DX Chillers

The DX Air Conditioner system uses a refrigerant vapor expansion and compression cycle to cool air coming in through a supply plenum and returns it to the area that needs cooling through the return. The unit effectively circulates refrigerant through a series of condensers and evaporators, which warm air moves through and is cooled down before being pushed through the return. Another key feature of DX Packaged units is the advantage of having the entire cooling system self-contained in one unit. This allows for the installation on top of or alongside a building without too large of a footprint, and are generally less expensive to install.

 
Chiller units also use a vapor expansion/compression cycle for liquid refrigerant, much like the DX units. The refrigerant is continuously transformed from a liquid, to a vapor, and back again. This process cools down the refrigerant which is passed through an evaporator. Warm water coming through a 2-5 inch radius supply hose is passed over the evaporator and cooled off to the desired temperature. Typically the cooled water is used for existing air handler systems.

Refrigerants and DX chillers

Direct-expansion (DX) chillers, one of many products that have traditionally used HCFC-22, are found in many industrial plant applications (Fig. 1). Plant engineers, therefore, should have an interest in how the phaseout impacts DX chillers. After all, chillers purchased today have a service life well into the 21st century when the phaseout will have begun to take effect.

The impact will vary from country to country. In countries with a late phaseout date, DX chillers containing HCFC-22 will be sold for some time. In countries with an early phaseout date, existing DX chillers may continue to operate with recycled HCFC-22 and not need to switch refrigerant. New DX chillers sold in countries with an early phaseout date must use refrigerants other than HCFC-22.