Energy-efficient cooling in data centers

Data centers need a lot of energy to operate all the equipment and systems. They have an annual electricity consumption of 1,661 Gwh, which is equivalent to 2.8% of Switzerland’s entire electricity consumption. Both from an ecological and economical standpoint, it is worthwhile to measure and optimize a data center’s energy consumption. The savings potential, especially for older installations, is substantial. Since electricity costs make up the lion’s share of the operating costs, each optimization pays off.

The largest electricity consumer is usually the air conditioning. Depending on the cooling principle, 20% to 30% of a data center’s overall electricity consumption is used for air conditioning. That’s why I want to dedicate my first report to enclosures. For a number of years, we have been using the cold aisle principal in our Green data center in Lupfig, and it has worked very well.
 

Designing spaces with cold aisles and raised floors

The most important rule of thumb for cooling is to consistently separate the cold air from the warm air. In our case, the cold aisle principal with raised floors has worked well. The racks are grouped and enclosed. We use circulating air units to force the cold air over the raised floors in the insulated cold aisles. The air ultimately flows back out at the rear of the rack and this slightly warmed air remixes with the uncooled ambient air.

The temperature difference between the air flowing into and out of the rack determines the cooling requirements and therefore the performance of the cooling infrastructure. In our case, the maximum temperature in the enclosed rack is 26°C.

Interesting facts:
 

For an optimal result, the following steps are important:

• Measure the temperature reference value both where the air enters the cold aisle and at its highest point.
• Prevent hotspots and evenly distribute the thermal load in the rack.
• Properly insulate enclosures since the smallest gaps reduce the efficiency.
• Keep raised floors clean and clear of obstacles so that the air circulation is not interrupted.
• Each degree of cooling that is saved yields up to 6% energy savings in the data center.

What we have learned in the Green Datacenter:

In order to benefit from the advantages of enclosures, we had to adjust the regulation several times over a good six-month period. To achieve an even temperature, the dimensioning of the entering cool air had to be carefully controlled. If the cold air is let in under too much pressure, it causes the server ventilators to turn on. But if the air volume is too low, it does not cool. At the start of the project, the temperature difference between the room and the cold aisle was barely noticeable. Now there is a 6°C to 8°C difference. Patience pays and you have to: measure, regulate, measure, regulate…

I will talk about calculation and measurement in the next blog article.