CPD Presentation Evaporative cooling in data centres

Evaporative Cooling in Data Centres
Colt Technical Seminar

A brief history of Colt


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
I J O’Hea,
Colt Founder

Current UK Business markets



Smoke Control



Solar Shading



Natural Ventilation



Louvre



Environmental Comfort Control

Data Centre Ventilation

Covering:
1.
2.
3.

4.
5.

Current Trends
Current Guidance on Temperature & Humidity in Data Centre
Applying Evaporative Cooling
a) The Evaporative Cooling Phenomena
b) Inside an Evaporative Cooler
c) UK Weather Trends
d) Evaporative Cooling Plant Layout
Energy Consumption
Air Filtration & Hygiene

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 supplierneutral 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.

Shown on a psychrometric chart…

Allowable

Recommended

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 – Outline Principle

Evaporative Cooling & Air
Handling Process

CRAC Unit

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
Sensible

Latent

Latent

38ºC / 30% RH

25ºC / 90% RH

25ºC / 50 % RH

18.5ºC / 90% RH

Desorption medium

Controls

Water pump
Filtration
Fan

Sump

UK Weather Patterns
Occurances of Temperature Vs. Humidity
120

100

Humidity (Rel.%)

80

Havant

60

40

20

0
-10

-5

0

5

10
Tem perature (deg.C)

15

20

25

30

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 lowerhumidity 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.

Final Discharge
From the
data centre

Ambient Air Intake

Mixing Channel
To the data
centre

Control Dampers

Evaporative Cooler


From the
data centre

To the data
centre

Cold Day


From the
data centre

To the data
centre

Cooler Day


From the
data centre

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

PUE & Energy Consumption
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

( 50kW + 5kW )
PUE (1.1) =
50kW

PUE & Energy Consumption
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.

Applying Evaporative Cooling - CFD

Supply air – cold aisle

Exhaust air – hot aisle

IT equipment in racks draws in cold
air and exhausts hot air. This can
be several megawatts of heat!

Typical section through hot & colt aisle of a data centre

Air Filters
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.

Hygiene
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 ventilation
and air-conditioning equipment"

CPD Presentation Evaporative cooling in data centres

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CPD Presentation Evaporative cooling in data centres