high performance-chilled-water-systems ashrae-chicago

High Performance Chilled Water Systems

Mick Schwedler, PE, LEED® APManager Applications EngineeringTrane

Normal Performance Chilled Water Systems ASHRAE/IESNA 90.1 (LEED Prerequisite)

System configuration

Design parameters

System control

ASHRAE Standard 90.1-2007 Purpose

“… Provide minimum requirements for the energy-efficient design of buildings except low-rise residential buildings”

Purpose ofANSI/ASHRAE/IESNA Standard 90.1-2010

To establish minimum energy efficiency requirements of buildings, other than low-rise residential buildings for:

1. design, construction, and a plan for operation and maintenance, and

2. Utilization of on-site renewable energy resources.

Publication and Final Savings Estimates Performed by Pacific Northwest National

Laboratory (PNNL) Savings of 90.1-2010 compared to

90.1-2004

Savings shared are modeled as of January 2011

Include ventilation changes in ASHRAE 62.1 between 1999 and 2007 versions

90.1 Progress Indicator Including receptacle loads in modeling

Including receptacle load in % savings calculation

Energy cost savings %

25.5Ventilation rate changes

between 62.1-1999 and 62.1-2007

Energy savings %

90.1 Progress IndicatorExcluding receptacle loads in % savings calculation only

Including receptacle loads in modeling

Excluding receptacle load in % savings calculation

Energy cost savings %

32.6Ventilation rate changes

between 62.1-1999 and 62.1-2007

Energy savings %

LEED Energy and Atmosphere LEED 200910% energy cost savings beyond 90.1-2007

LEED 2012Public Review 2: September 2011 EA Prerequisite: 10% average energy cost and source

energy savings beyond 90.1-2010 (new construction) EA Credit: Credit for reductions beyond 10%

90.1-2010Chiller EfficienciesPaths A & B

Equipment Type Size CategoryUnits

Before 1/1/2010 As of 1/1/2010c Test Procedureb

Path A Path Bd

Full Load IPLV

Full Load IPLV ARI 550/590

Air-cooled<150 tons EER ≥9.562 ≥10.416 ≥9.562 ≥12.50 NA NA

≥150 tons EER ≥9.562 ≥10.416 ≥9.562 ≥12.75 NA NA

Water Cooled Electrically Operated, Positive Displacement

<75 tons kW/ton≤0.790 ≤0.676

≤0.780 ≤0.630 ≤0.800 ≤0.600

≥75 tons and < 150 tons kW/ton ≤0.775 ≤0.615 ≤0.790 ≤0.586

≥150 tons and < 300 tons kW/ton ≤0.717 ≤0.627 ≤0.680 ≤0.580 ≤0.718 ≤0.540

≥300 tons kW/ton ≤0.639 ≤0.571 ≤0.620 ≤0.540 ≤0.639 ≤0.490

Water Cooled Electrically Operated,

Centrifugal

<150 tons kW/ton ≤0.703 ≤0.669≤0.634 ≤0.596 ≤0.639 ≤0.450≥150 tons and

< 300 tons kW/ton ≤0.634 ≤0.596

≥300 tons and < 600 tons kW/ton

≤0.576 ≤0.549≤0.576 ≤0.549 ≤0.600 ≤0.400

≥600 tons kW/ton ≤0.570 ≤0.539 ≤0.590 ≤0.400

Must meet both full and part load requirements

Heat rejection equipment Fan speed control 7.5 and

greaterCapability to operate at 2/3

fan speed or less

ExceptionsClimates > 7200 CDD50

(e.g. Miami)

1/3 of fans on multiple fan application

Hydronic system design and control Pump isolation

Chilled and hot water reset if >300,000 BtuhException: Variable flow systems that

reduce pumping energy

90.1-2007Hydronic System Design & ControlThese provisions apply if pump system power > 10 hp:

Must be variable flow unless … Pump power ≤ 75 hp ≤ 3 Control valves

Limit demand of individual variable-flow pumps to 30% of design wattage at 50% flow (e.g., use VSD) Pump head > 100 ft Motor > 50 hp

WatersideEnergy Recovery required Service Water Heating24 hrs per day and

Heat rejection > 6 MMBtuh and

SWH load 1 MMBtuh

Recover smaller of60% of heat rejection

Preheat water to 85°F

ConfigurationNormal Performance Chilled Water

productionpumps

two-way valve

distributionpump

distributionloop

productionloop

Design ParametersNormal Performance Chilled Water Plant ARI 550/590 Standard Conditions44°F chilled water

