In the HVAC world, DX stands for Direct Expansion. It refers to a refrigeration system where the evaporator coil (the part that gets cold) is in direct contact with the air stream being cooled. Unlike centralized chilled water systems that use an intermediate fluid (water) to carry cold to different rooms, a DX system uses the refrigerant itself to absorb heat directly from your indoor air. This makes DX units simpler, faster to install, and significantly more cost-effective for residential homes and small-to-medium commercial spaces.
The “Expansion” part of the name comes from the Expansion Valve, a critical component that drops the pressure of the liquid refrigerant, causing it to flash-freeze the evaporator coil. Because the cooling happens “directly” at the source, DX systems are incredibly efficient at dehumidification and provide rapid temperature drops. However, as buildings get larger, the distance refrigerant can travel is limited, which is why DX is the king of residential split systems but often gives way to chilled water in massive high-rise developments.
To see if a DX system is the most efficient choice for your property size, use the Cooling Technology & Load Auditor below.
What is a DX unit in HVAC
In HVAC, DX stands for Direct Expansion and it is a form of HVAC unit that cools indoor spaces or rooms with a liquified condensed refrigerant. DX unit is one of the most common air conditioning units used both in residential and commercial buildings in the United States.
How does a DX HVAC system work
A DX system cools the air by transferring condensed refrigerant to the heat exchanger located inside the building. It has a component called an evaporator where the refrigerant expands as heat is being generated and absorbed, before ultimately turning it into gas.
After this, the unit then pumps refrigerant into the compressor that will compress the gas and transmit it to another heat exchanger and condenser located outside the building. The heat that was taken in by the refrigerant is then released back to outdoor and the once cooled, compressed air will be converted back to liquid form.
The liquified refrigerant is then pumped back into the evaporator and the cycle will be repeated over and over again.
Types of DX air conditioning system
There are different types of DX air conditioning systems, but the most common ones are the self-contained, pre-mad,e and factory-assembled units. Each of these types is equipped with fans, filters, controllers, and refrigeration units.
Other forms of DX air conditioning systems based on the requirement, capacity, and room air conditioning include; Split system, heat pump, multi-headed units, cassette system, ducted system, and packaged unit with extra condensed options which could be air-cooled or water-cooled.
Water-cooled DX system
In this type of DX system, the condenser uses water-cooling to remove heat from the system. That is, the refrigerant is cooled by water flowing over the condenser coils and then distributed through a cooling tower that cools it down for proper ventilation. The water is then redistributed and the whole process will be repeated over again.
Unlike almost every other unit that used finned-type condensers, the water-cooled DX system uses shell and tube-like condensers.
Split DX system
When it comes to ductless DX air conditioning, the Split is the most common type there is. They are popularly used at homes and in commercial air conditioning because they are cost-effective and energy-efficient.
They consist of all the basics DX systems and more and are split over two units. It has a condensing unit located outside which consists of some components like; condenser coil, contender fan motor, capacitors, electrical printed circuit (PC) boards, and compressor. The evaporator fan coil found inside the unit consists of the evaporator coil, evaporator motor fan, expansion valves, filters, and electric PC boards. The two units ( the evaporator and the condensing unit) are connected with pipework and interconnecting cables.
There is no fixed location for the installation of the DX split system when it comes to the indoor unit, outdoor unit, direction or the length of pipe to be used. It can be installed in many ways: it can be wall-mounted, ceiling hung, bulkhead-hiding unit, or can be placed directly on the floor. Given the flexibility in the different layouts of the split system, it has become the top choice among homeowners and building managers.
Disadvantages of the direct expansion system
The only disadvantage of using a direct expansion system is they are expensive to operate and maintain.
💡 Pro Diagnostic Tip: Because DX systems rely on the constant flow of high-pressure refrigerant, even a minor leak or a clogged filter can cause the evaporator to freeze solid. If your DX unit has stopped blowing cold air or has shut down entirely, check the indoor control board for diagnostic flashes. Use our HVAC Error Code Index to identify if a low-pressure lockout has occurred.
Is DX system HVAC worth it
Yes, the DX system is worth buying, and here are a few reasons why you should consider getting one.
- It makes less noise compared to other types of HVAC units.
- Although might be expensive, but compared to some other units like the rooftop VTF system, it is cheaper.
- It costs less to install a DX system.
- It consumes lesser energy.
- It regulates humidity levels.
- It requires a small ceiling or floor space.
- It is easy it adjust, balance, and test the system.
- It is not affected by fluctuating load conditions.
- It can be directed to a particular section without having to operate the system for the entire building.
💡 Pro Diagnostic Tip: One limitation of basic DX systems is that they typically operate as “All or Nothing.” If you want to use a DX unit to cool a multi-story home with different temperature needs, you must integrate a zoning system. Read our guide on Is Zoned HVAC Worth It? to see how dampers can make your DX unit behave like a much more expensive centralized system.
Differences between DX unit and split unit
There is no apparent difference between a DX system and a split unit because they both work the same way and if there’s going to be any, it will be in their overall performance and configuration.
DX system vs VRF system
VRF means variable flow refrigerant unit and here are a few comparisons between the DX system and VRF system.
- DX expansion uses customary indoor and outdoor units when refrigerants are expanded in the evaporator and when the air passing through it is being cooled. While VRF is equipped with an advanced control system and outdoor unit (usually containing one or more compressors) and one (or more) indoor units with adjustable loads.
- VRF can respond to variation in space load conditions. Whereas, DX can only make limited or no adjustments to variations in space load conditions.
- VRF is more expensive compared to DX systems.
DX system vs chilled water system
- Compared to chilled water systems, DX systems are more energy-efficient.
- The chilled water system can be used for large residential buildings whereas the DX system can only be used to cover small spaces. 3. The air used for cooling effect in DX system passes over the cooling coil of the refrigeration system, while in the chilled water system, the refrigeration system will be used to cool down the water first before it is later converted to chilled air which cools the room or spaces.