instrumentation for monitoring central chilled-water plant efficiency.pdf

ASHRAE Guideline 22-2012Supersedes ASHRAE Guideline 22-2008

Instrumentation for Monitoring

Central Chilled-WaterPlant Efficiency

Approved by the ASHRAE Standards Committee on July 20, 2012, and by the ASHRAE Board of Directors on July 26, 2012.

ASHRAE Guidelines are scheduled to be updated on a five-year cycle; the date following the guideline number is the year ofASHRAE Board of Directors approval. The latest edition of an ASHRAE Guideline may be purchased on the ASHRAE Web site(www.ashrae.org) or from ASHRAE Customer Service, 1791 Tullie Circle, NE, Atlanta, GA 30329-2305. E-mail:[email protected]. Fax: 404-321-5478. Telephone: 404-636-8400 (worldwide) or toll free 1-800-527-4723 (for orders in US andCanada). For reprint permission, go to www.ashrae.org/permissions.

2012 ASHRAE ISSN 1049-894X

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accepted industry practices. However, ASHRAE does not guarantee, certify, or assure the safety or performance of any products, components,or systems tested, installed, or operated in accordance with ASHRAEs Standards or Guidelines or that any tests conducted under itsStandards or Guidelines will be nonhazardous or free from risk.

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ASHRAE Guideline Project Committee 22Cognizant TC: TC 9.1, Large Building Air-Conditioning Systems

SPLS Liaison: Robert G. Doerr

*Denotes members of voting status when the document was approved for publication

Charles G. Arnold, Chair* James B. Rishel*Thomas E. Cappellin* Michael M. Roberts*Kenneth L. Gillespie, Jr.* Michael. C. A. SchwedlerThomas B. Hartman Daryl K. Showalter*Mark C. Hegberg Ian D. Spanswick*Roy S. Hubbard, Jr. Laurance S.Staples, Jr.John L. Kuempel, Jr.* John I. Vucci*

ASHRAE STANDARDS COMMITTEE 20112012

Carol E. Marriott, Chair Krishnan Gowri Janice C. PetersonKenneth W. Cooper, Vice-Chair Maureen Grasso Douglas T. ReindlDouglass S. Abramson Cecily M. Grzywacz Boggarm S. SettyKarim Amrane Richard L. Hall James R. TaubyCharles S. Barnaby Rita M. Harrold James K. VallortHoy R. Bohanon, Jr. Adam W. Hinge William F. WalterSteven F. Bruning Debra H. Kennoy Michael W. WoodfordDavid R. Conover Jay A. Kohler Craig P. WraySteven J. Emmerich Eckhard A. Groll, BOD ExOAllan B. Fraser Ross D. Montgomery, CO

Stephanie C. Reiniche, Manager of Standards

SPECIAL NOTEThis Guideline was developed under the auspices of ASHRAE. ASHRAE Guidelines are developed under a review process, identifying

a guideline for the design, testing, application, or evaluation of a specific product, concept, or practice. As a guideline it is not definitive butencompasses areas where there may be a variety of approaches, none of which must be precisely correct. ASHRAE Guidelines are writtento assist professionals in the area of concern and expertise of ASHRAEs Technical Committees and Task Groups.

ASHRAE Guidelines are prepared by project committees appointed specifically for the purpose of writing Guidelines. The projectcommittee chair and vice-chair must be members of ASHRAE; while other committee members may or may not be ASHRAE members, allmust be technically qualified in the subject area of the Guideline.

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CONTENTS

ASHRAE Guideline 22-2012Instrumentation for Monitoring Central Chilled-Water Plant Efficiency

SECTION PAGEForeword................................................................................................................................................................... 2

1 Purpose .......................................................................................................................................................... 22 Scope ............................................................................................................................................................. 23 Definitions....................................................................................................................................................... 24 Utilization ........................................................................................................................................................ 25 Chilled-Water Plant Types and Instrumentation ............................................................................................. 36 Data Gathering and Trending ......................................................................................................................... 77 Calculations .................................................................................................................................................... 78 References ..................................................................................................................................................... 8

Informative Appendix AExample Instrument Specifications Table.................................................................... 9Informative Appendix BDetermination of kW/ton ............................................................................................ 11Informative Appendix CUncertainty Impacts on Measurement Requirements................................................ 12Informative Appendix DData Gathering and Trending .................................................................................... 15Informative Appendix EExample Specification Language............................................................................... 16Informative Appendix FExample Application................................................................................................... 28Informative Appendix GExamples of Analyzed Data ...................................................................................... 35Informative Appendix HBibliography ............................................................................................................... 39

NOTE

Approved addenda, errata, or interpretations for this guideline can be downloaded free of charge from the ASHRAE Web site at www.ashrae.org/technology.

2012 ASHRAE1791 Tullie Circle NEAtlanta, GA 30329www.ashrae.org

All rights reserved.




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2 ASHRAE Guideline 22-2012

(This foreword is not part of this guideline. It is merelyinformative and does not contain requirements necessaryfor conformance to the guideline.)

FOREWORDGuideline 22 was developed by ASHRAE to provide a

source of information on the instrumentation and collection ofdata needed for monitoring the efficiency of an electric-motor-driven central chilled-water plant. A minimum level of instru-mentation quality is established to ensure that the calculatedresults of chilled-water plant efficiency are reasonable. Sev-eral levels of instrumentation are developed so that the user ofthis guideline can select the level that suits the needs of eachinstallation.

The basic purpose served by this guideline is to enablethe user to continuously monitor chilled-water plant efficiencyin order to aid in the operation and improvement of that par-ticular chilled-water plant, not to establish a level of efficiencyfor all chilled-water plants. Therefore, the effort here is toimprove individual plant efficiencies and not to establish anabsolute efficiency that would serve as a minimum standardfor all chilled-water plants.

It is recognized that there are different needs for monitor-ing the efficiency of a chilled-water plant. In most cases, theprincipal objective is to maintain and improve the efficiency ofthe chilled-water plant. There are also cases where greateraccuracy is desired for monitoring chilled-water plant effi-ciency. The instrumentation section allows the user to deter-mine the required accuracy for the application.

The user of this guideline should be aware that the qualityof the instrumentation directly affects the results obtained and,therefore, the accuracy of the chilled-water plant efficiency. Asa result, special attention should be given to the selection ofinstrumentation in order to ensure that the expected result isdelivered.

Chilled-water plant efficiency is expressed in differentterms. This guideline uses the recognized term for chilled-water plant efficiency, which is coefficient of performance(COP). While the guideline uses COP, it is understood thatin areas using inch-pound (I-P) units, kW/ton is the commonterm for determining chilled-water plant efficiency.Appendix B of this guideline provides the information nec-essary to derive chilled-water plant efficiency when usingkW/ton. Also, in Appendix E, an example specification isprovided for designers of chilled-water plants who wish toincorporate the monitoring of COP or kW/ton into specifi-cations for new plants or modifications of existing plants.

It should be pointed out that this guideline does not offerany information on the design of a chilled-water plant. It isapplicable to all electric-motor-driven chilled-water plantsregardless of their configuration or types of chillers, coolingtowers, pumps, and other parasitic electric chilled-water plantloads. This guideline is designed to help plant managers andoperators achieve and maintain a desired level of efficiencyfor their chilled-water plants.

This is a revision of ASHRAE Guideline 22-2008. Thisguideline was prepared under the auspices of ASHRAE. It maybe used, in whole or in part, by an association or governmentagency with due credit to ASHRAE. Adherence is strictly on a

voluntary basis and merely in the interests of obtaining uni-form standards throughout the industry.

The changes made for the 2012 revision are as follows:

Updated references Minor editorial changes

1. PURPOSEThis guideline defines recommended methods for

measuring chilled-water plant thermal load and energy useand for calculating chilled-water plant efficiency.

2. SCOPE2.1 This guideline includes

a. recommendations for methods and devices used to mea-sure electrical usage, fluid flow, and temperature, and

b. procedures for acquiring the necessary data and calculat-ing system efficiency.

2.2 These procedures are for site-specific application. Theydo not discuss the comparison of collected data between dif-ferent sites, nor do they recommend that data obtained beapplied in this manner.