2.4 gpm/ton chilled water (10°F T)

3.0 gpm/ton condenser water (10°F [9.3] T)

ControlNormal Performance Chilled Water Plant Chilled water distribution pump

P at most remote load

Cooling tower fans55°F (as cold as possible)

Constant speed condenser water pumps

All these “normal” assumptions will be examined

High PerformanceChilled Water Plants Standard high performance

Reduced flow rates, increased ∆Ts

Variable primary flow

Advanced high performance Equipment capabilities

System configurations

System control

a history ofChiller Performance

ASHRAE Standard 90

0.0NBI “best”

available90-75(1977)

90-75(1980)

90.1-89 90.1-99

centrifugal>600 tons

screw150-300 tons

scroll<100 tons

reciprocating<150 tons

chilled water plant design …ProvocationAre our “rules of thumb” …

44 F chilled water supply

10 F T for chilled water system

3 gpm/ton condenser water flow

… in need of repair?

High Performance Design Parameters ASHRAE GreenGuide and CoolTools™

Chilled water T: 12°F to 20 °F

Condenser water T: 12°F to 18 °F (multi-stage)

Kelly and Chan Chilled water T: 18°F

Condenser water T: 14.2°F(3.6 - 8.3% energy savings in various climates)

chilled water plant …humid climateBase Design: 450 Tons 0.5% design

wet bulb: 78 F

Entering condenser water temperature (ECWT): 85 F

Evaporator and condenser temperature differences: 10 F

Coil, valve and chilled water piping pressure drop: 80 ft

Condenser water piping pressure drop: 30 ft

Pump efficiency: 75%

Pump motorefficiency: 93%

traditional design …humid climateSystem Energy Consumption

2.4/3.0

Chilled /Condenser Water Flows, gpm/ton

TowerCondenser Water PumpChilled Water PumpChiller (100% Load)

traditional vs. low-flow design …System Summary At Full Load

2.4/3.0 1.5/2.0

comparison …humid climateSystem Summary At 75% Load

2.4/3.0 1.5/2.0

comparison …humid climateSystem Summary At 50% Load

2.4/3.0 1.5/2.0

comparison …humid climate System Summary At 25% Load

2.4/3.0 1.5/2.0

traditional vs. low-flow design …humid climateSavings Summary

25% 50% 75% 100%

High PerformanceDesign Parameters

41/16 42/14 43/12 44/10

Chilled water supply temperature/DeltaT

Chilled waterpumpChiller

Pipe Size Example90.1-2010 Table 6.5.4.5

Past DesignPractice

ASHRAE GreenGuide

∆T (°F)

Flow(gpm)

Pipe Size

∆T (°F)

Flow(gpm)

Pipe Size

Chilled Water

10 1920 10 16 1200 8

Condenser Water

9.4 2400 14 14 1600 12

800 ton system

3,000 hours of operation

Chilled water, variable flow

Condenser water, constant flow

High PerformanceDesign OptionsEither …

Take full energy (operating cost) savings

Or …

Reduce piping size and costExperienced designers use pump,piping and tower savings to select aneven more efficient chiller

Reduced flow works for all chiller manufacturers Logan Airport - Boston:

$426,000 Construction cost savings

7.3% operating cost savings

Large Chemical Manufacturer -Greenville $45,000 Excavation and concrete savings

6.5% Operating cost savings

Computer Manufacturer - San Francisco Existing tower, pipe savings

2% Operating cost savings (tower not changed)

Low flow works for retrofit applications Chilled water side

Coil It’s a simple heat transfer device Reacts to colder entering water

by returning it warmer

Ideal for system expansion

Low flow works for retrofit applications

Condenser side retrofit opportunity Chiller needs to be

replaced

Cooling needs haveincreased by 50%

Cooling tower wasreplaced two years ago

Condenser pump and pipes are in good shape

Condenser side retrofit opportunity

Existing Retrofit

Capacity (tons) 500 750

Flow rate (gpm) 1500 1500

Condenser Entering WaterTemperature (F)

Condenser Leaving WaterTemperature (F)

95 103

Design Wet Bulb (F) 78 78

25% 50% 75% 100%

System Load

3.0 gpm/ton2.0 gpm/ton

Humid climatesLow flow works for short piping runs too

Condenser Water Side Only - original

25% 50% 75% 100%

System Load

3.0 gpm/ton2.0 gpm/ton

Humid climatesLow flow works for short piping runs too

Condenser Water Side OnlyZERO piping pressure drop

High Performance Design Parameters Low flow benefits systems - no

matter whose chiller is being used

Low flow works extremely well on existing systems

Low flow works on short piping runs

always, always,Always Remember …

Oh, by the way...

