Questions and answers about cooling and energy performance in data centers

Interview with Consultant Fabian Buda
News | 21.02.2023

Fabian Buda, Consultant of the Data Center Group, was asked in an interview about various topics related to cooling. He describes the advantages and disadvantages of water cooling, advantages of direct water cooling, the influence of the cooling type on certifications, the energy consumption of cooling in a data center as well as the additional air cooling despite water cooling for certain infrastructures. Furthermore, he clarifies key data center energy performance terms. What are PUE and WUE and what influence does the type of cooling have on these values? What is the average power consumption of a data center in Germany and what data center categories are distinguished?

Air vs. water cooling - What are the advantages and disadvantages?

The advantage of air cooling is that you can use the existing, classic IT, which you can get everywhere. Water cooling is exotic for various applications in today's world, because it is standardized only in certain areas. That's why air cooling is mostly used, because you can get all the components there. Another advantage of air cooling is that it can be used in existing premises. The existing infrastructure does not have to be completely rebuilt, but grown structures can be used. Water cooling requires a higher investment to be able to provide the required technology. Say: "I have an interface, now you can work with water cooling." So there is always a one-time capital expenditure needed at the beginning. But once I have the water cooling, it means significantly more efficient operations. Higher temperatures in the flow lead to higher temperatures in the return, which can be reused for other purposes, such as heating. This can mean preheating for heating or new low energy applications for direct use. Data centers in Sweden are already operating at higher temperatures that can be used for surrounding districts. Various campuses in Dresden of Munich feed a district heating network, which is mainly supplied by the data center. In the future, I don't see the data center as an energy consumer that consumes electricity and emits warm air and thus pollutes its environment, but rather works in symbiosis with the city. This is currently still considered exotic. Currently, one uses electricity and generates warm air and releases it into the environment. This makes no sense from my point of view. We have the current political situation and the heat turnaround, which should open eyes. Currently, we still have a boom in Germany in data centers, the potential of which we should exploit. We should show that we have potential energy sources that we can easily tap.

What are the advantages of direct water cooling in a server?

The advantages of direct water cooling, i.e. chip cooling, are that you don't have the physical insulator air. You don't have to convert energies to certain carrier media (water-air-water), but have the direct surface therm (water-copper-chip). Thus one has a very good heat conductor and can drive much higher temperatures. Disadvantage is the best practice standard because we are creatures of habit. People recognize the technology air as a protective shield, but water is seen as a danger they don't want in their data center. People don't recognize the changing nature of technology and the safeguards that have been proven for decades. The assumption that there is no need for water technology in the data center world also makes the technology disproportionately expensive.

Does the issue of certification play a role in data center cooling choices?

When it comes to certification, it comes to the big challenge of reconciling the completely standardized certification catalogs of the recognized bodies, because they see the server as a non-failure-tolerant point in the middle. Everything around it must be failure-tolerant and available. So the infrastructure has to be redundant in terms of power source or cooling, but can't cope with the information that the server landscape itself is redundant, so only the capacity drops if a server connected to a water source fails, but a second server is still available. The DIN EN 50600 standard, which is recognized in Germany and Europe, does not even think that data center cooling with water is possible.

What is the energy consumption of cooling in a data center?

The energy consumption for cooling is currently 10-15%. In classic data centers, the value can rise up to 70%, as the systems do not run at efficient temperatures. Often, server rooms are cooled far too much in this case.

Why is air cooling used in server rooms of water cooling?

Air cooling is needed in addition to water cooling to cool special infrastructures such as the power supply for the servers or network infrastructures. These require cooled air.

What is the PUE (Power Usage Effectiveness)?

The PUE is the ratio of the electrical power used for the entire data center in relation to the electrical power of the IT. PUE should not be evaluated as a metric for sustainability, but rather as a performance indicator for an individual site. PUE cannot be compared across sites as a metric because different conditions apply to each site. Availability is not a factor in PUE because many data centers have a much higher availability requirement, i.e. they need more electrical power to maintain availability in standby mode. The PUE does not provide any information on this. You can run highly sustainable data centers that have a poor PUE, but need to be available for certain IT applications.

What is WUE (Water Usage Effectiveness)?

In today's world, water as a resource plays a very important role. Therefore, it is important to look at WUE on an ongoing basis. When asking about the use of water, there is also the question of availability. The water table is dropping and data center operators need to be concerned as they use water as a resource heavily. Data Center Group is reluctant to use water for adiabatic. We use classical air cooling for this purpose to completely exclude hazards such as legionella, vapor formation and consequently the BlmSchG. Thus we use PUE and power efficiency, but can be sure that we do not spend the most precious resource on earth, water.

What is the average power consumption of a data center in Germany?

There are different data center categories. The classic in-house data center, which you have in your own basement, has a range from 3 kW to a low 100 kW. Edge data centers are available for a certain range of customers, where several companies share an area or a building. These have a range from 100 kW up to 3 MW. Furthermore, there are hyperscaler data centers, also called colocation operators, which usually start at 3 MW, but classically have 10-30 MW.


Picture: © Jonathan Schöps / #190707855 / (standard licence)


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