Cooling Solutions – CoolTherm®

1. In what capacity ranges is Knürr’s CoolTherm® Rack available?

The CoolTherm® is available with cooling capacities of between 10 and 35 kW.
There is hardly any requirement for capacities below 10 kW, but it requested, smaller capacities can also be catered for at any time. Therefore are also Knürr solutions available like CoolAdd® respectively rack added and built in cooling units.

2. Are any special components (especially servers) required for CoolTherm®?

All components that are used in a conventional rack can be used in the CoolTherm® without restriction. The servers are freely accessible from the front and rear, as with a normal rack. Especially for blades a save environment is guaranteed.

3. Is the room air heated by the additional heat from these racks?

The cooling system in the rack functions fully independent of the room air. All of the dissipated heat is diverted via the cooling water circulation to the outside.

4. Can heat volume diversion be controlled in accordance with heat loss?

With the three-way-valve the cooling capacity is controllable according to the current heat load.
Furthermore with use of controlled AC fans, the air circulation volume is adjusted to the respective cooling requirement and the power consumption of the system is consequently minimised.

5. How is the airflow routed in the rack and what advantages does this provide?

The heat exchanger installed on the lowest level of the rack blows the cooling air with a temperature between 20 and 25 °C (ASHRAE-Standard) from below to the front of the server. Each server takes in its cooling air from the front and releases it to the rear with a temperature increase, depending on equipment. The heated air is in turn sucked up behind the servers and pushed with redundant fans through air ducts in the rear door down into the heat exchanger.
Advantages:
- Closed air circulation
- Clear airflow with minimum flow diversions
- Very high cooling capacity on the smallest installation space

6. Are the servers cooled equally over the entire rack height or are the higher racks cooled less?

Because of the type of airflow (see above) and the high surrounding air volume, all servers are equally supplied with cooling air from the front, even with irregular load distribution over the height. The construction of the rack prevents heated air from the rear reaching the front without being cooled.

7. Can the CoolTherm® be operated with opened doors?

With opened front door without limitation, the back-cooled air from the heat exchanger is given through the special air duct shape that no interaction to the room will occur.
In all no heat is given off into the room.
Is the rear door opened during operation, the cooling air circulation is interrupted and the dissipated heat is given off into the room.

8. Why did Knürr decide to position the heat exchanger on the rack bottom cover and not on the roof or in one of the side or rear panels?

The main reason for this is the consequential securing of the system against leakage risks. Water-carrying components are exclusively positioned with CoolTherm® on the lowest level of the rack where the connection to the cooling water system is made. Even with a leakage (which is highly improbable), water can never reach the electronic components. Positioning on the roof is therefore ruled out in every case.
This argument also applies with add-on on the side or in one of the doors, if perhaps, with limits.
One argument against add-on on the side panel is the fact that the rack no longer fits into the spacing of the rack suites in the computer centre because of its considerably increased width.
Also the evenly distributed air before the server level can not be ensured with a vertical inlet.
Overall, installation on the lowest level of the rack is the most compact, most cost-efficient and safest solution.

9. How is the water connected to the Knürr CoolTherm® racks?

The connection to the building system is made from below via the standard screw-fitting techniques tried, tested and proven in building mechanics. Knürr recommends the use of the Knürr connection set with flexible hoses and adjustable valves. The contained special valves of this set can be used for easy air bleeding as well as the necessary hydraulic alignment and eventual pressure checks.

10. Can air-cooled and water-cooled server racks be operated beside one another in a computer centre?

The racks are fully compatible in their dimensioning without any further requirements. For water-cooled racks only the cooling water installation must be available.

11. In what dimensions is the CoolTherm® rack available?

Currently in 700 and 800 mm width, 1200 / 1300 mm depth up  1800 mm (29 HU) up to 2400 mm (44 HU) height. Knürr shows responsibility to the server market where 950mm deep servers are offered.
CoolTherm is as special size available with a depth up to 1500 mm.

