Tuesday 8 November 2011

Pumpable ice for data center air conditioning

Pumpable ice air conditioning is not a particularly new technology, but it offers the opportunity to reduce the operational electric power costs of air conditioning a Data Center. As part of the same package the technology can provide standby cooling capability without significantly loading the UPS while there is a major outage of mains power.

Pumpable ice is a slurry of fine ice crystals suspended in chilled water. There are several technologies currently in daily use in the manufacturing and food industries which generate and store pumpable ice. The same technology is used aboard some fishing vessels to provide cooling to preserve fresh fish. The systems are robust and have an engineering history.

The ice slurry can be stored in large insulated tanks to act as a store of thermal energy for cooling requirements. The ice slurry is approximately five times more efficient at cooling than chilled water, so the pipework involved in transporting pumpable ice can be more narrow than those used for an equivalent chilled water system.

Here's a related Youtube video.

The pumpable ice can be generated overnight using cheaper off-peak electricity (approx one third of peak day prices) and stored in a thermal accumulator. The cooler night time air can improve the efficiency of the ice making process. During the day when electricity is changed at peak rates the ice slurry can be drawn from the thermal accumulator to provide a coolant source for the main air conditioning of the building. This will reduce the use of expensive day-time electricity. It can also be used to reduce peak loads on the main building water chillers. Pumpable ice cooling systems can cope with megawatt types of cooling loads as well as smaller loads. Some ice systems are designed for retro-fitting to existing chiller systems without the risk of compromising existing building chilled water systems.

If the thermal accumulators containing the ice slurry are of sufficient capacity it is possible to sustain an extended main chiller outage which could occur in the gap between a power outage and the successful start up of the building generator. Some battery backed power would be required to service the pumps for the pumpable ice. In data centers using energy dense technologies such as servers and network switches there is a serious risk of meltdown in a few minutes if coolant is not available. Each equipment cabinet in the data center might be dumping many kilowatts of heat load into the confined space of the technology room leading to serious thermal damage of the equipment. If the standby generator does not start quickly to power main cooling the results can be catastrophic.


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