chilled water plant design - direktori file...

© 2003 American Standard Inc.

Chilled Water Plant Design

Agenda

Earthwise System

Variable Primary Flow

Series Configuration

Case Study – 20,000RT Project Parallel, primary/secondary, low temp, YK

Series-counter, primary/secondary, low temp, low flow YD

Series-counter, primary/secondary, low temp, low flow CDHG

Series-counter, VPF, low temp, low flow, CDHG

Goal:Minimize Capital & Operating Costs

Improve:Reliability, Efficiency, & Comfort

Energy ConsumptionFirst Cost

Good for Business...

Offers lower first cost and lower operating cost.

Good for the Environment:

Reduced utility generated greenhouse gas emissions.

Reduces pumping costs...

A low flow, low temp, high efficiency system

Leverages today’s technology

Equipment - Chillers, Controls

System options

EarthWise Chilled Water Systems:

chillers

+$

+$

control

s

piping,

pumps

–$

Low Flow Chilled Water Plant Design …A Paradigm Shift - New ―Rules of Thumb‖

New ―rules of thumb‖

44° (6.7°) Lower chilled water supply

(such as 41° F = 5 ° C)

Larger T across evaporator

(such as 16° F= 8.9° C)

that’s at 1.5 gpm/ton

Lower flows through condenser

(such as 15°F = 8.4° C or 2 GPM/ton)

that’s something less than 3.0 gpm/ton

Tons = gpm * t / 24t (°C) gpm/ton

11 (20oF)

10 (18oF)

8.9 (16oF)

7.8 (14oF)

6.7 (12oF)

5.6 (10oF)

4.4 (8oF)

3.3 (6oF)

2.2 (4oF)

1.2

1.3

1.5

1.7

2.0

2.4

3.0

4.0

6.0

Pumps are

working.

Chillers are

working.

example chilled water plant …

Design Formulas

Chiller technology improvements

Cataloged at standard ARI conditions

Year

kW/ton

0.90

0.80

0.70

0.60

0.50

2000199519901985198019751970

Affect of reduced flow on pumps

Pump is smaller (lower cost)

Pump uses less power

0

20

40

60

80

100

0 20 40 60 80 100

% Waterflow

% Full load power

System Power

chiller chiller

pumpspumps

tower

tower

Traditional

System

Low Flow

Evaporator &

Condenser

Summary : EarthwiseTM Systems

Pump size

Tower size

Piping Size

Operating Cost

First Cost

How about Coil ?

Chilled water side

Coil

It’s a simple heat transfer device

Reacts to colder entering waterby returning it warmer

LMTD = TD2 - TD1

Ln (TD2 / TD1)

temperature

distance

80 F

air

55 F

TD2

44 F54 F water

TD1

LMTD44° F = 17.44

LMTD41° F = 18.13

41 F

57 F

How about Tower ?

Condenser side opportunity

Q=U A1 delta T1 = U A2 delta T2

Delta T1 = 94.2-78 = 16.2F (34.6-25.6 = 9 C)

Delta T2 = 99.1-78 = 21.1F (37.3-25.6 = 11.7 C)

A1*16.2 = A2*21.1

A2 = 0.77 A1

Tower exchanges heat between the entering (warmest) water temp and the ambient wet bulb

Low Flow Chilled Water Plant Design …

What are other’s saying??? Kelly and Chan (Vanderweil Engineering)

HPAC January 1999: Optimizing Chilled Water Plants”

Chilled water T: 18° & Condenser water T: 14.2°F

“With the same cost chillers, at worst, the annual operating cost with lower flows be about equal to “standard” flows but still at a lower first cost”

PG&E: CoolTools™ Chilled water T: 12°F to 20 °F

Condenser water T: 12°F to 18 °F (multi-stage)

0

200

400

600

41/16 42/14 43/12 44/10

Chilled water supply

temperature/DeltaT

kWh

/to

n/y

ear

Chilled waterpump

Chiller

© 2003 American Standard Inc.

