chiller plant optimization smid
TRANSCRIPT
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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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Chicago Weather 12 x 5 73.3% 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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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
SPLV vs. IPLV The Life Cycle Point
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
Determinants of Chiller Energy
Consumption
SPLV vs. IPLV The Life Cycle Point
Questions
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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 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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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
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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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75% Load The Life Cycle Point
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
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 temperaturesleading to unintended calculation
error.
4 Steps to Optimize Chiller staging:
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Questions?