ASHRAE-D-21513-20100324

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Heat Gain from Electrical and Control

Equipment in Industrial Plants

ASHRAE Research Project 1104-TRP

PHASE I – PART A:

CLASSIFICATION

PART B:

TEST PLAN

Warren N. White, Ph.D.

Department of Mechanical and Nuclear Engineering

and

Anil Pahwa, Ph.D.

Department of Electrical and Computer Engineering

Kansas State University

June 10, 2001

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List of Figures

FIGURES

Figure 1: ASD Test Apparatus . . . 35

Figure 2: Apparatus for Testing Losses in Circuit Breakers . . . 46

Figure 3: Apparatus for Testing Losses in Reactors . . . 54

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List of Tables

TABLES

Table 1: Equipment to be Investigated . . . 3

Table 2: Equipment Categories . . . 3

Table 3: Equipment Table Summary . . . 7

Table 3a: Equipment Table Summary (continued) . . . 8

Table 4: Limits for Temperature Rises . . . 19

Table 5: Influence of 20 oC Change in Ambient Temperature on Load Loses . . . 20

Table 6: Components of Composite Equipment . . . 56

Table 7: Electric Power Equipment to be Tested . . . 75

Table 8: Budget for Testing for ASHRAE TRP 1104. . . 76

Table 9: Phase II Time Schedule for Completion of Work . . . 77

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Introduction and Executive Summary

In order to size the required equipment, the HVAC design engineer must be able to estimate with certainty the amount of energy added from various heat sources and lost through various heat sinks located in a room. Heat could be added from several sources such as the presence of many people in a classroom or office, solar radiation through windows, and incandescent room

lighting. A sink could consist of outside doors and windows in winter or a basement floor or wall that remains at an essentially constant temperature throughout the year. By closely estimating the heat gain or loss, the HVAC equipment will not be undersized with insufficient capacity or oversized with costly unutilized excess capability.

Building and industrial plants make use of electrical power for many uses such as lighting, driving motorized devices, HVAC, and energy transmission and distribution throughout the structure. All of this electrical equipment contributes to the total heat load. Estimating the total amount of rejected heat is a necessary part of sizing the heating and refrigeration equipment required for the building.

The primary source of information available to the design engineer for estimating the electrical equipment rejected heat is the paper by Rubin (1979). In this well used document, the rejected heat values for transformers, power distribution equipment, motors, switchgear, and power cables, to name a few, were presented in tables for a range of equipment sizes common to indoor equipment. The data presented by Rubin was obtained from the paper presented by Hickok (1978) and from other, unspecified manufacturers. Hickok, who worked for GE at the

publication time of his paper, states, “The data are on General Electric products …” At no point in either Hickok’s paper or in Rubin’s paper is there a discussion of measurement procedure or measurement uncertainty. Rubin’s motivation for publishing the data was to aid the HVAC design engineer. Hickok’s motivation in his paper was to aid the factory engineer in identifying plant locations where efficiency could be improved. Hickok’s motivation is easy to appreciate since the energy price shocks provided by two oil embargoes made increasing efficiency of existing plants, buildings, and factories the first choice in reducing the costs of production. McDonald and Hickok (1985) later co-authored an update of Hickok’s 1978 paper with much of the same data.

The information provided by these papers is dated. Since the oil embargoes of the 1970’s, many electrical equipment manufacturers have taken pains to increase the efficiency of their products. At the same time, advances in power electronics and computer control have made much of the technology reflected in the 1970 equipment obsolete. Another change that has occurred since Rubin published his work is that the manufacturing standards that apply to the various items of power equipment have been re-issued and updated several times. These standards could provide details for measuring the power loss in the equipment where, perhaps, originally none existed. Also, the standards might specify a maximum level of uncertainty for performing the

measurements and any data reported by a manufacturer claiming to follow the standard could be deemed reliable. Thus, there is a need to update the 20 years old information presented by Rubin. A recent addition to the published information regarding motor heat gains is contained in Chapter 11 of the 1997 ASHRAE Fundamentals Handbook which provides a table of “Heat

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Gains from Typical Electric Motors” for fractional horsepower AC motors up to 250 horsepower three phase motors.

The purpose of this work is to provide a means of estimating the rejected heat of specific electrical equipment by a means similar to Rubin, but which accounts for updated data, current testing standards, level of use, and more than one power equipment manufacturer. To

accomplish this goal, the work is divided into phases consisting of an assessment of the

availability of reliable data and a testing phase for providing a reference for those data deemed uncertain. Phase I of this project consists of an assessment part and a test planning part. The assessment part (Part A) requires a review of the heat loss measurement procedures included in the manufacturing standards for each type of power equipment included in this study along with a survey of the measurement procedures used by manufacturers when the standards do not cover this type of measurement. Based on the results of this assessment, a testing program is planned (Part B of Phase I) to verify loss information supplied by manufacturers. Phase II consists of the execution of the data gathering and testing program.

This document describes the assessment and test - planning phase of the investigation. The organization of the material to be presented includes a summary of the Phase I conclusions and the recommendations concerning the Phase II work. Also included, is a description of the method or strategy used in the assessment. The results of the assessment will then be presented followed by a recommendation for those types of equipment to be included in the testing phase. The remainder of the report contains an examination of each type of equipment, the

manufacturing standards relevant to the assessment, and a discussion supporting the conclusions reached in the assessment.

Heat Loss and Heat Transfer

The equipment rate of heat losses to be determined in this work represent constant values from steady operation. The device rejecting heat is assumed to have reached thermal equilibrium with the surroundings and no thermal transient process is taking place. Thus, all heat loss occurring in a device is additional heat added to the surroundings. The manner in which the heat transfer takes place is not of a concern. Heat convection to the surroundings and conduction to surrounding structures is not hard to appreciate as viable transfer mechanisms. Any thermal radiation is assumed to be absorbed by the surrounding structures (perhaps after several

absorptions and re-emissions) and the eventual manifestation of the radiant energy is an increase in room temperature in the absence of any environmental control.

