HIGH PERFORMANCE CHILLED WATER SYSTEMS … · ... Efficiencies at full load at AHRI (Standard MEPS)...

2/13/2013

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EarthWise HVAC

Simon Hoe: [email protected]

HIGH PERFORMANCE CHILLED WATER SYSTEMS

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EarthWise HVAC –High Performance CHW Plants

• Low Flow Low Temperature Systems

• Variable Flow Systems

– Variable CHW

– Variable CDW

• Chillers Piping Configurations

• Chiller Tower Optimization

• Pumping Optimization

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LOW FLOW LOW TEMPERATURE HIGH EFFICIENCY SYSTEMS

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Low Flow, Low TemperatureHigh Efficiency

piping

~/~/––$$

ductwork

~/~/––$$

+/+/--$$

air handlers

+/+/--$$

+/+/--$$controls

chillers

+/+/--$$

FIRST COST &OPERATING COST

COMFORT,ACOUSTICS &EFFICIENCY

1.1.Slow the Slow the

FlowFlow

2.2.Drive the Drive the

Chiller Chiller

HarderHarder

3.3.Chillers Chillers

more more

efficient efficient

than than

ancillariesancillaries

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Low Flow Low Temperature

• Low flow CHW and/or CDW improves system efficiency at part load

– Pumping power reduction more than offset slight increase in chiller power

• Low flow also decreases infrastructure costs

– Piping, valves

– Insulation

– Pumps

– Towers

• CT sizing can reduce with warm (design) condenser water and lower flows

• Re-invest some of the capital back into higher efficiency chillers, towers, coils and controls

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Chiller Efficiency (Code vs Best in Class)

3.0

3.5

4.0

4.5

5.0

5.5

6.0

6.5

7.0

7.5

8.0

0 500 1000 1500 2000

MEPS AU2008

1970s

1980s

1990s

2000s

2010s

kW

CO

P

Note: Efficiencies at full load at AHRI (Standard MEPS) conditions – water-cooled chillers

Higher Higher efficiencies efficiencies today allowtoday allowfor better for better

chiller chiller utilizationutilization

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CHW Design Parameters

Parameter Past/Conventional EarthWise

Leaving CHW, [oC] 6 ~ 7 4 ~ 6

CHW δδδδT, [K] 5 ~ 7 9 ~ 12

CHW Flow, [L/s/MW] 34 ~ 48 20 ~ 26

Leaving CDW, [oC] 35 36 ~ 38

CDW δδδδT, [K] 5.5 8 ~ 10

CDW Flow, [L/s/MW] 54 28 ~ 35

CooltoolsTM Chilled Water Plant Design Guide (Dec 2009) recommends

� 6.7 to 11.1K δT on chilled water and

� 6.7 to 10K δT on condenser δT

Steven Taylor (ASHRAE Dec 2011), “Clearly life-cycle costs will be lower, the higher the

(chilled water) δT ...” within the range of their analysis (up to 13.9K δT)

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• Chiller efficiency improvements

– Minimum code requirements: MEPS compliant

– AHRI or Eurovent certified; assurance of performance

• CHW Plant Ancillaries do Count !

– CHW pumps

– CDW pumps

– Cooling Tower fans

• CHW Plant System Efficiency [COP] defined by

– Total Power Input includes power input of chillers and ancillaries

CHW Plant Efficiency

COOLING CAPACITY [kW]

TOTAL POWER INPUT [kW]

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CHW Plant Efficiency Scale

Source: Thomas Hartman, 2001

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CHW Plant Efficiency

• Conventional CHW plants spend significant portion of operational hours at part load

• Ancillaries’ power input are significant at part load

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

25% 50% 70% 100%

Tower Fans

CDS Pumps

EVP Pumps

Chillers

Plant Capacity

% T

ota

l kW

in

pu

t

Note: Based on two screw chillers in parallel, AHRI conditions and sequenced.

