Upgrading Existing ChW Systems

8/13/2019 Upgrading Existing ChW Systems

1/68

2008 Trane

2010 Trane

Upgrading ExistingChilled-Water

Systems

Kevin Rice, ComprehensiveSolutions Account Executive


2/68

2010 Trane

Existing Buildings Gordon Holness, 2009 ASHRAE President*

75% to 85% of all the buildings that willexist in urban areas in 2030 exist today.

Energy efficiency in existing buildings ourgreatest opportunity for a sustainablefuture.

we can sustain our future by rebuildingour past.

*Presidential address, June 2009


3/68

2010 Trane

Business Climate Budgets

Capital budgets limited, meet ROI

Pressure to reduce operating costs

Maintenance

Deferred (ignored?)

Enhanced to keep equipment workinglonger

Sustainability reduce energy use


4/68

2010 Trane

Upgrade Goals Use existing equipment and infrastructure

whenever possible

Reduce energy use but not at theexpense of comfort or the process

Show internal rate of return consistentwith present internal requirements


5/68

2010 Trane

The Building HVACSystem


6/68

2010 Trane

Chilled-Water System

pumpcoil

controlvalve

air-cooledchiller


7/68

2010 Trane

Existing Chilled-WaterSystems

Chiller

Pumps and pipes

Chilled waterCondenser water

Cooling towers and fans

System controls

Pictures
http://localhost/var/www/apps/conversion/tmp/scratch_3/Pictureshttp://localhost/var/www/apps/conversion/tmp/scratch_3/Pictures


8/68

2010 Trane

Chiller Products


9/68

2010 Trane

Upgrade options

Change the Chiller

Retrofit

Replace

Select different design parameters

Change system configuration

Enhance controls


10/68

2010 Trane

Chiller Upgrade Options

Comply with ASHRAE 90.1

Add a variable speed drive

Replace the chiller

Size the new chiller properly

Compare same-price new chiller options

Variable speed drive

High efficiency


11/68

2010 Trane

ASHRAE 90.1

Two Paths in 90.1-2010

Once a path is chosen, both full and part loadrequirements must be met

Positive displacement chillers evaluated only atAHRI Standard 550/590 standard conditions

Chilled water: 44F leaving, 2.4 gpm/ton

Condenser water: 85F entering, 3.0 gpm/ton

Centrifugal chiller requirements must be adjustedfor non-standard conditions


12/68

2010 Trane

ASHRAE 90.1Air-cooled Chillers

Capacity

(tons)

2007 2010 Path A 2010 Path B

Full

Load

IPLV Full

Load

IPLV Full

Load

IPLV


13/68

2010 Trane

ASHRAE 90.1Water-cooled positive Displacement Chillers

Capacity

(tons)2007 2010 Path A 2010 Path B

Full

Load

IPLV Full

Load

IPLV Full

Load

IPLV


14/68

2010 Trane

ASHRAE 90.1Water-cooled Centrifugal Chillers

Centrifugal chiller requirements must be adjusted for non-standardconditions

All requirements in kW/ton.

Chiller performance must be less than or equal to the requirements inthe table

Capacity

(tons)

2007 2010 Path A 2010 Path B

Full

Load

IPLV Full

Load

IPLV Full

Load

IPLV


15/68

2010 Trane




Replace the chiller




High efficiency


16/68

2010 Trane

Overhauled Chillers


17/68

2010 Trane

Adding a VSD to anExisting Chiller

Comply with ASHRAE 90.1 requirementsfor retrofits

Ensure that modification will not result in anincrease in annual energy consumption

Understand how a drive may benefitchiller performance

Perform return on investment analysis


18/68

2010 Trane

Drive impact on existingchiller performance

Demand rises 2-4% at design conditions

Largest benefit at lower condenser water

temperatures


19/68

2010 Trane

2006AmericanStand

ardInc.

Lift versus Load

lift

lvg evaporator water

lvg condenser water

lift PcndPevp

lift Tlvg cndTlvg evp

load gpm (Tent evpTlvg evp)

800 gpm

load = 500 tons

2 gpm/ton

58F(T)


20/68

2010 Trane

compressorwork

2006AmericanStand

ardInc.

Compressor Work and Chiller Efficiency

cooling capacity/load

head/li

ft

lvg evapwater

lvg cond

water

500 tons

58F


21/68

2010 Trane

Lessons Learned

To reduce lift:

Decrease condenserpressure by reducingleaving-tower water

temperature

Increase evaporatorpressure by raisingchilled water setpoint

VSDs optimize chiller liftefficiency 41Flvg evap

water

lvg condwater

45F

73F

99F

compressorwork


22/68

2010 Trane

Drive impact on existingchiller performance

700-Ton Chiller VSD Retrofit

0

50

100

150

200

250

300

350

400

450

500

0 200 400 600 800

Tons

kW

Existing-85F

VSD-Retrofit-85F

Existing-75F

VSD-Retrofit-75F

Existing-65F

VSD-Retrofit-65F

No savings at constant ECWT

Savings at reduced ECWT


23/68

2010 Trane

Drive Retrofit:Issues to consider

Utility rates? DemandCharge? Ratchet?

