NBSIR 77-1387

Evaluation of A Test Method

for Measuring Microwave Oven

Cooking Efficiency

Owen B. Laug

Institute for Applied Technology

National Bureau of Standards

Washington, D C. 20234

September 1977

Prepared for Federal Energy Administration

Washington, D.C. 20461

NBSIR 77-1387

EVALUATION OF A TEST METHOD

FOR MEASURING MICROWAVE OVEN

COOKING EFFICIENCY

Owen B. Laug

Institute for Applied Technology

National Bureau of Standards

Washington, D C. 20234

September 1977

Prepared for Federal Energy Administration

Washington, D.C. 20461

O* *

U S. DEPARTMENT OF COMMERCE, Juanita M. Kreps, Secretary

Dr. Sidney Harman, Under Secretary

Jordan J. Baruch, Assistant Secretary for Science and Technology

NATIONAL BUREAU OF STANDARDS. Ernest Ambler, Acting Director
.
Table of Contents

Page

Foreword

Introduction 1

Background 1

Approach 2

IEC Test Procedure Evaluation 2

Efficiency of Cooking Foods 5

Annual Consumption 8

Litton Procedure 9

Proposed Test Procedure for Microwave Cooking Appliances 10

SECTION 1 PURPOSE 10

SECTION 2 SCOPE 10

SECTION 3 DEFINITIONS 10

SECTION 4 GENERAL TEST CONDITIONS 11

SECTION 5 PERFORMANCE TEST PROCEDURE 11

SECTION 6 OVERALL ANNUAL ENERGY CONSUMPTION 13

Conclusions 14

APPENDIX 14

Bibliography 17

List of Figures and Tables

Page

Fig. 1 Normalized Efficiency vs Final Temperature 18

Table I Standard Test Procedure Data on Oven A 19

Table II Standard Test Procedure Data on Oven B 20

Table III Standard Test Procedure Data on Oven C 21

Table IV Standard Test Procedure Data on Oven D 22

Table V Standard Test Procedure Data on Oven E 23

Table VI Test Data on Various Foods Cooked in Oven A 24

Table VII Test Data on Various Foods Cooked in Oven B 25

Table VIII Test Data on Various Foods Cooked in Oven C 26

Table IX Test Data on Various Foods Cooked in Oven D 27

Table X Test Data on Various Foods Cooked in Oven E 28

Table XI Summary of Oven Efficiencies Measured With The

Standard Test Procedure & Foods 29
-
FOREWORD

This work was performed as a part of NBS technical support to the

Federal Energy Administration (FEA) Energy Conservation Program for

Appliances as required by the Energy Policy and Conservation Act (Pub. L.

94-163) and the Energy Conservation and Production Act (Pub. L. 94-385).
.
Introduction

This report describes the results of laboratory tests made in support

of a test method recommended to FEA for determining the energy efficiency

and average annual energy consumption of microwave cooking appliances. The

objective in the selection and development of a method has been one which

is simple, repeatable, and correlates with actual consumer usage. In

addition, the laboratory method should be able to be combined with consumer

use pattern data to obtain estimated annual cost of operation. The work

described herein does not relate to consumer use patterns.

By necessity a variety of microwave ovens had to be selected for use in

evaluating a procedure. Since the purpose of the work has been to develop

a standard test method, the results of data reported should not be used for

purposes of rating the particular ovens tested, rather the data are intended to show the workability of the method. The limited sampling of

models could result in ratings that are misleading. Therefore, the

appliances selected for use are identified in this report by alphabetical

letters A through E.

packground

In the search for a suitable test procedure, two basic methods were

found to exist. The first was a procedure in the process of being adopted

by the International Electrical Commission referred to as IEC-SC-59H

Methods of measuring performance of microwave cooking appliances for

household and similar purposes . The second procedure was proposed by

Litton which claims to be applicable to all types of cooking appliances

including microwave ovens. The Litton procedure was basically designed as

a method for determining the annual energy consumption of ranges and

microwave ovens by utilizing a standard menu from which water equivalents

are derived. The main drawback to this method is that it appears time

consigning and raises some fundamental questions when used for comparative

purposes between electric ranges, conventional ovens, and microwave ovens.

A more complete discussion of the Litton procedure is presented later.

The (IEC-SC-59H) procedure (hereafter referred to as the IEC

procedure) consists of heating measured quantities of water to determine

the power output and efficiency. The Association of Home Appliance

Manufacturers (AHAM) is in favor of this procedure. On August 3, 1976,

AHAM presented to NBS their proposed standard test method for ranges and ovens including microwave ovens. Their test method for microwave ovens was essentially the same as an earlier IEC version with some minor

modifications, together with a method of determining annual energy

consumption.
Approach

The evaluation of the test methods was performed on five different

manufactured ovens of the counter top variety. The newer combination types

(i.e. conventional and microwave in the same cavity) were not tested

because at the time only one manufacturer had models available and the

market penetration was limited. The microwave ovens choosen for test

ranged in advertised power ratings from 450 to 675 watts. The following

lists some of the pertinent specifications and features of the ovens

tested:

Oven Power-Watts Cavity Volume-nr Features

A 625 0.037 Cook by time or temp. 3 level setting

B 675 0.029 Defrost & slow cook

Digital clock

C 450 0.021 Defrost setting

D 650 0.031 Variable level

heat control

E 600 0.025 Defrost setting

Carousel turntable

Two approaches were taken in evaluating the IEC test procedure. First,

the test procedure was performed exactly as specified a number of times on each oven to determine the repeatability and identify any problems. The

second approach was to measure the heat input to various types of foods

cooked in each of the microwave ovens. The heat input to the food divided

by the energy input to the appliance gives the efficiency of cooking a given food. These efficiency measures are compared with the efficiencies

obtained by the IEC standard test procedure. The value of this technique

is to show how well the test procedure correlates with actual use.

IEC Test Procedure Evaluation

The IEC test procedure prescribes four test loads of water containing

one-percent by weight of sodium chloride. The load sizes specified are:

275 ml, 500 ml, 1000 ml, and 2000 ml. Each load is heated in the microwave

oven until a temperature rise of about 25 +5°C is achieved. The actual

temperature rise is measured and the time is recorded. Initial efforts to

follow this procedure met with some difficulty because as will be shown

later there is no practical way of monitoring temperature while the

microwave oven is operating. Therefore, it was necessary to make a few

trials to obtain the desired temperature rise. The amount of time depends

on the oven power and the load size. However, with some experience the

2
testor soon is able to gauge the length of time required to obtain the

specified temperature rise. The disadvantage of this method is that an inexperienced testor must make several trials before beginning an actual

measurement.

The reason for fixing or standardizing on a temperature rise rather

than time is that as the temperature of the water increases the measured

efficiency begins to drop off. The coupling of microwave energy into the

water apparently decreases with temperature and at higher temperatures

there is a greater amounj of heat lost to the surroundings as well as some evaporative cooling . Therefore, if time were specified rather than

temperature higher wattage ovens would produce a greater temperature rise

resulting in a lower efficiency, hence, penalizing the more powerful ovens. The effect of temperature on efficiency was examined in each of the ovens

by measuring the temperature rise and input energy of a 3000 ml water load.