Chilled Water System Optimization

• Decoupled Systems

• Variable Flow Systems

• Series Chiller Configuration

Decoupled Systems moving to…

Variable Flow Systems

Primary-secondary and VPF comparison

VPF

No secondary pumps

Chiller and pump staging not necessarily connected

Bypass line and valve for minimum flow control

Reduced installed cost

Reduced operating cost

Primary-secondary

Primary pumps

Secondary pumps

Chiller and primary pumps staged in pairs

Bypass line (no valve) allows constant evaporator water flow

CHW system type Primary/ secondary

Variable primary flow

Cooling load, tons 500 500

Total CHW flow rate 1,000 1,000

Primary pump head, feet

50 120

Secondary pump head, feet

70 NA


Design Conditions :

ARTI-21CR/611-20070-01

CHW system type Primary/ secondary

Variable primary flow

CHW pump equip cost, $ 10,516 7,358

CHW pump installation cost, $ 2,857 1,486

Piping & fittings installed cost, $ 19,070 NA

VFD / Starter installed cost, $ 9,860 14,550

Bypass / decoupler installed cost, $ 1,328 929

Bypass valve installed cost, $ NA 1,548

Flow meter installed cost, $ NA 1,800

Total installed cost, $ 43,631 27,671

Total installed cost, $ Base -15,960

Total installed cost, % Base -37


VPF SystemMinimum flow and control

VFDmodulating control valvefor minimum chiller flow

controlvalve

bypass line

P

P

P

P

VPF system - when to use?

Flows vary

Chillers with adaptive controls

Operator understands plant operation

Retrofits - even small jobs

Why consider VPF now?

Chiller control sophistication

First cost savings

Pump space

Pump wiring

Piping and connection

Operating cost savings

Pumps

Cooling Tower

Feedforward Control

Feedforward control is an open loop predictive control strategy that measures and compensates for load changes by using entering water temperature as an indication of load change.

With feedforward control, the chiller can respond faster to load changes.

Feedforward Control

Flow compensation works by calculating a new delta temperature as flow changes.

Maintains stability at low flow rates

Rejects disturbance caused by variable flow

UCP2 Feedback

42 º?? º

UCP 2

CH 530

CH 530 Feedback

42 º?? º

Feedforward

Σ

Capacity Control

w/o Water Flow Compensation

30

40

50

60

70

80

90

100

110

120

130

0:00:00 0:10:00 0:20:00 0:30:00 0:40:00 0:50:00

Time (hour:min:sec)

Wat

er T

emp

[deg

F]

-500.00

-300.00

-100.00

100.00

300.00

500.00

700.00

900.00

1,100.00

1,300.00

1,500.00

Wat

er F

low

[gp

m]

Evaporator Water Flow

Evap Entering Water Temp

Evap Leaving Water TempChiller off Chiller

off

Chiller on

50% Flow Reduction

With Compensation

Capacity Control

with Water Flow Compensation

30

40

50

60

70

80

90

100

110

120

130

0:00:00 0:10:00 0:20:00 0:30:00 0:40:00 0:50:00

Time (hour:min:sec)

Wa

ter

Te

mp

[d

eg

F]

-500.00

-300.00

-100.00

100.00

300.00

500.00

700.00

900.00

1,100.00

1,300.00

1,500.00

Wa

ter

Flo

w [

gp

m]

Evaporator Water Flow

Evap Entering Water Temp

Evap Leaving Water

Temp

variable primary flow

Advantages

Reduces capital investment

Saves mechanical-room space

Improves system reliability

VPF advantages

Lower Capital Cost

Fewer …

Pumps

Motors

Pump bases

Starters and wiring

Fittings and piping

Less labor

VPF advantages

More Available Space

Opportunity to …

Add other equipment

Select larger, more efficient chillers

Improve service access

VPF advantages

Improved Reliability

Provides system with …

Fewer pumps and accessories

Better balance between pumps and chillers online

VPF advantages

Greater Flexibility

any flow rate …

any T

chiller selection

Considerations

Evaporator flow limits (consult manufacturer)

