Server Room Temperature and Network Closet Cooling: What Small Offices Get Wrong

The recommended range

ASHRAE, the engineering society whose guidelines data centers follow, recommends an inlet air temperature of 18 to 27 °C (about 64 to 81 °F) for IT equipment. Inlet means the air entering the front of the equipment, not the temperature of the room by the door. Equipment can survive hotter conditions for a while, but heat shortens the life of power supplies, fans and batteries.

How much heat your equipment makes

Nearly every watt your equipment draws turns into heat. One watt equals about 3.41 BTU per hour, the unit air conditioners are rated in. So a closet drawing 1,000 watts produces roughly 3,410 BTU per hour of heat that has to go somewhere. Your UPS or PDU display shows the actual draw; add some headroom for growth.

What small offices get wrong

• A closed closet with no ventilation. Heat builds up all day and peaks at night and on weekends, when the building turns off its air.
• Relying on building air. Many NYC buildings shut down or reduce cooling after hours and on weekends. Your switches don't.
• Blocking airflow. Equipment pulls air in the front and pushes it out the back. Boxes, cable bundles and a wall right behind the rack trap hot air.
• Stacking equipment with no gaps or blanking panels, so hot exhaust gets pulled back into the front.
• No temperature alerts. Nobody knows it's 35 °C in the closet until something fails.

Fixes, from cheapest up

1. Clear the front and back of the rack and dress the cabling.
2. Add a temperature sensor that sends alerts. Many UPS network cards and switches support this.
3. Add a louvered door or an exhaust fan ducted out of the closet, if the building allows it.
4. Install a dedicated cooling unit sized to the heat load, with its own power and a plan for condensate. In NYC buildings this often needs landlord approval.

Don't forget power

Cooling and power go together. A UPS keeps the network up through short outages, but if the cooling unit isn't on backup power, a long outage turns into a heat problem. Planning the closet as a whole is part of a proper network closet build.

Sources

• TechTarget: Data center temperature and humidity guidelines (ASHRAE)

Technical figures checked against the sources above. Standards and product details change; confirm with the manufacturer for your equipment.