NATL INST. OF STAND & TECH

I llll A 111 Ob 430756

NBSIR 87-

Performance of Instantaneous

Gas-Fired Water Heaters

James E. Harris

Joseph Greenberg

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Building Technology

Building Environment Division

Gaithersburg, MD 20899

May 1987

Final Report

Prepared for: Building Equipment Division

ice of Buildings and Community Systems ^ >. Department of Energy

100 shington, DC 20585

U56

I). 87-3557

1)87

NBSIR 87-3537

PERFORMANCE OF INSTANTANEOUS

GAS-FIRED WATER HEATERS

James E. Harris

Joseph Greenberg

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Building Technology

Building Environment Division

Gaithersburg, MD 20899

May 1987

Final Report

Prepared for: Building Equipment Division

Office of Buildings and Community Systems

U.S. Department of Energy

Washington, DC 20585

U.S. DEPARTMENT OF COMMERCE, Malcolm Baldrige, Secretary

NATIONAL BUREAU OF STANDARDS, Ernest Ambler. Director

ABSTRACT

Four different instantaneous, gas-fired water heaters were tested to

develop a test method to determine recovery efficiency (Er) and energy

factor (EF) . All four of the water heaters were from foreign countries

(West Germany, the United Kingdom, France and Japan). Various flow

rates and water draws were used during the tests to determine their

influence on the recovery efficiency and energy factor. In addition,

the pilot light power consumption was measured to determine the effect

of a variable pilot light power rate on the energy factor. The use of

recovery efficiency as a performance index seems appropriate for these

units, however, the use of energy factor, as presently calculated,

needs further study.

m
DISCLAIMER

This report is intended to provide the baseline for the development of

test procedures for instantaneous water heaters and not to judge the

performance of the water heaters for any specific application.

Although the units tested were not identified by manufacturer,

inclusion of a given unit in this report in no case implies a

recommendation or endorsement by the National Bureau of Standards, and

the presentation should not be construed as a certification that any

unit would provide the indicated performance. Similarly, the omission

of a unit does not imply that its capabilities are more or less than

those of the included units.

IV
ACKNOWLEDGEMENTS

The authors wish to acknowledge the contribution of Douglas L. Hawk,

Mechanical Engineering Student at the University of Maryland, for

efficiently and professionally conducting the tests described herein

and to Dianna Mills for her efforts in typing this document for

publication.

v
TABLE OF CONTENTS

Page

ABSTRACT ill

DISCLAIMER iv

ACKNOWLEDGEMENTS v LIST OF TABLES. viii

LIST OF FIGURES. . ................................................. ix

NOMENCLATURE. . x

1 . INTRODUCTION. 1

1.1 Objective 1 1.2 Theory of Operation 2 1.3 Potential Applications. 3

2. SCOPE AND TEST PROCEDURES..... 4

2.1 Scope. 4

2.2 Test Set-up and Laboratory Conditions................... 5 2.3 Measuremen ts Taken. ...... o. ........ 7 2.4 Test Procedures 7

3. TEST DATA 9

4. TEST RESULTS AND CALCULATIONS 10

4.1 Water Flow Rate Versus Temperature Rise 10

4.2 Calculation of Recovery Efficiency 13

4.3 Portable Combustion Efficiency Analyzer Results 14

4.4 Calculation of Energy Factor 14

5. DISCUSSION 17

5.1 Determination of Unit GPM at a Temperature Rise of 77 °F. 17

5.2 Determination of Recovery Ef fic iency ...................

.

19

5.3 Determination of Energy Factor 20

6. CONCLUSIONS 21

7. REFERENCES 22

APPENDIX A - COMPUTATIONS AND FORMULAS USED A-l

1.0 Gas Correction Factor A-l

2.0 Energy Used During a Test A2

3.0 Mean Outlet Hot Water Temperature....................... A-2

4.0 Mean Water Supply Temperature. ......................... . A-3

5 o 0 Rec ove ry Efficiency.. ..........oo.©..®...®.®.. .......... A—

3

6.0 Daily Water Heating Energy Consumption.................. A-4

7.0 The Flow Rate During a Draw A-4

vi
8.0 Power (Firing Rate) Determination . . A-5

9.0 Daily Hot Water Energy Consumption.... A-5

10.0 Pilot Light Energy Consumption Rate..................... A-5

11.0 Average Daily Energy Consumption A-6

12.0 Energy Factor..... A-6

APPENDIX B - UNITS CONVERSION TABLE: SI/ INCH-POUND/S I. .......... . B-l

vn
LIST OF TABLES

Page

Table 1 a Test Data - Unit

Table lb Test Data - Unit

Table 1c Test Data - Unit

Table Id Test Data - Unit

Table 2a Summary Data, Er

Table 2b Summary Data, Er

Table 2c Summary Data, Er

Table 2d Summary Data, Er

F©.GoeooG©«o.e.®o.© 0 Ooo«©oo©.©. .....««»

OoOO©OOOC0OO©OO©OO©oe©O0OOCGOC©OGO©OOQO

U.oeoo.o.. .000.0.0. .QQa.o.oGOeOGO.OOQCC

To.e.«o»ce©.oc.e.o©oo©.©.«©o®®. .«©..©.©

, and EF - Unit F.... ...... .............

• and EF Unit O. o .... o .

.

, and EF ~ Unit H

, and EF ~ Unit I. .........oo.. ...... o..

24

25

26

27

28

29

30

31

Vlll
LIST OF FIGURES

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Page

Instantaneous Gas-Fired Water

Heater Test Set-Up ......... . ....... * ... . 23

Temperature Rise vs. Flow Rate - Unit F. . . ............

.

32

Temperature Rise vs. Flow Rate - Unit G 33

Temperature Rise vs. Flow Rate - Unit H.. 34

Temperature Rise vs. Flow Rate - Unit I..... 35

Recovery Efficiency (Er) and

Energy Factor (EF) vs. Flow Rate - Unit F. ............

.

36

Recovery Efficiency (Er) and

Energy Factor (EF) vs. Flow Rate - Unit G 37

Recovery Efficiency (Er) and

Energy Factor (EF) vs. Flow Rate - Unit H 38

Recovery Efficiency (Er) and

Energy Factor (EF) vs. Flow Rate - Unit I 39
NOMENCLATURE

Cc Daily hot water energy consumption (Btu/day)

Cf Correction factor to convert measured gas to Standard Cubic

Feet (SCF) (dimensionless)

Cwh Daily water heating energy consumption (Btu/day)

Cy Average daily energy consumptions derived from cold tank

recovery test (Btu/day)

Er Recovery efficiency (dimensionless)

EF Energy factor, the ratio of daily hot water energy

consumption to the daily energy consumption with a particular

water heater (dimensionless)

Fr Flow rate of water (gallons per minute)

H Higher heating value of gas (Btu/SCF)

k Specific heat of water (8.25 Btu/(gallon - °F))

P Power used by water heater (Btu/hour)

Pa Atmospheric pressure in inches of mercury (Note: if the

pressure is in Millibars, then multiply by 0.02953 to convert

to inches Hg)

Pg Gas pressure (inches Hg) note: to convert inches of water to

inches Hg, multiplied by 0.07343)

Pr Pilot light energy consumption rate (Btu/hr)

Pwv Water vapor pressure, partial (inches Hg)

Q Heat supplied to water heater during a test (Btu)

R Recovery rate (gallons/hour)

Ta Ambient air temperature ( °F)

Tcp Combustion products temperature in the stack ( °F)

Td Time of draw (minutes)

Tg Temperature of the natural gas at the gas meter ( °F)

Th Hot water temperature during a draw ( °F)

Tha Average hot water temperature during a draw ( °F)

x
Ti Inlet (supply) water temperature ( °F)

Tia Average inlet (supply) water temperature ( °F)

U The nominal daily hot water usage

Vol The measured volume of gas used during a test (cubic feet)

Ww Weight of water drawn (pounds)

1 INTRODUCTION

Four different instantaneous, gas-fired water heaters were tested to

develop a test method to determine the recovery efficiency, Er, and

energy factor, EF, for these units. Although thermal efficiency and

standby loss tests have been defined by the American Gas Association

and published as ANSI Standards [1,2]*, the tests were not prepared in

the contex of an integrated, overall energy conservation program for

water heaters. These water heater types have been called by a number

of other descriptive names: i.e. in-line, tankless, demand, point of

use, geyser and instantaneous. In this report, the designation

"instantaneous" will be used. These water heaters are of interest for

their potential to save energy since they should have lower standby

losses, perhaps higher recovery efficiencies and energy factors than

storage type gas-fired water heaters currently in use.

1.1 Objective

The objectives of these tests were: (1) to establish a baseline for

the development of an appropriate test method for instantaneous water

heaters; (2) to characterize the performance of instantaneous, gasfired water heaters; (3) to use the test data to determine a method of

calculating a recovery efficiency, Er, and energy factor, EF , for

instantaneous water heaters; (4) to judge the adequacy of using these

* Note: Numbers in brackets refer to references at the end of the

report

.
factors to rate instantaneous water heaters and; (5) to assess the

suitability of these factors in comparing the performance of

instantaneous water heaters to storage type water heaters.

1.2 Theory of Operation

Instantaneous water heaters provide hot water on demand. Because these

are tankless heaters., they avoid some of the standby losses, namely

flue and jacket losses, usually associated with storage type units.

Most of the currently produced units have integral controls to modulate

the firing rate of the main burner as a function of water flow rate or

outlet water temperature although some of the older units have fixed

firing rate burners. In addition, most units have some minimum flow to

activate (turn-on) the main burner. The main burner also is provided

with the usual proof-of-f lame sensor device along with high temperature

and other safety features required for automatic, gas-fired appliances.

Units which incorporate flow sensor devices are activated by variable

water flow rates to modulate the gas flow rate to the main burner.

These units generally have a knob on the control panel to provide a

convenient means to manually set the regulated temperature rise of the

hot water. Turning this knob adjusts the flow sensor control mechanism

which controls main burner modulation. Other heaters use a thermal

sensing bulb filled with an expandable fluid that expands and contracts

in response to the temperature changes of the water in the finned-tube

heat exchanger. The expanding fluid actuates a bellows that increases

the opening of the main burner gas control valve to modulate the burner

firing rate to control the hot water temperature within a certain

2
range. This second type is a thermostatically modulated control

whereas the first type is a flow modulated control.

