Working Principle of Dry Cooling Coil

A dry cooling coil (or dry coil) is a heat exchanger operating under a special mode in air conditioning and refrigeration systems. Its core characteristic is that the coil surface temperature is higher than the indoor air dew point temperature, therefore no condensation is produced during operation; it is in a "dry" state. This contrasts sharply with ordinary "wet coils" (which handle sensible heat and latent heat, producing condensation).

Core Definition and Working Principle: Operating conditions for a dry cooling coil: When the temperature of the chilled water flowing through the coil is sufficiently high (typically 2-3°C higher than the indoor air dew point temperature), the coil surface temperature will not cause water vapor in the air to condense. Therefore, only sensible heat exchange (cooling) occurs, not latent heat exchange (dehumidification).

Typical inlet and outlet water temperatures: Inlet water approximately 12-14℃, outlet water approximately 17-19℃ (temperature difference approximately 5℃)

Typical face velocity: ≤2.5 m/s, to ensure heat exchange efficiency and prevent water blowing.

Working process: Low-temperature chilled water (temperature above dew point) flows through copper tubes, absorbing heat from the air passing through the fins. After the water temperature rises, it returns to the chiller unit. Because there is no condensation on the surface, the coils maintain high heat transfer efficiency and prevent bacterial growth.

Typical application scenarios:

3.1 Cleanrooms/Operating Rooms: Dry coils are standard equipment in cleanroom air conditioning systems. The fresh air handling unit (MAU) handles the entire moisture load (dehumidification), while the dry coils only control the indoor temperature, without producing condensation, thus avoiding bacterial growth and the risk of cleanroom contamination.

3.2 Data Centers/Server Rooms: Server rooms have high sensible heat loads and extremely low latent heat loads. Dry coils or dry coolers can efficiently remove heat, and no water enters the server room area, ensuring equipment safety.

3.3 Dry Cooling System

In a dry cooler, ethylene glycol solution or water flows through the coils, and air cools the fluid. The coils always operate in a "dry" state (no evaporation), achieving water conservation.

Key Points for Selecting Dry Cooling Coils

Confirm Operating Mode: Determine whether it is a true dry coil (no condensate) or a dry cooler (dry chiller). The former is used for cleanroom temperature control, while the latter is used for industrial fluid cooling.

Calculate Sensible Heat Load: Dry coils do not handle latent heat; therefore, the sensible heat of the room (equipment, lighting, personnel sensible heat) must be strictly calculated during selection.

Determine Inlet Water Temperature: The inlet water temperature must be at least 2-3°C higher than the indoor dew point temperature. For example, in a room at 24°C/50%RH (dew point approximately 13°C), the inlet water temperature should be approximately 15-16°C.

Face Wind Speed ​​Control: To reduce noise and prevent water splattering, the face wind speed is recommended to be controlled at 2.0-2.5 m/s. Excessive airflow velocity increases fan energy consumption and may trap condensate.

Number of rows and fin spacing: For cleanroom environments, 3-4 rows of pipes with a fin spacing ≥2.5mm are recommended to prevent dust accumulation and cleaning difficulties.

Material selection: Standard environments use copper pipes with aluminum fins and a galvanized steel frame; humid/corrosive environments can use stainless steel pipes/stainless steel fins or epoxy coating; food/pharmaceutical applications recommend all stainless steel.