Title 24 Requirements for Computer Rooms and Data Centres
A room whose primary function is housing electronic equipment, at a design power density above 20 watts per square foot, is a computer room. Above 10 kW of rack load it needs air barriers, and fan power is capped at 27 W per kBtu/h of net sensible cooling.
20 W/sq ft is the definition and the trigger
A computer room is a room within a building whose primary function is to house electronic equipment and that has a design equipment power density exceeding 20 watts per square foot of conditioned floor area. Rooms above that density must comply with the section.
Note that this is a density test, not a size test and not a name test. A modest server room in an office building can be a computer room under the code; a large room full of desks with computers on them is not, because the density is nowhere near it. There is no separate definition for a "data centre" — a data centre is computer rooms.
Air containment from 10 kW
Computer rooms with air-cooled computers in racks and an ITE design load exceeding 10 kW — about 2.8 tons — per room must include air barriers.
Ten kilowatts is a low bar. That is a handful of well-populated racks, so the requirement reaches server rooms rather than only purpose-built facilities. Air containment means physically separating cold supply air from hot exhaust — hot-aisle or cold-aisle containment — so the cooling system is not fighting its own return air. Without it, hot exhaust mixes back into the intake and the plant works harder to deliver the same result.
The fan power cap
Total fan power at design conditions for each fan system must not exceed 27 watts per kBtu/h of net sensible cooling capacity.
Net sensible capacity is the operative term. A computer room load is almost entirely sensible — servers produce heat and no moisture — so rating the fan power against sensible capacity measures the system against the work it actually does. Using total capacity would flatter a system designed for a load that does not exist here.
Economizers, and the two temperature sets
Each cooling system must include an integrated economizer, and there are two routes with genuinely different thresholds:
- Air economizer — capable of 100 per cent of the cooling load at 65°F to 80.6°F supply air, with outside air at or below 65°F dry-bulb or 50°F wet-bulb
- Water economizer — capable of 100 per cent of the load at the same supply temperatures, with outside air at or below 50°F dry-bulb or 45°F wet-bulb
The air route gets the more generous outside-air condition, which means it can free-cool for far more hours in most of California. The water route needs genuinely cool outside air but brings no outside air into the room — which matters where contamination or humidity control is a concern.
Why the supply range goes to 80.6°F
The upper figure looks warm for a server room, and that is deliberate. Equipment tolerances allow far higher intake temperatures than the traditional cold data hall assumed, and every degree of allowed supply temperature buys many more hours of economizer operation. A room designed to run at 65°F throws away most of the free cooling the climate offers.
What to establish early
The design power density, the ITE load per room, and whether the cooling system can free-cool at the stated conditions. All three are decided at mechanical design, and air containment in particular is very hard to add to a room already built and populated.