As the flow rate of the hot water is increased, the firing rate of the

main burner is increased to maintain the hot water discharge

temperature at or near the particular temperature set point. Further

increases in flow rates of the hot water beyond that corresponding to

the maximum firing rate will result in a corresponding decrease in the

hot water temperature as the flow rate is above the range of

modulation. In all types of instantaneous gas-fired water heaters, a

cessation of hot water flow extinguishes the main burner.

All of the units have pilot lights which are started by manually

operating a push button to activate a piezoelectric spark igniter. The

pilot light remains activated enabling it to ignite the main burner as

often as required to satisfy any subsequent hot water draws. Pilot

lights may be manually extinguished to save energy if hot water usage

is not anticipated for an extended time.

1.3 Potential Applications

In domestic household applications, instantaneous water heaters may be

installed:

(1) In a central location, as a replacement for a storage type water

heater in typical use in the U.S. In this application, some

standby losses may be reduced since there is no stored hot water

and no associated jacket losses.

3
(2) In series with a separately fired hot water storage tank, where

the hot water is stored in the tank at a reduced temperature.

When hot water is drawn, the instantaneous water heater serves as

a booster heater to increase the water temperature to some higher

value. Energy may be saved from reduced standby losses of the

storage tank because of the lower temperature of the stored water.

(3) Locally at selected hot water usage points where each

instantaneous water heater operates independently. In addition to

the reduction of the standby losses by the elimination of jacket

and flue losses, there may be reduced piping heat losses since

pipe runs to the point of use would generally be shorter.

(4) In conjunction with an insulated storage tank with a circulating

pump and suitable controls allowing the system to function as a

indirect-f ired storage type water heater. In this configuration,

flue losses may be reduced as a contributor to the standby losses

and it is possible that the recovery efficiency may be higher than

that of conventional gas-fired storage water heaters because of

the use of finned tube heat exchangers. Also, instantaneous water

heaters with reduced firing rates might be used if the hot water

were stored in an insulated storage tank. Some efficiencies

gained may be offset, however, because of the required water

circulating pump and controls.

2. SCOPE AND TEST PROCEDURES

2.1 Scope

Four (4) instantaneous natural gas-fired water heaters were tested.

They all vary in water heating capability and all are manufactured

4
overseas namely: West Germany, Great Britain, France, and Japan. It

should be emphasized that the testing conducted on these units were not

meant to evaluate the units themselves but rather to aid in the

development of meaningful test procedures on a generic basis for all

instantaneous type water heaters.

2.2 Test Setup and Laboratory Conditions

The test setup for instantaneous gas-fired water heater testing is

shown in Figure 1. Units were designated F, G, H, and I (letters A

through E were used for tests of other types of water heaters not

reported herein) and each unit tested separately through the manual

setting or control of the appropriate gas and water valves. The

testing setup also allowed the required instrumentation to be used

efficiently with a minimum of change or modification.

The supply water temperature was conditioned to the desired temperature

(normally 70 °F**) in the conditioning tanks and circulated by a pump to

ensure that the inlet supply water to the instantaneous heaters was of

a uniform temperature during testing. Appropriate valves were set so

that the domestic supply water pressure was used to pressurize the

water system to force the flow of water as required by the hot water

** Note: In this report inch-pound units are generally used to be

consistent with DOE and other published test procedures although

some temperature data were collected in degrees Celsius. An S/I

conversion table is included in Appendix B.

5
draws Water flow rates were set by control valves and the flow rate

was monitored by a flow meter.

The total volume of water drawn during the test was measured by using a

120 gallon collecting tank mounted on a balance beam scale. The

balance beam was fitted with an electrical switch which controlled a

valve on the supply water inlet to the instantaneous water heater

being tested. After water flow was initiated, the outlet hot water

coming from the instantaneous water heater was collected in the 120

gallon tank, the weight of the incoming water gradually leveled the

balance beam. When a predetermined weight representing the total water

volume to be drawn was reached, the electrical switch on the balance

beam was activated. This stopped the supply water flow to the water

heater and ended the test. The actual flow rate was calculated by

timing and weighing the total water flow.

During certain tests, a portable combustion efficiency analyzer was

used to determine combustion efficiency. This measurement was to be

compared later to the calculated water heater efficiency for

correlation.

Tests were conducted at a laboratory ambient temperature of

approximately 70 °F. All water heaters were tested with draw tests

since the burner is activated only by a draw. A traditional recovery

test [3] which draws no water was not a suitable type of test for an

instantaneous type water heater. Although this type of water heater

6
has no storage tank, a recovery efficiency was calculated for each test

(see Section 4, Test Results and Calculations). The pilot light gas

consumption rate was measured for all water heaters tested.

2.3 Measurements Taken

The following measurements were taken and recorded for each test.

1. Ambient air temperature, Ta

2. Natural gas inlet temperature, Tg

3. Inlet (supply) water temperature, Ti

4. Outlet (hot) water temperature, Th

5. Stack (combustion products) temperature, Tcp

6. Amount of hot water drawn during a test (in pounds), Ww

7. Time of draw (in minutes, used to accurately measure flow rate),

Td

8. Barometric air pressure (in milli-bars and converted to inches of

mercury) , Pa

9. Higher heating value of natural gas and converted to Btu per SCF,

H

10. Inlet (supply) natural gas pressure measured in inches of water

column and converted to inches of mercury, Pg

11. Quantity of natural gas used in cubic feet and converted to

standard cubic feet, Vol.

2.4 Test Procedures

In general, the following procedures were followed for the testing of

each instantaneous gas-fired water heater:

7
Water in the conditioning tanks was prepared for use as the inlet

(supply) water for the instantaneous heater test by heating or

cooling, as needed, to bring the supply water to the desired

starting temperature.

The drain valve on the 120 gallon water collecting tank was opened

to ensure that the tank was empty. The valve was then closed and

the balance beam was set to activate the switch so as to stop the

flow of supply water after the required weight of hot water was

collected from the instantaneous water heater being tested.

Water control valves were set to provide domestic water line

pressure to the supply tanks.

The water heater to be tested was isolated by turning off the cold

water supply valves to all other water heaters. The appropriate

gas valves were set to assure that only the water heater to be

tested had natural gas supplied, then, the pilot light was ignited

by following the specific instructions for the particular water

heater.

The datalogger was set to record the necessary thermocouple

measurements (input supply water temperature, outlet hot water

temperature, and ambient air temperature) at one minute intervals.

The natural gas meter and the barometric pressure were read.

The test was initiated by opening the water inlet valve to the

instantaneous water heater using the flow meter to set the nominal

test flow rate. Simultaneously, the datalogger and timer were

started

.

While a draw was being made and the water heater burner was

activated, the natural gas pressure and the portable combustion

8
efficiency analyzer were read. The portable combustion efficiency

analyzer which measures combustion products and temperatures was

used only for a selected number of tests.

9. When the draw was complete the scale beam tipped to cause the cold

water supply control valve to close and terminate the water flow.

The elapsed time since the start of the draw was recorded as well

as the natural gas meter reading.

10. The tank drain valve was then opened to empty the 120 gallon

collecting tank, and the datalogger reset to prepare for the next

test

.

3 . TEST DATA

A number of tests were conducted on each of the four instantaneous

water heaters. The test data are shown in Tables la, lb, lc, and Id

for Units F, G, H, and I, respectively. Each tested unit is shown

along with an identifying test number and each test series is

identified by sequential test numbers. The higher heating value of the

gas, H, is the same for all the tests conducted within the series.

As can be observed, the hot water flow rates were varied from

approximately 1 gallon per minute (GPM) to approximately 3 GPM although

several tests were conducted at a hot water flow rate of approximately

4 GPM for Unit H. For each test, the total amount of hot water drawn

is also indicated, varying from 5 gallons to 50 gallons. Most tests,

however, were conducted using a total volume of 21.4 gallons which

corresponds to the first draw volume of the proposed simulated use test

for storage type water heaters [4]. The simulated use test for storage

9
type water heaters is conducted by drawing a total of 64.3 gallons in

three equal draws of 21.4 gallons each.

The measured inlet and outlet temperature, in degrees Celsius, is also

shown in Tables la through Id along with the correction factor, Cf,

used to convert measured gas to "standard" cubic feet, SCF; the cubic

feet of gas used during the test, CuFt; and the higher heating value

for the gas used, H. The measured pilot light energy consumption for

each unit is also indicated along with the corresponding hourly BTU

rate.

For convenience, the inlet and outlet water temperatures as well as the

outlet minus inlet water temperature, Tl , are also shown in degrees

Fahrenheit. Finally, the Btu content of the gas, Q, used for each test

is calculated as the product of (Cf)(Vol)(H) and indicated in Tables la

through Id.

4. TEST RESULTS AND CALCULATIONS

4.1 Water Flow Rate Versus Temperature Rise

In order to characterize each of the tested units regarding its ability

to provide hot water, the data shown indicating flow rate, GPM, and

temperature rise, Tl , from Tables la through Id were plotted. The

results for Units F, G, H and I are shown in Figures 2, 3, 4, and 5,

respectively. For each graph, the results for the 21.4 total draw test

series are generally connected by lines for clarity. In addition, the

total gallons of water drawn for each test is indicated.

10
For Unit F, the draw rates varied from approximately one to three GPM

as shown in Figure 2. As can be seen, the congruency of the GPM versus

Temperature Rise lines are rather scattered and some of the data points

at draw rates of approximately 1 GPM, for a total draw of 5 and 10

gallons, are somewhat anomalous. The predominant GPM versus

Temperature Rise trend is approximately linear from about a temperature

rise of 68°F at 1 GPM to 45°F at 3 GPM as represented by two of the

draws from the 21.4 gallon series tests and the 15 gallon draw tests.

The third 21.4 gallon series plot is offset from the others. Note that

Unit F cannot provide hot water at a temperature rise of 77 °F which

represents water heated from an inlet temperature of 58°F to an outlet

temperature of 135 °F. It does, however, provide hot water above a

temperature rise of 55°F at 2 GPM. This temperature rise represents

hot water at 113 °F if the inlet water is 58°F; which is a water

temperature considered useful for most domestic hot water uses.