Assessment Results

The scope of the equipment specified in ASHRAE TRP – 1104 is listed in Table 1. The equipment review is divided into three categories. The first category consists of equipment for which either well defined methods for loss determination are specified in the manufacturing standards . The third category includes equipment for which there is no standard either requiring or describing any heat loss tests and for which no heat loss data could be found. The second

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category includes all equipment satisfying neither of the first and third category descriptions. Items in the second category represent a wide range of different conditions. The best description for this category is that information is available on equipment heat losses however the

measurement quality is unknown. The manufacturing standards covering rate of heat loss

Equipment Size Range

Electric Motors 10 – 4000 hp (reg. and high efficiency) Medium Voltage Switchgear (breakers,

heaters, and auxiliary compartments)

5 kV, 7.2 kV, and 13.8 kV with 1200, 2000, and 3000 amp breakers

Unit Substation Components (including breakers, heaters, bus losses, and auxiliary compartments)

800, 1600, 2000, 3200, and 4000 amp frame sizes

Transformers 300 – 2500 kVA and 120/208/600 V units

below 300 kVA

Reactors Standard Sizes

Panelboards Standard Sizes for 120, 125, and 600 V Cable and Cable Trays 0.6, 5, and 15 kV of widths 12” – 30”

Battery Chargers 100 to 600 amp

Inverters 20, 30, 50, 75, and 100 kV - single phase 150 kV – three phase

DC Switchgear 125 VDC for 100 to 1500 amp

Manual Transfer Switches 0.6 kV for 150, 260, 400, 600, 800, an 1000 amp

Motor Control Centers (starters, breakers, auxiliary relay compartments, bus losses, and space heaters)

Standard NEMA sizes

Variable (adjustable) Speed Drives 25 to 500 hp – three phase Table 1: Equipment to be Investigated

Category 1 Category 2 Category 3

Transformers Cable and Cable Trays Transfer Switches Motors Adjustable Speed Drives

Battery Chargers

Inverters Reactors

Circuit Breakers

Substation Components (heaters, bus losses, and auxiliary compartments) Panelboards

Motor Control Centers

Medium Voltage and DC Switchgear Table 2: Equipment Categories

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measurement of the second category equipment are in some cases excellent and in other cases poor or nonexistent. In the case where the standards for equipment in the second category provide good information regarding heat loss measurements, the following of the standards by the manufacturing community is not commonplace.

Table 3 is a summary of the results of the equipment under consideration including relevant standard numbers and overall results from the manufacturer surveys regarding losses. The details of the survey are included in the body of the report. The justification for the equipment classification is contained in the report sections to follow the Executive summary where the each device is discussed. The discussion in the sections to follow will support and expand the

information shown in Table 3.

The organization of Table 3 reflects the equipment classification, the results of finding and examining the relevant manufacturing standards, the results of the manufacturer survey, and finally the number of manufacturers reporting data through either their web pages, catalogs, or though their responses to the survey. The columns of Table 3 are arranged in the same order in which the equipment items are covered in the text of this report. The first category equipment is contained in the two equipment columns toward the left of the table. The third category

equipment item is contained in the rightmost column of the table. The three columns of the second category equipment labeled as Composite Devices consist of those devices which are made up of several different pieces of equipment, some of which are contained in the other columns of the table. The devices that fall into this distinction will be treated in a different way when the heat losses are discussed in the report. The leftmost column of the table contains subject headings regarding the standards search, the manufacturers survey, the deficiencies of the available data, the category the equipment item is placed into, and finally the details of the test plan. The lower part of the table contains space where additional manufacturing standard information is provided.

For each equipment piece, the relevant standard describing the power loss or efficiency

determination is listed. In some cases, there is more than one standard and in others cases there are no standards that address power loss. Where possible, the article number which addresses rate of heat loss and/or efficiency is listed. In some cases, such as NEMA MG 1, the loss testing procedures are spread over many articles. Whether the standard is commonly used by

manufacturers or not is also indicated in the table.

The next few lines of the table summarize the results of the manufacturer survey. The

approximate number of manufacturers is listed in the table. The source of manufacturer names for a given equipment item was the NEMA web site which has a search engine for such

purposes. The word approximate is used since the names of manufacturers obtained from NEMA for a specific equipment piece would consist of only NEMA members and this may exclude some foreign manufacturers. Any list of manufacturers for a particular equipment item would include both OEMs and equipment service companies. The immediate task once a group of names is obtained from NEMA is to eliminate all companies that are not OEMs. If a company did not have extensive information on their web site and if they did not respond to the survey, then the type of company might not be easy to determined. Also shown for some of the

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OEMs of this particular equipment type and size found (number following slash). The number of manufacturers contacted in the survey is listed. This number might be smaller than the

approximation number of manufacturers for the reasons just cited. The number of manufacturers who responded to the survey is also listed. Not all manufacturers who responded to the survey supplied data. Some responded that they were not an OEM or did not make products in the range under question. Finally, the number of manufacturers reporting heat gains is listed. This is the number of different manufacturers providing information through either a web site and/or a response to the manufacturer survey. The source of the data is next listed in the table which, in many circumstances, is the web site and/or catalog. The assessed quality of the data next follows in the table. Usually the data was classified as good or uncertain. When no data are available, the quality is listed as N/A.

Deficiencies in the data are next listed in the table. All of the five situations that apply are checked with an “X” in the table. If a standard detailing how heat loss and/or efficiency is available but not used by industry then the line titled “Standard but not used” receives a check. If the significant standard applying to the manufacture and testing of the device does not address heat loss or efficiency, then the box on the line of “Standard not germane to heat loss” is

checked. If the available loss data is measured in a way consistent with a standard, then the box titled “Data available and consistent” is marked. If the opposite is true then the box

corresponding to “Data available but not consistent” is marked. If no data is available, then the “Data not available” cell is marked.

