Skip to content

types of cooling coil in ahu

In an Air Handling Unit (AHU), cooling coils are essential components for cooling the air before it is circulated into the space. These coils can be designed in various ways depending on the application, energy efficiency, and cooling needs. Here are the most common types of cooling coils used in AHUs:

1. Chilled Water Cooling Coils

  • Description: These are the most commonly used cooling coils in AHUs, especially in commercial and large-scale applications. They use chilled water (typically between 4°C to 7°C) as the cooling medium.
  • Components: The coils are made from copper or aluminum tubes, and the chilled water is circulated through these tubes, which cools the surrounding air as it passes over the coil.
  • Application: Suitable for environments where cooling loads are variable, such as office buildings, shopping malls, and hospitals.

2. Direct Expansion (DX) Coils

  • Description: DX coils use refrigerants (such as R-22, R-410A) for cooling instead of chilled water. The refrigerant directly evaporates inside the coil to absorb heat from the air.
  • Components: The coil is typically made of copper tubes with aluminum fins, designed to maximize surface area for heat exchange.
  • Application: Common in smaller AHUs, where using a centralized chilled water system is not practical or necessary. They are used in systems where space or cost constraints are an issue, such as in smaller offices or retail spaces.

3. Evaporative Cooling Coils

  • Description: These coils use water evaporation as a cooling process. Water is sprayed or dripped over the coil, and the air passing over the coil is cooled by evaporation.
  • Components: Made from materials like aluminum or plastic, and the water is typically recirculated for efficiency.
  • Application: More common in areas with dry climates. They are an energy-efficient solution for cooling but work best in low humidity areas.

4. Cooling Coils with Glycol

  • Description: These coils use a glycol-water mixture as the cooling medium. Glycol is used when the temperature needs to be lower than what can be achieved with just water, or when the system needs to be protected from freezing.
  • Components: Similar to chilled water coils, but the fluid running through them is a mixture of water and glycol.
  • Application: Ideal for cold storage facilities, breweries, or cold climates where the freezing point of water would cause problems.

5. Two-Stage Cooling Coils

  • Description: These systems use a combination of different cooling methods to enhance cooling capacity. For instance, they might use a chilled water coil in combination with a DX coil.
  • Components: The system has two sets of coils, with one typically using water or glycol and the other using refrigerant, arranged in series or parallel for more effective temperature control.
  • Application: Often used in larger, more complex HVAC systems that require precise control of temperature and humidity.

6. Finned Tube Coils

  • Description: These are specialized coils that incorporate fins to increase the surface area for heat exchange. Finned tubes can be used in both chilled water and DX systems.
  • Components: Copper or aluminum tubes with aluminum fins, increasing the efficiency of heat transfer.
  • Application: Common in both commercial and industrial systems, particularly when the cooling load is high and space for heat exchange is limited.

7. Plate Heat Exchanger Coils

  • Description: In these systems, heat exchange happens between two separate plates or walls that allow fluids to pass through in alternating layers. It’s typically used when air and water are separated.
  • Components: Made of stainless steel or similar materials, with multiple thin plates stacked to maximize heat exchange.
  • Application: Used in high-efficiency or high-capacity systems, where the heat transfer between two fluids needs to be maximized.

Each type of coil has its strengths and is chosen based on the specific requirements of the HVAC system, the size of the building, energy efficiency needs, and the local climate.

Tags: