High Capacity Chillers 97

High Capacity Chillers:

Do we have Options?

by

Leslie T. Taniyama, V.P.Power and Systems Inspection Group – Hawaii Office

Phone (808) 955-6418

Email: [email protected]

May 7, 2006

Power & SystemsInspection Group

Commercial Office High Rise Buildings,


Commercial Office High Rise Buildings,Campuses,



Large Retail Malls and Stores



Large Retail Malls and Stores andAirports




Require Large Chilled WaterCentral Plants.






What are the Choices:





What are the Choices:In Equipment?





What are the Choices:In Equipment?

And in Designs?


Chiller Arrangements

The need to provide solutions for diverse building/facility operations

and its usage created various chiller arrangements.

Only recently has manufactures endorsed flow change through its

cooler/heat exchangers.

Centrifugal Chillers were reserved for the larger capacities over 250

Tons where rotary screw filled the lower capacities.

Recent developments in Centrifugal chiller designs, Screw chiller

designs and chiller plant configurations and designs have evolved to

allow for creative opportunities for energy efficiency and functional

improvements.


Chiller Arrangements

Parallel Lead/Lag Chillers

Series Connected Chilled Water

Series-Series Counter Flow

Chiller Selections

Centrifugal Chillers

Screw Chillers

Hybrid – Centrifugal / Screw Combination


Chiller Lift

The following analysis considers refrigerant lift calculations in the

comparisons of the chiller arrangements.

The reason why lift is considered, especially for centrifugal chillers, it

is somewhat proportional to the work performed by the compressor.

It is also more important for Centrifugal Chillers as lift control is crucial

in maintaining optimization of the inlet guide vane and vfd algorithms

of the chiller.

Screw compressors positively displaces refrigerant and is not as

concerned with surge conditions associated with centrifugal chillers.

Let’s look at the arrangements with the following conditions:

CWS = 75 °F, CWR = 85 °F

CHWS = 44 °F, CHWR = 54 °F


CH-2 CH-1

Parallel Chiller Arrangement

CHWS = 44 °F

CHWR = 54 °F

CWS = 75 °F

CWR = 85 °F

CHWS = 44 °F

CHWR = 54 °F

CWS = 75 °F

CWR = 85 °F

Assumption: Condenser Approach = 1.5 °F = CWR – Condenser Refrigerant Temperature.

Evaporator Approach = 1.5 °F = CHWS – Evaporator Refrigerant Temperature.

Lift = Condenser Refrigerant Temperature – Evaporator Refrigerant Temperature = ~Work

= ( CWR – 1.5°F ) – ( CHWS – 1.5) = ( 85°F – 1.5 ) – (44°F – 1.5 ) = 83.5°F – 42.5°F

= 41°F for both chillers.

NOTE: If standard design of CWS = 85 °F, Lift = 51 °F.


CH-2 CH-1

Series Chiller Arrangement

CHWR = 54 °F

CWS = 75 °F

CWR = 85 °F

CHWS = 44 °F

CWS = 75 °F

CWR = 85 °F




= ( CWR – 1.5°F ) – ( CHWS – 1.5)

CH1Lift = 83.5 - 42.5 = 43°FCH2Lift = 83.5 – 57.5 = 36°F.

CHW’ = 49 °F


CH-2 CH-1

Series-Series CounterflowChiller Arrangement

CHWR = 54 °F

CWR = 85 °F

CHWS = 44 °F

CWS = 75 °F




= ( CWR – 1.7°F ) – ( CHWS – 1.5)

CH1Lift = 78.3 - 42.5 = 35.8°FCH2Lift = 83.3 - 47.5 = 35.8°F.

CHW’ = 49 °F

CW’ = 80 °F


Let’s Review the Lift Differences

Chiller ArrangementParallel Lead/Lag Chillers



CH1-Lift*41.0 °F

CH2-Lift*41.0 °F






CH1-Lift*41.0 °F

43.0 °F

CH2-Lift*41.0 °F

36.0 °F






CH1-Lift*41.0 °F

43.0 °F

35.8 °F

CH2-Lift*41.0 °F

36.0 °F

35.8 °F


Why should I be concerned about Lift?

Centrifugal Chiller 19XRV

0

10

20

30

40

50

60

70

0 1 2 3 4 5 6 7 8 9 10

Chiller Load

Re

frig

era

nt

Lif

t (D

P) Fully Loaded Chiller,

CWS=85CWR=95

Chiller Unloads,CWS=85CWR=90

Crosses Surge LineAnd goes into surge


CH-2

CH-1

Rarely Would The Load Drop in Half.Right? ? ?