VSD adds inefficiency

If chiller was oversized the demandmay be lower

How often will it operateat advantageousconditions?

24/7 operation may be beneficial

Economizer reduces the loads atadvantageous conditions

How much energy isconsumed by the coolingtower?

Need to balance tower and chillerenergy

Is the chiller oversized forthe load?

Load reduction in conjunction withreduced CW temperatures may offersignificant savings


24/68


25/68

2010 Trane

Chiller Plant Analyzer


26/68

2010 Trane




Replace the chiller




High efficiency


27/68

2010 Trane

Chiller Replacement

Correctly size the new chiller

Determine actual building load

Downsize chiller if possible

If more tonnage is needed, higher efficiencyallows present electrical system to serve

Replace with higher efficiency chiller

Reduce demand and consumption

Constant speed or variable speed?


28/68

2010 Trane

Chiller Replacement:Constant or Variable Speed?

Different than retrofit where only VSDmakes economic sense

Compare same price VSD chiller andhigher full load efficiency chiller

Make sure each chiller meets ASHRAE 90.1full and part-load requirements

Use comprehensive analysis to determinewhich to purchase


29/68


30/68

2010 Trane

Same-price Chiller:Example Performance

600-ton Replacement Chiller Performance

0

50

100

150

200

250

300

350

400

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

% Load

kW

High_efficiency_85F

VSD_85F

High_efficiency_75F

VSD_75F

High_efficiency_65F

VSD_65F


31/68


32/68

2010 Trane

Guidance:VSD or High Efficiency?

High efficiency

Significant demandcharges

Humid climates

Multiple chillers in theplant

Economizer that

reduces low load/lowlift operating hours

VSD

Many hours at lowcondenser water

temperature and lowload

Perhaps only on onechiller

Factor in replacement

of VSD whenperforming life cycleassessment


33/68

2010 Trane

Upgrade options

Change the Chiller

Retrofit

Replace

Change design parameters


Enhance controls


34/68

2010 Trane

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?


35/68

2010 Trane

Design Parameters

Many chilled watersystems selected at:

Chilled water

44F 2.4 gpm/ton (10F T)

Condenser water

85F Entering

3 gpm/ton (9.4F T)

ASHRAE GreenGuideGuidance

Chilled water

12F to 20F T 2.0 to 1.2 gpm/ton

Condenser water

12F to 18F T

2.5 to 1.6 gpm/ton


36/68

2008 Trane

High PerformanceDesign Parameters

Kelly and Chan

Chilled water DT: 18F

Condenser water DT: 14.2F

(3.6 - 8.3% energy savings in variousclimates)


37/68

2008 Trane

a history of

Chiller Performance8.0

ASHRAE Standard 90

ch

illerefficiency

,COP

6.0

4.0

2.0

0.0NBI best

available90-75(1977)

90-75(1980)

90.1-89 90.1-99

centrifugal>600 tons

screw150-300 tons

scroll


38/68

2008 Trane

Efficiency changesin the past 35 years

Chiller COP increased up to 75%

Pumps? motors more efficient

Cooling towers? motors more efficient,fill design has changed


39/68

2008 Trane

Retrofit applicationsand reduced flow - evap

Chilled water side

Coil

Its a simple heat transfer device

Reacts to colder entering waterby returning it warmer

Ideal for system expansion


40/68


41/68

2010 Trane

Retrofit applicationsand reduced flow - cond

Condenser side retrofit opportunity

Chiller needs to bereplaced

Cooling needs haveincreased by 50%

Cooling tower wasreplaced two years ago

Condenser pump andpipes are in good shape


42/68

2010 Trane

Retrofit applicationsand reduced flow - cond

Existing Retrofit

Capacity (tons) 500 750

Flow rate (gpm) 1500 1500Condenser Entering Water

Temperature (F)

85 88

Condenser Leaving Water

Temperature (F)

95 103

Design Wet Bulb (F) 78 78


43/68

2010 Trane

Upgrade options

Change the Chiller

Retrofit

Replace



Enhance controls


44/68

2010 Trane

Variable Primary FlowSystems


45/68

2010 Trane

VPF System RetrofitBenefits

Reduced pumping costs

Ability to respond to Low T Syndrome


46/68

2010 Trane

Flow requirementsVPF System

Limits (consult manufacturer)

Absolute flows - Minimum and maximum

Always need a method to allow minimum flow(bypass)

