Mike Smid - TEC Vice President – Commercial Sales

Chilled Water Optimization Class

Agenda

•  Objective •  Weather •  Determinants of Chiller Energy Consumption •  SPLV vs. IPLV •  The “Life Cycle Point” •  Questions

Objective Design and implement a chilled water system that reliably delivers real and verifiable energy savings, running under the operating conditions encountered in everyday life.

Three Pillars: System Performance

Optimize total energy (not sub components)

System Reliability Under normal operating conditions Under stress

Verifiable Energy Savings Accurate, appropriate metrics

Agenda

•  Objective •  Weather •  Determinants of Chiller Energy

Consumption •  SPLV vs. IPLV •  The “Life Cycle Point” •  Questions

Chicago Weather 24 x 7 73.8% of hours have less than 70 F entering condenser water

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95-90 85-80 75-70 65-60 55-50 45-40 <40

Ent.

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ater

(F)

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rs o

f Ope

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Dry Bulb (F)

Ent Cond 80-85 F 75-80 F 70-75 F <70 F

Chicago Weather 12 x 5 73.3% of hours have less than 70 F entering condenser water

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ater

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Dry Bulb (F)

Ent Cond 80-85 F 75-80 F 70-75 F <70 F

Charlotte Weather 24 x 7

68% of hours have less than 70.4 F entering condenser water

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Charlotte Weather 12 x 5

58% of hours have less than 70 F entering condenser water

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Cooling Tower

• As the ambient wet bulb drops colder condenser water can be delivered to the chiller(s).

• VFD’s on centrifugal chillers track the weather.

Agenda

•  Objective •  Weather •  Determinants of Chiller Energy

Consumption •  SPLV vs. IPLV •  The “Life Cycle Point” •  Questions

Like pumps, chiller energy consumption is a function of mass flow and differential pressure.

kW = Tons × Lift

Compressor Input kW ~

Mass Flow X Lift

Load

Chiller

Cooling Tower

Compressor/Cycle Efficiency

Chiller Efficiency

For refrigerant to condense, it must be warmer than leaving condenser water.

95 F + 2F approach = 97F

To boil, refrigerant must be colder than leaving chilled

water.

44F – 2F approach = 42F

Refrigerant temperatures are based on leaving water temperatures!

54F 44F

85F 95F

Compressor Work (Lift)

42 F / 40 PSI 97 F / 120 PSI 82F / 90 PSI

SAT. LIQUID

SAT. VAPOR

Refrigerant Effect (Capacity)

Heat Rejection

Enthalpy

SCT

Reduced Lift

Pres

sure

42

82

97

SST

Lower Lift = Less Work = Lower kW

Compressor Work (Lift)

VFD Driven Chillers take advantage of lift and / or load reduction to reduce energy consumption.

VFD Driven Chillers take advantage of lift and / or load reduction to reduce energy consumption.

Mechanical unloading

Variable speed unloading

Chiller Efficiency

0 10 20 30 40 50 60 70 80 90

100

14% 20% 25% 31% 37% 43% 49% 56% 62% 68% 75% 81% 87% Total Building Load %

Ope

ratin

g H

ours

Individual Chiller Load %

Design Day 85°F (29.4°C) ECWT

Min Tower 55°F (12.8°C) ECWT

92% 100%

Two Chiller Plant Staging

Distribution of ton-hours

VFD Driven Chillers take advantage of lift and/or load reduction to reduce energy consumption.

VFD Driven Chillers take advantage of lift and/or load reduction to reduce energy consumption.

One chiller at 100% load

Two chillers at 100% load each

Two Chiller Plant Efficiency

Agenda

•  Objective •  Weather •  Determinants of Chiller Energy

Consumption •  SPLV vs. IPLV •  The “Life Cycle Point” •  Questions

Agenda

•  Objective •  Weather •  Determinants of Chiller Energy

Consumption •  SPLV vs. IPLV •  The “Life Cycle Point” •  Questions

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Performance Metrics Full Load, IPLV

AHRI 550/590 IPLV

% Load Weight Condition

100% 1% 44 F / 85 F

75% 42% 44F / 75 F

50% 45% 44F / 65F

25% 12% 44F / 65F

ARI 550/590 section D2 states:

“The equation (IPLV) was derived to provide a representation of the average part load efficiency for a single chiller only. …”

Full Load has two components: 100% load and design conditions.

