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Chiller Plant:
Fundamentals & Optimization

Julian R. de Bullet
ASHRAE Distinguished Lecturer
julian@debullet.com
 Big Plant Layout

60,000
60 000 Tons
40/58 F Chilled Water
80,000 USgpm Chilled
Water
48 Dia. Pipe

93/103 F Cond.
Water
180,000 USgpm Cond.
Water
54 Dia.
Dia Pipe
 Big Plant Layout

Large Chilled Water Range

Is a Must
Using 18F T
48 Pipe - $500/ft
5000 ft = $2.5M
5800 hp @ 200 head
(Its
(It s Over 10
10,000
000 hp @ 10
10F
F
T)
Lower The Supply Water
Temperature To Balance
LMTD
No Pump Or Pipe Savings
From Lower SWT
Fan Savings
Full Load Vs. Annual Load

Peak Month Cooling Load Profile Chiller Design

Performance
140

120

100
d(Tons)

80
Load

60

40

20

0
1

11

13

15

17

19

21

23
Hours
 Full Load Vs. Annual Load
Same Chiller, Base Loaded
0.6 Accounting For Condenser
Relief
0.5
0.55 kW/ton At AHRI
Conditions
0.4

0.3

0.2

Chiller W/ VFD, Base Loaded

0.1
Accounting For Condenser
Relief
0

Fully Loaded W/C Centrifugal W/C Centrifugal VFD

 Full Load Vs. Annual Load

Chiller
58%

Fans
24% Tower
Pumps 5%
13% Chiller
Fans 33%
Design Performance 43%

Tower
2%
Pumps
22%

Annual Energy Usage

 Full Load Vs. Annual Load
Summary

Full Load Or Daily Load

Profiles Are A Poor
Indicator Of Overall
System Performance

There Is No Substitute
For Annual Energy
Analysis
Crunching the numbers
 Air Cooled vs. Water Cooled

Avoid Tower, Pump And Piping

No Water Cost For Tower
Higher kW Than Water Cooled
Chillers
Compressor Work Tracks
Drybulb Not Wetbulb
Very Good NPLVs
Excellent Choice For Schools
With Reduced Summer Hours
Air Cooled Vs. Water Cooled

Summary

Water Cooled Is More Energy Efficient

May Not Be More Cost Effective

Water And Maintenance Costs

May Not Have Acceptable Life Cycle Analysis

Single Vs. Parallel Vs. Series

All Constant Flow Systems

All Have Same Total Pump Power

Single Chiller Design

800 Ton Load

52F Chilled Water 3 Way Valves
R t
Return

2400 Usgpm
95F

2400 Usgpm Chilled

Water Pump
67 kW Cooling Tower
40 kW

2400 Usgpm Condenser

85FSupply
Water Pump
To Chiller
33.5 kW

44F Chilled Water

800 Ton Chiller Supply
0.55 kW/ton
Parallel Chiller Design

800 Ton Load

54F Chilled Water
R t
Return

2400 Usgpm Chilled 2400 Usgpm

Water Pump 95F
67 kW

Two 1200 Usgpm

Condenser Water Pumps Two Cooling Towers
16.8 kW Each 20 kW Each

85FSupply
To Chiller

44F Chilled Water

Two 400 Ton Chillers Supply
0.55 kW/ton
Series Chiller Design
800 Ton Load
54F Chilled Water
R t
Return

2400 Usgpm
95F

Two Cooling Towers

20 kW Each

Two Nominal 400 Ton Chillers.

Two 1200 Usgpm Lag 1 Produces 440 Tons
Condenser Water Pumps Lead 2 Produces 360 Tons
16.8 kW Each 85FSupply
To Chiller

Lag Chiller Lead Chiller 44F Chilled Water

2400 Usgpm Chilled Supply
Water Pump
67 kW
Series-Counterflow Chiller Design

54F Chilled Water 800 Ton Load

Return

2400 Usgpm
95F

One Cooling Tower

40 kW

Two Nominal 400 Ton Chillers.