Pump heads at 400/250 kPa, cross-flow towers

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VARIABLE FLOWCHILLED WATER SYSTEMS

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13.0°C300 L/s

5.0°C300 L/s

13.0°C

13.0°C 5.0°C100 L/s

1

13.0°C 5.0°C100 L/s

2

13.0°C 5.0°C100 L/s

3

100 L/s(each)

Bypass

Primary–only CVDesign

Primary–only CVDesign

Primary CVpumpsPrimary CVpumps

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13

13.0°C250 L/s

5.0°C250 L/s

11.7°C

11.7°C 5.0°C100 L/s

1

11.7°C 5.0°C100 L/s

2

11.7°C 5.0°C100 L/s

3

100 L/s(each)

Bypass

Primary–only CVPart Load

Primary–only CVPart Load


5.0°C50 L/s

14

13.0°C300 L/s

5.0°C300 L/s

13.0°C

13.0°C 5.0°C100 L/s

1

13.0°C 5.0°C100 L/s

2

13.0°C 5.0°C100 L/s

3

100 L/s (each)

bypass(decoupler)

Primary–secondaryDesign

Primary–secondaryDesign


secondaryVV pumpssecondaryVV pumps

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15

13.0°C250 L/s

5.0°C250 L/s

11.7°C

11.7°C 5.0°C100 L/s

1

11.7°C 5.0°C100 L/s

2

11.7°C 5.0°C100 L/s

3

100 L/s(each)

bypass(decoupler)

Primary–secondaryPart load

Primary–secondaryPart load


SecondaryVV pumpsSecondaryVV pumps

5.0°C50 L/s

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Variable primaryDesign

Variable primaryDesign

13.0°C

300 L/s

5.0°C

300 L/s

13.0°C

∆∆∆∆P

13.0°C 5.0°C100 L/s

1

13.0°C 5.0°C100 L/s

2

13.0°C 5.0°C100 L/s

3

((((or flow meter)Primary VVpumpsPrimary VVpumps

0 L/s

150 L/s(each)

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Variable primaryPart load

Variable primaryPart load

13.0°C

250 L/s

5.0°C

250 L/s

13.0°C

∆∆∆∆P

13.0°C 5.0°C83.3 L/s

1

13.0°C 5.0°C83.3 L/s

2

13.0°C 5.0°C83.3 L/s

3

0 L/s

Primary VVpumpsPrimary VVpumps

125 L/s(each)

((((or flow meter)

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Variable primarySystem Flow <

Chiller Min Flow

Variable primarySystem Flow <

Chiller Min Flow

13.0°C

20 L/s

5.0°C

20 L/s

9.0°C

∆∆∆∆P

9.0°C 5.0°C40 L/s

1

OFF

2

OFF

3

5.0°C20 L/s


1 pump 40 L/s

((((or flow meter)

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VPF - Advantages

• Less capital...more space

• Energy efficient

– Pumping savings during most operating conditions, down to minimum flow

– Pumping kW ∝ {Flow} 2.0 to 2.8

• Improves reliability of system with manifold

arrangement

• Separates pumping duty from cooling duty

– Not operating pumps to start chillers

• Chillers can fully realize its maximum capacity

– Over-pumping during part load to fully load chillers before bringing on the next chiller

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VPF Chiller Selections

• Flow ‘range-ability’

– Ratio of minimum to design flow rates

– Aim for 1:2 ratio as a minimum

– Better ratios with larger centrifugal chillers than smaller screw type due to HX combinations available

– Higher velocities (high number of passes) will have higher design δP but also better range

� High design δP does not mean high energy consumption as chiller plant runs at part load most of the time