2.3 The procedures also do not discuss

a. any plants except electrically driven chilled-water plants,b. design and operation of central chilled-water plants,

except for recommending the instrumentation used todetermine plant efficiency, or

c. selection, application, or operation of system compo-nents.

3. DEFINITIONSFor the definitions of key terms used in this guideline,

refer to ASHRAE Terminology of Heating, Ventilation, AirConditioning, and Refrigeration.1

4. UTILIZATION4.1 This guideline allows the user to monitor chilled-waterplant efficiency and to make modifications to the setpoints ofthe system such that the overall efficiency of the chilled-waterplant is improved. In order to properly evaluate the efficiencyof the chilled-water plant, it is first necessary to accuratelymeasure the variables that will determine this efficiency.

The efficiency of the chilled-water plant, which is definedin this guideline as coefficient of performance (COP), isdependent upon the energy use of a number of different piecesof equipment, including, but not limited to, the following:

chillers, evaporator pumps, condenser pumps, and cooling towers.

Each piece of equipment can have a significant impact onchilled-water plant efficiency.




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ASHRAE Guideline 22-2012 3

This guideline is entirely focused on reporting the oper-ational efficiency of existing plants. For information relatingto achieving efficiency during the initial design of a chilled-water plant, refer to recognized standards such as ANSI/ASHRAE/IESNA 90.1, Energy Standard for Buildings ExceptLow-Rise Residential Buildings,2 as well as to the ASHRAEHandbooks.3, 4, 5, 6

Since the design and layout of chilled-water plants varieswidely depending upon their specific applications, this guide-line addresses common chilled-water plant layouts for instru-mentation and collection of data. Applications that includethermal energy storage and heat recovery are more complexand may require a more sophisticated approach than thisguideline provides. If some modification of the data collectionand analysis method were made to include the additionalequipment used in such applications, this variation on themethodology of this guideline could be used to give an overallchilled-water plant efficiency.

Chilled-water plant efficiency is not dependent upon anyone device; rather, it is the overall match of system compo-nents that determine efficiency.

4.2 Informative Appendix E of this guideline provides asample specification that can be used when management pre-fers to contract the determination of chilled-water plant effi-ciency to an outside vendor or agency. For this guideline to becited in a specification, the following plant-specific informa-tion must be provided:

Equipment whose power is to be included. Equipment whose power is not to be included (if any). Thermal cooling loads to be included. Thermal cooling loads not to be included (if any). The maximum allowable error tolerance in the result. A summary of how the gathered data should be stored

and presented.

5. CHILLED-WATER PLANT TYPES AND INSTRUMENTATION5.1 Primary/Secondary Chilled Water. Detailed inFigure 5-1 is an example primary/secondary chilled-watersystem. The diagram provides a set of typical points thatcould be measured to give an overall chilled-water plant COP.These points can be reduced or expanded upon as the userdeems necessary.

5.2 Primary or Variable Primary Flow System. Detailedin Figure 5-2 is an example primary flow system. A systemsuch as this normally utilizes variable-frequency drives on thechilled-water pumps, as is specified by some requirements ofANSI/ASHRAE/IESNA Standard 90.1.2 The diagram pro-vides a set of typical points that could be measured to give anoverall chilled-water plant COP. These points can be reducedor expanded upon as the user deems necessary.

5.3 Instrumentation. To measure chilled-water plant effi-ciency, appropriate instrumentation is required to achieve theexpected result of this guideline. An instrumentation tablesuch as Table 5-1 should be used to define the instrumentrange, measurement range, and measurement accuracy foreach piece of equipment that uses electric energy. The specific

instrument and the measurement range are dependent on thecapacity of equipment for the specific chilled-water plant. SeeInformative Appendix A, Instrument Specifications Table, foran example of the data that should be provided in the table.

Depending on the specific application, the user maydecide to measure chilled-water plant efficiency with or with-out the pump energy required to distribute water to the loads.

Data calculation and archiving of this data should be toone order of magnitude greater than the measurement accu-racy. Operator interface display resolution should be consis-tent with the measurement accuracy; the recommendation ofthis guideline is that the resolution should be the same magni-tude as the midpoint of the measured value multiplied by theaccuracy.

5.4 Data Quality. The quality of any measurement isdependent upon the measurement location, the capability ofthe measurement sensor and the data-recording instrument,and the sampling method employed. This guideline recom-mends that the instrumentation selected for monitoring cen-tral chilled-water plant efficiency have the capabilitiesdescribed in Sections 5.4.1 and 5.4.2 below.

Note: If pre-existing instrumentation is already installedon the equipment, one may consider making use of it. To beconsidered, however, such instrumentation should first meetthe data integrity recommendations of this guideline and bebudgeted for the added costs for calibration and maintenancethat this guideline recommends.

5.4.1 Data Recording Device. The selection of a datarecording device is dependent upon the following factors:

Quality of the device (accuracy, precision, drift, rate ofresponse).

Quantity and type of inputs required. Installation restrictions. Signal conditioning. Measurement range. Resources available to purchase and support the device.

Digital data acquisition instrumentation is now the typicalhardware of choice to gather field data. This is true whether thedata is gathered by a portable instrument or by a permanentlyinstalled building automation system (BAS). However, BAShardware is typically not designed for the kind of data acqui-sition this guideline recommends, and its ability must bedemonstrated before it can be used with confidence (SeeHeinemeier et al.).7 Building management system (BMS)control requirements are not always compatible with measure-ment and monitoring requirements.

Characteristics to consider for the data recording deviceinclude:

Scan Rate. It is always best to strive for an order ofmagnitude higher scan rate than the period of the processbeing measured. This is especially true with dynamicprocesses.

Time Measurement Characteristics. Performancemeasurements are directly affected by the resolution, accu-racy, and precision of the data recording device internal




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Figure 5-1 Example of primary/secondary chilled-water plant.

Figure 5-2 Example of primary-only chilled-water plant.




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TABL

E 5-

1

Inst

rum

enta

tion

Tabl

e

IDP

oint

Des

crip

tion

Mea

sure

men

t R

ange

Sens

or T

ype

or

Cal

cula

tion

Met

hod

Inst

alla

tion

L

ocat

ion

Inpu

t T

ype

Inst

rum

ent

Ran

ge

End

-to-

end

Acc

urac

y(%

of

read

ing

unle

ss n

oted

)

Dat

a R

esol

utio

n

Ref

resh

In

terv

al

(min

)

Tre

nd

Inte

rval

(m

in)

Pow

er M

easu

rem

ents

kW01

Chi

ller

1 Po

wer

kW02

Chi

ller

2 Po

wer

kW03

Prim

ary

ChW

Pum

p 1

Pow

er

kW04

Prim

ary

ChW

Pum

p 2

Pow

er

kW05

Seco

ndar

y C

hW P

ump

3 Po

wer

kW06

Seco

ndar

y C

hW P

ump

4 Po

wer

kW07

Chi

ller

1 C

W P

ump

Pow

er

kW08

Chi

ller

2 C

W P

ump

Pow

er

kW09

Coo

ling

Tow

er F

an 1

Pow

er

kW10

Coo

ling

Tow

er F

an 2

Pow

er

Flo

w M

easu

rem

ents

FT01

Chi

lled

Wat

er F

low

FT02

Con

dens

er W

ater

Flo

w

TT

01C

hille

d W

ater

Sup

ply

Tem

pera

ture

TT

02C

hille

d W

ater

Ret

urn

Tem

pera

ture

TT

03C

onde

nser

Ent

erin

g W

ater

Tem

pera

ture

TT

04C

onde

nser

Lea

ving

Wat

er T

empe

ratu

re

TT

05A

mbi

ent D

ry-B

ulb

Tem

pera

ture

TT

06A

mbi

ent W

et-B

ulb

Tem

pera

ture

Cal

cula

ted

Val

ues

CC

01C

hWPl

ant T

herm

al C

oolin

g O

utpu

t

CC

02ch

illed

-wat

er p

lant

Eff

icie

ncy

CC

03Pl

ant H

eat o

f R

ejec

tion




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clock per unit of time. Most systems provide reasonablecapabilities.