Chillers
Chiller 1 Produces 440 Tons 85FSupply
Chiller 2 Produces 360 Tons To Lead Chiller

2400 Usgpm Chilled One 2400 Usgpm

Water Pump 89F Supply
Condenser Water Pump
67 kW To Lag Chiller
33.6 kW
44F Chilled Water
Supply
Piping Diversity - 3 Way Valves
Coil Bypass
Line
Flow Is Constant At Each Coil
Delta T Changes With Load

CW Pump Sized For

Connected Flow

44F Supply

Coil
Chiller Chiller Sized For
Peak Load 3 Way Valve
Two Way Valves

Temperature Range Across

Load Remains Constant.
Flow Varies With Load

CW Pump Sized For

Chiller Flow Rate
At D
Design
i D
Delta
lt T

Chiller Sized For

Peak Load
2 Way Valve
Standard Primary Loop Layout
51.5F Return Water Building Load
To Chiller 51.5F 54F 600 Tons
44F (50% Load)
Two 400 Ton Chillers 480 gpm Flow Through
Each At 300 Tons Decoupler
(Balanced Load)

Chiller 1- On
Two Primary Pumps Flow
Each At 960 gpm

Chiller 2- On

44F

Secondary Pump
Chiller 3- Off
1440 gpm
Variable Flow Vs. Constant Flow
Summary

Variable Flow Required

For Systems Over 10 HP
(
(6.4.3.1)
)
Modulate Down To 50%
Exceptions
Where Minimum Flow Is
Less Than Flow Required
By Equipment And <
75HP
Variable Primary Flow Design

Bypass
yp Line
Used to Ensure Minimum
Flow Through Chillers

VFD Primary Pump

Apply Diversity to Flow

Use 2 Way Valves

Flow Meter

Automatic Isolating Valves

Variable Flow Vs. Constant Flow
500000

450000

400000
Pump Work Cut
350000 In Half

300000
kWh

250000
Notice Pump Work
200000 Half Chiller Work!
150000

100000

50000

0
Chillers Pumps Towers Fans

Variable Primary
y Flow 2 Chiller Primary/Secondary
y y Flow 2 Chiller Parallel Flow
Equipment - Performance
Improve Chiller Full Load kW/Ton From 0.55 To
0.45
An 18% Improvement In Chiller Provides Only
7% Improvement In Operating Cost
Chiller Price Goes Up Exponentially
Run Chiller Chiller Pumps Tower Fan S.A. Fan Total
kW/ton ($/yr) ($/yr) ($/yr) ($/yr) ($/yr)
1 0.55 24,435 15,209 1,441 24,512 65,597
2 0 54
0.54 23 988
23,988 15 207
15,207 1 441
1,441 24 509
24,509 65 145
65,145
3 0.53 23,541 15,206 1,441 24,507 64,695
4 0.52 23,095 15,204 1,441 24,504 64,244
5 0.51 22,648 15,202 1,441 24,501 63,792
6 0.5 22,202 15,201 1,441 24,499 63,343
7 0.49 21,755 15,199 1,441 24,496 62,891
8 0.48 21,309 15,197 1,441 24,493 62,440
9 0 47
0.47 20 863
20,863 15 196
15,196 1 441
1,441 24 491
24,491 61 991
61,991
10 0.46 20,416 15,194 1,441 24,488 61,539
11 0.45 19,970 15,192 1,441 24,485 61,088
 ARI Standard 550/590-98

Know y
your Standards!
99% Of All
Operating
p g Hours Are
At Part Load
The New Industry ARI Standard -1998

Part Load Analysis

y (IPLV)
( )
% Load Old % Hrs New % Hrs
100 17 1
75 39 42
50 33 45
25 11 12

Systems Solution
Various 500 Ton Chillers

.6

.505
.5
IPLV

.403
.4
4

.365
.337

.3
WSC WDC WSC w/VFD WDC w/VFD

Notes: WSC = Single Compressor Centrifugal Chiller

p
WDC = Dual Compressor Centrifugal
g Chiller
VFD = Variable Frequency Drive
Analyze your design!
Equipment - Properties

Different Chillers Operate Differently

VFD Chillers Need Condenser Relief
Duals Are Most Efficient At 50% Load
Absorption And Gas Driven Chillers Operate On a
different Fuel
System Must Take Advantage OF Chiller Properties
To Get Best Results

Pa
Partt Load Pe
Performance
fo mance Is Us
Usually
all Mo
More
e Important
Impo tant
Than Full Load Performance
Single vs. Dual Compressor Chillers

