chilled water system optimization

POWERFUL BUSINESSPOWERFUL BUSINESS““Facing a Dynamic Energy Future Facing a Dynamic Energy Future ””

CHILLED WATER SYSTEM CHILLED WATER SYSTEM OPTIMIZATONOPTIMIZATON

Presented by

David A. Rogers, P.EHarold A. Hougham, P.E.

CHILLED WATER SYSTEM OPTIMIZATONCHILLED WATER SYSTEM OPTIMIZATON

ENGINEERING APPLIED TO OPERATIONS

(Retro Commissioning)

THE CONCEPT

SYSTEM FUNDAMENTALS

THE PROCESS

THE RESULTS


THE CONCEPT


SYSTEM FUNDAMENTALS


THE THREE RULES FOR HYDRONIC SYSTEMS OPTIMIZATION

PUMP LESS WATER

PUMP LESS WATER

PUMP LESS WATER


“Distribution System DELTA T

Drives the Plant (s)”


SyllabusSystems ConceptsSimple FormulasRules of Thumb

System ConfigurationsHydraulic Profile

System ComponentsDelta T

Flow Limited PlantHow your System works – Now/Optimized


Systems Concepts

A system is a group of components that when connected and operating

provide a desired result.


Systems Concepts

ProductionProduction DistributionDistribution LoadLoad


Systems Concepts

Chillers

LoadPumps

Pumps

Cooling Tower


Systems ConceptsChilled Water System

Dec

oupl

er

Secondary Pumps

Load

Distribution System

Production System

Primary Pumps

Chillers

Data & Controls


Simple FormulasChilled Water Delta T = T return water - T supply water

GPM/TON = 24/Delta T

Pump Affinity Laws = Q1/Q2=N1/N2H1/H2=(Q1/Q2)2BHP1/BHP2=(Q1/Q2)3

Q = Flow, N = rpm, H = Head

BHP = Brake Horsepower


Simple Formulas

Chilled Water Delta T = T return water – T supply waterChilled Water Delta T = 60 – 42 = 18 degrees.

CHWR T = 60oF

CHWS T = 42oF

Cooling Coil

Control ValveChilled Water Delta T


Simple Formulas

How many tons of cooling are served by a 6,000 gpm/12 degree delta T distribution system?

GPM = 6,000

Delta T = 12 degrees

24/Delta T = 24/12 = 2 GPM/Ton

Tons Cooling = GPM/(24/Delta T) = 6,000/2 = 3,000 tons

HOW MANY CHILLERS DO I HAVE ON LINE TO SERVE THIS 3000 TON LOAD?

GPM/Ton = 24/Delta T


Simple Formulas

What is the approximate required pumping horsepower if I cut system flow in half while still serving the same cooling load?

10,000 GPM requires 240 BHP

5,000 GPM requires ? BHP.

Q1 = 10,000 GPM, Q2 = 5,000 GPM, BHP1 = 240

BHP2 = BHP1(Q2/Q1)3 or BHP2 = 240(5,000/10,000)3 = 240/8 ≈ 30 BHP

Pump Affinity LawsPump Affinity Laws can be used to estimate system performance

but should be modified to reflect system performance.


Rules of Thumb•Water Always Flows from a Higher Pressure to a Lower Pressure.

•Minimum Delta P for a control valve = 5 psig

•Minimum Delta P for a Bldg Interface = 20 psig

•Distribution System Delta T should always be ≥ Production System Delta T

•Production System Delta T should always be < Chiller Delta T


Rules of ThumbMinimum Delta P Across a Control Valve is 5 psig

WHAT HAPPENS IF DELTA P IS ZERO?

Delta P = 18 – 11 = 7 psig

Cooling Coil

Control Valve

P3= 11 psig P1= 18 psig


Rules of ThumbMinimum Delta P Across a Building Interface is 20 psig

WHAT HAPPENS IF DELTA P IS 10 PSIG?

