| All objects or features inside ducts, such as diversions, filters, roller-shutter flaps, curvatures, T-pieces and silencers cause an increase in flow resistance and thus an obstacle to the flow of air. If the duct has many such features and is very long, the size of the recommended free cross-section (radius) of the duct must be checked by an expert.
There are appropriate fire safety measures prescribed to prevent fire from spreading through ventilation ducts. DIN 4102, part 6 requires the installation of automatic fire safety flaps whenever ventilation ducts pass through a wall.
If the duct is long or unfavourably laid, the dynamic pressure can be over 50 P a (5 mmWH). In this case there is a risk that the cooling ventilator of a screw-type compressor can not over-come the dynamic pressure in the duct. This means that cooling air stops flowing and the entire cooling effort for the compressor collapses. In this case an auxiliary ventilator will have to be installed.
The air inlet and outlet flaps as well as the ventilators should, for economical reasons, be controlled by a thermostat in the installation room.
The cooling-air ducts must never be mounted directly on the compressor housing. Compensators that remove tension and stop the transmission of vibration must always be used.
A cooling-air duct with sound-insulation cladding radiates less heat to the surroundings and also suppresses noise that comes out of the compressor with the exhaust air.
BOGE generally recommends that the task of installing the ducts and any associated construction work be given to a specialist company.
With multiple units, each compressor must have its own air inlet and outlet duct.
When using a collective duct for multiple units, automatic check flaps must be used to prevent heated cooling-air flowing over a compressor that is switched off in the installation room and heating the inlet air. |