Engineering-Unit Conversion Methods. Converting ofsensor output to engineering units is typically provided bymost equipment utilizing the linear scalar and offsetmethod (y = mx + b). Advanced systems provide for poly-nomial curve fitting or point-to-point interpolation. Manysystems offer some form of temperature conversion tablesor standard equations for resistance temperature detectors(RTDs) and/or thermocouples (TCs). Engineering unitsare extremely helpful in performing on-line sensor cali-brations, troubleshooting, and inter-channel calculations(using concurrent data from more than one channel).

Math Functions. It is desirable to have the ability tomanipulate the sampled data as it is scanned. One mayalso need to determine individual channel interval aver-ages, minimums, maximums, standard deviations, andsamples per interval and perform inter-channel calcula-tions, including obtaining averages and loads. BASs typi-cally are not provided with the ability to perform time-interval-based averaging intervals; however, some newersystems can be configured to provide the required data.

Data Archival and Retrieval Format. Most limited chan-nel data recording devices provide for archival of averagedor instantaneous measured data in a time series recordformat that can be directly loaded into a spreadsheet.

In general, using a BAS as the data-recording instrumentshould be considered only after careful review of its capabil-ities. Some BASs cannot record and archive data at regularintervals; however, some newer systems can be configured toprovide the required data.

5.4.2 Sensors. Sensor selection is dependent upon thequality (accuracy, precision, drift, rate of response), quantity,installation restrictions, method of measurement required,signal output requirements (or signal conditioning), measure-ment range, turndown, the capabilities of the intended datarecording device, and the resources available to purchase and/or support it.

5.5 Calibration. It is highly recommended that instrumen-tation used in measuring the information required to evaluatechilled-water plant efficiency be calibrated with proceduresdeveloped by the National Institute of Standards and Technol-ogy (NIST). Primary standards and no less than third-orderNIST traceable calibration equipment should be utilizedwherever possible. Calibration by NIST is considered firstorder, an independent lab calibration against the NIST stan-dard is second order, and a users calibration against the inde-pendent lab instrument (a transfer standard) is consideredthird order.

5.6 The Uncertainty of the Measurement. It should beunderstood that any measurement of chilled-water plant effi-ciency includes a degree of uncertainty; this is true whether ornot the degree of uncertainty is specifically specified. Mea-surements made in the field are especially subject to potentialerrors. In contrast to measurements made under the controlledconditions of a laboratory setting, field measurements are typ-

ically made under less predictable circumstances and withless accurate and less expensive instrumentation. Field mea-surements are vulnerable to errors arising from variable mea-surement conditions (the method employed may not be thebest choice for the conditions of the specific application),from limited instrument field calibration (typically due to thefact that field calibration is more complex and expensive),from the simplified data sampling and archiving methodsemployed, and from limitations in the ability to adjust instru-ments in the field. Table 5-2 provides a range of maximumallowable measurement error requirements of individual mea-surements to meet a desired overall uncertainty in the result-ing efficiency.

It is recommended that the installed instrumentation becapable of calculating a resultant COP within 5% of the truevalue. As Table 5-2 shows, only the measurement errors listedin the first three rows of the table are capable of meeting thisrecommendation.

See Informative Appendix C for a discussion of how thedesired uncertainty in the result impacts individual sensorselection. See also ASHRAE Guideline 14, Measurement ofEnergy and Demand Savings, Annex A: Physical Measure-ments,8 for a detailed discussion of sensors, calibration tech-niques, laboratory standards for measurement of physicalcharacteristics, equipment testing standards, and cost anderror considerations.

TABLE 5-2 Impacts of Measurement Errors

Measurement Error (% of Reading)

Result Error (%)

% Power (e.g., kW)

% Flow (e.g., gpm, L/s, lb/h)

% T(e.g.,F, C)

% Capacity (e.g., ton,

kW, ton-h)

% COP(or kW/ton, kWh/ton-h)

1 1 2 2.24 2.45

1.5 2 2 2.83 3.20

1.5 3 3 4.24 4.50

1.5 3 4 5.00 5.22

3 5 5 7.07 7.68

3 7 7 9.90 10.34

3 7 12 13.89 14.21

3 10 10 14.14 14.46

3 10 12 15.62 15.91

3 10 15 18.03 18.28

5 15 15 21.21 21.79

5 10 20 22.36 22.91

5 7 24 25.00 25.50

5 10 25 26.93 27.39

5 15 25 29.15 29.58




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6. DATA GATHERING AND TRENDING6.1 Averaging Calculation Method. The measured valuesfrom instruments are unlikely to be constant; they can fluctu-ate to a greater or lesser extent depending on the installed con-ditions and the instrument employed. For calculation, display,and recording purposes, all data should be continuously aver-aged over a short time period to remove the fluctuations(smoothing) and provide meaningful data to work with. Formore detailed information about averaging, refer to Informa-tive Appendix D in this guideline.

7. CALCULATIONS7.1 Computation of the Coefficient of Performance (COP)

7.1.1 For an electric-motor-driven chilled-water plant, theterm COP is a dimensionless ratio consisting of the workdone, Wd, divided by the work applied, Wa.

7.1.2 The work done, Wd, is the standard heat transferequation for all chilled-water solutions under steady-stateconditions:

For I-P units,

Wd = mw cp T (Btu/h), (1) (I-P)wheremw = water flow rate in lb/h,cp = specific heat at constant pressure in Btu/(lbF),

andT = temperature difference in F.

For SI units,

Wd = mw cp T (kW), (1) (SI)wheremw = water flow rate in kg/s,cp = specific heat at constant pressure in kJ/(kgK),

and T = temperature difference in C.

7.1.3 The work applied, Wa, is the sum of all electricalenergy inputs to the chilled-water plant:

For I-P units,

Wa = 3413 kW (Btu/h), (2) (I-P)whereWa = electrical power in kW.

For SI units,

Wa = kW (kW), (2) (SI)

whereWa = electrical power in kW.

7.1.4 The basic equation for COP for all chilled-watersolutions is therefore expressed as follows:

For I-P units,

(dimensionless) (3) (I-P)

For SI units,

(dimensionless) (3) (SI)

7.2 Determination of COP for Chilled-Water Plants Uti-lizing Standard Water

7.2.1 Chilled-water plants in US locations measure theflow rate, , in gallons per minute (gpm).

For I-P units, therefore,

, (4) (I-P)

where is flow in gpm.

For S-I units,

L/s = = mw , (4) (SI)where is flow in L/s.

7.2.2 For I-P units, although the specific heat, cp, for purewater at temperatures from 40F to 60F ranges from 1.006 to1.002, it is generally accepted as 1.0 for standard water atthese temperatures. For SI units, although the specific heat,cp, for pure water at temperatures from 4.44C to 15.55Cranges from 4.203 to 4.185 kJ/(kgK), it is generally acceptedas 4.19 kJ/(kgK) for standard water at these temperatures.

7.2.3 The differential temperature, T, for chilled-waterplants is the difference between the temperature of the waterreturning to the plant from the distribution system, T2, and thewater supplied by the chilled-water plant to the distributionsystem, T1.

7.2.4 The equation for COPw for a chilled-water plant uti-lizing standard water is therefore expressed as follows:

For I-P units,

(5) (I-P)

For SI units,

(dimensionless) (5) (SI)

7.3 Determination of COP for Chilled-Water Plants Uti-lizing Other Solutions of Water

7.3.1 Solutions of water and chemicals are used in chilled-water plants to alter the freezing point. For I-P units, typicalsolutions are the glycols that have specific gravities greaterthan 1 and specific heats less than 1. Equation 5 (I-P) can bealtered for glycols (or other solutions) since all specific grav-ities used herein are related to that for water.

COPWdWa-------

mw cp T3413 kW--------------------------------= =

COPWdWa-------

mw cp TkW--------------------------------= =

mw8.34 lb/gal 60 min/h------------------------------------------------------

mw500---------= = or mw; 500=

COPw500 1 T2 T1

3413 kW---------------------------------------------------------=

T2 T1 6.826 kW--------------------------------- (dimensionless)=

COPw 4.19 T2 T1

kW-------------------------------------------------=




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For I-P units, therefore,

, (6) (I-P)

where

s = flow of the glycol solution in gpm,sg = specific gravity of the glycol solution

(dimensionless), and

cpg = specific heat of the glycol solution in Btu/(lbF).