In the section of the table titled “Recommended Testing,” the action to be taken with each device is listed. First the source of the data to be used in completing or building the loss tables is listed. For the Category I equipment, this is listed as “Manufacturers” while for Category II equipment, this is listed as “Man. and test” for Manufacturer and Test meaning that the data is coming from both sources. For Category III equipment, this is listed as “Test.” The purposes of the test are listed in the next line. The number of different sizes of each device to be tested is provided on the next line of the table. On the line of the table designating the number of test sizes, there are some notes for the equipment classified as “Composite Devices.” The composite devices or equipment are Category II items which can be characterized as consisting of a collection of many different components. Some of these different components are already listed in the table and no additional tests for these devices are needed. Some of the components of the composite devices are found in more than one composite device. If the composite device component is not already listed in the TRP 1104 Work Statement then some testing will need to be done but the testing of the component is mentioned in the table only once. In order to provide some estimation of the variation of the power losses of identical pieces of equipment, it would be beneficial to test more than one device of a given size and manufacturer. In order to best utilize the financial resources and the generosity of manufacturers, it is recommended that we test one device of a given size and manufacturer and then estimate the repeatability of the measurement through a knowledge of the manufacturer’s quality control. The use of one device for testing is especially viable when there exists manufacturer data to which a comparison can be made. In those cases where there is not a large amount of data, it is recommended that at least two identical items be tested. The number of identical items to be tested is listed on the next line of the table. The source of the equipment for the testing is specified as either loan or donation. There is money in the original project budget for building the test apparatus for measuring heat losses, however there are not

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sufficient financial resources for purchasing all the equipment to be tested. In order to appreciate how the losses of the same size equipment might vary from manufacturer to manufacturer, the number of different manufacturers from which to obtain equipment is listed on the next line of the table. In all cases where testing is warranted, it is recommended that equipment be obtained from at least 2 different manufacturers.

The lower portion of Table 3 contains additional standard information that did not fit in the upper area of the table.

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F irst C ategory S econd C ategory

E quipm ent T ype: T ransfo rm ers M otors

C ables & C able T rays

A djusta ble S peed D rive s

B a ttery

C ha rgers Inverters R eactors

C ircuit B reak ers M C C C o m ponen ts R eview T ype R eview S ubcategory R eleva nt S ta ndard s

S tan dard/D ate S ee B e lo w S ee B e lo w IE E E 83 5 IE E E 995 N E M A P E -5 N one IE E E C 57.16 IE E E C 37.09 N o ne

Is S tandard S pec ific to H eat G ains? Yes Yes Ye s Yes Y es N one Yes N o N /A

H eat G ain A rticle N o. S ee B e lo w S ee B e lo w Intro pp. 1-4 5 S ect. 5/ 19 87 8 .8 N /A 7.1, 11.4 5.1 4 / 1 999 N /A

U sed b y Industry? Yes Yes N /A N o N o N /A N o Yes N /A

M anufacturers

A ppro xim ate N um be r 30 2 7 36 21 4 18/4 33 /5 17/5 2 6

N um ber C ontacted 20 0 0 21 4 8 0 17 2 8

N um ber of R eplied 5 N /A 0 5 1 0 0 4 2

# R ep ortin g V alues fo r H ea t G a ins 2 N /A 0 7 3 3 1 2 2

H ow is data reported? W e b, C ata log , S ee B e lo w W eb, C at. F orm ula W e b, C at. W eb W eb W e b W eb, C a t. W eb, C at. Q u ality of data G oo d G oo d G ood U ncertain U nc ertain U ncertain U ncertain U ncertain U n certain D eficienc ies in D a ta

S tan dard but n ot used X X X

S tan dards not g erm a ne to heat loss X X X

D ata ava ilible a nd co nsisten t X X X

D ata ava ilible b ut not con sis tent X X X X X X

D ata not a vaila ble R ecom m ende d T estin g

D ata S ource M an ufacture rs M an ufacture rs C alculation M an. and test M an. and test

M an. an d

test M an. a nd test

M an. a nd

test M an. an d test

P urpo se of T est V e rify V erify V erify V erify V erify V erify

N um ber of T est S izes 2 3 2 3 2 S ee N ote 1

N um ber of T ypes w ithin each size >2 > 2 > 2 > 1 > 1 N /A

E quipm ent S ource

Loan or D onatio n Loan or D o nation Loan or D o nation P urchase P urc hase, D o nation, an d Lo an P urchase, D onation , and Loan

# o f d ifferent M an. E quipm ent to test 3 3 3 2 2 2 o f e ach item

A dd . S tan d./S ectio n/D ate IE E E C 57.1 2.90 IE E E 115 IE E E 83 5 IE E E 995

N E M A P E -5, 1 985 IE E E C 57.16 8.0, 9.4 / 199 9 4.1-4.6/19 95 1 994 S ect. 5/ 19 87 8 .8 / 1996 199 6 IE E E C 57.1 2.91 IE E E 112 8.0, 9.4 / 199 5 5,6 / 199 6 N E M A T P 2-1998 IE E E 113 - 1985 4.0 / 199 8 N E M A M G -1

N ote 1: LV C B , A S D , and enclosure s tested e lse w here - D is sconnect sw itches - test w ith m otor starters, m otor starters - 2 sizes, B us bars - calculatio n, space heaters - 2 sizes, A uxiliary com p artm ents - N ote 2: M V and D C C B , bu s ba rs, aux iliary com partm ents , space heaters, and enclosure s tested e lse w here - P otential, co ntrol pow e r, and current tra nsform ers - get m anufa cturer data

N ote 3: LV C B , bus b ars, an d en clo sures investigated e lse w here

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Testing

Equipment Accuracy Data

Source _No. of Man. No. of Sizes Total tests Add. Man. Req. Total No. to Test Add. Funds Req.

Transformers Sufficient Published Data

Motors Sufficient Published Data

Cables and Cable Trays

Sufficient Calculations

Bus Bars Sufficient Calculations

Reactors Fair Published Data

/Measurements

2 / 5 3 6 2 12

Motor Starters Fair Published Data /Measurements

2 / 5 2 2 2 8

20K

Space Heaters Sufficient Published Data /Measurements 2 2 4 Low Voltage Circuit Breakers Fair/ Not Certain Published Data /Measurements 1 / 5 3 3 3 12 17K Medium Voltage Circuit Breakers Fair/ Not Certain Published Data /Measurements 1 / 5 3 3 3 12 430K Adjustable Speed Drives Fair/ Not Certain Published Data /Measurements 2 1 Size each 2 3 6 41K Battery Chargers Fair/ Not Certain Published Data /Measurements Wait 3 410K Inverters Not Certain Published Data 2 3 6 320K Auxiliary Compartments Not Certain Published Data Manual Transfer Switches Not Available Not Available

TABLE 3a: EQUIPMENT SUMMARY (continued)

Table 3a lists different equipment categories, an assessment of the accuracy of the study results, the source of the equipment heat loss data, the number of different manufacturers from which test equipment will be obtained, the number of test sizes, the total number of items to be tested with the TRP – 1104 budget, the additional manufacturers necessary to test to change the accuracy designation, the total number of tests required to have a “Sufficient” accuracy

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Manufacturers” column, the table entry of “i / j’ denotes “i” manufacturers out of a total of “j” manufacturers found in this work. The assessment of accuracy is divided into three designations being “Sufficient,” “Fair”, and “Not Certain.” The designation of “sufficient” is applied to that equipment for which the results will be a realistic representation of the heat losses of this particular device and size. The next level of accuracy designation is “Fair” which is used in those situations where the subset of the different manufacturer products to be tested is deemed too small to warrant a “Sufficient” designation. In the case of reactors and combination motor starters, only 40% of the manufacturers found in this study can be tested using the equipment obtained through purchases and donations. The last designation of accuracy is “Not Certain” which is used for those situations where the only information available is manufacturer published data having neither documented test methods nor uncertainty. The “Not Certain” designation is used for auxiliary compartments and inverters since manufacturer loss data is available, however no test articles are available. The accuracy of some equipment items in Table 3a have been classified as “Fair/Not Certain” which has been applied in those situations where the sample of equipment to test is too small to draw conclusions. The “Fair/Not Certain” designation has been applied to low and medium voltage circuit breakers, adjustable speed drives, and battery

chargers.

The seventh column of Table 3a lists the number of additional manufacturers required. This figure refers to the number of other company manufactured equipment items that need to be tested in order to change the accuracy designation from “Fair” to “Sufficient.” The criterion for making this accuracy transition is to test 75% or more of the manufacturers, found in this study, of a particular equipment item and size. The last column of the table presents the expense of additional equipment to purchase so as to change the accuracy designation from that listed to “Sufficient.” For reactors and combination motor starters, this additional equipment expense is totaled together.

Based on Table 3a, there are several testing options available each with an additional expense for equipment purchase. These testing options are:

1) No additional expense – Accuracy per column of Table 3a.

2) 20K – Accuracy of transformers to combination motor starters in Table 3a is “Sufficient.”

3) 37K – Accuracy of transformers to low voltage breakers in Table 3a is “Sufficient.” The 37K include to 20K from the second testing option.

4) 1240K – Accuracy of transformers to inverters in Table 3a is “Sufficient.” This figure includes the 37K from the third testing option.

The total budget for TRP – 1104 is $138K. The second option listed above would bring the total project budget up to $158K. The third testing option would bring the total project budget up to $175K.

Note that the increase in expense for testing is exclusively for equipment purchase. Funding for equipment purchase does not incur university overhead. Also, purchases by Kansas State University are not subject to sales tax. Thus, every additional dollar for equipment purchase goes exclusively to that purpose.

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Conclusions and Recommendations

From the foregoing, it is evident that not all of the equipment listed in the TRP – 1104 work statement will be able to be tested. Even so, advantage still exists in continuing with the Phase II investigation. An examination of Table 3a shows that 50% of the items listed have received an accuracy designation of either “Sufficient” or “Fair.” Thus, the project as budgeted provides approximately half of the information desired. If additional funds were available for equipment purchase, the priority for using these funds would be:

• Purchase additional reactors and combination motor starters to change the accuracy designation for these two equipment items from “Fair” to “Sufficient.” While the selected reactor test items completely bracket the available equipment, only small to medium size combination motor starters are to be tested. The limiting factor for testing the NEMA 4 and NEMA 5 starters is expense.

• Purchase additional low voltage breakers. Owing to expense, only small to medium frame sizes are being tested in this work.

If $20K or $37K were available for equipment purchase, this would allow the additional testing of the reactors and the combination motor starters and possibly low voltage circuit breakers. The priority established in the above list is dictated by what additional testes are possible given a limited amount of additional funds.

The purchase of adjustable speed drives, battery chargers, and inverters for testing purposes is very expensive owing to the great expense of these power electronic devices.

As stated earlier, there is advantage in continuing with the Phase II investigation. The benefits of the Phase II work can be summarized as:

• This is the first update to the tables originally presented by Rubin in the late 70’s. The Phase II information will consist of test data and recently collected information from manufacturers.

• In addition to the updated loss information, methods of predicting losses for fractions of full load capacity and variations of room temperature will also be provided in the Phase II work.

• The tests and test methods will be documented so that the test procedures can be repeated and/or applied to new equipment.

• A design guide for using the accumulated heat loss information will be a product of the Phase II efforts. A significant feature of the results to be presented is that Phase II marks the start of being able to attach significance to the quality of estimated heat loads.

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In addition to the above recommendations, several conclusions are drawn on the basis of the Phase I work. These conclusions are:

• The Phase II work should continue since this allows the opportunity to begin the updating of Rubin’s work. As stated earlier, calibrated heat loss information for approximately half of the items listed in Table 3a can be developed in Phase II. In addition to the tested data, manufacturer published data has been gathered – even for some equipment devices for which testing will involve significant additional expense.

• There is a significant need for the information to be developed in this study. • The scope of this project is very larger.

• Serious consideration should be given to updating and refining the heat loss information through continued testing and future projects.

• The current study goes a long way in providing the necessary information and establishing a firm foundation for any future work and investigations in this area. • So that no testing opportunity is lost, recruitment of equipment will continue

throughout the testing portion of Phase II.

References

American Society of Heating, Refrigeration, and Air-Conditioning Engineers, 1997 ASHRAE Fundamentals Handbook, Chapter 28, “Nonresidential Cooling and Heating Load Calculations,” ASHRAE, 1997.

Hickok, Herbert N., “Electrical Energy Losses in Power Systems,” IEEE Transactions on Industry Applications, vol IA-14, no. 5, Sep-Oct 1978, pp. 373-387.

