HVAC Duct Calculator for Engineers
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Transcript of HVAC Duct Calculator for Engineers
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1Taylor Engineering, LLC
HVAC System DesignMark Hydeman, P.E., FASHRAETaylor Engineering, LLC
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2Taylor Engineering, LLC
it takes 2,000 to 3,000 times the
volume of air to cool what you can
with water!
How do you effectively fight a fire?
With air, or with water?
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State of the present: with air
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Air system design overview
Data center layout
Airflow configurations
Distribution: overhead or underfloorControl: constant or variable volume
Airflow issues
Economizers Humidity control issues
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Server airflow front toback or front to back andtop are recommended
2004, American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (www.ashrae.org). Reprinted by permission from
ASHRAE Thermal Guidelines for Data Processing Environments. This material may not be copied nor distributed in either paper or digital form
without ASHRAEs permission.
Data center layout
Cold Aisle
Hot Aisle
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Data center layout
2004, American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (www.ashrae.org). Reprinted by permission from
ASHRAE Thermal Guidelines for Data Processing Environments. This material may not be copied nor distributed in either paper or digital form
without ASHRAEs permission.
Underfloor Supply
Cold Aisle
Hot Aisle
Only 1 pressurezone for UF!
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Data center layout
2004, American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (www.ashrae.org). Reprinted by permission from
ASHRAE Thermal Guidelines for Data Processing Environments. This material may not be copied nor distributed in either paper or digital form
without ASHRAEs permission.
Overhead Supply
Cold Aisle
Hot Aisle
You canincorporate VAVon each branch
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Elevation at a cold aisle looking at racks
Typical temperature profile with UF supply
Too hot Too hot
Just right
Too cold
There are numerous references in ASHRAE. See for example V. Sorell et al; Comparison of
Overhead and Underfloor Air Delivery Systems in a Data Center Environment Using CFD
Modeling; ASHRAE Symposium Paper DE-05-11-5; 2005
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Elevation at a cold aisle looking at racks
Too warm Too warm
Just right
Typical temperature profile with OH supply
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Aisle capping
2004, American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (www.ashrae.org). Reprinted by permission from
ASHRAE Thermal Guidelines for Data Processing Environments. This material may not be copied nor distributed in either paper or digital form
without ASHRAEs permission.
Cold Aisle Caps
End cap
Hot aisle lid
APC reprinted with permission
Cold Aisle
Hot Aisle
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Aisle capping
2004, American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (www.ashrae.org). Reprinted by permission from
ASHRAE Thermal Guidelines for Data Processing Environments. This material may not be copied nor distributed in either paper or digital form
without ASHRAEs permission.
Cold Aisle Caps
LBNL has recently performed
research on aisle capping
Cold Aisle
Hot Aisle
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Overhead (OH) vs. Underfloor (UF)
Issue Overhead (OH) Supply Underfloor (UF) Supply
Capacity Limited by space and aisle velocity. Limited by free area of floor tiles.Balancing Continuous on both outlet and branch. Usually limited to incremental changes by
diffuser type. Some tiles have balancing
dampers. Also underfloor velocities canstarve floor grilles!
Control Up to one pressure zone by branch. Only one pressure zone per floor, canprovide multiple temperature zones.
Temperature
Control
Most uniform. Commonly cold at bottom and hot at top.
First Cost Best (if you eliminate the floor). Generally worse.
Energy Cost Best. Worst.Aisle Capping Hot or cold aisle possible. Hot or cold aisle possible.
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Airflow design disjoint
IT departments select servers and racks
Engineers size the fans and cooling
capacity
Whats missingin this picture?
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Airflow with constant volume systems
Hot spots Higher hot aisle
temperature
Possible equipment
failure or degradation
ServersSupplyHVAC VV _
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Least hot spots Higher air velocities
Higher fan energy
Reduced economizer
effectiveness (due tolower returntemperatures)
ServersSupplyHVAC VV _
Airflow with constant volume systems
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Note most of these observations apply tooverhead and underfloor distribution
With constant volume fans on the serversyou can only be right at one condition ofserver loading!
