Datacenter cooling fundamentals

Why cooling matters

Every watt a device consumes turns into heat. A dense server rack can put out 5 to 30 kW of heat. Without proper cooling, temperatures climb fast and you get:

• Thermal throttling — hardware slows itself down to survive
• Premature failures — disks, PSUs and CPUs age faster when hot
• Unplanned downtime — emergency shutdowns when thresholds trip

ASHRAE’s recommended envelope for server inlet air is 18-27 °C. Equipment tolerates more (class A1 allows up to 32 °C), but staying in the recommended band is what protects component lifespan.

Hot aisle / cold aisle

The standard layout alternates cold aisles (where racks draw air in) and hot aisles (where they exhaust):

   Cold air (CRAC / raised floor)
        ▼                ▼
  [front] Rack [rear] | [rear] Rack [front]
        cold aisle    →    hot aisle

Key rules:

• Rack fronts face the cold aisle; rears face the hot aisle.
• Fill every empty U position with blanking panels — otherwise hot air recirculates to the front.
• Seal gaps under and between racks if you have a raised floor.

Containment

For better efficiency, enclose one of the aisles with doors and a roof:

• Cold aisle containment: traps the cold air so it only goes through equipment.
• Hot aisle containment: captures the exhaust and ducts it back to the cooling units.

Either way, the goal is the same: stop hot and cold air from mixing.

Cooling types

Basic BTU sizing

To size cooling, you need to know how much heat your equipment generates:

1 kW of electrical load = 3,412 BTU/h of heat

Example: a rack drawing 8 kW produces 8 × 3,412 = 27,296 BTU/h. Ten racks like it need roughly 273,000 BTU/h of cooling capacity.

Rule of thumb: add a 20-30% margin for inefficiencies and future growth.

PUE: Power Usage Effectiveness

PUE measures how efficiently a facility uses energy:

PUE = Total facility energy / Energy consumed by IT equipment

A PUE of 1.5 means that for every watt your servers use, another 0.5 W goes to cooling, lighting and other overhead.

Thermal monitoring

Temperature sensors are your early-warning system:

• Ambient sensors: air temperature and humidity in aisles and racks.
• In-device sensors: CPUs, PSUs and disks report their own temperature via SNMP or IPMI.
• Alert thresholds: alarm on rising temperature before it becomes critical.

CreaRack’s Network Observatory can poll temperature sensors on your devices via SNMP, chart the readings on its dashboards and raise alerts when thresholds are crossed.

Best practices

1. Keep hot and cold aisles separated — no mixed-orientation racks.
2. Install blanking panels in every empty rack position.
3. Monitor temperature and humidity continuously.
4. Redundancy: at least N+1 in cooling units.
5. Preventive maintenance: clean filters, correct refrigerant levels.
6. Plan capacity before installing high-density equipment.

Related

• [[crearack—redes-infra—alimentacion]] — the electrical load that becomes heat
• [[crearack—redes-infra—cableado]] — cabling affects airflow
• [[crearack—redes-infra—monitorizacion]] — monitoring thermal sensors
• [[crearack—monitoring—que-es-observatory]] — dashboards for sensor data
• [[crearack—monitoring—configurar-snmp]] — read temperatures via SNMP
• [[crearack-tech—guides—capacity-planning]] — technical capacity planning guide

Véase también

• [[crearack—redes-infra—alimentacion]]
• [[crearack—redes-infra—cableado]]
• [[crearack—redes-infra—monitorizacion]]
• [[crearack—monitoring—que-es-observatory]]
• [[crearack—monitoring—configurar-snmp]]
• [[crearack-tech—guides—capacity-planning]]