The GPM versus Temperature Rise characterization for Unit G is shown in

Figure 3. In this case, the GPM versus Temperature Rise lines are

fairly congruent and linear from a temperature rise of approximately

85°F at 1.7 GPM to a temperature rise of 47 °F at 3.2 GPM. These lines

represent hot water draws of 5 gallons, 21.4 gallons, and 50 gallons.

As can be seen, Unit G is capable of producing hot water at a

temperature rise of 77 °F, again, representing the heating of water from

an inlet temperature of 58°F to an outlet temperature of 135 °F at a

flow rate of approximately 1.9 GPM. For Unit G, the range from 1 GPM

and 1.7 GPM represents main burner modulation range at these lower flow

11
rates. These points are rather scattered and tend toward a higher

temperature rise with an increase in flow rate, as might be expected

within this flow rate range.

Unit H exhibits the trend in GPM versus Temperature Rise

characteristics as shown in Figure 4. From a temperature rise of

approximately 86 °F at 1 GPM to a temperature rise of approximately 45 °F

at 4 GPM, the trend appears somewhat uniform with the exception of the

7.5 gallon data points. In addition, the lines exhibit little

similarity within the overall range. This unit will deliver hot water

at a temperature rise of 77 °F with a flow rate of approximately 1.7

GPM.

Unit I, the unit with the highest firing rate in Btu/hr input of the

four units tested also exhibited a somewhat linear characteristic with

reasonable similarities from a temperature rise of approximately 89°F

at 2.2 GPM to a temperature rise of approximately 69°F at 3 GPM, if the

single 81 °F temperature rise at 3 GPM data point is not included (see

Figure 5). Data points at flow rates less than approximately 2.2 GPM

represent the unit operating within the range of modulation. This unit

provides the highest flow hot water rate of approximately 2.6 GPM at a

temperature rise of 77°F of the four units tested. It should be noted

that Unit I was not operated at its maximum output due to gas line

supply restrictions.

12
4.2 Calculation of Recovery Efficiency

Using the test data shown in Tables la through Id a Recovery

Efficiency, Er, was calculated for each test using the equations in

Appendix A. These calculated Er ' s are shown in Tables 2a through 2d

along with the individual values used for the calculation. It should

be noted that the Er calculation is based on the active operation of

the instantaneous water heater for the actual water volume heated and

the actual temperature rise achieved during the test. The water volume

is not normalized to any particular volume and the fuel consumed by the

pilot light is ignored during the water heater's quiescent period (the

time in which the pilot alone is burning and no water is being drawn).

The Er for the four units tested varied from approximately 0.72 to

0.90.

The Er for each unit tested was plotted as a function of water flow

rate and is shown in Figures 6, 7, 8, and 9, for Units F, G, H, and I,

respectively. As can be seen, the lines connecting the points which

represent each test series are not congruent. However, the aggregate

of the points plotted indicate a general trend showing a higher Er with

increased flow rate with an increase in Er ranging from approximately

0.05 to 0.1 between the draw rates of 1 GPM and 3 GPM. The Er for

Units F, G, and H all seem to lie nominally between 0.75 and 0.85 while

Unit I shows a nominal Er range from 0.80 to 0.90.

Generally, the Er appears to be somewhat sensitive to the flow rate and

the temperature rise used for the calculation, as represented by the

13
differences of the plotted lines and the small increase in Er at the

higher flow rates.

4.3 Portable Combustion Efficiency Analyzer Results

A portable combustion efficiency analyzer was used during several tests

conducted on Unit H in order to determine if there was any correlation

between the calculated Er and the combustion efficiency. The

combustion efficiency analyzer measures the flue gases and analyzes the

combustion products and temperatures. A comparison of the combustion

efficiencies displayed by the analyzer and the calculated Er for tests

22 through 28 for Unit H is as follows:

Combustion Calculated

Test Efficiency Recovery Efficiency

H22 .779 .783

H23 .775 .797

H24 .754 .739

H25 .766 .766

H26 .794/. 787 .798

H27 .789/. 780 .786

H28 .791/. 787 .801

The two combustion efficiency values for tests 26H, 27H, and 28H are

given because the analyzer showed two different readings during course

of the tests; the second readings were taken about 30 seconds after the

first readings. The analyzer updated its reading once each second. As

can be noted s the values for the two methods used to determine Er

compare rather closely.

4.4 Calculation of Energy Factor

Energy Factors, EF , were also calculated for each test using the

equations in Appendix A. The calculated EF ' s are shown in Tables 2a

through 2d. The EF is based on a 24 hour simulated use test and

14
assumes that a total number of gallons of heated water is drawn at a

specified flow rate. It further assumes that during the 24 hour

simulated use test, the pilot light of the instantaneous water heater

is burning while no water is drawn. The EF is calculated as the ratio

of the energy content of a day's supply of hot water divided by the

total energy required to provide the hot water plus the energy used by

the pilot light during the time hot water is not being drawn.

The EF ' s calculated for each test for an assumed number of different

daily water usages are shown in Tables 2a through 2d. The energy

consumption of the pilot light for each unit is also shown. It should

be noted that these calculations are determined from the actual test

data to reflect the EF for the total daily water usages of 20, 40,

64.3, and 80 gallons.

The EF ' s for each test as a function of water flow rate for Units F, G,

H, and I are shown in Figures 6, 7, 8, and 9 respectively, along with

the plots for Er versus Flow Rate shown in these figures. For clarity,

data for a total flow (U) of 64.3 gallons are not shown since the

curves would tend to overlap with the data shown for total water drawn

for 40 and 80 gallons. The 64.3 gallon data, however, if plotted would

fall between the 40 and 80 gallon plots and have the same general shape

as the 40 and 80 gallon plots.

All of the EF curves for each of the units tested generally follow the

same trends. As can be observed, the greater the total amount of water

drawn, the higher the EF. This follows from the fact that the EF is

15
calculated over a 24 hour period and the larger the hot water draw the

shorter the standby time. It is the energy consumed during this

standby time that has a very measurable effect on the EF . As the

standby time is decreased by a longer water draw, the EF approaches the

Er. The limiting case is when water is drawn continuously for a 24

hour period and there is no standby time when only the pilot light is

burning

.

It should also be noted that generally the higher the flow rate for a

given total draw, the lower is the resulting EF. This is related to

the standby time of the instantaneous water heater. If the amount of

water to be drawn is removed at a greater flow rate, the recovery time

is shortened increasing the standby time and lowering the EF, assuming

a constant burning pilot during the standby period.

The Energy Factor is also a function of the pilot light energy

consumption rate. The pilot light energy consumption rates for the

various units are as follows:

Unit F 340 Btu/hr

Unit G 357 Btu/hr

Unit H 643 Btu/hr

Unit I 896 Btu/hr

Generally, the higher the pilot light energy consumption rate, the

lower the EF for a given Er. For example, the Units with the smallest

pilot light energy consumption rates (Units F and G) have Energy

Factors of approximately 0.42 for a total hot water draw of 20 gallons

at 3 GPM. For the same conditions, Unit H with a pilot light

consumption rate of 643 Btu/hr has an EF of approximately 0.35 and

16
Unit I, with a pilot light consumption rate of 896 Btu/hr has an EF of

approximately 0.32.

Finally, it should be noted that the EF ' s shown in Figure 6, 7, 8, and

9 vary in congruency and are sensitive to varying degrees to the

parameters which are used for the EF calculations. Also, the EF 1 s that

show a positive slope derive this slope by following the positive

modulating range slope shown for the GPM versus Temperature Rise plots

for each Unit.

5. DISCUSSION

5.1 Determination of Unit GPM at a Temperature Rise of 77 °F

In viewing the graphs of Er and EF with their multiple points as shown

in Figures 6, 7, 8, and 9, one might question which of these points

represents the Er and EF for the four instantaneous water heaters

tested. Since the basis for these factors originate from the points

found on the GPM versus Temperature Rise curves shown in Figures 2, 3,

4, and 5, a method for selecting a single point is desirable.

For consistency of comparison, it is advantageous to conduct all water

heater tests under the same test conditions. Toward that end, the

units should be tested at a flow rate of 3 GPM at a temperature rise of

77 °F with 135 °F outlet water, the same conditions recommended for

testing all residential water heaters [4]. If that temperature rise at

that flow rate cannot be achieved, then the highest flow rate

obtainable by the unit which produces a temperature rise of 77 °F should

17
be used. Units G, H, and I can heat water to a temperature rise of

77°F, at lower flow rates than 3 GPM. Unit F could not achieve a

temperature rise of 77 °F at any flow rate (see Figure 2).

Because of the incongruity of the GPM versus Temperature Rise curves

crossing the 77 °F temperature rise line, it appears that a single draw

test would be inappropriate. The testing of instantaneous water

heaters should use a number of draws and temperature rises and be run

often enough to characterize the performance of the particular water

heater under test. One way of accomplishing this would be by drawing

20 gallons of water at a temperature rise of 80°F, 77°F, and 75°F,

defined as a draw series, and repeating these draws for a total of

three series. This would represent a total of 9 water draws of 20

gallons each. The measured GPM versus Temperature Rise can then be

plotted on a graph and the series lines connected. If the intersection

of the series lines with the 77 °F constant temperature rise line (see

Figures 2 through 5) is observed to have a GPM spread of 0.2 GPM or

less, the average of the three intersections should be used as the GPM

output of the instantaneous water heater at a temperature rise of 77 °F.

If the spread is greater than 0.2 GPM, repeat the tests for 3

additional series totaling an additional 9 draws of 21.4 gallons each.

These additional measured GPM versus Temperature Rise points are added

to the original graph, then the lines are connected and the

intersections of the six lines crossing the constant temperature rise

line of 77 °F averaged. The average of these points would represent the

18
GPM output of the instantaneous water heater at a temperature rise of

77 °F.

5.2 Determination of Recovery Efficiency

The single flow rate required to provide a water temperature rise of

77 °F should be used to calculate the Er for the water heater. Since

the Er as a function of flow rate is fairly constant (see Figure 6, 7,

8, and 9), errors in GPM versus Temperature Rise measurement or

inconsistent unit operation due to burner firing tolerances should have

little effect on the resulting Er. This procedure should be modified

if, for any reason, other units tested exhibit characteristics that are

significantly different from these four tested units.

The comparison of Er's between instantaneous water heaters seems to be

a reasonable index of relative performance. This is true even though

the maximum flow rate at a temperature rise of 77 °F varies among water

heaters. Since the Er, as a function of flow rate, is fairly constant,

the calculated values should not be significantly affected.

