Mechanical: Airflow Management
Goal: The efficiency and effectiveness of a datacenter conditioning system is heavily influenced by the path, temperature and quantity of cooling air delivered to the IT equipment and waste hot air removed from the equipment.
- Objective 1: Eliminate mixing and recirculation of hot equipment exhaust air. Efficiency is improved by removing waste hot air at the highest possible temperature.
- Strategies: There are three strategies for obtaining this goal:
- Hot Aisle/Cold Aisle: Arrange the IT equipment so that all heat is exhaust into hot aisles, and all air intakes draw from cool aisles. Cool air is supplied only into the cold aisle, with return air being drawn directly from the hot aisle. [Chart].
More > Air Management [See Chapter 1 of the Design Guidelines Sourcebook] - Rigid Enclosures: Build rigid enclosures to fully separate the heat rejected from the rear of IT equipment from the cool air intakes on the front.
More > Air Management - Flexible Strip Curtains: Arrange IT equipment racks to form hot aisles and cold aisles. Use flexible strip curtains to improve the separation by blocking open space above the racks.
More > Air Management [See Chapter 1 of the Design Guidelines Sourcebook] - Blank Unused Rack Positions. Standard IT equipment racks exhaust hot air out the back and draw cooling air in the front. Openings that form holes through the rack should be blocked in some manner to prevent hot air from being pulled forward and recirculated back into the IT equipment.
More > Air Management [See Chapter 1 of the Design Guidelines Sourcebook] - Design for IT Airflow Configuration. Some IT equipment does not have a front-to-back cooling airflow configuration. Configure racks to ensure that equipment with side-to-side, top-discharge, or other airflow configurations reject heat away from other equipment air intakes.
More > Air Management [See Chapter 1 of the Design Guidelines Sourcebook] - Select Racks with Good Internal Airflow. Select equipment racks that do not have an internal structure configuration that would obstruct smooth cooling airflow through the installed IT equipment.
More > Air Management [See Chapter 1 of the Design Guidelines Sourcebook]
- Hot Aisle/Cold Aisle: Arrange the IT equipment so that all heat is exhaust into hot aisles, and all air intakes draw from cool aisles. Cool air is supplied only into the cold aisle, with return air being drawn directly from the hot aisle. [Chart].
- Metric: Return air temperature. Higher is better. Higher return temperatures allow for greater savings from economization and lower fan volume requirements; the higher the Delta T between supply and return, the greater the reduction in fan power possible.
- Strategies: There are three strategies for obtaining this goal:
- Objective 2: Maximize return air temperature by supplying air directly to the loads. Cooling air should be supplied directly to the IT equipment air intake location; unlike with office spaces, the average room condition is not the critical parameter.
- Strategies: There are two strategies for obtaining this goal:
- Use Appropriate Diffusers: Standard office style diffusers, designed to create a fully mixed environment and avoid creating drafts, are inappropriate for datacenters. Diffusers should be selected that deliver air directly to the IT equipment, without regard for drafts or throw concerns that dominate the design of most office-based diffusers.
More > Air Management; Economizer [See Chapters 1 and 2of the Design Guidelines Sourcebook] - Position Supply and Returns to Minimize Mixing and Short Circuiting. Diffusers should be located to deliver air directly to the IT equipment. At a minimum, diffusers should not be placed such that they direct air at rack or equipment heat exhausts, but rather direct air only towards where IT equipment draws in cooling air. Supplies and floor tiles should be located only where there is load to prevent short circuiting of cooling air directly to the returns; in particular, do not place perforated floor supply tiles near computer room air conditioning units using the as a return air path.
More > Air Management; Economizer [See Chapters 1 and 2 of the Design Guidelines Sourcebook] - Minimize Air Leaks in Raised Floor Systems. In systems that utilize a raised floor as a supply plenum, minimize air leaks through cable accesses in hot aisles, where supply air is essentially wasted. Also implement through policy or design control of supply tile placement to ensure that supply tiles are not placed in areas without appropriate load and/or near the return of the cooling system, where cooling air would short-circuit and, again, be wasted.
More > Air Management [See Chapter 1 of the Design Guidelines Sourcebook] - Optimize Location of Computer Room Air Conditioners. In large datacenters, a Computational Fluid Dynamics model may be practical to determine the best location for cooling units. Simple steps should also be considered, such as minimizing the distance between Computer Room Air Conditioner units and the largest loads to reduce the opportunities for leakage from underfloor supply plenums or overhead supply ducting.
More > Air Management [See Chapter 1 of the Design Guidelines Sourcebook] - Provide Adequately Sized Return Plenum or Ceiling Height. Overhead return plenums need to be sized to allow for the large quantities of air flow that is required. Common obstructions such as piping, cabling trays, or electrical conduits need to be accounted for when calculating the plenum space required. Blockages can cause high pressure drops and uneven flow. Often the uneven flow cannot be rectified by balancing and uneven return results in short circuiting of cooling air and cold spots near the return fan.
More > Air Management [See Chapter 1 of the Design Guidelines Sourcebook] - Provide Adequately Sized Supply. Underfloor supply plenums need to be sized to allow for the large quantities of air flow that is required. Common obstructions such as piping, cabling trays, or electrical conduits need to be accounted for when calculating the plenum space required. Blockages can cause high pressure drops and uneven flow, resulting in cold spots in areas where cooling air is shortcircuiting to the return path.
More > Air Management [See Chapter 1 of the Design Guidelines Sourcebook] - Use an Appropriate Pressure in Underfloor Supply Plenums. Too high a pressure will result in both higher fan costs and greater leakage and short circuiting of cooling air. Too low a pressure can result in hot spots at the areas most distant from the cooling supply air point and result in poor efficiency 'fixes' such as a lowering of the supply air temperature or overcooling the full space just to address the hot spots.
More > Air Management [See Chapter 1 of the Design Guidelines Sourcebook]
- Use Appropriate Diffusers: Standard office style diffusers, designed to create a fully mixed environment and avoid creating drafts, are inappropriate for datacenters. Diffusers should be selected that deliver air directly to the IT equipment, without regard for drafts or throw concerns that dominate the design of most office-based diffusers.
- Strategies: There are two strategies for obtaining this goal:
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