This load was divided equally into six 500 ml beakers placed contiguously

in the center of the load carrying surface. Each run was started with the

water load at room temperature and the time for each run increased from the

last run by three minutes so that the sixth and final run was 18 minutes.

Fig. 1 sunmarizes the effect of final temperature on measured efficiency.

The curve represents the average normalized efficiency of the five ovens as

a function of final temperature. At a 45°C final temperature (a 25°C rise

above a 20°C initial) a plus or minus +5°C change will produce about a + 2.5$ change in efficiency. If it is desired to tighten this spread it may

be done of course by reducing the tolerances on the initial temperature and

temperature rise specifications. The original IEC version specified a final test load temperature of 45 + 5°C whereas the updated version

specifies a 25 + 5°C rise together with a 20 + 5°C initial temperature.

This allows the tolerance of the final temperature to be +10°C and could

result in as much as a +5% spread in efficiency.

The measurement of temperature rise of the water load directly effects

the accuracy and repeatability of the efficiency measure. It is not

recommended to monitor the temperature of the water load while heating in

the microwave oven for two reasons: First, if alcohol or mercury

thermometers are used errors will occur due to the heating of alcohol and

the mercury column can behave as an antenna. A shielded thermocouple wire can be used, however, caution should be taken to insure that the wire which

passes between the door and seals does not re-radiate microwave energy

outside the oven causing a possible health hazard. The second reason for

not monitoring the temperature of a water load while heating is that the

temperature distribution of the water in a vessel from top to bottom is not

uniform. As much as a 5 to 7°C difference between top and bottom has been

observed. Placing the thermocouple junction midway between the bottom and

top surface of the water provides an average temperature which closely

matches the temperature obtained by thorough stirring. However, in order

to obtain the most accurate results, the water should be thoroughly

stirred before recording the temperature. This is somewhat impractical to

3
do while the oven is operating and more so when more than one container is

used.

When the load is divided among more than one container a sequential

measurement of the final water temperature of each container is necessary.

It is important to make these temperature measurements rapidly before the

load begins to cool. As little as a 1°C drop in final temperature before

measurement can result in a 4% error of efficiency.

A technique was developed to measure the final temperature of the water

with minimum delay and maximum stirring. Polystyrene foam lids were

fabricated for each size breaker and thermocouple wires inserted through a small hole in the center of the lids. The thermocouple junction was positioned so that when the lid is put in place the junction protrudes

about half way down into the water. A multi-channel thermocouple indicator

and magnetic stirrer were used. The technique of measuring final

temperature after a run is as follows: The beaker to be measured is

withdrawn from the oven and placed on the top plate of the stirrer. A

2.5cm length magnetic stirring bar is dropped into the water, the

polystyrene foam lid with the thermocouple is placed on the beaker and the

stirrer is turned on. In less than 10 seconds of stirring the temperature

has stabilized and a reading is made. This process is repeated for each

beaker. With this technique a two beaker load can be measured in less than

20 seconds with minimal cooling.

The updated version of the IEC test method changed the distribution of

the 1000 ml and 2000 ml loads. In the original version one 500 ml size

glass beaker having a nominal inside diameter of 85 mm was specified to be

used for all loads. The 1000 ml load was specified to be placed in equal

portions of 500 ml each located continguously side by side in the center of

the load carrying surface. The 2000 ml load was specified to be placed in

equal portions of 500 ml in four containers located contiguously in a square array in the center of the load carrying surface. The updated IEC

test specified a 1000 ml size glass beaker having a nominal 110mm inside

diameter to be used for the 1000 ml and 2000 ml loads. The 1000 ml load is

contained in one 1000 ml beaker and the 2000 ml load is contained in two

1000 ml beakers each located contiguously side by side. The effect of this

change is simply to reduce the nimber of beakers in which the final

temperature of the water must be measured and the distribution of the load.

Tests were conducted with each version to examine what effect if any this

change would have on the results of efficiency. Tables I thru V shows the

test data and resultant efficiencies obtained for three complete

replications of the latest IEC test procedure. A fourth run was made on the 1000 and 2000 ml load size using the original proposed distributions

(i.e. two and four 500 ml beakers for the 1000 ml and 2000 ml load

respectively). The rated efficiency was computed for each run by averaging

the specific efficiencies of each load. For each oven the rated efficiency

determined from each run did not deviate more than 0.5%. The good

repeatability obtained from these runs is mainly attributed to the uniform

4
technique of measuring the final temperature. The specific efficiencies

obtained in run 4 on each oven do not differ significantly from the

specific efficiencies of the 1000 and 2000 ml loads in runs 1 thru 3.

Furthermore, if the specific efficiencies obtained from run four are substituted for the specific efficiencies of the 1000 and 2000 ml loads of

runs 1, 2, or 3 and averaged, the rated efficiency is not significantly

altered. Thus, there is little difference in the measured efficiency using

the updated IEC version of load distribution.

Examination of tables I thru V shows that the specific efficiency can,

depending on the oven vary up to 10 percentage points from the small load

size (275 ml) to the large load size (2000 ml). Generally the efficiency

continues to increase with load size up to 2000 ml. The IEC test procedure

specifies that the rated efficiency of an oven is determined by averaging

the specific efficiency of the four loads. This method of averaging

assumes that the use factor of each simulated load is equal. If however,

survey data showed that most foods cooked are at predominately lighter or heavier loads than the laboratory simulation, then perhaps a weighing

factor might be introduced or the range and size of the loads adjusted. An

alternate method of determining the rated efficiency is to sum the output

energies and divide by the sun of the input energies for each of the four

loads. This method will result in a slightly different answer for the

rated efficiency. For the time being, however, the simple averaging of the

specific efficiencies to obtain the rated efficiency seems to be as good a way as any.

The addition of salt to the water was not extensively investigated.

Generally distilled water without any salts will yield a higher efficiency,

perhaps as much as 5%. No significant difference was found between

distilled water and tap water in this area. Although in the IEC procedure

it is specified that the salt is to be added to distilled water, specified,

the addition of 1% by weight of sodium chloride produces a salt solution

which totally overwhelms the salts and mineral deposits of most drinking

water so that drinking water seems perfectly adequate for this test. Use

of distilled water is perhaps simply an added precaution, and generally is

readily available in most laboratories.

Efficiency of Cooking Foods

A second approach investigated is the direct measurement of heat input

to various types of foods cooked in a microwave oven. The heat input to

the food divided by the energy input to the appliance provides a meaningful

measure of the efficiency of the appliance under conditions of actual use. The purpose of this investigation was to show how well actual efficiencies

of cooking foods correlated with efficiencies determined by the standard

test procedure which uses water as the food substitute load.