CHWR = 54 °F

CWS = 75 °F

CWR = 95 °F

CWS = 75 °F

CWR = 95 °F

CHWR = 44 °FCHWR = 54 °F

CHWR = 54 °F

1,000 GPM

n.c.

1,000 GPM

CHWR = 44 °F


CH-2

CH-1

Let’s Lag On the CH2

CHWR = 54 °F

CWS = 75 °F

CWR = 95 °F

CWS = 75 °F

CWR = 95 °F

CHWR = 44 °FCHWR = 54 °F

CHWR = 54 °F

1,000 GPM

500 GPM

500 GPM

CHWR = 49 °F

CH-2 Valve Opens andCH-1 flow drops in HALF,Reducing load in half.




0

10

20

30

40

50

60

70

0 1 2 3 4 5 6 7 8 9 10

Chiller Load

Re

frig

era

nt

Lif

t (D


CWS=75CWR=85

Chiller Unloads slowly,CWS=65CWR=70

Does NOTCross Surge Line

Maintains Optimization




0

10

20

30

40

50

60

70

0 1 2 3 4 5 6 7 8 9 10

Chiller Load

Re

frig

era

nt

Lif

t (D


CWS=75CWR=85

Chiller Unloads slowly,CWS=65CWR=70

Does NOTCross Surge Line

Maintains Optimization

The lower the load is on the chiller,The lower the cooling tower water

Temperature needsTo be to maintain optimization.


Carrier 19XRV Centrifugal Chiller w/ VFD500 N. Tons

Condenser Water and Load Characteristics

85

82.5

80

77.5

75

72.5

100%

75%

50%

25%

0.40

0.45

0.50

0.55

0.60

0.65

0.70

0.75

0.80

0.85

0.90

0.95

1.00

1.05

kW

/To

n

CWS Temp

Cap

acit

y (%

)

CWST vs 19XRV Chiller

Efficiency (kW/Ton)

1.000-1.050

0.950-1.000

0.900-0.950

0.850-0.900

0.800-0.850

0.750-0.800

0.700-0.750

0.650-0.700

0.600-0.650

0.550-0.600

0.500-0.550

0.450-0.500

0.400-0.450

Capacity (%)

CWS = 75 °F

Efficiency

kW/Ton

100% 0.461

75% 0.469

50% 0.498

25% 0.732


Carrier 23XRV Screw Chiller w/ VFD500 N. Tons

Condenser Water and Load Characteristics

85

82.5

80

77.5

75

72.5

100%

75%

50%

25%0.40

0.45

0.50

0.55

0.60

0.65

0.70

0.75

0.80

0.85

0.90

0.95

1.00

1.05

kW/Ton

CWS Temp

Lo

ad

%

CWST vs 23XRV Chiller Eff 23XRV

Efficie ncy (kW/Ton)

1.000-1.050

0.950-1.000

0.900-0.950

0.850-0.900

0.800-0.850

0.750-0.800

0.700-0.750

0.650-0.700

0.600-0.650

0.550-0.600

0.500-0.550

0.450-0.500

0.400-0.450

Capacity (%)

CWS = 75 °F

Efficiency

kW/Ton

100% 0.466

75% 0.437

50% 0.455

25% 0.601


Let’s Review the Efficiency DifferencesOf the Centrifugal VFD Chiller and

The VFD Screw Chiller

19XRV 85 °F 82.5 °F 80 °F 77.5 °F 75 °F 72.5 °F

100% 0.586 0.552 0.520 0.490 0.461 0.434

75% 0.642 0.590 0.549 0.508 0.469 0.431

50% 0.727 0.665 0.609 0.552 0.498 0.450

25% 0.902 1.023 0.918 0.825 0.732 0.657

23XRV 85 °F 82.5 °F 80 °F 77.5 °F 75 °F 72.5 °F

100% 0.583 0.544 0.508 0.474 0.446 0.419

75% 0.573 0.534 0.496 0.466 0.437 0.406

50% 0.616 0.572 0.532 0.493 0.455 0.418

25% 0.859 0.784 0.715 0.657 0.601 0.550

CentrifugalVFD Chiller

ScrewVFD Chiller

Note: When a VFD operated centrifugal chiller

operates un-optimized, its efficiency worsens by as

much as 100% (0.469 kW/Ton vs. 0.820 k W/Ton).


Chiller Lift Considerations

CWR = 85 °F

CWS = 75 °FAPPR = 4 °F

CHWR = 54 °F

CHWS = 44 °FAPPR = 4˚F

Cooler

Condensor

SRT = 40°F

SCT = 89 °F

35 psig

104 psig


R134a PT Chart

High Capacity Chillers 97

Documents

Transcript of High Capacity Chillers 97