Airport terminals are enormous, continuously occupied volumes that run ventilation 24 hours a day, every day of the year. A mid-size terminal of 50,000 m2 at a modest 6 to 10 air changes per hour moves 300,000 to 500,000 m3/h of outdoor air. Heating that make-up air from a -15 degrees C winter design to a 20 degrees C supply is a 4 to 5 MW load before a single passenger is served, and cooling the same volume in summer is comparably large. Because the building never shuts down, every percent of recovery compounds into millions of kilowatt-hours per year and shows up directly on the utility bill.
The scale of the prize
At 400,000 m3/h, the sensible heating load is q = 400000 x 1.2 x 1.005 x 35 / 3600, about 4.7 MW. A plate or wheel recovery core at 75% effectiveness returns roughly 3.5 MW to the supply airstream, cutting boiler or preheat coil capacity and the associated fuel bill by a comparable fraction. Even a 5-point rise in effectiveness, from 70% to 75%, is worth about 235 kW of continuous heating plant at design conditions, which over a heating season translates into hundreds of tonnes of avoided CO2.
| Climate | Dominant load | Best recovery type | Typical saved capacity |
|---|---|---|---|
| Cold (Helsinki) | Heating | Counterflow plate, 80%+ | 3.5 to 4.5 MW |
| Temperate (Chicago) | Heating + cooling | Plate or wheel | 2.5 to 3.5 MW |
| Humid (Miami, Singapore) | Latent cooling | Enthalpy wheel, 70% latent | Large reheat + cooling cut |
Wheel vs plate in a terminal
Unlike hospitals, terminals have no strict supply-exhaust separation requirement for public conformance spaces, so a rotary enthalpy wheel is often the most cost-effective choice: it recovers both sensible and latent energy at 75% to 85% sensible and 60% to 70% latent, which is decisive in humid climates where reheat and dehumidification dominate plant energy. Plate exchangers win where modularity and low carryover matter, and where the make-up air unit has a tight pressure budget. Either way the core should sit upstream of the cooling coil so the recovered energy pre-conditions the air before the expensive refrigeration stage, lowering both coil size and compressor runtime.
Sizing the core for the real load
Terminal loads swing hard between a packed security queue at 06:00 and an empty concourse at 03:00, so size the core near the average duty rather than the peak and provide parallel cores or a bypass for the rare peaks. Keep face velocity in the 2.0 to 2.5 m/s band where plate effectiveness stays high and pressure drop stays under 300 Pa; above 3 m/s the extra fan energy erodes the saving. Redundancy matters in a 24/7 operation, so split the recovery across two smaller cores so a single fouled unit never takes the whole concourse off recovery.
Control sequence that protects the saving
The recovery core should be the first stage the controls touch. In heating, modulate the preheat coil downstream of the wheel so the burner only tops up what the core cannot deliver; in cooling, place the core ahead of the cooling coil so recovered energy does the pre-conditioning before refrigeration. Add an economizer interlock that opens the bypass whenever outdoor air is within a degree or two of the return, so the terminal free-cools instead of forcing air through a core it no longer needs. For the underlying efficiency maths see heat exchanger efficiency and the commercial building recovery overview, which scales the same logic to offices and retail.
Specifying a unit for your project?
EN159 builds plate, rotary, heat-pipe and counterflow air-to-air exchangers for commercial, industrial and healthcare duty. Send airflow (m3/h), inlet temperatures and available space and we will size it.
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