A water calorimeter was used to measure the heat in a given sample of

cooked food. The container used for the calorimeter was a Dewar wide mouth

jar fitted with a polystyrene foam lid to minimize heat transfer to the

ambient. The procedure developed is as follows: A given quantity of food

5
is cooked in the microwave oven until it is done. The degree of doneness

is not critical and determined primarily by following the recipes provided

with the appliance. However, overdoneness generally will result in a lower

efficiency. Often, it was found that for an unfamiliar dish several trial runs had to be made in order to determine the desired doneness. The food

sample is weighed before cooking and immediately after. After cooking and

weighing the food it is quickly transferred to a calorimeter containing a known initial temperature and quantity of water. The mixture is thoroughly

stirred until the final equilibrium temperature is reached. If no heat is

lost from the calorimeter during the test the heat given up by the food

must equal the heat gained by the water in the calorimeter. The

approximate total heat expressed in joules that went into the food and the

heat required to drive off moisture in the food is expressed below. (See

Appendix I)

Q = h(M

fl - Mf2 ) + (Mw

+ M

fl )(t2

- t

1 )(4.19) (1)

where h

M

M

M

fl

T2

w

heat of vaporization of water

at 10CTC = 2260 J/g

initial weight of food - grams

final weight of food - grams

weight of water in calorimeter - grams

final temperature of system °C

initial temperature of system °C

The advantage of this technique is that the final temperature of the food

does not need to be measured, the distribution of the temperature

throughout the food does not affect the measurement, and the specific heat

capacity of the food does not need to be accurately known. (See Appendix

I)

Often foods are cooked in a microwave oven from the frozen state. When

frozen foods are introduced into the oven, heat is required to raise the

food to a temperature of 0°C, thaw it, and raise it to the final done

temperature. This amount of heat can also be measured by employing the

water calorimeter. Two identical samples of frozen food of the same weight

must be selected or prepared before freezing. One sample is put in the oven from the freezer, cooked, reweighed, and put in the calorimeter. The

second sample is removed from the freezer and directly transferred to the

calorimeter. The water is thoroughly stirred and the new temperature is

recorded. The approximate heat required to thaw the food and bring it to room temperature is (see appendix I)

Q “ (Mw

+ M

fl )(tl " V (4 * 19) (2)

6
where is the final temperature of the system °C.

For frozen foods which are cooked, the heat determined from equation 2 is

added to the heat determined in equation 1.

Once the total heat into the food (Q^,) has been measured and the input

energy (E) to the appliance recorded during the cooking interval, then the

specific efficiency of cooking a given food may be obtained from the

expression below.

Qt

efficiency = 36oQ-g; (3)

where

the factor 3600 is used to convert the customarily measured units of input

energy (E in ) in watt-hours to joules.

The above technique was used to measure the efficiency of cooking a variety of foods either from the frozen state or from room temperature. A

total of nine food items were cooked in each of the five ovens. The

selection of the food items and portion size was not comprehensive nor chosen from a standard menu, but simply a variety of foods chosen to

demonstrate a technique. Tables VI thru X show the resultant efficiencies

of cooking nine foods some of which were frozen. An average efficiency for

each oven based on the specific efficiency of each food item is also shown.

The cooking of six bacon strips consistently produced a lower efficiency

in each of the ovens. This is primarily due to the small size of the load

and perhaps its low thin profile. However, heating a half loaf of bread of

similar weight resulted in efficiencies over 30% in each of the ovens. No

attempt was made to extensively analyze the apparent differences among

foods. The technique shows, however, that there are real differences in

efficiencies for various foods.

Table XI summarizes the rated efficiencies for each of the five ovens determined by the standard IEC test procedure and from cooking foods. This

table shows that the efficiencies are quite similar. Moreover, the ranking

of ovens by either method is very close. Oven E clearly stands out to be

the most efficient by either method. Ovens A and B are next and C & D

last. In fact, efficiency figures shown are so close that ranking is

somewhat meaningless since they are all very similar with the exception of

oven E.

One can conclude from the data shown in table XI that the efficiencies

determined by the standard test method utilizing multiple loads of water

are realistic values which correlate reasonably well with actual food

cooking efficiency. Although the efficiency values obtained from cooking

foods are consistantly lower than the values obtained from the test

procedure, the important distinction is that the relative ranking of the

ovens by efficiency correlate well by either method.

7

l
Annual Consumption

The proposed AHAM standard for determining the Annual Consumption of a microwave oven is outlined below.

1. Representative Consumption

From a Range Energy Field test conducted by AHAM it was found that for

a family of four where a microwave oven was used along with conve

surface units and ovens, annual consumption was 88 kWh (3.17 x 10

2. Energy Factor

The energy factor (i.e. the average of the rated efficiencies) of

microwave ovens monitored in the AHAM field test is 0.3885 .

3. Energy into the food

From the data in 1 and 2 above, it can be determined that the energy

actually used to cook food was:

0.3885 x 88 kWh = 34.188 kWh (1.23 x 108J)

4. Annual Microwave Oven Consumption

gtional

J ) •

To determine annual consimiption of any oven, divide the standard energy

into the food (34.183 kWh) by the energy factor (rated efficiency) of the

microwave oven being tested,

Annual Energy Consumption, kWh 34.188

energy factor

The above determination seems to be a valid method of determining

annual energy consumption. The representative consumption is based on survey information. A separate project is underway to survey 150

experienced users of microwave ovens to substantiate the AHAM figure. The

energy factor was determined by taking the average of the rated

efficiencies of the ovens used in the AHAM field test. It is interesting

to note that the AHAM field tests average is 0.3885 and the average of ovens A thru E (tables I - V) produces a value of 0.3868 .

A four place figure for energy factor is quite meaningless in view of

the accuracy and repeatibility of the procedure. Rounding off the energy

factor to two significant figures would produce a more meaningful value of

0.39.

The method of determining annual microwave oven consumption should have an additional term to account for the energy features such as clocks when the oven is in the normal off condition. In the proposed standard to FEA the

power rating of a feature in watts times 8.76 was added to the annual

microwave energy consumption. This term can become significant in relation

8
to the energy consumed for actual cooking. In fact, one oven evaluated had

a digital clock display which consumed an average of 7 watts anounting to over 40* of the annual cooking energy consumption!

Litton Procedure

The Litton method of measuring the energy consumption of electric

ranges, combination ranges, and microwave oven proposes the use of water as the universal test load. A water test load is defined after a total

standard menu has been cooked under a controlled test with consistent

techniques, heat settings, and end doneness. Once the menu is properly

utilized with rise in food temperature and cooking time recorded, a water

conversion is made for each food item by heating a like volume of water

according to the specific cooking time. The result is a group of specified

rises in water temperatures which represent various food items of a menu. Once the specification is established other ovens are then tested by

bringing the specified water volumes to the standard temperature

represented by each food item. The input energy to attain the specified

temperature rises is recorded. The total input energy for a 7-day menu is

recorded and multiplied by 52 weeks to obtain the annual consumption.

