By varying how much air each zone gets.

Supply temperature stays roughly constant.

Each zone throttles to hold its own setpoint.

One plant then serves many different loads.

Fan power falls as demand falls.

That is why it dominates commercial buildings.

Often only the box.

Controls are frequently a separate line.

Actuators may or may not be fitted.

Reheat coils are usually an option.

Assuming a complete assembly causes site delays.

Confirm the scope item by item.

Commissioning, more than product selection.

Every box has a minimum and maximum flow.

Both must be set and proved at the box.

Instruments are required, not observation.

Absence of complaints proves nothing.

Budget the commissioning time properly.

It is where energy quietly disappears.

Set too high, zones get more air than they need.

That air then has to be reheated.

Cooling and heating fight across the building.

Nobody complains, so nobody investigates.

Review minimums against actual occupancy.

Ideally one zone with one thermal behaviour.

Combining a south facade with an interior room fails.

The controller can only satisfy one sensor.

The other space is always wrong.

Zoning errors cannot be fixed by controls.

Settle zoning before selecting terminals.

Terminals sit above occupied ceilings.

Throttling generates noise at high pressure drop.

Manufacturers publish sound data by pressure.

Excess inlet pressure is the usual cause.

Attenuation after the fact is expensive.

Check sound at the actual design pressure.

Enough to reach the controller and the actuator.

Boxes sit above ceilings, often above other services.

An access panel must be provided beneath.

Commissioning and fault-finding both need it.

Panels are omitted surprisingly often.

Record the location of every box.