Initial situation
An ADVANSOR refrigeration plant of the model series Valuepack XS3 is to be soundproofed. The plant is located in a corner inside the building, therefore only 2 sides can be provided with a sound barrier.

Basic concept of the sound enclosure
The basic structure of the sound enclosure consists of aluminum plug-in frames in whose profile frames the lockable service doors are mounted. The service doors are mounted around the plant so that service and maintenance work can be carried out without obstructing or changing the sound enclosure. In the area of the electrical control cabinet, 2 hinged doors are installed to allow easy access.

The remaining service doors are based on aluminum panels with a thickness of 1.5 mm and are designed with an internal insulation of 40 mm. The insulation is held in the panels by perforated plates which can be easily removed so that the insulation can be cleaned or replaced if necessary. The insulation material is polyethylene foam sheets (StratocellWhisper). The material has very good sound absorbing properties. The insulation is also moisture resistant, does not build up mold, can be cleaned with a high-pressure cleaner and complies with fire protection class B-S2-d0 (flame retardant).
The soundproofing is closed on the long side and narrow side as well as in the roof. On the back side and on the narrow side of the pipework the walls of the building form the closure.

The sound enclosure has the following dimensions: 3'100 x 1'500 x 2'500 mm (L x W x H) with a weight of 406 kg and is designed for a maximum For the supply of cold air and for the discharge of warm air, mesh openings with a mesh size of 1.5 x 1.5 cm are provided.

The sound reduction over the frequency band from 63 to 8,000 Hz is between 19 and 20 dB(A). 

After a few weeks on the high seas, two SilentMode acoustic hoods from the H- and V-series were installed in Queensland Australia and from now on ensure quiet operation of a DAIKIN VRV system and a DAIKIN multi-split climate unit.

The DAIKIN units are of the following models:
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VRV Unit
DAIKIN VRV RZQ250LY1 with an air volume of 11'000 m3/h. at full load.
The dimensions of the sound hood are:
1'700 x 1'700 x 2'250 mm (L x W x H)

Air conditioning multi split unit
DAIKIN RZQ140 LY1 with double fan and an air volume at full load of 4,800 m3/h.
The dimensions of the sound hood are:
1'700 x 950 x 1'800 mm (L x W x H)

Both acoustic enclosures are made entirely of seawater-resistant aluminum and have been powder-coated in two RAL colors, 7016 (base frame) and RAL 9003 (service doors).

The air chambers of the two systems, one with vertical air outlet (DAIKIN VRV) and one with horizontal air outlet, are hermetically separated in the hood so that an air short circuit between the air inlet and air outlet is prevented.
The systems and the SilentMode acoustic hoods were installed by our customer "Clamroc Construction" Mr. Tony Parente in a residential building he designed in Queensland, Australia.

There are numerous pictures of fantastic houses on the website of the company "Clamroc Construction": https://lnkd.in/dvYyXcVY
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For further information, please contact us on the following E-mail Address: info@silent-mode.com

We are often asked how big the performance loss of a heat pump, air conditioning or refrigeration system is when it is equipped with a soundproof hood?
In order to give an answer to this, we first have to determine which fan key figures the system has, or how large the static pressure of the fans is in Pascal. Axial fans with a maximum static pressure of 20 Pascal are often used in these systems. If the systems are also designed for heat recovery, the static pressure is usually much higher because the air has to be discharged via appropriate channels. Axial fans are suitable for large air volumes that have to be transported over short distances, i.e. typically when using heat pumps, air conditioning and refrigeration systems with direct air outlet in horizontal or vertical direction. Due to their design, centrifugal fans usually generate a significantly higher pressure than axial fans and are therefore suitable for extracting air over greater distances where branches or bends cause a significant pressure loss.

