Selecting the Right
Air Handling
Approach for Data
Centers
Data Center Systems, Inc.
info@datacsi.com
PROPRIETARY INFORMATION: The information contained in this presentation is the property
of Emerson Network Power and is subject to change without notice. Except as specifically
authorized in writing by Emerson Network Power, the holder of this presentation shall keep all
information contained herein confidential and shall protect same in whole or in part from
disclosure and dissemination to all third parties.
The Dynamic Data Center Industry
Traditional Systems
Progressive Systems
 Perimeter cooling with raised
 Variety of deployment schemes
floor
 Cool temperatures with tight
temperature and humidity control
 Availability is only concern
 Increasing temperatures and
wide humidity levels accepted
 Availability and efficiency
concerns
Questions to Ask
What is the target
PUE?
What are the
whitespace
specifications?
What specific site
considerations are
there?
What is the
financial model for
the project?
What is the load
deployment plan?
How would a
design respond to
Value
Engineering?
Air Handler Technologies
Chilled
Water
Indirect
Evaporative
• Most often used for traditional
operating range of DC conditions
• High efficiency economizer use
or high water temperatures
• High efficiency system without
use of outside air
• Indoor or outdoor application
• Uses elevated DC conditions
Direct
Evaporative
Direct
Expansion
• Lowest initial & operation costs
• Requires use of outside air and
wide range of data center
conditions
• Requires outdoor equipment
• High efficiency requires
economizer or evap. condensing
• Supports modular deployment
Air Handler Technology Comparison
Chilled
Water
Indirect
Evaporative
Direct
Evaporative
Direct
Expansion
$ / kW
$850 - $1100
$600 - $700
$300-$500
$800 $1000
Mechanical PUE
1.2 – 1.4
1.15
1.05 - 1.1
1.2 – 1.3
Raised Floor
YES
NO
NO
NO
Outside Air In DC
Some Designs
NO
YES
Some Designs
Typical Unit Size (kW)
250 – 400
250 – 350
250 – 350
200 - 500
Design RAT (°F)
~90
95-105
95-105
~90
Typical SAT (°F)
65-70
70-75
65-85
65-70
Humidity
40-60%
40-60%
25-80%
40-60%
(Typical Application)
Chilled Water
Air Handlers
Typical Deployments
•
•
Vertical units along perimeter or in gallery discharging
into raised floor
Horizontal units in gallery or outside the building – may
not have raised floor for air distribution
Key Positive Aspects of System
•
•
•
Can deliver relatively precise data center conditions
Can be very efficient with elevated water loop
temperatures
Indoor units are typically easy to service and commission
Areas to be Cautious
•
•
•
Significant upfront cost associated with chiller plant
Economizer operation often abandoned in a few years
Water usage, storage, and treatment
Chilled
Water
Energy Saving Strategies
Outside Air Economizing
Water Side Economizing
Cooling Tower Only
•
•
•
•
•
Often requires outside
wall access
Requires Temp &
Humidity sensors to
control indoor moisture
Easy to shut off outside
air if required
Plate frame heat
exchanger in series with
chiller allows for partial
economizing
•
•
Coils design for 75 EWT
and 105 EAT
Only cooling towers
used with heat
exchangers between
loops
Small side stream chiller
may be used
Chilled Water Air Handler
Control Components
Return Air
Temp Sensors
Chilled
Water
Filter
Gauges
Supply Air
Temp Sensors
Fluid Flow
Sensors
Airflow
Measurement
Fan Power
Meters
8
Indirect Evaporative
Air Handlers
Typical Deployments
•
•
•
Large units deployed outside the data
Raised floor is often utilized
Full containment system with elevated supply and return
temperatures critical for high efficiency
Key Positive Aspects of System
•
•
•
•
High efficiency systems with mechanical PUE < 1.2
Downsized electrical infrastructure
Low cost per kW initial cost
Low peak power consumption
Areas to be Cautious
•
•
•
Typical design of 100 to 102 °F RAT has minimal thermal
“ride-through” time
Makeup air required for positive pressure in the space
Water usage, storage, treatment
Indirect Evaporative
Typical System Components
Indirect
Evaporative
Filters
Supply Fan
Array
Optional Trim
Cooling Coil
Return
Air
~102 °F
Heat
Exchanger
Supply
Air
~75 °F
Indirect Evaporative
Typical System Components
Mist
Eliminator
Scavenger
Air
Indirect
Evaporative
Option
Condenser
Coil
Spray
Nozzles
Scavenger
Air
Heat
Exchanger
Recirc
Pump
Sump
Basin
Compressor
Section
Indirect Evaporative
Operation Modes: Dry HX
Supply Air
Temp Control
Indirect
Evaporative
Amb
Cooling
Mode
Dry Bulb
(°F)
Wet
Bulb
(°F)
(gp
m)
Clg.