Rate-of-change tolerance

Flow ―range-ability‖

Difference between design flow rate and evaporator’s minimum flow limit

chiller selection considerations

Evaporator Flow Limits

traditional limits 3.0 11–12

revised limits: standard 1.5 —tubes

high- 2.0 —performancetubes

flooded or falling-film evaporators

water velocity, fps

minimum maximum

4.6-to-1 turndown

1.9-to-1 turndown

variable flow Selection


Evaporator Flow Limits

Purpose:

Lower limit … • refrigerant carryover

• controller stability

• heat transfer

Upper limit … • erosion

• affordable pressure

drop


Rate-of-Change Tolerance

allowable flow-rate change*

chiller (compressor) type (% of design flow per minute)

• centrifugal 10% for process cooling30% for comfort cooling

• helical-rotary 10% for process cooling30% for comfort cooling

• scroll 10% for all applications

* Tolerances pertain specifically

to Trane chillers

What are other’s saying???

Variable Primary Flow Chilled Water

Plant Design …

VFP systems:

• Reduces total annual plant energy 3-8%

• Reduces first cost 4-8%

• Reduces life-cycle cost 3-5%*

*Relative to conventional Decoupled chilled-water systems.

VPF SystemMore information

Http:/trane.com/commercial/library/newsletters.asp (1999 and 2002)

―Don’t Ignore Variable Flow,‖ Waltz, Contracting Business, July 1997

―Primary-Only vs. Primary-Secondary Variable Flow Systems,‖ Taylor, ASHRAE Journal, February 2002

―Comparative Analysis of Variable and Constant Primary-Flow Chilled-Water-Plant Performance,‖ Bahnfleth and Peyer, HPAC Engineering, April 2001

―Campus Cooling: Retrofitting Systems,‖ Kreutzmann, HPAC Engineering, July 2002

Parallel VPF Systems

Series Configuration

Systems

58° F 50° F

42° F

moving to…

Series configuration -when should I use it?

Gas/electric (hybrid) fuel mix

Mixed chillers

Low-flow systems

Series configuration -benefits

Fuel flexibility

Control flexibility

Low distribution costs

VPF system configurationsSeries arrangement

Simple loading of either chiller

More efficient

upstream Chiller can be Absorption, Screw, etc….

VFD

VPF system configurationsSeries-Parallel Flow

VFD

41°F57°F

47.98°F

103.85°F 89.6°F89.6°F

89.6°F89.6°F

103.85°F

103.85°F103.85°F

570/730 Tons Simplex

45/55 split

VPF system configurationsSeries-Counter Flow

VFD

41°F57°F

48.96°F

103.82°F 89.6°F

96.63°F

89.6°F

103.82°F

96.63°F

650 Tons * 2 Simplex

50/50 split

Single

Compressor

Chiller

103.85° F

Lift

62.85° F

41° F

105.6° F

Lift

57.62° F

47.98° F

Series-Parallel flow

Arrangement

Upstream Chiller

102.12° F

Lift

61.12° F

41° F

Downstream Chiller

Upstream chiller: 105.6 - 47.98 = 57.62

Downstream chiller: 102.12 - 41 = 61.12

Average lift: 59.37 (vs. 62.85 for single compressor)

VPF system configurationsSeries-Parallel Flow

Single

Compressor

Chiller

103.82° F

Lift

62.82° F

41° F

103.82° F

Lift

54.86° F

48.96° F

Series-Counter flow

Arrangement

Upstream Chiller

96.63° F

Lift

55.63° F

41° F

Downstream Chiller


Downstream chiller: 96.63 - 41 = 55.63

Average lift: 55.24 (vs. 62.82 for single compressor) (vs. 59.37 for series parallel flow (7%))

