Duct (flow)

 Duct (flow)

The required airflows include, for example, supply air, recirculated air, and compressed air. Ducts usually also supply ventilation air as part of the supply air. Therefore, air ducts are one way to ensure adequate indoor air quality as well as thermal comfort.

The duct system is also called ductwork. Duct design is the design (output), magnification, optimization, detailing, and detection of weight loss through a duct system.

Materials Used:

Ducts can be made from the following materials:

Galvanized steel:

Medium galvanized steel is the standard and most commonly used material in ductwork as the zinc coating of this metal prevents rusting and avoids the cost of painting. For insulation purposes, metal ducts are usually lined with fiberglass blankets (duct liner) or wrapped externally with fiberglass blankets (duct cover). When required, a double-walled duct is used. This cover is usually covered with a cover, followed by a 1–2 "layer of fiberglass cover inside a hard outer pipe.

Rectangular ductwork is usually made to fit with special metal outlets. For ease of handling, it usually comes in 4 'sections (or joints). Round duct is manufactured using a continuous spiral forming machine that can make a circular duct in almost any diameter when using the correct die shape and to any length which is appropriate, but the most common stock sizes range from 4 "to 24" with 6 "- 12" being the most commonly used. The stock pipe is usually sold in 10 ’joints. There are also 5 'joints of the non-spindle type pipe available, which are commonly used in residential applications.

Aluminum (Al):

Aluminum ductwork is lightweight and quick to install. Also, custom or special shapes of ducts can be easily made in-store or on-site.

Duct construction begins with finding the duct outline on the preinsulated aluminum panel. The parts are usually cut at 45 °, bent if necessary to obtain the various fittings (i.e. angles, tapers), and finally assembled with glue. Aluminum tape is applied to all grooves where the outer surface of the aluminum foil is cut. A variety of flanges are available to suit different installation requirements. All internal connections are sealed with a sealant.

Aluminum is also used to make a round spiral duct, but it is much more common than galvanized steel.

Polyurethane and phenolic insulation panels (pre-insulated air duct):

Traditionally, air ductwork is made of sheet metal that is first applied and then weakened by insulation. Today, the galvanized steel duct was usually made by a sheet metal fabrication shop and covered with a duct cover before installation. However, ductwork made from rigid insulation panels does not require additional insulation and can be installed in a single step. Both polyurethane and phenolic foam panels are made with factory-activated aluminum alloys on either side. The thickness of the aluminum foil can vary from 25 micrometers for indoor use to 200 micrometers for outdoor use or for higher mechanical properties. There are various types of rigid polyurethane foam panels available, including a water-cooled panel to allow the foaming process to be achieved by using water and CO2 instead of CFC, HCFC, HFC, and HC gases. Most manufacturers of polyurethane or phenolic foam panels use pentane as a foaming agent instead of the mentioned gases.

A tight phenolic insulation ductwork system is listed as a Class 1 air duct to UL 181 Level for Safety.

Fiberglass duct board (preinsulated non-metallic ductwork):

Fiberglass duct board panels provide built-in thermal insulation and the inner surface absorbs [sound], helping to provide quiet operation of the HVAC system. The knife automatically moves out a groove with 45 ° sides that does not penetrate the full depth of the duct board, thus providing a thin section acting as a hinge. The duct board can then be folded across the groove to produce a 90 ° fold, making the duct shape rectangular in the size you want. The duct is then closed with external staples and special aluminum tape or metal backing.

Flexible blackening:

Flexible ducts (also known as flex) are usually made of flexible plastic over a metal wire coil to form a tube. They have several arrangements.  The insulation is surrounded by a protective cover and is usually made up of polyethylene or metallic PET. It is commonly sold as boxes containing 25 'of duct compressed into a 5' length. It is available in diameters from as little as 4 "to as large as 18", but the most common are even sizes from 6 "to 12".

A flexible duct is very convenient for connecting supply air outlets to the tight ductwork. It is usually fastened with long zip ties or a metal band clamp. However, weight loss is higher than for most other duct types. Therefore, designers and installers try to keep their installed lengths (e.g.) short, e.g. less than 15 feet or so, and try to minimize efforts. Connections in flexible blackout must be avoided. Some flexible duct markets prefer to avoid using flexible ducts on the aerial parts of HVAC systems, but flexible ducts can accept moderate negative pressures.