PUE
Cold
Dry
35
30
-
1.08
Wet HX +
Trim Cooling
Supply Air
Vol Control
Wet HX
Dry HX
50 °F 65 °F
Indirect Evaporative
Operation Modes: Wet HX
Supply Air
Temp Control
Indirect
Evaporative
Amb
Cooling
Mode
Dry Bulb
(°F)
Wet
Bulb
(°F)
(gp
m)
Clg.
PUE
Warm
Wet
68
57
2.5
1.09
Wet HX +
Trim Cooling
Supply Air
Vol Control
Wet HX
Dry HX
65 °F
69 °F
Indirect Evaporative
Operation Modes: Wet + Trim HX
Supply Air
Temp Control
Indirect
Evaporative
Amb
Cooling
Mode
Dry Bulb
(°F)
Wet
Bulb
(°F)
(gp
m)
Clg.
PUE
Warm
Wet +
Trim
68
57
2.5
1.16
Wet HX +
Trim Cooling
Supply Air
Vol Control
Wet HX
Dry HX
69 °F
Indirect Evaporative
Heat Exchanger Technology
Aluminum Plate
Polymeric Tubing
•
•
•
•
DC and Scavenger Air travel in
90° paths separated by
aluminum
Dry efficiency 60-70%
Wet Efficiency 75–85%
•
•
Indirect
Evaporative
DC air travels through tubes &
Scavenger Air flows
perpendicularly around tubes
Dry efficiency 40-50%
Wet Efficiency 75–85%
Indirect Evaporative
Water Treatment / Scale Prevention



Indirect
Evaporative
Scale is result of dissolved minerals forming solids on surfaces
exposed to water
Critical to control or mitigate on any evaporative system
Provides medium for biological growth
Four Critical Methods of Scale Prevention
● Engineered
spray system
that ensures
“overspray”
● Conductivity
controller set
to desired
cycles of
concentration
● Control SOO
that minimize
on/off cycles
● Retain local
water quality
company to
maintain water
quality levels
Indirect Evaporative
Performance Across the US
Indirect
Evaporative
PUE 1.10
PUE 1.11
PUE 1.10
PUE 1.11
PUE 1.12
PUE 1.13
PUE 1.14
PUE 1.14
Indirect Evaporative
Operational Control Strategies
Indirect
Evaporative
Unit Control Strategies
System Control Strategies
•
•
•
•
Unit capacity controlled to supply
air setpoint
Control in real-time at optimum mix
of scavenger fan & water usage
Makeup air unit controlled by
return air humidity levels
•
•
Supply fan speed controlled by
plenum pressure
Cold aisle dampers controlled by
rack sensor readings
Coordinate units for standby
operation to prevent fighting
Supply Pressure
Control
Unit Capacity
Coordination
Rack
Sensors
Supply Air
Temp Control
Cold Aisle
Control Dampers
Direct Evaporative
Air Handlers
Typical Deployments
•
•
•
Large units deployed outside the data
Slab floor with hot aisle / cold aisle row arrangement
Full containment system with elevated supply and return
temperatures as design points
Key Positive Aspects of System
•
•
•
•
Very high efficiency systems with mechanical PUE < 1.1
Low kW per unit – downsizes electrical infrastructure
Lowest cost per kW initial cost
Lowest peak power consumption
Areas to be Cautious
•
•
•
•
Wider temperature and humidity ranges
Reduced level of control
Water usage and water storage
Water treatment
Direct Evaporative
Typical System Components
Outside Air
Dampers
Return
Air
Return Air
Dampers
Bypass
Damper
Direct
Evaporative
Supply Fan Isolation
Array
Damper
Supply
Air
Outside
Air
Filters
Evap Media
Evap Media
Sump Basin
Optional Trim
Cooling Coil
Direct Evaporative
How Evaporative Cooling Works
Evaporative Cooling Process
•
Dry bulb temperature of air is
reduced while wet bulb remains the
same
86 / 66
•
•
Ex. (86 °F – 66 °F) x 0.89 = 18 °F
•
•
Ex. (86 °F – 18 °F) = 68 °F / 66 °F
89%
Direct
Evaporative
Direct Evaporative
Modes of Operation
Zones of Operation
Direct
Evaporative
Pittsburgh, PA Example
Typical Design SA Range
•
65 – 85 °F Dry Bulb
•
25 – 80 % RH
Mechanical
Cooling
Typical Design SA Range
•
65 – 85 °F Dry Bulb
•
25 – 80 % RH
0 Hours
(0.0%)
1,756 Hrs
(20.0%)
4,012 Hrs
(41.8%)
OA
Only
OA & RA
Mix
OA & RA + Hum
OA w/ Evap
Clg
2,749 Hrs
(31.4%)
243 Hours
(2.8%)
Direct Evaporative Operation
Cold Ambient Conditions
Return Air Damper
87°F
70% Open
Bypass Damper
50% Open
Direct
Evaporative
Typical Cold Ambient
Supply Temperature
Fan Operation
65 °F to 72 °F
60%
67°F
27°F
MAT
Outside Air Damper Evap Media Pump
Top:
50% Open
Bottom: 0% Open
Supply Air
Setpoint Zone
On: 1 Stages (of 4)
MAT
Direct Evaporative Operation
Cool Ambient Conditions
Return Air Damper
33% Open
89°F
Bypass Damper
100% Open
Direct
Evaporative
Fan Operation
60%
67°F
56°F
Supply Air