The solution is to employ variable speedserver and distribution fans
Airflow with constant volume systems
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Partial flow condition
Best energy performancebut difficult to control
ServersSupplyHVAC VV _
Airflow with variablevolume systems
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How Do You Balance Airflow?
Spreadsheet
CFD
Monitoring/SiteMeasurements
Image from TileFlow
http://www.inres.com/Products/TileFlow/tileflow.html,
Used with permission from Innovative Research, Inc.
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Thermal report
From ASHRAEs Thermal Guidelines for Data Processing Environments
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Whats the server airflow?
SUN SUN DELL DELLV490 V240 2850 6850
num fans 9 3 n/a n/atotal CFM (max) 150 55.65 42 185total CFM (min) 27 126fan speed single speed variable 2 speed 2 speedfan control n/a inlet temp. 77F inlet 77F inletForm Factor (in U's) 5 2 2 4heat min config (btuh) 798 454heat max config (btuh) 5,459 1,639 2,222 4,236heat max (watts) 1,599 480 651 1,241dT min config - 13 - 3dT max config 33 27 48 21servers per rack 8 21 21 10CFM/rack (hi inlet temp) 1,200 1,169 882 1,850CFM/rack (low inlet temp) 1,200 567 1,260max load / rack (kW) 13 10 14 12
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Best air delivery practices Arrange racks in hot aisle/cold aisle configuration Try to match or exceed server airflow by aisle
Get thermal report data from IT if possible Plan for worst case
Get variable speed or two speed fans on servers if possible Provide variable airflow fans for AC unit supply
Also consider using air handlers rather than CRACs for improvedperformance (to be elaborated on later)
Use overhead supply where possible Provide aisle capping (preferably cold aisles, refer to LBNL
presentation for more details) Plug floor leaks and provide blank off plates in racks Draw return from as high as possible Use CFD to inform design and operation
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Air-side economizer
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Air-Side Economizer issues
Hygroscopic dust
LBNL is doing some research on this
Design humidity conditionsSee following slides
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Design conditions at the zone
2005, American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (www.ashrae.org). Reprinted by permission from
ASHRAE Design Considerations for Data and Communications Equipment Centers. This material may not be copied nor distributed in either
paper or digital form without ASHRAEs permission.
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San Francisco
BAROMETRIC PRESSURE: 29.904 in. HG
PSYCHROMETRICCHARTNormal TemperatureI-P Units
16 FEET
Weather Hours
360 to 321
320 to 281
280 to 241
240 to 201
200 to 161
160 to 121
120 to 81
80 to 41
40 to 1
30 35 40 45 50 55 60 65 70 75 80 85 90 95 100
DRY BULB TEMPERATURE - F
.001
.002
.003
.004
.005
.006
.007
.008
.009
.010
.011
.012
.013
.014
.015
.016
.017
.018
.019
.020
10
15
20
25
30
35
40
Chart by: HANDS DOWN SOFTWARE, www.handsdownsoftware.com
15%
25%
10%RELATIVEHU
MIDITY
20%
30%
40%
50%
60%
70%
80%
90%
30
35
35
40
40
45
45
50
50
55
55
60
6065
65 70
7075WETBULBTEMPERATURE-F
75
80
13.0
14.0VOLUME-CU.FT.PERLB.DRYAIR
H
UMIDITYRATIO-
POUNDSMOISTUREPER
POUND
DRYA
IR
Class1;Allow
NEBS;Recommend
Class1;Recommend
San Francisco Climate Data Binswith Data Center Guideline Zones
BAROMETRIC PRESSURE: 29.904 in. HG
PSYCHROMETRICCHARTNormal TemperatureI-P Units
16 FEET
Chart by: HANDS DOWN SOFTWARE, www.handsdownsoftware.com
X
Design Target
Upper Allowed Humidity Limit
Lower Allowed Humidity Limit (20%RH)