Instantaneous water heaters that do not have the ability to deliver

water at a temperature rise of 77 °F cannot be compared by this index of

performance. With regard to the index itself, it is doubtful that a Er

for instantaneous water heaters can be directly compared to a Er for

storage type water heaters with any meaning. One difference is that

the instantaneous water heater will generally supply less than the 3

GPM flow rate as is used for storage type heaters. Another is that

once the flow rate at a temperature rise of 77 °F for an instantaneous

19
water heater is determined, it can produce this flow of hot water

indefinitely. This area of comparison needs further investigation and

study

.

5.3 Determination of Energy Factor

Once a flow rate at a temperature rise of 77 °F is determined, the EF

for the unit can be determined given a total daily draw of hot water

and the pilot energy consumption rate. Although the EF is somewhat

sensitive to flow rate, it seems adequate to determine this index at

the, single, representative flow rate at the flow rate output of 77 °F

as described in 4.1. However, the Energy Factor is sensitive to the

total water drawn and the pilot light energy consumption rate.

An argument could be made that since instantaneous water heaters are

designed to deliver an unlimited supply of hot water at a given

temperature rise and flow rate, any index for these units which is

based on a specific total water delivery may be misleading. For

example, the less water that is used, the lower the EF ; although the Er

remains the same. And this decrease in Energy Factor is not caused by

the operation of the unit but rather by the effects of the energy used

by the pilot light.

Another consideration in using the EF as a performance index is that

the units are designed to be turned-off, that is, the pilot light is

extinguished when the unit is not in use. The pilot lights, however,

are easily started by manually operating a push button to activate a

piezoelectric spark igniter. Although this mode of operation is common

20
overseas, such operation has been basically untested as a viable mode

of operation by individuals in the United States who have been

conditioned to not having to activate their pilot lights on their

storage type water heaters. In considering a performance index, it is

questionable as to whether or not the water heater should be penalized

by assuming that the user will not make full use of the built-in energy

saving potential associated with this type of water heater. As for the

pilot energy consumption rate, the point is moot if the pilot light is

turned off after each use. This area also requires additional

investigation and study to determine its usefulness as a performance

index for instantaneous water heaters and as a common denominator to

compare the performance of storage type water heaters.

6. CONCLUSIONS

Based on an analysis of the data for the tests conducted on four

instantaneous water heaters, the following general conclusions are

submitted

:

1. The actual flow rate characteristics at a temperature rise of 77 °F

for the instantaneous water heaters should be determined by a

series of tests.

2. The use of Er as a performance index to compare different

instantaneous water heaters seems appropriate.

3. The EF determination for instantaneous water heaters is sensitive

to the given total number of gallons drawn, the flow rate, and the

pilot light energy consumption rate.

21
7. REFERENCES

[1] American National Standard for Gas Water Heaters, Volume 1

Automatic Storage Water Heaters with Inputs of 75,000 BTU Per Hour

or less - ANSI-Z21 „ 10 » 1 -1 984

.

[2] American National Standard for Gas Water Heaters, Volume IllCirculating Tank, Instantaneous, and Large Automatic Storage Water

Heaters - ANSI-Z21 . 10 .3-1 984.

[3] Federal Register . Vol. 42, No. 192, October 1977, pages 54200-

54119, as amended by Federal Register . Vol. 43, No. 203 ,

October 19, 1978, pages 48986-48987 and Federal Register . Vol. 44,

No. 175, September 7, 1979, pages 52632-52640.

[4] Federal Register . Part II, Department of Energy, Office of

Conservation and Renewable Energy, 10 CFR part 430, Energy

Conservation Program for Water Heaters; Public Hearing; Proposed

Rule, pages 4870 - 4889, dated February 8, 1984.

[5] NBSIR 86-3412; DOE/NBS Forum on Testing and Ratine Procedures for

Consumer Products: October 2-3. 1985 : R. D. Dikkers; July 1986.

22
INSTANTANEOUS GAS-FIRED WATER HEATER TEST SET-UP

Instantaneous water heaters

Insulated

Supply

Water

Tank

Controlled

temperature

Thermocouple

wires

Ambient

temp

Water

meter

Control

valve ^l,

• Thermocouple locations

Electric —

Timer Natural

1 solenoid

valve

gas Relay

power source

Scale

Contact

switch

connected

to scale

balance

beam

NOTES:

- Valves on hot water outlets are gate valves -

adjustable to regulate flow rate through heater - Valves on cold water inlet lines are ball valves - Valve on hot water line after water meter was used to regulate flow rate - Network of lines and valves allowed quick isolation and start-up of each unit when

switching between units (only one heater was tested at a time) - When balance beam on scale tipped, relay shut solenoid valve to cut off water flow - Each heater had a pressure-relief valve - Thermocouple connections on hot water outlets were insulated (immersion-type connections)

- Analyzer was used only on some of the tests - combustion efficiency was calculated by

apalyzer based on percentage excess air from measured oxygen and stack temperature.

Figure 1. Instantaneous Gas-Fired Water Heater Test Set-Up.

23
Table la„ Test Data - Unit F

TEST DATA - UNIT F

t t * i i 1 % FLOW ANT TIME T (C) T(C) T (F) T(F) T (F) CF GAS H Q PILOT

UNIT TEST (Delta (BTU/ (BTU/

(6pt) (Gal) (Min) (Out) (In) (Out) (In) T) (CuFt) CuFt) (BTU) Hr)

F 2 2.15 15.0 6.98 52.67 22.40 126.81 72.32 54.486 0.981 8.930 1032 9040.66 340

F 3 2.25 15.0 6.67 51.05 22.33 123.89 72.19 51.696 0.901 8.002 1032 8101.16 340

F 4 2.31 15.0 6.49 50.78 21.95 123.40 71.51 51.894 0.981 7. 939 1032 8036.37 340

F 5 1.07 15.0 14.02 57.72 21.11 135.90 70.00 65.898 0.981 10.545 1032 10675.67 340

F 7 1.07 15.0 14.02 58.41 20.67 137.14 69.21 67.932 0.978 10.915 1032 11016.47 340

F 8 3.19 15.0 4.70 45.67 22.15 114.21 71,87 42.336 0.976 6.350 1032 6395.92 340

F 9 3.24 15.0 4.63 46.63 21.74 115.93 71.13 44.802 0.976 6.715 1032 6763.56 340

F 10 1.00 5.0 5.00 44.95 21.38 112.91 70.48 42.426 0.973 2.000 1032 2008.27 340

F 11 3.62 5.0 1.38 45.29 21.17 113.52 70.11 43.416 0.973 2.083 1032 2091.62 340

F 12 3.49 10.0 2.87 45.82 20.91 114.48 69.64 44.838 0.972 4.335 1032 4348.46 340

F 13 3.33 10.0 3.00 46.98 22.26 116.56 72.07 44.496 0.970 4.445 1032 4449.62 340

F 51 0.93 5.0 5.37 63.47 14.41 146.25 57.94 88.308 0,972 4.580 1036 4612.02 340

F 52 0.78 10.0 12.78 62.88 15.01 145.16 59.02 86.166 0.972 9.180 1036 9244.19 340

F 53 0.95 21.4 22.62 57.98 23.37 136.36 74.07 62.298 0.974 14.355 1036 14485.11 340

F 54 1.53 21.4 13.95 54.01 23.23 129.22 73.81 55.404 0.973 12.235 1036 12333.22 340

F 55 1.95 21.4 10.97 52.18 22.50 125.92 72.50 53,424 0.973 11.550 1036 11642.72 340

F 56 2.62 21.4 8.18 48.09 22.05 118.56 71.69 46.872 0.973 9.917 1036 9996.61 340

F 57 3.11 21.4 6.88 45.66 21.78 114.19 71.20 42.984 0.972 9.068 1036 9131.40 340

F 87 0.98 21.4 21.75 59.05 21.44 138.29 70.59 67,698 0.974 16.242 1038 16420.86 340

F 88 1.55 21.4 13.81 55.18 21.08 131.32 69.94 61,380 0.984 14.140 1038 14442.48 340

F 89 2.10 21.4 10.21 51.32 21.45 124.38 70.61 53.766 0.983 12.185 1038 12433.01 340

F 90 2.53 21.4 8.46 48.63 21.18 119.53 70.12 49.410 0.983 10.930 1030 11152.47 340

F 91 3.08 21.4 6.95 46.71 20.29 116.08 68.52 47.556 0.983 10.490 1038 10703.51 340

F 101 1.08 21.4 19.81 57.93 20.93 136.27 69.67 66.600 0.982 15.990 1036 16267.46 340

F 102 1.65 21.4 12.97 54.55 21.15 130.19 70.07 60.120 0.982 13.930 1036 14171.71 340

F 103 2.12 21.4 10.09 52.12 21.32 125.82 70.38 55.440 0.981 12.650 1036 12856.40 340

F 104 2.63 21.4 8.14 48.32 21.46 118.98 70.63 48.348 0.982 10.840 1036 11028.10 340

F 105 2.99 21.4 7.15 46.54 21.66 115.77 70.99 44.784 0.982 10.005 1036 10178.61 340

I - Measured Data

24
Table lb . Test Data - Unit G

TEST DATA - UNIT 6

* t t 1 * 1 * t FLOW AMT TIME TIC) TIC) T (F) T IF) T(F) CF GAS H 6 PILOT

UNIT TEST (Delta (BTU/ (BTU/

(6pa) (Ball (Min) (Out) (In) (Out) (In) T) (CuFt) CuFt) (BTU) Hr)

G 29 2.22 5.0 2.25 56.96 20.80 134.53 69.44 65.088 0.965 3.432 1035 3427.80 357

8 30 2.11 5.0 2.37 59.92 21.00 139.86 69.80 70.056 0.965 3.617 1035 3612.57 357

6 31 2.07 5.0 2.42 60.24 21.10 140.43 69.98 70.452 0.965 3.670 1035 3665.50 357

6 32 1.63 5.0 3.07 67.48 21.20 153.46 70.16 83.304 0.966 4.383 1035 4382.17 357

6 58 1.01 21.4 21.10 61.49 21.66 142.68 70.99 71.694 0.975 16.060 1036 16222.21 357

