# Facility cooling and final heat rejection

Canonical: https://semiaifoundry.com/learn/atlas/cooling-plant/
Revision: 2026-10-07
Rights: https://semiaifoundry.com/ai-atlas/licenses.html

Thermal infrastructure · Atlas v1.3.0

# Facility cooling and final heat rejection

Carries heat from IT equipment to the outdoor environment or an approved reuse path.

[Explore in Atlas](https://semiaifoundry.com/ai-atlas/#cooling-plant)Building-to-campus thermal infrastructure

Learning objectiveDistinguish cooling-system COP from full-facility power accounting.

## The mechanism

Heat removed from a processor has not vanished; it moves through successive thermal interfaces and fluid or air circuits. The facility cooling chain eventually rejects that heat outdoors or directs it into a useful heat-recovery application. Depending on climate and design, equipment can include heat exchangers, dry coolers, cooling towers, chillers, pumps, and air-handling systems. The atlas follows one unit of heat from the rack to its final destination and keeps water flow distinct from electrical energy use. Different arrangements trade energy and water consumption differently, so liquid cooling alone does not determine the total environmental footprint. Facility performance must be assessed across the complete heat-removal system and its operating conditions.

1.  Collect heat from IT and supporting equipment.
2.  Transport it through the selected facility cooling stages.
3.  Reject or reuse the heat while accounting for the supporting energy and water flows.

## Science and assumptions

### Cooling energy boundary

$$
\mathrm{COP}=\frac{\dot Q_{\mathrm{removed}}}{P_{\mathrm{cooling}}},\qquad P_{\mathrm{facility}}=P_{IT}+P_{\mathrm{support}}
$$

Cooling COP is heat removed divided by cooling electrical power. Facility power is IT power plus support power.

Symbols and units

COP

Cooling coefficient of performance

dimensionless

Q̇\_removed

Heat removed within the specified cooling boundary

W

P\_cooling

Electrical input to that cooling boundary

W

P\_facility

Total facility real power

W

P\_IT

IT equipment real power

W

P\_support

All non-IT support real power within the facility boundary

W

A cooling system uses supporting power to transport heat. Measuring only the chip loop omits the pumps, fans, chillers, and other facility functions that may contribute to the complete system.

Assumptions Steady accounting within an explicitly chosen boundary; COP is a cooling-performance ratio, while total facility accounting also includes non-cooling loads.

## Engineering example

Synthetic plant removes 1 MW of heat with 0.2 MW of cooling electricity, so COP = 5. If IT load is 1 MW and other support uses 0.1 MW, facility input is 1 + 0.2 + 0.1 = 1.3 MW at that boundary; COP is not the facility/IT ratio.

## Distinctions and tradeoffs

Liquid cooling at the chip does not by itself imply zero water use or zero cooling energy across the facility.

Cooling choices trade energy, water, and operating range. Local climate and system boundaries change the comparison.

Cooling capacity constrains sustainable compute density. The building must carry away the heat generated by active hardware.

## Specifications and interfaces

Energy balance

Heat is transported and rejected

Cooling does not destroy energy.

Equipment mix

Design- and climate-dependent

No universal requirement for every listed component.

Water-use metric

Liters per kWh of IT energy

Site water-use effectiveness has a defined system boundary.

### Interfaces

Rack and facility return loops Input

Collected heat

Environment or reuse system Output

Rejected or recovered thermal energy

## Check your understanding

### Where does removed processor heat ultimately go?

1.  It is erased by the coolant
2.  It becomes extra training accuracy
3.  To an external heat sink or a heat-reuse system

Answer and reasoning

To an external heat sink or a heat-reuse system

Cooling transfers energy through the system. A complete explanation must identify the final heat destination.

## Evidence and scope

The example uses steady matched boundaries and invented loads. Heat-rejection method, environmental conditions and other support equipment affect actual power and water use; circulating water is not automatically consumed water.

No current calculator directly models this lesson’s main mechanism. Use the library for related bounds while retaining their stated omissions.

## Sources

-   [US Department of Energy — Data-Center Cooling Water Efficiency](https://www.energy.gov/cmei/femp/cooling-water-efficiency-opportunities-federal-data-centers)

[Published lesson data](https://semiaifoundry.com/ai-atlas/lesson-data/cooling-plant-b358ef0e7cccb5b9.json) · [Atlas releases and licensing](https://semiaifoundry.com/ai-atlas/licenses.html)

## Continue exploring

### Foundations

-   [Coolant distribution unit and separated loops](https://semiaifoundry.com/learn/atlas/cdu/)

### Related lessons

-   [Integrated accelerator rack: GB200 NVL72 example](https://semiaifoundry.com/learn/atlas/rack/)
-   [Rack power shelf and DC busbar](https://semiaifoundry.com/learn/atlas/power-shelf/)