What does this mean when designing acoustic hoods?
For the systems, which are mostly designed with axial fans, it is important to dimension the acoustic hood volume in such a way that the air volume required by the system can be transported through the limited atmospheric space of the acoustic hood. Furthermore, the free areas that must allow unhindered circulation of the supply air and exhaust air are decisive. This means that the air openings of the acoustic hoods must be designed for the air volume required by the systems under full load. If the air opening, for example at the air inlet, is too small, there is a pressure loss on the condenser, which in speed-controlled systems leads to a higher fan speed and thus increases the noise of the system and the electrical input power. If the air outlet is dimensioned too small, the stagnant air creates a resistance that can no longer be pushed away by the fans and, in the worst case, can lead to a standstill of the system.

So the correct dimensioning of the free air inlet and outlet surfaces is a decisive factor in the design of noise protection hoods.
But even if the free air surfaces are dimensioned correctly, a lack of separation of the air chambers between the air inlet and air outlet can lead to a massively deteriorated performance of the system because in this case there is an air short circuit between the air inlet and air outlet. This means that with a heat pump, for example, the cold air cannot be completely discharged and mixes with the incoming air, which can lead to massive cooling of the incoming air. Keep in mind that the air outlet from a heat pump is around 7 to 9° below the ambient temperature. In the case of an air conditioning or refrigeration system, the exact opposite is the case, but here too the separation of the air chambers is a decisive factor so that the system performance is not reduced by an air short circuit in the acoustic hood. Even small gaps in the air separation are sufficient here to enable recirculation, so it is important to separate the air chambers hermetically.

Properly designed acoustic hoods with a hermetic separation of the air chambers do not lead to a reduction in the system performance in annual operation.
This is the case when the system pressure drop does not exceed 20 to 25 pascals, since this pressure drop is compensated by the static pressure of the fans. This is also the reason why the dimensions of acoustic hoods in systems with larger air volumes are relatively large in order to prevent baffles and to allow the air to flow in and out unhindered. A correctly dimensioned acoustic hood offers the following advantages in addition to noise reduction:

Protection of the installation from atmospheric agents such as: hail, snow, rain, wind and pollution with leaves that can deposit on the condenser and cause pressure loss.

Selectable air line enables air diversion for systems that are close together in order to prevent air short circuits between the systems.

Due to the selectable air flow, systems can also be installed in front of obstacles, since the air diversion can be designed flexibly.

Protection against access by unauthorized persons and against vandalism.

Protection from direct wind on the condenser and fans.

Further information: www.silent-mode.com to edit.

Initial position
An OCHSNER heat pump from the "AIR-85-C14A" model series was used as part of a renovation project. The outdoor unit is designed as a table evaporator. The system has the following dimensions: 2,225 x 1,940 x 1,340 mm L x W x H. The system has 2 axial fans with a maximum volume flow at full load of 20,000 m3/h.

The heat pump is located outside of a kindergarten in Stuttgart.
 
Acoustic enclosure concept 
The basic structure of the acoustic hood is an aluminum plug-in profile frame, the service doors around the system are integrated into this profile frame. The service doors are based on aluminum panels with a thickness of 1.5 mm with internal 40 mm thick insulation made of Stratocell® Whisper, the material has one of the best sound-absorbing properties available on the market.
 
The acoustic hoods have the following dimensions: 2,800 x 2,500 x 1,700 mm (L x W x H) with a weight of 375 kg.
The air openings and the free air inlet openings are designed with around 15% above the required air volume of the system. The air flow is offset to the sides, so that no air short circuit can occur between the exhaust air and supply air. With the air deflection by 90°, the airborne sound is broken, which leads to a significant reduction in the exit noise. The air outlet speed is around 1.98 m/sec.

Noise reduction
The all-round noise reduction across the frequency spectrum from 63 to 8,000 Hz is between 19 and 20 dB(A), with a pressure loss of around 20 Pa.
 
Adaptation to the environment
The acoustic hood was made entirely of aluminum and powder-coated in the RAL color: 5022 (night blue).

Additional Information
info@silent-mode.com
​www.silent-mode.com (German)
www.silent-mode.net (English)
www.silent-mode.it (Italian)