This Air-Cooled Heat Exchanger spreadsheet from 3D-LABS follows ASME standards and gives instant, checkable results for practising engineers — no manual derivation required.
This spreadsheet sizes air-cooled heat exchangers (fin-fan coolers) per API 661 (7th Edition, 2013) and ASME Section VIII Div 1 for tube bundle design. It calculates the required bare tube area, selects fin geometry, determines the number of tube rows and bundle width, sizes the fan (airflow, power, tip speed), and produces the API 661 Data Sheet — the standard document required for all EPC procurement packages.
What standard does this calculation follow?
API 661 7th Edition (2013) for air-cooled heat exchangers, ASME Section VIII Div 1 for tube bundle pressure containment (tubes, tubesheets, headers), TEMA (9th Ed.) for tube layout patterns, and API 660 for shell-and-tube vs air-cooled selection criteria.
What formula is used?
Required bare tube area: A = Q / (U × LMTD × Ff), where Q = duty (W), U = overall heat transfer coefficient (W/m²·K), LMTD = log mean temperature difference (°C), Ff = fouling factor. Fan airflow: Qa = Q / (ρa × Cp,a × ΔTa), where ρa = 1.2 kg/m³ at 30°C. Fan power: P = Qa × ΔP / (η_fan × η_motor), where ΔP = tube bundle + plenum pressure drop (Pa).
Frequently Asked Questions
What standard governs air-cooled heat exchanger design?
API 661 7th Edition (2013) is the primary standard for air-cooled heat exchangers used in petroleum, petrochemical, and gas processing. It covers tube bundle design, fan selection (maximum tip speed 61 m/s for forced draft, 58 m/s for induced draft), noise limits (85 dB(A) at 1 metre), and acceptance testing. Tube bundles are also designed to ASME Section VIII Div 1.
What is the typical overall heat transfer coefficient U for an air-cooled exchanger?
For bare tubes: U = 30–50 W/m²·K (gas cooling), 60–120 W/m²·K (liquid cooling), 100–180 W/m²·K (condensing). For finned tubes (26 fins/inch aluminium, high-fin): U = 450–700 W/m²·K based on bare tube area. API 661 Appendix A provides default U values for common services.
What is the maximum allowable fan tip speed per API 661?
API 661 7th Ed. Clause 5.3.4.1 specifies maximum fan tip speed of 61 m/s for forced draft and 58 m/s for induced draft configurations. This limits noise and blade stress. Fan diameter is typically 30–60% of bundle width.
What’s Included
An instant Excel download with the complete formula set, a worked numerical example, and reference to the governing standard — ready to adapt to your own project inputs.