1.2

0.8
KW/Ton
n

0.6

0.4

0.2

0
0 20 40 60 80 100

% Chiller Plant Load

Two Single Chillers Two Dual Chillers
Equipment
Summary

Be Careful That High Performance

Equipment Can Pay For Itself
Ask For A Couple Of Selections And Some
Budget Pricing

Understand And Take Advantage Of

Chillers Operating Properties
Range Vs. Supply Water Temperature

Flow (Usgpm) = Load (tons) x 24 / Temp. Range (F)

Increasing Range Reduces Flow
Reduces Pipe, Pump And Motor Size

Pump Power (hp) = Flow (Usgpm)x Head (ft) / 3960 x Eff.

Eff
Reducing Flow Reduces Pump Work
This Is A Good Goal
It Will Affect Every Part Of the Chilled Water System
Everything Must Be Considered
Range Vs. Supply Water Temperature
Fan Work Savings For Small Changes (2 to 4F)
Dont Save Enough To Offset Chiller Penalty
Especially For VAV
20% Airflow Decrease
35% Static Decrease
49% Power Decrease
Dont Lower Supply Water Temperature Just To
Save Fanwork
Dont Lower To Ensure Design Water Temperature
Will Be Available At Coil
If You Assume Water Will Be 2F Warmer At Coil
Then You Assume 20% Of Chiller Capacity Lost To
Heat Gain!
Range Vs. Supply Water Temperature
97F
118.3 psig
R-134a

Standard ARI HEAT OF

2

Conditions CONDENSATION
T2
95F

URE
1 ERAT
54- 44F Chilled Water EM P
DT
FL UI
E R
NS
DE
85 - 95F Condenser CO
N

Water LIFT
85F T1
(F)

10F Range 54F T1

CO
2F Approaches In Heat O L ER
FLU
ID TEM
Exchangers 1
P ERAT
U RE
T2
44F
55F Lift On
HEAT OF
VAPORIZATION
2
Compressor
42F SATURATED SUCTION TEMPERATURE {TR}
36.6 psig
R-134a
Range Vs. Supply Water Temperature
Change To 14F Range
Smaller Pumps, Pipes
etc.
etc
Maintain Supply Water
Temperature
LMTD Increases
Improves Chiller
Performance
Hurts Chilled Water Coil
Performance
Deeper Coils Required
Increased Fan Static
Pressure
Range Vs. Supply Water Temperature

Maintain 14F Range

L
Lower S
Supply
l WWater
Temperature To 42F
4% Increase In
Compressor Lift
Chiller Performance
Suffers
Chilled Water Coil
Performance
Improves
Range Vs. Supply Water Temperature
VAV Office Bldg In New York City
Fixed Supply Water Temperature
Design Conditions
Increase Chilled Water Range From 10 To 24F
Fan Motor Goes From 94.8 HP To 114.7 HP (21%)
Pump Goes From 38.5 HP to 16 HP (58%)

Chiller Chilled Water Coil Fan Total

Run Capacity Perform Temp Range Pump APD Rows/fins TSP Motor size Power
Tons KW/ton (F) HP (in. w.c.) (in. w.c.) (HP) (HP)
1 400 0.546 10 38.5 0.62 5/10 3 94.8 426.1
2 400 0 546
0.546 12 32 1
32.1 0 66
0.66 5/11 3 04
3.04 96 420 9
420.9
3 400 0.547 14 27.5 0.7 6/10 3.08 97.3 417.6
4 400 0.547 16 24 0.79 6/12 3.15 99.5 416.3
5 400 0.543 18 21.4 0.87 8/9 3.25 102.7 415.3
6 400 0.543 20 19.2 0.94 8/11 3.32 104.9 415.3
7 400 0.543 22 17.5 1.1 10/10 3.48 109.9 418.6
8 400 0.543 24 16 1.25 12/10 3.63 114.7 421.9
Range Vs. Supply Water Temperature

Fixed Supply Water Temperature

Increase Chilled Water Range From 10 to 24F
Annual Energy Analysis
System Peaks At 16F Range

