upgrading existing chw systems
TRANSCRIPT
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Upgrading ExistingChilled-Water
Systems
Kevin Rice, ComprehensiveSolutions Account Executive
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Existing Buildings Gordon Holness, 2009 ASHRAE President*
75% to 85% of all the buildings that willexist in urban areas in 2030 exist today.
Energy efficiency in existing buildings ourgreatest opportunity for a sustainablefuture.
we can sustain our future by rebuildingour past.
*Presidential address, June 2009
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Business Climate Budgets
Capital budgets limited, meet ROI
Pressure to reduce operating costs
Maintenance
Deferred (ignored?)
Enhanced to keep equipment workinglonger
Sustainability reduce energy use
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Upgrade Goals Use existing equipment and infrastructure
whenever possible
Reduce energy use but not at theexpense of comfort or the process
Show internal rate of return consistentwith present internal requirements
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The Building HVACSystem
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Chilled-Water System
pumpcoil
controlvalve
air-cooledchiller
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Existing Chilled-WaterSystems
Chiller
Pumps and pipes
Chilled waterCondenser water
Cooling towers and fans
System controls
Pictures
http://localhost/var/www/apps/conversion/tmp/scratch_3/Pictureshttp://localhost/var/www/apps/conversion/tmp/scratch_3/Pictures -
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Chiller Products
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Upgrade options
Change the Chiller
Retrofit
Replace
Select different design parameters
Change system configuration
Enhance controls
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Chiller Upgrade Options
Comply with ASHRAE 90.1
Add a variable speed drive
Replace the chiller
Size the new chiller properly
Compare same-price new chiller options
Variable speed drive
High efficiency
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ASHRAE 90.1
Two Paths in 90.1-2010
Once a path is chosen, both full and part loadrequirements must be met
Positive displacement chillers evaluated only atAHRI Standard 550/590 standard conditions
Chilled water: 44F leaving, 2.4 gpm/ton
Condenser water: 85F entering, 3.0 gpm/ton
Centrifugal chiller requirements must be adjustedfor non-standard conditions
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ASHRAE 90.1Air-cooled Chillers
Capacity
(tons)
2007 2010 Path A 2010 Path B
Full
Load
IPLV Full
Load
IPLV Full
Load
IPLV
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ASHRAE 90.1Water-cooled positive Displacement Chillers
Capacity
(tons)2007 2010 Path A 2010 Path B
Full
Load
IPLV Full
Load
IPLV Full
Load
IPLV
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ASHRAE 90.1Water-cooled Centrifugal Chillers
Centrifugal chiller requirements must be adjusted for non-standardconditions
All requirements in kW/ton.
Chiller performance must be less than or equal to the requirements inthe table
Capacity
(tons)
2007 2010 Path A 2010 Path B
Full
Load
IPLV Full
Load
IPLV Full
Load
IPLV
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Chiller Upgrade Options
Comply with ASHRAE 90.1
Add a variable speed drive
Replace the chiller
Size the new chiller properly
Compare same-price new chiller options
Variable speed drive
High efficiency
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Overhauled Chillers
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Adding a VSD to anExisting Chiller
Comply with ASHRAE 90.1 requirementsfor retrofits
Ensure that modification will not result in anincrease in annual energy consumption
Understand how a drive may benefitchiller performance
Perform return on investment analysis
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Drive impact on existingchiller performance
Demand rises 2-4% at design conditions
Largest benefit at lower condenser water
temperatures
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2006AmericanStand
ardInc.
Lift versus Load
lift
lvg evaporator water
lvg condenser water
lift PcndPevp
lift Tlvg cndTlvg evp
load gpm (Tent evpTlvg evp)
800 gpm
load = 500 tons
2 gpm/ton
58F(T)
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compressorwork
2006AmericanStand
ardInc.
Compressor Work and Chiller Efficiency
cooling capacity/load
head/li
ft
lvg evapwater
lvg cond
water
500 tons
58F
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Lessons Learned
To reduce lift:
Decrease condenserpressure by reducingleaving-tower water
temperature
Increase evaporatorpressure by raisingchilled water setpoint
VSDs optimize chiller liftefficiency 41Flvg evap
water
lvg condwater
45F
73F
99F
compressorwork
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Drive impact on existingchiller performance
700-Ton Chiller VSD Retrofit
0
50
100
150
200
250
300
350
400
450
500
0 200 400 600 800
Tons
kW
Existing-85F
VSD-Retrofit-85F
Existing-75F
VSD-Retrofit-75F
Existing-65F
VSD-Retrofit-65F
No savings at constant ECWT
Savings at reduced ECWT
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Drive Retrofit:Issues to consider
Utility rates? DemandCharge? Ratchet?
