Server Room Air Conditioning: Keeping a Small Server Room Cool

IT rooms and comms cupboards

Plenty of small and medium businesses run their servers, network switches and storage from a converted storeroom with a single wall split on the wall. It works, until a hot afternoon, a blocked drain or a power cut proves it doesn't. A little planning goes a long way.

Why comfort units fall short as server room air conditioning

A normal wall split is a comfort unit. It's designed to keep people comfortable in an office or bedroom for part of the day, with the load rising and falling as the sun moves and people come and go. A server room is a very different job.

It never gets a break

IT equipment produces heat around the clock, so the aircon runs around the clock too. Comfort units can do this, but continuous duty means more wear on fans and compressors, which makes regular servicing far more important than it would be in an office.

The heat is almost all "dry" heat

Comfort units spend part of their effort removing moisture from the air, because people breathe and sweat. Servers don't add moisture, they only add heat. Purpose-built close-control units are designed for that kind of load, which is why larger server rooms often use them instead of ordinary splits.

Winter nights can be a problem

On the Highveld, a frosty winter night is exactly when a comfort split may be asked to cool a warm server room while the outdoor unit sits in the cold. Every unit has an outdoor temperature range it is designed to cool in, listed in its specifications. If the room needs cooling all year, check that range, or ask whether a low-ambient option is needed for that model.

The remote's temperature isn't the rack's temperature

A split measures air at the indoor unit, usually high on the wall. What matters is the air going into the front of the equipment, which can be several degrees different. That's why a separate sensor at the racks is so useful.

Working out the heat load

Nearly all the electricity your IT equipment uses ends up as heat in the room. That makes the starting calculation simpler than most people expect: one kilowatt of equipment load is roughly 3,412 BTU/h of heat the aircon has to remove. Add the other sources on top.

Heat source	What to consider
Servers, switches and storage	Use measured power draw where possible, not the label maximum
UPS and batteries	Some energy is lost as heat while charging and running
Lighting and people	Small in most server rooms, but not zero
Sun and building	External walls, roof exposure and west-facing windows add heat in summer
Future growth	New equipment tends to arrive faster than budgets for new cooling

Sizing is where many small rooms go wrong, either undersized from day one or outgrown after a couple of years of new kit. Our article on what size aircon you need covers the general principles, but a server room should be sized from its actual equipment load rather than a floor-area rule of thumb.

What temperature should a server room be?

Colder isn't automatically better. ASHRAE (the American Society of Heating, Refrigerating and Air-Conditioning Engineers) publishes thermal guidelines for data processing environments. For most common IT equipment, its recommended range for the air entering the equipment is 18 to 27°C. Running the room at 16°C won't make servers more reliable, but it will cost more in electricity and push the aircon harder.

Your equipment manufacturer's specifications have the final say, especially for older or specialised hardware, so check those alongside the guidelines.

Redundancy: planning for the day a unit fails

Every aircon eventually needs a repair. When the only unit in a server room stops, temperatures can climb quickly, and an emergency call-out at 2am is no one's idea of a plan. The usual answer is two units, each able to handle the full heat load on its own.

• Duty and standby. One unit does the work while the other waits. If the duty unit fails or the room gets too warm, the standby unit starts.
• Alternating operation. A controller swaps the units over on a schedule so both share the running hours, and you find out a standby unit is faulty before you actually need it.
• Separate circuits. Ideally each unit has its own electrical circuit, so one tripped breaker doesn't take out both.

Changeover controllers are available for many split systems, but compatibility depends on the units, so this is something to plan at installation stage rather than add later.

Monitoring and alarms

A server room usually has nobody in it. Without monitoring, the first sign of a cooling failure is often a server shutting itself down. A basic setup costs little compared with the equipment it protects:

1. Temperature sensor at rack inlet height. Many UPS units and network devices can take an add-on sensor, or a standalone monitor can be used.
2. Alerts that reach a person. Email, SMS or app notifications to more than one person, with a clear threshold below the point where equipment is at risk.
3. Humidity and water sensors. A leak sensor on the floor under the indoor units is cheap insurance against condensate problems.
4. A written response plan. Who gets the alert, who can get to site, and which equipment can be shut down first if cooling can't be restored.

Load shedding, generators and UPS power

This is the gap that catches many businesses out. A UPS keeps servers running during an outage, but the aircon is rarely on the UPS, so the servers keep making heat while nothing removes it. In a small, sealed room that can become serious surprisingly fast.

• Generator sizing. If there's a generator, confirm it's sized and wired to carry the server room aircon, including the extra current when the compressor starts.
• Automatic restart. Check that the units restart by themselves when power returns. Not every unit or setting does, and nobody may be there to press the button.
• Surge protection. Power returning after an outage can carry spikes that damage control boards. Ask your electrician about surge protection at the distribution board.
• Graceful shutdown. If cooling can't be kept running, set up the UPS software to shut equipment down in a controlled way before the room overheats.

Businesses looking at solar or inverter backup for the cooling itself will find the trade-offs explained in running an aircon on solar or inverter backup.

Keep condensate away from the racks

Every aircon produces water when it cools. In a server room, the worst place for that water is directly above live equipment. Avoid mounting indoor units over racks wherever possible, run drain lines away from equipment with a steady fall, and if a condensate pump is needed, include it on the service schedule since pumps do fail. A blocked drain that goes unnoticed in an office is a nuisance; in a server room it can take down the business.

When to get a proper assessment

Ask for a server room air conditioning assessment if the room already runs warm on summer afternoons, if you're adding equipment, if there's only one aircon, or if you're moving IT into a new space. A technician can look at the actual load, the room's construction and your power setup, then recommend a layout that fits.

ARS designs and installs commercial air conditioning for offices and business premises across Gauteng, and can put server room units on a maintenance plan so filters, drains and changeover controls are checked regularly. To talk through your setup, request a free quote or call 0861 995 092.