Engineering tool
Dry cooler sizing calculator
Check a duty before you send it: heat load or flow for water and glycol loops, ITD and approach to your design ambient, and what a catalogue rating is worth at your site. Results update as you type.
Method
How the calculator works
Heat load: Q [kW] = flow [m³/h] × density [kg/m³] × specific heat [kJ/kg·K] × ΔT [K] ÷ 3600. Solving for flow gives the flow needed to carry a heat load at a chosen ΔT.
ITD is the fluid inlet temperature minus the air inlet temperature. Approach is the fluid outlet temperature minus the air inlet temperature. A dry cooler cannot cool the fluid below the air temperature, so the approach must be positive, and a small approach needs a large coil.
Re-rating: for the same coil, fluid, flow and fluid inlet temperature, capacity scales roughly with ITD: Q at site ≈ Q at catalogue × (Tin − Tsite) ÷ (Tin − Tcatalogue). This is why a unit rated at 25 °C ambient loses so much capacity at a 40 °C site.
Fluid data
Fluid properties used
Approximate values at about 40 °C, concentrations by mass. Freeze points are approximate.
| Fluid | Density (kg/m³) | Specific heat (kJ/kg·K) | Freeze point |
|---|---|---|---|
| Water | 992 | 4.18 | 0 °C |
| Ethylene glycol 20 % | 1021 | 3.89 | ≈ −8 °C |
| Ethylene glycol 30 % | 1031 | 3.72 | ≈ −15 °C |
| Ethylene glycol 40 % | 1041 | 3.54 | ≈ −24 °C |
| Ethylene glycol 50 % | 1051 | 3.35 | ≈ −36 °C |
| Propylene glycol 20 % | 1011 | 4.00 | ≈ −7 °C |
| Propylene glycol 30 % | 1017 | 3.89 | ≈ −13 °C |
| Propylene glycol 40 % | 1024 | 3.75 | ≈ −21 °C |
| Propylene glycol 50 % | 1030 | 3.60 | ≈ −33 °C |
FAQ
Dry cooler calculation questions
How do you calculate the heat load on a dry cooler?
Multiply volume flow by fluid density, specific heat and the fluid temperature drop: Q [kW] = flow [m³/h] × density [kg/m³] × cp [kJ/kg·K] × ΔT [K] ÷ 3600. Glycol mixtures have lower specific heat than water, so the same flow and ΔT carry less heat.
What is ITD on a dry cooler?
ITD (inlet temperature difference) is the fluid inlet temperature minus the air inlet temperature. For a given coil, fluid and flow, dry cooler capacity is roughly proportional to ITD, which is why capacity falls as ambient rises.
What is a typical approach temperature for a dry cooler?
Approach is the fluid outlet temperature minus the air inlet temperature. Selections commonly use 5–10 K; tighter approaches are possible but need more coil surface and fan power, and a dry cooler cannot cool fluid below the air temperature.
Application notes