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 minutebest


47/68

2010 Trane

Chiller Control

Variable Water Flow

30

40

50

60

70

80

90

100

110

120

130

3:50:00 3:55:00 4:00:00 4:05:00 4:10:00

Time (hour:min:sec)

WaterTemp[degF]

-500

-300

-100

100

300

500

700

900

1100

1300

1500

Flow[gpm]Evaporator Water Flow

Evap Entering Water Temp

Evap Leaving Water Temp


48/68

2010 Trane

Specify and install properflow control devices


49/68

2010 Trane

Conversion: Constantto Variable Flow

Confirm existing chillers and controls canoperate with variable evaporator flow

Ensure evaporator flow rate can stayabove minimum

New bypass or 3-way valves

Ensure flow rate changes are belowallowable chiller allowances


50/68


51/68

2010 Trane

Convert Primary Secondaryto Variable PrimaryVariable Secondary

Placeholder for

Manifolded P-S

System picture

(Beth to supply)

VFDs

T

DP

DP


52/68

2010 Trane

More informationVPF System

Http:/trane.com/commercial/library/newsletters.asp (1999 and 2002)

Dont Ignore Variable Flow, Waltz, Contracting

Business, July 1997

Primary-Only vs. Primary-Secondary Variable FlowSystems, Taylor, ASHRAE Journal, February 2002

Comparative Analysis of Variable and ConstantPrimary-Flow Chilled-Water-Plant Performance,Bahnfleth and Peyer, HPAC Engineering, April 2001

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


53/68

2010 Trane

Upgrade options

Change the Chiller

Retrofit

Replace



Enhance controls


54/68

2010 Trane

Control Options

Proper number of chillers

Pump control

Chiller-tower optimization


55/68

2010 Trane

Number of chillersoperating

Operate one at nearly full load or two atpart load?

Examine IPLV assumptions


56/68

2010 Trane

VSDs and centrifugal chillers

A Closer Look at IPLV

VSDs improve part-lift performance, so running two chillerswith VSDs at part load seems more efficient than one chiller atdouble the same load, but is dependent on condenser watertemperature

Load ECWTWeighting kW/Ton

100% 0.01 85F 0.572

75% 0.42 75F 0.420

50% 0.45 65F 0.308

25% 0.12 65F 0.372


57/68

2010 Trane

Chiller power only

45% Plant load


58/68

2010 Trane

Chillers plus pumps

45% Plant load


59/68


60/68

2010 Trane

Chilled Water PumpControl

Valve positionPump

Pressure

Sensor

Communicating

BASPump Speed

pump-pressure optimization


61/68

2010 Trane

Position (% open)

of critical valve

75%

65%

Increase pump static pressure setpoint

Reduce pump static pressure setpoint

No action

p p p p

Control Logic90.1-2007 Addendum ak

This will be required for many systems by 90.1-2010


62/68

2010 Trane

optimal condenser water control

ChillerTower Interaction

condenser water temperature, F

400

74

energyconsumption,

kW

76 78 80 8272

300

200

100

084

tower

chiller

total

optimalcontrol point


63/68

2010 Trane

chillertower optimization

An Example

720,000 ft hotel

2 chillers, 2 tower cells

Control strategies Make leaving-tower water cold

as possible (55F)

Optimize system operation

Entering-condenser setpointequals design 85F for humid climates,80F for dry climates


64/68

2010 Trane

chillertower control strategies

North America350K

annu

aloperatingcost,

$USD

300K

250K

200K

150K

100K

50K

0Mexico City Orlando San Diego Toronto

55F lvg tower

optimal control

design ECWT

control strategy:


65/68

2010 Trane

annu

aloperatingcost,

$USD

500K

400K

300K

200K

100K

0Dubai Paris Sao Paulo Singapore

55F lvg tower

optimal control

design ECWT

control strategy:

chillertower control strategies

Global Locations


66/68

2010 Trane

chillertower optimization

Operating Cost Savings

operatingcostsavin

gs,chiller

+tow

erannualcosts,

%

14

0

12

10

8

6

4

2

location

Dubai

Paris

SaoPa

ulo

Singap

ore

Mexico

City

Orland

o

SanDiego

Toront

o


67/68

2010 Trane

Upgrading chilledwater systems

Retrofit or replacechiller

Comply with 90.1requirements

Consider same-pricehigh efficiencyreplacement

Select different designparameters

Reduce flow rates byincreasing T

Chilled water

Condenser water

Consider VPF

Update controls

Number of chillers

operating

Pump pressureoptimization

Chiller-tower

optimization

Perform analysis


68/68

References

Upgrading Chilled-Water Systems,ASHRAE Journal, November 2009.

Documents

Upgrading Existing ChW Systems