pg&e optimizing chilled water plants - rv 13 1 day version

8/12/2019 PG&E Optimizing Chilled Water Plants - RV 13 1 Day Version

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Presented by:

Steve Taylor

The PG&E Pacific Energy Center Presents:The PG&E Pacific Energy Center Presents:

Optimizing the Design and Control ofOptimizing the Design and Control of

Chilled Water PlantsChilled Water Plants

March 7, 2012

Taylor Engineering LLCAlameda, CA

http://www.taylor-engineering.com



LogisticsLogistics

SafetyRestroomsRecycling

Cell phone etiquette

2

Review formsWebinar etiquette

PG&E Resources• Rebates• Tool Lending Library• Marlene Vogelsang ([email protected])



HandoutsHandouts

You can get a copy of the handoutsin PDF format as follows:• Type the following link into your web

browser: -

3

engineering.com/ftp/PECClassHandouts.html

• Click on the link for the Chilled Water PlantClass on 3/7/2012 to download the Acrobatfile of the presentation.



About Steve TaylorAbout Steve TaylorPrincipal, Taylor EngineeringEducation• Stanford University, BS Physics, 1976• Stanford University, MS Mechanical Engineering, 1977

ASHRAE• Fellow• Standard 62 Indoor Air Quality, 8 years, chair

• Standard 90.1 Energy Standard, Chair HVAC Subc., 14 years• Standard 55 Thermal Comfort

4

• Guideline 16 Economizer Dampers, chair • Guideline 13 Specifying Direct Digital Control Systems, chair • TC 4.3 Ventilation, vice-chair • TC 1.4 Control Theory & Applications, chair • Author “Fundamentals of Design and Control of Central Chilled Water Plants” Course• Distinguished Lecturer

USGBC LEED• Indoor Environmental Quality TAG, vice chair UMC/IAPMO (California Mechanical Code)• Mechanical Technical Committee, member and ASHRAE Liaison

CSU• Mechanical Review Board, member



Who are You?Who are You?

Consulting Engineers?Design/Build Engineers?Contractors?

5

Building Owners/Engineers?Equipment rep/supplier/manufacturer?Commissioning authority?Other?



AgendaAgenda

Introduction 9:00 AMCHW Distribution Systems 9:15 AMBreak 10:45 AMCHW Distribution System Balancing 11:00 AM

6

str ut on ystems :Lunch 12:00 PMSelecting CHW Distribution Systems 1:00 PMSelecting CHW ∆T 1:30 PMSelecting CW ∆T 2:00 PMSelecting Chillers 2:30 PMOptimizing control sequences 3:00 PMQuestions 4:15 PMCompletion 4:30 PM



ResourcesResourcesCoolTools™ Chilled Water Plant Design and Specification Guide,PG&E Pacific Energy Center Balancing Variable Flow Hydronic Systems. ASHRAE JournalOct 2002, Atlanta GA.Primary-Only vs. Primary-Secondary Variable Flow Systems.ASHRAE Journal February 2002, Atlanta GA.

Degrading Chilled Water Plant Delta-T: Causes and Mitigation,ASHRAE Transactions January 2002, Atlanta GA. AC-02-06

7

Sizing Pipe using Life Cycle Costs, ASHRAE Journal, October2008 – and LCC Piping spreadsheetWaterside Economizing in Data Centers: Design and ControlConsiderations, ASHRAE Transactions 2009, LO-09-015Optimized Design & Control of Chilled Water Plants, ASHRAEJournal• Part 1: Chilled Water Distribution System Selection• Part 2: Condenser Water Distribution System Design• Part 3: Pipe Sizing and Optimizing ∆T• Part 4: Chiller & Cooling Tower Selection• Part 5: Optimized Control Sequences

All are available at no charge from http://www.taylor-engineering.com/publications/artic les.shtml



Design Guide ScopeDesign Guide Scope

New Construction• Hydronic design

• Chiller selection

Retrofit• Replacement

chillers

8

• Cooling tower selection• Control optimizations• Commissioning

• on o s• Control optimization• Commissioning



Optimizing Energy UsageOptimizing Energy Usage

Chillers• Type, efficiency, size, VSD

Cooling Towers• Fan type, efficiency, approach, range, speed control, flow

turndownChilled Water Pum s

9

• Arrangement, flow rate (delta-T), pressure drop, VSD

Condenser Water Pumps• Flow rate (delta-T), pressure drop

Air Handling Units• Coil sizing, air-side pressure drop, water-side pressuredrop



Pop Quiz 1Pop Quiz 1

What happens to componentenergy usage if we lower CWSsetpoint?• Chiller

• Towers• Pumps



Pop Quiz 3Pop Quiz 3

What happens to componentenergy usage if we lower CW flowAND the CWS setpoint?• Chiller

• Towers• Pumps



14

SystemsSystems



Water Distribution System ClassesWater Distribution System Classes

Constant Flow• No control valves• 3-way control valves

Variable Flow• Primary-Only• Primary/Secondary

(/Tertiary)• Primar /Distributed

15

Secondary

• Primary/Variable SpeedCoil Secondary



CHILLER

CHWPUMP

SUPPLY WATERTEMPERATURE

Constant FlowConstant FlowSingle Chiller, Single Coil, No Control ValveSingle Chiller, Single Coil, No Control Valve

16

OPTIONALSTORAGE

TANK

COIL

SUPPLY AIRTEMPERATURE

Works also for boilers that havemodulating burners and verygood turndown, e.g. ≥10 to 1



Constant FlowConstant FlowTwo Chillers, Single Coil, No Control ValveTwo Chillers, Single Coil, No Control Valve

CHILLER #2

CHWPUMP


VFD

CHILLER#1

17

OPTIONALSTORAGE

TANK

COIL

SUPPLY AIRTEMPERATURE



Constant FlowConstant FlowSingle Chiller, Multiple CoilsSingle Chiller, Multiple Coils

CHILLER

CHWPUMP

COIL

18

3-WAY VALVE



CHILLER

CHWPUMP


VFD

Variable FlowVariable FlowSingle Chiller, Multiple CoilsSingle Chiller, Multiple Coils

19

COIL2-WAY VALVE

DP SENSOR

3-WAY VALVE



CHILLER #1

CHWPUMPS


CHILLER #2

Constant FlowConstant FlowMultiple Parallel Chillers, Multiple CoilsMultiple Parallel Chillers, Multiple Coils

CH2 240 gpm

CH1 240gpm How many

chillers do weneed to run?

20

COIL

3-WAY VALVEBallroom A 240 gpm

Ballroom B 240 gpm

Ballroom A240 gpm

100% Loaded

Ballroom B0 gpmUnoccupied



Variable FlowVariable Flow

Vary Flow Through Coil Circuit• Two-way valves• Variable speed coil pump

Confi urations

21

• Primary-secondary• Primary-secondary variations

• Primary-only



Variable Flow Chilled WaterSystems

Old Paradigm• Controls respond to changes in CHW

temperature

• Variable flow causes low temperature trips,

22

locks out chiller, requires manual reset(may even freeze)

• Hence: Maintain constant flow through

chillers



Primary/SecondaryPrimary/Secondary

23




ON

ON

100gpm

100gpm

100gpm

24

ON

OFF

100gpm

100gpm

0 gpm



Variable FlowVariable FlowPrimary/Secondary, Multiple Chillers and CoilsPrimary/Secondary, Multiple Chillers and Coils

CHILLER #1

PRIMARYPUMPS

CHILLER #2

COMMON LEG (DECOUPLER)

25

COIL2-WAY VALVE

V F D

V F D

SECONDARYPUMPS

DP SENSOR



Variable FlowVariable FlowPrimary/Secondary, Series Flow, Multiple ChillersPrimary/Secondary, Series Flow, Multiple Chillers

26



Variable FlowVariable FlowPrimary/Distributed SecondaryPrimary/Distributed Secondary

