Ultra-Low Sound Air-Cooled Chillers

Air-cooled chillers provide significant advantages for many facility operators and owners. The elimination of a cooling tower greatly reduces the complexity of the system and significantly eases the maintenance of the system. For smaller facilities without the resources of large institutional owners, this reduced maintenance can be critical.

Therefore it is very common to see air-cooled chillers on smaller facilities such as public schools and small office buildings. However, this suitability does carry with it some costs--Air-cooled chillers are usually significantly less efficient than water-cooled chillers and, now with the advent of super-low sound cooling towers, often much noisier. The noise problem can be very significant with this sort of equipment in that a large proportion of the facilities that utilize this technology are located near or in residential areas.

In an earlier post I discussed how the Smardt air-cooled Turbocor chillers significantly change the balance between water-cooled and air-cooled chillers with respect to efficiency and sound. However, it is worth investigating the sound issue in more depth.

Recently, manufacturers have spent some effort in addressing the sound issue on their air-cooled chillers. This has generally been approached by providing low sound fans and addressing the compressor noise. Two products that are currently being marketed as low-sound chillers approach compressor sound in different ways. One product utilizes screw compressors with a VSD to reduce compressor sound at low loads. Another utilizes scroll compressors with elaborate compressor sound enclosures. This approach yields published sound data which is excellent at all chiller load conditions. Until recently, this chiller has been considered by many engineers to be the quietest air-cooled chiller n the market.

The Smardt chiller, of course, uses the extremely low-sound Turbocor compressor, and variable-speed ultra-low sound fans. It is reasonable to believe that this combination would make for a very favorable comparisons with these other low-sound chiller options.

And this expectation is borne out by the data. Smardt air-cooled chillers compare extremely favorably against the variable speed screw chillers as this graph illustrates:


Two things should be noted: First, the comparison here is between a 177 ton screw and a 200 ton Smardt chiller, and second that even at 100% load, the Smardt chiller is far quieter than the screw at 25% load. The difference is even more significant in the lower octave bands that carry so well over distance.

Comparing the Smardt Chiller to the acoustically treated scroll chiller also yields an extremely favorable comparison:



This comparison of 120 ton chillers shows that while both approaches yield extremely low sound levels overall, the Smardt chiller beats the competitor in 5 of 8 octave bands. And the advantage for the competitor in two of the other bands is slight. It also shows the significant effect of A-weighting sound data. In this graph, the red line represents the published sound data from the manufacturer. Close reading of this data indicates that it is not bare sound power, but A-weighted sound power. This method of reporting sound data takes very significant credits into effect, especially in the lower octave bands:

Octave band center frequency (hz)	Weighting
31.5	-39
63	-26
125	-16
250	-9
500	-3
1k	0
2k	1
4k	1
8k	-1

The dark blue data show the raw, uncorrected sound data for this chiller.

If acoustics are a design consideration for your air-cooled chiller product, Smardt offers a solution that is unmatched in the industry.

Extra: Audio Comparison of compressor noise

85 dBA screw compressor
73 dBA Turbocor compressor

Both measured at 1.0 m away from compressor. Your speaker volume will affect the output, but the comparison should be clear if the volume is not adjusted between clips.

Extra extra:

This link has sound files that illustrate the amplitude of a decibel, to give perspective to the graphs above.