12. Two or three fans are installed in the CoolTherm®.
Can in case of one fan failure the required determined nominal heat load dissipated?

The fans are installed redundantly, i.e. one alone or two are sufficient to operate the system at full capacity. Only the internal rack temperature rises insignificantly here (a few degrees).

13. Do Knürr CoolTherm® racks have to be maintained?

All components of CoolTherm® rack are designed for a very long lifetime. In addition to this, CoolTherm® design is fault tolerant with respect to all critical components, i.e., the rack delivers nominal cooling capacity if a single failure occurs. Fan speed is monitored. If a fan should fail a corresponding information is dispatched on the network. The system is fully operational with one defective fan. Fan control unit is also monitored. In case of a fan control unit failure CoolTherm® automatically switches to "maximum cooling" mode. The same happens in case of a 3-way-valve failure.
For maximum availability operation Knürr recommends the conclusion of a service contract including one annual maintenance inspection by Knürr service engineers.

14. What advantages does a water-cooled solution provide in the computer centre when compared with an air-cooled solution?

Use of water-cooled racks enables installation and alignment of high-performance servers and server racks with the highest possible packing densities, even for higher cooling capacities above 4-6 kW per rack. This result in very significant savings with investment costs and the operating costs of a computer centre. For details and exact values, see TCO* study.
*) TCO = Total Cost of Ownership

15. Is a raised floor required for the installation?
If yes, what is the necessary height?

A raised floor is not required for routing the cooling water pipes, the pipes can basically also be installed in channels or at the floor.
A main cooling pipe in a raised floor requires approx. 150 mm; a rack feed requires approx. 50 mm installation height.

17. How is the dew point build-up/condensation build-up prevented in the CoolTherm® system?

Condensation build-up with passing below the dew point can only occur at the coldest points in the rack, which are the cooling surfaces in the heat exchanger. The heat exchanger is configured so that any possible condensation of the airflow is removed and diverted.
General Knürr recommends an operation with 12°C supply cold-water temperature. Any more safety brings the use of the Knürr CoolTrans Unit to avoid the condensate formation, which automatically adjust the supply cold-water temperature according to the ambient conditions.

18. Is it ensured that the air volume required for the cooling is also available in the rack?

As even the rack is not vacuum-tight, a pressure balance occurs between the surroundings and the rack interior. The rack is consequently completely filled with air. The cooling capacity depends on the air quantity circulating inside the rack, which is ensured by the corresponding configuration of fans and heat exchangers.

19. Can the Knürr CoolTherm® structure system also be operated together with the Knürr CPU cooling solution?

With very high performance losses of a CPU ( >100 W, for example), the air cooling of the CPU in the server becomes problematic, especially in servers with very low installation spaces, such as Blade or Pizzabox servers. In cases such as this, the CPUs should be cooled directly with water.
A combination with the CoolTherm® rack cooling is possible at all times as only approx. 50-60% of the entire dissipated heat of a server is diverted per CPU cooling; with higher cooling capacities this is even necessary.

20. How is water prevented from causing faults in the rack in the event of a pipe break?

Careful selection of the components practically prevents the possibility of a pipe breaking. Should a leak nevertheless occur in the cooling water system in the rack, the positioning of all water-carrying parts on the lowest level of the rack ensures that water can never reach above this level in the server.
A water sensor is also offered as an option, with which even the smallest leaks can be detected immediately.

21. Why do Knürr not offer a 2-rack solution, i.e. the combined cooling of two racks with one air/water heat exchanger as is provided by other manufacturers?

Knürr essentially offer autonomous individual racks for three reasons:
- Complete flexibility with setting up water-cooled racks, compatibility with air-cooled racks, exchange and mixed equipping possible.
- Rack-individual control of the cooling capacity
- Optimum securing of availability with independent systems

22. Which experiences are present with the CoolTherm® solution running in operational use?
Are there references for this?