Although the Litton procedure was not specifically performed in the lab

it was judged to be rather cumbersome and time consuming to perform in

relation to the I EC procedure. Furthermore, there is no question that

water is a good test load for microwave ovens and the two methods would

probably not result in a significantly different ranking of the ovens. However, total annual consumption figures by the two methods may be quite

apart from each other. The Litton procedure bases the annual energy

consumption on a standard menu which may not correlate well with actual use patterns for microwave ovens.

In order to perform the Litton procedure it is necessary to monitor the

temperature of the water in the container while the oven is operating.

Their recommendation is to use a thermocouple positioned in the water

halfway from the bottom of the pan and top surface of the water, not

touching any sides. The thermocouple cord is placed so that the door can

be closed and the oven operated. As mentioned previously it is undesirable

to do this both from an accuracy and safety standpoint.

There are also serious questions aside from procedure as to whether the

use of a water test load in a conventional oven is meaningful. The

coupling of energy to water in a container being heated in a conventional

oven may be quite different than food. No known study of this has been

made. Much more effort would be required to show that water can be used

satisfactorily on a comparative basis for all types of cooking appliances.

9
Proposed Test Procedure for Microwave Cooking Appliances

The following test procedure based on the IEC-SC-59H procedure was

submitted to FEA. The NBS studies were concerned primarily with

establishing the connection between efficiencies in water heating and the

cooking of real foods. The IEC procedure contains certain additional

operational requirements (Sec 5.2.1) which are included for maintaining

uniformity but were not investigated for optimality in the present tests.

SECTION 1 PURPOSE

1.1 This test procedure is proposed as a standard method of determining the

power output, efficiency, and annual energy consumption of microwave

cooking appliances.

SECTION 2 SCOPE

2.1 This procedure applies to microwave cooking appliances as defined in

3.2

using electro-magnetic energy in one or more of the Industrial,

Scientific, and Medical Equipment bands above 300 MHz to heat food.

These ovens are primarily intended for household use.

2.2 This procedure includes definitions, standard test conditions, test

procedures, and performance evaluation for microwave cooking

appliances.

SECTION 3 DEFINITIONS

3.1 Compartment

The space enclosed by inner walls and doors into which food is placed

to be heated or cooked by microwave energy.

3.2 Microwave Oven

A "microwave oven" is an appliance designed to heat food in a compartment by means of microwave energy.

3.3 Nameplate

A plate permanently attached to the microwave cooking appliance on which the electrical ratings and other identification appear.

3.4 Rated voltage

The voltage assigned to the appliance by the manufacturer.

10
3.5 Shelf

A horizontal food supporting surface in the cavity of a microwave

cooking appliance.

SECTION 4 GENERAL TEST CONDITIONS

4.1

Electrical Supply

4.1.1 Frequency

Conduct all tests at nameplate frequency + 1% unless

otherwise specified.

4.1.2 Voltage

Conduct all tests at nameplate voltage. The test voltage is

to be maintained within + 1% at the inlet to the power supply

cord when the oven is operated under loaded conditions.

4.2

Ambient Temperature

The ambient temperature is to be maintained at 20° + 5°C (72 + 9°F).

SECTION 5 PERFORMANCE TEST PROCEDURE

5.1 Instrumentation

All instruments used during the Standard Measurement Tests are to be

accurate within + 2% unless otherwise stated.

5.2

Microwave Power Output Measurement

5.2.1 Test Loads

Microwave power output measurements are to be made with the

microwave cooking appliance connected to its rated supply

voltage and frequency and operating at its maximum microwave

power setting with a load of a) 275 ml + 1%, b) 500 ml + 1%,

c) 1,000 ml + 1% d) 2,000 ml + V%, of distilled water at an initial temperature of 20 + 5

e

C and containing 1% by weight

NaCl

.

The 275 ml and 500 ml loads are to be placed in a thin wall

glass vessel having an inside diameter of approximately 85 mm

at the center of the load carrying surface provided by the

manufacturer.

11
The 1000 ml load is to be placed in a thin wall glass vessel

having an inside diameter of approximately 110 mm at the

center of the load carrying surface provided by the

manufacturer.

The 2000 ml load is to be placed in equal portions of 1000 ml

in two 110 mm diameter glass vessels located side by side in

the approximate center of the load carrying surface provided

by the manufacturer.

The testing time is the elapsed time while the magnetron is

operating at full power (heat up time is not counted) and the

duration of the test is until the temperature rise of

the water load is 25 + 5°C. The time to reach the final

water temperature and the actual initial and final water

temperature should be recorded. The final temperature of the

water must be measured after stiring sufficiently to

create a uniform temperature distribution.

The tests are to be conducted using the following sequence:

2000 ml, 1000 ml, 500 ml, and 275 ml. The oven is to be

stabilized with the room ambient of 20 + 5°C prior to the

start of the test sequence and there should be a one minute

rest period between loads for the purpose of changing the

load.

5.2.2 Computations

Calculate the Microwave Power Output for each test load as follows:

Microwave Power Output (watts) = ^

where

W = size of the water load in milliliters (ml),

cubic centimeters (cc), or grams (g)

(275, 500, 1000, 2000)

At = Temperature rise of the load in degrees

celcius, i.e., final water temperature

(°C) minus initial water temperature (°C)

t = elapsed time in seconds at full microwave

power.

Calculate the Average Microwave Power Output (Po) by

calculating the simple average of the Microwave Power Output

for each test load.

12
5.3

Rated Efficiency

5.3.1

Calculate the Specific Microwave efficiency (e) for each load as follows:

Po x t

e = E 3^00

where: Po = the Average Microwave Power Output (watts) for a given load.

t = the elapsed time of the test (seconds)

E = the electrical input energy in watt-hours

measured by an induction energy rneter.

5.3.2

Calculate the rated efficiency of the microwave oven (e ) as the simple average of the specific efficiency for eacK®1 test load.

e (275)

* e (500)

* e (1000)

* e (2000)

e (avg) " 4

SECTION 6 OVERALL ANNUAL ENERGY CONSUMPTION

6.1 Representative Consumption

From the AHAM Range Energy Field Test it was found that for a family

of four where a microwave oven was used along with conventional g surface units and ovens, annual consumption averaged 38 kWh (3.17 x 10~'J).

6.2 Ene rgy fa ctor

The energy factor (EF rnwo) of the microwave ovens monitored in the

AHAM field test is 0.388

6.3

Standard Energy into the Food

From the data in 6.1 and 6.2 the average annual energy used to cook

food is:

0.383 x 88 = 34.2 kWh (1.23 x 108 J)

6.4

Annual Microwave Oven Consumption

The annual consumption of any oven is determined as follows:

ANNUAL ENERGY

34.2 kWh + pRF ( 8>76 )

—

A CONSUMPTION = 3.6 x 10

u (joules) _

e (avg) _

13
where: e, x = the rated efficiency of an oven as

^ s; determined in 5.3.2

PRF = Power Rating of Feature, watts

8.76 = Number of thousand hours in a year

3.6 xlO^ = Energy conversion factor to convert

kilowatt-hours to joules

Conclusions

A standard test method based on the IEC-SC-59H procedure has been

verified in the laboratory on five microwave ovens. It has been

recommended to FEA for their use in the energy conservation program for

appliances. The results of the verification show that the method is

repeatable to within 0.5%, relatively easy to perform, and requires a minimum of special techniques or apparatus. The Litton procedure is not

recommended because it requires considerably greater time to perform than

that required for the IEC procedure. Furthermore, it is questionable

whether the procedure as proposed can be meaningfully used for comparative

purposes among the various types of cooking appliances, particularly the

conventional oven. Among the five microwave ovens tested the rated

efficiency determined from the IEC procedure ranged from 36.3% to 42.2%.