Run C.W. Range Chiller Pumps Tower Fan S.A. Fan Total
(F) ($/yr) ($/yr) ($/yr) ($/yr) ($/yr)
1 10 26,074 15,175 1,591 28,275 71,115
2 12 26,096 13,784 1,593 28,560 70,033
3 14 26,167 12,792 1,594 28,846 69,399
4 16 26 211
26,211 12 055
12,055 1 597
1,597 29 350
29,350 69 213
69,213
5 18 26,081 11,489 1,601 30,070 69,241
6 20 26,126 11,034 1,604 30,574 69,338
7 22 26,259 10,784 1,619 31,726 70,388
8 24 26,358 10,487 1,625 32,810 71,280
Range Vs. Supply Water Temperature
Switch To Constant Volume With Reheat
Increase Chilled Water Range From 10 to 24F
Annual Energy Analysis
System Peaks At 14F
Fan Penalty Outweighs Pump Savings

Run C.W. Range Chiller Pumps Tower Fan S.A. Fan Total
((F)
F) ($/yr) ($/yr) ($/yr) ($/yr) ($/yr)
1 10 40,035 19,842 2,821 70,957 133,655
2 12 40,034 18,013 2,821 71,954 132,822
3 14 40,224 16,728 2,831 72,396 132,179
4 16 40,327 15,765 2,839 73,657 132,588
5 18 40,174 15,025 2,852 75,455 133,506
6 20 40,285 14,429 2,863 76,715 134,292
7 22 40 526
40,526 13 963
13,963 2 884
2,884 79 595
79,595 137 193
137,193
8 24 40,772 13,692 2,912 82,283 139,659
Range Vs. Supply Water Temperature

Declining Supply Water Temperature (44 To 38F)

Increase Chilled Water Range From 10 To 24F
Annual Energy Analysis
System Peaks At 16F Range And 42F SWT

Run C.W. Range C.W. S.T. Chiller Pumps Tower Fan S.A. Fan Total
(F) (F) ($/yr) ($/yr) ($/yr) ($/yr) ($/yr)
1 10 44 26,074 15,175 1,591 28,275 71,115
2

12 44
Not As Good As 16F Range And 44F SWT!
26,096 13,784 1,593 28,560 70,033
3 16 44 26,211 12,055 1,597 29,350 69,213
3 14 42 27,733 12,790 1,593 28,573 70,689
4 16
6 42 27,779
, 9 12,039
,039 1,593
,593 28,570
8,5 0 69,981
69,98
5 18 40 29,371 11,462 1,594 28,584 71,011
6 20 40 29,351 11,002 1,596 28,872 70,081
7 22 38 30,365 10,623 1,596 28,881 71,465
Condenser Water Range

Increase Condenser Water Range From 10 To 15F

Annual Energy Analysis
System Peaks At 10 Range
It Costs More To Operate A System At Higher Ranges

Run Cond .W. Range Chiller Pumps Tower Fan S.A. Fan Total
(F) ($/ )
($/yr) ($/ )
($/yr) ($/ )
($/yr) ($/ )
($/yr) ($/ )
($/yr)
1 10 26,074 15,175 1,591 28,275 71,115
2 11 27,084 14,562 1,592 28,283 71,521
3 12 27,517 14,049 1,592 28,286 71,444
4 13 28 094
28,094 13 616
13,616 1 592
1,592 28 290
28,290 71 592
71,592
5 14 28,527 13,245 1,592 28,293 71,657
6 15 29,057 12,923 1,593 28,297 71,870
Condenser Water Relief
 Optimizing Starter Selections

Try Different Starters

Solid State Starters Have Different Size

Breaks Than Wye Delta Starters
lid S
Solid
S State S
Starters Are
A Now
N Ch
Cheaper
In Most Cases - Try Both Ways
Depending
p g Upon
p Size Breaks
Try Unit Mounted And Free Standing -
Size Breaks Can Make Different
Selections Appear
Check VFD Sizing Expensive At Very
Bottom Of Amp Rating
Annual WB In Major US Cities
80.0

70.0

60.0

50.0

40.0

30.0

20.0 Strong Candidates For

VFD Chillers
10.0

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Los Angeles Washington DC Atlanta Chicago Miami
AVAILABILITY OF REFRIGERANT
(Dupont & ICI Projections)

M Tonnes (000)

300

250

200
HFC134a
150
HCFC22 HFC410A
100

50 HCFC123

0
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Year
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