IPLV is a weighted average of four specific operating points.

Chicago Weather 24 x 7 73.8% of hours have less than 70 F entering condenser water

0

10

20

30

40

50

60

70

80

90

0

100

200

300

400

500

600

700

800

900

95-90 85-80 75-70 65-60 55-50 45-40 <40

Ent.

Con

d W

ater

(F)

Hou

rs o

f Ope

ratio

n

Dry Bulb (F)

Ent Cond 80-85 F 75-80 F 70-75 F <70 F

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Performance Metrics System based metrics – SPLV (System Part Load Value)

ARI 550/590 section D2 states:

“The equation (IPLV) was derived to provide a representation of the average part load efficiency for a single chiller only. However, it is best to use a comprehensive analysis that reflects the actual weather data, building load characteristics, operational hours, economizer capabilities and energy drawn by auxiliaries such as pumps and cooling towers, when calculating the chiller and system efficiency. This becomes increasingly important with multiple chiller systems because individual chillers operating within multiple chiller systems are more heavily loaded than single chillers within single chiller systems.”

Actual Local Weather Load Profile Operating Hours Economizer Pump, Tower Energy Chiller Staging

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Chiller Staging Chicago Office Building

87.5%

62.5%

37.5%

100% Bin

75% Bin

50% Bin

25% Bin

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1 3

4

5

3 x 400 Ton Chillers: CH-1 (black), CH-2 (Yellow), CH-3 (Blue) M

inim

um B

uild

ing

Load

2

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Performance Metrics 100% Building Load

Design Day Weather Fully Leased Fully Occupied Full Solar Load Full Equipment and Lighting Load Full Ventilation Rates

< 1% of the operating hours – OR MAYBE NEVER

1

1

Are the chillers sized to meet the building load exactly … or were they maybe oversized … just a little.

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Performance Metrics 100% Chiller Load

Design Leaving Chilled Water Design Entering Condenser Water No Low Delta T Syndrome! No safety factors when chillers sized Tubes fouled to AHRI selection level Assumes Chillers not oversized !!!

•  Far more ton-hours occur at points 3 and 5 than at point 1

•  Variable speed chillers have better 100% load efficiency at points 3 and 5 due to lower lift.

3 5 1

1

3333

5

5

55

85F 70F 60F

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Performance Metrics SPLV vs. IPLV

Weighting significantly different. SPLV reflects multiple chiller plant staging SPLV reflects local condenser water temperatures

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Performance Metric IPLV weighting issue (multiple chillers)

IPLV (kW/Ton) Single Chiller Plant

Actual Plant

Chiller A Chiller B Chiller C 100% 0.640 0.536 0.577 75% 0.420 0.399 0.390 50% 0.280 0.291 0.267 25% 0.260 0.341 0.301 IPLV 0.325 0.337 0.314 SPLV 0.399 0.373 0.362

2,000 Ton Hotel, with (4) 500 Ton chillers Worldwide Study

75% Load “The Life Cycle Point”

75% Load “The Life Cycle Point”

2,000 Ton Hotel, with (4) 500 Ton chillers Worldwide Study

600 Ton Office, with (2) 300 Ton chillers

Carrier Worldwide Study

75% Load “The Life Cycle Point”

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Back Up

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System Based Decisions Chiller Staging

Component Calculation

(1) Chiller at “full load”* 0.575

(2) Chillers at 50% load* 0.295

Delta 0.280

Capacity (tons) 300

Savings (per hour) 84 kW

Compare efficiency at the same temperatures. Compare the AHRI tolerance at the load points Compare the pump power consumption Consider the minimum evaporator flow rate

System Calculation (1) Chiller at 100% load, 65 F Condenser Water, no AHRI tolerance 0.338 x 1.05% = 0.355

(2) Chillers at 50% load, 65 F Condenser Water, no AHRI tolerance 0.295 x 1.10% = 0.325

Capacity (tons) 300

Chiller Savings 9 kW

Condenser pump power (750 gpm x 30 ft wg) 6.8 kW

Evaporator pump power (600 gpm x 20 ft wg)* 3.6 kW

Extra pump power 10.4 kW

Net Savings (per hour) -1.4 kW

* Constant flow application, use minimum flow rate calculation for variable flow systems.

*Submittal data at 100% and 50% load is often based on two different condenser water temperatures leading to unintended calculation error.

4 Steps to Optimize Chiller staging: 4

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Questions?