6 59 1.65 21.4 12.97 69.00 21.58 156.20 70.84 85.356 0.971 18.180 1036 18288.28 357

e 60 2.10 21.4 10.19 60.44 21.55 140.79 70.79 70.002 0.970 14.850 1036 14923.06 357

6 61 2.53 21.4 8.45 54.11 21.56 129.40 70.81 58.590 0.970 12.355 1036 12415.79 357

6 62 3.16 21.4 6.78 47.36 21.50 117.25 70.70 46.548 0.970 9.815 1036 9863.29 357

6 79 1.06 21.4 20.19 62.87 21.43 145.17 70.57 74.592 0.969 17.270 1033 17286.87 357

8 80 1.65 21.4 12.97 66.91 20.91 152.44 69.64 82.800 0.976 18.442 1033 18593.37 357

6 81 2.10 21.4 10.19 59.79 21.20 139.62 70.16 69.462 0.976 15.315 1033 15440.71 357

6 82 2.68 21.4 7.98 51.56 21.06 124.81 69.91 54.900 0.976 12.425 1033 12526.98 357

6 83 2.68 21.4 7.98 51.18 20.76 124.12 69.37 54.756 0.976 12.375 1033 12476.57 357

6 84 2.66 50.0 18.77 50.88 20.17 123.58 68.31 55.278 0.977 28.990 1033 29257.90 357

6 85 2.63 50.0 18.98 50.64 19.64 123.15 67.35 55.800 0.977 29.205 1033 29474.88 357

6 86 3.02 21.4 7.08 48.87 21.56 119.97 70.81 49.158 0.972 10.970 1038 11068.03 357

6 106 1.06 21.4 20.19 62.56 21.90 144.61 71.42 73.188 0.983 17.205 1036 17521.37 357

6 107 1.35 21.4 15.85 62.05 22.19 143.69 71.94 71.748 0.983 16.590 1036 16895.06 357

6 108 1.63 21.4 13.13 66.94 22.31 152.49 72.16 80.334 0.974 18.255 1036 18420.46 357

6 109 1.87 21.4 11.44 65.97 22.43 150.75 72.37 78.372 0.981 17.330 1036 17612.76 357

6 110 2.08 21.4 10.29 61.57 22.55 142.83 72.59 70.236 0.981 15.620 1036 15874.86 357

8 111 2.64 21.4 8.11 53.33 22.60 127.99 72.68 55.314 0.981 12.290 1036 12490.52 357

6 112 3.16 21.4 6.77 48.63 22.60 119.53 72.68 46.854 0.982 10.795 1036 10473.64 357

t = Measured Data

25
Table lc. Test Data - Unit H

TEST DATA - UNIT H

$ I I 1

II II 91 II II II II — 1II II II 10

+*

II II II

1

II II H

00 II II II II II

1 FLOW AMT TIME T (C) T(C) T (F) T(F> T(F) CF GAS H 6 PILOT

UNIT TEST (Delta (BTU/ (BTU/

(Spe) (Gal) (Min! (Out) (In) (Out) (In) T) (CuFt) CuFt) (BTU) Hr)

H 14 1.28 5.0 3.92 67.94 21.50 154.29 70.70 83.592 0.973 4.555 1035 4587.14 643

H 15 1.36 5.0 3.67 67.98 21.50 154.36 70.70 83.664 0.969 4.570 1035 4583.32 643

H 16 3.86 14.2 3.67 47.48 21.50 117.46 70.70 46.764 0.967 6.850 1035 6855.79 643

H 17 3.84 14.1 3.67 47.00 21.40 116.60 70.52 46.080 0.965 6.845 1035 6B36.61 643

H 18 1.83 5.0 2.73 64.55 21.38 148.19 70.48 77.706 0.969 4.150 1035 4162.10 643

H 19 1.78 5.0 2.82 64.52 21.40 148.14 70.52 77.616 0.968 4.095 1035 4102.70 643

H 20 4.07 11.3 2.78 45.84 21.42 114.51 70.56 43.956 0.966 5.110 1035 5109.03 643

H 21 3.99 11.1 2.78 46.70 21.40 116.06 70.52 45.540 0.967 5.165 1035 5169.36 643

H 22 2.34 5.0 2.13 60.58 21.78 141.04 71.20 69.840 0.963 3.690 1035 3677.84 643

H 23 2.38 5.0 2.10 60.65 21.73 141.17 71.11 70.065 0.962 3.640 1035 3624.24 643

H 24 1.37 5.0 3.66 67.34 21.69 153.22 71.03 82.181 0.965 4.590 1035 4584.38 643

H 25 1.59 5.0 3.15 65.87 21.57 150.57 70.83 79.740 0.965 4.300 1035 4294.73 643

H 26 3.00 5.0 1.67 52.63 21.38 126.73 70.48 56.250 0.962 2.920 1035 2907.36 643

H 27 2.08 5.0 2,40 62.24 21.24 144.03 70.23 73.800 0.963 3.885 1035 3872.20 643

H 28 3.49 5.0 1.43 48.58 21,08 119.44 69.94 49.500 0.962 2.560 1035 2548.92 643

H 40 2.21 7.5 3.39 58.30 14.49 136.94 58.08 78.858 0.973 6.040 1036 6088.49 643

H 41 2.21 7.5 3.39 57.54 14.59 135.57 58.26 77.310 0.973 5.920 1036 5967.53 643

H 42 1.10 7.5 6.80 57.27 15.21 135.09 59.39 75.701 0.978 6.100 1036 6180.57 643

H 43 1.04 7.5 7.23 60.33 15.88 140.59 60.58 80.010 0.977 6.570 1036 6649.97 643

H 44 1.01 7.5 7.43 61.41 13.36 142.54 56.05 86.490 0.973 7.020 1036 7076.36 643

H 45 1.61 7.5 4.65 61.17 13.78 142.11 56.80 85.302 0.971 6.535 1036 6573.92 643

H 46 2.30 7.5 3.27 60.73 13.11 141.31 55.60 85.716 0.970 6.355 1036 6386.27 643

H 63 1.05 21.4 20.48 68.98 22.26 156.16 72.07 84.096 0.972 19.495 1036 19631.31 643

H 64 1.65 21.4 12.97 62.30 22.14 144.14 71.86 72.283 0.970 16.550 1036 16631.43 643

H 65 2.05 21.4 10.44 61.59 21.64 142.86 70.95 71.910 0.970 15.755 1036 15832.51 643

H 66 2.53 21.4 8.46 57.88 21.60 136.18 70.88 65.304 0.969 14.025 1036 14079.47 643

H 67 3.13 21.4 6.83 52.86 21.46 127.15 70.63 56.520 0.969 11.870 1036 11916.10 643

H 92 1.04 21.4 20.58 71.77 21.25 161,19 70.25 90.936 0.974 21.970 1038 22211.93 643

H 93 1.64 21.4 13.05 66.44 21.34 151.59 70.41 81.180 0,976 18.710 1038 18954.88 643

H 94 2.13 21.4 10.05 62.38 20.80 144.28 69.44 74.844 0.977 16.880 1038 17118.45 643

H 95 2.55 21.4 8.39 58.78 21.09 137.80 69.96 67.842 0.975 15.075 1038 15256.65 643

H 96 3.17 21.4 6.75 52.01 21.28 125.62 70.30 55.314 0.974 12.208 1038 12342.43 643

H 113 1.05 21.4 20.38 71.15 22.61 160.07 72.70 87.372 0.984 20.990 1036 21397.71 643

H 114 1.68 21.4 12.74 65.27 22.60 149.49 72.68 76.806 0.982 17.760 1036 18068.17 643

H 115 1.33 21.4 16.09 68.06 22.59 154.51 72,66 81.846 0.982 19.390 1036 19726.46 643

H 116 2.09 21.0 10.07 63.08 22.10 145.54 71.78 73.764 0.969 17.040 1036 17106.18 643

H 117 2,64 21.4 8.11 57.44 22.31 135.39 72.16 63.234 0.969 14.655 1036 14711.92 643

H 118 3.06 21.4 6.99 53.39 22.50 128.10 72.50 55.602 0.969 12.790 1036 12839.68 643

I = Measured Data

26
Table Id. Test Data - Unit I

TEST DATA - UNIT I 11 1 11 1 1 0 11 i 1 8 i11I11

«»1 181 1 111 1 18 1 tv II II II II II II II II II II II II II II 11 0I 1 1 t

*

11 1 1 B

t FLOW AHT TINE T (C) TIC) T (F) T (F) T (F) CF GAS H 5 PILOT

UNIT TEST (Delta (BTU/ (BTU/

(6pt) (Gal) (Min) (Out) (In) (Out) (In) T) (CuFt) CuFt) (BTU) Hr)

