01 / THE BIG PICTURE
Start with the essentials.
Two different questions are often mixed together: how does the system cool the room air, and how does the equipment release heat outside? Understanding the difference makes equipment descriptions and quotations clearer.
02 / STEP BY STEP
How the system works.
- 01
Identify the room cooling coil
Does it receive chilled water or refrigerant? This distinguishes chilled-water cooling from DX at the air coil.
- 02
Identify the source equipment
A chilled-water coil connects to a water system and chiller. A DX coil connects to a refrigeration system.
- 03
Identify heat rejection
An air-cooled condenser uses outdoor air; a water-cooled condenser transfers heat to water.
- 04
Describe the complete system
Use the equipment type, cooling medium and actual model together when making an enquiry.
03 / LOOK A LITTLE CLOSER
The details that matter.
Chilled water
Water circulates through cooling coils in AHUs or FCUs. The chiller removes heat from the returning water, and pumps circulate the water through the system.
Direct expansion / DX
Refrigerant absorbs heat directly at the air-cooling coil. Wall splits, many packaged systems and VRF systems use this approach. An AHU may also contain a DX coil.
Air-cooled and water-cooled
These terms describe condenser heat rejection when discussing chillers. Both air-cooled and water-cooled chillers can supply chilled water to a building.
04 / AT A GLANCE
Keep these distinctions clear.
| Term | What it describes | Meaning |
|---|---|---|
| Chilled water | Medium at the cooling coil | Water circulates between plant and building coils. |
| DX | Medium at the cooling coil | Refrigerant cools the air directly at the coil. |
| Air-cooled chiller | Heat rejection method | Condenser releases heat to outdoor air. |
| Water-cooled chiller | Heat rejection method | Condenser releases heat to a water circuit. |
THE KEY TAKEAWAY
“Water-cooled” and “DX” are not opposite choices in the same classification. Describe the actual equipment and circuit to avoid confusion.
05 / COMMON QUESTIONS
Good questions to ask.
Can an AHU have either type of coil?
Yes. AHUs may be designed with chilled-water or DX coils, among other arrangements.
Is a cooling tower the same as a chiller?
No. In a typical water-cooled plant, the chiller removes heat from chilled water and the tower rejects heat from condenser water to the outdoors.
Further reading
Carrier: chillersThis guide explains typical arrangements. Equipment selection, technical settings and repair procedures must follow the actual system design and manufacturer’s instructions.
