ASHRAE 90.4 is the energy standard written for data centers instead of applying office rules to them. It uses performance metrics for cooling and power distribution so designers can choose their own technologies while keeping overhead within limits. It is related to ASHRAE 90.1.

Does ASHRAE 90.4 set a PUE limit?

No. ASHRAE 90.4 uses MLC and ELC values, which separate cooling efficiency from power distribution losses. Operators still track PUE in operation, because 90.4 judges the design and does not follow the facility after commissioning.

Which ASHRAE 90.4 edition applies to my project?

Whichever your energy code adopted. Oregon, Virginia and Washington reference sections of 90.4-2019, while the 2024 IECC points to 90.4-2022. Confirm with the local code official before the design team runs compliance calculations.

How can an operator check 90.4 design assumptions in practice?

By metering cooling, distribution losses and IT load separately and comparing them with the design values. Aqueduct reads those feeders and shows loading and power factor, so operators can see where real overhead departs from design and use load disaggregation to explain it.

Glossary

Data centers

What is ASHRAE 90.4?

Definition

ASHRAE Standard 90.4 is the energy standard for data centers, setting minimum efficiency requirements for their design and operation through limits on mechanical load and electrical loss.

Scope

Per ASHRAE, it applies to data centers whose conditioned floor space has a power density above 20 watts per square foot and IT equipment loads above 10 kW. It covers new data centers and additions or alterations that need new mechanical or electrical systems. Since 2019, ASHRAE 90.1 has referenced 90.4 as an alternative path for large computer rooms.

The two compliance metrics

The mechanical load component (MLC) is the power for cooling, fans, pumps and heat rejection divided by data center power. The electrical loss component (ELC) sums the worst-case losses of each segment of the power chain, and the 2022 edition removed the incoming service segment from it.

ASHRAE now points DOE partners to the 2025 edition, but a project must meet the edition its energy code has adopted.

Comparing design overhead with operation

90.4 is checked at design, yet its terms map to real feeders. On the Aqueduct electrical twin, cooling feeders, UPS and distribution losses and IT load each show as a measured block with kVA loading and power factor, so operators can see whether overhead in service matches the design calculation.

What is ASHRAE 90.4?

Scope

The two compliance metrics

Comparing design overhead with operation

ASHRAE 90.4: common questions

See Aqueduct on your own facility.