ASHRAE Journal - February 2009 - 54

Return Air Plenum Hot Aisle Cold Aisle Hot Aisle Computer Room Air Conditioning Unit Raised Floor Figure 2: Hot-aisle/cold-aisle air-distribution approach. of the hot-aisle and cold-aisle air system.1 The hot-aisle and cold-aisle configuration helps in separating the cold airstream from the hot (exhausted) airstream and minimizing mixing of those airstreams at the IT equipment. In implementations where hot-aisle and cold-aisle configuration is not used, warm air and cold air will mix, causing lower return air temperature to the CRAC unit, and raising the supply air temperature to the datacom equipment. This can create a potentially harmful situation for the equipment in the cabinets. If not addressed, this condition can contribute to increased equipment failures and system downtime,1 which can compromise performance and reliability of datacom equipment. • The use of fan-powered cabinets is used in high power density data centers where hot spots are created by the high density racks. Fan-powered cabinets increase the cooling capacity and improve airflow. Figure 3 shows a typical fan powered cabinet where “hot exhaust air that would normally be expelled into the hot aisle is gathered and propelled upwards, where it is ducted into the return air plenum. This eliminates recirculation at the rack and improves CRAC unit efficiency and capacity. Blanking panels must be used with these [fan] devices.”7 Technology advances on a daily basis. A system installed today might require several changes or additions a few months later. Sufficient system flexibility should be provided to accommodate any changes. Conclusions Return Air Cabinet Fan (Typical) Rack Supply Air Figure 3: Fan-powered rack cabinet. References 1. ASHRAE. 2004. Thermal Guidelines for Data Processing Environments, Table 2.1. 2. 2007 ASHRAE Handbook—HVAC Applications, Chapter 17. 3. ASHRAE. 2006. Liquid Cooling Guidelines for Datacom Equipment Centers. 4. Menuet, R. and W.P. Turner. 2006. “Continuous Cooling is Required for Continuous Availability: Data Center Managers Need to Match Their Availability Expectations to the Appropriate Class of Continuous Cooling.” The Uptime Institute. Retrieved January 4, 2007. www.uptime.com. 5. ASHRAE. 2005. Design Considerations for Datacom Equipment Centers. 6. Sullivan, R.F. 2002. “Alternating Cold and Hot Aisles Provide More Reliable Cooling for Server Farms.” www.uptimeinstitute. org. 7. Hannaford, P. “Ten Steps to Solving Cooling Problems Caused by High-Density Server Deployment.” APC White Paper 42, Revision 2. Retrieved November 9, 2007, from www.apc.com. ashrae.org February 2009 Cooling system redundancy contributes positively to system reliability, maintainability, flexibility, and overall system performance. Many methods exist to obtain or increase system redundancy. However, each method must be evaluated based on the system’s response to failure. Also, separation of cold supply air from warm exhaust air at the room level, or at the rack level, is necessary to increase the overall system cooling capacity and improve its performance for higher reliability. Examples of air-distribution approaches used are the hot-aisle and cold-aisle approach or fan-powered cabinets. 54 ASHRAE Journal

