When it comes to selecting components for liquid cooling, there are a lot of materials out there to choose from and it can seem a little overwhelming.
Not to worry… the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) has made some wonderful recommendations for what supply lines, connectors, pumps, manifolds and hardware materials we should be using for closed loop systems.
Here are our top 5 things you should consider when selecting connections for building a liquid (water) cooling server / supercomputer.
1. Wetted Materials
The types of materials you choose are very important. ASHRAE recommends the following materials for supply lines, connectors, pumps, manifolds and hardware that make up the closed loop.
- Brass with less than 15% zinc content and without lead content
- Stainless steel – 304L or 316L –
It is common for stainless steel manufacturers to provide Certified Material Test Reports (CMTRs) for their components. Request the CMTR at time of purchase.
- EPDM rubber – peroxide cured –
Ask for a certificate of conformance related to the peroxide curing process.
2. Wetted Materials to Avoid
According to ASHRAE, you should never use any of the following materials as part of your closed loop water cooled system:
- Brass with greater than 15% zinc (unless corrosion inhibitor is added to protect high zinc brass) or brass containing lead
- Irons (non-stainless steel)
3. Proof Pressure Testing
Your closed loop systems may include items such as flexible hoses. If this is the case, a test certificate from the manufacturer of these items should be requested. The test certificate should specify the media used to test the component, the pressure the item was tested to and the length of time the pressure was held.
While pressure testing hose assemblies, it is common for water to be used as a test media. You should insist that your component be delivered completely dry and free of residue.
During the hose assembly fabrication process, it is possible for debris to be left in the component. Specify the level of cleanliness you require, from dust free to high purity.
4. Keep your system free of debris
The nature of a closed loop system creates the potential for entrapped debris to break free and restrict the flow rate of your cooling media.
Strainers or side-stream filters may sometimes be needed to remove debris from the line.
Items such as hose assemblies may become sources of entrapment, depending on the style of hose used and the way it was installed.
ASHRAE 184.108.40.206 explains in detail some of the various design and operating criteria to consider when layout out your TCS.
5. The Velocity of Liquid in your TCS
The velocity of the water in the rack’s liquid cooling loop piping must be controlled to ensure that mechanical integrity is maintained over the life of the system.
Velocities that are too high can lead to erosion, vibration, and water hammer, while other velocities that are too low can lead to lower pressure drop and lower pumping power required to transport the liquid.
If there is any flexible tubing required, it should be maintained below 5 ft/s (1.5 m/s).
That’s our list of top 5 things to consider, but of course there may be other things to consider depending on the complexity of the system. What do you think? Let us know in the comments.
*REF: Liquid Cooling Guidelines for Datacom Equipment Centers, 2nd Edition.