By R. Stephen Spinazzola, P.E.
All good things must end, and so it is for the current paradigm for data center design. Today’s approach to data center design has not changed for over 30 years, and therein lies the problem. The computer equipment has changed drastically, but the cooling approach has not. The existing method cannot effectively cool the heat dissipation generated by today’s computers.
Why is this happening now? What has happened that has made the old tried and true method cease to be effective? The answer is actually simple. Cooling the entire room to cool the equipment does not remove the heat from the computer cabinets fast enough. Today’s computers dissipate heat at up to 10 times faster than what was produced just three years ago. The result is persistent hot spots and equipment failure.
The current approach is to place all of the electronic equipment in either racks or cabinets sitting on a raised floor. In most facilities, the raised floor acts as a supply plenum to deliver conditioned air into the room to cool the equipment and can also serve as wire management for power, data, or both. Air-conditioning units (ACUs) also sit on the raised floor and provide cool air into the raised floor plenum to cool the room and take their return air directly from the room.
Until 1999, a densely packed cabinet produced about 2 KW to 3 KW of heat. Then came the one U (1U) server (in the computer industry, 1U is a unit of vertical measure in a cabinet that is 1.75-inches in height). This is a device that produces up to 190 watts in a 1U tall box (up to 42 can be stacked in a single cabinet). This translates into about 8 KW in a cabinet. In 2001, along came the blade server, which allows for up to 20 servers stacked vertically in a 3U high chassis, and up to 14 chassis in a single cabinet (or 280 servers in a cabinet). This generates up to 14 KW of heat dissipation per cabinet – and there is more technology in the works.
So what? The upper limit of the current cooling method is about 3.6 KW per cabinet. This is the wall! As the density of electronic equipment has been increasing, so has the temperatures within the cabinets. Constant operation at elevated temperatures shortens the life of electronic equipment, and results in persistent shutdowns and failures.
Baltimore-based architectural/engineering firm RTKL Associates Inc. has developed a totally new concept: Cool the cabinet, not the room. At the core of the solution is a special cabinet called the “Tower of Cool” (patent pending). This cabinet takes the conditioned supply air into the base of the cabinet, and uses three supply fans to push the air through a specially designed front door that evenly distributes the cool air into each piece of electronic equipment. A specially designed rear door also extracts the heat with the assistance of three exhaust fans. The result is the ability to maintain the electronic equipment inside the cabinet at optimum operating temperatures without cooling the room.
There are two other benefits to the use of the Tower of Cool technology – a system that is less expensive to build, and less expensive to operate. By extracting the heat from the cabinet and not mixing it with room air, the air can be returned back to the ACU at higher temperatures. This is called High Delta T Cooling (HDTC, patent pending). In a conventional data center, air is supplied to the underfloor plenum at 55 degrees F. and returned to the ACU at 75 degrees F. With the Tower of Cool, the air is returned at a higher temperature (anywhere between 75 and 95 degrees F.), substantially reducing the amount of cooling air required to cool the data center.
Field testing has proven a 50-percent reduction in the total air supply to a data center using Tower of Cool vs. conventional technology. This drastic increase in efficiency comes back to the basic premise: Cool the equipment, not the room.
Energy costs are based on $0.08/KWH
Gross Building Area: 127,500 SF
Raised Floor Area: 91,700 SF
Equipment Load: 12.7 Megawatts (6,600 circuits, approx. 138 watts/SF)
Cooling Plant: 5,140 Tons (5.0 Megawatts connected electrical load)
Air Side Cooling: 122 ACUs on the raised floor 4,250 Cabinets with 1.5 Circuits per Cabinet
Gross Building Area: 105,000 SF
Raised Floor Area: 66,400 SF
Equipment Load: 12.7 Megawatts (6,600 circuits, approx. 191 watts/SF)
Cooling Plant: 4,620 Tons (4.3 megawatts connected electrical load)
Air Side Cooling: 61 ACUs on the raised floor 3,150 Cabinets
Shell @ $35/SF (125,000 SF) = $4,463,000
Infrastructure = $52,048,000
Cabinets (4,720 @ 1,025/Cab.) = $4,838,000
Energy (PV, 10 Yrs., 6%) = $62,150,000
Present Value = $124, 061, 000
Shell @ $35/SF (105,000 SF) = $3,675,000
Infrastructure = $48,822,000
Cabinets (3,150 @ 2,010/Cab.) = $4,838,000
Energy (PV, 10 Yrs., 6%) = $59,080,000
Present Value = $124, 061, 000
PV Savings: 6,152,000 (10.0 of first cost)
R. Stephen Spinazzola, P.E. is vice president of RTKL, a multi-disciplined architectural and engineering firm, and co-inventor of the High Delta T Cooling system. He is based in the firm’s Baltimore office. For more information on the company and its “Tower of Cool,” visit the RTKL website (www.RTKL.com).