– Low flow designs may have poorer range-ability unless piped in series

– Consult manufacturers with experience

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VPF System Considerations

• System level Controls, not stand alone loops

• Basic operation

– Enable plant

– Control pumps

– Start lead chiller

– Start and stop lag chillers

– Vary flow to demand with dynamic reset

– Manage chiller and bypass operation at low flow

• Managing lead-lag

• Transient flows

• Sequence of Operation

• System integrator with experience

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Variable primaryControls

Variable primaryControls

∆∆∆∆P

40 L/s

1

OFF

2

OFF

3


((((or flow meter)

SYSTEM

LEVEL CONTROLS

∆∆∆∆P

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System Options and Analysis

• No one ideal flow or temperature for all jobs

– There is a trend of lower operating costs with lower flows up to a certain point

• Need comprehensive analysis, not spreadsheet

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Full Load – System Input kW

0

50

100

150

200

250

300

350

400

450

500

Parallel AHRI Parallel AHRI, VPF

Low Flow CHW

Low Flow CHW & CDW

Tower Fans

CDS Pumps

EVP Pumps

Chillers

Note: Based on two screw chillers in parallel, sequenced. AHRI conditions compared to Low

Flow CHW 5.5/15.5C; Low Flow CDS 28/36C. Pump heads at 400/250 kPa, cross-flow towers

Syste

m k

W

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75% Load – System Input kW

0

50

100

150

200

250

300

350


Low Flow CHW

Low Flow CHW & CDW

Tower Fans

CDS Pumps

EVP Pumps

Chillers



Syste

m k

W

26


0

20

40

60

80

100

120

140

160

180

200


Low Flow CHW

Low Flow CHW & CDW

Tower Fans

CDS Pumps

EVP Pumps

Chillers



Syste

m k

W

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0

20

40

60

80

100

120

Parallel AHRI

Parallel AHRI, VPF

Low Flow CHW

Low Flow CHW & CDW

Tower Fans

CDS Pumps

EVP Pumps

Chillers



Syste

m k

W

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Variable Condenser Flow (VCF)

• System efficiency of VCF improvements are less compared to VPF on CHW

– Tower static head remains constant

– Chiller power increases due to higher lift at low flow

– Less or not effective on lift sensitive chillers (VSD)

• Possible Improvement on system efficiency especially at low loads < 50% - requires system level

optimization controls

• Care with centrifugal chillers with surge limit and loss

of VSD benefit

– More sensitive with single stage centrifugals

– Check unloading at various condenser flows and temperatures

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CHILLER PIPING & CONFIGURATIONS

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Parallel - Parallel

6.7oC, 47 L/s1100 kW1100 kW

1100 kW1100 kW 6.7oC, 47 L/s12.2oC

12.2oC

34.6oC 34.6oC29.4oC,

59 L/s

Note: Based on two screw chillers in parallel, sequenced at AHRI conditions. Pump heads at

400/250 kPa, cross-flow towers. System COP includes chillers, pumps & tower fans

25 kW

25 kW

20 kW20 kW

29.4oC,

59 L/s

27.9 KWaterside

Lift

COP 6.1

COP 6.1

COP

Chillers 6.1

System 4.6

34.6oC

6.7oC

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Series - Parallel

5.5oC,

52.4 L/s

1080 kW1080 kW 1020 kW1020 kW15.5oC

34.7oC 34.7oC29.4oC,

57 L/s

Note: Based on two screw chillers in series evap low flow, parallel cond. Pump heads at


28 kW

19 kW21 kW

29.4oC,

62 L/s

24.6 KWaterside

Lift

COP 5.8COP 6.8

COP

Chillers 6.3

System 5.0

29.2 K

10.1oC

34.7oC

10.1oC

5.5oC

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Series – Counter-flow

5.5oC,

52.4 L/s

1200 kW1200 kW 1000 kW1000 kW15.5oC

36.1oC28.0oC,

75.5 L/s

Note: Based on two screw chillers in series evap low flow, counter-flow cond. Pump heads at


28 kW

25 kW31.7oC

26.0 KWaterside

Lift

COP 6.3COP 6.4

COP

Chillers 6.4

System 5.2

26.2 K

10.1oC

36.1oC31.7oC

10.1oC

5.5oC

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Parallel ConfigurationLarge Capacity Plants

36.0oC

Note: Based on two duplex centrifugal chillers in series evap low flow, counter-flow cond.

