Air conditioning and heating systems

Air conditioning and heating systems


Air conditioning and heating systems use a network of ducts to distribute and circulate air around a building to all the conditioned rooms. With well designed ductwork the comfortable indoor environment a building needs can be achieved in an efficient and quiet way.

Why duct design is important

A poorly designed duct system costs the user money. Improper insulation and/or leaks in the air distribution system lower the efficiency of the system. A more efficient design will incur no extra costs and save the user money in heating and cooling bills.

Duct work that leaks does not distribute the conditioned air evenly throughout the building, rooms may be too cold or too hot. Conditioned air can be forced out of the building and unconditioned air drawn in, also increasing running costs.

An air distribution system that is under sized or has many bends can lead to low air flow rates and high air velocities. The low air flow rates cause inefficiencies in running the conditioning equipment and high air velocities are noisy.

Good duct design

The objectives of a well designed air distribution system are, to provide a comfortable environment for room occupants, facilitate the systems heating and cooling functions, and to be easy to install. Doing all these things as economically as possible.

A well designed system will

  1. Provide conditioned air that will maintain the desired temperature and humidity levels
  2. Is properly sealed so that there are no leaks allowing unconditioned air to enter the system from outside.
  3. Is properly sized so it allows the most efficient use of the equipment possible.
  4. Is properly insulated to reduce rises/falls in temperature of the conditioned air before exiting a duct outlet.

Supply duct systems

Trunk and branch system

This system looks like you would expect from the name, the main trunk comes from the supply and smaller ducts branch out from it to the different conditioned areas. It is a simple system that is adaptable to most situations and can be easily integrated into the conditioned space, but the many different sections mean it can have more places for leaks too occur.

There are a few variations to the trunk and branch system. The most common and simplest to design is a trunk that is one size. There is a limit to the length of the trunk of approx 7m, any longer than this and air velocities become too low and there is poor air flow into the branches closest to the blower. Having your air system central to the ductwork you can supply an area approx 14m long.

A trunk reduction system reduces the cross sectional area of the trunk to keep the pressure and velocity of the airflow up. This means there is better airflow into the branches closest to the blower. This system is more complex to design.

Spider system

The spider system is a variation of the trunk and branch system. There are multiple trunks connected to the central supply, these lead to mixing boxes. Small branches then distribute the air to various outlets.

Radial System

In this type of system there is no trunk supply to the branches. All the ducts that distribute the air throughout the conditioned space are connected directly to the air handling system. Usually this configuration has a centrally positioned air supply with the ducts extending in a radial fashion, although this is not mandatory.

Perimeter loop system

This system uses a main duct which has the outlets and surrounds the conditioned space and it is connected to a centrally positioned air supply. It is more complex to design and can be difficult to install

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