In comparison the average efficiencies determined by cooking nine food

items ranged from 32% to 38%. One can conclude that the efficeincies

determined by the standard test method utilizing multiple loads of water

are realistic values which correlate well with actual food cooking

efficiency.

APPENDIX

This method of measuring the heat into the food is derived from the

technique known as the method of mixtures for measuring the average

specific heat capacity of a material. A water calorimeter is used as follows. The food is heated in the oven and when it has reached the

desired doneness it is quickly transferred to the calorimeter, the water

thoroughly stirred, and the new temperature recorded. If no heat is lost

from the calorimeter during the test, the heat given up by the food during

cooling must equal the heat gained by the water and calorimeter.

Let the subscripts f and w stand for food and water respectively.

Then, assuming all specific heat capacities to be constant and neglecting

losses in the calorimeter,

M

f

C f(t

3 - t2

) = Mw

Cw

(t2 - t

:

) (1)

14
where is the mass of the cooked food

is the mass of water in the calorimeter

is the specific heat of the food

Cwis the specific heat of water

t^ is the final temperature of the cooked food

X*2 is the final temperature of the calorimeter system

t^ is the initial temperature of the water in the

calorimeter

Equation 1 is the heat liberated by the food equal to the heat absorbed by

the water. However, we must account for the heat in the food from an initial room temperature to the final system temperature t2

in order to

obtain the total heat in the food. If the initial temperature of the food

is the same temperature as the initial temperature of the water in the

calorimeter (room temperature) then the total heat in the food from

temperature t^ to t^ becomes

g = Vw(t

2

- t

l

) M

fCf (t2

- t

l

) (2)

The only quantity in equation (2) which may be unknown is the specific heat

capacity of the food, Cp However, this quantity does not need to be known

accurately. In practice the mass of the water in the calorimeter is chosen

to be much greater than the mass of the food so that the major quantity of

heat measured is in the first term of equation (2). Then, if we assume

that Cf = C even a fairly large error is that assumption will not greatly

affect the total accuracy of the heat determination. With this assumption

and the specific heat of water equal to 4.19 J/g.°C equation 2 becomes

Q - + ^

f )(t

2

- t

x

) (4.19) (3)

The only practical measure that has to be observed is to keep the ratio of

Mw

to Mj. in a range so that the resultant temperature difference (t

2

- ti) can be accurately measured. Of course if the specific heat capacity of the

food under test is known, then equation 2 is used.

The above assumption (Cf=Cw

) becomes even more realizable when the heat

of vaporization is accounted for in the total. The loss of mass of the

food during the cooking process is attributed to the water that is driven

off in the vapor phase. If the additional heat of vaporization is added to

equation 3 then the total heat that went into the food and heat required to

drive off some of the water is

15
Q

t

= h (Mfl - M

f2 ) + (Mw

+ M

fl )(t2

- t

1 )(4.19) (4)

where h equals the heat of vaporization of water at

100°C = 2260 J/g

(Mfi -M^

2

) is the weight loss of food from cooking

When foods are cooked from a frozen state additional energy is required

to warm the food to 0°C, thaw it, and raise the temperature to room

temperature. This additional amount of heat can also be measured by

employing the water calorimeter. A sample of frozen food is removed from

the freezer, weighed and quickly transferred to the calorimeter which

contains water at room temperature. The mixture is thoroughly stirred and

the final temperature recorded.

Let the subscripts f and w stand for food and water respectively. Then

the heat required to thaw the food and raise it to the final equilibrium

temperature recorded in the calorimeter is

The total heat required to bring a sample of food up to room temperature

is the sum of equations 5 & 6 which yields,

Q = M (5)

where t^ is the final equilibrium temperature

The heat required to raise the food temperature from t^ to t-^ is

Q = M

f

C

f

( t^— t|j

)

( 6 )

Q = ^w

Cw W(t-^ U - tjj) + (t-^ - t^)

1

( 7 )

Applying the same assumptions as previously explained

(i.e. Cf = Cw =4.19 J/g°C then equation 7 becomes

Q = (Mw

+ M

f )(t

1 - t

n

) (4.19) ( 8 )

16
Bibliography

[1] Sears and Zemansky, University Physics, Third Edition,

Addison-Wesley Publishing Co.

[2] Ringle, Charles E. and David, Beatrice D.

,

"Measuring Electric Field Distribution in a Microwave

Oven" Food Technology Dec. 1975

[ 3 ] Van Zante, Helen J., The Microwave Oven

Houghton Mifflin Co. Boston

[ 4 ] N. K. Albrecht and M. E. Purchase, A Comparison of

Methods for Determining the Wattage Output and Energy

Distribution in Microwave Ovens
FIG. 1

Normalized

Efficiency

vs

Final

Temperature

FINAL

TEMPERATURE

'C
o

§

•H

TJ O

0 -H -p <*-1

CTv

CTv no

noo

=r

CTV no

>>o

c

CDHO

O -H 0 <P

O. Cm

00 w

o

•rH Cm GO oo in vo in no CO VO no -=r -=3

" -=r no • • • • • • • • • • • • • -=r oo i—

-=r vO CTv o •=r vO c rH ^T rH no no =t no no =r =r no no -=r -=f =r

-P E2

3 t, a, 0

co

(D 3 •—

co in

.=r cm VO CM in

CM OO in no

on no t— nj no no t— no no no c— =r

rH cm =r oo rH no =r OO •—

CM =r 00

no

oo

=r

-P3 X

CO -P in CO 1—

vO vO -=r CM

cx 0 -P • • • -p 2 0 vO CM t— no CTv 0 -=T 3 O 2 1—

vO O -=r CM Ov O a, -=r X" in in =r .=3- -=r

no cn in cr> ^r C'— vO

cr\ CM cn 0 n od no no 0 ^r rH CM in -=r in in n n

O LO O h a\ a>

rH i—( no o o n o n- -—I cr* rH rH CO

o o in o n C— i—I CTn 0v CTs rH rH nO rH ocnno

<

Cl 0 no no vO n rH rH C— O 00 .=r no vo n no 0 rH CTv rH C\J «—

O c c E w O

0 0 0 -H O n .=r no vo -=r VO -^T no n -=r vO no no vo -=r -=r no no n Cm- no >0

Em K CM CM CM CM CM CM CM CM CM CM CM CM CM CM CM CM CM CM CM CM CM

CTv vO VO n <H CTv vO X" O vocnt-^i—

vO X" vO C'- vO n

B O c— vO n OO vO Cm- vO ^3- c— vO CO n n OO vo x- -=3- no n Cm no

•H

IX 0 0

Em

-=r X- X- x- .=r •=r x- x- .=3- -=r x- -=r

rH

cd vo no 0 0 0 OO f- vO vo vO no no CM •—rH n n n n n n

p> ex c_> CM cm CM CM CM rH 1 1 rH 1 1 1 1 CM CM CM CM CM 0 0 0000 •d E 0 CM CM CM CM CM CM CM CM CM CM CM CM CM CM CM CM CM CM CM CM CM 2 CD M H