Setpoint Zone
Outside Air Damper Evap Media Pump
Top:
100% Open
Bottom: 33% Open
Off: 0 Stages (of 4)
MAT
Direct Evaporative Operation
“Just Right” Conditions
Return Air Damper
0% Open
92°F
Bypass Damper
100% Open
Direct
Evaporative
Fan Operation
60%
70°F
70°F
Supply Air
Setpoint Zone
Outside Air Damper Evap Media Pump
Top:
100% Open
Bottom: 100% Open
Off: 0 Stages (of 4)
Direct Evaporative Operation
Hot Ambient Conditions
Return Air Damper
0% Open
105°F
Bypass Damper
~25% Open
Direct
Evaporative
Fan Operation
75%
83°F
95°F
Outside Air Damper Evap Media Pump
Top:
100% Open
Bottom: 100% Open
On: 4 Stages (of 4)
Supply Air
Setpoint Zone
Direct Evaporative Operation
Hot and Humid Conditions
Return Air Damper
0% Open
105°F
Bypass Damper
25% Open
Direct
Evaporative
Fan Operation
75%
83°F
115°F
Return
Air
Supply Air
Outside
Air
Outside Air Damper Evap Media Pump
Top:
100% Open
Bottom: 100% Open
On: 4 Stages (of 4)
Trim Cooling Coil
On: Full Capacity
Supply Air
Setpoint Zone
Direct Evaporative
Control Strategies
Direct
Evaporative
Unit Control Strategies
System Control Strategies
•
•
•
•
Unit capacity controlled to supply
air setpoint range
Power metering on supply fan,
pumps, and exhaust fan for energy
optimization
Fan speed controlled by rack inlet
temperature sensors
•
•
Flooded room with hot aisle
containment
Coordinate units for standby
operation to prevent fighting
Monitor server fan power
consumption to minimize site
power consumption
Server Fan
Power Cons.
RA / OA Mod.
Dampers
Supply Fan
Power Mtr
SA Temp
Sensor
RA / OA Temp
Sensors
Evap Bypass
Dampers
Direct Expansion
Air Handlers
Typical Deployments
•
•
Roof mounted units in single or two story buildings
Often requires supply and/or return ductwork for air
distribution
Key Positive Aspects of System
•
•
Easily accommodates modular build outs
Evaporative condensing with outside air can result in very
efficient systems
Areas to be Cautious
•
•
•
Low ambient conditions can often cause operation issues
Existing building may require roof structure to be
improved
Comfort units don’t have the optimal refrigeration circuits
Direct Expansion
Typical Components
Exhaust
Hood
Outside
Hood
Filters
Return Air
Dampers
Direct
Expansion
Supply Fan
Mixing
Dampers
Digital Scroll
Compressors
Cooling
Coil
Evaporative
Condensing
Section
Direct Expansion
Control Strategies
Direct
Expansion
Unit Control Strategies
System Control Strategies
•
•
•
•
Unit capacity controlled to supply
air setpoint
Unit controlling economizer based
on supply temp and enthalpy
Fan speed controlled by pressure
setpoint in space or supply plenum
Enthalpy
Based Economizer
•
•
Rack inlet sensors used to verify
fan airflow volume
Coordinate units for standby
operation to prevent fighting
Return air pressure monitored for
proper space pressure control
Lead / Lag or
Common Capacity
Operation
Rack Inlet
Sensors
Frequently Asked Questions
Contact Tifft Gannon directly for clarifications or further information
if your question is not answered – tifft.gannon@emerson.com
 What percentage of trim cooling capacity is designed for evaporative







systems?
Is there a unit size that is too big and what are the issues at that size?
How would someone use both waterside and airside economizing in a
chilled water system?
What percentage of data center are using supply air temperatures up to 85
°F?
Are any of these systems better at handling low load situations?
What systems are best for Canadian installations that see temperatures to 40 °F?
How many stages of cooling control are there on direct evaporative
systems?
What happens when my customer predicted return air temperature comes in
much lower than what they told me?
For Further Information Contact Data
Center Systems
952.403.9900
PROPRIETARY INFORMATION: The information contained in this presentation is the property
of Emerson Network Power and is subject to change without notice. Except as specifically
authorized in writing by Emerson Network Power, the holder of this presentation shall keep all
information contained herein confidential and shall protect same in whole or in part from
disclosure and dissemination to all third parties.