VSD adds inefficiency
If chiller was oversized the demandmay be lower
How often will it operateat advantageousconditions?
24/7 operation may be beneficial
Economizer reduces the loads atadvantageous conditions
How much energy isconsumed by the coolingtower?
Need to balance tower and chillerenergy
Is the chiller oversized forthe load?
Load reduction in conjunction withreduced CW temperatures may offersignificant savings
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Chiller Plant Analyzer
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Chiller Upgrade Options
Comply with ASHRAE 90.1
Add a variable speed drive
Replace the chiller
Size the new chiller properly
Compare same-price new chiller options
Variable speed drive
High efficiency
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Chiller Replacement
Correctly size the new chiller
Determine actual building load
Downsize chiller if possible
If more tonnage is needed, higher efficiencyallows present electrical system to serve
Replace with higher efficiency chiller
Reduce demand and consumption
Constant speed or variable speed?
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Chiller Replacement:Constant or Variable Speed?
Different than retrofit where only VSDmakes economic sense
Compare same price VSD chiller andhigher full load efficiency chiller
Make sure each chiller meets ASHRAE 90.1full and part-load requirements
Use comprehensive analysis to determinewhich to purchase
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Same-price Chiller:Example Performance
600-ton Replacement Chiller Performance
0
50
100
150
200
250
300
350
400
0% 20% 40% 60% 80% 100%
% Load
kW
High_efficiency_85F
VSD_85F
High_efficiency_75F
VSD_75F
High_efficiency_65F
VSD_65F
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Guidance:VSD or High Efficiency?
High efficiency
Significant demandcharges
Humid climates
Multiple chillers in theplant
Economizer that
reduces low load/lowlift operating hours
VSD
Many hours at lowcondenser water
temperature and lowload
Perhaps only on onechiller
Factor in replacement
of VSD whenperforming life cycleassessment
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Upgrade options
Change the Chiller
Retrofit
Replace
Change design parameters
Change system configuration
Enhance controls
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chilled water plant design
ProvocationAre our rules of thumb
44 F chilled water supply
10 F T for chilled water system
3 gpm/ton condenser water flow
in need of repair?
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Design Parameters
Many chilled watersystems selected at:
Chilled water
44F 2.4 gpm/ton (10F T)
Condenser water
85F Entering
3 gpm/ton (9.4F T)
ASHRAE GreenGuideGuidance
Chilled water
12F to 20F T 2.0 to 1.2 gpm/ton
Condenser water
12F to 18F T
2.5 to 1.6 gpm/ton
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High PerformanceDesign Parameters
Kelly and Chan
Chilled water DT: 18F
Condenser water DT: 14.2F
(3.6 - 8.3% energy savings in variousclimates)
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a history of
Chiller Performance8.0
ASHRAE Standard 90
ch
illerefficiency
,COP
6.0
4.0
2.0
0.0NBI best
available90-75(1977)
90-75(1980)
90.1-89 90.1-99
centrifugal>600 tons
screw150-300 tons
scroll
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Efficiency changesin the past 35 years
Chiller COP increased up to 75%
Pumps? motors more efficient
Cooling towers? motors more efficient,fill design has changed
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Retrofit applicationsand reduced flow - evap
Chilled water side
Coil
Its a simple heat transfer device
Reacts to colder entering waterby returning it warmer
Ideal for system expansion
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Retrofit applicationsand reduced flow - cond
Condenser side retrofit opportunity
Chiller needs to bereplaced
Cooling needs haveincreased by 50%
Cooling tower wasreplaced two years ago
Condenser pump andpipes are in good shape
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Retrofit applicationsand reduced flow - cond
Existing Retrofit
Capacity (tons) 500 750
Flow rate (gpm) 1500 1500Condenser Entering Water
Temperature (F)
85 88
Condenser Leaving Water
Temperature (F)
95 103
Design Wet Bulb (F) 78 78
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Upgrade options
Change the Chiller
Retrofit
Replace
Change design parameters
Change system configuration
Enhance controls
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Variable Primary FlowSystems
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VPF System RetrofitBenefits
Reduced pumping costs
Ability to respond to Low T Syndrome
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Flow requirementsVPF System
Limits (consult manufacturer)
Absolute flows - Minimum and maximum
Always need a method to allow minimum flow(bypass)
Flow rate changes 2% of design flow per minute