Pump heads at 400/250 kPa, cross-flow towers. System COP includes chillers, pumps & tower fans

4 off

2.5MW,

COP 6.59

COP

Chillers 6.6

System 5.7

28.0oC,

349 L/s

116 kWp

113 kWp

5.5oC,

217 L/s16.5oC

30.5

K

5.5oC

36.0oC

Waterside

Lift

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Parallel ConfigurationLarge Capacity Plants

36.0oC

Note: Based on two duplex centrifugal chillers in parallel evap low flow, counter-flow cond.


2 off

5.0 MW,

COP 6.91

COP

Chillers 6.9

System 6.0

28.0oC,

344 L/s

115 kWp

115 kWp

5.5oC,

217 L/s

16.5oC

26.0

K

10.0oC

36.0oC

Waterside

Lift

26.0

K

5.5oC

31.5oC

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Series – Series (counter-flow)Large Capacity Plants

15.5oC

36.0oC28.0oC,

340 L/s

Note: Based on two duplex centrifugal chillers in series evap low flow, counter-flow cond.


127 kWp

113 kWp

31.6oC

23.2

K5.5MW,

COP 7.5

COP

Chillers 7.4

System 6.3

10oC

4.5MW,

COP 7.2

5.5oC,

238 L/s

23.8

K

10oC

33.8oC36.0oC

12.7oC

24.3

K

5.5oC

29.8oC31.6oC

7.7oCWaterside

Lift

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Summary of EarthWise Chiller Plant Configurations

• Low flow CHW and CDW improves system COP

• Series connection improves performance at full and part load

• Use variable flow to improve pumping efficiency

– VPF with Series chillers maximizes pump savings

• Potential savings with variable condenser water flow at low loads

• Couple with overall chiller, pump and tower

sequencing strategy

• Include optimal tower water control

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CHILLER, TOWER AND PUMPING OPTIMIZATION

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Chiller – Tower Optimization

�Cooling Load

�Condenser watertemperature

�Chiller design

�Wet-bulb

�Condenser watertemperature

�Heat Rejection Load

�Tower Design

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Condenser water controlAt Part Load

• Hot ?

– 26 to 29ºC minimizes tower fan power, increases chiller power

• Cold ?

– 15ºC minimizes chiller power, increases tower fan power

• Wet-bulb + 3K approach ?

– Assumption that Load ∝ WB ... Not always true !

– Approach is not fixed

• Optimized ?

– Dynamic reset based on load & ambient to minimize system energy

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Chiller – Tower Optimization25% Chiller Load, 14°CWB

CT Cold Basin, °C

Po

wer

Inp

ut,

kW

0

10

20

30

40

50

60

70

80

90

14 16 18 20 22 24

CT kW

CH AFD kW

Total

CH non-AFD kW

Total

Note: AFD = adjustable frequency drive

OPT

OPT

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Chiller – Tower Optimization

TRACER

SYSTEM LEVEL

CONTROLS

TRH

FF

FF

TT

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Pumping Optimization

• Variable Flow CHW systems

• System Level critical valve reset

– Keeps critical valve near fully open

– Dynamic reset of δP set point

• Minimizes pumping power

• Better coil and temperature control

• Better acoustics Air Handling Units

Control

Valves

Pressure

Differential

Controller or

Transmitter

VFD

VV CHWPTRACER

SYSTEM LEVEL

CONTROLS

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Questions or Comments

Simon Hoe: [email protected]

HIGH PERFORMANCE CHILLED WATER SYSTEMS … · ... Efficiencies at full load at AHRI (Standard MEPS)...

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