McDonald, William J. and Hickok, Herbert N., “Electrical Energy Losses in Power Systems,” IEEE Transactions on Industry Applications, vol. IA-21, no. 3, May – June 1985, pp. 803-819. Rubin, I. M., “Heat Losses from Electrical Equipment in Generating Stations,” IEEE Transactions on Power Apparatus and Systems, vol. PAS-98, no. 4, July-Aug. 1979, pp. 1149-1152.

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Phase I –Results

The Method

The method or strategy behind the assessment is described here. This is important information since this documents the approach taken and future inquiries along these lines can make use of this strategy and/or improve the strategy through modification. Without this information, any future inquiry would have to start from scratch as this study did. The strategy consists of a sequential process through which the conclusions regarding a specific type of equipment were reached. The specific types of equipment are listed in Table 1.

The steps of the assessment process consist of:

1) One very important source of information is equipment manufacturers.

Manufacturers of a particular equipment item were located through a search of the National Electrical Manufacturers Association web site located at the URL (http://www.nema.org/standards/) which has a manufacturers and product search capability. This search provided the starting point for any contact with equipment manufacturers. Together with the manufacturer name, recording the web site address together with e-mail address provides a means for making contacts and the location of information relevant to specific equipment.

2) In parallel to the effort of identifying equipment manufacturers, the manufacturing standards for the equipment under study relevant to heat loss were identified. The identification process began by creating a list of manufacturing standards relevant to the type of equipment. This was first attempted by searching manufacturer web sites for the specific standards that were followed in the equipment production. An improved method of accumulating this information was through the Global Engineering Documents web site (http://global.ihs.com) by clicking on the link to Document Search. This gives one the capability of searching for standard documents having a particular phrase or word in the title. The advantage offered by this search is the ability to receive titles of standards that are applicable to the product of interest from many standard organizations. Also, by doing a search on a partial standard number, for example C57, many standard titles from ANSI and IEEE related to transformers could be found. The list of relevant standards were refined by excluding those standards that did not address equipment heat loss or efficiency. In addition to the standards specified in the TRP-1104 work statement, standards from ANSI, NEMA, and UL were included in the review.

3) The relevant standards for each product were acquired. The number of standards to be examined is so large that the purchase of these documents was not an option.

Standards were acquired through Inter-Library Loan at the Hale Library at Kansas State University. A problem of searching other libraries for the standards is that many libraries do not list individual standards by number in their holdings, they only list that they have e.g. NEMA or ANSI standards.

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4) Each of the acquired standards were reviewed to determine if the standard requires power loss measurements to be made and if so how are the measurements to be performed and what are the uncertainty levels of the test procedures. The process of reviewing standards is best summarized as the determination of the heat gain

measurement requirements, measurement methods, measurement uncertainty, and measurement reporting. Based upon the results of the standard review, the specific equipment item was placed into one of two broad classes. One class consisted of those devices for which clear power loss measurement information was present while the other class consisted of those devices for which no power loss information was presented in the standard. While the standards helped in the eventual classification of the equipment, they were not used exclusively in the final equipment classification required by the TRP-1104 work statement. An example where no heat loss standards were found is the transfer switch. In contrast to the transfer switch example just cited, the availability of a document requiring and describing the measurement of heat loss does not necessarily mean that manufacturers will use the standard. Heat loss information was found for battery chargers in the standard NEMA PE 5 covering utility type battery chargers; however, no manufacturer was found that claimed to follow this relevant standard that specifies how battery charger efficiency is to be determined.

5) Contact though e-mail was made to the companies included on the NEMA obtained manufacturer lists to inquire about dissipated heat from their products. The

motivation behind this step was to acquire information useful to the eventual classification of the equipment. Since a contact was being made with equipment manufacturers, information not only relevant to the classification was sought but also information useful to other parts of the study. For each type of power equipment involved in the survey, a contact letter was written which explained the nature of the project and requested information relevant to this study. The requested information consists of the name and number of the standards followed in determining the loss numbers or the procedures used to determine the losses in the case where no loss determination procedures are specified in the standards. Also, the manufacturer is requested to supply loss numbers for their products or to specify the web pages and/or public company documents where loss figures are presented. In doing this company contact, the web address of that part of the company’s web site which best

corresponds to the product of interest was noted. The home web page address of the companies contained on the product manufacturer lists can also be found on the NEMA web site at the address (http://www.nema.org/membership/members.html).

Also the e-mail address to which the letter of contact is sent was recorded. In this fashion, we are able to put together an e-mail distribution list for the various products so that if we need to seek additional information at some time in the future, this can be quickly done. An example of the contact letter is included in the Appendix. This step was not done for every piece of equipment under study, e.g. cables, since it was not expected that power losses would vary from manufacturer to manufacturer and excellent cable loss models are available.

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6) Each of the equipment types is documented regarding applicable standards, loss measurement methods, and results of the manufacturer survey. From the

accumulated data, the equipment is classified into one of three categories as specifies by the TRP-1104 work statement. The overall results of the assessment are

summarized in the Introduction and Executive Summary section. The justification behind the classification is presented in each of the equipment sections of the report to follow. The manufacturer lists are not included in this document. The first

category consisted of those products for which the standards require specific tests for loss determination. Included in this first category are devices that have very well documented information regarding the power loss mechanisms and test procedures from which loss information can be accumulated and reported. This first category includes transformers and motors. The second category included those devices where there was some information that could be used to help in the loss determination but verification of the information was needed. The devices in this category are reactors, DC and medium voltage switchgear, circuit breakers, panelboards, motor control centers, inverters, battery chargers, adjustable speed drives, plus cables and cable trays. The remainder of the power equipment constitutes the third category that includes transfer switches. The third category is characterized by the situation where there is both an absence of loss data and the standards do not require the rate of heat losses to be measured.

7) From the assessment determined in the previous steps, a test plan is devised to provide the information necessary to complete this study for each of the equipment items listed in the ASHRAE TRP 1104 work statement. In case of the first category equipment, the information will be gathered from manufacturer web sites and through personal contacts. For the equipment in the second and third categories, the test plan involves experimental procedures for building and/or verifying the information necessary to complete this study. Both the steps of the test plan and the necessary experimental apparatus are described for each of the required equipment items.

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First Category

The first category consists of transformers and motors. Each of the first category equipment types will be examined here.

