Keep it cool
When row after row of servers run continuously, the data center is bound to get hot. To maintain optimal temperature, we must remove the heat generated by the servers. The downside is that data center cooling usually accounts for an additional 40-80% of the electricity required to power the servers. At Green Mountain, we use the natural conditions of a wet, cold climate to cool our data centers. By using “free cooling” from indirect air or our unique fjord cooling solution, we achieve both higher efficiency and cost reductions.
What is free cooling of a data center?
We often use the expressions “Free cooling” or “Natural cooling”. They describe a technology that cools the inside of the data center using naturally cold air or water from the environment outside. This contrasts with traditional mechanical refrigeration solutions, which have far higher power consumption. In other words, since we are based in a cold and wet Nordic climate, we can take advantage of these conditions to save energy and cooling costs. An additional benefit is the reduction of synthetic refrigerant gases such as HFK (hydrofluorocarbons), minimizing the environmental risk of leakage.
Energy-efficiency in data center cooling
We often use the PUE metric to measure a data center’s energy efficiency. (A consortium called The Green Grid originally developed this metric.) PUE is short for Power Usage Effectiveness. It is determined by dividing the data center’s overall power consumption by the power consumed by the IT equipment.
Theoretically, the PUE is therefore somewhere between 1.0 and infinity. In more practical terms, the PUE considers the power consumed by the cooling solution, UPSs and transformers, lighting, access control, and the management system. In a typical redundant setup, power is secured by a dual-UPS infrastructure. The nature of a UPS, where the power is rectified and derectified generates a loss of 3 – 5%, meaning that the UPS alone has a partial PUE (pPUE) of 1.06 – 1.10. If you add the transformer losses, the overall electrical infrastructure loss leads to a PUE above 1.10.
The Uptime Institute has reported that the average PUE in 2019 was 1.56. At Green Mountain, we have designed the facility to achieve a PUE of 1,2 or below. We often obtain PUE values close to 1.10. The reason for this is our efficient cooling solution. You can find more information about PUE on the Green Grid website.
Data center cooling from the fjord and the air
As mentioned earlier, we use two different free-cooling methods in our data centers. Read more about our unique fjord cooling solution and air-cooling solutions below.
A unique fjord cooling solution
Our mountain hall facility, SVG-Rennesøy, has its data center cooling source available from the adjacent deep-water fjord. This is a so-called threshold fjord where the fjord inlet is shallower. Whereas the middle of the fjord is very deep. (150 m. See picture) As a consequence, there is a constant temperature of 8 °C (46F) at a depth below 75 meters.
So how does it work?
The solution is brilliantly simple. The water enters our cold-water basin solely by gravity, from pipes reaching a depth of 100 meters. This chilled 8˚C-water circulates through a titanium heat exchanger before discharging back into the fjord. In this closed-loop system, the chilled fresh water circulates around the facility via redundant/compartmentalized paths. This means that there is no extra water usage. Moreover, the heated seawater discharged back into the fjord has no negative environmental impact either. (See illustration below)
Robust and duplicated solution
The data center cooling solution (including the cooling station, chilled-water pipework, and pumps) is fully duplicated, providing a N+N configuration. Both systems are active in normal operation and are built for redundancy and concurrent maintenance. Server rooms have N+N chilled water available under the raised floor. In-row cooling is installed to the client’s specification using hot-isle technology. The solution is highly flexible and can support standard power densities from 2-6 kW/m2, as well as high-density solutions up to 40kW/m2.
With limited moving parts (circulating pumps), the solution is extremely robust and reliable. This simple design reduces the need for service and repairs, lowering maintenance costs compared to mechanical cooling systems. Furthermore, at the water inlet, there is no algae growth, reducing the need to clean our titanium heat exchanger.
The cooling station instrumentation is fully integrated with our DCIM system, which handles monitoring, reporting, and incident management. Moreover, the cooling station’s operation is fully automated. It self-adjusts to changes in capacity, and we can continuously monitor the cooling station’s status.
- Free cooling solution securing extremely low PUE
- Using an adjacent fjord with a stable water temperature of 8°C (46 F)
- Using gravity to raise water from a depth of 100 m to a water basin
- Closed-loop system – no water usage
- 3 kW of power = 1000 kW of cooling
Indirect Adiabatic and Evaporating cooling system
Not all sites have access to a deep-water fjord with a constant supply of cold water. Our other data centers, therefore, use the Norwegian cold climate to cool their facilities. At our TEL-Rjukan site, the median temperature is 13 °C. The sun does not shine on the data center for 6 months out of the year. As a result, the Indirect Adiabatic and Evaporating cooling system from Schneider Electric provides 330 days of free cooling each year. This system uses the same technology as our innovative SVG-Rennesøy cooling, but it uses air instead of water. In addition to outside air, we can spray water on the cooling unit to achieve adiabatic and evaporative effects, extending efficiency on those few warm days.
How does it work?
This system works by blowing cold air through a heat exchanger to cool the air supplied to the data center. It is similar to water-to-water heat exchanges. However, it increased in size as the air needs more volume to exchange the same amount of energy as the water.
The benefits of indirect cooling (as opposed to direct) are that the air used for cooling the data center is in a closed loop. It is not exposed to external conditions regarding pollution and humidity. This gives us fewer variations in the environment and no contamination from the outside air.
In Rjukan, we use evaporative cooling only during summer operations. Adding water to the outside air for a few days when outside temperatures are too high. By doing this, we are lowering the dew point on the cooling units. This enables them to be more efficient and not dependent on low outside temperatures.
Flexible and scalable cooling solution
Green Mountain participated in the development of this system and brought our requirements for a scalable cooling solution into the development phase. The use of an indirect air-cooling solution increases flexibility and scalability and reduces the overall cost of the data center. The cooling solution consists of single units with capacities of either 250kW or 500kW. We can add cooling units to the data center infrastructure as IT equipment capacity increases. The principle for this design is to have a modular approach. We can easily scale up either within a module or by adding additional modules. The cooling solution is designed for precision cooling with hot-aisle containment in data rooms. As there are very few movable parts and minimal piping, the need for maintenance and the risk of failure decrease.
- Efficient cooling solution utilizing outside air for indirect heat exchange
- Indirect free cooling = no ingress of dust or pollutant
- Free cooling at wet bulb temperatures below 23° C Net sensible capacity: 250kW/500kW
- Choice of DX or CW for supplemental cooling
- EC fans: Auto-adjustable airflow match IT equipment