Negligible time of possibleconcern for humidification
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Los Angeles
BAROMETRIC PRESSURE: 29.808 in. HG
PSYCHROMETRICCHARTNormal TemperatureI-P Units
105 FEET
Weather Hours
396 to 353
352 to 309
308 to 265
264 to 221
220 to 177
176 to 133
132 to 89
88 to 45
44 to 1
30 35 40 45 50 55 60 65 70 75 80 85 90 95 100
DRY BULB TEMPERATURE - F
.001
.002
.003
.004
.005
.006
.007
.008
.009
.010
.011
.012
.013
.014
.015
.016
.017
.018
.019
.020
10
15
20
25
30
35
40
Chart by: HANDS DOWN SOFTWARE, www.handsdownsoftware.com
15%
25%
10%RELATIVEHUM
IDITY
20%
30%
40%
50%
60%
70%
80%
90%
30
35
35
40
40
45
45
50
50
55
55
60
6065
65 70
7075WETBULBTEMPERATURE-F
75
80
13.0
14.0VOLUME-C
U.FT.P
ERLB.D
RYAIR
H
UMIDITYRATIO-
POUNDSMOISTUREPER
POUND
DRYAIR
Class1;Allow
NEBS;Recommend
Class1;Recommend
Los Angeles Climate Data Binswith Data Center Guideline Zones
BAROMETRIC PRESSURE: 29.808 in. HG
PSYCHROMETRICCHARTNormal TemperatureI-P Units
105 FEET
Chart by: HANDS DOWN SOFTWARE, www.handsdownsoftware.com
X
Design Target
Upper Allowed Humidity Limit
Lower Allowed Humidity Limit (20%RH)
Only a few hours of possibleconcern for humidification
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BAROMETRIC PRESSURE: 29.893 in. HG
PSYCHROMETRICCHARTNormal TemperatureI-P Units
26 FEET
Weather Hours
270 to 241
240 to 211
210 to 181
180 to 151
150 to 121
120 to 91
90 to 61
60 to 31
30 to 1
30 35 40 45 50 55 60 65 70 75 80 85 90 95 100
DRY BULB TEMPERATURE - F
.001
.002
.003
.004
.005
.006
.007
.008
.009
.010
.011
.012
.013
.014
.015
.016
.017
.018
.019
.020
10
15
20
25
30
35
40
Chart by: HANDS DOWN SOFTWARE, www.handsdownsoftware.com
15%
25%
10%RELATIVEHU
MIDITY
20%
30%
40%
50%
60%
70%
80%
90%
30
35
35
40
40
45
45
50
50
55
55
60
6065
65 70
7075WETBULBTEMPERATURE-F
75
80
13.0
14.0VOLUME-CU.FT.PERLB.DRYAIR
H
UMIDITYRATIO-
POUNDSMOISTUREPER
POUND
DRYA
IR
Class1;Allow
NEBS;Recommend
Class1;Recommend
Sacramento Climate Data Binswith Data Center Guideline Zones
BAROMETRIC PRESSURE: 29.893 in. HG
PSYCHROMETRICCHARTNormal TemperatureI-P Units
26 FEET
Chart by: HANDS DOWN SOFTWARE, www.handsdownsoftware.com
Sacramento
X
Design Target
Upper Allowed Humidity Limit
Lower Allowed Humidity Limit (20%RH)
Negligible time of possibleconcern for humidification
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Lower humidity limit
Mitigate electrostatic discharge (ESD) Recommended procedures
Personnel grounding Cable grounding
Recommended equipment Grounding wrist straps on racks Grounded plate for cables Grounded flooring Servers rated for ESD resistance
Industry practices Telecom industry has no lower limit The Electrostatic Discharge Association has removed humidity control as a primary
ESD control measure in their ESD/ANSI S20.20 standard
Humidity controls are a point of failure and are hard to maintain Many data centers operate without humidification This needs more research
And for some physical media (tape storage, printing and bursting) Old technology not found in most data centers It is best to segregate these items rather than humidify the entire data center
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ESD control: floor grounding
Image from Panduit, reprinted with permission
W t Sid E i
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Water-Side Economizer
Integrated
Heat
Exchanger in
series with
chillers on
CHW side
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Economizer Summary
Air-Side Economizers Provides free cooling when
dry-bulb temperatures arebelow 78F-80F.
May increase particulates(LBNL research indicates thisis of little concern).
Should be integrated to bemost effective.
