HomePressure EquipmentAir cooler sizing
    Pressure Vessels & Heat Exchangers

    Engineering tool

    Air Cooler — Plot Area & Fan Power

    Air-side preliminary sizing of an air cooled heat exchanger. It does not compute the heat transfer surface — that is a rating job, and it belongs to whoever builds the unit. It answers the question that comes first and that the vendor cannot answer for you, because it is about your plant: how much air, how much ground, how many fans and how many kilowatts of electrical load.

    Process side

    Set the process flow to 0 to use the duty field instead. For a condensing service that is the way in: specific heat does not describe it.

    Air & site

    The air temperature rise is a design choice, not a datum: a smaller rise means more air and more fan power, a larger one means more surface. Typically 10 to 25 K.

    With induced draft the fans handle the hot air leaving the bundle, which is less dense: same duty, more volume and more power.

    Bundle geometry

    Bay width is normally a transport constraint. API 661 asks for at least two fans per bay and a fan area of at least 40% of the face area.

    Fans

    Bundle footprint

    65 m²

    2 × 10.0 × 3.26 m

    Fans

    4

    ⌀ ≥ 3.06 m

    Absorbed power

    44 kW

    11.0 kW per fan

    Intermediate resultValueRelation
    Thermal duty4,400 kWQ = qm · cp · (T₁ − T₂)
    Air outlet temperature55.0 °Ct₂ = t₁ + Δt
    Approach25.0 KT₂ − t₁
    LMTD, counter-current41.86 K(ΔT₁ − ΔT₂) / ln(ΔT₁/ΔT₂)
    Air mass flow218.7 kg/sqm,air = Q / (cp,air · Δt), cp = 1.006
    Site atmospheric pressure98.95 kPap = 101.325 · (1 − 2.256e-5·h)^5.2559
    Air density at the fan1.1186 kg/m³ρ = p / (R·T), T = 35 °C
    Volumetric air flow195.5 m³/sqv = qm,air / ρ
    Total face area65.2 m²A = qv / v_face
    Bay width3.26 mW = A / (n_baie · L)
    Minimum fan diameter3.06 mD = √(4·ratio·A / (π·n_fan))
    Fan shaft power41.9 kWP = qv · Δp / η_fan
    Absorbed power per motor11.0 kWP / (η_trasm · n_fan)
    Specific fan power10.0 kW/MWelectrical per thermal

    What this does not cover

    This is the air side only. It says nothing about the heat transfer surface, the fin geometry, the tube-side pressure drop, the number of passes, winterisation and recirculation, noise, or the mechanical design of headers and structure. The footprint is the bundle alone: plenum, walkways, structure and maintenance access all add to it. It is a screening calculation, not a verification, and carries no warranty.

    Need the real design?

    We design air cooled heat exchangers to API 661 for the manufacturers who build them: thermal rating, header and tube bundle mechanical design to ASME VIII and PED, and the supporting structure. Send us the datasheet.

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