Transformers

Of all the equipment studied in this work, the state of the art for transformer losses is among the best defined. According to the insulating medium, transformers are divided into two categories which are liquid immersed units and dry-type units. The testing and manufacturing standards are written according to this insulating distinction. The sizes of the transformers covered in this study range up to 2.5 MVA. Specifically, the types of transformers under consideration are unit sub-station transformers from 0.3 to 2.5 MVA plus power and lighting transformers 300 KVA and below.

Review of Environmental Heat Gains

Standards

The method of testing to determine the total power losses for both dry and liquid immersed core and coils are specified in IEEE Std. C57.12.90 for liquid immersed windings and IEEE Std. C57.12.91 for dry type windings. Also relevant to the loss determination are IEEE Std. C57.12.00 and Std. C57.12.01 since these documents specify what is to be measured and also specify measurement uncertainty and IEEE Std. C57.12.80 which defines many terms used in the other cited documents.

Two other useful documents related to losses are NEMA TP 1 and NEMA TP 2 for distribution transformers. NEMA TP 1 defines a “Class 1” efficiency for distribution transformers which is presented in the form of a table. The table lists the minimum efficiency necessary for “Class 1” designation for both single and three phase units as a function of rated KVA. There is a table for dry type units and another table for liquid immersed units. For dry type units, the table in the standard makes a distinction between low voltage and medium voltage transformers. The “Class 1” efficiency essentially defines an upper limit for rejected heat. NEMA TP 1 and NEMA TP 2 observe the test codes presented in IEEE Std. C57.12.90 and C57.12.91. Dry type power and lighting transformers are covered in NEMA ST 20 which observes IEEE Std. C57.12.01 and C57.12.91.

Equipment Heat Losses

As stated earlier, it is assumed that the device under discussion is operating in a “steady state” capacity. Thus, it is assumed that the transformer has been operated in the current condition for a sufficient period of time that all thermal transients have decayed to the point that they can no longer be detected. Under these conditions, any energy loss is in the form of heat that travels to the local environment. The manner in which the heat transfer takes place is not of a concern. Heat convection to the surroundings and conduction to surrounding structures is not hard to

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appreciate as viable transfer mechanisms. Any thermal radiation is assumed to be absorbed by the surrounding structures (perhaps after several absorptions and re-emissions) and the eventual manifestation of the radiant energy is an increase in room temperature in the absence of any environmental control.

The definitions of total losses as defined by the standards are slightly different for liquid – immersed units and for dry type units. Each of these two cases will be treated separately. Not included in the loss figure is any power required for cooling fans, oil pumps, or any other

ancillary equipment. For units of 2.5 MVA or less, this is not an issue since the primary cooling means is free convection, however, forced air cooling is an option available on some larger unit substation transformers. The power consumed by the fan must be included in any loss figures. The rating and efficiency of the fan motor determines the environmental heat gain created by a forced air fan. The fan heat loss is small compared to that of the transformer. Units having a forced air cooling option will have different capacities and heat losses for each cooling mode, i.e. self cooled or forced air.

It should be noted that for both dry and liquid immersed type windings, both IEEE Std.

C57.12.00 and C57.12.01 state that transformers conforming to those standards are suitable for operation at rated KVA so long as the ambient temperature does not exceed 40 oC and the average ambient temperature does not exceed 30 oC in a 24 hour period.

To be presented in the following text is a discussion of no load and load losses for both dry and liquid immersed windings. The influence of the ambient temperature on losses will also be discussed. It will be shown that the variable to which the losses are the most sensitive is the load current while the ambient temperature does not play a significant role in determining the total losses.

Before discussing the different transformer types, the measurement of the winding resistance will be covered first since this is common to both transformer insulation types. The winding

resistance is measured after the unit has remained de-energized for a specific time (three to eight hours for liquid immersed units and 24 to 72 hours for dry type units) in a draft free area. The use of the time span is to assure that the unit is in thermal equilibrium with the environment and, thus, the winding temperature is known. Once the base resistance value is measured, the

winding resistance is used as a means of measuring the average winding temperature. The variation of resistance with temperature is determined by

k m k s m s T T T T R R ++++ ++++ ====

where Rm is the measured cold resistance at temperature Tm in oC, Rs is the resistance

corresponding to some other average winding temperature Ts in oC, and Tk is 234.5 oC for copper

windings or 225 oC for aluminum windings.

Liquid Immersed Units: The total losses are defined as the sum of the load losses and the no

load losses. The load losses are determined at rated frequency and current then corrected to the reference temperature. To conduct the load test, one winding is short circuited while the other winding is excited to the point where rated current flows in the windings. The losses occurring

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load losses are small and the measured losses attributable only to load losses. The no load losses are determined at rated frequency and voltage and are reported at the no load loss standard reference temperature. The standard reference temperature for load losses of liquid immersed transformers is 85o C. The standard reference temperature for no load losses is 20o C. In general, transformer losses vary with core and coil temperature. The use of the reference

temperature is to express these measurements on a basis that allows comparison with other units. The following discussion illustrates how transformer losses are reported using the reference temperatures.

The no load losses occur when the unit is excited at rated voltage and frequency in the absence of any load current. No load losses are made up of core losses (hysteresis, eddy-current, and

magneto-striction), dielectric or insulation losses, and winding I2R created by the no load excitation current and the circulating current which might be present in parallel windings. The transformer core contributes the greatest portion of the no load losses. The no load losses are essentially a constant value, however, the losses are a very mild function of core temperature which influences core steel resistivity, hysteresis losses, and stress caused by magnetostriction (the 120 Hz. hum one hears from an energized unit). Also, how the losses vary with core temperature is determined by core design and by the way an individual unit is constructed, i.e. matched units may have different loss variations with core temperature change. The constraints under which the no load loss measurements are made is that rated sinusoidal voltage is applied to a unit where the average insulating liquid temperature is within ± 10oC of the 20oC reference temperature and the difference between the top and bottom liquid temperature does not exceed 5oC. Should the test conditions differ from those presented by the standards, a correction is applied to the measured data through the calculation of

((((

))))

