Demand control ventilation (DCV) varies outdoor air with occupancy using CO₂ sensors, so you are not conditioning and recovering a fixed maximum airflow when a space is empty. Pairing DCV with an energy recovery ventilator (ERV) compounds the savings: you move less air and reclaim more of its energy. Done well, the two controls talk to each other so the ERV and the outdoor-air damper track the same signal.
Why combine them
An ERV recovers a percentage of the energy from whatever airflow passes through it. If DCV cuts that airflow by 30% during low occupancy, you save both the fan energy and the heating or cooling of that air – while the ERV still recovers the same percentage from the reduced stream. The ERV does the "free" recovery; DCV avoids moving air you do not need. The two together routinely beat either strategy alone by a wide margin in intermittently occupied spaces.
Control logic that works
- Sensor: CO₂ in the return or occupied zone, setpoint typically 800 to 1,000 ppm above outdoor background.
- Outdoor-air damper: modulates between a code minimum and the design maximum based on the highest CO₂ reading.
- ERV bypass: opens when recovery would fight the load, for example in very mild weather when you want free cooling.
Sensor placement and code
Place CO₂ sensors where people actually sit, not near the door or a return grille that reads stale air prematurely. DCV must still respect the minimum outdoor-air fraction in ASHRAE 62.1; recovery never reduces that minimum. Our ASHRAE 90.1 guide explains when recovery is mandated, and the ERV guide covers the device side.
| Mode | OA flow | ERV state |
|---|---|---|
| Empty | Minimum | Recover |
| Half full | ~50% | Recover |
| Full | Design max | Recover / bypass if mild |
Savings example
A 2,000 m² office with design outdoor air of 6,000 m³/h and average occupancy of 40% cuts airflow to about 3,000 m³/h. With a 75% effective ERV and a 25 K heating differential, recovered energy drops from about 52 kW to 26 kW, and fan power falls with roughly the cube of flow. See the air-to-air basics and efficiency for the device background.
Commissioning and proving the savings
Demand-control systems tend to fail in commissioning rather than in design, so verify the CO₂ reset before claiming any saving. Confirm the outdoor-air damper modulates smoothly between the code minimum and the design maximum and that the ERV tracks it without hunting. A variable-occupancy space such as a school gym or a divisible conference room is the clearest demonstration: log CO₂, outdoor-air flow and recovered kilowatts for a month and show that air quality stayed within target while energy fell. Keep the ASHRAE 62.1 minimum outdoor-air fraction as a hard floor in the controller so an over-aggressive setpoint can never starve the space of fresh air. Trend the data so the next retrofit decision rests on evidence rather than on a hopeful assumption.
Specification checklist
- Set the CO₂ setpoint against measured outdoor background, not a generic number.
- Place sensors in the occupied zone, away from doors and stale-air returns.
- Never let DCV drop below the ASHRAE 62.1 minimum outdoor-air fraction.
- Drive the ERV damper and the outdoor-air damper from one control signal.
- Enable an ERV bypass for mild weather to allow free cooling.
- Trend CO₂ and airflow together to prove indoor air quality held up.
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.
Request a quote