DUCTS
Ducts
also provide most commonly accessible parts of the supply air chamber, ventilation air and
which removes the air inside the room to the machine for re circulation . As such,
the proper design of duct system is the one method which provides an acceptable
indoor air quality as well as comfortable thermal variation.
DIFFERENT TYPES OF DUCTS
SUPPLY AIR DUCT
The duct which
supplies the conditioned air from the equipment which should make that air conditioned to the outer space which should be
conditioned is called supply air duct.
RETURN AIR DUCT
The duct which carry the
recirculating the conditioned air from the conditioned area circulates back to the air conditioning device is called as return air duct .
FRESH AIR DUCT
The duct device which sucks the
outside air from the atmosphere is called fresh air duct.
LOW PRESSURE DUCT:
When the duct is having a static pressure below 50 mm of water gauge, this type of duct is said to be a low pressure duct.
HIGH PRESSURE DUCT:
When the static pressure is from 150
to 250 mm of water gauge, the duct is said to be a high pressure duct.
LOW VELOCITY DUCT:
When the velocity of the air in the
duct is up to 600 m/min, the duct is said to be low velocity duct.
HIGH VELOCITY DUCT:
When the duct is having an air velocity more than 600 m/min, the duct is said to be high velocity
duct.
DIFFERENT DUCT SHAPES
Round duct carry more air with less
friction loss than ducts of any other shape with the same cross sectional area.
Square duct will have less friction loss
compared to that rectangular ducts.
Aspect ratio of rectangular ducts
should be kept as low as possible.
THINGS TO TAKEN IN CONSIDERATION
High static pressure and velocity
will result in noise, but the low velocity system will result in less fan motor
static and duct size, resulting in less noise.
Flexible ducts made up of aluminum
foil are also available in the market, but flexible ducts contain a high
friction so the length of each flexible duct is limited to 1.5 meters.
DIFFERENT TYPES OF DUCTS BASED ON
MATERIALS
Galvanized stainless steel
Aluminum duct
Fabric material duct
Flexible aluminum foil ducts
DUCT INSULATION
Insulations are provided for ducts
in order to prevent leakage of conditioned air from the duct to the
surroundings called thermal insulation. Additional to this one more insulation is used to
prevent the sound from duct to the conditioned room called acoustic insulation.
DESIRABLE PROPERTIES OF INSULATING MATERIALS
Low thermal conductivity.
Impervious to water vapor.
Resistance to fire.
Mechanical strength.
Easiness of laying.
MATERIALS USED FOR DUCTS
Expanded polystyrene
Polyurethane foam
Low density thermo coal
Plaster of Paris
Canvas
Wood
Cork, etc.
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