Better chiller efficiency, but high P

VPF system configurationsSeries-Counter Flow

Example : …

Let’s prove it from Topss Selection :

650-ton chiller

44.6°F chilled water with 9°F T

3 gpm/ton condenser water flow

initial selection

condenser flow rate:3 gpm/ton

Downstream chiller:

chilled water flow 1950 gpm (system)

condenser water flow 1300 gpm (chiller)

leaving chilled water 41°F

chiller capacity 45% of system total

Series-parallel Flow

downstream chiller:

Bundle size : 630


Upstream chiller:



leaving chilled water 47.98°F



upstream chiller:

Selection #25


Downstream chiller:



leaving chilled water 41°F


Series-counter Flow

downstream chiller:

Less pressure drop

Series-counter Flow

Upstream chiller:



leaving chilled water 48.96°F


Series-counter Flow

upstream chiller:

Selection #7

Series-counter Flow

series system advantages:

better price & ROI

1

1. Series counter flow:Selection # 7 + 30.585Kw/ton, ave $307,366/chiller

2. Series parallel flow:Selection #41 + 250.615 kw/ton, ave $318,049/chiller

2

44.6/53.9F; 89.6 F / 3gpm/ton

Dubai 20,000 Tons Plant

Base Case:

10 Chillers

Evaporators and condensers piped in parallel

Cooling towers

Primary-Secondary chilled water system

Condenser water pumps

0.780 kW/ton at specified conditions


Series-Series Counter flow

5.43 cents / kWh

$0.0068 / gallon of water

Economics

Base Case Layout

56 F

40 F

•Chilled water 56 - 40 F (16 ° T)

•Condenser flow rate of 3 gpm/ton

(10 ° T)

Alternative 1 – YD Chiller

Four 5000 ton chiller modules

Series-Counterflow

Primary-Secondary

0.703 kW/ton

Fewer pumps

Reduced chilled water flow rate (increased T)

Alt 1: Series Counterflow

104.5°F 99.7°F 95°F

57.25°F 48.2°F 39.2°FUpstream chiller Downstream chiller

Compressor Lift

Single

Compressor

Chiller

104.5° F

Lift

65.3° F

39.2° F

104.5° F

Lift

56.3° F

48.2° F

Series-

Counterflow

Arrangement

Upstream Chiller

99.7° F

Lift

60.5° F

39.2° F

Downstream Chiller


Downstream chiller: 99.7 - 39.2 = 60.5

Average lift: 58.4 (vs. 65.3 for single compressor)

Better chiller efficiency

Alt 2: Decreased condenser rates, Trane Duplex chillers

Increased T (reduced flow) of chilled and condenser water

Reduced installed cost

Pipes

Pumps

Cooling towers

Chiller module is more efficient .650 kW/ton

Duplex chillers ―lift‖

Base cooling tower conditions

104.4° F

95° F

range 10° F

approach = 8° F87° F design

wet bulb

3 gpm/ton

Base cooling tower conditions

Base

Flow rate (gpm) 6000

Design wet bulb (deg F) 87

Approach (deg F) 8

EWT (deg F) 104.4

LWT (deg F) 95

Fan power (kW) 96

Affect of reduced flow on cooling towers

Reduce ―box size,‖ or...

Reduce fan power, or...

