by worthman » Tue Dec 01, 2009 10:55 pm
David,
The standard approach would be to line the enclosure walls. I often specify 75mm mineral wool such as rockwool, minimum density 48 kg/m3, behind perforated metal, 25% minimum open area. Expanded metal (or expamet as it is known in UK) is cheaper than perforated steel panel.
Be careful if placing any loose material below a chiller fan, as the fans typically extract air upwards and can shift several cubic meters per second, so anything loose could be sucked into the fans. If this is a commercial chiller, then it might be best to contact a specialist manufacturer in this area.
I've been involved on noise reduction for chillers in quite a few situations and have never come across placing material below it, as it will become soaked when it rains, catch dirt etc. Wall mounts or a direct attenuation of the fans is more common. Wall treatment has the added benefit that it removes a reflection path which can undermine the screening from the enclosure.