2

0

0

N

•H00

CmO

62

t

rH rH rH CM rH rH rH CM 1

1 rH 1

1 CM CM ^r

s—V ' V ' * * v-/ v*

y

'—

w V—

' s—<- O 0 O O O O 0 0 O O O 0 O O

O 0 O O O O 0 0 O O O 0 O O n n O O n n 0 0 n n O 0 n n 1—1

1

1 rH rH rH 1—

a 0 n O 0 O n 0 0 0 n O 0 0 O O

0 N ml c-~ O 0 O 0 0 0 c

O 0 0 O O

0 •H CM n 0 O CM n 0 0 CM n 0 0 O O

-J CO rH CM t—1 CM 1—1 CM rH CM

cc o2

CM no -=r

19
TABLE

II

Standard

Test

Procedure

Data

>1o

c

a> •H

T3 O

<D -H

4-> —

cc u

(\J GOCOvO

COoo

oooo

>>o

o C

•H 0) Lh -H •H O

O -H O Cm Q.Cm

CO W

O'. O in CM vO 3 co OO CM ,—

in O OO iH 3 0- o 5

in 0— o o in CO o rH o o OO oo 3" oo OO 3" 3" oo oo 3" 3 3" 3"

COO

CO 4J 6d

Cl 0)

Cl) 5

CO

VO in c—

CM vO vO CO

CM 3" CM C— O

5 5

o CM CM in CO CM CM n OV CM CM n CO MO OO i-H CM 3" 00 i—1 CM 3" CO rH CM 3" CM

CMCO3

4^3 Sco -P o 0O VO oo vO C

co CTN co C~- o rH ov vO a a> 43 • • • • • • • • • • • • • • 4-3 ^ 03 CM vO 3 av rH OO .—

CM n OO co CO i—i CM 3 O 3 OO .—

C

c— O'. CM CO CO oo CM vD C

co C

O CL. -3 n in n 3- n n n 3- n n n n n

•H

E- O O O CD vO CO

CO

LO 3co o o vO CO

LO

-3

" OO o o vo co

LO3OO oOOin3OO

OQ

C C

O CD>

a 03 rH CM 0- O vO n O i-H ON OO n 3 O vO 0- OO CM OO rH CM

fci CO o 0) •H o n CM 3 OO 3 n CM n 3 oo n CM 3 n CM OO vO VO OO •—1 OO H cc CM CM CM CM CM CM CM CM CM CM CM CM CM CM CM CM CM CM CM CM CM

rH 3 vO O'. OO co. vO n O rH CT

vO n n o vO vO CM CM 00 rH CM

03 a o

C E o 0- 3 vO n vO vO oo vO n 3 vO oo n vO OO 3 10- t— 3 CM 3 •H 0) -3 -=r 3 3 3 3 3 3 3 3 3 3 3 .=r 3 3 3 3 3 3 3 Cl-, H

aJ oo -=r rH OO OO O O O O O OO O rH O O (T> CO O O O O

4-4 9* o CM CM CM CM CM rH rH rH iH iH rH rH rH 1 1 1 1 O O rH rH rH iH

*H E o CM CM CM CM CM CM CM CM CM CM CM CM CM CM CM CM CM CM CM CM CM

cos-

<V a

£

CmO

CD • Nl O

•H 2

GO ^

rH i—rH CM I—.—I rH CM rH rH rH CM CM CM

v / --

- V ' V ' • ' V / V / S / -—' v / '—/ V / V—*' o o o o o O O O O o O o o o

o o o o o o O O o o O o o o n n o o n n O O n n o o n n rH 1—

rH rH 1—

1—

-o a> n o o o n o o o n O o o O O cd N ml t— o o o C— o o o 0- O o o O o

O -H CM n o o CM n o o CM n o o O o -J CO »—

CM .—

CM i—i CM rH CM

3 O

CC 2

CM OO

20
TABLE

III

Standard

Test

Procedure

Data

•ov

.P8,

o

§

o

•HCm

CmU

M3nOcn

cmnOon o

M3 on

>r0

0 c

•H <D 03 CM on C\J M3 CO rH -=r on on CM CM un

<M -H • • • • • • • • • • •H O O' C— 03 rH on on O rH On 33 0 O 00 O -H

d) Cm

CM on on CM on -=r CM on 33 33 on

CL Cm CO w

ono

-p ^

COCD X

c c

Q. CD CM 03 CM M3

CM M3 1—

1

ScS O E- 33 M3 On 6*1 33 no •O On 1—

1

CM 33 On r—

I

CM

LO

• C— CM ITi 33 no on

on rH c\j 33

c—

LPl CM o

oun

-P3 C

co -p on M3 0 33 1—1 CO un M3 un 0 CM on 0 M3

CX <D -p • • • • • • • • • • • • • *p 3 cd 1—i M3 an 33 0 e- M3 iH t— 33 00 CM CM t

3 O 5 CM O rH un CM no on un 1—

i

e'- on 33-f—

1

on O Cu on 33 33 33 on on -3T 33 on en 33 33 33 -3

-

ii o o un o o •h <d crv on ^3- un

&—* CO <—I CM 33

o in o o o n 3- in

rH CM 33 o un o o o o o on 3- un 33 un H (\1 3 C\] =r

g §

<5

Q. CD E co a) -h

E-h (X

o

o

•HCEO<D O

IX E-t

aJ

1—1 CM O On On 0 t'- 0 0 un 00 rH rH 0 un un o- 0 on rH no

un M3 33 0033 un on un 00 M3 J=3

" X" un E" on 0 no on 0- on -=r CM CM CM CM CM CM CM CM CM CM CM CM CM CM CM CM CM (M CM iH CM

CM On on O O no CM 33 on co 33 c— un on 00 un t'- on CM 0 un E- 0- un unno no un M3 on e- no un M3 un 33 rH CO moo 0 un 33 33 •=3- 33 33 33 •33 33 33 x- 33 33 33 33 X- 33 33 33 33 33 33

rH E- m 1—1 rH M3 un 33 on on m3 no 33 on on O O On on On On

CM rH rH ! 1

1

1 rH rH rH rH r-1 1 1 rH 1

1 rH 1—

1

1 11

1 OOOO CM CM CM CM CM CM CM CM CM CM CM CM CM CM CM CM CM CM CM CM CM

i

2

<1) 8

<1> •

(S3 O

•H 2

10 W

00 CM CM 6 O 0 0 O O 0 0 O O 0 0 O

Q-. O 0 0 O O 0 0 O O 0 0 O

O un un 0 O un un 0 O un un 0 O

rH 1—i rH 1—1 rH rH

CMO

Oun

33o

oun

TJ <D un O 0 O un 0 0 0 un O 0 O O O

aj N ml c

O O O t- 0 0 0 c

O 0 O O O

O -H CM un 0 O CM un 0 0 CM un 0 O O O

_j co rH CM 1

1 CM rH CM rH CM

3 O

03 2 CM on 33

21
TABLE

IV

Standard

Test

Procedure

Data

I

|k

|l

i

.

