The demands placed on IT systems continue to increase with no end in sight.
However, the necessary increases in server performance also come with great increases in heat dissipation. Some companies hardly pay heed to the warning signals and accept the high operating costs and potential system failures. But the ideal solutions are modular rack climate controls built with liquid cooling systems. Compared to conventional double-bottom cooling, these systems are able to combine the seemingly contradictory goals of higher availability with reduced costs. The following article will show how the liquid cooling system presents an efficient alternative to provide the best possible protection for your investment with its modular design concept.
Today, compact servers mounted in racks achieve computing performance that was unthinkable of super computers only a few years ago. Modularity makes it possible to retrofit and summon computing power in server racks ‘on demand’. However, the extreme miniaturisation also means high heat losses, which must be kept in check. All electronic components are extremely heat-sensitive and this impacts on the availability of the computer and its service life. Each degree that exceeds ideal conditions shortens the service life. To put it another way, high-performance servers such as the new blade servers generate waste heat that could power a sauna!
Computing performance versus climate control
In the past, computing performance was not only slower, but the packaging density of the active components was not what it is today. Of course cooling has always been necessary, but accelerating natural cooling with the appropriate fan system was often sufficient. Today it is possible for a single CPU to produce more than 130 W/cm². This is equivalent to two standard incandescent lamps on the surface area of a fingernail! What is still easily manageable in a single system can become a challenge in a rack with its increased packaging density. Thus, the task of data centre climate control takes on a whole new meaning. Despite a great range of cooling concepts, it is becoming more and more problematic to dissipate heat losses by means of air cooling.
Practical measurements and experiences show that, at best, 3-5 kW of heat losses per rack can be managed using classic double-bottom cooling present in many data centres. In more complex installations, blade servers already reach a heat loss of 10 kW per rack. An additional doubling of heat production due to increasing efficiency and decreasing component size is foreseeable.
This problem is by no means limited to installations for large corporations. Dropping costs for high MIPS (million instructions per second) and FLOPS (floating point operations) as well as increasing demands placed on systems affect medium-sized companies in the same way. Here in particular, lavish data centre rooms with double-bottom cooling systems are the exception. Therefore, without taking the appropriate countermeasures, one either has to go without additional computing power or sacrifice more precious floor space and set up only partially-loaded racks in well-ventilated rooms. Few businesses are able to afford this luxury in today’s world. Furthermore, this method also does not guarantee safe system operation because it is difficult to predict where exactly the air circulates and where potential hotspots may emerge.
The air routing of the double-bottom cooling systems, which was introduced with the advent of mainframes, has partly outgrown the extremely high demands because mainframes did not generate high heat losses in relation to performance and volume. In addition, truly large systems already began using liquid cooling some time ago – a trend that is now catching up with compact, highly efficient computer systems, particularly blade servers. Even with double-bottom cooling systems, the cool air heats up as it passes through more simply constructed systems from rack to rack, which means in some cases the ‘last’ systems in the room may not receive an adequate supply of cool air. In the worst case scenario, when the air distribution is not designed correctly, this can actually end up sucking the cooled air out of the enclosures. This, combined with backflows at the end of the series, can lead to the emergence of hot spots and ‘climatic short circuits’.
Ulrich Terrahe, chair of Schnabel, an independent engineering firm specialising in the planning of data centres, explained: “The greatest difficulty presented by room airconditioning is the even distribution of air around all computer components. It is extremely difficult to create the correct air supply conditions at every point in the room and for every IT component that has to be cooled. In contrast, enclosure cooling has the advantage that an independent ‘micro climate’ is created within each rack. This micro climate is in line with the manufacturer’s regulations for air supply conditions. Thus, enclosure cooling is the better-performing and more effective system.”
No tricks or double bottoms
An efficient alternative to double bottom solutions is the ‘on-site’ cooling of rack installations that are under high thermal stress. This cooling method makes it possible to forego expensive building installations and at the same time provides cooling directly to the heat source. The modularity of each solution is important for investment security as cooling needs increase alongside the great leaps in performance seen in computer technology. Companies are just now becoming aware of this fact because the classic infrastructures were planned with adequate – and expensive – reserves (read oversized) and were, for a long time, adequate. Ulrich Terrahe explains: “Modularity will gain immense importance because power and cooling needs continue to grow along with developments in server and computer technology.”