not good enough
10% of design flow per minute borderline 30% of design flow per minute
many comfort cooling applications
50% of design flow per minutebest
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Chiller Control
Variable Water Flow
30
40
50
60
70
80
90
100
110
120
130
3:50:00 3:55:00 4:00:00 4:05:00 4:10:00
Time (hour:min:sec)
WaterTemp[degF]
-500
-300
-100
100
300
500
700
900
1100
1300
1500
Flow[gpm]Evaporator Water Flow
Evap Entering Water Temp
Evap Leaving Water Temp
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Specify and install properflow control devices
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Conversion: Constantto Variable Flow
Confirm existing chillers and controls canoperate with variable evaporator flow
Ensure evaporator flow rate can stayabove minimum
New bypass or 3-way valves
Ensure flow rate changes are belowallowable chiller allowances
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Convert Primary Secondaryto Variable PrimaryVariable Secondary
Placeholder for
Manifolded P-S
System picture
(Beth to supply)
VFDs
T
DP
DP
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More informationVPF System
Http:/trane.com/commercial/library/newsletters.asp (1999 and 2002)
Dont Ignore Variable Flow, Waltz, Contracting
Business, July 1997
Primary-Only vs. Primary-Secondary Variable FlowSystems, Taylor, ASHRAE Journal, February 2002
Comparative Analysis of Variable and ConstantPrimary-Flow Chilled-Water-Plant Performance,Bahnfleth and Peyer, HPAC Engineering, April 2001
Campus Cooling: Retrofitting Systems,Kreutzmann, HPAC Engineering, July 2002
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Upgrade options
Change the Chiller
Retrofit
Replace
Change design parameters
Change system configuration
Enhance controls
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Control Options
Proper number of chillers
Pump control
Chiller-tower optimization
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Number of chillersoperating
Operate one at nearly full load or two atpart load?
Examine IPLV assumptions
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VSDs and centrifugal chillers
A Closer Look at IPLV
VSDs improve part-lift performance, so running two chillerswith VSDs at part load seems more efficient than one chiller atdouble the same load, but is dependent on condenser watertemperature
Load ECWTWeighting kW/Ton
100% 0.01 85F 0.572
75% 0.42 75F 0.420
50% 0.45 65F 0.308
25% 0.12 65F 0.372
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Chiller power only
45% Plant load
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Chillers plus pumps
45% Plant load
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Chilled Water PumpControl
Valve positionPump
Pressure
Sensor
Communicating
BASPump Speed
pump-pressure optimization
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Position (% open)
of critical valve
75%
65%
Increase pump static pressure setpoint
Reduce pump static pressure setpoint
No action
p p p p
Control Logic90.1-2007 Addendum ak
This will be required for many systems by 90.1-2010
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optimal condenser water control
ChillerTower Interaction
condenser water temperature, F
400
74
energyconsumption,
kW
76 78 80 8272
300
200
100
084
tower
chiller
total
optimalcontrol point
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chillertower optimization
An Example
720,000 ft hotel
2 chillers, 2 tower cells
Control strategies Make leaving-tower water cold
as possible (55F)
Optimize system operation
Entering-condenser setpointequals design 85F for humid climates,80F for dry climates
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chillertower control strategies
North America350K
annu
aloperatingcost,
$USD
300K
250K
200K
150K
100K
50K
0Mexico City Orlando San Diego Toronto
55F lvg tower
optimal control
design ECWT
control strategy:
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annu
aloperatingcost,
$USD
500K
400K
300K
200K
100K
0Dubai Paris Sao Paulo Singapore
55F lvg tower
optimal control
design ECWT
control strategy:
chillertower control strategies
Global Locations
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chillertower optimization
Operating Cost Savings
operatingcostsavin
gs,chiller
+tow
erannualcosts,
%
14
0
12
10
8
6
4
2
location
Dubai
Paris
SaoPa
ulo
Singap
ore
Mexico
City
Orland
o
SanDiego
Toront
o
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Upgrading chilledwater systems
Retrofit or replacechiller
Comply with 90.1requirements
Consider same-pricehigh efficiencyreplacement
Select different designparameters
Reduce flow rates byincreasing T
Chilled water
Condenser water
Consider VPF
Update controls
Number of chillers
operating
Pump pressureoptimization
Chiller-tower
optimization
Perform analysis
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References
Upgrading Chilled-Water Systems,ASHRAE Journal, November 2009.