[[[[

m r T

]]]]

m r) P(T )1 T T K T ( P ==== ++++ −−−−

where P(Tm) is the no load losses at the measurement temperature Tm in oC, P(Tr) is the no load

losses at the reference temperature Tr (20oC), KT is an empirically derived constant having units

of oC-1. A suggested value for KT in the absence of other information is 0.00065 (o C)-1 as stated

in IEEE Std. C57.12.90. Given the no load loss value at the reference temperature, the no load loss value at some temperature can be determined from this last result by turning the last equation around to produce

T r m r m K ) T T ( 1 ) T ( P ) T ( P −−−− ++++ ====

where P(Tm) is now the no load losses at some other temperature Tm. Notice that the losses

decrease as the temperature Tm increases. To illustrate how insensitive the no load loss is to core

temperature variation, evaluate the expression just presented with the suggested constant and a temperature difference of 65 oC (i.e. 85 oC – 20 oC), the decrease in no load losses is a factor of 4%. Also consider that the 85oC number used in this calculation is the standard load loss winding reference temperature, not the core temperature. Under load, the winding is the hottest part of the transformer. The core and insulating liquid would be at lower temperatures. Thus, the actual difference between the no load losses at the no load reference temperature and the no

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load losses under load conditions will be smaller than 4%. The change in no load losses is then on the same order as the loss measurement uncertainty (to be presented in a later section). From this brief argument, it is seen that the omission of the temperature correction provides a slightly conservative figure for the no load losses should the transformer core temperature

increase. To account fo the increase in core temperature, one suggestion is to evaluate the loss at the temperature value of 55oC for Tm, a figure close to the average of the 20oC and the 85oC

reference temperatures. This would compensate for some of the reduction in loss with core temperature increase. It should also be appreciated that little change would occur in overall heat load if the no load losses at the reference temperature of 20oC were used. Also, the inference that the no load losses are an even weaker function of ambient temperature than with core temperature is a valid conclusion. The recommendation of this work is to treat the no load loss as a constant.

Load losses are measured when rated current flows in both the excited and the unexcited windings. The load losses include winding I2R and eddy-current losses, stray magnetic field losses in the transformer structures or tank, and losses associated with circulating currents in parallel connected windings or strands. The load losses are broken into two parts being the stray losses (caused by eddy currents induced in transformer structures such as core clamps, shields, and tank surfaces) and the winding I2R losses. The load losses are determined by wattmeter measurements. Once the load losses are determined, the unit is de-energized and the winding resistance is measured. The winding resistance determines the average winding measurement temperature, Tm. By calculating the I2R loss and subtracting this from the load losses, the stray

losses are determined. The stay loss decreases with temperature (resistivity increases with temperature that, in turn, limits the induced currents causing stray loss) while the I2R loss increases with winding temperature. Variation of load losses with winding temperature for a transformer is described by     ++++ ++++ ++++     ++++ ++++ ==== m K k m r K m K m s T T T T ) T ( P T T T T ) T ( P ) T ( P

where P(T) is the power loss at the desired temperature T specified in o C, Ps(Tm ) is the stray

loss at the measured temperature Tm specified in o C, Pr(Tm) is the winding I2R loss at the

measurement temperature, and TK is the same as defined previously. Note that this calculation

applies to both liquid immersed and dry type units as well with the exception that the standard

reference temperature for liquid immersed load losses differs from that for dry type load losses. In performing the load tests, IEEE Std. C57.12.90 states that no ambient temperature correction need be applied to the data provided the ambient temperature is within the range of 10 to 40 oC.

Dry Type Units: The total losses of a transformer are the sum of the no load losses at room

temperature (25 oC ) and the load losses at the standard reference temperature. The standard reference temperature for load losses is the highest rated winding temperature rise plus 20 oC. A temperature rise is defined as a measured temperature less the ambient temperature. The highest rated temperature rise is determined by the insulation class and is shown in Table 4. The

information for Table 4 is taken from IEEE Std. C57.12.01. The highest average winding temperature rise under full load is a transformer nameplate item. The highest average

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temperature rise is dependent on the type of winding insulation and can range from 75o C to 150o C. Any loss figure or efficiency reported for a unit would incorporate this temperature value.

Insulation System Temperature Class (oC) Highest Average Winding Temperature Rise (oC) 130 75 150 90 180 115 200 130 220 150 Table 4: Limits for Temperature Rises (assuming 40oC

maximum ambient temperature and 30 oC average ambient temperature)

The standards do not specify the necessity for temperature correction of the no load losses for dry type windings. IEEE Std. C57.12.91 does acknowledge that the no load losses are a function of core temperature. The recommendation for this work is to treat the no load losses as constant. Ambient Temperature Influence

When the ambient conditions differ from those assumed by the standards (30 oC), IEEE Std. C57.12.91 specifies a correction for the average winding temperature for dry type windings. The standards are concerned with determining the average winding temperature which would occur when the ambient temperature differs from the expected 30oC. If the ambient temperature differs from this figure, then C57.12.91 supplies a formula for correcting the measured average winding temperature occurring at the current ambient temperature to the average winding temperature which would occur if the ambient were 30oC. The concern of this work is just the opposite in that the average winding temperature occurring at an ambient temperature other than 30oC is of interest given that the reference temperature rise occurs at an ambient of 30oC. The

recommendation is to take this correction and use it in reverse. The reversed temperature correction takes the form

n ra k r a k r r cr T T T T T T T T _      ++++ ++++ ++++ ++++ ====

where Tr is the load loss reference temperature rise, Tcr is the corrected average winding

temperature rise, Tk is as defined previously, Tra is the standard ambient temperature (30oC), and

Ta is the new ambient temperature. The suggested value for the exponent n is 0.8 for ventilated,

self cooled units, 1.0 for ventilated units with forced air, and 0.7 for sealed units. This

expression applies to dry type units. However, since liquid immersed units are also sealed this expression can be used for those units. For liquid immersed units, IEEE Std. C57.12.90 does not specify a temperature correction, however it does state that an appropriate temperature correction can be used.

By knowing the new average winding temperature, the load loss formula can be evaluated to find the new load losses corresponding to the new ambient temperature. Through this means, the

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influence of the environment on transformer load losses can be determined. It will be seen that the change in losses produced by this calculation will be small and the recommendation in this work is to ignore the influence of ambient temperature on load losses.

