cpd presentation evaporative cooling in data centres

Evaporative Cooling in Data Centres Colt Technical Seminar

I J O’Hea,Colt Founder

A private company founded in 1931

I J O’Hea OBE (1897 - 1984)

2012 Group turnover £151 million

Manufactures in the UK, Holland, Germany, Saudi Arabia, China and

Brazil

A brief history of Colt

Current UK Business markets

Smoke Control

Solar Shading

Natural Ventilation

Louvre

Environmental Comfort Control

Data Centre Ventilation

Evaporative Cooling in Data Centres

1. Current Trends

2. Current Guidance on Temperature & Humidity in Data Centre

3. Applying Evaporative Cooling

a) The Evaporative Cooling Phenomena

b) Inside an Evaporative Cooler

c) UK Weather Trends

d) Evaporative Cooling Plant Layout

4. Energy Consumption

5. Air Filtration & Hygiene

Covering:

Trends

•It is estimated that 1.5% of the total UK energy consumption can be attributed to data centres and within the next 4-6 years it is thought that IT equipment power demand will account for a 10% portion of the 2010 National Grid capacity.

•The data market is estimated to grow by approximately 80% each year which corresponds to a data centre power-growth rate of approximately 20% each year.

•40-60% of the 10 year total-cost-of-operation of a data centre is electrical power.

•A low PUE has, therefore, become the dominant trend and reducing the energy consumption of the cooling system is the most straightforward and immediate way of achieving this.


Trends

Many professional bodies are promoting this ideological change, most notably The Green Grid (Maturity Model), The European Commission (EU Code of Conduct for Data Centres), ASHRAE and BREEAM.

Relative to the more popular, traditional forms of data centre air cooling, evaporative coolers are both inexpensive to buy, run and maintain, and contain no refrigerants or chemicals.


Current Guidance on Temperature & Humidity in Data Centres

The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) publish guidance on air supply conditions within data centre environments. This guidance sets out temperature and humidity bands for the air supply, and is widely considered the benchmark for data centres in the UK.

Before ASHRAE first published this guidance in 2004, there were no supplier-neutral standards for data centre temperature and humidity and typical data centre supply air operating temperatures were 18-20ºC.



The 2004 ASHRAE guidance defines two operating conditions – ‘recommended’ and ‘allowable’.

These supplier-neutral limits were defined by the IT Equipment Manufacturers who formed the ASHRAE technical committee 9.9 responsible for the standard, and were designed to not void new or legacy IT equipment warranties.

The ‘recommended’ operating condition gives a temperature range of 18-27ºC, an RH of less then 60% and a dew point of 5.5-15ºC. The minimum RH is set by the lower dew point limit.

The ‘allowable’ operating condition gives a temperature range of 15-32ºC, and RH of 20-80% and a maximum dew point of 17ºC. The minimum dew point limit is set by the lower RH limit.




Allowable

Recommended

Shown on a psychrometric chart…

Yet, most data centre operators still choose to operate their data centres at the lower end of this scale, with only a few operating above 20ºC (often in the range of 22-24ºC). A minority of the data centres are operating above 24ºC.



ASHRAE are presently trying to encourage more companies to take advantage of the recommended and allowable envelopes – by demonstrating through examples and case studies that this higher temperature and humidity envelopes do not cause a higher risk of IT equipment failure.

A recent ASHRAE journal article, for example, found that high humidity is rarely an issue in most data centres and concluded that "it is difficult to make a case for actively controlling humidity in data centres." Typically, the temperature of IT equipment is significantly higher than that of the air supply dew-point, and furthermore most IT equipment is rated for operation up to 80% RH.

A direct-air evaporative cooling system takes advantage of these wider operating parameters – to provide air at desirable conditions, whilst offering significant cost savings over traditional cooling methods

This is a direct-air system

The evaporative cooling system described herein is a ‘direct-air’ system, meaning that outside air is conditioned and delivered directly into the data centre environment.


Applying Evaporative Cooling


Applying Evaporative Cooling – Outline Principle

CRAC Unit

Evaporative Cooling & Air Handling Process


Applying Evaporative Cooling - The Evaporative Cooling Phenomena

Dry warm air is passed across a wetted desorption medium, the water evaporates from the media and is absorbed by the air. The energy needed for evaporation is taken from the air, whereupon the cooling takes place. After the humidification the latent energy content is higher, the sensible energy content is lower and therefore, the temperature of the air is lower.

Or in simpler terms, effectively pass warm ‘dry’ air across a wetted media, thereby exchanging energy and reducing internal air temperature.


