Keep it cool
When row after row of servers run constantly, the data room is bound to be hot. In order to maintain an 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. In Green Mountain we use the natural conditions of a wet and 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 where you cool the inside of the data center by using naturally cold air or water from the environment outside. This contrasts with using traditional mechanical refrigeration solutions with a 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 cost. 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 metric PUE to measure the energy efficiency of a data center. (A consortium called The Green Grid originally developed this metric.) PUE is short for Power Usage Effectiveness. It is determined by dividing the overall power consumption in the data center divided 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 amount of power consumed by the cooling solution, loss in UPS’s and transformers, lights, access control and the management system. In a normal redundant setup, the 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 loss of the transformers, the overall loss in the electrical infrastructure leads to a pPUE of above 1.10.
The Uptime Institute has reported that the average PUE in 2019 was 1.67. In Green Mountain we have designed the facility for a PUE at or below 1,2. 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 at the Green Grid web page.
Data center cooling from the fjord and the air
As mentioned earlier, we use two different methods of free cooling for 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, SVG1-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 8C (46F) at a depth below 75 meters.
So how does it work?
The solution is brilliantly simple. The water enters our cold-water basin through use of gravity only, from pipes reaching 100-meter depth. 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 sea water 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 solution. Both systems are active in normal operation, built for redundancy and concurrent maintenance. Server rooms have N+N chilled water available under the raised floor. In-row-cooling is installed to client specification using hot isle technology. The solution is highly flexible and can support standard power densities from 2-6 kW/m2, as well 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 production reducing the need for cleaning of our titanium heat-exchanger.
The cooling station instrumentation is fully integrated with our DCIM system which handles monitoring, reporting and incident management. Moreover, the operation of the cooling station is fully automated. It self-adjusts according to changes in capacity, and we can continuously monitor the status of the cooling station.
- Free cooling solution securing extremely low PUE
- Using adjacent threshold fjord with stable water temperature of 8°C (46 F)
- Using gravity to raise water from 100 m depth to 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 constant supply of cold water. Our other data centers are therefore using the Norwegian cold climate as a source to cool the facilities. At our RJU1-Rjukan site we have a median temperature of 13C. The sun does not shine on the data center for 6 months out of the year. As a consequence, the Indirect Adiabatic and Evaporating cooling system from Schneider Electric gives us 330 days of free cooling every year. This system is based on the same technology as our innovative SVG1-Rennesøy cooling, but it uses air instead of water. In addition to the outside air we can spray water on the cooling unit to achieve the Adiabatic and an Evaporative effect to extend the efficiency on those few warm days.
How does it work?
This system works by blowing the cold air trough a heat-exchanger in order to cool down the air being supplied into the datacenter. 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) is that the air used for cooling the datacenter is in a closed loop. It is not exposed to the outside conditions with regards to pollution and humidity. This gives us fewer variations in the environment and there is also no contamination from the outside air.
In Rjukan, it is only during summer operation that we make use of the evaporative cooling. Adding water to the outside air for a few days when outside temperatures are too high. By doing this we are lowering the dewpoint on the cooling units. This enables them to be more efficient and not dependent on a low outside temperature.
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 the flexibility, scalability and reduces the overall cost of the data center. The cooling solution is based upon single units with a capacity of either 250kW or 500kW. We can add cooling units into the data center infrastructure as the capacity of the IT equipment increases. The principle for this design is to have a modular approach. Where we can easily scale up either within a module or with adding additional modules. The cooling solution is designed for precision cooling with hot aisle containment in the data rooms. As there are very few movable parts and piping needed, the need for maintenance and risk of failure reduces.
- 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