Classrooms pack many children into a small volume and generate CO₂ and moisture quickly, so code minimum ventilation rates are high – often 4 to 8 litres per second per person. Without recovery, heating or cooling all that outdoor air is expensive and can push schools to under-ventilate. An ERV makes high ventilation rates affordable while keeping indoor air quality where it should be.
The classroom load in numbers
A 30-student room at 6 L/s per person needs about 650 m³/h of outdoor air. In winter that air must be heated from -5°C to +20°C; in summer cooled and dehumidified. Recovery returns most of the energy already paid for on the exhaust side, so the heating and cooling plant sees a much smaller net load. The result is that a school can meet ventilation codes without a punishing energy bill.
What works in schools
- Plate ERV per classroom or per cluster – simple, quiet and easy to commission, with no rotating parts in the occupied space.
- Central ERV on the AHU serving multiple rooms, with ducted exhaust and balanced pressure.
- Enthalpy wheels where humidity control is a priority in humid climates, with a wash section for air quality.
Air quality and acoustics
School units must be quiet (keep terminal units below about 35 dBA in the room) and must not recirculate contaminants; a plate or enthalpy device transfers energy, not air, so supply stays separated from exhaust. Use CO₂ or occupancy sensing to confirm ventilation keeps pace with a full room, and service filters on a visible schedule so performance does not drift over the term.
| Setting | OA need | ERV saving |
|---|---|---|
| Classroom (30 pupils) | ~650 m³/h | 70% to 80% |
| Hall / gym | 2,000+ m³/h | 65% to 75% |
| Staff room | ~300 m³/h | 70% to 80% |
Payback across a campus
Recovering 75% on 650 m³/h against a 25 K winter difference saves about 650 ÷ 3,600 × 1.2 × 25 × 0.75 ≈ 4.1 kW per classroom continuously through the heating season – and that repeats across dozens of rooms. See the ERV guide, DOAS systems, efficiency and air-to-air basics.
Pairing with DOAS and proving air quality
In many schools the ERV sits inside a dedicated outdoor-air system, or DOAS, that delivers conditioned fresh air to each room, which keeps the recovery device on the central, easily serviced air path rather than scattered across rooftops. The payoff is twofold: the winter heating load and the summer dehumidification load both fall, and the smaller remaining load lets a modest heat pump or chiller serve the building comfortably. To prove the investment, log CO₂ in a representative classroom across a full school day; the trace should stay within target even at peak occupancy, demonstrating that high ventilation rates are now affordable rather than a budget line to be cut. Put filter changes on the termly calendar so the unit keeps performing instead of quietly drifting as the screens load up.
Specification checklist
- Base outdoor-air rates on actual occupancy, not the worst-case design alone.
- Keep classroom terminal noise below about 35 dBA for learning.
- Use plate or enthalpy devices so supply and exhaust air never mix.
- Add CO₂ or occupancy sensing to confirm ventilation keeps up.
- Put filter changes on a visible termly schedule to stop drift.
- Scale the payback across the whole campus, not one room, to show value.
Specifying a unit for your project?
EN159 builds plate, rotary, heat-pipe, run-around coil and counterflow air-to-air exchangers. Send airflow (m3/h), inlet temperatures and available space and we will size it.
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