The worldwide first computer centre equipped with autonomous water-cooled server racks, GridKa at the Karlsruhe Research Centre, was put into operation with CoolTherm®. Since autumn 2003, 1,300 high-performance servers have been working in productive operation in 35 racks. The installed cooling capacity is currently 350 kW with expansion by factor 3. The planned overall cooling capacity will be over 1 MW.
This is only one example of number worldwide successful working CoolTherm solutions for different applications.

23. For what applications and situations should I use water-cooled structure systems?

Always when the cooling capacity of the room air-conditioning is not sufficient to cope with today’s high-performance servers.
With an optimum configuration in recently planned computer centres the limit here is at approx. 1,000 – 1,200 W/m²; in older computer centres this is often well below this, whereby a maximum 4 kW can be coped with per rack in the best case scenario. Racks fully packed with Blade servers by contrast can already achieve 35 kW today. The solution to deal with this could be to only load racks to a quarter of their spatial capacity – or to use Knürr CoolTherm® liquid-cooled server racks.

24. What additional infrastructure is required along with the rack and the corresponding pipes in order to be able to operate the system?

The required infrastructure corresponds for the most part with the infrastructure already used in conventional thermally managed computer centres. The “colds” (n+1 redundant) generate cold water systems (chillers) that are distributed over the cooling water system in the computer centre on air circulation refrigeration equipment or even on ceiling cooling equipment.
The only additionally required component is the pipe routing to the individual racks, which is installed with in facility management well known pipe systems, flexibly and cost-effectively.

Knürr as vendor of solutions for the whole chilled water delivery chain can offer chiller, pipework and water transportation. There are a large number of high efficiency chillers and pump stations.

27. What basic disadvantages of the current air-cooled solutions are removed by water cooling?

The main problem with conventional cooling is the routing of very large cooling air volumes through raised floors, hanging ceilings and inside rooms. The water cooling assumes the task of carrying out the critical heat transport through these areas. As water can transport 3,500 times as much heat per volume as air can, very small lines are sufficient for transporting very large heat volumes.
Cooling with air is not problematic in a rack with clear airflow inside a closed-off space.

28. Can accessories and other equipment from the 19” superstructure racks also be used in the CoolTherm®?

The installation conditions in the CoolTherm® are no different than those of the standard air-cooled 19” racks. All components and accessory parts can be used without restriction.

29. Do Knürr have the necessary certificates for operation and performance of this system?

There are still no special standards for liquid-cooled server racks, therefore there are also no certificates. As a pioneer in this area, Knürr have equipped the first operative computer centre with CoolTherm® racks and has the required know-how and the required equipment (thermo simulation, climatic test chamber) to guarantee the performance, security and reliability of the system. The rack does of course meet all existing relevant standards for conventional racks.

30. Where can I find out more about the CoolTherm® solution or about the requirements of water-cooled systems or the “musts” for water-cooled systems?

The best place to look is in the new Knürr brochure on liquid cooling, in printed form or on the Knürr website.

31. Are there options for testing very specific heat/heat loss situations in preliminary stages?

Knürr can “tailor make” solutions to meet every conceivable requirement right from the very first step, both with thermo simulation and by testing in climatic test chambers.

32. How can I convince my company/OU of the advantages of a water-cooled solution?

- Knürr liquid cooling brochure
- Existing TCO study
- Knürr expert presentations
- Inspection of reference material
- Specific planning studies

Thermal Management

33. Where can I ask for professional advice on CoolTherm® at Knürr?

Knürr sales engineers provide qualified advice and direct contact as required to Knürr experts in engineering, product management and development.

34. What additional products and services do Knürr offer in the computer and data centre infrastructure area?

- Cooling solutions for all requirement levels, from fans to liquid cooling
- Racks/cabinets, from simple LAN products to the heavy load rack, MaxLoad
- An extensive range of accessories for professional cabling
- 1 HU TFT drawers and KVM switches for administration
- Power supply and distribution, UPS systems, socket strips
- Security solutions such as RMS (Rack Monitoring System) and electronic locking, @lock