For SI units, specific gravities are greater than 1 andspecific heats less than 4.19 kJ/kg. Equation 5 (SI) can bealtered for glycols since all specific gravities used herein arerelated to that for water.

For SI units, therefore,

, (6) (SI)

where

s = flow of the glycol solution in L/s, = density of the glycol solution in kg/m3, andcpg = specific heat of the glycol solution in kJ/(kgK).

Note: See Informative Appendix B of this guideline forthe determination of kW/ton for electric-motor-driven chilled-water plants.

8. REFERENCES1ASHRAE Terminology of Heating, Ventilation, Air Condi-

tioning, and Refrigeration, American Society of Heat-ing, Refrigerating and Air-Conditioning Engineers, Inc.,Atlanta, 1991.

2ANSI/ASHRAE/IESNA Standard 90.1-2007, Energy Stan-dard for Buildings Except Low-Rise Residential Build-ings, American Society of Heating, Refrigerating andAir-Conditioning Engineers, Inc., Atlanta, 2007.

32009 ASHRAE HandbookFundamentals, American Soci-ety of Heating, Refrigerating and Air-ConditioningEngineers, Inc., Atlanta, 2009.

42008 ASHRAE HandbookHVAC Systems and Equipment,American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc., Atlanta, 2008.

52007 ASHRAE HandbookHVAC Applications, AmericanSociety of Heating, Refrigerating and Air-ConditioningEngineers, Inc., Atlanta, 2007.

62010 ASHRAE HandbookRefrigeration, American Soci-ety of Heating, Refrigerating and Air-ConditioningEngineers, Inc., Atlanta, 2010.

7Heinemeier, K.E., H. Akbari, and S. Kromer, Monitoringsavings in energy savings performance contracts usingenergy management and control systems, ASHRAETransactions 102(2), 1996.

8ASHRAE Guideline 14-2002, Measurement of Energy andDemand Savings, Annex A, American Society of Heat-ing, Refrigerating and Air-Conditioning Engineers, Inc.,Atlanta, 2002.

COPgs sg cpg T2 T1

6.826 kW------------------------------------------------------------=

COPgs cpg T2 T1

1000 kW----------------------------------------------------------=




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s ap

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INFO

RM

ATI

VE A

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DIX

A

EXA

MPL

E IN

STRU

MEN

T SP

ECIF

ICAT

ION

TABL

E

TABL

E A-

1 Ex

ampl

e In

stru

men

t Spe

cific

atio

n T

able

IDP

oint

Des

crip

tion

Mea

sure

men

t R

ange

Sens

or T

ype

or C

alcu

lati

on M

etho

dIn

stal

lati

on

Loc

atio

nIn

put

Typ

e*In

stru

men

tR

ange

End

-to-

End

A

ccur

acy

(% o

f re

adin

g un

less

not

ed)

Dat

aR

esol

utio

n

Ref

resh

In

terv

al

(min

)

Tre

nd

Inte

rval

(m

in)

Pow

er M

easu

rem

ents

5C

hille

r 1

Pow

er30

to 2

88 k

WT

rue

root

-mea

n-sq

uare

(R

MS)

, thr

ee-p

hase

, int

e-gr

ated

equ

ipm

ent,

stan

d-al

one

anal

og o

utpu

t or

netw

orke

d po

wer

met

erA

I0

to 3

00 k

W1

.0%

0.1

kW1

1

6C

hille

r 2

Pow

er30

to 2

88 k

WT

rue

RM

S, th

ree-

phas

e, in

tegr

ated

equ

ipm

ent,

stan

d-al

one

anal

og o

utpu

t or

netw

orke

d po

wer

m

eter

AI

0 to

300

kW

1.0

%0.

1 kW

11

7Pr

imar

y C

hille

d-W

ater

Pu

mp

1 Po

wer

12 to

15

kWT

rue

RM

S, th

ree-

phas

e, in

tegr

ated

equ

ipm

ent,

stan

d-al

one

anal

og o

utpu

t or

netw

orke

d po

wer

m

eter

AI

0 to

25

kW1

.0%

0.01

kW

11

8Pr

imar

y C

hille

d-W

ater

Pu

mp

2 Po

wer

12 to

15k

WT

rue

RM

S, th

ree-

phas

e, in

tegr

ated

equ

ipm

ent,

stan

d-al

one

anal

og o

utpu

t or

netw

orke

d po

wer

m

eter

AI

0 to

25

kW1

.0%

0.01

kW

11

9Se

cond

ary

Chi

lled-

Wat

er

Pum

p 3

Pow

er2

to 1

0 kW

Var

iabl

e-fr

eque

ncy-

driv

e (V

FD) b

us o

utpu

t for

kW

AI

0 to

25

kW3

.0%

0.01

kW

11

10Se

cond

ary

Chi

lled-

Wat

er

Pum

p 4

Pow

er2

to 1

0 kW

VFD

bus

out

put f

or k

WA

I0

to 2

5 kW

3.0

%0.

01 k

W1

1

11C

hille

r 1

Chi

lled-

Wat

er

Pum

p 5

Pow

er50

to 5

4 kW

Tru

e R

MS,

thre

e-ph

ase,

inte

grat

ed e

quip

men

t, st

and-

alon

e an

alog

out

put o

r ne

twor

ked

pow

er

met

erA

I0

to 7

5 kW

1.0

%0.

01 k

W1

1

12C

hille

r 2

Chi

lled-

Wat

er

Pum

p 6

Pow

er50

to 5

4 kW

Tru

e R

MS,

thre

e-ph

ase,

inte

grat

ed e

quip

men

t, st

and-

alon

e an

alog

out

put o

r ne

twor

ked

pow

er

met

erA

I0

to 7

5 kW

1.0

%0.

01 k

W1

1

24C

oolin

g To

wer

Fan

1

Pow

er5

to 2

2 kW

VFD

bus

out

put f

or k

WD

I0

to 2

5 kW

3.0

%0.

01 k

W1

1

25C

oolin

g To

wer

Fan

2

Pow

er5

to 2

2 kW

VFD

bus

out

put f

or k

WD

I0

to 2

5 kW

3.0

%0.

01 k

W1

1

*AI

= a

nalo

g in

put;

DI

= d

igita

l inp

ut; C

= c

alcu

late

d va

lue;

#C

4 =

cons

tant

for

con

vert

ing

chill

ed-w

ater

flo

w ti

mes

T

to to

ns; #

C5

= c

onst

ant f

or c

onve

rtin

g co

nden

ser

wat

er f

low

tim

es

T to

tons

.




--`,,`,,,,,`,`,`,`,,,,``,,,``,``-`-`,,`,,`,`,,`---


Flo

w M

easu

rem

ents

26C

hille

d-W

ater

Flo

w80

0 to

240

0 gp

mH

ot ta

pped

inse

rtio

n vo

rtex

she

ddin

gA

I0

to 3

000

gpm

3.0

%1

to 1

5 ft

/min

1 gp

m1

1

27C

onde

nser

Wat

er F

low

1000

to 3

000

gpm

Hot

tapp

ed in

sert

ion

vort

ex s

hedd

ing

AI

0 to

400

0 gp

m3

.0%

1 to

15

ft/m

in1

gpm

11

Tem

pera

ture

Mea

sure

men

ts

32C

hille

d-W

ater

Su

pply

Tem

pera

ture

38 to

55

F10

00 o

hm th

erm

isto

r or

res

ista

nce

tem

pera

ture

de

tect

or (

RT

D)

AI

35 to

75

F0

.2F

0.0

1F

11

33C

hille

d-W

ater

Ret

urn

Tem

pera

ture

42 to

60

F10

00 o

hm th

erm

isto

r or

res

ista

nce

tem

pera

ture

de

tect

or (

RT

D)