27



Variable FlowVariable FlowPrimary/Secondary/TertiaryPrimary/Secondary/Tertiary

28



Variable Flow Chilled Water SystemsVariable Flow Chilled Water Systems

New Paradigm• Modern controls are robust and very

responsive to both flow and temperature

variations

29

• Variable flow OK within range and rate-of-change spec’d by chiller manufacturer



Variable FlowVariable FlowPrimaryPrimary- -only, Multiple Chillersonly, Multiple Chillers

CHILLER #1

PRIMARYPUMPS

CHILLER #2

FLOWMETER

VFD

VFD

PRIMARYPUMPS

VFD

30

2-WAY VALVECOIL

DP SENSOR



Variable FlowVariable FlowPrimary, Bypass ValvePrimary, Bypass Valve

Location• Near chillers

Best for energyControls less expensiveControl more difficult to

tune – fast response•

31

Smaller pressurefluctuations (easier tocontrol)Keeps loop cold for fastresponse

Sizing• Sizing critical when at

chillers/pumps• Different size if pump has

VFD or not

Flow measurement• Flow meter

Most accurateNeeded for Btu calc forstaging

• DP across chiller Less expensive

Accuracy reduced as tubesfoulOne required for each chiller



Primary CHW Pump OptionsPrimary CHW Pump Options

32

Dedicated Pumping Advantages:• Less control complexity• Custom pump heads w/ unmatchedchillers• Usually less expensive if each pumpis adjacent to chiller served• Pump failure during operation doesnot cause multiple chiller trips

Headered Pumping Advantages:• Better redundancy• Valves can “soft load” chillers with primary

onlysystems

• Easier to incorporate stand-by pump



Balancing Variable FlowS stems

33

See “ Balancing Variable Flow Hydronic Systems ” ASHRAE Journal Oct 2002



Variable Flow Balancing OptionsVariable Flow Balancing Options

1. No balancing• Relying on 2-way control valves to automatically provide

balancing

2. Manual balance• Using ball or butterfly valves and coil pressure drop

• Using calibrated balancing valves (CBVs)

35

3. Automatic flow limiting valves (AFLVs)4. Reverse-return5. Oversized main piping6.

Undersized branch piping7. Undersized control valves8. Pressure independent control valves

• Not studied in our ASHRAE paper



Piping Systems AnalysisPiping Systems Analysis

Heating system• 540 gpm• 400 VAV reheat coils• Constant speed pumps

• Based on actual building in Oakland

36

Cooling system• 1,200 gpm• 20 Floor-by-floor AHUs• Variable speed pumps

All valves: 2-way modulatingAnalyzed using Pipe-Flo



HW Piping Floor PlanHW Piping Floor Plan

37



Typical Coil PipingTypical Coil Piping

Options 1, 4, 5, 6, & 7

38

Option 2



Typical Coil PipingTypical Coil Piping

Option 3

39

Option 8



Option 1: No BalancingOption 1: No BalancingAdvantages• No balancing labor • Coils may be

added/subtractedwithout rebalance

Disadvantages• Imbalance during

transients or ifsetpoints areimproper

• Control valves near

40

pumps can be over-pressurized,reducingcontrollability



Option 2: Manual w/CBVsOption 2: Manual w/CBVs

Advantages• Valves can be used for

future diagnosis (flow canbe measured)

• Reduced over-

pressurization of control

Disadvantages• Added cost of calibrated

balancing valve• Higher balancing cost• Complete rebalance

may be required if coilsadded/subtracted

41

• Slightly higher pumphead due to balancingvalve

• Coils may be starved ifvariable speed drivesare used without DPreset

• Slightly higher pumpenergy depending onflow variations andpump controls



Starved Loads with CBVs and Fixed DPStarved Loads with CBVs and Fixed DPSetpoint: Design ConditionSetpoint: Design Condition

12 PSID38 PSID45 PSID

20

60

50

40

30

70

P R

E S S U R E P S I G

42

VFD L o a d

L o a d

DP

100 GPM5 PSID

100 GPM5 PSID

5 PSID

28 PSID, Cv=19

5 PSID

2 PSID

PUMP CLOSE LOAD REMOTE LOAD

10

0



Starved Loads with CBVs and Fixed DPStarved Loads with CBVs and Fixed DPSetpoint: No Remote Flow ConditionSetpoint: No Remote Flow Condition

12 PSID12 PSID19 PSID

20

60

50

40

30

70

P R E S S U R E P S I G

43

56 GPM

1.6 PSID

0 GPM

0 PSID

1.6 PSID

8.8 PSID

12 PSID

0 PSID

VFD L o a d

L o a d

DP

PUMP CLOSE LOAD REMOTE LOAD

0



Option 3: Automatic Flow LimitingOption 3: Automatic Flow LimitingValvesValves

Advantages• No balancing labor • Coils may be

added/subtracted withoutrebalance

Disadvantages• Added cost of strainer and

flow limiting valve• Cost of labor to clean

strainer at start-up

•Higher pump head andenergy due to strainer and

44

ow m ng va ve• Valves have custom flow

rates and must beinstalled in correct location

• Valves can clog or springs

can fail over time• Control valves nearpumps can be over-pressurized, reducingcontrollability



Option 4: ReverseOption 4: Reverse- -returnreturn

45



Reverse Return ConfigurationsReverse Return Configurations

C/C

C/CH/C

H / C

H / C

H/C

46

C/C

C/C

Reverse return riser (elevation)

Reverse return on floor (plan)

H/C H/C



Option 4: ReverseOption 4: Reverse- -returnreturnAdvantages• No balancing labor • Coils may be


• No significant over-

Disadvantages• Added cost of reverse-

return piping• Not always practical

depending on physical

layout of system

47

valves close to pumps.

• Usually lower pump headdue to reverse-returnpiping having lower

pressure drop than mains(due to larger pipe)



Option 5: Oversized Main PipingOption 5: Oversized Main Piping

C/C

C/C

6” 6”

C/C

C/C

2” 2”

3” 3”

48

Standard main design

C/C

C/C

Oversized main riser

6” 6”C/C

C/C

6” 6”

4” 4”



Option 6: Undersized Branch PipingOption 6: Undersized Branch Piping

Advantages• No balancing labor • Reduced cost of smaller

piping• Coils may be


Disadvantages• Limited effectiveness and

applicability due to limitedavailable pipe sizes

• High design and analysiscost to determine correctpipe sizing

50

• e uce over-pressurization of controlvalves close to pumpswhere piping has beenundersized

coils where piping hasbeen undersized

• Coils may be starved ifvariable speed drives areused without DP reset

• Slightly higher pumpenergy depending on flowvariations and pumpcontrols



Option 7: Undersized Control ValvesOption 7: Undersized Control Valves

Advantages• No balancing labor • Reduced cost of smaller

control valves• Coils may be


Disadvantages• Limited effectiveness and

applicability due to limitedavailable control valvesizes (Cv)

• High design and analysiscost to determine correct

51

• e uce over-pressurization of controlvalves close to pumpswhere control valves havebeen undersized

•Improved valve authoritywhich could improvecontrollability wherecontrol valves have beenundersized

• Coils may be starved ifvariable speed drives arewithout DP reset

• Slightly higher pumpenergy depending on flowvariations and pumpcontrols



Option 8: Pressure Independent Control ValvesOption 8: Pressure Independent Control Valves

Advantages• No balancing labor • Coils may be

added/subtractedwithout rebalance

• No over-pressurization

Disadvantages• Added cost of strainer and

pressure independent controlvalve

• Cost of labor to clean strainerat start-up

• Hi her um head and ener

52

to pumps

• Easy valve selection –flow only not Cv

• Perfect valve authority

will improvecontrollability• Less actuator travel and

start/stop may improveactuator longevity

due to strainer and pressureindependent control valve

• Valves have custom flow ratesand must be installed in correctlocation

• Valves can clog or springs canfail over time



PICVs May Improve ∆T?PICVs May Improve ∆T?