Blackening clothes:

This is of course an air circulation device and is not intended to be a medium for conditioned air. So the term duct dressing is somewhat misleading; the Clothing air distribution system is the most accurate name. However, because it often replaces the hard work of a duct, it is easily seen just as a duct. Usually made of polyester material, cloth ducts can provide a more evenly distributed and balanced mixture of the condensed air in a special place than a conventional duct system. They can also be made of finials or orifices.

Clothing ducts are available in a variety of colors, with options for silk screening or other forms of decoration, or in porous (air-permeable) and non-porous fabrics. The appropriate suitability so, air-coated clothing is recommended as it does not normally create condensation on its surface and can therefore be used where the air is supplied below the dew point. Moisture-removing material can be healthier for residents. It can also be treated with an anti-microbial agent to prevent bacterial growth. Porous material also tends to require less maintenance as it reacts with dust and other air pollutants.

Clothing made from over 50% recycled materials is available, allowing it to be proven as a green product. The material can also be flammable, which means that the fabric can still burn, but will disappear when the heat source is removed.

Clothing ducts are not considered for use in roofs or concealed areas. However, results for use in elevated floor applications are available. Cloth blackening is usually less weighted than other normal blackening and therefore puts less pressure on the structure of the building. Minimum weight allows easier installation.

Clothing ducts need at least a certain range of airflow and static pressure for them to work.

Blackened with PVC low profile:

PVC low profile blackening has been developed as a cost-effective alternative to steel low profile blackening. Low-profile ducting has been used extensively in apartment and hotel ventilation since 2005. Low-profile ducting has grown significantly due to the space available in roof caves to reduce cost. much low-profile PVC ducting manufacturers have struggled to achieve or maintain compliance, and some construction projects have to go back to using the more expensive steel option.

Irrigation:

The finish for weather-exposed exterior ductwork may be coated with aluminum or zinc/zinc alloy steel, multilayer laminate, fiber-reinforced polymer, or other waterproof coatings.

Duct system parts:

In addition to the ducts themselves, there are many other components in complete ducting systems.

A duct system often starts at an air handling unit. The blowers in the air handling device can create a large vibration, and the large area of ​​the duct system would provide this sound and vibration to the occupants of the building. To avoid this, shock absorbers (flexible sections) are usually inserted into the duct just before and after the air handling device. The rubber canvas-like material in these sections allows the air handler to shake without causing much vibration to the connected ducts. The same flexible section can reduce the noise that can occur when the ductwork is engaged and when positive air pressure is introduced into the ductwork.

Downstream of the air handler, the supply air duct often forks, supplying air to many individual air spaces such as diffusers, grilles, and tables. When the system is designed with the main duct flowing into multiple branch ducts, filters called removals to allow a small portion of the flow in the main duct to move into each branch duct. Removals can be made into round or rectangular openings cut into the wall of the main duct. Many small metal tabs are usually removed which are then bent to attach the removal to the main duct. Round versions are called round versions. Other capture designs use a snap-in attachment method, sometimes combined with an adhesive foam gasket for a better seal. The outside of the extraction then connects to the rectangular, oval, or round branch duct.

Stack and head boots:

Ducts, especially in homes, must allow air to travel directly within relatively thin walls. These straight hooks are called stacks and are formed by very wide and very thin rectangular sections or oval sections. At the base of the stack, a stack shoe transitions from a large round or rectangular duct to a thin wall-mounted duct. At the top, a stack head can move back to normal black while a recording head allows moving to an air table on a wall.

Volumetric control dampers:

Ducting systems often need to provide a means of varying the amount of airflow to different parts of the system. Volumetric control dampers (VCDs; not to be confused with smoke/fire dampers) provide this function. In addition to the control provided by the diffusers or diffusers that disperse air into individual rooms, dampers can be installed in the ducts themselves. These dampers can be manual or automatic. Zone dampers provide automatic control in simple systems while variable air volume (VAV) allows control of solemn systems.