Building

Pressure Compensating Control Valve

Delta P = 40 – 18 = 22 psig

Pout= 18 psig

Pin= 40 psig


Rules of Thumb

Distribution Delta T = 58 – 42 = 16 degrees

Production Delta T = 56 – 42 = 14 degrees

Distribution System Delta T should always be ≥ Production System Delta T

Secondary Pumps

Load

Distribution System

Production System

Primary Pumps

ChillersTPS=42oF TDS=42oF

TDR=58oFTPR=56oF


Rules of ThumbProduction System Delta T < Distribution System Delta T

58

58

58

58

Distribution CHWR

6.4

12.8

14.4

16

Production Delta T

1648.440800

1654.8801600

1656.4901800

16581002000

Delta T

Production CHWR

Chiller % Load

Load in

Tons


Rules of Thumb

0.5

0.55

0.6

0.65

0.7

0.75

1009080706050403020

% Full Load

KW

/Ton

CHILLER 3

CHILLER 4&5

CHILLER 6&7

Production System Delta T should always be < Chiller Delta T


System Configurations

• Primary/Secondary – Constant Flow/Variable Flow• Primary Only – Constant Flow• Variable Primary Flow (VPF) – Variable Flow• Multiple Plants/Common Distribution Loop

–Plant 1 – Primary/Secondary–Plant 2 – Primary Only–Plant 3 –Primary/Secondary


Primary/SecondaryConstant Flow/Variable Flow

Secondary Pumps

Load

Distribution System

Production System

Primary Pumps

Chillers


Primary OnlyConstant Flow

Load

Distribution SystemProduction

System

ChillersSecondary Pumps

Primary Pumps


Variable Primary FlowVariable Flow

Load

Production/Distribution System

Chillers

Production/Distribution Pumps


Multiple Plants on a Common Distribution Loop


Hydraulic ProfileA graphical representation of the

dissipation of system head.

Ft o

f H

ead

Distance


Hydraulic ProfilePrimary/Secondary System

Ft o

f Hea

d


Hydraulic ProfileTwo Plants Common Distribution Loop

Ft o

f Hea

d


Hydraulic ProfileThe Hydraulically Most Remote Point

Hydraulically most remote point & location of VFD DP sensor

Physically most remote point

Distance

Ft o

f H

ead


Hydraulic ProfileBuilding System/Hydraulically Most Remote Point

Ft o

f Hea

d


System Components

• Chillers• Cooling Towers• Pumps•Control Valves/Cooling Coils


Chillers/Cooling Towers


Chiller Performance

P-1

Pressure

Enthalpy

CompressorWork

Point 4

Point 3 Point 2

Point 1

LIFT

Pressure = CTemperature = C

Pressure = C

Q2-3 = m(h2 – h3)

Q4-1 = m(h4 – h1)W1-2 = m(h2 – h1)

h3 = h4

COP = Output/InputCOP = Q4-1/W1-2


Cooling Tower PerformanceEntering Condenser Water 95

degrees

Leaving Condenser Water 85 degrees

Outside Air Wet Bulb Temperature 76 degrees

Range 95 – 85 = 10 degrees

Approach 85 – 76 = 9 degrees


Cooling Tower Performance

0.5

2.5

2.0

1.5

1.0

Tow

er S

ize

Fact

or

Approach30252015105

ConstantsHeat LoadRangeWet Bulb


Pumps

How They Work

Arrangements


Pumps – How They Work


Pumps – How They Work

Velocity

PressureA

BC

A

B C

Flow Path

Suction

Centrifugal Pump

Outlet Tip of Impeller Vane

Discharge

Inlet Tip of Impeller Vane


NPSH = Net Positive Suction HeadPumps – How They Work

Velocity

PressureA

BC

A

B C

Flow Path

Suction

Centrifugal Pump

Outlet Tip of Impeller Vane

Discharge

xxxx

Vapor Bubbles

Collapsing Bubbles

Pump Impeller Blade


Pumps – How They WorkTypical Pump Curve


Pumps – How They WorkVariable Frequency Drives


Pumps – How They WorkVariable Speed Pump Curves


Pumping Arrangements

Hea

d Ft

.

Hea

d Ft

.


Cooling Coil/Control Valve

ConfigurationsHow They Work


Cooling Coil/Control ValveConfigurations

Entering Air 70 degreesLeaving Air 55 degrees

CHWS 42 degrees

CHWR 56+ degrees

CONTROL VALVE

COOLING COILDelta T: 56 – 42 = 14 degrees


How They Work“Control Valves Waste Energy”

Cooling Coil/Control ValveFt

of H

ead


Cooling Coil/Control ValveHow They Work

Valve Seat Fixed

Valve Disc Not FixedValve Shaft

Actuator Arm Connected to the Valve Shaft

FLOW


Cooling Coil/Control ValveHow They Work


Delta T• Difference between CHW Return & CHW Supply

and Chilled Water Supply TemperaturesDelta T = TCHWR Delta T = TCHWR -- TCHWSTCHWSQ = C x Q = C x GPMGPM x x Delta TDelta T

• For the same Q if delta T is low then GPM is high & if delta T is high then GPM is low!

