Chiller Plant Optimization Smid

8/11/2019 Chiller Plant Optimization Smid

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Mike Smid - TEC

Vice President Commercial Sales

Chilled Water Optimization Class


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Agenda

Objective

Weather

Determinants of Chiller Energy Consumption

SPLV vs. IPLV

The Life Cycle Point

Questions


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Objective

Design and implement a chilled water systemthat reliably delivers real

and verifiable energy savings, running under the operating conditionsencountered in everyday life.

Three Pillars:

System Performance

Optimize total energy(not sub components)

System Reliability

Under normal operating conditions

Under stress

Verifiable Energy SavingsAccurate, appropriate metrics


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Agenda

Objective

Weather Determinants of Chiller Energy

Consumption

SPLV vs. IPLV The Life Cycle Point

Questions


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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


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


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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).

VFDs on centrifugal chillers track the weather.


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Agenda

Objective

Weather

Determinants of Chiller Energy

Consumption


Questions


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

kW = Tons Lift

Compressor Input kW ~

Mass Flow X Lift

Load

Chiller

Cooling

Tower

Compressor/Cycle

Efficiency

Chiller Efficiency


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For refrigerant to

condense, it must bewarmer than leaving

condenser water.

95 F + 2F approach = 97F

To boil, refrigerant must be

colder than leavingchilledwater.

44F 2F approach = 42F

Refrigerant temperatures are based on leavingwatertemperatures!

54F

44F

85F

95F

Compressor Work (Lift)


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42 F / 40 PSI

97 F / 120 PSI

82F / 90 PSI

SAT.

LIQUID

SAT.

VAPOR

Refrigerant Effect

(Capacity)

Heat Rejection

Enthalpy

SCT

Reduced Lift

Pressure

42

82

97

SST

Lower Lift = Less Work = Lower kW

Compressor Work (Lift)


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

Mechanicalunloading

Variablespeedunloading

Chiller Efficiency


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0102030

405060708090

100

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

Op

eratingHours

Individual

Chiller

Load %

Design Day

85F (29.4C)

ECWT

Min Tower

55F (12.8C)

ECWT

92% 100%

Two Chiller Plant Staging

Distribution of ton-hours


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

One chiller at 100% load

Two chillers at100% load each

Two Chiller Plant Efficiency


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Agenda

Objective

Weather


Consumption


Questions


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Agenda

Objective

Weather


Consumption


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 arepresentation of the average part load efficiency for a

single chil ler only.

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

IPLV is a weighted average of four specific operating points.


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900

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


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Performance MetricsSystem based metrics SPLV (System Part Load Value)

ARI 550/590 section D2 states:

The equation (IPLV) was derived to provide a representation of theaverage 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 capabilitiesand energy drawn by auxiliaries such as pumps and cooling towers, whencalculating 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

6

13

4

5

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

Minim

umBuildingLoad

2


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Performance Metrics

100% BuildingLoad

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 buildingload exactly or were they maybe

oversized just a little.


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Performance Metrics

100% ChillerLoadDesign 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 chillershave better 100% load

efficiency at points 3

and 5 due to lower lift.

35 1

1

3

3

3

3

5

5

5

5

85F70F60F


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Performance Metrics

SPLV vs. IPLV

Weighting significantlydifferent.

SPLV reflects multiple chiller plant stagingSPLV 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 0.39050% 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


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

Worldwide Study

75% Load The Life Cycle Point


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

Worldwide Study


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600 Ton Office, with (2) 300 Ton chillers

Carrier Worldwide Study



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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 temperaturesleading to unintended calculation

error.

4 Steps to Optimize Chiller staging:

4


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Questions?

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Chiller Plant Optimization Smid