You may also do this with air

Variable-Primary-Flow Systems

variable-flowpumps

controlvalve

checkvalves

VPF Savings First cost: 4-8%

Annual energy: 3-8%

Life-cycle cost: 3-5%

http://www.arti-21cr.org/ARI/util/showdoc.aspx?doc=1085

Flow requirementsVPF System Limits (consult manufacturer)

Absolute flows - Minimum and maximum

Flow rate changes 2% of design flow per minute

not good enough 10% of design flow per minute borderline 30% of design flow per minute

many comfort cooling applications 50% of design flow per minute

Always need a way to ensure minimum flow (bypass)

Chiller ControlVariable W ater Flow

3:50:00 3:55:00 4:00:00 4:05:00 4:10:00Tim e (hour:m in:sec)

]Evaporator W ater F low

Evap Entering W ater Tem p

Evap Leaving W ater Tem p

More informationVPF System Http:/trane.com/commercial

/library/newsletters.asp (1999 and 2002)

“Primary-Only vs. Primary-Secondary Variable Flow Systems,” Taylor, ASHRAE Journal, February 2002

“Don’t Ignore Variable Flow,” Waltz, Contracting Business, July 1997

“Comparative Analysis of Variable and Constant Primary-Flow Chilled-Water-Plant Performance,” Bahnfleth and Peyer, HPAC Engineering, April 2001

“Campus Cooling: Retrofitting Systems,” Kreutzmann, HPAC Engineering, July 2002

High Performance Chilled Water Plants Standard high performance

Advanced Equipment capabilities

System control

Equipment CapabilitiesHigh Performance Chilled Water Plant Constant speed0.570 FL / 0.479 IPLV

Higher efficiency “same price” optionsVariable speed (spend money on drive)

Constant speed (spend money on copper)

Purchase both a drive and more heat exchange surface

Down to 0.45 kW/ton FL available (22% reduction)

Same-price Chiller: Example Performance

Option Full Load(kW/ton)

IPLV(kW/ton)

VSD 0.572 0.357High Efficiency 0.501 0.430

Same-price Chiller: Example Performance

0% 20% 40% 60% 80% 100%

% Load

600-ton Replacement Chiller Performance

High_efficiency_85°FVSD_85°FHigh_efficiency_75°FVSD_75°FHigh_efficiency_65°FVSD_65°F

Example Office building

Two 400-ton chillers

Comparisons Base system - constant speed

AFD on both chillers

High efficiency for both chillers

AFD on one chiller

High efficiency for one chiller

What is the actual utility rate? Utility costs ‘Combined’ utility rates ($0.10 / kWh)

Actual utility rates ($12 / kW and $0.06 / kWh)