*

>.oc

o> •H

•o o

O -H

-P Cm

(0 d-l VC w

m

M3

on

CMM3CO

Cr- M3on

>>o

o c

•H d> rH CT3 OO ro vO OO r- LO 0- 03 =r tr- c

Cm -H ft*L • • • • • . . . • • . • • • •H O rH OO oo M3 rH M3 OO rH cr\ 03 LO in t

O -H

d) Cm

Q. Cm 00 W

on m ro ro OO ro ro ro OO ro ro ro ro ro

-p §3 3 g

CX <D

ono

r—

3 CM vO ro oo

CM OO M3 03

OO

03 LO ro LO O O oo CM 03 CM M3 CM OO CM M3 CM M3 •o rH rH CM LO i—

CM LO C~- i—CM LO CM o

LO

-P3 G

CO -P LO o E— O t— 3- M3 CM tr- LO O CM M3 t—

Cl d> -P . . . • . • • • • . . . . -P 5 n3 CM oo CM i—1 M3 CO OO 03 vO CM LO 03 LO M3

3 O £ CM rH CM 03 i—

03 CM o rH ro OO 00 O VC -=r LO LO =r 3" LO LO LO LO 3- O' O'

d)E O LO o o O o LO LO o o LO LO o LO o

•H CD rH >i 03 LO 03 03 03 M3 03 03 03 03 03 H co rH CM ro r—

ro 1—ro rH ro

c Q

G

Cl d) 6 co CJ LO CM CM OO O'- C- MO M3 C~- C'— M3 03 ro ro LO C— C— LO t— c

o d3 d) -H o c

c— M3 CM CM rH CM 3- ro ro rH =r 3" CM CM O =r CM 03 CM LO >o

EH PC CM CM CM CM CM CM CM CM CM CM CM CM CM CM CM CM CM CM H CM CM

i—

3

G &

rH CO CM m3- OO tCM CM CM O M3 O ro ro OO O CM O CM CM

co 03 OO C

3- 3- CO =r M3 LO LO ro LO M3 ro ro LO LO CO O CO M3

ci) o 3" 3

- 3- 3- 3- 3- 3- 3" 3- 3

- 3- 3- 3" 3- 3- 3- 3- 3- 3- 3

iu H

rH

cd M3 M3 o LO LO rH rH M3 LO LO ro o 1

1 o o ro ro LO LO LO LO

•H

.p CX co rH 1

1 rH rH rH CM CM rH rH rH rH rH 1 1 rH i—

o o o o o o •H a o CM CM CM CM CM CM CM CM CM CM CM CM CM CM CM CM CM CM CM CM CM

COG

d> •3a

rH rH rH CM rH i—

rH CM rH i—

i—

CM CM ^r

V— v-/ - '—

/

3—/ —* M-X N / '—

/

V ' ' o o O o o o o O o o o o O o Cm o o o o o o Q o o o o o o o

O lo LO o o LO LO O o LO LO o o LO LO

rH 1—i—1—rH r—1 (D • N O

•H 2

oo

•o CD LO O O o LO O o o LO o o o O o cc3 N i—1

1 c- o O o f- O o o C o o o O o

O •H E! CM LO O o CM LO o o CM LO o o O o

00 r—CM r—

CM 1—CM i—1 CM

3 O

vc 2

CM on =r

22

25.7
TABLE

V

Standard

Test

Procedure

Data

td c c O CD>

I

TJ O

'll 4-> Ol

CTj Ch

cc td

C\J =T

C\J ^T

ON

i—

^T

o

o c

•H CD 3=r on CO -d- •=r o PO CM CM cr* on rH Cm -H • • • • • • • • • •H O on »—

LO LO CM LO tO to rH i—

O -H on 2d" =r 2d~ co =T PO

CD O

atw

00 Cd

LO ^r

=r lO

•=r

-P ho 3 £-1 CL CD

co

CD 3

O

•o

P

3 £-. Cl cd -p 5

3 O O Pl.

CO P

-P

ctJ 5

5

o

•H CD

E

-1 CO

CL CD S CO O

(D-rl O e-< a

^ a

•HCEOCD o Ct4 H

2

CD $

Cm

°iJ O

CD • N O

00

3 O

PS 3

ono

X

PO

LO CM CO po

CM

lO

LO PO to on

oo

CM LO o o PO CM PO 2d- CM 00 PO ^r CM =r oo <—

CM 2d" 00 i—

CM CM

CM

-=r

LO t

•=r LO LO 2d" l—

1—

CM LO LO CO 2d" LO

• • • • • • • • • • • • • • CO -=r 23" CM - LO 0 0 LO O LO O 1—

to to

P~- LO LO 2=r O to LO PO 1 1 LO O PO co CM PO LO LO =T =r LO LO =r 2d" LO to 2d" LO

LO o LO 0 LO 0 LO O LO 0 LO 0 LO 0 C— rH CO CO to rH CO CO to 1—

CO CO co CO

rH 11 PO rH 11 PO 1—

1 1 PO rH PO

0- OO PO CM -=r 0- LO LO PO to LO PO CO c— 0 CO 1—1 2d" VO 1—

.=r LO LO LO LO 2d" LO =r lo LO 2d" PO •=r PO CO co 10 to

CM CM CM CM CM CM CM CM CM cm CM CM CM CM CM CM CM PD PlJ CM CM

CM PO LO CO LO O- PO O CO LO to LO PO LO LO O PO O PO LO O

0- LO 0- LO LO lO LO O- LO LO to LO 2d" LO LO -=r lO -ST lO lO

-=r 2^ =t 2d* .=r 2d" -=r 2d" 2d" =r jqCTJ LO CO to =r -=r PO LO 2d" PO PO O 1 1 O co co O O CO CO CO CO