5,000,000 5,000,000 BtuhBtuh = C x = C x 1000 1000 gpmgpm x x 10 F10 F= C x = C x 500 500 gpmgpm x x 20 F20 F


Low Delta T / Flow Limited Plant

Chiller

Decoupler

Load Typical

Pressure Compensating Valve Typical

2,000 Ton Chillers, 14 degree delta T, 3,429 gpm each Secondary Pump P-2,

Variable Flow 42 degree CHWS

DistributionLoop

ProductionLoop

Chiller

Chiller

38.3

50

50

100

Percent Loaded

50

50

54

56

Distribution CHWR

8

8

12

14

Dist.Delta T

6900

6000

4000

3429

Distribution Gpm

(3)6000102872300

(2)400068582000

(2)400068582000

(1)200034292000

On Line Tonnage

Production Gpm

Load in Tons


Delta T Flow Limited PlantCENTRIFUGAL CHILLER EFFICIENCIES

0.5

0.55

0.6

0.65

0.7

0.75

1009080706050403020

% Full Load

KW

/Ton

CHILLER 3

CHILLER 4&5

CHILLER 6&7


Delta T Flow Limited Plant

Estimated Annual Part Load Chiller Savings due to Increased Efficiency for non Flow

Limited Operations

• Flow limited average kw/ton = 0.55• Non flow limited average kw/ton = 0.523• Annual average part load = 2000 tons• Annual part load hours of operation = 8,000• Cost of electricity including demand = $0.14• Estimated annual part load chiller

savings due to increased efficiency of operation =

(0.55-0.523)(2000)(8000)(0.14) = $60,480


High Delta T / Full Load Plant

Chiller

Decoupler

Load Typical

Pressure Compensating Valve Typical

2,000 Ton Chiller, 14 degree delta T, 3,429 gpm Secondary Pump P-2,

Variable Flow 42 degree CHWS

DistributionLoop

ProductionLoop

100

100

100

Percent Loaded

60

58

56

Distrib. CHWR

18

16

14

Dist.Delta T

2667

3000

3429

Distribution Gpm

5634292000

5634292000

5634292000

Production CHWR

Production Gpm

Load in Tons


High Delta T / Part Load Plant

80

90

90

100

Percent Loaded

62

60

58

56

Distrib.Gpm

1920

2400

2700

3429

Distribution Gpm

2053.234291600

1854.634291800

1654.634291800

145634292000

Dist.Delta T

Production CHWR

Production Gpm

Load in Tons


Chilled Water Cost VariablesVariables Constants

Average Annual Cooling Load 4,500 Tons Flow 500Electric Chiller/Tower/Condenser & Production Pumps 0.9 Kw/Ton Ton 12000 BtuhAbsorption Chiller/Tower/Condenser & Production Pumps 0.3 Kw/Ton Power 0.746 Kw/HpDistribution System Delta T 11 Degrees F Max Speed 60 HzCost of CHP Electrical Power $0.065 $/Kwh GPM/Ton 24Power Factor 0.9 System Curve Constant 0.8Pump Efficiency 0.87 MM 1,000,000Pump Design Flow 15000 GPMPump Design Head 155 FtPump Hp 750 Hp AssumptionsElectric Chiller Capacity 2000 TonsAbsorption Chiller Capacity 1385 Tons Absorption Chillers are always lead chillersNumber of Electric Chillers 1 Electrical Cost includes all byproduct burdensNumber of Absorption Chillers 2 Building Pumping is not considered a CHP operatioElectric Chillers 12 Delta TAbsorption Chillers 16 Delta T

Costs not IncludedCalculations

Capital FundingDistribution Flow 9818 GPM Sinking FundsDistribution Pump Hp each 210 Hp Load Flow AdministrativeDistribution Pumping Kw each 200 KwAbsorption Chillers Operating 2 2Electric Chillers Operating 1 2Number of Distribution Pumps Running 1Percent rpm each pump 65%Annual Average Cost of Cooling $5.57 $/MMBtuElectric Chillers Flow 4000 GPMAbsorption Chillers Flow 2078 GPM


How does your System work Now ?

Existing Distribution System Maximum Delta T = ??degrees

Existing Distribution System Average Delta T = ?degrees

Chillers – Staging?System Pumping Energy – Optimized or not

Optimized? (Control Delta P)


How should your System work when Optimized?