AI

35 to

75

F0

.2F

0.0

1F

11

34C

onde

nser

Ent

erin

g W

ater

Tem

pera

ture

55 to

90

F10

00 o

hm th

erm

isto

r or

res

ista

nce

tem

pera

ture

de

tect

or (

RT

D)

AI

50 to

110

F0

.2F

0.0

1F

11

35C

onde

nser

Lea

ving

Wat

er

Tem

pera

ture

55 to

100

F10

00 o

hm th

erm

isto

r or

res

ista

nce

tem

pera

ture

de

tect

or (

RT

D)

AI

50 to

110

F0

.2F

0.0

1F

11

42A

mbi

ent D

ry-B

ulb

Tem

pera

ture

32 to

110

FIn

wea

ther

sta

tion

in f

ully

sha

ded

loca

tion

or

vent

ilate

d en

clos

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AI

20

to 1

40F

0.3

F0

.01

F1

5

43A

mbi

ent W

et-B

ulb

Tem

pera

ture

20 to

85

FIn

wea

ther

sta

tion

in f

ully

sha

ded

loca

tion

or

vent

ilate

d en

clos

ure

AI

0 to

100

F0

.3F

0.0

1F

15

Cal

cula

ted

Val

ues

51C

hille

d-W

ater

Pla

ntT

herm

al C

oolin

g O

utpu

t50

to 1

000

tons

(Dif

fere

nce

of 2

mea

sure

d va

lues

) [#

33, #

32]

mul

-tip

lied

by m

easu

red

valu

ed [

#26]

mul

tiplie

d by

a

cons

tant

#C

4*C

N/A

3%

tons

0.1

tons

15

54C

hille

d-W

ater

Pla

nt

Eff

icie

ncy

0.3

to 0

.8 k

W/to

n(S

um o

f mea

sure

d va

lues

) [#5

, #6,

#49

a, #

49b,

#9,

#1

0, #

24, #

25]

divi

ded

by c

alcu

late

d va

lue

[#51

]C

N/A

5%

kW

/tons

0.01

kW

/ton

15

55C

hille

d-W

ater

Pla

nt

Hea

t of

Rej

ectio

n0

to 1

300

tons

(Dif

fere

nce

of 2

mea

sure

d va

lues

) [#

35, #

34]

mul

-tip

lied

by m

easu

red

valu

ed [

#27]

mul

tiplie

d by

a

cons

tant

#C

5*C

N/A

3%

tons

0.1

tons

15

*AI

= a

nalo

g in

put;

DI

= d

igita

l inp

ut; C

= c

alcu

late

d va

lue;

#C

4 =

cons

tant

for

con

vert

ing

chill

ed-w

ater

flo

w ti

mes

T

to to

ns; #

C5

= c

onst

ant f

or c

onve

rtin

g co

nden

ser

wat

er f

low

tim

es

T to

tons

.

TABL

E A-

1

Exam

ple

Inst

rum

ent S

peci

ficat

ion

Ta

ble

(con

tinu

ed)

IDP

oint

Des

crip

tion

Mea

sure

men

t R

ange

Sens

or T

ype

or C

alcu

lati

on M

etho

dIn

stal

lati

on

Loc

atio

nIn

put

Typ

e*In

stru

men

tR

ange

End

-to-

End

A

ccur

acy

(% o

f re

adin

g un

less

not

ed)

Dat

aR

esol

utio

n

Ref

resh

In

terv

al

(min

)

Tre

nd

Inte

rval

(m

in)




--`,,`,,,,,`,`,`,`,,,,``,,,``,``-`-`,,`,,`,`,,`---


(This appendix is not part of this guideline. It is merelyinformative and does not contain requirements necessaryfor conformance to the guideline.)

INFORMATIVE APPENDIX BDETERMINATION OF kW/ton

B1. DETERMINATION OF kW/tonB1.1 A popular measurement of energy consumption inareas using I-P units for an electric-motor-driven chilled-water plant is kW/ton, where the total energy consumption inkWh is divided by the ton-hours of cooling generated by thatplant. It is the inverse of COP since it is the work applied, Wa,divided by the work done, Wd. The work applied is merely thesum of the kWh consumed by the chilled-water plant. Thework done is determined in ton-hours of cooling. One ton-hour of cooling is equal to 12,000 Btu/h, so:

(tons) (B-1)

B1.2 The kW/ton for all water solutions is therefore:

(kW/ton) (B-2)

B1.3 For most chilled-water plants using standard water,Equation B-1 is changed by substituting with 500 Qw inEquation B-2 and changing cp to 1.0. Therefore:

(kW/ton)

Substituting (T2 T1) for T yields

(Kw/ton) (B-3)

B1.4 It is often desirable to convert one of the two terms,kW/ton or COP, to the other. This is done by making a con-stant equal to Qw (T2 T1) kW. Now Equation 5 forCOPw in Section 7.2.4 becomes 6.826 and Equation B-3for kW/tonw becomes 24 . Solving forresults in

= 6.826 COPw = 24 kW/tonw

or or (B-4)

B1.5 Equation B-4 is applicable to all water solutions,including glycols.

Wdmw cp T

12 000--------------------------------=

WaWd------- kW

mw cp T12 000--------------------------------

--------------------------------------=

kW500 T

12 000--------------------------------- -------------------------------------- 24 kW T------------------------=

kW/tonw24 kW

T2 T1 ---------------------------------=

COPw3.517

kW/tonw---------------------= kW/tonw

3.517COPw---------------=




--`,,`,,,,,`,`,`,`,,,,``,,,``,``-`-`,,`,,`,`,,`---



INFORMATIVE APPENDIX CUNCERTAINTY IMPACTS ON MEASUREMENT REQUIREMENTS

The material for this appendix is taken largely from apaper written by Stephen Treado and Todd Snouffer in 2001entitled Measurement Considerations for the Determinationof Central Plant Efficiency. It was published in ASHRAETransactions 107(1):401.C-1

C1. INTRODUCTIONIn order to evaluate chiller efficiency and operate the

chiller at its highest efficiency, it is necessary to accuratelymeasure the variables that determine chiller efficiency and tohave the capability of modifying control points to manipulateoperating efficiency (Kaya 1991).C-2

Chilled-water plants are rarely instrumented to provide anefficiency measurement. However, if the boundaries of thecentral plant control volume are taken in their broadest sense,several electrical power measurements must be made, andchilled-water measurements must be made at the inlet andoutlet of the chilled-water distribution system. For ratingpurposes, the Air-Conditioning, Heating, and RefrigerationInstitute (AHRI) has developed a standard for measuring full-load and part-load chiller efficiency (AHRI 550/590).C-3 Thisstandard specifies the operating conditions, including coolingcapacity and chilled-water temperatures. While efficienciesmeasured using this procedure may be valid, they may not beindicative of the chiller efficiency that might be obtained inactual practice due to differences in operating conditions(Austin 1991; Schwedler 2003).C-4, C-5

C2. MEASUREMENT EQUIPMENTC2.1 Electrical Power. The accurate measurement of elec-trical power usually presents the least challenge in terms of res-olution, accuracy, and reliability. Appropriate sensors andtransducers are commercially available covering a wide rangeof voltage and current inputs. It is important that the measure-ment system give an accurate indication of true RMS power,including any effects of power factor. Care must be taken toensure that the sensors and transducers are capable of accu-rately measuring the frequencies at which the equipment isoperating, including any significant harmonic content. The pri-mary consideration in this regard is the fundamental frequencyof the electrical power input, which is typically 50 or 60 Hz butmay vary for different equipment depending upon the locationof the power sensing elements. Accuracies of better than 1% arereasonably achievable with newer instrumentation.

C2.2 Temperature. The primary temperature measure-ments for determining cooling capacity are the supply andreturn chilled-water temperatures. In addition, in order to pro-vide information for chiller operation and optimization, con-denser water temperature, outdoor dry- and wet-bulbtemperatures, and evaporator refrigerant temperature mayalso be needed. These parameters are useful for the determi-

nation of the most efficient operating condition for a chilled-water system.

