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Colocation Series #5 – Cooling

Stulz CRAC UnitEquipment hosted in a datacentre generates heat. To ensure the uninterrupted operation of the equipment, sufficient cooling needs to be provided in order to maintain an optimal operational environment. Maintaining temperature is a key consideration but it is also important to maintain the right humidity and airflow levels.

Datacentres utilise air-conditioning units, also known as Computer Room Air Conditions (CRAC) or Computer Room Air Handlers (CRAH) units. These are larger, more fault-tolerant and higher-end versions of your office air-conditioner. CRAC units come in many sizes, form-factors and utilise a range of different cooling concepts but the purpose remains the same: to remove the heat, cool the environment and in some cases, maintain the optimal humidity levels.

From a simplistic standpoint, CRAC units blow out cold air which keeps the room and the equipment cool. The actual definition of cold does vary and the actual temperature is generally determined by the provider. ASHRAE (the American Society of Heating, Refrigerating and Air-Conditioning Engineers) releases various recommendations and white-papers relating to optimal temperatures of operation in a datacentre environment. This process is also undertaken by a number of ICT equipment vendors and air-conditioning suppliers. In short, there is no single right answer.

A temperature between 20 and 22 degrees was generally considered the norm. Since then, in the pursuit of higher levels of efficiency, many of the old attitudes towards cooling have changed. Numerous recent studies have proven that servers are far more tolerant to marginally higher temperatures and therefore can quite happily run effectively at temperatures exceeding 24 degrees+. Google is widely believed to operate their servers at intake temperatures of ~27 degrees, far higher than your average server room. The catalyst for this rise in temperature is energy efficiency, environmental factors and, ultimately, cost savings.

The complete datacentre cooling lifecycle is outside the scope of this article but I have included some links below which outline a number of topics. Within this article, I will briefly outline how the Heywood House datacentre is cooled, how the environment is monitored and how Wi-Manx utilises free-cooling to achieve higher levels of efficiencies and a lower PUE.

Heywood House Cooling

Our Isle of Man datacentre uses a combination of cooling technologies:

  • Cold aisle containment
  • Chilled Water
  • Free Cooling

Cold-Aisle Containment

Cold-Aisle containment in our Isle of Man datacentre

Aisle containment is a system designed to ensure separation of hot and cold air in a datacentre environment. Wi-Manx uses a cold-aisle containment system alongside high-end CRAC units from the renowned manufacturer Stulz. Cold aisle containment means the cold air is distributed into an enclosed corridor at the front of the racks and the exhaust air is expelled to the rear. The aisle concept ensures the front and back of the racks are fully separated. The separation achieved through the aisle system delivers higher levels of efficiencies when compared to traditional systems. The cold-aisle concept is explained here.

Chilled Water

Our datacentre uses a chilled water system. This system uses chilled water that flows around the datacentre in a secure, steel pipe-work system. This water is then supplied to the CRAC units which then use this to cool the datacentre environment. Chilled water is one of the most common systems used in datacentre environments as it is proven to be reliable, energy efficient and supports a variety of cooling deployments.

For the water to remain chilled, it needs to be cooled by an external device – this could be in the form of a chiller or a dry-air-cooler. Outdoor dry-air coolers leverage the free-cooling concept.

Free Cooling

Free Cooling is a term coined to describe a means of leveraging the natural environment and ambient temperatures to aid air conditioning systems. In effect, if the outdoor temperature is 19 degrees C and the indoor temperature is to be maintained at 22 degrees C, then it makes sense to try and use the temperatures as they exist outside of the datacentre.  Free Cooling is a large topic in itself with many different technologies and definitions that vary from vendor to vendor.

The Free Cooling used at Heywood House consists of high performance dry-air-coolers which use the ambient temperatures of the Isle of Man to cool the chilled-water loop.