Double acoustic bonnet for 2 Daikin VRV units

Initial situation
Two Daikin VRV units "RXYQ10P7W1B and RXYQ8P7W1BU" are to be equipped with a sound enclosure. The units have the following dimensions: 930 x 765 x 1'685 mm L x W x H. Dimensions of the combined unit: 1'860 x 765 x 1'685 mm (L x W x H).

The units are located in Chemnitz at a supermarket.

The units each have 1 axial fan with a maximum air volume flow at full load of 11'100 m3/h and a max. static pressure of the fans of 78 Pascal. The air outlet is towards the top. The combined units have 2 axial fans and a combined air volume of 22'100 m3/h in full load operation.

SilentMode Acoustic enclosure concept 
The basic structure of the acoustic bonnet for accommodating both units is an aluminium plug-in profile frame, into which the service doors around the unit are integrated. The service doors are based on 1.5 mm thick aluminium panels with 40 mm thick Stratocell® Whisper insulation inside, which is one of the best sound-absorbing materials available on the market.

Because the laminated polyethylene foam absorbs sound rather than reflecting it, it is an excellent alternative to many noise control materials used today. The insulation is also moisture resistant, does not build up mould, can be rinsed off with a high-pressure cleaner and complies with the fire protection class: B-S2-d0 (flame retardant).

The acoustic bonnet has the following dimensions: 2'660 x 1'685 x 2'660 mm (L x W x H) with a weight of 379 kg. The acoustic bonnet is designed for a maximum air volume of 23'500 m3/h.

The air openings and the free air inlet openings are designed with about 8% above the required air volume of the system. The air routing is laterally offset so that no air short-circuit can occur between the extract and supply air. The 90° air deflection breaks up the airborne sound, which leads to a significant reduction of the outlet noise.

The sound reduction over the frequency band amounts to 17 - 19 dB(A) depending on the operating condition of the units.

Efficiency increase
Since the units are located in a niche with 3 closed walls (roof and both sides), the targeted air routing also prevents an air short-circuit between the exiting air, which would otherwise be recirculated from the roof and sucked back in by the units. This increases the performance of the units and thus leads to a lower input power - i.e. less power consumption of the units.

For furher Information: www.silent-mode.net

Installation of the acoustic bonnet seen from the courtyard side.

View of the acoustic enclosure from the air inlet side

View of the VRV acoustic bonnet from the inner courtyard side

Air chamber separation to avoid recirculation of the exhaust air