53

NBCIP Test Lab (as reportedby manufacturer)



Controllability & TransientsControllability & TransientsPercent of design flow

(percent of design coil sensible capacity)with all control valves 100% open

Maximumpressure drop

of control valverequired fordesign flow,

feet

Maximum flowthrough closest coil

Minimum flowthrough most

remote coil

Balancing Method

CHW HW CHW HW CHW HW

1 No balancing 20.5 44.4 143%(106%)

212%(119%)

73%(89%)

75%(96%)

54

anua a anceusing calibrated

balancing valves(100%) (100%) ( 100%) ( 100%)

3 Automatic flowlimiting valves

20.5* 44.4* 100%(100%)

100%(100%)

100%(100%)

100%(100%)

4 Reverse-return 1.2 10.4 103%(100%)

150%(109%)

99%(100%)

85%(97%)

5 Oversized main piping 7.0 20.9 122%(103%) 173%(112%) 94%(99%) 82%(97%)

6 Undersized branch piping

19.5 NA 142%(106%)

NA 73%(100%)

NA

7 Undersized controlvalves

8.0 NA 120%(103%)

NA 86%(89%)

NA



Energy & First CostsEnergy & First Costs

Incremental First Costsvs. Option 1Pump head,

feet

Annual PumpEnergy,

$/yr $$ per design

gpmBalancing Method

CHW

HW CHW HW CHW HW CHW HW

1 No balancing 58.5 82.7 $1,910 $3,930 – – – –

55

2 Manual balance using calibrated balancing valves

60.3 83.6 $1,970 $3,970 $7,960 $47,530 $6.60 $88.00

3 Automatic flow limiting valves 66.6 90.8 $2,170 $4,310 $11,420 $50,750 $9.50 $94.00

4 Reverse-return 55.3 80.0 $1,810 $3,800 $28,460 $17,290 $23.70 $32.00

5 Oversized main piping 45.0 59.3 $1,470 $2,820 $12,900 $7,040 $10.80 $13.00

6 Undersized branch piping 58.5 NA $1,910 NA ($250) NA ($0.20) NA7 Undersized control valves 58.5 NA $1,910 NA ($2,340) NA ($2.00) NA



RanksRanks Balancing Method Controllability

(all conditions)Pump Energy

Costs First Costs

1 No balancing 7 3 32 Manual balance using calibrated

balancing valves 4 6 6

3 Automatic flow limiting valves 7 7 7

4 Reverse-return 2 2 5

56

vers ze ma n p p ng

6 Undersized branch piping 6 4 27 Undersized control valves 5 4 18 Pressure independent control

valve 1 8 87



Conclusions & Recommendations forConclusions & Recommendations forVariable Flow Hydronic SystemsVariable Flow Hydronic Systems

Automatic flow-limiting valves are not recommended on any variableflow system• They only limit flow for transients which has little or no value

Calibrated balancing valves are also not recommended for balancingvariable flow systems• But useful for future diagnostics on small low pressure drop coils – just leave them

wide open (no throttling)

57

24/7 chilled water systemsUndersizing piping and valves near pumps improves balance and costsare reduced, but significant added engineering time requiredPressure independent valves should be considered on very largesystems (>100 ft head) for coils near pumps

• Cost is high but going down now with competition• When costs are competitive, this may be best choice for all jobs

For other than very large distribution systems, option 1 (no balancing)appears to be the best option• Low first costs with minimal or insignificant operational problems



Break Break



Problems caused by DegradingProblems caused by Degrading ∆∆∆∆∆∆∆∆ TT

Q= 500 X GPM X ∆ T

59

For a Given Load Q, When ∆∆∆∆ T Goes Down, GPM Goes upResult:• Increases pump energy• Can require more chillers to run at low load, or coils will be

starved of flow• Can result in reduced plant effective capacity: chiller capacitywithout the capability of delivering it

ResourceJanuary 2002 ASHRAE Symposium Paper, “Degrading ChilledWater Plant Delta-T: Causes and Mitigation



42 oF80%

Primary/secondary “death spiral”Primary/secondary “death spiral”

Chillers staged by Load

60

52 oF

42 oF

When ∆∆∆∆ T Degrades,Secondary Flow

Exceeds Primary50 oF

46 oFVFD

VFD



∆∆∆∆∆∆∆∆ T Degradation in Large Chiller PlantT Degradation in Large Chiller Plant(January through March)(January through March)

l t a T

( ° F )

35°F-40°F40°F-45°F

7.0°F-7.5°F

9.5°F-10.0°F

Coincident WetBulb Ranges

Design∆Τ=10 oF

0 100 200 300 400 500 600 700 800

Approximate hrs/yr

E v a p o r a t o r

D e

45°F-50°F50°F-55°F55°F-60°F

2.0°F-2.5°F

4.5°F-5.0°F



Causes of DegradingCauses of Degrading ∆ TT

1. Causes that can be avoided by properdesign or operation of the chilled watersystem;

2. Causes that can be mitigated, but

62

overall energy savings; and

3. Causes that are inevitable and simplycannot be avoided



DegradingDegrading ∆ TT#1. Causes that can be eliminated by design/operation#1. Causes that can be eliminated by design/operation

Improper Setpoints or Calibration• e.g. dropping coil SATsp by 2ºF will double the flow rate and halve the

∆TUse of Three-way Valves• Instant response is not a valid reason for 3-way valves

No Control Valve Interlock• i.e. valve open when fan is off

Coils Piped Backwards (parallel flow vs. counter-flow)

63

Uncontrolled Process Loads• need isolation valves

Incorrectly Selected Control Valves• Oversized valves hunt and result in higher average flow• Undersized actuators have insufficient close-off pressure

Incorrectly Selected Coils• Common problem when new buildings don’t follow the campusstandard ∆T

Improper “Bridge” Connection & Control• Bridge valve cannot raise the CHWRT without starving the load



DegradingDegrading ∆ TT#2 Measures that improve#2 Measures that improve ∆ T but energy tradeT but energy trade- -off off

Chilled Water Reset to Lower ChilledWater Supply Temperature• Lowering CHWST by 1ºF increases ∆ T by 1

to 2ºF but reduces chiller efficiency

64

• Net effect could be better (if high pumpenergy) or worse (low pump energy)



Coil Pumps to Prevent ∆∆∆∆ T Degradationat Low Flow Due to “Laminar FlowEffect”

DegradingDegrading ∆ TT#2 Measures that improve#2 Measures that improve ∆ T but energy tradeT but energy trade- -off off

65

coil pump energy is very high



12

14

16

18

20

r e e s - F )

Dual Row, 5/8" TubesFull Row, 5/8" TubesFull Row, 1/2" Tubes

Laminar Flow “Problem:”Laminar Flow “Problem:”Real or Myth?Real or Myth?

Data from MajorCoilManufacturer’s ARIcertified ratingprogramdeveloped fromlab tests

0

2

4

6

8

10

0%20%40%60%80%100%

% Sensible Load

D e l t a - T

( d e g

LaminarFlow



Primary/Secondary vs. Primary/SecondaryPrimary/Secondary vs. Primary/Secondarywith Coil Pumpswith Coil Pumps

P/S/T withconstant

∆∆∆∆ T25.00

30.00

35.00

40.00

45.00

50.00

p k W

67

P/S withdegrading

∆∆∆∆ T

0.00

5.00

10.00

15.00

20.00

0% 20% 40% 60% 80% 100%

% Plant Load

P u

3-chiller/3-pump plant,total 1440 gpm

Conclusion: even if the laminar flow problem were real, coilpumps are not a good solution. They add to both first costsand energy costs.



