Jablines, France — Photo from Unsplash by @jules_bss

Water in Data Centres

How is water used in data centres?

Water is so important — without it we die, it is that simple and hard. What fascinated me is that increasingly medium to large data centres are beginning to use a great deal of water. When I started writing about artificial intelligence the last thing I expected to do was write about refrigeration circles, but here we are. After all considering supply chain all artificial intelligence needs to use data centres to some extent to run their machine learning algorithms. At least a great deal of servers, that could mean similar issues discussed here.

Data centres need cooling.

I had a friend who is an engineer explain me the process and he immediately showed me this circle.

So what do you see here?

Well, this is how refrigeration works to some extent.

The refrigeration cycle contains four major components:

1. Compressor.
2. Condenser.
3. Expansion device.
4. Evaporator.

Refrigerant remains piped between these four components and is contained in the refrigerant loop. The refrigerant begins as a cool vapour and heads to the first component: the compressor.

So how does this happen in a data centre?

Well the answer is not uniform.

However, one could draw a general outline.

All data centres need cooling, yet how it is performed is different in practice.

Different methods of cooling were shared by Kaylie Gyarmathy on the 17th of January 2020 on Vxchng.

• “Calibrated Vectored Cooling (CVC). A form of data center cooling technology designed specifically for high-density servers. It optimizes the airflow path through equipment to allow the cooling system to manage heat more effectively, making it possible to increase the ratio of circuit boards per server chassis and utilize fewer fans.”
• “Chilled Water System. A data center cooling system commonly used in mid-to-large-sized data centers that uses chilled water to cool air being brought in by air handlers (CRAHs). Water is supplied by a chiller plant located somewhere in the facility.”
• “Cold Aisle/Hot Aisle Design. A common form of data center server rack deployment that uses alternating rows of “cold aisles” and “hot aisles.” The cold aisles feature cold air intakes on the front of the racks, while the hot aisles consist of the hot air exhausts on the back of the racks. Hot aisles expel hot air into the air conditioning intakes to be chilled and then vented into the cold aisles. Empty racks are filled by blanking panels to prevent overheating or wasted cold air.”

Uptime Institute has drawn up an informative diagram.

Legacy raised floor cooling. Source: Uptime Institute.

In the above image you can also see a raised floor and CRAC (explained below).

• “Raised Floor. A frame that lifts the data center floor above the building’s concrete slab floor. The space between the two is used for water-cooling pipes or increased airflow. While power and network cables are sometimes run through this space as well, newer data center cooling design and best practices place these cables overhead.
• Computer Room Air Conditioner (CRAC). One of the most common features of any data center, CRAC units are very similar to conventional air conditioners powered by a compressor that draws air across a refrigerant-filled cooling unit. They are quite inefficient in terms of energy usage, but the equipment itself is relatively inexpensive.”

In this manner it is about handling the air.

HAR via cabinet exhaust ducts (active and passive). Photo by Uptime Institute.

• “Computer Room Air Handler (CRAH). A CRAH unit functions as part of a broader system involving a chilled water plant (or chiller) somewhere in the facility. Chilled water flows through a cooling coil inside the unit, which then uses modulating fans to draw air from outside the facility. Because they function by chilling outside air, CRAH units are much more efficient when used in locations with colder annual temperatures.”
• “Critical Cooling Load. This measurement represents the total usable cooling capacity (usually expressed in watts of power) on the data center floor for the purposes of cooling servers.”

But cooling can be done directly in the chip. As you can see from these chords circling into the chip with water.

Image from Gigabyte here presenting Asetek InRackLAAC™.

• “Direct-to-Chip Cooling. A data center liquid cooling method that uses pipes to deliver coolant directly to a cold plate that is incorporated into a motherboard’s processors to disperse heat. Extracted heat is fed into a chilled-water loop and carried away to a facility’s chiller plant. Since this system cools processors directly, it’s one of the most effective forms of server cooling.”

Schematic of a Typical Data Center Evaporative Cooling System. Photo by Federal Energy Management Program.

• “Evaporative Cooling. Manages temperature by exposing hot air to water, which causes the water to evaporate and draw the heat out of the air. The water can be introduced either in the form of a misting system or a wet material such as a filter or mat. While this system is very energy efficient since it doesn’t use CRAC or CRAH units, it does require a lot of water. Data center cooling towers are often used to facilitate evaporations and transfer excess heat to the outside atmosphere.”

An overhead view of the server infrastructure in a Google data center.

• “Free Cooling. Any data center cooling system that uses the outside atmosphere to introduce cooler air into the servers rather than continually chilling the same air. While this can only be implemented in certain climates, it’s a very energy-efficient form of server cooling.”

If not, then what about immersion?

• “Immersion System. An innovative new data center liquid cooling solution that submerges hardware into a bath of non-conductive, non-flammable dielectric fluid.”

…Or perhaps even more experimental immersion. Microsoft is experimenting with immersing servers underwater.

Microsoft Testing Undersea Immersion Cooling — photo from Submer

• “Liquid Cooling. Any cooling technology that uses liquid to evacuate heat from the air. Increasingly, data center liquid cooling refers to specifically direct cooling solutions that expose server components (such as processors) to liquid to cool them more efficiently.”

So there you go.

These are a few ways that people are trying to cool data centres.

Fifteen thousand scientists from 184 countries issued a dire warning to humanity in 2017.

Figure 1: Three graphs from World Scientists’ Warning to Humanity: A Second Notice.

As such we have to ensure both that we do not infringe upon freshwater resources or emit too much carbon. Data centres (and refrigeration in general) can of course do both.

Therefore, it is vital we better understand this aspect of digital infrastructure.

One kast recommendation is Custodian data centres. They are doing a lot of YouTube videos explaining what happens in data centres.

A shoutout to Custodian for bringing people in and helping us to understand how these structures and practices work.

This is #500daysofAI and you are reading article 342. I am writing one new article about or related to artificial intelligence every day for 500 days. My focus for day 300–400 is about AI, hardware and the climate crisis.