-P Q. O CM 1 1 rH rH rH O rH rH H r—

rH rH rH 0 0 11

1

1 0000 •H s 0 CM CM ClJ CM CM CM CM CM CM CM CM CM CM CM OlI ClJ CM CM CM CM CM

rH rH 1

1 CM 1—

1—

1 1 CM 1 (1—

rH CM CM

v / M-/ S r' >

s v ' V-/ N / ' V—

'—/ V ' ' S 0 O O O O 0 0 O O O O 0 O 0 0 O O O O 0 0 O O O O 0 O 0

LO LO O O LO LO 0 O LO LO O 0 LO 10

rH 1—

1—

rH 1—

1—

a CD to O O O LO O O O LO O O O O O

CTJ N ml to O O O to O O O tO O O O O

0 •H CM LO O O CM LO O O CM LO O O O O

_) 00 1—

CM 1—

CM 1—

CM rH CM

CM po

23
TABLE VI Test Data on Various

Foods Cooked in Oven A

Energy

Food Item

Initial

Weight

Weight

Loss

Cooking

Time

Into

Food

Input

Energy Efficiency

grams grams sec. joules joules %

4 Potatoes 755.0 144 1080 47. 8x10

4 4

132x10 36

Corn 10 oz Frozen Pouch 316.5 23.5 390 18.4 47.6 39

Bread 1/2

Loaf 130.0 5 90 2.74 8.96 31

Salisbury

Steak (Frozen) 156.5 12 210 9.86 25.5 39

4 Hot Dogs 181.0 7.5 110 4.61 13.4 34

6 Bacon

Strips 115.7 31.2 270 8.53 32.8 26

Lima Beans

16 oz Can 491 40 420 18.9 51.2 37

Fresh Beans

1/2 lb 227 67.9 480 21.4 58.6 37

Lima Beans

Frozen Pouch 305.5 38.0 540 22.9 65.9 35

35 AVG

24
TABLE VII Test Data on Various

Foods Cooked in Oven B

Energy

Food Item

Initial

Weight

Weight

Loss

Cooking

Time

Into

Food

Input

Energy Efficiency

grams grams sec. joules joules %

4 Potatoes 674.0 179.0 1020

4

52.5x10 I46xl0

4

36

Com 10 oz Frozen Pouch 305.0 13.0 270 15.5 39.0 40

Bread

1/2 Loaf 138.0 15.5 90 4.86 13.1 37

Salisbury

Steak (Frozen) 153.0 15.0 180 10.2 26.3 38

4 Hot Dogs 174.2 7.7 90 4.75 12.8 37

6 Bacon Strips 112.8 23.8 225 6.91 32.2 21

Lima Beans

16 oz Can 483.0 43.0 420 20.3 60.7 34

Fresh Beans

1/2 lb 227.0 27.0 240 11.2 35.0 32

Lima Beans

Frozen Pouch 297.0 71.0 540 30.3 77.4 39

35 AVG

25
TABLE VIII Test Data on Various

Foods Cooked in Oven C

Food Item

Initial

Weight

Weight

Loss

Cooking

Time

Energy

Into

Food

Input

Energy Efficiency

grains grams sec. joules joules %

4 Potatoes 819.0 126.0 1200 45.6x10^

4

131x10 35

Corn 10 oz Frozen Pouch 300.0 26.0 420 18.5 47.0 39

Bread

1/2 Loaf 130.0 2.0 45 1.80 5.11 35

Salisbury

Steak (Frozen) 154.5 15.0 240 10.3 26.3 39

4 Hot Dogs 178.5 9.2 135 4.90 14.6 34

6 Bacon

Strips 112.0 33.4 450 9.04 12.6 19

Lima Beans

16 oz Can 491.3 23.3 420 15.0 45.7 33

Fresh Beans

1/2 lb 227.0 21.5 270 9.61 29.2 33

Lima Beans

Frozen Pouch 290.0 28.0 480 19.8 52.2 38

34 AVG

26
TABLE IX Test Data on Various

Foods Cooked in Oven D

Energy

Food Item

Initial

Weight

Weight

Loss

Cooking

Time

Into

Food

Input

Energy Efficiency

grams grams sec. joules joules %

4 Potatoes 712.0 130.0 900 43.3xl0

4

123xl0

4

35

Corn 10 oz Frozen Pouch 306.5 6.5 300 14.2 39.8 36

Bread

1/2 Loaf 92.0 3.5 90 2.02 6.70 30

Salisbury

Steak (Frozen) 155.5 12.5 210 10.1 28.0 36

4 Hot Dogs 178.5 5.0 95 4.14 12.9 32

6 Bacon

Strips 117.3 35.2 360 9.47 48.2 20

Lima Beans

16 oz Can 497.5 41.0 420 20.2 56.2 36

Fresh Beans

1/2 lb 227.0 44.7 360 15.6 48.1 32

Lima Beans

Frozen Pouch 300.5 45.0 540 25.3 73.0 35

32 AVG

27
TABLE X Test Data on Various

Foods Cooked in Oven E

Energy

Food Item

Initial

Weight

Weight

Loss

Cooking

Time

Into

Food

Input

Energy Efficiency

grams grams sec- joules joules %

4 Potatoes 680.0 57.0 660 29.4x10^ 4

75.1x10 39

Com 10 oz Frozen Pouch 310.0 18.0 360 16.3 40.3 40

Bread

1/2 Loaf 105.5 11.0 90 3.89 10.1 38

Salisbury

Steak (Frozen) 178.0 12.5 210 10.0 23.8 42

4 Hot Dogs 177.3 6.9 110 4.64 12.2 38

6 Bacon

Strips 103.0 32.0 270 8.60 30.2 28

Lima Beans

16 oz Can 490 38.0 420 18.7 47.1 40

Fresh Beans

1/2 lb 162.5 40.5 300 12.4 33.6 37

Lima Beans

Frozen Pouch 315.9 27.9 420 20.0 47.2 42

38 AVG

28
TABLE XI Sumnary of Oven Efficiencies

Measured With The Standard Test Procedure & Foods

Oven Test Procedure

Avg. Efficiency

A 40.0

B 38.5

C 36.3

D 36.4

E 42.2

Cooking Foods

Avg. Efficiency

35

35

34

32

38

29
NBS-1 14A (REV. 7-73)

U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR RF. PORT NO.

NBSIR 77-1387

2. Gov t Accession

No.

3. Recipient s Accession No.

4. H I 1. 1 AND SUBTITLE 5. Publication Date

Evaluation of a Test Method for Measuring Microwave Oven

Cooking Efficiency 6. Performing Organization Code

7. AUTHOR(S)

Owen B. Laug

9. PERFORMING ORGANIZATION NAME AND ADDRESS

8 . Performing Organ. Report No.

10. Project/Task/Work Unit No. NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

11. Contract/Grant No.

12. Sponsoring Organization Name and Complete Address (Street, City, State, ZIP) 13 Type of Report 8t Period Covered

Federal Energy Administration

Washington, D. C. 20461 14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

16. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here.)

A standard test procedure for measuring the energy efficiency of microwave ovens

has been developed and tested on current representative products. The test method

is based on the International Electrical Commission (IEC-SC-59H) procedure for

measuring performance of microwave cooking appliances. The results of laboratory

tests show that the method is repeatable, easy to perform, and requires a minimum

of special techniques or apparatus. A technique was developed to measure the

efficiency of cooking various foods in the ovens. The efficiencies determined by

the standard test method are shown to be realistic and correlate well with the

efficiencies determined by cooking a variety of foods.

17. KEY WORDS ("six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name; separated by semicolons

)

Energy efficiency; Microwave oven

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For Official Distribution. Do Not Release to NTIS

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