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Evaporative Cooling: Towards Zero Cooling for UK Datacentres

Cooling datacentres during the hot summer months does not need to be expensive. Using the cooling power of water it’s possible to achieve low energy cooling with Colt International’s Direct Air Evaporative Cooling Systems.

Direct Air Evaporative Cooling
provides a cost-effective low energy solution for UK datacentres by utilising the free cooling power of our Northern European climate. This free cooling air is regulated by recirculated server exhaust air with occasional adiabatic assistance in the summer months when the cooling power of water is used to reduce the temperature inside the datacentre with only a small quantity of electricity needed for the fan that circulates the air.

MetOffice figures for London show that the ambient temperature is 19?C or less for over 8300 hours per annum. This means that for approximately 95% of the year the system takes filtered outside air and carefully mixes it with warm recirculated server exhaust air to maintain temperature and relative humidity levels within the stringent A1 standards of the ASHRAE (American Society of Heating, Refrigerating and Air-Conditioning Engineers) Data Centre Thermal Guidelines.

For comparison a free cooling chiller can deliver 100% free cooling for only 12% of the year. So for around 88% of the year mechanical cooling is required. (based on 12/18?C water temperatures and 25% glycol, which give optimum free cooling opportunity.)

We calculate for the UK based on 50kW N+1, a regular chilled water arrangement without free-cooling would consume 96,300kWh for the chilled water plant and 43,700kWh for the in-row units. A total of 140,000kWh. The same but with a free-cooling arrangement would consume 61,000kWh for the chilled water plant and 43,700kWh for the in-row units. A total of 104,700kWh.

A direct air free-cooling system would consume 49,000kWh only.

On costs at 10p per kWh, per annum:-


£14,000.00 (400%)

FC Chiller

£10,500.00 (300%)

Direct Air

£3,500.00 (100%)

Over 10 years this would save nearly £70,000 per 50kW of IT load - or over £1.4M for a 1MW IT load. It is also around 20-30% cheaper to purchase.

on365 have the exclusive UK datacentre application rights to Colt International’s Coolstream Evaporative Cooling Systems. We are primarily commissioning them in our containerised datacentre projects where we believe they offer the following key features and benefits;

  • Delivers annualised PuE of 1.08: Guaranteed!
  • Best in Class: unique control system allows control of relative humidity levels after the adiabatic cooling process.
  • Use EC fans for maximum efficiency.
  • 90% efficient: evaporative cooling delivers 4 to 7 times more economy than conventional systems consuming around 4kW of electrical energy for every 50kW of cooling capacity and 100l of water per hour whilst in full adiabatic cooling mode.
  • Environmentally friendly and safe: Coolstream runs on fresh air and water only and requires no CFC or similar refrigerants so no F gas compliance.
  • Air quality guaranteed: Evaporative cooling involves supplying 100% filtered, fresh air in.
  • Simple & reliable technology means low running and maintenance costs.
  • Integrated water quality control system and VDI hygiene certificate.



  • Pelco
  • Schneider Electric Partner
  • APC Partner