Causes of DegradingCauses of Degrading ∆ TT#3. Causes That Cannot Be Eliminated#3. Causes That Cannot Be Eliminated

Air Economizers and 100% Outdoor AirSystems

60 oF

42 oF

CHWST(Design CHWRT of62, based on design

68

Degrading Coil Effectiveness with AgeCHWST Setpoint ResetOthers as Yet Undetermined?

SAT EAT<<60 oFCHWRT



ConclusionsConclusions

Design, Construction, and OperationErrors that Cause Low DT can andShould be Avoided

But Other Causes for Low DT can Never

69

Conclusion: At Least Some DTDegradation is Inevitable

Therefore: Design the CHW Plant to Allowfor Efficient Chiller Staging DespiteDegrading DT



Some SolutionsSome Solutions

Use Variable Speed Drives on Chillers so thatthey Operate Efficiently at Low LoadDesign CHW Distribution System so Chillers canhave Increased Flow So They can be More Fully

Loaded at Low DT

70

• Primary-only pumping• Unequal chiller and primary pump sizes, headered pumps

so large pump can serve small chiller • Low design delta-T in primary loop

Insures low ∆T in secondaryHigher primary loop first costs & energy costs

• Primary/secondary pumping with check valve in commonleg



Check Valve in the Common LegCheck Valve in the Common Leg

71

CHECKVALVE INCOMMON

LEG



Supposed DisadvantagesSupposed DisadvantagesCheck Valve in Common LegCheck Valve in Common Leg

Circuits are not Hydraulically Independent• So what?

Flow Rate may Exceed Maximum Allowed byChiller Manufacturer• Seldom a real problem - pump capabilities usually fall off

fast enough due to high chiller ∆∆∆∆ P• –

72

excursions should not be a problem

• Resolved by using high design ∆∆∆∆ Ts (or adding auto-flowlimiting valves at chillers as last resort)

Pumps in Series may Force Control Valves Open• Not true with variable speed driven secondary pumps.

Primary Pumps may Ride Out Their Curves andOverload• Seldom a real problem - pump capabilities usually fall off

fast enough due to high chiller ∆∆∆∆ P, and motor may beselected to avoid this problem.



Real DisadvantagesReal DisadvantagesCheck Valve in Common LegCheck Valve in Common Leg

Possible Dead-heading SecondaryPumps if Primary Pumps are Off andChiller Isolation Valves are Closed

• Logically interlock secondary pumps to

73

primary pumps

“Ghost” Flow through InactiveChillers with Dedicated Pumps• Use isolation valves rather than dedicated

pumps



Check Valve in the Common LegCheck Valve in the Common Leg

Recommendation• For fixed speed chillers, put the check valve in

the common leg. Make sure pumpdesign/controls address secondary pump dead-heading and ghost-flow issues. Select a check

74

valve with low pressure drop (i.e. swing check,not spring)

• For variable speed chillers, do not put checkvalve in common leg. It has little value (unlessDT degradation is severe) since chiller plant willnot be inefficient by staging chillers on beforethey are fully loaded.



75

SystemsSystems



Condenser Water Systems

Old paradigm: constant flow & speedNew paradigm: variable flow & speed• Control logic to maximize efficiency?

76



$400,000

$500,000

$600,000

Variable Speed CW Pumps

OaklandOfficeBuilding

77

$

$100,000

$200,000

$300,000

C

& C

C

C &



Condenser Water Pump OptionsCondenser Water Pump Options

COOLINGTOWER #1

COOLINGTOWER #2

COOLINGTOWER #3

CHILLER #1

CHW PUMP #1

COOLINGTOWER #1

COOLINGTOWER #2

COOLINGTOWER #3

CHILLER #1

CHW PUMP #1

78

Dedicated Pumping Advantages:• Less control complexity• Custom pump heads w/ unmatched chillers• Usually less expensive if each pump isadjacent to chiller served and head pressurecontrol not required and no watersideeconomizer

Headered Pumping Advantages:• Better redundancy• Valves can double as head pressure control• Easier to incorporate stand-by pump• Can operate fewer CW pumps than chillersfor fixed speed pumps•Easier to integrate water-side economizer

CHILLER #2

CHILLER #3

CHW PUMP #2

CHW PUMP #3

CHILLER #2

CHILLER #3

CHW PUMP #2

CHW PUMP #3

OPTIONAL



Tower Isolation OptionsTower Isolation Options

1. Select tower weir dams& nozzles to allow onepump to serve alltowers

• Always most efficient• Almost always least

expensive

COOLINGTOWER #1

COOLINGTOWER #2

COOLINGTOWER #3

79

• Usually possible with 2 or 3cells

2. Install isolation valveson supply lines only

• Need to oversize equalizers

3. Install isolation valveson both supply & return

• Usually most expensive• Easiest to design• Valve sequencing issues and

possible failure

COOLINGTOWER #1

COOLINGTOWER #2

COOLINGTOWER #3

COOLINGTOWER #1

COOLINGTOWER #2

COOLINGTOWER #3



NonNon--integrated waterintegrated water- -side economizer (WSE)side economizer (WSE)

Don’t do this!

41F

Twb 36F

Twb 41F

44F

You have to shut off the economizer to

Heat

Exchangerin parallelwith chillers

44F 60F

44F

49F

>46F

satisfy the load!



Integrated waterIntegrated water- -side economizerside economizerPrimary OnlyPrimary Only

Bypass forWSE-only

V -1



Example WSE SavingsExample WSE Savings

~2%

84

~30% ~24%

~48%



Data Center in Santa ClaraData Center in Santa Clara

85

Cooling Tower

CWS

What’s Missing from this Picture?

A heat exchanger, pipe andtwo pumps



LunchLunch



Design ProcedureDesign Procedure



Design ProcedureDesign Procedure

Select Chilled Water Distribution SystemSelect Temperatures, Flow Rate andPrimary Pipe SizesSelect Cooling Tower Design Criteria

88

Finalize Piping System Design, SelectPumpsDevelop Optimum Control System and

Control Sequences



SecondaryPump w/ VFD

at ChillerPlant

2-Way ControlValves atAHUs

SecondaryPump w/ VFD

at ChillerPlant

2-Way ControlValves atAHUs


90



Primary/Distributed SecondaryPrimary/Distributed Secondary

DistributedSecondary

Pump w/ VFD -Typical at each

Building

No Secondary

91

Central Plant

umps aPlant

Distributed P/S versus



Distributed P/S versusConventional P/S or P/S/T

Advantages• Reduced Pump HP - Each Pump Sized for Head

From Building to Plant• Self-balancing• No Over-pressurized Valves at Buildings Near Plant

• Reduced Pum Ener Particularl When One or

92

More Buildings Are off Line

• No Expensive, Complex Bridge Connections Usedin P/S/T Systems

• Similar or Lower First Costs

Disadvantages (vs. P/S)• Pump room needed at building• Higher expansion tank pre-charge and size



Hybrid systemsHybrid systems

94

Advantages of VFD Coil Pumps versus



Advantages of VFD Coil Pumps versusConventional P/S system

Reduced Pump HP• Each pump sized for head from coil to plant• Eliminated 10 feet or so for control valves

Self-balancing• No need for or advantages to balancing valves, reverse return

Lower Pum Ener

95

• No minimum DP setpoint• Pump efficiency constant

Better Control• Smoother flow control - no valve hysteresis

• No valve over-pressurization problemsUsually Lower First Costs Due to EliminatedControl Valves, Reduced Pump and VFD HP

Disadvantages of VFD Coil Pumps



Disadvantages of VFD Coil Pumpsversus conventional P/S system

Cannot Tap into Distribution Systemwithout Pump• May be problem with small coils (low flow, high

head pump)

