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Determining the Cooling Requirements for Data Center Support Zones


In large data center facilities, the data halls and other critical IT load areas are typically supported by the UPS rooms, battery rooms and electrical rooms to power the mission-critical equipment. Consider a situation where the support zones contain equipment that’s sensitive to heat, meaning an environment that’s too hot will impact capacity; then cooling is required.

Rooms containing traditional static uninterruptible power supply (UPS) systems are good examples of this. There can be significant heat loads and if the units exceed an internal temperature limit, many will shut down and transfer to static bypass impacting the capacity. High heat (within reasonable limits) doesn’t typically reduce a battery’s capacity but will impact its overall life requiring more frequent replacement. Depending on what’s inside an electrical room, ventilation may be sufficient. So it actually depends on what kind of equipment is installed in the rooms and how sensitive the equipment is to the heat.

This article explores the requirements of these critical support areas from a Tier III and Tier IV data center perspective.

UPS Room

Tier III data centers may contain one or more UPS rooms. Tier III requires concurrently maintainable cooling such that the space is kept within the manufacturer’s operating temperature range. If there is one room, then this room must have at least one redundant cooling unit. This can be accomplished with two units each sized to carry 100 percent of the load or three units each sized to carry 50 percent of the heat load. The power to the cooling units must be concurrently maintainable as well.

The room heat load will be a summation of the heat produced from the UPS in the room when carrying the design load, lighting loads, personnel occupancy loads and building skin loads. The building skin load should be calculated at the ASHRAE N=20 year maximum dry bulb temperature for the site. If there are two redundant UPS rooms, the cooling for the rooms must be concurrently maintainable between the two rooms. This means that each room is allowed to have only N cooling with no redundant units in the room as the other room cooling unit provides the redundancy.

Tier IV data centers must have at least two UPS rooms, each containing sufficient UPS to support the design IT load. The two rooms are required to meet compartmentalization requirements. Each room is only required to have N cooling with no redundant units as the cooling units in the complementary room will provide the redundancy. However, the power and other mechanical equipment (chilled water production, where used) must be designed to provide this redundancy between the two rooms. The cooling must be concurrently maintainable and fault tolerant between the two rooms. Additionally, for Tier IV continuous cooling extends to the UPS rooms as the UPS equipment is susceptible to rapid changes in temperature much the same way IT equipment is.

Battery Room

There is no requirement for cooling in the battery room as long as the room will not exceed the manufacturer’s operating temperature range when the batteries are producing the most heat load (charging or discharging). Depending on the type of battery used, the local codes will have other ventilation requirements.

Typically the battery rooms are required to be equipped with suction systems for explosive gases such as hydrogen. Suction inlets must be located on the floors and ceilings. Air removed by suction must be discharged to the atmosphere outside the building in compliance with EN Standard 50272-2:2001: “Safety requirements for secondary batteries and battery installations – Part 2: Stationary batteries.” Suction starts as soon as gas is detected or during charging. Batteries that may release gases during charging should be located in a separate room. If the ventilation for the room is tied to the battery being able to be charged, then the ventilation must be concurrently maintainable. For example in the U.S., more jurisdictions are requiring the ventilation be tied to the charging of VLA (flooded) batteries. If the ventilation isn’t operating the UPS must trip the batteries. This requirement means the ventilation system is critical, since it directly impacts UPS capacity.

One thing to remember is that batteries are susceptible to low temperatures. Typically battery capacity is defined at 20 degrees C (68 degrees F). If the temperature falls below 20 degrees C, then the capacity starts to drop. This is the same reason car owners sometimes face problems with starting batteries in the winter months. If there is a risk of low temperatures in the battery room, concurrently maintainable steps must be taken to ensure the capacity does not fall below the design limits.

Tier IV sites must have at least two battery rooms for compartmentalization if the batteries are not installed in the UPS room. This may require concurrently maintainable and fault tolerant ventilation or cooling between the rooms depending on the situation.

Electrical Rooms

Cooling requirements depend on the equipment installed. If the rooms contain only switchgear and transformers, then typically heat is not an enemy of capacity and ventilation is sufficient to maintain a room below the manufacturer’s operating limits. However, if static transfer switches or other electronic equipment is installed, then cooling is typically required. For Tier III, any required cooling would have to be concurrently maintainable. Tier IV data centers must have at least two rooms (compartmentalization requirements) and the cooling must be concurrently maintainable and fault tolerant between the rooms.

For electrical support rooms, the requirement for cooling, and sometimes heating and ventilation, is dependent on the equipment installed and the impact of heat or rapid changes in temperature on the equipment as far as capacity is concerned. Once cooling, heating or ventilation is determined to be required, then the cooling, heating or ventilation must meet the requirements of the Tier objective just as it would for any other critical system.

 

For more information:

To learn more about how IBM can help you progress on your journey to greater data center efficiency, contact your IBM representative or visit the following website:
http://www-935.ibm.com/services/us/en/it-services/business-continuity/site-and-facilities/.

Syed Ahsan Baqi is an experienced engineering consultant.



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