It contains compressors and can run without ambient help.

Evaporative equipment has none.

That means no separate backup plant is needed.

It also means it costs more and is more complex.

It consumes no water in return.

The two suit different climates and site policies.

The ambient below which free cooling starts contributing.

It is not fixed by the chiller alone.

Loop temperature moves it as much as hardware does.

A warmer loop starts free cooling sooner.

That buys hours at no hardware cost.

Ask for it against the site's design temperatures.

It covers a much wider band of ambient.

Full free cooling needs genuinely cold weather.

Partial hours accumulate most of the annual saving.

The coil does part and compressors do the rest.

Single annual percentages hide this entirely.

Ask for full and partial hours separately.

Raise the chilled water temperature.

Modern IT tolerates warmer supply than assumed.

Every degree widens the free cooling window.

It costs nothing in equipment.

Liquid cooled halls widen it further still.

Design the loop temperature deliberately.

Almost always, and it must be in the sizing.

The free cooling coil is exposed to ambient.

Freezing would split it.

Glycol reduces heat transfer and raises pumping power.

Use the lowest concentration the climate needs.

Over-dosing is common and quietly costly.

Multiple smaller machines rather than one large one.

Loss of one then costs part of the capacity.

It also improves part load efficiency.

Pipework must let a machine be isolated.

That valving is easy to omit at design stage.

Agree the failure case before selection.

The ambient conditions every figure assumes.

Full and partial free cooling hours for the site.

Glycol type and concentration used in the rating.

Sound levels at the boundary.

Part load efficiency, not only full load.

Spares and service cover in the region.