Applying Evaporative Cooling - The Evaporative Cooling Phenomena

Sensible

Latent Latent

Sensible

38ºC / 30% RH

25ºC / 50 % RH

25ºC / 90% RH

18.5ºC / 90% RH



Fan

Desorption medium

Filtration

Controls

Water pump

Sump

UK Weather Patterns


Occurances of Temperature Vs. Humidity

0

20

40

60

80

100

120

-10 -5 0 5 10 15 20 25 30

Temperature (deg.C)

Hu

mid

ity

(Rel

.%)

Havant

Within the UK, for a large portion of the year, the external ambient temperatures fall within the ASHRAE limits, allowing free-cooling to take place. That is to say, outside air is delivered directly into the data centre, bypassing the evaporative cooler.

During periods of warmer weather, where ambient temperatures exceed the ASHRAE limits, the air is cooled by the evaporative cooler - The UK’s temperate climate is well suited to evaporative cooling, as during spells of warm weather, humidity is generally lower. Therefore, during warmer weather, the potential for cooling is greater.

However, owing to the nature of the evaporative cooling principle, conditioned air leaving the cooler is of a high humidity (up to 90% relative humidity), which is in excess of the maximum humidity levels set out in the ASHRAE guide.



For that reason, before the air is ultimately provided to the data centre, it needs to be carefully pre-conditioned so that both the temperature and humidity are within desirable limits.

This is achieved by mixing the conditioned humid air from the cooler with lower-humidity outside ambient air, which increases the temperature and reduces the relative humidity, and therefore creating air at desirable conditions.

During periods of cooler weather, where outside ambient temperatures are below the ASHRAE limits, the waste heat exhausted by the IT equipment is recycled back into the supply air system and mixed with external ambient air to raise its temperature.





From the data centre

To the data centre

Evaporative Cooler

Final Discharge

Ambient Air Intake

Mixing Channel

Control Dampers




To the data centre

Cold Day




To the data centre

Cooler Day




To the data centre

Warm Day

This whole cause and effect process is automated by a sophisticated controls system.

Using that methodology, for most of the UK, we are able to provide air to the data centre within the ASHRAE acceptable limits for over 99% of the year.

This ability to provide high volumes of cool air, within the limits of the ASHRAE guidance, and at a significantly cheaper rate than the traditional cooling techniques, means that Evaporative Cooling has significant potential within the Data Centre Market



It its simplest form, PUE is an energy ratio of the Total Data Centre Input Power over the IT Power Load.

The PUE for the cooling can be itemised separately (described as a ‘partial PUE’). For example, a data centre with a 50kW IT load that requires 25kW of power to cool has a partial cooling PUE of 1.5 – commensurate with well designed traditional cooling systems.

A direct-air evaporative cooling system can have a PUE of less than 1.1, meaning for a 50kW IT load, the power consumption of the Evaporative Cooling system is less than 5kW


PUE & Energy Consumption

kW

kWkWPUE

50

550)1.1(

The lower the PUE, the lower the energy consumption of the data centre.

A Colt direct-air evaporative cooling system has a partial cooling PUE of approx. 1.08.

Consider a 1MW IT Load. That’s a potential saving of over £400,000 annually in electricity costs when compared to a traditional cooling system with a PUE of around 1.5.

Evaporative Cooling – 80kW to cool 1000kW IT equipment. 80kW x 8760hrs/yr = 700,800kWhrs x 0.12p/kWhr = £84,096

Traditional Cooling – 500kW to cool 1000kW IT equipment. 500kW x 8760hrs/yr = 4,380,000kWhrs x 0.12p/kWhr = £525,600

£441,504 saving annually using Evaporative Cooling.


PUE & Energy Consumption


Applying Evaporative Cooling - CFD

Typical section through hot & colt aisle of a data centre

IT equipment in racks draws in cold air and exhausts hot air. This can

be several megawatts of heat!

Supply air – cold aisle Exhaust air – hot aisle

The desorption medium built in the Evaporative Cooler has a cleaning effect, as dust and pollen adhere to wet surfaces. However, the desorption medium does not have a classifiable filter effect.

ASHRAE recommend a minimum of MERV 8, which is equivalent to the UK G4 specification filter

Optional air filters to filter class G4, M5 or F7 in accordance with EN 779:2012 for higher standards of air purity.

A filter switch monitors the pressure difference and when dirty sends a message to the remote control or the BMS.


Air Filters

Smart design of the Colt Coolstream, operation with drinking water, monitoring of the circulating water and periodic drying times ensure proper hygiene, making a disinfection of the water unnecessary.

The Colt Coolstream Evaporative Cooler is the only unit of its type certified according to VDI 6022 - "Hygiene requirements for ventilationand air-conditioning equipment"


Hygiene

The End

Any Questions?

cpd presentation evaporative cooling in data centres

Design

data centres trends

data centre temperature

data centres current

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data centre environments

data centre operators

evaporative coolers

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