​Acoustic enclosure for a Mini VRF system U-5LE2E8 installed on a flat roof near Frankfurt am Main.

Starting position
A "Panasonic Mini VRF system U-5LE2E8" was installed on an intermediate roof between two single-family houses near Frankfurt.

The system has the following dimensions: 980 x 370 x 996 (+ 200 vibration dampers) mm (W x D x H).

At maximum output, the system has an air volume of 4,320 m3 / h, the static pressure of the fan is around 15 to 20 Pascal. When planning the acoustic hoods, we assumed a static pressure of <15 Pascal.

By means of the acoustic hood, the noise level is reduced to the neighborhood, the next window is around 7 meters away from the acoustic hood.

Acoustic hood concept
The air inlet is at the rear (condenser side towards the roof). This enables us to achieve an even air flow to the condenser without causing a pressure loss due to excessive air deflection.

The air outlet is on the front side (fan side), front left. A deflector plate was also installed here at the air outlet, which ensures the air outlet speed of 1.4 meters / sec. continues to insulate.

In this way, we achieve a continuous flow of exhaust air without creating an air short circuit. With an air outlet speed of around 1.4 m/sec. hardly any sound is transmitted via the air outlet.

The basic structure of the acoustic hood is based on aluminum system profiles which have the advantage of being light in weight when mounted on the roof. Around the system as well as in the enclosures roof, aluminum sheets were installed as easy-to-open service doors with a thickness of 1.5 mm with internal 50 mm insulation made of closed-cell, semi-rigid and sound-absorbing polyethylene foam sheets (Stratocell Whisper). Due to its sound-absorbing properties, this foam is one of the most innovative materials for sound control in HVAC systems.

The insulation is UV and water resistant and non-flammable. The isolation does not build up bacteria or fungi. And has strong sound insulation across all frequency bands. In this way we prevent masking effects that often occur when eliminating high-frequency sound bands and which lead to an increase in the tonality of the compressor sound.

The insulation is also light and hardly increases the weight of the service doors.

Sound hood dimensions
The acoustic hood has the following dimensions: 1,700 x 1,300 x 1,100mm (W x H x D) / weight including service doors 127 kg. The acoustic hood is made entirely of aluminum and was subsequently powder-coated in RAL color 7016 to match the color of the roof.

Sound reduction between 18 to 20 dB (A)