FOCUS on COOLING
THE LATEST IN CRAC TECHNOLOGY
Bedrock CRAC technology continues to improve and seems to be getting closer and closer to the racks as a way to maximise cooling control and power
CRAC (Computer Room Air Conditioner) (also of course HVAC, Heating, Ventilating, and Air Conditioning) is a foundational data center technology – as essential as the servers themselves.
A bit like UPS, another very core technology not subject to much change as far as the lay person is concerned, CRAC/HVAC has been steadily improving over the years. One landmark innovation was coupled cooling solutions, which put the CRAC near the load in order to increase the efficiency of the whole facility. Another is a widespread move to include variable speed/ secondary chilled water pumps and high efficiency fans in such kit.
As part of that move – and as we cram more compute power into our data centers – older ways of using this resource are being questioned. For one, as a rule we are now urged to work these units at higher tolerances than in the past: CRAC units operate more efficiently when they are supplied warmer air and also don’t wear out as fast, so the days of “meat locker” temperatures for computing to work are probably mostly gone for good. Today’s data center manager is encouraged to ascertain the maximum operating temperature supported by the manufacturers and keep the system working in that area.
Most CRAC still tends to be ambient (built into the walls), but is increasingly moving closer and closer to the nodes themselves. A specialist firm in this market is Datacentience (www. datacentience.com
), which last January launched its “delta T” cooling range, which it claims turns the proprietary approach of the existing high density cooling players on its head by being able to fit into any manufacturers’ IT cabinet along
Rowbot hot aisle
the lines of other standard data center kit like a blade server chassis or Cisco switch.
The product – “CRAC in a rack” basically – has been designed to slide into any standard 42U cabinet from the front, meaning in effect that the rear void of the rack becomes the return air plenum for the hot air discharge from the servers – so heat never enters the computer room.
The device, it is claimed, delivers up to 50kW of cooling for less than 1kW of input power with typical waterside pressure drop less than 30kPa, thus also saving on chilled water pumping costs. The unit uses electronically commutated DC fan motors to reduce energy drain, while a lower unit water side pressure drop minimises the load on the chilled water pump. These factors can improve energy consumption by up to 50% for the same cooling performance as down flow CRAC units using conventional raised floor air distribution, claims the firm. It also offers The Row Build Out Tool (RowBOT), a modelling program for implementing a rack and row-level cooling solution, whether for a new data center or within an existing installation.
One thing that tends to get less attention than it should in data center cooling discussions is humidity, which is just as much a drag on operational efficiency and even health and safety than dissipation of heat. Low humidity can cause static discharge and high humidity can cause condensation – both extremes creating treacherous conditions for IT and networking
Rowbot cold aisle
equipment. Air conditioning systems help control humidity by cooling the return space air below the dew point. ASHRAE recommends a temperature range of 16–24°C and humidity range of 40–55% with a maximum dew point of 15°C as optimal for data center conditions, so CRAC must be tuned to provide an environment as close to this as possible.
In response, APC has produced its InRoom Perimeter Cooling Solutions family, which it says can cool up to 5kW per rack (getting into the high density space), maintain humidity, and cool non-racked IT loads.
Finally Rittal (www. tinyurl.com/2vfw7ju
) is also very active in the CRAC market. Its RimatriX5 system has a 30% more energy efficient fan approach, based on using water or Dx refrigerant R407c in a closed heat exchanger.
The cooled air is filtered and blown under positive pressure to the false floor, from where it rises into the cold aisle while the system has a repositioned fan within a raised floor. An added benefit of moving the fan into the floor void also allows for an air-to-water heat exchanger to be installed thereby offering a greater heat transfer rate and the system is available in output ratings up to 118kW effective cooling capacity and can be easily integrated into an existing IT infrastructure in terms of both hardware and software, says Rittal.
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