Server Rack Cooling in Australia: When Fans Are Enough and When They Are Not
Server Rooms · Rack Cooling · Australia
Server rack cooling is sized by the rack's IT load in kilowatts, and the critical distinction is that rack fans only move air around a room while a cooling unit actually removes heat from it, so a fan tray solves a hot spot but never a hot room. As a working rule an air cooled rack needs roughly 270 cubic metres per hour of airflow for every kilowatt it draws, and above about 8 kW per rack ordinary room cooling starts to run out. Indigi Power and Cooling designs and installs precision cooling for racks, comms rooms and data halls across Australia, and is an Indigenous and Veteran-owned business registered with Supply Nation and ICN Gateway.
Search for server rack cooling and almost every result is a product: a 1RU fan tray, a thermostat kit, a set of rack fans, or a portable air conditioner on wheels. Those things all have a place, but they answer a much narrower question than the one most people are actually asking, which is usually some version of "my rack is running hot, what do I do about it".
The honest answer depends almost entirely on one number: how many kilowatts that rack draws. Below a certain load the problem is airflow and a hundred dollar accessory genuinely fixes it. Above that load no amount of fans will help, because the heat has nowhere to go, and continuing to add fans just makes a hot room noisier. This guide walks through both cases in order, with the thresholds that separate them.
How much heat does a server rack actually produce?
Practically all the electricity a rack draws is converted to heat. If the power distribution unit reads 4.2 kW, then 4.2 kW of heat is entering the room, which is about 14,300 BTU per hour. There is no meaningful energy leaving as light or sound or useful work, so measuring the load at the PDU is the single most reliable input to any cooling decision.
| Rack type | Typical load | Heat output | Airflow required |
|---|---|---|---|
| Network and comms rack | 0.5 to 1.5 kW | 1,700 to 5,100 BTU/hr | 135 to 400 m³/hr |
| Small business server rack | 2 to 4 kW | 6,800 to 13,600 BTU/hr | 540 to 1,080 m³/hr |
| Virtualisation or storage rack | 6 to 12 kW | 20,500 to 41,000 BTU/hr | 1,600 to 3,250 m³/hr |
| GPU or HPC rack | 30 kW and above | 102,000 BTU/hr and above | 8,100 m³/hr and above, or liquid cooling |
The airflow figures come from a standard heat transfer calculation at a typical server temperature rise of around 11 degrees Celsius, which works out at roughly 270 cubic metres per hour, or about 160 cubic feet per minute, for every kilowatt of load. Compare that to a typical 1RU four fan tray, which moves a few hundred cubic metres per hour at best, and the limits of the fan tray approach become obvious very quickly.
Moving air is not the same as removing heat
This is the point the product listings never make. A rack fan tray, a roof fan kit and a set of rack mounted extraction fans all do exactly one thing: they move air from inside the cabinet to outside the cabinet. The heat is still in the room. If the room has adequate cooling and the problem is a pocket of stagnant hot air trapped at the top of a sealed cabinet, that is a real fix and a cheap one. If the room itself is heating up, fans simply relocate the problem and add their own small heat load while doing so.
The test is straightforward. Measure the room temperature away from the rack over a full day, ideally including a warm afternoon. If the room stays comfortable and only the cabinet is hot, buy fans and blanking panels. If the room temperature climbs steadily through the day, the room needs cooling capacity, and no rack accessory will change that. Our server room heat load calculator converts your rack loads into the kilowatts of cooling the room actually requires.
Server rack cooling options, in order of capacity
The options form a ladder. Each rung handles more kilowatts and costs more to install, and the right choice is the cheapest rung that comfortably covers your load with a margin for growth.
| Option | Handles up to | What it actually fixes | Indicative cost |
|---|---|---|---|
| Blanking panels and cable sealing | Any load | Hot exhaust recirculating back to the intake through empty rack units | Tens of dollars per rack |
| Rack fan tray or roof fan kit | About 1.5 kW | Stagnant air in a closed cabinet, in a room that is otherwise cool | Typically under $500 |
| Wall mounted precision cooling unit | About 3 to 8 kW per room | A genuinely hot comms room, with continuous duty and humidity control | $8,000 to $15,000 installed |
| Downflow CRAC with containment | Rooms of 20 to 100 kW | Multiple racks, hot aisle mixing, and the need for N+1 redundancy | $25,000 to $45,000 installed |
| In-row or in-rack cooling | 15 to 30 kW per rack | A dense pod inside a hall that cannot be cooled by perimeter units | Project specific, typically $45,000 and above |
| Rear door heat exchanger | 30 to 60 kW per rack | A GPU or HPC rack installed into an existing air cooled room | Project specific, requires a water or refrigerant loop |
Why a portable air conditioner is not a server rack cooling solution
Portable units appear at the top of most server rack cooling searches because they are cheap, available and require no installation. They are also the most common cause of an avoidable outage in small comms rooms, for reasons worth listing plainly.
A single hose portable unit exhausts room air out the window and draws replacement air in through every gap in the room, so a meaningful share of its rated capacity is spent cooling air it just pulled in from outside. It condenses water into an internal tank that has to be emptied, and it shuts down when that tank is full, which reliably happens on the hottest weekend of the year. It has no humidity control worth the name, its compressor is not rated for continuous duty, and it has no alarm output, no monitoring and no redundancy. When it fails, nothing tells anyone.
A portable unit is a reasonable emergency measure while a proper unit is on order, provided the condensate is plumbed to a drain and someone is watching the room temperature. It is not a design solution, and it should never be the permanent answer for a room holding equipment the business depends on.
