UPS
WATER CHILLERS
FOCUS on COOLING
Ice, Ice, Baby
Water chillers are useful – but cost a lot to run, with some estimates putting them as consuming around 30% of average cooling overhead. But until other options come along, is there really an alternative?
Water chillers are very mainstream products in industrial facilities, where they are used to cool the water used in their heating, ventilation and air-conditioning units. In a data center context, they are becoming of increasing interest as density rises and we generate more heat per rack. Chilled water solutions offer a much greater cooling capacity, i.e., you can achieve higher densities than air alone. However, some data center guys (e.g., those who have come through the IT route rather than the traditional facilities route) don’t like the idea of liquid cooling media next to the electrical load.
However, those that are used to using liquid cooling would probably attest to the fact that you get a very tiny proportion of failures due to leakages in pipework, and so on.
Chillers complement your CRAC and humidifier technologies, and are sometimes dubbed ‘Computer Room Air Handler (CRAH)’ systems. These use chilled water installed on the data center floor and connected to outside chiller plant, designed to move air through the data center via a fan system so as to deliver cool air to the servers and extract warmed-up exhaust air from the room. A chiller produces chilled water via a refrigeration process to feed the CRAH with the cold water it needs.
Useful, sure - but chillers are also notoriously thirsty consumers of electricity in their own right and require dedicated power supplies and significant portions of annual energy budgets - and may in fact account for the largest percentage of a data center’s electricity bill.
They also need a source of water, preferably already at low temperature so as to reduce the energy load involved in lowering its temperature further. This water, after absorbing the heat from the computers, is cycled through an external cooling tower, allowing the heat to dissipate. The chillers themselves, along with integrated heat exchangers, are typically located outside of the data center.
There are a number of different engineering solutions as to how to design the best sort of chiller and there are also choices available between putting chillers on the perimeter or much nearer/between the racks. For instance TechXact offers its BRACH + MOLL external water chiller (
www.techxact.com/water-chiller.html), which features liquid line shut-off valve, charge connection, liquid line sight glass, filter dryer, electronic expansion valve, safety valve, pressure transducers to relay information on high and low pressure values and relative condensing and evaporating temperatures for display on the controller, and high and low pressure switches.
One new approach is that typified by IBM’s so-called Cool Battery. This uses a phase- change material storage device that is installed between the chillers and the data center which gets “charged” during off-peak hours when the outside temperature is more favourable and utility rates are lower. It is then “discharged” during peak hours when it can absorb transient increases in data center cooling load—avoiding any need for start-up of additional chillers when utility rates are higher. Overall system efficiencies can be maximised, resulting in significant energy and cost savings while a typical useful life of 15 to 20 years means this innovative thermal storage solution is held to be very effective in both cold and warm climates, and is both energy- and space-efficient when compared to chilled water or ice storage alternatives.
Intel has been working on slightly different lines with its heat recovery (HR) chillers which work
by capturing heat produced by data center servers and other equipment to warm the rest of the building in winter and provides year-round hot water for bathroom and kitchen use. In this approach, the electricity used by the chillers ‘pays’ for itself by reducing the need for juice needed to run boilers for heating the rest of the building. In one experiment, a pioneering ‘green’ data center it operates in Israel, the building uses two chilled water loops: a high-temperature loop producing water at 13C supplies the data center air handlers, and a low-temperature loop producing chilled water at 5C supplies the rest of the building. This retrofit system cost approximately $168,000. “Even so, we achieved substantial estimated annual savings of approximately $235,000 annually due to reduced fuel consumption, resulting in an ROI of about 1.7 months,” the company claimed.
SOWHAT ELSE IS ONTHE MARKET TODAY? Rittal has developed its Liquid Cooling Package, a high density cooling solution that uses an air/ water heat exchanger. The unit is a modular, upgradeable, and temperature-neutral cooling concept offering up to 30kW cooling output, with three cooling modules possible per equipment rack; controlled variable speed fan and water flow based on actual heat load generated in cabinet; constant temperature cold air provided at the front intake. It can be bayed between two 42U racks and is said to offer high energy efficiency in removing waste heat with no temperature impact in the room.
Liebert (a brand of Emerson Network Power) offers a range of water Based Cooling Module and Racks , using its XDP-W Coolant Pumping Unit to supply cooling water to high heat density racks. The Liebert XDK and Liebert XDR modules offer an alternative to critical applications where the hot aisle/cold aisle approach to cooling is not practical, it says. The pumping unit houses the isolating heat exchanger between the Liebert XDR-W or Liebert XDK-W and the building’s
www.datacenterdynamics.com
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