96

unless Duplex Coil Pumps are AddedPossible Low Load TemperatureFluctuations

• Minimum speed on pump motor • May need to cycle pump at very low loads



PrimaryPrimary- -only Systemonly SystemHeadered Pumps & Auto Isolation ValvesPreferred to Dedicated Pumps:• Allows slow staging• Allows 1 pump/2 chiller operation• Allows 2 pump/1 chiller operation if there islow ∆T

97

BYPASSVALVE

Flow Meteror DP Sensor Across Chiller

Advantages of primary only versus



Advantages of primary-only versusprimary/secondary system

Lower First CostsLess Plant Space RequiredReduced Pump HP

•Reduced pressure drop due to fewer pump

98

,• Higher efficiency pumps (unless more expensive

reduced speed pumps used on primary side)

Lower Pump Energy

• Reduced connected HP• “Cube Law” savings due to VFD and variable flow

through both primary and secondary circuit

P EP E



Pump EnergyPump EnergyPrimary vs. Primary/Secondary (3Primary vs. Primary/Secondary (3- -chiller plant)chiller plant)

25.00

30.00

35.00

40.00

Primary-

99

0.00

5.00

10.00

15.00

20.00

10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

% GPM

P u m p

k

Primary-only

secondary

Disadvantages of primary only versus



Disadvantages of primary-only versusprimary/secondary system

Failure of Bypass Control• Not as fail-safe - what if valve or controls fail?• Must avoid abrupt flow shut-off (e.g. valves interlocked with

AHUs all timed to stop at same time)• Must be well tuned to avoid chiller short-cycling

Flow Fluctuation when Staging Chillers On

100

• Flow drops through operating chillers• Possible chiller trips, even evaporator freeze-up• Must first reduce demand on operating chillers and/or slowly

increase flow through starting chiller; causes temporary highCHWS temperatures

(Problems above are seldom an issue with verylarge plants, e.g. more than 3 chillers)



PrimaryPrimary- -only System Stagingonly System Staging

1000 GPM

0 GPM

0 GPM

101



PrimaryPrimary- -only System Stagingonly System Staging

500 GPM

0 GPM

102

500 GPM

Variable FlowVariable Flow



Variable FlowVariable FlowPrimary/Secondary with CHW StoragePrimary/Secondary with CHW Storage

Advantages• Peak shaving• Simplifies chiller staging• Provides back-up for chiller

failure• Secondary water source for fire

department

103

• Secondary water source forcooling towers

Disadvantages• Installed cost• Space



Primary-only vs. Primary/Secondary

Use Primary-only Systems for:• Plants with many chillers (more than three) and with

fairly high base loads where the need for bypass isminimal or nil and flow fluctuations during staging

are small due to the large number of chillers; and

104

• Plants where design engineers and future on-siteoperators understand the complexity of the controlsand the need to maintain them.

Otherwise Use Primary-secondary• Also for plants with CHW storage



Pipe SizingPipe Sizing



Accurately sizing pump head

107

Guessing at pump heads• Wastes money in oversized pumps, motors and (sometimes)

VFDs and (sometimes) need for impeller trimming• Wastes energy (minor impact w/VFD or if impeller is trimmed)

Calculating pump heads• Takes about 20 minutes of engineering time

Guessing cannot possibly be cost effective!

d hd h



LCC SpreadsheetLCC Spreadsheet

108Available for free from the TE ftp site

l f d hl f d h



Simplified Pipe Sizing ChartSimplified Pipe Sizing ChartMaximum GPM for

High Performance Constant Flow,Constant Speed System

2000 4400 0 2000 4400 0 1/2 5.0 3.9 3.0 1.8 1.8 1.8 3/4 12 9.0 7.0 4.6 4.6 4.6

1 19 14 11 8.9 8.9 8.91 1/4 34 26 20 15 15 151 1/2 57 43 34 24 24 24

2 73 55 44 51 51 442 1/2 100 77 60 81 77 60

2000 4400 0 2000 4400 0 1/2 7.8 5.9 4.6 1.8 1.8 1.8 3/4 18 14 11 4.6 4.6 4.6

1 29 22 17 8.9 8.9 8.91 1/4 51 39 30 15 15 151 1/2 88 67 52 24 24 24

2 120 84 67 51 51 512 1/2 160 120 91 81 81 81

Maximum GPM for

High Performance Variable Flow, VariableSpeed System

109

3 180 140 110 140 140 1104 320 240 190 280 240 1905 430 330 260 430 330 2606 700 530 420 700 530 4208 1,200 900 720 1,200 900 720

10 1,900 1,500 1,200 1,900 1,500 1,20012 2,900 2,200 1,700 2,900 2,200 1,70014 4,000 3,000 2,400 4,000 3,000 2,40016 4,900 3,800 3,000 4,900 3,800 3,00018 7,000 5,300 4,200 7,000 5,300 4,20020 7,700 5,800 4,600 7,700 5,800 4,600

24 12,000 8,900 7,100 12,000 8,900 7,10026 14,000 11,000 8,500 14,000 11,000 8,500

Available from the ftp site

3 270 210 160 140 140 1404 480 360 290 280 280 2805 670 510 390 490 490 3906 1,100 800 630 770 770 6308 1,800 1,400 1,100 1,500 1,400 1,10010 2,900 2,200 1,800 2,700 2,200 1,80012 4,400 3,300 2,600 4,200 3,300 2,60014 6,000 4,600 3,600 5,400 4,600 3,60016 7,400 5,700 4,500 7,200 5,700 4,50018 10,000 8,000 6,300 9,200 8,000 6,30020 11,000 8,800 7,000 11,000 8,800 7,000

24 17,000 13,000 11,000 17,000 13,000 11,00026 21,000 16,000 13,000 20,000 16,000 13,000



Optimum ∆TOptimum ∆T

Fl d ∆TFl d ∆T



Flow rate and ∆TFlow rate and ∆T

TGPM500 ∆=Q

111

Load from LoadCalc’s (Btu/hr)

Conversion“constant”

=8.33 lb/gal *60 minutes/hr

Flow rate(GPM)

TemperatureRise or Fall (ºF)

CHWCHW ∆∆∆∆∆∆∆∆ TT T d ffT d ff



CHWCHW ∆∆∆∆∆∆∆∆ TT TradeoffsTradeoffs

Typical Range 8° F to 25° F

First Cost smaller coil smaller pipe

112

mpac sma er pumpsmaller pump motor

Energy Costimpact

lower fan energy lower pump energy



Ch i th “Ri ht” CHWCh i th “Ri ht” CHW ∆∆∆∆∆∆∆∆ TT



Choosing the “Right” CHWChoosing the “Right” CHW ∆∆∆∆∆∆∆∆ TT

Both energy and first costs arealmost always minimized by pickinga very high ∆T (>18°F to 25°F)

Savings even greater with systems

117

that have• Water-side economizers• CHW thermal energy storage



Sh tSh t t P dt P d



ShortShort- -cut Procedure:cut Procedure:

Use 42°F CHWSTUse 8 row 10 fpi coils• Standard 62.1 limit

119

using coil program; sum to determineplant flow and gpm-weighted averageCHWRT

This may result in a colder CHWST than would be possible with therecommended procedure but if CHWST is reset based on load, the energyimpact is small. First costs may be lower since pumps can be slightlysmaller.