I 33 2.37 10.0 4.22 67.64 21.60 153.75 70.88 82.872 0.974 7.745 1036 7815.20 896

I 34 2.50 10.0 4.00 64.99 21.59 148.98 70.86 78.120 0.974 7.520 1036 7588.16 896

I 35 J 2.15 10.0 4.65 70.03 21.47 158.05 70.65 87.408 0.974 8.355 1036 8430.73 896

I 36 2.25 10.0 4.44 68.21 21.29 154.78 70.32 84.456 0.974 7.970 1036 8042.24 896

I 37 2.66 10.0 3.77 54.95 12.74 130.91 54.93 75.978 0.974 7.165 1036 7229.94 896

I 38 2.66 10.0 3.76 54.84 13.04 130.71 55.47 75.240 0.974 7.110 1036 7174.45 896

I 39 2.21 10.0 4.52 62.82 13.77 145.08 56.79 88.290 0.971 8.300 1036 8349.43 896

I 47 2.48 5.0 2.02 59.90 13.80 139.82 56.84 82.980 0.966 3.780 1036 3782.93 896

I 48 2.56 5.0 1.95 59.16 14.32 138.49 57.78 80.712 0.966 3.635 1036 3637.82 896

5 49 2.34 10.0 4.28 61.08 13.50 141.94 56.30 85.644 0.967 7.980 1036 7994.46 896

I 50 2.38 5.0 2.10 61.15 13.45 142.07 56.21 85.860 0.967 3.940 1036 3947.14 896

I 68 1.59 21.4 13.45 49.82 21.29 121.68 70.32 51.354 0.972 11.035 1036 11112.16 896

I 69 2.17 21.4 9.85 70.45 21.20 158.81 70.16 88.650 0.969 18.630 1036 18702.36 896

I 70 2.57 21.4 8.32 64.24 21.18 147.63 70.12 77.517 0.969 16.380 1036 16443.62 896

I 71 2.97 21.4 7.20 58.68 21.16 137.62 70.09 67.536 0.968 14.165 1036 14205.34 896

I 72 2.99 21.4 7.17 58.26 21.04 136.87 69.87 66.996 0.967 14.145 1033 14129.60 896

I 73 2.99 21.4 7.17 59.14 21.43 138,45 70.57 67.878 0.968 14.240 1033 14239.20 896

I 74 2.96 21.4 7.23 59.44 21.61 138.99 70.90 68.094 0.965 14.290 1033 14244.92 896

I 75 2.06 21.4 10.38 70.49 21.51 158.88 70.72 88.164 0.966 18.750 1033 18710.21 896

I 76 1.50 21.4 14.27 49.38 21.18 120.88 70.12 50.760 0.969 10.860 1033 10870.61 896

I 77 3.01 21.4 7.10 57.36 20.75 135.25 69.35 65.898 0.966 13.820 1033 13790.67 896

I 78 2.99 21.4 7.17 65.40 20.44 149.72 68.79 80.928 0.963 17.020 1033 16931.14 896

I 97 1.62 21.4 13.22 50.98 20.99 123.76 69.78 53.982 0.980 11.305 1038 11499.90 896

I 98 2.09 21.4 10.23 65.82 20.55 150.48 68.99 81.486 0.980 16.275 1038 16555.58 896

I 99 2.52 21.4 8.50 64.90 21.10 148.82 69.98 78.840 0.975 16.290 1038 16486.29 896

I 100 2.97 21.4 7.20 59.24 21.11 138.63 70.00 68.634 0.973 14.015 1038 14154.79 896

I 119 1.63 21.4 13.13 51.47 22.14 124.65 71.85 52.794 0.974 11.480 1036 11584.05 896

I 120 2.19 21.4 9.77 70.52 21.91 158.94 71.44 87.498 0.970 18.642 1036 18733.72 896

I 121 2.66 21.4 8.05 63.53 21.81 146.35 71.26 75.096 0.970 15.930 1036 16008.38 896

I 122 2.81 21.4 7.62 61.14 21.83 142.05 71.29 70.758 0.970 14.860 1036 14933.11 896

* = Heasured Data

27
Table 2a. Summary Data, Er, and EF - Unit F

SUMMARY - UNIT F

FLOW ANT T(F) T (F) T (F) :

1 1 1m

i

i

ii i i

2 EF EF EF EF PILOT

UNIT TEST (Delta : s (20 (40 (64.3 (80 (BTU/

(Bps) (Sal

)

(Out) (In) T) s : Spd

)

Gpd) Gpd) gpd) Hr)

F 2 2.15 15.0 126.8 72.3 54.5 : : 0.746 ; : 0.446 0.559 0,618 0.640 340

F 3 2,25 15.0 123.9 72.2 51.7 : : 0.790 : : 0.451 0.575 0.642 0.667 340

F 4 2.31 15.0 123.4 71.5 51.9 : 2 0.799 : 2 0.455 0.581 0.648 0.674 340

F 5 1,07 15.0 135.9 70.0 65.9 ; : 0.764 : ; 0.488 0.597 0.652 0.672 340

F 7 1.07 15.0 137.1 69.2 67.9 s : 0.763 ; : 0.493 0.601 0.655 0.674 340

F 8 3.19 15.0 114.2 71.9 42.3 ; ; 0.819 : 2 0.419 0.556 0.633 0.663 340

F 9 3.24 15.0 115.9 71.1 44.8 2 : 0.820 2 2 0.431 0.566 0.642 0.671 340

F 10 LOO 5.0 112.9 70.5 42.4 : 2 0.871 2 2 0.435 0.583 0.669 2 0.703 340

F li 3.62 5,0 113.5 70.1 43.4 ; 2 0.856 : ; 0.434 0.577 0.659 0,690 340

F 12 3.49 10.0 114.5 69.6 44.8 ; : 0.851 : 2 0.440 0.581 0.660 0.691 340

F 13 3.33 10.0 116.6 72.1 44.5 2 : 0.825 : 2 0.431 0.567 0.644 0.673 340

F 51 0.93 5.0 146.2 57.9 88.3 s : 0.790 s : 0.550 0.650 0.698 0.715 340

F 52 0.78 10.0 145.2 59.0 86.2 ; : 0.769 ; : 0.536 0.634 0.681 0.697 340

F 53 0.95 21.4 136.4 74.1 62.3 ; : 0.759 : : 0.476 0.587 0,644 0.665 340

F 54 1.53 21.4 129.2 73.8 55.4 2 s 0.793 2 s 0.466 0.589 0.653 0.678 340

F 55 1.95 21.4 125.9 72.5 53.4 s s 0.810 : : 0.464 0.591 0.660 0,685 340

F 56 2.62 21.4 118.6 71.7 46.9 2 : 0.828 2 2 0.443 0.578 0.653 0.682 340

F 57 3.11 21.4 114.2 71.2 43.0 s 2 0.831 s 2 0.426 0.564 0.643 0.673 340

F 87 0.98 21.4 138.3 70.6 67.7 2 s 0.728 2 ; 0.478 0.578 0.629 0.647 340

F 88 1.55 21.4 131.3 69.9 61.4 : 2 0.750 : : 0.469 0.579 0.634 0.655 340

F 89 2.10 21.4 124.4 70.6 53.8 : 2 0.763 2 : 0.450 0.567 0.629 0.652 340

F 90 2.53 21.4 119.5 70.1 49.4 2 : 0.782 : 2 0.440 0.564 0.631 0.657 340

F 91 3.08 21.4 116.1 68.5 47.6 2 : 0.784 : : 0.433 0.559 0.628 0.654 340

F 101 1.08 21.4 136.3 69.7 66.6 2 ; 0.723 • ; 0.472 0.573 0.623 0.641 340

F 102 1.65 21.4 130.2 70.1 60,1 : 2 0.749 2 : 0.465 0.575 0.631 0.652 340

F 103 2.12 21.4 125.8 70.4 55.4 : 2 0.761 : : 0.455 0.570 0.631 0.653 340

F 104 2.63 21.4 119.0 70.6 48.3 : : 0.774 2 2 0.433 0.556 0.623 0.648 340

F 105 2.99 21.4 115.8 71.0 44.8 : 2 0.777 : 2 0.419 0.545 0.615 0.642 340

28
Table 2b. Summary Data, Er, and EF - Unit G

SUMMARY - UNIT G

i 1 11 11 FLOW AMT T (F) T (F) T (F) : : Er : : EF EF

II II II II II

UII

LxJ

II II II EF PILOT

UNIT TEST (Delta : 2 (20 (40 (64.3 (80 (BTU / (Spa

)

(Gal) (Oat) (In) T) : : Gpd) Gpd) Gpd) Gpd) Hr)

6 29 2.22 5.0 134.5 69.4 65.1 : : 0.783 : : 0.483 0.599 0.658 0.680 357

G 30 2.11 5.0 139.9 69.8 70.1 : : 0.800 : : 0.503 0.619 0.678 0.699 357

6 31 2.07 5.0 140.4 70.0 70.5 : : 0.793 : : 0.502 0.615 0.673 0.694 357

6 32 1.63 5.0 153.5 70.2 83.3 : : 0.784 : : 0.528 0.632 0.683 0.701 357

G 58 1.01 21.4 142.7 71.0 71.7 : : 0.780 : : 0.501 0.612 0.668 0.688 357

6 59 1.65 21.4 156.2 70.8 85.4 : : 0.824 ; 2 0.550 0.661 0.715 0.735 357

G 60 2.10 21.4 140.8 70.8 70.0 : : 0.828 : : 0.514 0.636 0.698 0.720 357

G 61 2.53 21.4 129.4 70.8 58.6 : : 0.833 : : 0.480 0.610 0.680 0.706 357

G 62 3.16 21.4 117.2 70.7 46.5 : : 0.833 : 2 0.433 0.570 0.648 0.678 357

G 79 1.06 21.4 145.2 70.6 74.6 ; 0.762 : : 0.500 0.605 0.658 0.677 357

G 80 1.65 21.4 152.4 69.6 82.8 : : 0.786 s : 0.528 0.633 0.684 0.703 357

G 81 2.10 21.4 139.6 70.2 69.5 : : 0.794 : : 0.500 0.614 0.673 0.694 357

G 82 2.68 21.4 124.8 69.9 54.9 : : 0.774 : : 0.448 0.568 0.632 0.656 357

G 83 2.68 21.4 124.1 69.4 54.8 : : 0.775 : : 0.448 0.568 0.633 0.657 357

G 84 2.66 50.0 123.6 68.3 55.3 : : 0.779 s 2 0.451 0.572 0.637 0.661 357

G 85 2.63 50.0 123.2 67.4 55.8 : : 0.781 s 2 0.453 0.574 0.639 0.663 357

G 86 3.02 21.4 120.0 70.8 49.2 : : 0.784 s : 0.430 0.556 0.625 0.652 357

6 106 1.06 21.4 144.6 71.4 73.2 : : 0.737 I : 0.486 0.588 0.638 0.656 357

G 107 1.35 21.4 143.7 71.9 71.7 : : 0.750 : 2 0. 488 0.592 0.645 0.663 357

6 108 1.63 21.4 152.5 72.2 80.3 : : 0.770 : : 0.516 0.619 0.669 0.687 357

6 109 1.87 21.4 150.7 72.4 78.4 : : 0.786 : : 0.518 0.625 0.678 0.698 357

6 110 2.08 21.4 142.8 72.6 70.2 : : 0.781 : : 0.496 0.608 0.664 0.685 357

G 111 2.64 21.4 128.0 72.7 55.3 : : 0.782 : : 0.452 0.574 0.639 0.663 357

6

II

CM

II II II 3.16 21.4 119.5 72.7 46.9 : : 0.790 : : 0.422 0.551 0.623 0.650 357

29
Table 2c. Summary Data, Er, and EF - Unit H

SUMMARY - UNIT H

FLOW ANT T (F) T(F) T(F) : i Er i : EF EF

II II II II II

Ll_

II

Ui

II II II EF PILOT

UNIT TEST (Delta s : (20 (40 (64.3 (80 (BTU/

(Bps) (Gal

)

