Server equipment within a rack generates heat, which can build-up to create uneven temperatures or hot-spots in the rack to the point where the equipment could overheat, causing failure, or in the worst case, a fire.
The more equipment that is contained within the racks, the higher the temperature will be, giving rise to a greater need for cool air from your air conditioning system. As the air conditioning system needs to work harder, more energy is used to drive the airflow and exchange the heat, leading to higher running costs.
Maximising this airflow's efficiency within server racks will give long term benefits, including reduced running costs and improved equipment reliability, which leads to longer working life for the system. It is usually easy to identify areas within the rack to make improvements to ensure both cool incoming and hot exhaust airflows are directed to maximum benefit. Additional detailed analysis with thermal cameras can be carried out to identify hot spots and other areas of concern within the racks. Depending on the rack layouts, consolidation of heat-generating hardware within particular cabinets whilst confining passive equipment such as patching to others could improve cooling efficiency.
The use of cold or hot-aisle containment is also a very efficient aid to cooling: Find out more about Cold & Hot Aisle Containment
Server Rack Design
A server rack is basically a four-post frame with side panels and front and rear doors. The side panels are usually unvented and removable. The front door can be solid or glass vented or fully meshed, and the back door may be optional or similar to the front door. Equipment is fitted into the rack via the 19" rack uprights either directly as in the case of switches or using slide rails attached between the front and rear 19” uprights. Thermal and environmental monitoring and management is essential within any server room.
It is vital to ensure that the cooling air is supplied via the front of the rack, and reaches all the active equipment within the rack and passes the warmer air out efficiently. Any gaps, open doors or left offside panels reduce efficiency by allowing air to escape without carrying out its cooling purpose. Ensuring these major leakage points are addressed gives several benefits, e.g. efficient airflow reduces demand improving energy efficiency. It can also support more server equipment within the racks for the same energy use, and the removal of hot-spots cuts fire risk and improves the operating life of the equipment.
Managing and Improving Air Flow Efficiency in the Server Rack
Server rack airflow management requires open or unsealed spaces that reduce airflow efficiency be minimised. Consider the following points for improving airflow efficiency:
- Rack U Spacing: In many cases, not all the vertical U will be used as extra space may be needed to cope for future expansion – in this case, ensure any empty ‘U’ is covered with a suitably sized blanking plate sized to prevent any air gaps.
- Equipment Positioning: Layout equipment with care within the rack. As heat rises, it may be necessary to consider which equipment generates the most heat and where to fix this to minimise possibilities of lower-placed equipment heating higher placed equipment – bear in mind that some UPS systems with batteries require an ambient temperature of 20-25˚C
- Equipment Consolidation: Improvements in airflow and cooling efficiency can be improved by considering consolidating active equipment in separate racks to passive equipment such as patch panels. Three well-optimised server racks could be more efficient and cost less to cool than two poorly laid out racks.
- Side Panels and 19” Uprights: The space between the side panels and the 19” rails, with the equipment installed, can exacerbate bypass airflow, which occurs when cooling air does not pass through the equipment space before being exhausted. This will need to be investigated and sealed if necessary.
- Rack Roof: If a roof fan tray is present, it is vital to ensure adequate airflow space around the tray inside and outside the rack to avoid any adverse effects on the cooling.
- Front Door: Door style is important; whichever door style is used will depend on the overall design of the cooling system for the rack. Vented front doors are usually used within uncontained or cold-aisle setups, and solid unvented doors can be used where a hot-aisle design draws air from below and exhausts warm air to top ducts.
- Rear Doors: The rear door is usually needed for access to inputs and power terminals, and in many cases, will be a solid door. Care needs to be taken to ensure any bypass airflow is minimised and that exhaust air is directed efficiently back to the air conditioner.
- Temperature Monitoring: Ambient temperatures within a server rack can vary, so temperature or temperature and humidity sensors should be located within the rack to both the front and rear at the bottom, middle and top sections of the racks. It is also advisable to include sensors for smoke and water detection.