Example Building



Example Building

16TH FLOOR

120

6THFLOOR

AUXFAN-

COILS &CRUs

Example Building



Example Building

Load

tons

Main system piping 1100 1056 Non-noise sensitive, variable 8” 1400 18.9

SectionGPM at25 °°°° F ∆∆∆∆ T Application Pipe size

MaximumGPM

Resulting∆∆∆∆ T

Load

tons



MaximumGPM

Resulting∆∆∆∆ T

Load

tons



MaximumGPM

Minimum∆∆∆∆ T

Fromsimplified

Table VFVS

121

flow, ~4400 hrs

Main riser to 6 th floor 820 787 Noise sensitive, variable flow,2000 hrs

8” 1500 13.1

Piping to main AHU coils 140 134 Non-noise sensit ive, variableflow, 2000 hrs

3” 210 16.0

Piping to main aux. coils 260 250 Noise sensit ive, variable flow,8760 hrs

4" 280 22.3

flow, ~4400 hrs


8” 1500 13.1


3” 210 16.0


4" 280 22.3

Minimumaverage ∆∆∆∆ Tthis circuit

flow, ~4400 hrs


8” 1500 13.1


3” 210 16.0


4" 280 22.3

Coil Selection Example



Coil Selection Example

122

Condenser Water (Tower) RangeCondenser Water (Tower) Range



Condenser Water (Tower) RangeCondenser Water (Tower) Rangeat Constant CWSTat Constant CWST

∆∆∆∆ T

Low High

Typical Range 8 °°°° F to 20 °°°° F

123

First Cost Impact smaller condenser smaller pipesmaller pump

smaller pump motorsmaller cooling tower

smaller cooling tower motor

Energy Costimpact

lower chillerenergy

lower pump energylower cooling tower energy

Condenser Water RangeCondenser Water Range



Condenser Water RangeCondenser Water Rangeat constant Tower Fan Energyat constant Tower Fan Energy

400

500

600Tower Fan

CW pumpChiller

124

0

100

200

300

73/16 73.5/14 74.5/12 75.5/10

CWST/Delta-T

k W h / t o n / y e a

LCC Analysis 1000 ton Plant



LCC Analysis – 1000 ton Plant

Chicago

125

15F ∆T LCC best forall climates analyzed

Recommended Procedure:



Recommended Procedure:

Determine CW Flow Rate at 15°FPick primary pipe sizes (pumps, headers,main risers) in “critical circuit”• Use pipe sizing spreadsheet or shortcut tables

126

n max mum ow or eac p pe s ze anrecalculate ∆T for these flow rates• Use pipe sizing spreadsheet or shortcut tables

The largest ∆T is then the plant design ∆TAdjust CW Flow up per selected ∆T

This procedure attempts to minimize cost by reducing pipe sizeas much as possible, but then taking full advantage of theresulting pipe size to minimize ∆T to reduce chiller energy.



Cooling Tower SelectionCooling Tower Selection



Cooling Tower SelectionCooling Tower Selection

180%190%200%210%

200%-210%190%-200%180%-190%170%-180%160%-170%

150%-160%

128

5

7

9

11

13

15

1719

1110

98

76

54

32

10%

10%20%30%40%50%60%70%80%90%

100%110%120%130%140%150%160%

% D e s i g n

C a p a c i t y

Approach (°F)

Range (°F)

140%-150%130%-140%120%-130%110%-120%100%-110%90%-100%80%-90%70%-80%60%-70%50%-60%40%-50%30%-40%20%-30%10%-20%0%-10%

Cooling Tower Approach & RangeCooling Tower Approach & Range



Cooling Tower Approach & RangeCooling Tower Approach & Range

ASHRAE Standard 90.1Rating Conditions

95 ° F

129

WETBULB TEMPERATURE

85 ° F

75 ° F

Propeller fan towersPropeller fan towers



Propeller fan towersPropeller fan towers

130

Tower Fan ControlTower Fan Control




One Cell Tower

131

Free Cooling~ 15% of Capacity

Single SpeedFan

Two-Speed or Variable-SpeedFan

% Capacity

% Power





60%

70%

80%

90%

100%

Two 1-Speed Fans

One 1-Speed Fan andOne 2-Speed Fan

Two Cell Tower

132

0%

10%

20%

30%

40%

50%

0 % 5 % 10% 1 5% 2 0% 2 5% 3 0% 35% 40 % 4 5% 50% 5 5% 6 0% 6 5% 7 0% 7 5% 80% 85 % 9 0% 95% 1 00

%

% Capacity

% P o w e r

Two 2-Speed Fans

Free Cooling Below 15%Capacity

Two Variable Speed



Tower Efficiency LCCTower Efficiency LCC



Tower Efficiency LCCTower Efficiency LCC

ASHRAE Efficiency:

The flow rate the tower cancool from 95F to 85F at 75Fwetbulb temperature divided byfan power (GPM/HP)

134

90 GPM/HP 70 GPM/HP 50 GPM/HP

1000 ton

OaklandOffice

Tower ApproachTower Approach



Tower ApproachTower Approach

Oakland Office Oakland Data Center

135

Optimum Approach TemperatureOptimum Approach Temperature



Optimum Approach TemperatureOptimum Approach Temperature

15

20

25

30

+

CA

A

136

0

5

10

0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000

0

50CW A CDDT T 001.027 −∆−=

Tower Efficiency GuidelinesTower Efficiency Guidelines



Tower Efficiency GuidelinesTower Efficiency Guidelines

Use Propeller Fans• Avoid centrifugal except where high static needed or

where low-profile is needed and no prop-fan optionsavailable.

• Consider low-noise propeller blade option and high

137

.Efficiency• Minimum 80 gpm/hp for commercial occupancies• Minimum 100 gpm/hp for 24/7 plants (data centers)

Approach• Commercial occupancies: See previous slide8°F to 9°F for Bay Area

• 24/7 plants (data centers): 3°F



Break Break

CHILLER SELECTIONCHILLER SELECTION



CHILLER SELECTIONCHILLER SELECTION

139

Part-Load Ratio



Chiller Procurement ApproachesChiller Procurement Approaches



Chiller Procurement ApproachesChiller Procurement Approaches

Better Approach• Pick a short list of vendors based on past

experience, local representation, etc.• Request chiller bids based on a performance

s ecification. Multi le o tions encoura ed.

141

• Adjust bids for other first cost impacts• Estimate energy usage of options with a detailed

computer model of the building/plant

• Select chillers based on lowest life cycle cost• Bid the chillers at end of design developmentphase

Chiller Bid SpecificationChiller Bid Specification



Chiller Bid SpecificationChiller Bid Specification

Don’t Specify:• Number of chillers• Chiller size• Chiller efficiency

• Chiller unloading

Do Specify:• Total design load• Anticipated load profile• Minimum number of

chillers and redundancy

142

mechanism• As much as possible

• Design CHW/CW enteringand leaving temperaturesand/or flows (or tables ofconditions)

• Available energy sources

• Physical, electrical orother limitations

• Acoustical constraints• Acceptable refrigerants

Sample Load ProfileSample Load Profile



pp

60 0

70 0

80 0

143

0

10 0

20 0

30 0

40 0

10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

Percent Load

H o u r s p e r y e a



Zero Tolerance DataZero Tolerance Data



30%

35%

40%

45%

10F Delta-T

ARI 550/590 Tolerance Curve

145

0%

5%

10%

15%

20%

25%

0% 20% 40% 60% 80% 100% 120%

% of Full Load

% T o l e r a n c 15F Delta-T

20F Delta-T

Factory Tests and LiquidatedFactory Tests and LiquidatedD ClD Cl



Damage ClausesDamage ClausesCertified Factory Tests• Need to verify performance to ensure accurate

claims by chiller vendors in performance bids• Field tests are difficult or impossible and less

accurate

146

• Last chance to reject equipment

Liquidated Damage Clause• One-time penalty for failing tests as an option to

rebuilding or repairing chiller

Chiller Bid FormChiller Bid Form



Option:Manufacturer:Model:Compressor type:Refrigerant:Delivery lead time (weeks):

Chiller Performance Form

Fill out all yellow -highlighted cells. Others are f ixed or calculated automatically

Complete this w orksheet before completing Part Load and Full Load w orksheets (some fields are calculated automatically from the data on this sheet

Yellow: Fields to becompleted by Vendor

White: Fixed

147

Maximum CHW flow rate: Maximum CW flow rate:Minimum CHW flow rate: Minimum CW flow rate:Voltage/phase: 480/3 Minimum CW supply temperature:Full load amps:

CHW fouling factor: 0.0001 CW fouling factor: 0.00025Leaving CHWST: 42 Entering CWST:Entering CHWRT: 59 Leaving CWRT:Design CHW flow: Design CW flow:CHW DP (ft): CW DP (ft):

Design kW (w/o ARI Tolerance):Design capacity: 0 Design kW/ton: 0

Design Conditions

Gray: Calculatedfields

e s

Chiller Bid FormChiller Bid Form



Capacity Power Exit Temp Flow Rate Entering Temp Flow Rate Exit Temptons kW °F gpm °F gpm °F

43 550 85 700 8543 550 75 700 75

43 550 65 700 65

Evaporator Condenser

Please fill in all data on the "Start Here" tab before filling in the table. Please fill inthe yellow cells . The capacity and power inputs are for unmodulated operationassuming no power or current limits with all capacity control devices fully open.