Improves plant redundancy! Can work in conjunction with
water-side economizers ondata centers!
Need to incorporate relief.
Water-Side Economizers Provides low energy cooling
when wet-bulb temperaturesare below 55F-60F.
Avoids increased particulates(and low humidity if thatconcerns you).
Should be integrated to bemost effective (see previousslide).
Improves plant redundancy! Can work in conjunction with
air-side economizers on datacenters!
Both are proven technologies on data centers!
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A case study of two designs
Collocation facility in theBay Area
Side by side designs in
same facility over twophases
Motivation for the seconddesign was to reducecost
Case study wasdeveloped by LawrenceBerkeley National
Laboratory (LBNL) Data Centers 8.1 and 8.2
Both sections at ~30%build-out during
monitoring
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A tale of two designs: overview
Phase 1 Data Center (8.1)
26,200 ft2
27 W/ft2 design
Traditional under-floor designwith CRAC units
Air-cooled DX
Humidity controls (45%-55%)
Phase 2 Data Center (8.2)
73,000 ft2
50 W/ft2 design
Under-floor supply fromcentral AHUs with CHW coils
Water-cooled plant
Air-side economizers
No humidity controls
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A tale of two designs: a closer look
Normalized efficiency metric:servers
systemscooling
coolingkW
kW_
Data normalized to computer loads
-
0.20
0.40
0.60
0.80
1.00
1.20
1.40
1.60
Normalizedenergy
Computer Loads UPS Losses HVAC Lighting
~1/4 of the
normalized energy
Phase 1 Data Center (8.1)
Phase 2 Data Center (8.2)
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A tale of two designs: results
Phase 1 Data Center (8.1)
Around 2x the HVACinstalled cost ($/ft2)
Around 4x the energy bills(when normalized to serverload)
Acoustical problems
Higher maintenance costs
Lost floor space in datacenter due to CRACs
Phase 2 Data Center (8.2)
Preferred by the facilityoperators and data centerpersonnel
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Two data centers: summary
What made the difference?
Airside economizers
No humidity controlsWater-cooled chilled water system
AHUs instead of CRAC units
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Custom CRAH Unit (Large)
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Example CRAH Unit Comparison
Option 1
Model Std CRAC Custom Model 1 Custom Model 2Budget Cost 16,235$ 23,000$ 41,000$Number of units 21 13 4
net total cooling (btuh) 434,900 410,000 841,000net sensible (btuh) 397,400 399,000 818,000
sensible (tons) 33.1 33.3 68.2CFM 16,500 25,000 50,000
SAT 49.90 59.30 59.00airside dT 25.10 15.70 16.00
Internal SP 2 0.8 0.8 1.8 1.8no. fans 3 3 2
fan type Centrifugal Plenum Plenumno. motors 1 3 2
HP/motor 15 5 15total HP 15 15 30
BHP/motor 15 4.7 11.5Unit BHP 15 14.1 23
unit width 122 122 122
depth 35 36 72height 76 156 168filter type ASHRAE 20% MERV 13 MERV 13Water PD (ft) 13.5 ft 11.1 11.1
CHW dT 14F 20 20GPM 66.80 44.00 88.00
Total GPM 1,403 924 66%Total BHP 315 275 87%
Option 2
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34% less water flow 13% less fan energy
More if you consider the supply air temperature and airflow issues
Excess fan capacity on new units
36% higher cost for units, but Fewer piping connections Fewer electrical connections Fewer control panels No need for control gateway Can use the existing distribution piping and pumps (case study) Can use high quality sensors and place them where they make sense
Possibly less turbulence at discharge?
Example CRAH Unit Comparison
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Air cooling issues
Limitations on the data densities served (~200w/sf) Air delivery limitations Real estate
Working conditions Hot aisles are approaching OSHA limits Costly infrastructure High energy costs Management over time
Reliability Loss of power recovery Particulates
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Take Aways
Use air- or water-side economizers where possible Consider personal grounding in lieu of humidification Consider AHUs as an alternative to CRACs Consider VSDs on fans, pumps, chillers and towers Refer to ASHRAE, LBNL and Uptime Institute for more
recommendations
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State of the future: cooling with liquid