8 mm steel plate, price difference is small. Sound insulation difference is significant. Inner absorptive wool density and thickness affect mid-to-high-frequency absorption. 48 kg/m³ glass wool vs. 32 kg/m³, again small price difference, again significant performance difference. Damping layer material affects the steel plate's resonance characteristics. These details aren't visible on a quote sheet. Suppliers bidding low cut corners right here.

Procurement process typically only compares total price and promised noise reduction value. Noise reduction as a parameter, without third-party testing, relies entirely on the supplier's word. Writing 15 dB or 20 dB costs the same. Write higher, more competitive. After installation, buyer doesn't commission a testing agency to measure. Feels a bit quieter, acceptance passes. Whether the ventilation design is adequate, whether the panel specs are met, rarely anyone digs in.

If a compressor station genuinely needs noise reduction, the more reliable approach is selecting factory quiet models. 20% to 40% premium. Noise specs handled at the design stage. None of the problems of aftermarket add-ons. Sullair's quiet series is fairly mature in this positioning. About 30% premium. Over 10 dB lower than their standard series. That money spent on unit selection is far more reliable than spent on an enclosure.