Optimized Maximum Delta T = ?? degreesOptimized Average Delta T = ?? degrees

Chillers – Staging ??System Pumping Energy – Optimized or not

Optimized ??


THE PROCESS



Step #1

Chilled Water Systems Questionnairefor Initial System Evaluation

SYSTEM DATAROI


Step #2

Pre Project Staff Training


Step #3

Pre Project Measurement & Verification (M&V)

BEFORE AFTER

Data Historian/Sensors Project ?Data Historian/Sensors Project ?

CHILLED WATER SYSTEM OPTIMIZATONCHILLED WATER SYSTEM OPTIMIZATONStep #4

Chilled Water System Engineering Evaluation & Analysis


0100200300400500600700800

8 10 12 14 16 18 20 22 24

System Delta T

Pum

ping

HP

750 HP; 14,000 GPM; 8o∆ T;


Step #5

Report of Findings and Recommendations

ROI


Step #6

Implement Chilled Water System Optimization Construction Project


Step #7

Commission Chilled Water System Optimization Project


Step #8

Post Project M&V for Rebate Verification

BEFORE AFTER


Step #9

Post Project Staff Training

THE RESULTS


The University of California Davis Medical Center,

Sacramento



UCDMC1. 3,000,000 square feet Trauma

Center/Hospital/Clinic & Educational Buildings.

2. 26 MW CHP w/ Primary/Secondary 16 degree plant serving a 12 degree campus.

3. Each building was decoupled and pumped.

4. Average distribution system delta T was 8 degrees. Maximum delta T was 11 degrees.


ResultsOperations

1. 18 degree distribution system delta T w/ 114 degrees outside air temperature.

2. Central plant spare distribution pump and chiller capacity.

3. Some buildings performing in excess of 20 degree delta T.

4. Average system delta T is 12 degrees.


Results

Financial1. Financial data not available due to lack of system

instrumentation.

Energy2. Energy data not available due to lack of system

instrumentation.


Lessons Learned1. Create a system optimization sensor project to

facilitate data acquisition for pre & post project M&V.

2. Provide pre project staff/management training to facilitate a coordinated effort for all parties.

3. Develop a detailed Site Acceptance Test for control valve commissioning.

BIOTECHNICAL CORPORATION



Biotechnical Corp1. 3,000,000 square feet of R&D, Office & Production

across 25 buildings.

2. Three Central Plants on common distribution loop, 14,100 ton installed capacity.

3. Delta T performance was 6 degrees part load and a maximum of 11 degrees at full load.

4. A 14 degree campus.


ResultsOperations

1. Achieving distribution loop 20 degree Delta T @ full and part load.

2. Maximum flow distribution pumping requires 3 and not 4 operational pumps

3. Delayed major capital infrastructure expansion project for 3 years due to optimizing use of existing infrastructure.


Results

Financial1. Financial data not available due to lack of

system instrumentation.

Energy1. Energy data not available due to lack of

system instrumentation.


Lessons Learned1. Discovered other system issues that were masked

by poor system performance; Damper Failures, Sensor Calibration, etc.

2. Train installing controls contractor on Systems Optimization Concept and Process.

3. Verify AHU isolation valve arrangement and function prior to issuing contract requiring continued system operation during construction.

The University of Iowa

Hospital and Clinics



UIHC

1. 4,000,000 square feet of contiguous hospital/clinic space between five buildings.

2. Central Plant metered and billed for each building.

3. Each building is decoupled and pumped.


ResultsOperations

1. Resolved low chilled water pressure & flow to Operating Room Air handlers.

2. Resolved condensation issue on cooling panel ceilings in patient rooms.

3. Removed tertiary building pumps and reduced operation of building pumps


Results

Financial1. Savings $2,800,000 for the last 2 cooling seasons

primarily from penalty reduction.

2. Chilled Water billing based on building flow and an assumed Delta T of 16 Degrees.


Results

Energy1. Original simple payback estimate 5 years.

2. System instrumentation was not adequate to measure actual energy reduction.


Lessons Learned1. Building system instrumentation not adequate

to provide M&V for energy consumption.

2. Building system energy savings and production/distribution billed savings are not the same number.

3. Production/distribution system billed savings represented a simple payback of less than 9 months.


[email protected]@ra-solutions.comwww.ra-solutions.com

chilled water system optimization

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