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  • Writer's pictureAnne Lee

Direct Expansion (DX) Type of Central Air Conditioning

Updated: Feb 14




The Direct Expansion (DX) type of central air conditioning plants and the Chilled Water type of central air conditioning plants are the two different types of central air conditioning systems.


The DX system immediately passes the air that cools the room or space over the cooling coil of the refrigeration plant. In a chilled water system, the water is first cooled by the refrigeration system before being used to cool the air that is used to cool the rooms or spaces.


In direct expansion, or DX, central air conditioning systems, the refrigerant in the air handling unit's cooling coil immediately chills the air utilised to cool the area. The DX plants' cooling efficiency is better since the air is immediately chilled by the refrigerant.


However, it is not always practical to transport the refrigerant piping over great distances; as a result, direct expansion, or DX, central air conditioning systems are typically employed to cool small structures or single-story rooms.


3 main compartments of the DX type of central conditioning systems

1. The Plant Room

The compressor and condenser, two crucial components of the refrigeration system, are located in the plant room. Either an open type compressor or one that is semi-hermetically sealed is possible.


While open type compressors are cooled by water, semi-hermetically sealed compressors are cooled by air that is blown by a fan. Open compressors can be directly powered by a motor shaft through connection or by a belt through a pulley setup.


The condenser is a shell and tube device that uses water to cool it. The refrigerant cools more quickly because water travels along the condenser's shell side and the refrigerant along the tube side.


Although it can also be maintained in another suitable position, the cooling tower at the top of the plant room is where the water needed to cool the compressor and the condenser is cooled.


2. The Air Handling Unit Room

The air handling unit, which is maintained in a separate room, is the first thing the refrigerant enters after leaving the condenser in the plant room.


The evaporator, or cooling coil, the air filter, and the huge blower are all parts of the air handling unit, which is a large box-shaped device.


The refrigerant enters the cooling coil after exiting the thermostatic expansion valve, where it cools the air that is brought into the air-conditioned space.


The DX central air conditioning system's evaporator is a coil-type device covered in fins to improve the efficiency of heat transfer from the refrigerant to the air.


The air handling unit is connected to two different types of ducts: those that take in hot return air from the rooms and those that send chilled air to the rooms that need air conditioning.


The hot return air that has absorbed the heat from the room through the ducts can be absorbed thanks to the air handling unit's blower.


This air is then circulated over the cooling coil after passing through the filters. The cooled air is then circulated through ducts to the desired rooms by the blower.


3. Air Conditioned Room

This is the area that will actually receive cooling. It can be used for a living space, a hotel room, a portion of an office, or any other appropriate use.


All of the rooms that need cooling have ducts running from the air handling room.


The grills or diffusers that deliver the cooled air to the room are attached to the ducts. The heated air goes through a second set of grilles, into the return air duct, and finally into the room housing the air handling unit.


The air handling unit then circulates this air once more.


Despite the improved efficiency of DX plants, the air handling units and the refrigerant piping cannot be retained at very great distances because there will be lots of pressure drops along the route and cooling losses as well.


In addition, a lot of refrigerant will be required for the lengthy piping, which drives up the cost of the system and increases the risk of issues like refrigerant leaks.


Due to these factors, compact air conditioning systems of between 5 and 15 tonnes are typically employed in small buildings or with a limited number of rooms per level.


It is possible to build numerous direct expansion systems if there are significant air conditioning loads.


In such situations, one of the plants may be shut down and the other may operate at full capacity when the heat load is lower. At greater loads, the DX expansion mechanism operates more effectively.


Even if a plant malfunctions, cooling can still be accomplished using additional plants. Less people use the chilled water type of central air conditioning plants than the DX kind of central air conditioning plants.


What are the different types of DX type of central air conditioning?

Unitary air conditioning systems—factory manufactured, ready-made, self-contained units—are the most prevalent types of DX air conditioning. The refrigeration units in each DX system have fans, filters, and controls.


DX AC systems are available in a vast array of forms and capacities. DX units are available as room air conditioners, split systems, multi-head units, cassette systems, heat pumps, ducted systems, and packaged units, with extra air- or water-cooled condensing options, depending on specific requirements.


1. Ducted Systems

A common type of DX air conditioning system used in residential and business applications is ducted aircon.


Split DX units and ducted DX units are similar, however ducted DX units are often larger, serve more spaces, and have ducting with outlets and vents.


All of the fundamental components of a DX cooling and/or heating system are present in ducted DX devices.


With the exception of variations in air-blow direction, the design of ducted Dx outdoor units is very consistent (i.e. top-blow or side-blow).


When designing an HVAC system for a building's size, aesthetics, and architecture, ductless DX indoor units offer wider versatility.


To give a space an industrial feel, the ductwork that distributes air from the interior unit to the room or spaces might be concealed under the ceiling or left exposed.


The degree of customization offered by ducted DX air conditioning is increased by the variety of shapes, colours, and patterns of the outlets and vents that connect to the ductwork.


2. Packaged Units

All of the components are contained within one main unit, and ductwork distributes air to the appropriate indoor space, making package units a hybrid of a box room air conditioner and a ducted air conditioning system.


Large areas can be served by packaged units. They normally sit high on the roof and are primarily employed for commercial applications. Rooftop packed units are a result.


DX package units adhere to the fundamental principles of a DX air conditioning system; air is heated or cooled by direct heat transfer with refrigerant in the system. Package units can come in a variety of shapes and configurations.


3. Air-Cooled and Water-Cooled Systems

Larger packaged and ducted DX systems have the option of being water-cooled or air-cooled (condenser fan) (cooling tower). This is a reference to the condenser's mechanism of heat rejection.


This option expands the variety of Dx HVAC system configurations that are possible. Additionally, it enables greater DX system customization for every residential or commercial building.



In A Nutshell

Direct Expansion (DX) systems are a vital component of the central air conditioning system. There are three main types of DX systems - Split systems, Packaged systems, and VRF systems - each with its unique set of advantages and disadvantages.


Understanding the different types of DX systems is crucial for anyone looking to install a central air conditioning system in their home or business.


By considering factors such as cost, space, and energy efficiency, you can make an informed decision on which type of DX system is best suited for your specific needs.


Regardless of the type of DX system you choose, you can rest assured that it will provide you with a comfortable indoor environment and keep you cool during hot summer months.


TCW Group as an OEM hvac manufacturer, we manufacture DX systems and Chilled Water system that suitable for commercial and industrial HVAC systems. This included the corrosive, marine and hazardous environment

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