ASHRAE Journal - February 2009

Table of Contents for the Digital Edition of ASHRAE Journal - February 2009

ASHRAE Journal - February 2009
Contents
Commentary
Industry News
Letters
Meetings and Shows
Feature Articles
     Carbon Dioxide in North American Supermarkets
     Frost on Air-Cooling Evaporators
     Electronic Expansion Valves Versus Thermal Expansion Valves
     Anniversary Feature: Air Handling Unit Design for Energy Conservation
     Redundancy for Data Centers
Building Sciences
Washington Report
InfoCenter
Special Products
Emerging Technologies
People
Products
Classified Advertising
Advertising Index
ASHRAE Journal - February 2009 - ASHRAE Journal - February 2009
ASHRAE Journal - February 2009 - Cover2
ASHRAE Journal - February 2009 - 1
ASHRAE Journal - February 2009 - 2
ASHRAE Journal - February 2009 - Contents
ASHRAE Journal - February 2009 - 4
ASHRAE Journal - February 2009 - Commentary
ASHRAE Journal - February 2009 - Industry News
ASHRAE Journal - February 2009 - 7
ASHRAE Journal - February 2009 - 8
ASHRAE Journal - February 2009 - 9
ASHRAE Journal - February 2009 - 10
ASHRAE Journal - February 2009 - 11
ASHRAE Journal - February 2009 - 12
ASHRAE Journal - February 2009 - 13
ASHRAE Journal - February 2009 - Letters
ASHRAE Journal - February 2009 - 15
ASHRAE Journal - February 2009 - 16
ASHRAE Journal - February 2009 - A1
ASHRAE Journal - February 2009 - A2
ASHRAE Journal - February 2009 - A3
ASHRAE Journal - February 2009 - A4
ASHRAE Journal - February 2009 - A5
ASHRAE Journal - February 2009 - A6
ASHRAE Journal - February 2009 - A7
ASHRAE Journal - February 2009 - A8
ASHRAE Journal - February 2009 - A9
ASHRAE Journal - February 2009 - A10
ASHRAE Journal - February 2009 - A11
ASHRAE Journal - February 2009 - A12
ASHRAE Journal - February 2009 - A13
ASHRAE Journal - February 2009 - A14
ASHRAE Journal - February 2009 - A15
ASHRAE Journal - February 2009 - A16
ASHRAE Journal - February 2009 - A17
ASHRAE Journal - February 2009 - A18
ASHRAE Journal - February 2009 - A19
ASHRAE Journal - February 2009 - A20
ASHRAE Journal - February 2009 - A21
ASHRAE Journal - February 2009 - A22
ASHRAE Journal - February 2009 - A23
ASHRAE Journal - February 2009 - A24
ASHRAE Journal - February 2009 - A25
ASHRAE Journal - February 2009 - A26
ASHRAE Journal - February 2009 - A27
ASHRAE Journal - February 2009 - A28
ASHRAE Journal - February 2009 - A29
ASHRAE Journal - February 2009 - A30
ASHRAE Journal - February 2009 - A31
ASHRAE Journal - February 2009 - A32
ASHRAE Journal - February 2009 - A33
ASHRAE Journal - February 2009 - A34
ASHRAE Journal - February 2009 - A35
ASHRAE Journal - February 2009 - A36
ASHRAE Journal - February 2009 - A37
ASHRAE Journal - February 2009 - A38
ASHRAE Journal - February 2009 - A39
ASHRAE Journal - February 2009 - A40
ASHRAE Journal - February 2009 - Meetings and Shows
ASHRAE Journal - February 2009 -      Carbon Dioxide in North American Supermarkets
ASHRAE Journal - February 2009 - 19
ASHRAE Journal - February 2009 - 20
ASHRAE Journal - February 2009 - 21
ASHRAE Journal - February 2009 - 22
ASHRAE Journal - February 2009 - 23
ASHRAE Journal - February 2009 - 24
ASHRAE Journal - February 2009 - 25
ASHRAE Journal - February 2009 - 26
ASHRAE Journal - February 2009 -      Frost on Air-Cooling Evaporators
ASHRAE Journal - February 2009 - 28
ASHRAE Journal - February 2009 - 29
ASHRAE Journal - February 2009 - 30
ASHRAE Journal - February 2009 - 31
ASHRAE Journal - February 2009 - 32
ASHRAE Journal - February 2009 - 33
ASHRAE Journal - February 2009 -      Electronic Expansion Valves Versus Thermal Expansion Valves
ASHRAE Journal - February 2009 - 35
ASHRAE Journal - February 2009 - 36
ASHRAE Journal - February 2009 - 37
ASHRAE Journal - February 2009 - 38
ASHRAE Journal - February 2009 - 39
ASHRAE Journal - February 2009 -      Anniversary Feature: Air Handling Unit Design for Energy Conservation
ASHRAE Journal - February 2009 - 41
ASHRAE Journal - February 2009 - 42
ASHRAE Journal - February 2009 - 43
ASHRAE Journal - February 2009 - 44
ASHRAE Journal - February 2009 - 45
ASHRAE Journal - February 2009 - 46
ASHRAE Journal - February 2009 - 47
ASHRAE Journal - February 2009 - 48
ASHRAE Journal - February 2009 - 49
ASHRAE Journal - February 2009 - 50
ASHRAE Journal - February 2009 - 51
ASHRAE Journal - February 2009 -      Redundancy for Data Centers
ASHRAE Journal - February 2009 - 53
ASHRAE Journal - February 2009 - 54
ASHRAE Journal - February 2009 - 55
ASHRAE Journal - February 2009 - Building Sciences
ASHRAE Journal - February 2009 - 57
ASHRAE Journal - February 2009 - 58
ASHRAE Journal - February 2009 - 59
ASHRAE Journal - February 2009 - Washington Report
ASHRAE Journal - February 2009 - 61
ASHRAE Journal - February 2009 - InfoCenter
ASHRAE Journal - February 2009 - 63
ASHRAE Journal - February 2009 - 64
ASHRAE Journal - February 2009 - 65
ASHRAE Journal - February 2009 - 66
ASHRAE Journal - February 2009 - 67
ASHRAE Journal - February 2009 - Special Products
ASHRAE Journal - February 2009 - Emerging Technologies
ASHRAE Journal - February 2009 - 70
ASHRAE Journal - February 2009 - 71
ASHRAE Journal - February 2009 - 72
ASHRAE Journal - February 2009 - People
ASHRAE Journal - February 2009 - Products
ASHRAE Journal - February 2009 - 75
ASHRAE Journal - February 2009 - 76
ASHRAE Journal - February 2009 - Classified Advertising
ASHRAE Journal - February 2009 - 78
ASHRAE Journal - February 2009 - 79
ASHRAE Journal - February 2009 - Advertising Index
ASHRAE Journal - February 2009 - Cover3
ASHRAE Journal - February 2009 - Cover4
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