(Out) (In) T) : : 6pdl gpd) Gpd) Gpd) Hr)

H 14 1.28 5.0 154.3 70.7 83.6 •

: 0.752 s ; 0.410 0.533 0.600 0.626 643

H 15 1.36 5.0 154.4 70.7 83.7 : • 0.753 : : 0.411 0.533 0.601 0.627 643

H 16 3.86 14.2 117.5 70.7 46.8 : : 0.796 : : 0.308 0.445 0.535 0.572 643

H 17 3.84 14.1 116.6 70.5 46.1 : : 0.782 : ! 0.303 0.437 0.525 0.562 643

H 18 1.83 5.0 148.2 70.5 77.7 : : 0.770 : : 0.401 0.529 0.601 0.629 643

H 19 1.78 5.0 148.1 70.5 77.6 : : 0.780 : : 0.404 0.533 0.607 0.636 643

H 20 4.07 11.3 114.5 70.6 44.0 : : 0.803 : : 0.297 0.435 0.527 0.565 643

H 21 3.99 11.1 116.1 70.5 45.5 : : 0.807 : : 0.304 0.443 0.534 0.573 643

H 22 2.34 5.0 141.0 71.2 69.8 : • 0.783 : : 0.383 0.516 0.593 0.624 643

H 23 2.38 5.0 141.2 71.1 70.1 : : 0.797 : : 0.387 0.523 0.602 0.633 643

H 24 1.37 5.0 153.2 71.0 82.2 : : 0.739 : : 0.403 0.524 0.590 0.615 643

H 25 1.59 5.0 150.6 70.8 79.7 s : 0.766 : : 0.405 0.531 0.602 0.629 643

H 26 3.00 5.0 126.7 70.5 56.3 : : 0.798 : : 0.344 0.482 0.567 0.602 643

H 27 2.08 5.0 144.0 70.2 73.8 : : 0.786 : : 0.395 0.527 0.603 0.633 643

H 28 3.49 5.0 119.4 69.9 49.5 : : 0.801 : : 0.319 0.458 0.547 0.584 643

H 40 2.21 7.5 136.9 58.1 78.9 i s 0.801 : ; 0.412 0.545 0.621 0.651 643

H 41 2.21 7.5 135.6 58.3 77.3 s : 0.802 : s 0.408 0.542 0.619 0.648 643

H 42 1.10 7.5 135.1 59.4 75.7 : : 0.758 : 2 0.394 0.520 0.592 0.620 643

H 43 1.04 7.5 140.6 60.6 80.0 s : 0.744 : : 0.401 0.523 0.591 0.617 643

H 44 1.01 7.5 142.5 56.0 86.5 : : 0.756 : : 0.419 0.541 0.608 0.634 643

H 45 1.61 7.5 142.1 56.8 85.3 : : 0.803 : : 0.429 0.560 0.634 0.662 643

H 46 2.30 7.5 141.3 55.6 85.7 = : 0.830 : : 0.437 0.574 0.651 0.680 643

H 63 1.05 21.4 156.2 72.1 84.1 • : 0.756 : : 0.413 0.537 0.605 0.631 643

H 64 1.65 21.4 144.1 71.9 72.3 : : 0.767 : : 0.387 0.516 0.590 0.619 643

H 65 2.05 21.4 142.9 71.0 71.9 : : 0.802 : : 0.394 0.530 0.609 0.640 643

H 66 2.53 21.4 136.2 70.9 65.3 : : 0.819 : : 0.37B 0.518 0.603 0.636 643

H 67 3.13 21.4 127.1 70.6 56.5 s : 0.837 : : 0.352 0.496 0.588 0.625 643

H 92 1.04 21.4 161.2 70.3 90.9 ! : 0.723 : : 0.417 0.531 0.592 0.615 643

H 93 1.64 21.4 151.6 70.4 81.2 : : 0.756 : : 0.406 0.529 0.598 0.625 643

H 94 2.13 21.4 144.3 69.4 74.8 : : 0.772 : : 0.394 0.523 0.597 0.625 643

H 95 2.55 21.4 137.8 70.0 67.8 : : 0.785 : : 0.378 0.511 0.590 0.621 643

H 96 3.17 21.4 125.6 70.3 55.3 : : 0.791 : : 0.339 0.476 0.561 0.596 643

H 113 1.05 21.4 160.1 72.7 87.4 : : 0.721 : : 0.409 0.524 0.586 0.610 643

H 114 1.68 21.4 149.5 72.7 76.8 : : 0.750 : : 0.394 0.518 0,580 0.615 643

H 115 1.33 21.4 154.5 72.7 81.8 : : 0.733 : : 0.401 0.520 0.585 0.610 643

H 116 2.09 21.0 145.5 71.8 73.8 : : 0.748 : : 0.385 0.510 0.581 0.608 643

H 117 2.64 21.4 135.4 72.2 63.2 : : 0.759 : : 0.359 0.488 0.565 0.595 643

19 99 99 19 118 3.06 21.4 128.1 72.5 55.6 : : 0.765 : : 0.335 0.467 0.548 0.581 643

30
Table 2d. Summary Data, Er, and EF - Unit I

SUMHARY - UNIT I I 11 1 1 FLOW

1 1 11

—

1

XZ

1

<E

1 T(F) T (F) T(F) :

II II II

m

n

i

nii ii ii

: EF EF EF EF PILOT

UNIT TEST (Delta : : (20 (40 (64.3 (80 (BTU/

(Gps) (Gal) (Out) (In) T) : : Gpd) Gpd) 6pd) Gpd) Hr)

I 33 2.37 10.0 153.8 70.9 82.9 ; s 0.875 : : 0.369 0.521 0.616 0.655 896

1 34 2.50 10.0 149.0 70.9 78.1 : : 0.849 : i 0.353 0.499 0.593 0.631 896

I 35 2.15 10.0 158.1 70.6 87.4 : : 0.855 : : 0.377 0.525 0.616 0.653 896

I 36 2.25 10.0 154.8 70.3 84.5 ; : 0.866 : ; 0.372 0.522 0.615 0.653 896

I 37 2.66 10.0 130.9 54.9 76.0 : : 0.867 : : 0.350 0.499 0.596 0.636 896

I 38 2.66 10.0 130.7 55.5 75.2 : : 0.865 ; : 0.347 0.497 0.593 0.633 896

I 39 2.21 10.0 145.1 56.8 88.3 : : 0.872 : : 0.383 0.533 0.627 0.664 896

I 47 2.48 5.0 139.8 56.8 83.0 : s 0.905 : : 0.375 0.531 0.631 0.672 896

I 40 2.56 5.0 138.5 57.8 80.7 ; : 0.915 : i 0.371 0.529 0.630 0.672 896

I 49 2.34 10.0 141.9 56.3 85.6 : : 0.884 : : 0.378 0.531 0.627 0.665 896

1 50 2.38 5.0 142.1 56.2 85.9 : : 0.897 : : 0.381 0.536 0.634 0.673 896

I 68 1.59 21.4 121.7 70.3 51.4 : : 0.816 : : 0.267 0.404 0.502 0.544 896

I 69 2.17 21.4 158.8 70.2 88.7 : : 0.837 : : 0.377 0.521 0.609 0.644 896

I 70 2.57 21.4 147.6 70.1 77.5 : : 0.832 : : 0.348 0.492 0.583 0.620 896

I 71 2.97 21.4 137.6 70.1 67.5 : : 0.839 : : 0.321 0.466 0.561 0.601 896

I 72 2.99 21.4 136.9 69.9 67.0 ; : 0.837 : : 0.319 0.463 0.558 0.598 896

I 73 2.99 21.4 138.5 70.6 67.9 ; : 0.842 : : 0.323 0.467 0.563 0.603 896

I 74 2.96 21.4 139.0 70.9 68.1 : s 0.844 : : 0.324 0,469 0.565 0.604 896

I 75 2.06 21.4 158.9 70.7 88.2 : : 0.832 : : 0.374 0.518 0.605 0.640 896

I 76 1.50 21.4 120.9 70.1 50.8 : : 0.824 : : 0.266 0.404 0.503 0.546 896

I 77 3.01 21.4 135.2 69.4 65.9 : : 0.844 : : 0.317 0.462 0.558 0.599 896

I 78 2.99 21.4 149.7 68.8 80.9 s : 0.844 : : 0.359 0.504 0.596 0.633 896

I 97 1.62 21.4 123.8 69.8 54.0 : s 0.829 : : 0.278 0.418 0.516 0.559 896

I 98 2.09 21.4 150.5 69.0 81.5 ; : 0.869 : : 0.365 0.516 0.611 0.649 896

I 99 2.52 21.4 148.8 70.0 78.8 : : 0.844 : : 0.354 0.500 0.592 0.629 896

I 100 2.97 21.4 138.6 70.0 68.6 : : 0.856 : : 0.327 0.474 0.571 0.612 896

I 119 1.63 21.4 124.6 71.9 52.8 : : 0.805 : : 0.271 0.407 0.503 0.544 896

I 120 2.19 21.4 158.9 71.4 87.5 : ; 0.825 : : 0.371 0.513 0.600 0.635 896

I 121 2.66 21.4 146.4 71.3 75.1 : : 0.828 : : 0.341 0.484 0.575 0.613 896

I 122 2.81 21.4 142.1 71.3 70.8 ; : 0.837 : : 0.330 0.475 0.568 0.607 896

31
TEMPERATURE RISE vs FLOW RATE

FLOW RATE - GPM

Figure 2. Temperature Rise vs. Flow Rate - Unit F.

32
TEMPERATURE RISE vs. FLOW RATE

Figure 3. Temperature Rise vs. Flow Rate - Unit G.

33
TEMPERATURE RISE vs. FLOW RATE

Figure 4. Temperature Rise vs. Flow Rate - Unit H.

34
TEMPERATURE RISE vs. FLOW RATE

Figure 5. Temperature Rise vs. Flow Rate - Unit I.

35
RECOVERY EFFICIENCY (E r ) AND ENERGY FACTOR (EF)

vs. FLOW RATE

FLOW RATE - GPM

Figure 6. Recovery Efficiency (Er) and Energy Factor (EF) vs. Flow Rate

- Unit F.

