Excool

Excool Indirect Adiabatic and Evaporative Data Centre Cooling

In 2009 Excool manufactured a full scale model of the system and constructed a test chamber capable of reproducing outdoor air temperature and humidity conditions.  The research and development program lasted an initial 2.5 years.  Excool is now being installed on projects internationally.

The system uses outdoor air indirectly through a specially designed series of heat exchangers enabling cooling to take place without outdoor air entering the data hall, therefore air pollution hazards such as smoke and salt aerosols are kept out of the building.

How it Works

Air to air heat exchanger technology has been used in heat recovery devices for many years.  Excool have optimised this technology specifically for the application of adiabatic and evaporative cooling in data centres.

The Excool heat exchanger is manufactured from a composite material which unlike the more commonly used aluminium, makes it resistant to corrosion, more robust and leak tight.

With the use of specially designed adiabatic sprays the Excool product can maintain data centre internal temperatures of 24â?°C with ambients in excess of 35â?°C.  There has been a growing need for data centre cooling innovation, an acceptance of higher server inlet temperatures and better air management making efficient use of indirect adiabatic cooling a viable proposition.

Winter Operation

Air returning from the datahall is drawn through the heat exchanger by ECDC plug fans.  Cool outdoor as is drawn through a second air path in the heat exchanger by additional ECDC plug fans.  Supply temperature is controlled by a combination of the winter optimisation system and outdoor air fan speed.

Summer Operation

Moisture is added to the hot outdoor air which has the effect of lowering the dry bulb temperature.  A typical UK peak summer day may have a dry bulb of 35⁰C with a wet bulb temperature of 21⁰C.  By fully saturating the air the dry bulb temperature can be reduced to 21°C.  This reduced temperature air is then used as a cooling medium.

Optional DX Module

In more challenging environments it may be necessary to ‘top-up’ the cooling capacity with a partial DX supplementary cooling section.  This is an integrated module and is designed to supplement the heat exchangers.  It is sized as a small percentage of the overall cooling load.

The optional DX pack is added when the peak wet bulb temperature is less than 3.0⁰C cooler than the required supply air temperature.  In London the peak recorded wet bulb is 22.2⁰C (ASHRAE handbook).  The supply temperature under these conditions would be approx. 25.2⁰C.  If a supply temperature of 22⁰C is required only 25% of the load would be supported by the optional DX back-up.  This is unlike a direct air system which requires 100% mechanical cooling support if outdoor air cannot be deployed.

Reduced Electrical Infrastructure

The reduction in the dependency of mechanical cooling has a major impact on the size and cost of the electrical infrastructure.  When considering the lower capacity requirement of the electrical to mechanical power loads, the plant, equipment and machinery power infrastructure is reduced:

Diesel generator size reduces by approx. 60%

Transformer size reduces by approx. 70%

Proportional diesel storage, electrical distribution, switchgear savings etc.

Cooling only PUE

Typical cooling only PUE for a 1MW datahall in London based on 24⁰C supply, 36⁰C return, 75% average annualised demand and N+1 resilience would be 1.027.

This is calculated by analysing the systems energy requirements for every one of 8760 hours of temperature data for the typical reference year for London Heathrow.  It assumes the average load throughout the year is at 75% and that all units including the standby unit are operational.

• ‘Recommended’ and ‘Allowable’ refer to the environmental control envelopes recommended by ASHRAE TC 2011 Thermal Guidelines for Data Processing Environments
• Based upon 1MW IT load running at an annualised average of 75%
• Data source ASHRAE weather data viewer 4.0
• Supply temp 24⁰C, return 36⁰C.  Supply temp allowed to rise to 27⁰C (recommended) and 32⁰C (allowable)
• Aisle containment in place maintaining a 12KT between supply and return
• Resilience based on N+1 and pPUE calculated with all units running
• pPUE = (cooling input power + IT power) / IT power

Water Consumption

Typical water consumption for a 1MW load in London would be below 1500m3 per annum.  This equates to the average domestic use of 30 people.

Water Treatment

The system is complete with on board water treatment.  A clean potable water supply is required for normal operation and maintenance intervals.  The units have an automatic drain down and purge cycle to ensure all areas of potential bacterial growth are removed.  Unlike cooling towers any overspray is collected and drained and not re-circulated.  The system also employs cartridge based biological filters and scale inhibiting system.

High Quality Construction

The Excool product uses high quality components and materials to ensure long term reliability and resistance to corrosion.  Stainless steel framework and support structures are used throughout the unit.  Panels are a composite of PVC and aluminium.

The air movement is achieved using high efficiency ECDC fan and motor assemblies and the system pumps use robust stainless steel internal components for long life.

Witness Testing and Validation

Excool have committed significant financial resource to enable potential clients to see the product operating in simulated environmental conditions.  Equipment manufactured for specific projects can be witness tested to validate claimed performance.  The test facility is located at the company’s UK headquarters in the West Midlands.

In summary:

• Typically using an annualised average of 25-35kW and 1500m3 of water for every MW of cooling delivered, Excool represents a real change in low energy data centre cooling
• By innovative use of and by enhancing existing tried and tested well understood technologies, the product is very easy to understand and removes fear normally associated with new products
• The product uses less power and is directly coupled to the building.  The mechanical and electrical infrastructure is smaller, costs are lower and energy consumption typically 5-10% of conventional systems
• The use of tried and tested components enhance reliability, reduce complexity and make maintenance simpler