Full Load Data

148

43 550 60 700 6045 550 85 700 8545 550 75 700 7545 550 65 700 6545 550 60 700 6050 550 85 700 8550 550 75 700 7550 550 65 700 6550 550 60 700 60

43 550 85 400 8543 550 75 400 7543 550 65 400 6543 550 60 400 6045 550 85 400 8545 550 75 400 7545 550 65 400 65

Min =

Min =

Min =

Min =



Example ProjectsExample Projects



p jp j

Large Central Plant• Central plant serving industrial/office/research

park,

San Jose, CA. 17,000 tons total ca acit

151

Large High-rise Office Building• Office plus small data center, retail,

San Francisco, CA. 15 stories, 540,000 ft 2



San FranciscoSan Francisco

16 TH FLOOR

AUX-

HighHigh--riseriseOfficeOffice

1100 tons1100 tons

6TH FLOOR

COILS& CRUs

HighHigh- -RiseRiseOfficeOffice Description

1stCostRank

EnergyCostRank

Life CycleCost

Savings vsBase

LCCRank

vs.



OfficeOfficeTowerTower

ChillerChillerOptionsOptions

p

Trane #1 400 ton, 0.50 kW/t;700 ton, 0.55 Kw/ton 6 9 $142,016 10

Trane #2 400 ton w/VFD, 0.50 kW/t;700 ton, 0.55 Kw/ton 9 2 $22,092 4

Carrier #1 365 ton, 0.56 kW/t;735 ton, 0.50 kW/t 1 12 $173,962 12

Carrier #2365 ton w/VFD, 0.56 kW/t;735 ton, 0.50 kW/t 3 5 $21,246 3

Carrier #3365 ton w/VFD, 0.56 kW/t;735 ton w/VFD, 0.50 kW/t 8 4 $7,702 2

Mc ua #1200 ton, 0.50 kW/t;

SelectedChillers

A #1

A #2

B #1

B #2

B #3

ton ua . t 2 8 78,159 5

McQuay #2 550 ton dual, 0.56 kW/t550 ton dual, 0.56 kW/t 5 11 $141,179 9

McQuay #3400 ton dual, 0.53 kW/t;700 ton dual 0.53 kW/t 4 7 $112,419 8

McQuay #4200 ton, 0.53 kW/t;350 ton dual 0.57 kW/t;550 ton dual 0.59 kW/t 7 10 $147,440 11

York #1 550 ton w/VFD , 0.49 kW/t;550 ton, 0.48 kW/t 11 6 $104,078 7

York #2300 ton w/VFD , 0.50 kW/t;800 ton, 0.48 kW/t 10 1 $0 1

York #3365 ton w/VFD , 0.52 kW/t;366 ton, 0.51 kW/t366 ton, 0.51 kW/t 12 3 $92,421 6

C #2

C #3

C #4

D #1

D #2

D #3

LCC Assumptions:Discount rate 8%Electricity Escalation 0%Analysis years 15

Considering “Soft Factors”Considering “Soft Factors”



Why Option B3 was Selected over OptionD2:• Close in LCC (2nd behind Option D2) – within the

margin of error in the analysis

•

156

client due to zero ODP (D2 used R-123)

• Both Option B3 chillers had VSDs (only one inOption D2)

•Small chiller pump can operate large chiller (flowminimum/design ranges overlap)

• Option B3 hermetic, Option D2 is open-drive• Option B3 had lower first cost



158

OPTIMIZING CONTROLSOPTIMIZING CONTROLS

Optimizing Control SequencesOptimizing Control Sequences



Optimizing Control SequencesOptimizing Control Sequences

Cookbook Solution• Staging Chillers• Controlling Pumps

•Chilled Water Reset

159

• Condenser Water Reset

Simulation Approach



Staging Chillers, continuedStaging Chillers, continued



Variable Speed Chillers• Operate as many chillers as possible

provided load on each exceeds 30% to 40%load (actual value can be determined by

161

−below)

• Energy impact small regardless of staginglogic

• You MUST use condenser water reset toget the savings

Part Load Chiller Performancew/ Zero ARI Tolerance



70%

80%

90%

100%

Fixed Speed

Variable Speed

162

0%

10%

20%

30%

40%

50%

0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

% Load (with Condenser Relief)

% k W

Two-Chiller Plant Performanceat Low Load



40%

50%

60%

W

& C W

p u m p s )

Running two fixed speedchillers alw ays usesmore energy

163

0%

10%

20%

30%

0% 10% 20% 3 0% 40% 5 0%

% Plant Load

% P l a n t k W

( i n c l u d i n g

P C H

Variable Speed - one chiller

Fixed Speed - one chiller

Variable Speed - two chillers

Fixed Speed - two chillers

Running two VFD

chillers is more efficientuntil 35% load

Cautionary NoteCautionary Note



Staging logic must limit possibility forsurge operation for centrifugal chillersSome variable speed chillers don’tdynamically measure surge conditions

164

• ou w ose some o e sav ngs w pr mary-only variable flow systems because minimumspeed may have to be increased to avoid surge

• You may have premature tripping due to onset of

surge otherwise• This is only an issue with variable evaporatorflow systems (like primary-only variable flow)

Staging & Surge



Sur e Re ion

1 0 0 % s p e e d

9 0 %

8 0 %

One Chiller Two Chillers

165

R

e f r i g e r a n t H e a

Load

7 0 %

6 0 %

One Chiller Two Chillers

Controlling CHW PumpsControlling CHW Pumps



Primary-only and Secondary CHWPumps• Control speed by differential pressure

measured as far out in system as possible

166

an or rese se po n y va ve eman• Stage pumps by differential pressure PID

loop speed signal:Start lag pump at 90% speedStop lag pump at 40% speedFor large HP pumps, determine flow and speedsetpoints with detailed energy analysis

VSD Pump Power vs. Setpoint



70%

80%

90%

100%

W

DP setpoint = Design Head

DP setpoint = Head*.75

DP setpoint =Head/2

DP setpoint =Head/3

DP setpoint = 0 (reset)

167

0%

10%

20%

30%

40%

50%

0 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

Percent GPM

P e r c e n t P u m p

Chilled Water Setpoint ResetChilled Water Setpoint Reset



Reset Impacts• Resetting CHWST upwards reduces chiller energy but will

increase pump energy in VSD variable flow systems• Dehumidification

Reset with “open” or indirect control loops (e.g. OAT) can starve coilsand reduce dehumidification

−

168

humidity of supply determined almost entirely by supply airtemperature setpoint, not CHWST

Recommendations• Reset from control valve position using Trim & Respond logic• For variable flow systems with VSDs

Reset of CHWST and VSD differential pressure setpoint must besequenced − not independent like VAV systems since control valvesare pressure-dependentSequence reset of CHWST and DP − next slide