Temperature sensors can be located in wells inside waterpiping. Air temperature measurements require adequateshielding from radiation. If long sensor leads are anticipated,it may be desirable to connect the temperature sensors to trans-mitters that provide a 4-20 mA output to the central controlsystem. This approach may also simplify wiring by reducingthe number of signal leads required.

Temperature instrumentation should be installed close tothe upstream (inlet) of temperature-changing devices such aschillers and cooling towers but as far downstream (outlet) aspractical to ensure any temperature stratification in theoutflow is well mixed.

Several types of temperature sensors are available forthese applications. Following are examples listed from theleast accurate to the most accurate.

C2.2.1 Thermocouples have been utilized extensivelyand have the advantage of being rugged, self-powered, rela-tively low in cost, stable, and durable. The disadvantages ofthermocouples are the need for temperature compensation anda relatively large uncertainty of approximately 0.6C (1F).

Greater accuracy in the measurement of temperaturedifference can be obtained through the use of a differentialthermopile consisting of a series of thermocouple junctions.An uncertainty of 0.1C (0.18F) is possible. While not ascommonly encountered as other temperature sensing systems,this arrangement provides several advantages. First, themagnitude of the electrical signal produced by a thermopile isgreater than from a single thermocouple since each pair ofjunctions contributes to the thermopile voltage, thereby multi-plying the output in proportion to the number of thermocouplejunctions. Second, the array of junctions can be distributedover a cross section of the flow area, giving a more accurateindication of average temperature in cases where the fluidtemperature is not uniform. Third, temperature compensationis not required for a thermopile since temperature difference,and not absolute temperature, is being measured. The conver-sion of thermopile voltage to temperature is nearly linear overtypical temperature ranges for these applications. However,there still may be a need to know the absolute fluid tempera-ture in order to evaluate thermal properties, such as specificheat, and to provide operational information.

C2.2.2 Resistance temperature detectors (RTDs) arealso very accurate and nearly linear over typical temperatureranges of interest for these applications. They also requireexcitation voltages and are considerably more expensive thaneither thermocouples or thermisters. With proper calibration,uncertainties of better than 0.1C (0.18F) can be achieved.

C2.2.3 Thermisters provide greater sensitivity and accu-racy but are more costly. Thermisters require an external exci-tation circuit so that their resistance can be determined bymeasuring the voltage drop and current flow. Temperaturemeasurement accuracy is limited by the ability to measure thevoltage drop across the thermister and current flow. Thethermister itself can be calibrated to an uncertainty of 0.001C(0.0018F). The calibration must be performed at a minimumof three temperatures to enable an adequate curve fit for the




--`,,`,,,,,`,`,`,`,,,,``,,,``,``-`-`,,`,,`,`,,`---


temperature/resistance characteristics. With this procedure,system measurement uncertainties of better than 0.1C(0.18F) are easily obtained.

C2.3 Chilled-Water Flow Rate. The measurement ofchilled-water flow rate is the most difficult task in the processof determining chiller efficiency. That is because flow mea-surements are typically invasive and because flow rate is notuniform over most flow cross sections. The measurement offluid flow generally requires consideration of adequate runsof straight pipe or duct and minimization of turbulence-inducing elements. Calibration of flow rate measurement sys-tems is also a tricky prospect, since flow characteristics maydiffer between the calibration and the actual installation. Theeffect of this is that factory calibrations may not be suffi-ciently accurate for field installations, necessitating addi-tional field calibrations using transfer standards. In addition,some flowmeters create additional pressure losses, therebyaffecting system performance and reducing efficiency.

While laboratory flow measurement uncertainties of 1%or better are possible, field measurement accuracy will likelybe less, with uncertainties of 5% or greater commonlyencountered.

The selection of the appropriate flow sensor depends ona number of factors, including the magnitude of the flow rate,flow velocity, pipe size and type, as well as cost consider-ations. Since only a few flow sensors are required, cost maynot be a major concern. Durability and reliability are impor-tant considerations, and, in this regard, ultrasonic and pressuredrop meters may be of some advantage.

Meter calibration and installation are important issues forflowmeters. Sensing elements must be installed in accordancewith manufacturers instructions, including consideration ofrequirements for straight lengths of pipe and flow straighten-ing. Calibration can be accomplished by means of a transferstandard or by direct measurement. Flow conditions at cali-bration should closely match the conditions of use. Care mustbe taken to account for any effects of fluid properties, meterorientation, and flow disturbances, such as tees or bends. SeeASHRAE Guideline 14-2000, Measurement of Energy andDemand Savings, Annex A1.5, Liquid Flow,C-6 for a descrip-tion of the various types of flowmeters.

C3. CALIBRATION ISSUES

All sensors should be calibrated before installation unlessan in-situ calibration is to be conducted. Manufacturers cali-bration data may be sufficient as long as the installation condi-tions match the conditions of calibration. Manufacturerscalibration data should include documents of traceability tothe calibration facility and, ultimately, traceability to nationalstandards, typically NIST standards.

Periodic calibration checks and recalibration may berequired for measurement sensors. In addition, the entiremeasurement system must be maintained in proper calibra-tion, including not only the sensing elements but also voltageand current measurement devices and analog to digitalconverters. System calibrations should be checked on a regularbasis. It is also useful to make a determination of measurement

uncertainty in order to place error bands on chiller efficiencymeasurements.

Sensor calibrations may not be simply single values butmay be functions of the ambient conditions or the state of themeasured media. For this reason, supporting measurementsmay be necessary to allow the determination of the primarymeasurement value.

C4. MEASUREMENT RESOLUTION, ACCURACY, AND UNCERTAINTY

Three related parameters that can be used to describe thecapabilities of a measurement system are resolution, accuracy,and uncertainty. Resolution is the smallest change in themeasured quantity that can be detected. Accuracy is the capa-bility to indicate the true value of the measured quantity, whileuncertainty is the estimated value for the error in a measuredquantity, i.e., the difference between the measured value andthe true value. The overall resolution and error in the determi-nation of chiller efficiency involves the individual sensor char-acteristics and the form of the relation used to compute chillerefficiency.

Resolution is a function of sensitivity or responsivity ofthe sensor and the characteristics of the readout device. Obvi-ously, the resolution should be sufficient to provide therequired accuracy, but typically resolution will exceed abso-lute accuracy. Resolution should never be mistaken for accu-racy, however, since accuracy is limited by the uncertainty ofthe measurement, not the minimum resolvable measurementincrement. Measurement accuracy is determined by themeasurement uncertainty. Uncertainty includes both system-atic offset (bias) and random errors (precision). Calibrationcan help reduce bias, while random errors can be treated usingstatistical methods.

The required measurement accuracy is determined by theeventual use of the efficiency data. If the range of expected effi-ciency values is narrow and it is desired to be able to distinguishbetween small differences in efficiency, then obviously highaccuracy is required. For example, if chiller efficiency isexpected to vary by only 10% over the full range of operatingconditions, then a measurement uncertainty of only 1% mightnot be acceptable since this would represent one-tenth of thefull range. Since chiller efficiency tends to be in the range of3 to 7 COP (0.5 to 1 kW/ton), a measurement uncertainty of 1%of the reading would represent about 0.05 COP (0.01 kW/ton).

The contribution of the individual uncertainties to theoverall measurement error, in terms of probable errors, can becomputed using the root-sum square formula, as follows:

(C-1)

where

uN = individual uncertainty of variable N

= partial derivative of efficiency with respect tovariable N

N = mass flow rate, electrical power input, ortemperature difference

Errorrms uNN-------

2 1 2

=

nN-------




--`,,`,,,,,`,`,`,`,,,,``,,,``,``-`-`,,`,,`,`,,`---


For each sensor, the maximum individual uncertainty,given a desired overall uncertainty for chiller efficiency of uo,can be found from the following equation:

(C-2)

This relation provides the accuracies needed for individ-ual measurements in order to achieve the desired overall accu-racy; however, accuracy trade-offs can be made to achieve thesame overall uncertainty. Thus, for example, a smaller uncer-tainty in the electrical power measurement will allow a largeruncertainty in the flow measurement while still meeting theoverall measurement accuracy goal.

The following examples use a chiller from the NISTcentral plant to illustrate the uncertainty analysis. The individ-ual uncertainties shown are sample values.