Rittal is a successful provider of rack and climate control solutions and has produced modular systems that apply new concepts and ideas, integrate the various parts and permit ‘plug-and-play’ retrofitting. This is a great help for planners and operators of data centres. Beginning in the planning phase, Rittal provides a software solution that aids in determining the appropriate climate control components for each enclosure. A database contains information about enclosures and climate control components as well as the heat loss levels of common power electronics.
Liquid cooling in the rack
If heat losses of up to 20 kW per rack have to be dissipated, liquid-based climate control solutions such as air-water heat exchangers or CPU cooling systems come into consideration. One of the most recent developments from Rittal is the scalable climate control solution called the liquid cooling package (LCP). LCP allows for data centres to be temperature-neutral and expand without alterations to the room or space. The powerful liquid cooling for IT racks can reliably dissipate heat losses of 4 to 20 kW per rack. The cooling output can be scaled to a maximum of three climate control modules in its standard version at 4 kW to 12 kW total output. Optionally, up to 20 kW per rack is possible. The deciding factor is expandability during operation, tailored to the current climate control needs of each rack. In this way Rittal ensures the long-term protection of investments.
The rack-optimised design allows the air/water heat exchanger to be bayed with existing infrastructures. Instead of an enclosure side panel, it is attached as a slim ‘climate control enclosure’ and provides horizontal cool airflow within the rack, without hot spots in the upper portion and without sacrificing interior units. Optional air routing guarantees the even cooling of all equipment in the rack. The cooling output offers modular expandability. The LCP can also be mounted between two enclosures to cool both at the same time. The LCP creates a closed cooling circuit within the rack or between two racks. This rack-oriented cooling system is highly effective and the room where it is assembled remains temperature-neutral as recooling occurs via existing or new recooling units that are attached to the outside of the building. Placing the units on the rack means that temperatures do not have to be as low as with double bottom cooling systems. This enables higher coolant inlet temperatures as it is not necessary to cool an entire data centre to very low temperatures. An additional advantage is the level of customisation possible for the heat loads of each rack. In contrast, room airconditioning is oriented towards the individual hotspots. Thus, unfavourable conditions determine all temperature regulation parameters.
The higher inlet temperatures have a positive effect on the power and operational costs of the climate control system. These can be calculated, for the most part, from the performance requirements for ventilation, the circulation of coolant and the recooling of the cooling medium. Power costs increase as more cooling must be achieved with the help of cooling units. The duration of ‘free cooling’ time along with the outside temperature depends on the volumetric flow of the cooling medium and inlet temperature in the room (room air conditioning) or in the enclosure (enclosure climate control). In this case, the higher inlet temperature for an enclosure climate control enables longer use of free cooling.
Alongside the topic of climate control, it should not go unmentioned that the energy supply also has to be secured for powerful computer installations. For this, Rittal offers a coordinated portfolio of solutions as part of the RimatriX5 concept. This begins with the power supply equipped with intelligent sub-distribution as well as an uninterrupted power supply (UPS). Optimised space conditions in the rack as well as coordinated security and monitoring solutions are also taken into account.
Rittal offers an intelligent liquid cooling package solution that is able to meet today’s complex climate control needs. LCP is able to dissipate very high heat loads in a targeted and rack-specific manner. The application in enclosed enclosure systems allows higher intake temperatures so that the operating and power expenses are far less than with other common solutions. The plug-and-play capacity not only provides the option for upgrades on demand, but also the ability for the simple switching out of individual cooling modules for servicing purposes – even during active operation. The modular concept reduces the MTTR (mean time to repair) and ensures the shortest repair times. In turn, the highest level of availability is guaranteed. The adaption to 19” technology, which is gaining more and more importance, also meets the requirements of today’s data centre operators. The results come down to availability of company-relevant IT, and this is considerably improved thanks to the new solutions from Rittal.
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