CHWST/DP Setpoint Reset for VSDCHW System



y

Tmin+15ºF

DPmax

CHWDP

169

Back off on CHWST firstThen back off on DP setpoint first

Tmin5 psi

CHWsetpoint

DPsetpoint

se po n

CHW Plant Reset0 100%50%

CHW vs. DP Setpoint Reset



170

Plant with 150 ft CHW pump head



ModelsModels



Chillers• Hydeman et al, Regression Based Electric Chiller Model• Multi-point calibration using zero-tolerance manufacturer’s

data

Towers

173

• DOE-2.2 model calibrated using manufacturer’s data

Pumps• Multiple piping sections ∆P=C*GPM1.8• Pump efficiency from regression of manufacturer’s data

VFD and motor efficiency• Part load curves from Advanced VAV Design Guide

Chiller and Tower Staging by LoadChiller and Tower Staging by Load



174

Stage Stage Down Stage Up Number of Chillers Number of Tower Cells1 340 1 32 240 550 1 43 450 750 1 53 650 1600 2 5

4 1500 3 5

CW Pump Staging and SpeedCW Pump Staging and Speed



175

Sample of Custom Sequences



Enable Economizer when• CHWRT > 0.9*Twb + 12.3

When Economizer is off • When Load <= 380 Ton:

Run one chiller, three towers, one CWP

Control CW um %s eed = 80

176

Control Tower Fan speed to maintain CWST = 0.86*Twb + 13.5• Else when Load <=1170 Ton

Run two chillers, five towers, and two CWPsControl CW pump %speed=0.90 + 2.74*%Load^2 – 1.41*%LoadControl Tower Fan speed to maintain CWST = 0.92*Twb +10.5

• Else when Load >1170 Ton

Run three chillers, five towers, and three CWPsControl CW pump %speed=0.58 + 0.428*%Load^2 +0.125*%LoadControl Tower Fan speed to maintain CWST = 0.892*Twb + 13.4

Theoretical Optimum Plant PerformanceTheoretical Optimum Plant Performance(TOPP) Model Simulation Results(TOPP) Model Simulation Results



Run 0 980,000 40,900 76,000 113,000 1,210,000 Run 1 980,000 -0.16% 38,800 -5.14% 84,000 10.93% 113,000 0.00% 1,210,000 0.39%Run 2 1,010,000 3.85% 38,800 -5.13% 63,000 -17.33% 113,000 0.00% 1,230,000 1.85%

Run 3990 000 0.81% 58 000 41.88% 175 000 130.90% 113 000 0.00% 1 330 000 10.31%

CHW Pumps TotalAnnual Energy Usage (kWh/yr, % of TOPP)

Chillers Cooling Towers CW Pumps

177

, . , . , . , . , , .

Run 4 1,140,000 16.42% 4,600 -88.71% 335,000 340.74% 113,000 0.00% 1,590,000 31.73%Run Descriptions:Run 0: TOPP modelRun 1: Recommended control sequencesRun 2: Run 1 with the cooling tower CWS temperature controlled by wet-bulb resetRun 3: "Standard control sequence" with ARI 550/590 CW ResetRun 4: "Standard control sequence" with CW temperature fixed at design



CWRT-CHWST vs. %Load



10

20

30

40

50

60

, , 3

10

20

30

40

50

60

, , 3

10

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%CW Loop Flow vs. %Plant Load



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Generic Control SequencesGeneric Control SequencesAllAll--variable speed plantvariable speed plant



LIFT = A*PlantLoadRatio + B• Bounded by minimum LIFT at minimum PLR (frommanufacturer) and maximum LIFT (design lift)

• CWRT setpoint = LIFT + CHWST• Control CT fans to maintain CWRT

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oop ow a o = an oa a o• Bounded by chiller minimum CW flow (from manufacturer)

and 100%• CWLoopFlow = CWLoopFlowRatio *DesignCWFlow• Control CWP speed to maintain CWLoopFlow

Chiller and CW pump staging• Stage up at 60% CWLoopFlowRatio• Stage down at 50% CWLoopFlowRatio

LIFT = A*PlantLoadRatio + BLIFT = A*PlantLoadRatio + B



Coefficient A Coefficient B

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A = 9.235 + 0.002182 * C 55 + 0.351 * B + 75.775 * + 0.019 * / + 0.257 * A AC + 0.25 *AB = 112.384 + 0.00181 * C 55 + 5.286 * B + 734.447 * / + 67.574 * + 0.019 *

/ + 5.398 * A AC + 5.168 * A

CWLoopFlowRatio =CWLoopFlowRatio =C*PlantLoadRatio + DC*PlantLoadRatio + D



Coefficient C Coefficient D

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C = 0.0000811 * C 55 + 0.01293 * B + 3.486 * + 0.02476 * A AC + 0.07400 * A = 0.797 + 2.282 * + 0.002196 * A AC + 0.00795 * A

Plant Energy vs. TOPP: OaklandPlant Energy vs. TOPP: Oakland



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( 2)



Staging vs. PRL and LIFTStaging vs. PRL and LIFT



Chiller J, Chicago, D-3Chiller J, Oakland, D-3

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Chiller J, Miami, D-3 Chiller J, Atlanta, D-3

Revised Control SequencesRevised Control SequencesAllAll--variable plantvariable plant



LIFT = A*PlantLoadRatio + B• Bounded by minimum LIFT at minimum PLR (from manufacturer) andmaximum LIFT (design lift)

• CWRT setpoint = LIFT + CHWST• Control CT fans to maintain CWRT

CWLoopFlowRatio = C*PlantLoadRatio + D

•

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• CWLoopFlow = CWLoopFlowRatio *DesignCWFlow• Control CWP speed to maintain CWLoopFlow

CW pump staging• Stage up at 60% CWLoopFlowRatio• Stage down at 50% CWLoopFlowRatio

StagingPLR = E*LIFT + F• When PLR≤ StagingPLR, run one chiller • When PLR> StagingPLR, run two chillers• Minimum time before changing stages

With Real Sequences, Are VFDs onWith Real Sequences, Are VFDs onCW Pumps Cost Effective?CW Pumps Cost Effective?



Previous analysis assumed TOPP could beachieved with simple correlations on PLR, CWFlowCorrelations are not good for C and Dcoefficients

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Will real world sequences work well enough?Coefficient C Coefficient D

Even Optimum Savings are SmallEven Optimum Savings are Small



OaklandMiami AtlantaLas

Vegas Albuquerque Chicago

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Optimized Control SequencesOptimized Control SequencesOakland plantOakland plant



Both CS and VS• LIFT = 50*PlantLoadRatio + 2.5Bounded by minimum LIFT (9F per Trane)CWRT setpoint = LIFT + CHWSTControl CT fans to maintain CWRT

• StagingPLR = 0.013*LIFT + 0.067When PLR≤ StagingPLR, run one chiller When PLR> StagingPLR, run two chillers

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VS Only• CWLoopFlowRatio = 1.6*PlantLoadRatio + 0.13

Bounded by minimum CW flow (50% each chiller, 0.25 overall) and 100%CWLoopFlow = CWLoopFlowRatio *DesignCWFlowControl CWP speed to maintain CWLoopFlow

• CW pump stagingStage up at 60% CWLoopFlowRatio

Stage down at 50% CWLoopFlowRatio

CS Only• CW pumps stage with chillers

Answer: Not Cost EffectiveAnswer: Not Cost Effectivefor Office Buildingsfor Office Buildings



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SummarySummary



In this course, you have learned techniques todesign and control chiller plants for near-minimum life cycle costs, including:• Selecting optimum chilled water distribution system• Selecting optimum CHW supply & return temperatures

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• e ec ng op mum an ower range an approactemperatures, tower efficiency, and fan speed controls

• Selecting optimum chillers using a performance bid andLCC analysis

• Optimizing control sequences and setpoints

pg&e optimizing chilled water plants - rv 13 1 day version

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