AHU Components: Fans, Filters, and the Recovery Core

Anatomy of an Air Handling Unit

An AHU conditions outdoor air before it enters a building. The core components are: the supply fan, the exhaust fan, filters, coils (heating/cooling), and – increasingly – a heat recovery core. How these are arranged decides both air quality and energy use.

Fans

Supply and exhaust fans move the air. Their efficiency and the pressure drop across every component set the fan power. A recovery device that adds 100 Pa can quietly raise energy use by 10-20%.

Filters

Filters protect occupants and coils. Rating runs from coarse (ISO Coarse / MERV 8) to fine (ePM1 / MERV 13+). Cleaner air costs more pressure drop, so filter choice and recovery placement must be balanced together.

The recovery core

The recovery core – plate, rotary, heat pipe, or run-around coil – sits between the two airstreams. In a new build it is designed in; in a retrofit it is added to the exhaust riser (see retrofit guide).

Sizing the whole unit

Recovery must be sized with the AHU, not bolted on. Use our AHU selection calculation to balance effectiveness, pressure drop, and fan energy before ordering.

Coils and the recovery interaction

Heating and cooling coils sit on either side of the recovery core, and their duty shrinks as the core pre-conditions the air. Sizing coils on unrecovered design conditions wastes capacity and cost, while sizing them on recovered conditions lets the core do the first stage of work. The coil and core should be specified together so the plant is neither oversized nor starved at part load.

Controls and sequencing

The air handling unit controller ties fans, filters, coils, and the recovery core into one sequence. A well-written sequence modulates the core and bypass, trims coil output to the recovered air temperature, and protects filters and fans from overload. Poor sequencing can leave the recovery core fighting the coils, eroding the very savings it was installed for.

Commissioning the whole unit

Recovery only pays when the assembled air handling unit meets its spec as a system. Commission by measuring supply and exhaust airflow, the temperature rise across the core, and the total pressure drop, then comparing against the AHU selection calculation. Trend these values so filter loading, belt slip, or core fouling shows as drift rather than a sudden complaint. Balance effectiveness, pressure drop, and fan energy before sign-off.

Frequently Asked Questions

What are the main AHU components?
The supply and exhaust fans, filters, heating and cooling coils, and increasingly a heat recovery core.

How does the recovery core interact with coils?
It pre-conditions the air, shrinking coil duty, so size coils on recovered conditions rather than unrecovered design conditions.

Why size recovery with the whole AHU?
Bolt-on recovery can raise pressure drop and fight the coils. Integrated sizing balances effectiveness, pressure drop, and fan energy.

How do I verify AHU performance?
Measure supply and exhaust airflow, the core temperature rise, and total pressure drop against the AHU selection calculation, and trend for fouling.

Frequently Asked Questions

What are the main AHU components?

The supply and exhaust fans, filters, heating and cooling coils, and increasingly a heat recovery core.

How does the recovery core interact with coils?

It pre-conditions the air, shrinking coil duty, so size coils on recovered conditions rather than unrecovered design conditions.

Why size recovery with the whole AHU?

Bolt-on recovery can raise pressure drop and fight the coils. Integrated sizing balances effectiveness, pressure drop, and fan energy.

How do I verify AHU performance?

Measure supply and exhaust airflow, the core temperature rise, and total pressure drop against the AHU selection calculation, and trend for fouling.