36
RECOVERY EFFICIENCY (E r ) AND ENERGY FACTOR (EF)

vs. FLOW RATE

Figure 7. Recovery Efficiency (Er) and Energy Factor (EF) vs. Flow Rate

- Unit G.

37
RECOVERY EFFICIENCY (E r

) AND ENERGY FACTOR (EF)

vs. FLOW RATE

Figure 8. Recovery Efficiency (Er) and Energy Factor (EF) vs. Flow Rate

- Unit H.

38
RECOVERY EFFICIENCY (E r ) AND ENERGY FACTOR (EF)

vs. FLOW RATE

Figure 9. Recovery Efficiency (Er) and Energy Factor (EF) vs. Flow Rate

- Unit I.

39

Appendix A

COMPUTATIONS AND FORMULAS USED

In order to compute an energy factor to determine the annual cost of

operation of an instantaneous gas-fired water heater, the following

formulas are used in the order presented.

1.0 Gas Correction Factor

The correction factor, Cf, to determine the "standard" gas volume used

was determined using equation (1) where "standard" conditions are at

60 °F and 30.00 inches Hg (1016 millibars) atmospheric pressure. The

partial pressure of the water vapor was determined from tables of vapor

pressure of water at various temperatures, by entering the appropriate

gas temperature. The other pressures were taken from appropriate

instrument readings.

The correction factor, Cf, (dimensionless) to determine standard gas

volume used during a gas water heater test and is defined as:

Cf = ( 17 .64) (Pg+Pa-Pwv) /( Tg+460) (dimensionless) (1)

where: Pg is the gas pressure* (inches Hg)

;

Pa is the atmospheric pressure* (inches Hg)

;

Pwv is the water vapor pressure, partial (inches Hg)

;

Tg is the temperature of gas ( °F)

.

*NOTE: to convert inches of water to inches Hg

,

multiply by 0.07343; to convert millibars to inches Hg,

multiply by 0.02953.

A-l
2.0 Energy Used During a Test

The energy used during a test was determined by equation (2) where the

volume, Vol, of gas used during a test is corrected to standard

conditions using Cf and is converted to Btu using the higher heating

value of the gas.

The energy used during a test is defined as:

Q = ( Cf ) (H) ( Vol) (Btu) (2)

where: Cf is the correction factor as defined in 1.0;

H is the higher heating value of gas used (Btu per SCF)

;

Vol is the volume of gas used during a test as measured by

the gas meter (cubic feet).

3.0 Mean Outlet Hot Water Temperature

The mean value of the outlet hot water temperature, expressed in

degrees F, was determined by equation (4) and is defined as:

Twout = Tl+T2+...Tn/n (F) (4)

where: T1 is the hot water temperature at the end of the first

minute of the draw (°F);

T2 is the hot water temperature at the end of the second

minute of the draw (°F);

Tn is the hot water temperature at the start of the nth

minute of the draw (°F);

n is the number of outlet hot water temperature

measurements

.
4.0 Mean Supply Water Temperature

The mean value of the supply (cold) water temperature, expressed in

degrees F, was determined by equation (5) and is defined as:

Twin = Tl+T2 + ...Tn/n (F) (5)

where: T1 is the cold water inlet temperature at the end of the

first minute of the draw (°F);

T2 is the cold water inlet temperature at the end of the

second minute of the draw ( °F)

;

Tn is the cold water inlet temperature at the end of the

nth minute of the draw ( °F)

;

n is the number of supply water temperature measurements.

5.0 Recovery Efficiency

The recovery efficiency during a test was determined by equation (3)

and is defined as:

Er = (k) ( V) ( T1 ) /( Q) (dimensionless) (3)

where: k is the nominal specific heat of water during the

temperature ranges used (8.25 Btu/gallon °F)

;

V is the volume of the water draw during the test (U.S.

gallons)

;

T1 is the mean temperature rise ( °F) of the hot water drawn

during test and is equal to (Twout-Twin)

;

(Twout) is defined in 3.0;

(Twin) is defined in 4.0;

Q is defined in 2.0
6.0 Daily Water Heating Energy Consumption

The daily water heating energy consumption, expressed in Btu per day

and using an established daily hot water usage of 64.3 gallons was

determined by equation (6) and is defined as:

Cwh = (k)(U)(Tl)/( Er) (Btu/day) (6)

where: k, T1 and Er are defined in 5.0;

U is the established daily hot water usage, 64.3 gallons.

NOTE: When the value of U differs from 64.3 gallons,

the actual measured gallons is used for the

computations

.

The actual hot water temperature rise (Tl) is used instead of an

assumed or fixed value because the power input rate for most

instantaneous gas-fired water heaters is variable. In addition, the

actual temperature rise of the water is variable and it may differ

significantly from any fixed or assumed value.

7 .0 The Flow Rate During a Draw

The flow rate of hot water during a draw was determined by equation (7)

by weighing the water from a draw and timing the draw. The flow rate

is defined as:

Fr = Ww/( (Td) ( 8.25) ) (gal/min) (7)

where: Ww is the weight of the water during the draw in pounds;

Td is the duration of the draw in minutes;
8.25 is a constant to convert pounds of water to gallons of

water.

8.0 Power (Firing Ra te) Determination

The average power, in Btu/hour, input for a given test was determined

by equation (8) and is defined as:

P = (60 min/hour) (Q)/(Tb) (Btu/hour) (8)

where: Q is defined in 2.0;

Tb is the duration of the burner on time in minutes;

60 is a constant to convert minutes to hours.

9.0 Daily Hot Water Energy Consumption

The daily hot water energy consumption was determined by equation (9)

and is defined as:

Cc = (k)(U)(Tl) (Btu/day) (9)

where: k and T1 are defined in 5.0;

U is defined in 6.0.

10.0 Pilot Light Energy Consumption Rate

The pilot light energy consumption rate was measured for each unit.

These tests were conducted by measuring the volume of gas used by the

pilot light (Vol), correcting to a standard conditions by equation (1)

in 1.0 by determining the value of Cf and measuring the duration of the
pilot light energy consumption rate was then determined by equation

(10) and is defined as:

Pr = (Vol)(Cf)(H)/(Tp) (Btu/hour) (10)

where: Vol is the cubic feet of gas measured by the gas meter

during the pilot light test expressed in cubic feet;

Cf is defined in 1.0;

H is defined in 2.0;

Tp is the duration of the pilot light test in hours

(nominally 22 hours)

.

11.0 Average Daily Energy Consumption

The average daily energy consumption was determined by equation (11)

and is defined as:

Cy = Cwh+(Pr)(24-(U)/((60)(Fr))) (Btu/day) (11)

where: Cwh and U are defined in 6.0;

Pr is defined in 10.0;

Fr is defined in 7.0;

60 is a constant to convert minutes to hours and 24 is the

hours per day.

12.0 Energy Factor

The energy factor was determined by equation (12) and is defined as:

EF = ( Cc) /( Cy

)

(dimensionless) ( 12 )
where: (Cc) is defined in 9.0:

(Cy) is defined in 11.0.

A7
-.’Cr

>• V;
Appendix B

UNITS CONVERSION TABLE: SI/ INCH-POUND/SI

TO CONVERT MULTIPLY BY TO OBTAIN

gpm 0.06309 L/s

(Gallons/minute) (Liters/ second)

L/s 15.85 gpm

(Liters/ second) (Gal Ions /minute)

g 3.7 85 L

(Gallons) (Liters)

L 0.2642 g

(Liters) (Gallons)

in 2.54 cm

( Inches) ( Centimeters)

cm 0.3937 in

( Centimeters) ( Inches)

ft 0.3048 m

( Feet) (Meters)

m 3.281 ft

(Meters) (Feet)

BTU 1.055 kJ

(British Thermal Units) (Kilojoules)

kJ 0.947 9 BTU

(Kilojoules) (British Thermal Units)

TEMPERATURE ( T) . CONVERSION EQUATIONS :

For Temperature Use:

°F to °C: [ ( T) °F - 32 °F] ( 5/9) = (T)°C

°C to °F : [ ( T) °C( 9/ 5) + 32°F = (T)°F

FOR TEMPERATURE DIFFERENTIALS OR TOLERANCES USE :

°F to °C: (T) °F( 5/ 9) = (T) °C

°C to °F : (T) °C( 9/ 5) = (T) °F

B-l
NBS-114A iREv. 2 -ec) U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

1. PUBLICATION OR

REPORT NO.

2. Performing Organ. Report No. 3. Publication Date

SHEET (See instructions) NBSIR 87-3537 MAY 1987

4. TITLE AND SUBTITLE

Performance of Instantaneous Gas-fired Water Heaters

5. AUTHOR(S)

James E. Harris; Joseph Greenberg

6 . PERFORMING ORGANIZATION (If joint or other than N BS, see in struction s) 7 . Contract/Grant No. NATIONAL BUREAU OF STANDARDS ___________

DEPARTMENT OF COMMERCE 8. Type of Report & Period Covered

WASHINGTON, D.C. 20234

9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street. City. State , ZIP)

Building Environment Division

Office of Building Energy Research and Development

U.S. Department of Energy

Washington, D.C. 20585

10. SUPPLEMENTARY NOTES

| | Document describes a computer program; SF-185. FIPS Software Summary, is attached.

11.

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

bi bl iography or literature survey, mention it here)

Four different instantaneous, gas-fired water heaters were tested to develop a test

method to determine recovery efficiency (Er) and energy factor (EF). All four of the

water heaters were from foreign countries (West Germany, the United Kingdom, France

and Japan). Various flow rates and water draws were used during the tests to determine

their influence on the recovery efficiency and energy factor. -In addition, the pilot

light power consumption was measured to determine the effect of a variable pilot light

power rate on the energy factor. The use of recovery efficiency as a performance index

seems appropriate for these units, however, the use of energy factor as presently calculated, needs further study.

12. KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicolons)

appliance standards; energy conservation; geyser; instantaneous water heaters; in-line

water heaters; tankless water heaters

13. AVAILABILITY 14. NO. OF

PRINTED PAGES

(j£j Unlimited

|

| For Official Distribution. Do Not Release to NTIS 61

Order From Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402 15. Price

[Xj Order From National Technical Information Service (NTIS), Springfield, VA. 22161 $13.95

USCOMM-DC 6043-P80
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