Utility rate comparison

Simple paybacks, humid climate

Combined rate Actual rate

AFD 6.1 10.8on one chiller High efficiency 6.3 7.7

AFD 7.2 12.7on both chillers High efficiency 7.1 8.3

Using incorrect “combined” rate leads to incorrect decisions

Rule 1

Use actual utility rates

Temperate climatewith economizer

Annual operating cost

$20,000

$40,000

$60,000

$80,000

$100,000

Base case AFD on both chillers

High efficiency both chillers

AFD on one chiller

High efficiencyone chiller

Simple payback

Chiller plant operating costSimple payback

Temperate climate,no economizer

$20,000

$40,000

$60,000

$80,000

$100,000

AFD on one chiller

Simple payback

Humid climate,no economizer

$20,000

$40,000

$60,000

$80,000

$100,000

AFD on one chiller

Simple payback

Dry climate with economizer

$20,000

$40,000

$60,000

$80,000

$100,000

AFD on one chiller

Simple payback

024681012141618

Rule 2

Model ROI of each investment

Guidance: VSD or High Efficiency? High efficiency

Significant demand charges, especially ratchet charges

Climates where the wet bulb doesn’t vary substantially

Multiple chillers in the plant

Economizer that reduces low load/low lift operating hours

VSD Many hours at low

condenser water temperature – and low load

Perhaps only on one chiller

Factor replacement cost of VSD when performing life cycle assessment

High Performance Chilled Water Plants Standard high performance

System control

VPF System Minimum flow and bypass control

Single chiller

Retrofit

Controller

What may not be a good VPF application? Two packaged chillers

Limited evaporator configurations

Assume minimum flow is about 1.2 gpm/ton

In parallel

Wide ∆T (low flow) e.g 18°F ∆T is 1.33 gpm/ton

Why isn’t it a good application? Flow can only be turned down 10%

Variable-Volume Pumping System(series chillers)

57°F41°F

48.4°F

Bypass alternatives

Upstream chiller operating at higher temperature is more efficient

Series ChillersManual service bypass

Series Chiller Advantages Simplifies pumping and

sequencing No flow rate transitions

Makes VPF simple

Upstream chiller operates at elevated temperature Efficiency increases

Capacity increases 10% or more for

absorption

Simple preferential loading of chillers Adjust upstream

chiller’s setpoint Upward to unload Downward to load

System control

ControlNormal Performance Chilled Water Plant Chilled water distribution pump

P at most remote sensor

Cooling tower fans55°F (as cold as possible)

Somewhere else

Constant volume condenser water pumps

High PerformanceChilled Water Pump Control

Valve position Pump Pressure Sensor

Communicating BAS Pump Speed

Position (% open)of critical valve

Increase pump static pressure setpoint

Reduce pump static pressure setpoint

No action

pump-pressure optimizationControl Logic 90.1-2007 Addendum ak

High Performance Chiller-Tower Control

Plant Power vs CWS

1,000.0

1,200.0

60 62 64 66 68 70 72 74 76 78 80 82 84 86 88

Condenser Water Setpoint (°F)

Lowest condenser water temperature available from tower at this load and wet-bulb temperature

Chillers cannot meet load above this condenser water temperature

Optimal operation

1,550 tons, 65°F Wet-bulb T t

1,160 tons, 59°F Wet-bulb T

730 tons, 54°F Wet-bulb Temperature

Hydeman, et. al. Pacific Gas and Electric. Used with permission.

Cooling tower basicsFan energy consumption

0 20 40 60 80 100% Airflow

% Full load power

ambient wet bulb, °F

50 60 70 80

100% load

50% load

approach = 4

approach = 9

cooling tower performance factorsApproach and Wet Bulb

simple case: constant water flowOperating Dependencies

Wet bulb Condenser water

temperature Load Tower design

Load Condenser water

temperature Chiller design

condenser water control“Normal” Setpoint

Hot?e.g., 85°F, minimizes towerenergy consumption

Cold?e.g., 55°F, minimizes chillerenergy consumption

Optimized?

optimal condenser water controlChiller–Tower Interaction

condenser water temperature, °F

76 78 80 8272

chiller

optimalcontrol point

High Performance Chiller-Tower Control Braun, Diderrich

Hydeman, Gillespie, Kammerud

Schwedler,ASHRAE Journal

Cascia

Crowther and Furlong

chiller–tower optimizationAn Example …

720,000 ft² hotel

2 chillers, 2 tower cells

Control strategies Make leaving-tower water cold

as possible (55F)

Optimize system operation

Entering-condenser setpoint equals design …85°F for humid climates80°F for dry climates

chiller–tower control strategiesNorth America

0Mexico City Orlando San Diego Toronto

55°F lvg toweroptimal controldesign ECWT

control strategy:

0Dubai Paris Sao Paulo Singapore

55°F lvg toweroptimal controldesign ECWT

control strategy:

chiller–tower control strategiesGlobal Locations

chiller–tower optimizationOperating Cost Savings

location

chiller–tower optimizationPerspective on SavingsFor centrifugal chillers ≥ 300 tons, ASHRAE 90.1 requires …

0.576 kW/ton at full load

0.549 kW/ton at IPLV

… using ARI standard rating conditions

chiller–tower optimizationPerspective on Savings

EquivalentSavings, % chiller efficiency

0.0 0.576

2.8 0.560

4.5 0.550

6.2 0.540

14.0 0.495

Where’s the Meter?On theBUILDING

chiller–tower optimizationFinding “Near Optimal” Tower design

(flow rate, range, approach)

Chiller design Refrigeration cycle

(vapor compression vs. absorption)

Compressor type

Capacity control (variable-speed drive)

Changing conditions(chiller load, ambient wet bulb)

chiller–tower optimizationNecessities

System-level controls

Variable-frequency driveon tower fans

High-quality dewpoint sensor

Number of chillers operating Operate one at nearly full load or two at

part load?