The correction of load losses based on ambient temperature variations requires the knowledge of both portions of the load loss, namely the I2R loss and the stray loss. The I2R loss can be

determined from the winding resistance at the load loss reference temperature and the rated current. The winding resistance is not a nameplate item and must obtained from the

manufacturer.

As an example of this calculation, consider two separate evaluations of the last expression, one to provide the largest possible factor for temperature rise increase and another to provide the smallest possible factor given a 20oC increase in the ambient temperature. The calculations are summarized in Table 5.

Largest Smallest Notes

Reference Rise - oC 55 150 Tk - oC 225 234.5 Ta - oC 50 50 Tra - oC 30 30 n 0.7 0.7 Tcr - oC 57.5 155 Standard Reference Temperature - oC 85 180 Tm = Tcr + standard rise 107 205     ++++ ++++ r K m K T T T

T 1.07 1.06 factor for I2R loss

    ++++ ++++ m K r k T T T

T 0.93 0.94 factor for stray loss

Table 5: Influence of 20 oC Change in Ambient Temperature on Load Losses

The information in Table 5 shows the factor of how the losses will change with an increase of 20

o

C in the ambient temperature. Should the ambient temperature fall by 20 oC, the numbers in the last two lines of Table 5 are swapped. Depending on the size of the stray loss relative to the I2R loss, the new load losses are within ± 7% of the losses at the standard reference temperature. To put this in perspective, consider that the ambient temperature is changed by 67% and found that the load losses changed by less the 7%. Now consider if the winding current were to increase from 100% to 110%. A 10% change in current will produce at least a 21% increase in load loss (the “at least” stems from the possibility that the winding resistance could increase). Also, consider the case where the I2R loss is the same size as the stray loss. From the numbers in Table 5, it is seen that the load losses would be unchanged. If the I2R loses were three times larger than the stray loss, the increase in load losses for a 20 oC increase in ambient temperature

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If the changes in losses with ambient temperature were ignored, then the overall uncertainty of the load loss figure at the reference temperature would be slightly larger then ± 7%.

Measurement Uncertainty

Any manufacturer citing that they follow the standards specified previously would be providing believable data. In making any table related to transformer losses, it will be necessary to ascertain that the manufacturer follows these standards before using that information.

For all of the sizes of transformers included in this study, the standards require the manufacturer to either test a representative sample of a specific transformer size or to make direct

measurements on the unit in order to determine the loss values.

Units tested in accordance with IEEE Std. C57.12.90 or C57.12.91 (observed by NEMA TP1, TP2 and ST20) to determine losses must have a measurement uncertainty of ± 3% or less. Losses presented by manufacturers were interpreted as being the average of a test batch. The uncertainty of the average losses of a test batch would be smaller than ± 3% and the specific value would depend upon the number of units in the test batch being averaged. It is then seen that the ± 3% is an upper limit for loss uncertainty.

Manufacturers

A table of manufacturers was assembled using the method described earlier in this report. Of the thirty manufacturer names obtained from the NEMA web site, twenty manufacturers were sent e-mail requests for loss data and testing methods. Five manufacturers replied. Of the five, three manufacturers reported loss data. The three manufacturers who supplied the loss data are well known within the power and utility industry.

Information Deficiencies

All of the manufacturers examined in this work state that they follow IEEE Std. C57.12.90 and C57.12.91. The information supplied by these manufacturers is believable since it is known how the tests were made and the uncertainty of the results. Owing to the clear standards used by industry and the availability of good loss data, transformers are placed in Category I. The only information deficiency regarding transformer losses is the construction of the heat gain tables to present the results of this work

Test Plan

In order to complete the loss tables required in this work, the following tasks will be accomplished:

1) The loss data will be separated into that for dry type and liquid immersed units.

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2) For each transformer size required by the TRP 1104 work statement, the average and standard deviation of the manufacturer data for both no load and full load losses will be reported.

3) Additional contacts with larger (having significant market share/reputation) manufacturers of transformers will be made through a telephone survey to acquire more data points for the loss tables. If any new information is obtained, this new data will be included with the other information.

The reporting of load and no load data allows for diversity since the loss at some fractional current load level, say x, can be determined by

P(x) = PNL + PL x2

where P(x) is the power loss at a given per unit current load - x, PNL is the no load loss, and PL is

the full load loss. This expression provides an interpolation of the power loss as a function of load current.

These tasks are to be completed in Phase II of this project. No additional resources or equipment will be needed for the execution of the steps just listed.

References

IEEE Std. C57.12.00 – 1999 General Requirements for Liquid – Immersed Distribution, Power, and Regulating Transformers.

IEEE Std. C57.12.01 – 1998 Standard General Requirements for Dry-Type Distribution and Power Transformers Including Those with Solid Cast and/or Resin-Encapsulated Windings. IEEE Std.C57.12.80 – 1978 (R1992) Terminology for Power and Distribution Transformers. IEEE Std. C57.12.90 - 1999 Test Code for Liquid-Immersed Distribution, Power, and Regulating Transformers.

IEEE Std. C57.12.91 - 1995 Test Code for Dry-Type Distribution and Power Transformers. NEMA ST 20 – 1992 (R1997) Dry-Type Transformers for General Applications.

NEMA TP 1 – 1996 Guide for Determining Energy Efficiency for Distribution Transformers. NEMA TP 2 – 1998 Test Method for Measuring the Energy Consumption of Distribution Transformers.

ASHRAE-D-21513-20100324

Heat Gain from Electrical and Control

Equipment in Industrial Plants

ASHRAE Research Project 1104-TRP

PHASE I – PART A:

CLASSIFICATION

PART B:

TEST PLAN

Warren N. White, Ph.D.

Department of Mechanical and Nuclear Engineering

and

Anil Pahwa, Ph.D.

Department of Electrical and Computer Engineering

Kansas State University

June 10, 2001

Table of Contents

List of Figures

List of Tables

Introduction and Executive Summary

Heat Loss and Heat Transfer

Assessment Results

Conclusions and Recommendations

Phase I –Results

The Method

First Category

Transformers

Review of Environmental Heat Gains

Standards

((((

))))

[[[[

]]]]