Example 1Chiller electrical power E = 2100 kW 2.1 kW (0.1%

of reading)Chilled-water flow rate = 7000 gpm 210 gpm (3.0%

of reading) or 3.5106 lb/h 105,000 lb/hTemperature change of chilled water T = 12F 0.1F

(0.8% of reading)From Equation B-3, the chiller efficiency is 5.86 COP

(0.6 kW/ton). From Equation C-1, the average root-sumsquare error is 0.182 COP (0.0190 kW/ton) or 3.1%.

Example 2Using conditions similar to those in Example 1, assume

that conditions produce a smaller T. It is assumed that theactual performance is worse than in Example 1. How does thisaffect the uncertainty requirements for each measurement?

Chiller electrical power E = 1400 kW 1.4 kW (0.1%of reading)

Chilled-water flow rate = 7000 gpm 210 gpm (3.0%of reading) or 3.5106 lb/h 105,000 lb/h

Temperature change of chilled water T = 6F 0.1F(1.7% of reading)

From Equation B-3, the chiller efficiency is 4.4 COP(0.8kW/ton). From Equation C-1, the average root-sum squareerror is 0.152 COP (0.028 kW/ton) or 3.5%

Example 3

Using similar conditions as in Example 1, assume that thechiller is provided with one-half of its typical flow. It isassumed that the actual performance is close to that inExample 1. How does this affect the uncertainty requirementsfor each measurement?

Chiller electrical power E = 1100 kW 1.1 kW (0.1%of reading)

Chilled-water flow rate = 3500 gpm 105 gpm (3.0%of reading) or 1.75106 lb/h 52,500 lb/h

Temperature change of chilled water T = 12F 0.1F(0.8% of reading)

From Equation B-3, the chiller efficiency is 5.60 COP(0.628 kW/ton). From Equation C-1, the average root-sum-square error is 0.174 COP (0.020 kW/ton) or 3.1%

For an example of the effects of energy use, T, and vari-able flow for both COP and kW/ton calculations, please see"Guideline 22 Appendix C Uncertainty Table.xls." This filecan be downloaded for free from the ASHRAE Web site athttp://www.ashrae.org/G22.

C5. REFERENCES FOR APPENDIX CC-1Treado, S., and T. Snouffer, Measurement considerations

for the determination of central plant efficiency,ASHRAE Transactions 107(1):401, 2001.

C-2Kaya, A. Improving efficiency in existing chillers withoptimization technology. ASHRAE Journal 33(10):3038, 1991. See also Nugent, D., 1999, High efficiencychillers (Internet article).

C-3AHRI Standard 550-2003, Centrifugal or Rotary ScrewWater-Chilling Packages, Air-Conditioning, Heating,and Refrigeration Institute, Arlington, VA, 2003.

C-4Austin, S., Optimum chiller loading, ASHRAE Journal33(7):4043, Oct. 1991.

C-5Schwedler, M. Take it to the limit... or just halfway,ASHRAE Journal 40(7):3233,3639, 1998.

C-6ASHRAE Guideline 14-2002, Measurement of Energy andDemand Savings.American Society of Heating, Refrig-erating and Air-Conditioning Engineers, Inc., Atlanta.

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INFORMATIVE APPENDIX DDATA GATHERING AND TRENDING

D1. AVERAGING CALCULATION METHOD

The measured value from instruments is unlikely to beconstant and can fluctuate to a greater or lesser extent depend-ing on the installed conditions and the instrument employed.For calculation, display, and recording purposes, all datashould be continuously averaged over a short time period toremove the fluctuations (a calculation method commonlyreferred to as smoothing) and provide meaningful data towork with. This has the benefit that the information will moretruly reflect the true operating conditions of the plant. Thefollowing describes a method that can be used to providesmoothed data.

Once during each trend interval, calculate the instanta-neous COP (kW/ton).

Then average the current instantaneous value into thecurrent average with a weight of approximately 1/4 accordingto the following formula:

COP (kW/ton) =[3 COP (kW/ton) + Current COP (kW/ton)] / 4

Decreasing the current interval weighting is accom-plished by increasing the value of the multiplier (shownas 3 in the above expression) and the divisor (shownas 4 in the above expression). The multiplier is always1 less than the divisor.

Increasing the current interval weighting is accom-plished by decreasing the value of the multiplier and thedivisor (the multiplier is always 1 less than the divisor).

For greater stability, decrease the weighting of the currentintervals instantaneous COP (kW/ton). For more definitionand granularity, increase its weighting.

D2. DATA DISPLAY AND SHORT-TERM TRENDSThe COP (kW/ton) value is displayed on the chiller plant

operation workstation plant graphics. It is also recommendedthat the COP (kW/ton) be averaged over five-minute intervals;record these values on the data recording device and trend fora minimum of seven days along with outdoor air temperature(OAT), wet-bulb temperature (calculated from OAT andoutdoor air humidity [OAH]), plant power input (kW), andplant output (tons or kW).

D3. DATA RECOMMENDED FOR TRENDING OVER ENTIRE LIFE CYCLE OF PLANT

Note that the following values are intended for perfor-mance oversight and are trended in addition to normal equip-ment operating trends.

1. Average days outdoor air temperature (obtain the outsideair temperature every 30 minutes and find the average ofthese samples each day)

2. Days high temperature3. Days low temperature4. Days high wet-bulb temperature (calculate from OAT and

OAH)5. Chilled-water supply temperature (average, max and min if

chilled-water temperature is not fixed)6. Total ton-hours (kWh) production of chilled water for the

day7. Total kWh power input for each component for the day8. Average kW/ton (COP) for the plant for the day

It is also recommended that this daily data be recordedand archived for the entire life of the plant.




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INFORMATIVE APPENDIX E EXAMPLE SPECIFICATION LANGUAGE

This sample contract language is provided for the conve-nience of users who desire to hire an outside agency or vendorto install the instrumentation for monitoring the efficiency ofa central chilled-water plant. The sample language and exam-ple tables must be modified to fit the users particular needsand specific chilled-water plant. Although this contract isprimarily written in mandatory language (e.g., shall), its useis not required to meet the recommendations of this guideline.

I. Work Included

A. The contractor shall provide equipment, software, instal-lation, programming, functional testing, documentation,training, and training documentation capable of meetingthe performance monitoring requirements listed below.

II. System Description

A. The performance monitoring system is intended to pro-vide in-house operators and facilities staff with the meansto easily assess the current and historical performance ofthe facilitys chilled-water system and components withrespect to the performance metrics listed in Section III.

B. The performance monitoring system shall includeinstrumentation, data communication hardware andsoftware, and additional programmed and operationalsoftware capable of collecting and archiving all data suf-ficient to generate, visualize, and report the performancemetrics listed in Section III.

C. The performance monitoring system shall include soft-ware for analyzing and displaying both measured andcalculated data as described in Section VII.

D. The quality of any measurement is determined by theattributes of the sensor, any signal conditioning (if pres-ent), the data acquisition system and the wiring connect-ing them, any calibration corrections that are applied,the sensor installation, and field conditions. Accuracy,precision, linearity, drift or stability over time, dynamicor rate of response, range, turn-down, sample or scanrate, resolution, signal-to-noise ratio, engineering unitconversion and math functionality, and data storage andretrieval frequency are all terms used to describe thequality of the measurement system and its components.The level of measurement rigor required in this specifi-cation is intended to provide sufficient data quality overtime for identifying/establishing the specified perfor-mance metrics and benchmarks. Through-system mea-surement accuracy goals for individual measurementpoints and metrics are as shown in Table E-1. Individualinstrumentation requirements are provided in order tomeet these goals.

III. Performance Metrics and Data Points

A. The primary purpose of the performance monitoringsystem is to provide facility managers and operatorswith easily interpreted feedback on the current and his-torical performance of the facility chilled-water system.To this end, this section defines those aspects of perfor-mance that must be measured, calculated, and reported.The defined aspects of performance are referred to hereas performance metrics. Each key performance metric isdefined below, along with the control data points that arenecessary for calculating and reporting each metric.Instrumentation requirements, point names, and calcula-tion methods are specified in Section IV.