Examine IPLV assumptions

VSDs and centrifugal chillersA Closer Look at IPLV

VSDs improve part-lift performance, so running two chillers with VSDs at part load seems more efficient than one chiller at double the same load, but …is dependent on condenser water temperature

Load ECWTWeighting kW/Ton

100% 0.01 85°F 0.572

75% 0.42 75°F 0.420

50% 0.45 65°F 0.308

25% 0.12 65°F 0.372

Chiller power only45% Plant load

55 60 65 70 75 80 85

Available Tower Water Temperature (ºF)

ller k

1@90% Load2@45% Load

Operate 1 or 2 Chillers?Chiller kW Only

Chillers plus pumps45% Plant load

55 60 65 70 75 80 85Available Tower Water Temperature (ºF)

ller P

1@90% Load2@45% Load

Operate 1 or 2 Chillers?Chiller Plus Pump kW

Operate 1 or 2 chillers?Run 1 or 2 VSD Chillers?

60 65 70 75 80 85Available Tower Water Temperature (ºF)

ller P

1@90% Load2@45% Load1@80% Load2@40% Load1@70% Load2@35% Load1@60% Load2@30% Load1@50% Load2@25% Load

Operate multiple chillers here,otherwise single chiller

Operate 1 or 2 chillers? 45% plant load: One chiller until tower

temperature is < 65°F

40% plant load: One chiller until tower temperature is < 60°F

35% plant load and below: One chiller

High PerformanceCondenser Water Pump Control – Variable? Pump speed limits Tower static lift

Tower nozzles (minimum flow)

Condenser minimum flow

Pump speed reductions result in Increased leaving condenser water

temperature

Decreased cooling tower effectiveness

Possible chiller surge

High PerformanceCondenser Water Pump Control – Variable? The condenser water pump is the hardest

place to properly utilize a variable frequency drive during operation

There are successful installations

variable-flow condenser waterPump Speed Determining minimum speed

Variable flow affects:Pump

Cooling tower

Chiller

condenser water pumpMinimum SpeedDeterminants:

Minimum condenser flow Tower static lift Minimum tower flowNozzle selection

Performance

reducing flow & fan speedEffect on System

condenser water flow, %50 60 70 80 90 100

conditions:• 70% load• 50°F WB

fan speed

Varying fan and pump speed together

variable condenser water flowGuidance Can provide savings …Finding proper operating

points requires more time,more fine-tuning

Two-step process:1 Reduce design pump power

2 Is variable condenser-waterflow still warranted?

ROIHigh Performance Chilled Water Plants

EnergyPlus

Non-bin

Schematic tools that analyze in 30-45 minutes are available

Advanced high performance Equipment capabilities

System control

High performance chilled water plantWinchester Medical Center

Medical CenterWinchester, Virginia Five 750-ton chillers

0.571 kW/ton full load

Chilled water 58 to 42°F

Condenser water84 to 95°F(missed opportunity)

VFD’s

VFD’s on Chilled water pumps

Cooling tower fans

Condenser water pumps

Sophisticated control system with lots of Programming

Commissioning

Winchester Medical Center Working togetherOwner

Operators

Consulting engineer

Equipment provider

Controls provider

Service provider

Applications engineering

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s)0.00

tonskW/ton

WMC - August 12Chiller plant

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WMC - Sept 1-7Chiller plant Weekly-Summary

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1600.01/

tonskW/ton

Winchester Medical Center - Mark Baker

“Please use our data, names, etc. We're proud of our facility!”

“By the way, we're now operating @ -0.20 kW/ton. The power company just sent us our 1st check. Ha..Ha…”

Remember...

Without controls,it’s not a system.Without controls,it’s not a system.

The meter is on the building!

It’s a great time to be in this business!

high performance-chilled-water-systems ashrae-chicago

f chilled water

gpmton chilled water

receptacle load

leed energy andatmosphere

energyefficient design

service water heating

average energy cost

sourceenergy savings

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