Airflow inside the rack: the free improvements
Before spending anything, fix the airflow path. Servers are designed to draw cool air in at the front and exhaust it at the rear, and everything that breaks that path costs you cooling capacity you have already paid for.
Fit blanking panels in every empty rack unit, because an open U is a direct short circuit that lets hot exhaust curl back around to the intake. Dress cables so they do not block the rear exhaust path, particularly at the bottom of the rack where bundles tend to accumulate. Make sure the rack has perforated front and rear doors rather than glass, since a solid front door starves the servers regardless of how cold the room is. Keep at least the manufacturer's recommended clearance in front of and behind the cabinet. Never install a rack facing a wall in a small room and expect the exhaust to find its way back to the cooling unit.
In rooms with several racks, arrange them front to front and back to back so a cold aisle and a hot aisle form naturally. Even without formal containment, this single change often drops top of rack inlet temperatures by several degrees.
Temperature targets and monitoring
ASHRAE TC 9.9 recommends an equipment inlet temperature of 18 to 27 degrees Celsius, with relative humidity generally held below 60 percent. The measurement that matters is at the front of the rack, at the top, which is normally the hottest inlet in the room. A wall thermostat reading 22 degrees tells you very little about what the top server is breathing.
At minimum, fit a temperature sensor at the top front of each rack and set an alarm that reaches a person, not just a dashboard. Log the readings so that a slow drift upwards over months becomes visible before it becomes an incident. Most rack overheating events we attend were preceded by weeks of gradually rising temperatures that nobody was recording.
Rack and room cooling across Australia
Indigi Power and Cooling assesses, designs and installs cooling for single racks through to multi row halls, nationally from Brisbane, Sydney and Melbourne.
Brisbane and QLD
Brisbane CBD, Woolloongabba, Eight Mile Plains, Port of Brisbane, Gold Coast, Sunshine Coast, Ipswich, Townsville, Cairns
Rack level temperature surveys and comms room cooling upgrades from HQ.
Sydney and NSW
Sydney CBD, Parramatta, North Ryde, Macquarie Park, Western Sydney, Newcastle, Wollongong, Canberra (ACT)
High density pod cooling and containment retrofits in existing halls.
Melbourne and VIC
Melbourne CBD, Port Melbourne, Docklands, Dandenong, Tullamarine, Geelong, Ballarat, regional Victoria
Comms cupboard and small server room precision cooling installs.
Perth and WA
Perth CBD, Fremantle, Kalgoorlie, Pilbara, regional WA
Sealed cabinet and high ambient solutions for remote and mine sites.
Adelaide and SA
Adelaide CBD, Port Adelaide, Salisbury, Mount Gambier, Whyalla, regional SA
Rack airflow audits ahead of summer heat events.
Darwin and NT
Darwin CBD, Palmerston, Katherine, Alice Springs, remote NT sites
Humidity aware cabinet cooling for tropical and remote installations.
Western Australia, Tasmania and Pacific Islands: rack and room cooling work is scheduled alongside critical power visits so remote sites get a full inspection in one mobilisation. Contact us to discuss scheduling.
Frequently asked questions
Do server racks need cooling?
Yes. Almost all the electricity a rack draws becomes heat, so a rack pulling 4 kW puts about 14,300 BTU per hour into the room. Sealed cabinets also need internal airflow so hot exhaust does not build up at the top. Whether the answer is fans or a cooling unit depends on whether the room itself is getting hot.
How many fans does a server rack need?
There is no fixed number, because fans should be selected on airflow rather than count. A rack needs roughly 270 cubic metres per hour of airflow per kilowatt of load, so a 1 kW comms rack is usually satisfied by a two or four fan tray, while anything above about 1.5 kW needs the room to be cooled rather than the cabinet to be ventilated.
What temperature should a server rack be?
ASHRAE TC 9.9 recommends 18 to 27 degrees Celsius measured at the equipment air inlet, with relative humidity generally below 60 percent. Measure at the top front of the rack, which is normally the hottest inlet, rather than at a wall thermostat.
Can I use a portable air conditioner to cool a server rack?
Only as a temporary measure. Single hose portable units lose capacity to infiltration, collect condensate in a tank that shuts the unit down when full, are not rated for continuous duty, and provide no humidity control, alarms or redundancy. For a room the business depends on, a fixed precision cooling unit with a plumbed drain and alarm output is the correct solution.
How much cooling do I need per kilowatt of rack load?
Cooling capacity should match IT load close to one for one in kilowatts, plus about 10 to 20 percent for lighting, building fabric, people and losses. So four racks drawing 3 kW each need roughly 12 kW of IT cooling plus margin, or about 14 kW of installed capacity.
What is the difference between in-rack and in-row cooling?
In-rack cooling puts a cooling module inside or attached to a single cabinet, cooling that rack alone, which suits an isolated high density rack or a sealed enclosure. In-row cooling places a cooling unit between racks in a row, so it serves several adjacent cabinets by capturing hot exhaust at source. In-row is more common in data halls, in-rack in standalone or edge deployments.
Related services
- Server room cooling design and installation
- Server room heat load calculator
- CRAC installation and commissioning
- CRAC unit maintenance services
- Electrical switchroom cooling
- Server room UPS and cooling
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Rack running hot? Find out whether you need fans or cooling. Send us your rack count, the load in kilowatts from your PDU, and the room temperature on a warm afternoon. Indigi Power and Cooling is an Indigenous and Veteran-owned critical power and cooling specialist, registered with Supply Nation and ICN Gateway. Contact Indigi Power and Cooling |