B. To be of optimum use to building managers and opera-tors, the performance monitoring system should alsoprovide benchmarks that define the range of expectedperformance for each performance metric.

C. Chiller Efficiency (kW/ton): Instantaneous power inputper cooling output of each chiller. The objective is toachieve accuracy better than 2% for the kW/ton. Thisperformance metric requires the following performancemetrics and data points.

1. Chiller Power (kW): Instantaneous chiller powerinput.

2. Chilled-Water Output (tons): Instantaneous chilled-water cooling output from chiller.

D. Chilled-Water Plant Efficiency (kW/ton): Instantaneouspower input per cooling output versus required load.The objective is to achieve accuracy better than 4% forthe kW/ton for the chilled-water plant. This perfor-mance metric requires the following performance met-rics and data points.

1. Chilled-Water Plant Power (kW): Instantaneouschiller, chilled-water pumps (including primary,secondary, and others, if applicable), tower fans,and condenser water pumps power inputs.

TABLE E-1 Through-SystemMeasurement Accuracy Goals

Measurement Point or Metric Accuracy Goal

Outside ambient temperature (F) 0.2F

Outside ambient wet-bulb temperature (F) 0.2F

Water temperature (F) 0.1F, if 5F TWater delta temperature (F) 2% of reading

Water flow (gpm) 2% of reading, if >115 fps

Power (kW) 1.5% of reading

Chiller cooling output (tons) 3% of reading

Chiller cooling energy (ton-hrs) 3% of reading

Electric energy use (kWh) 3% of reading

Chiller performance (kW/ton) 4% of reading

Chilled-water plant performance (kW/ton) 4% of reading




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2. Chilled-Water Plant Thermal Cooling Output(tons): Instantaneous chilled-water plant coolingoutput.

E. Average Chilled-Water Plant Thermal Cooling Output(tons): 30-minute running average of the instantaneouschilled-water plant thermal cooling output.

F. Maximum Average Chilled-Water Plant Thermal Cool-ing Output (tons): Maximum 30-minute running aver-age of the instantaneous chilled-water plant thermalcooling output. Provide maximums for daily, monthly,and yearly time intervals.

G. Daily Chilled-Water Plant Thermal Cooling Energy(ton-hours): Total chilled-water plant thermal coolingoutput provided in a 24-hour period.

H. Maximum Daily Chilled-Water Plant Thermal CoolingEnergy (ton-hours): Maximum 24-hour total chilled-water plant thermal cooling output. Provide maximumsfor daily, monthly, and yearly time intervals.

I. Site Weather: On-site outdoor ambient air temperaturesobtained external to the building.1. Outdoor ambient air dry-bulb temperature (F)2. Outdoor ambient air wet-bulb temperature (F)

IV. Instrumentation and Data RequirementsA. Liquid Flowmeters

1. Each flowmeter shall have a rated instrument accu-racy within 1% of reading from 3.0 through 30 fpsand 2% of reading from 0.4 through 3.0 fps veloc-ity. Precision shall be within 1.0% of reading.Resolution of any signal conditioning and readoutdevice shall be within 0.1% of reading. The instru-ment shall be capable of measuring flow within thestated accuracy over the entire range of flow. Flow-meters shall be rated for line pressure up to 400 psi.These requirements include the sensor and any sig-nal conditioning.

2. Each flowmeter shall be individually wet calibratedagainst a volumetric standard accurate to within0.1% and traceable to the National Institute of Stan-dards and Technology (NIST). Flowmeter accuracyshall be within 0.5% at calibrated typical flowrate. A certificate of calibration shall be providedwith each flowmeter.

3. When dictated by multiple elbows and other distur-bances upstream and short available pipe runs, theflow measurement station shall provide compensationfor rotational distortion in the velocity flow profile.

4. Insertion-style flowmeters shall be provided withall installation hardware necessary to enable instal-lation and removal of flowmeters without systemshutdown. No special tools shall be required forinsertion or removal of the meter.

5. Inline-style flowmeters shall be installed with abypass assembly and isolation valves to enableinstallation and removal of these flowmeters with-out system shutdown.

6. Dual turbine, vortex shedding, or magnetic flowme-ter (per approved submittal).

7. Magnetic Full Bore Meter (Preferred): Sensor shallbe installed in a location clear from obstruction5 pipe diameters upstream and 2 pipe diametersdownstream, including pipe elbows, valves, andthermowells.

8. Insertion Vortex Shedding Meter: Sensor shall beinstalled in a location clear from obstruction10 pipe diameters upstream and 5 pipe diametersdownstream, including pipe elbows, valves, andthermowells.

9. Dual Turbine Meter: Flow sensing turbine rotorsshall be non-metallic and not impaired by magneticdrag. Sensor shall be installed in a location clearfrom obstruction 10 pipe diameters upstream and5 pipe diameters downstream, including pipeelbows, valves, and thermowells.

10. Verify that air vents or other air removal equipmentexists in the system piping. If none exists, install appro-priate air-removal equipment downstream of flowmeter.

B. Fluid Temperature Devices1. Each temperature measurement device shall have a

rated instrument accuracy within 0.1F (0.056C).Precision shall be within 0.1F (0.056C). Resolu-tion of any signal conditioning and readout deviceshall be within 0.05F (0.0278C). These require-ments include the sensor and any signal condition-ing.

2. Temperature measurement devices, including anysignal conditioning, shall be bath-calibrated (NISTtraceable) for the specific temperature range foreach application. Temperature measurement devicesused in differential temperature measurement shallbe matched and calibrated together by the manufac-turer. The calculated differential temperature used inthe energy calculation shall be accurate to within 2%of the difference (including the error from individualtemperature sensors, sensor matching, signal condi-tioning, and calculations).

3. All piping immersion temperature sensors shall beinserted in newly installed brass or stainless steelwells that are located downstream of flowmeterplacement and that allow for the removal of the sen-sor from the well for verifying calibration in thefield. Allow for at least 2 pipe diameters upstreamand 1 pipe diameter downstream clear of obstruc-tions. The well shall penetrate the pipe a minimumof at least 2 in. (50 mm) and a maximum of up tohalf the pipe diameter. The use of direct immersionsensors is not acceptable.

4. All piping immersion temperature sensors shall becoated with heat or (thermal) paste prior to beinginserted in the wells. The paste shall be rated andkeep consistency over the expected temperaturerange. A thermal-conducting metal oxide, a dielectricsilicon-based compound, is available with an opera-tional range of 65F to 400F (54C to 205C).

C. Btu Meters1. The entire Btu measurement system shall be manu-

factured by a single manufacturer and shall consist




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of a flowmeter, two solid-state temperature sensors,a Btu meter, thermowells, all required mechanicalinstallation hardware, and color-coded intercon-necting cable. The entire system shall be serializedand include NIST-traceable factory wet calibrationof the complete system. All equipment shall be cov-ered by a manufacturers transferable two-year NoFault warranty.

2. The requirements in A and B above apply.3. Each Btu meter shall provide a solid-state dry con-

tact output for energy total and analog outputs (420 mA or 010 VDC) for thermal rate, liquid flowrate, supply temperature, and return temperature.As an alternative to the analog outputs, the Btumeter shall provide serial communications compati-ble with the data acquisition system. The interfacemeter to the data acquisition system shall provideaccess to all available data.

4. The analog thermal rate output and dry-contactenergy output shall have a rated accuracy within2% of reading.

5. The maximum dry-contact energy increment shallbe no more than 1/10,000 of full scale (1000 tonsyields 0.1 ton-hours per pulse = 10,000 pulses perhour = 2.78 Hz).

6. The Btu meter electronics shall be housed in a steel8 10 4 in. NEMA-13 enclosure and shallinclude a front-panel-mounted two-line alphanu-meric LCD display for local indication of thermalrate, liquid flow rate, and supply and return temper-atures. A single 24 or 120 VAC connection to theBtu meter shall provide power to the meter elec-tronics and to the flowmeter. Each Btu meter shallbe factory programmed for its specific applicationand shall be re-programmable by the user using thefront panel keypad (no special interface device orcomputer required). A cer

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