Reduce ―approach temperature‖

Same cooling tower at reduced flow rate

105.1° F

93° F

range 12.1° F

approach = 6° F87° F design

wet bulb

2.42 gpm/ton

Same cooling tower at reduced flow rate

Base Same tower

lower flow

Flow rate (gpm) 6000 4840

Design wet bulb (deg F) 87 87

Approach (deg F) 8 6

EWT (deg F) 104.4 105.1

LWT (deg F) 95 93

Fan power (hp) 96 96

Affect of temperatures on the chiller

Decreased chilled water leaving temperature takes more power

Increased condenser water leaving temperature takes more power

Alt 2: Trane Duplex Series Counterflow

105°F 99°F 93°F

57.25°F 48.2°F 39.2°FUpstream chiller Downstream chiller

102°F 96°F

52.7°F 43.7°F

Trane Duplex Series Counterflow, ―Average Lift‖

Upstream chiller

upstream circuit: 105 - 52.7 = 52.3

downstream circuit: 102 - 48.2 = 53.8

Downstream chiller

upstream circuit: 99 - 43.7 = 55.3

downstream circuit: 96 - 39.2 = 56.8

Average lift: 54.5 vs. 65.3 for single compressorvs. 58.4 for ―other‖ series counterflow (7%)

Better chiller efficiency

Alt 2: Summary

Reduced flows: installed cost savings

Smaller condenser pipes

Smaller chilled water pipes

Smaller cooling towers

Smaller condenser pumps

Smaller chilled water pumps

Operating cost savings

Better chiller efficiency (reduced lift due to Trane Duplex modules)

Reduced pumping power

Reduced make-up water consumption

Alt 3: Variable Primary Flow Reduced number of

pumps

Fittings

Piping

Electrical connections

Controls

Responds to ―Low T Syndrome‖

Reduced operating costs

Base case: 10 parallel chillers, primary-secondary, 16 ° T Chilled water, 10 ° T condenser water

4 Chiller modules, series counterflowprimary-secondary 18 ° T Chilled water, 10 ° T condenser water

Trane Duplex modules, series counterflow, primary-secondary, 18 ° T Chilled water, 12 ° T condenser water

Trane Duplex modules, series counterflow, variable primary flow18 ° T Chilled water, 12 ° T condenser water

Alternatives

Case 1 (competitor) Case 2 (competitor) Case 3 TAS/Trane Case 4 TAS/TraneParallel R-134a Chiller Design Series R-134a Chilling Design Series R-123 Chilling Design Series R123 Chilling Design

Primary Secondary Pumping Primary Secondary Pumping Primary Secondary Pumping Variable Primary & Reduced Chw pipe

Tabreed Type, York Chillers JBR, York/Stellar YD Chillers JBR, TAS/Trane Optimal, TAS/Trane

