Dry Cooler / Fluid Cooler Calculator
Guide for dry cooler and fluid cooler sizing: approach temperature, glycol concentration, fan power, and ambient conditions.
1. Overview
A dry cooler (also called fluid cooler or dry fluid cooler) rejects heat from a process fluid to ambient air without evaporative cooling. The fluid circulates through finned-tube coils while fans force ambient air across the finned surface. Unlike cooling towers, dry coolers have no water consumption and minimal maintenance.
The key design parameter is the approach temperature — the difference between the fluid outlet temperature and the ambient air temperature. Lower approach temperatures require larger coil surface area.
2. Input Parameters
Air Side
| Parameter | Unit | Description |
|---|---|---|
| Dry Bulb Temperature | °C | Ambient air temperature (design condition) |
| Face Velocity | m/s | Air velocity across coil face (typically 2–4 m/s) |
| Altitude | m | Installation altitude |
Fluid Side
| Parameter | Unit | Description |
|---|---|---|
| Fluid Type | — | Pure Water, Ethylene Glycol, or Propylene Glycol |
| Inlet Temperature | °C | Hot fluid entering the cooler |
| Outlet Temperature | °C | Target fluid outlet temperature |
| Flow Rate | kg/h | Mass or volumetric flow rate |
3. Approach Temperature
The approach temperature (T_fluid_out − T_air_in) is the most critical design parameter:
| Approach | Coil Size | Application |
|---|---|---|
| > 10 K | Compact | Process cooling with high fluid temperatures |
| 5–10 K | Standard | General HVAC and industrial cooling |
| 3–5 K | Large | Data center cooling, free cooling |
| < 3 K | Very large | Economically challenging, consider hybrid coolers |
The fluid outlet temperature can never be lower than the ambient air temperature in a dry cooler. If lower temperatures are needed, consider an evaporative (wet) cooling tower or a hybrid cooler.
4. Glycol Effects
Glycol is commonly added for freeze protection in outdoor installations. However, it significantly impacts performance:
- 30% ethylene glycol: ~15% capacity reduction, ~40% higher pressure drop
- 50% ethylene glycol: ~25% capacity reduction, ~100% higher pressure drop
- Propylene glycol has even higher viscosity than ethylene glycol at the same concentration
Tip: Use the minimum glycol concentration needed for the expected minimum temperature plus a 5°C safety margin. Over-concentrating glycol wastes pump energy and reduces heat transfer.
5. Applications
- Data Centers: Free cooling when ambient temperature is low enough to reject server heat without mechanical refrigeration
- Process Cooling: Cooling process fluids (hydraulic oil, cutting fluid, glycol loops)
- Chiller Condenser Water: Rejecting heat from water-cooled chillers without a cooling tower
- Heat Pump Rejection: Heat rejection loop for water-source heat pump systems