Capacity-TR 20000 20000 20000 20000

Chiller kW 15600 14056 12994 12994

Number of chillers 10 4 4 4

kw/TR 0.78 0.703 0.650 0.650

Evaporator Water GPM 30000 26668 26668 26668

Evaporator Water T-In 55.94 57.25 57.25 57.25

Evaporator Water T-Out 39.92 39.2 39.2 39.2

Evaporator Water dT 16.02 18.05 18.05 18.05

Condenser Water GPM 60000 60000 48400 48400

Condenser Water T-In 95 95 93 93

Condenser Water T-Out 104.54 104.54 105.1 105.1

Evaporator Water bHP/pump 122 214 117 0

Evaporator Water kW 909 638 348 0

kW/pump 91 160 87 0

Condenser Water bHP/pump 136 341 293 293

Condenser Water kW 1016 1016 872 872

kW/pump 101.6 254 218 218

Distribution Pump bHP 1940 1362 1356 1823

Distribution Pump bHP 1445 1015 1010 1358

Fan bHP 1293 1293 1293 1293

Fan kW 963 963 963 963

Fan kW/TR 0.0482 0.0482 0.0482 0.0482

Water Consuptiom GPM 879 879 852 852

Water Consumption gallons/ton-hour 2.64 2.64 2.56 2.56

Equipment Power 19933 17689 16187 16187

Misc Power 268 268 268 268

kw/TR 1.010 0.898 0.823 0.823

Annual Full Load Operating Hours

Water Rate $/gal 0.0068 0.0068 0.0068 0.0068

Energy Rate $/kW-HR 0.0543 0.0543 0.0543 0.0543

Annual Water Cost Total 1,738,216$ 1,721,515$ 1,634,278$ 1,634,278$

Annual Energy Cost 4,087,975$ 3,858,686$ 3,346,897$ 3,316,355$

Total Annual Operating Cost 5,826,191$ 5,580,202$ 4,981,175$ 4,950,633$

Savings Vs. Case 1 245,989$ 845,016$ 875,558$

Savings Vs. Case 2 599,027$ 629,568$

Savings Vs. Case 3 30,541$

Power Consumption

Financial Considerations

Analysis of Alternative 20,000 ton District Cooling Designs for the UAE (87WB)

Chiller

Pumps

Cooling Tower

Energy Use

-

10,000,000

20,000,000

30,000,000

40,000,000

50,000,000

60,000,000

70,000,000

80,000,000

kWh

Ba

se

- 1

0 c

hille

rs

4 M

od

ule

s -

Pri

ma

ry/S

eco

nd

ary

Tra

ne

Du

ple

x

mo

du

les,

Pri

ma

ry/S

eco

nd

ary

Tra

ne

Du

ple

x

mo

du

les,

Va

ria

ble

Pri

ma

ry F

low

Dubai, 20,000 ton plant, Annual kWh

Primary pumps

Distribution pumps

Condenser pumps

Tower Fans

Chillers

Estimated operating cost

$-

$1,000,000

$2,000,000

$3,000,000

$4,000,000

$5,000,000

$6,000,000

Ba

se

- 1

0 c

hill

ers

4 M

od

ule

s -

Prim

ary

/Se

co

nd

ary

Tra

ne

Du

ple

x

mo

du

les,

Prim

ary

/Se

co

nd

ary

Tra

ne

Du

ple

x

mo

du

les, V

aria

ble

Prim

ary

Flo

w

Dubai, 20,000 ton plant, Estimated Annual Operating Cost

Annual Make-

up water costAnnual Electric

Cost

=$599,000

Net Present Valueutility savings only

Dubai, 20,000 ton plant, Net Present Value

$-

$1,000,000

$2,000,000

$3,000,000

$4,000,000

$5,000,000

$6,000,000

$7,000,000

$8,000,000

Alt 2-1 Alt 3-1 Alt 4-1

Significant benefits available

By

Reducing condenser water flow

Reducing chilled water flow

Duplex series-counterflow arrangement

Trane Duplex modules

Save

Both capital and operating costs

VPF saves additional

Capital costs

Operating costs


Series-Series Counter flow

Washington D.C. 10,500 tons chilled water plant

91.3 oF98.9 oF

55 oF37 oF

85 oF

45.1 oF

../../ctv/Applications/Series-Series Counter Flow.pdf

Conclusion :

Greater Focus on System Efficiency and …..

Lower Operating & Installation Cost Low-Flow Systems

annu

al e

nerg

y co

nsum

ptio

n, k

Wh

base case

chiller

cooling tower fans

low flow

750,000

600,000

450,000

300,000

150,000 pumps

0

2.4 gpm/ton

[0.043 L/s/kW]

44°F [6.7°C]

54°F[12.2°C]

85°F[29.4°C]

95°F[35°C]

3.0 gpm/ton

[0.054 L/s/kW]

ARI conditions1.5 gpm/ton

[0.027 L/s/kW]

41°F [5°C]

57°F[13.9°C]

85°F[29.4°C]

100°F[37.8°C]

2.0 gpm/ton

[0.036 L/s/kW]

low-flow conditions

evaporator

flow rate

condenser

flow rate

evaporator

flow rate

condenser

flow rate

Trend Toward Lower Flow Rates

EarthWise™

Chilled Water Systems

First

Cost

Operating

Cost

Exploit technology!

• Low flow

• Low temperature

• High efficiency

Leverage:

• Optimized Controls

• Variable Primary Flow

• Series Evaporators

Questions or Comments?

chilled water plant design - direktori file...

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