NBS

Fubli - cations

a nitn,

AlllDt

NBSIR 78-1460

The Degradation of Gas-Fired

Water Heaters

George F. Sushinsky

National Engineering Laboratory

National Bureau of Standards

Washington, D.C. 20234

June 1978

Final

-QC —

100

,U56

78-1460

U S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

^ T®wT Fifreas of Standards APR i? Ar>o>t A CC ' NBSIR 78-1460

£>G lOO

THE DEGRADATION OF GAS-FSRED

WATER H EATER S m n 9 - 1 V ,

George F. Sushinsky

National Engineering Laboratory

National Bureau of Standards

Washington, D.C. 20234

June 1978

Final

n £6 0614.04 ^

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. Director

Table of Contents

Page

1. INTRODUCTION 1

2. GAS-FIRED WATER HEATER CONSTRUCTION AND OPERATION 2

3. LITERATURE SURVEY 4 3.1 Water Composition and Scale Formation Tendency .... 6

3.2 Extent and Effect of Scale Formation ......... 7

4. SPECIMEN COLLECTION 7

5. LABORATORY FACILITIES 10

6. TEST PROCEDURES 13

7. RESULTS 18

7.1 Lifetime Degradation 19

7.2 Safety Degradation 19

7.3 Energy Efficiency Degradation 22

7.3.1 Sediment and Scale Accumulation 25

7.3.2 Burner System Adjustments 25

(a) Primary Air Supply 27

(b) Pilot Rate 27

7.3.3 Flue Baffle Effect 28

7.4 Performance Degradation . 33

8. CONCLUSIONS 36

Appendix A 38

REFERENCES 39

List of Tables

Page

Table 1 Cities Supplying Water with Scale-Forming

(1962 Data)

Tendenc ies 9

Table 2 Water Heater Specimen Characteristics 11

Table 3 Daily Demand Draw Schedule 17

Table 4 Energy Efficiency Degradation Results for

Used Water Heater Specimens

Tests of

24

Table 5 Effect of Baffle on Water Heater Recovery Ef f iciency 30
List of Figures

Page

Figure 1 Schematic of a Typical Gas-Fired Water Heater 3

Figure 2 General Design of an Appliance Gas Burner 5

Figure 3 Average State Hardness of Finished Public Water -Supplies 8

Figure 4 Water Heater Laboratory Set-Up 12

Figure 5 Effect of Water Temperature Differential on Gas-Fired

Water Heater Recovery Efficiency 14

Figure 6 Water Heater Life as a Function of the TDS Level of

the Water Supply 20

Figure 7 Stages of Anode Deterioration from New (bottom) to

Complete Disintegration (upper right) 21

Figure 8 Collapsed Flue of Specimen 2 23

Figure 9 Effect of Sediment Accumulation, on the Bottom of

Gas-Fired Water Heaters, on Water Heater Recovery

Efficiency 26

Figure 10 Flue Loss Alinement Nomograph 29

Figure 11 Effect of Baffle Length on the Recovery Efficiency

of a Gas-Fired Water Heater with an 8-cm Diameter

Off-Center Flue 31

Figure 12 Baffles Used to Assess the Effect of Baffle Length on Water Heater Recovery Efficiency 32

Figure 13 Baffles Used to Assess the Effect of Minor Baffle

Modifications on Water Heater Recovery Efficiency 34

Figure 14 Deteriorated Dip Tubes; Upper Dip Tube Piece Was Used

in Simulated Draw Tests 35
1 . INTRODUCTION

In a corner of the basement, in a closet, under a counter, or

sometimes, in the way stands the lonely water heater. A forgotten object

for the most part, the water heater continually works to provide hot water

for laundry, bathing, and other household uses. Unlike the residential

heating and cooling systems that are seasonally operated, the water heater

presents a constant drain on the household energy budget as it consumes, on

the average, 14 percent [1]* of the household energy used; it is second

only to residential space heating at 56 percent [1] of household energy

use. As such, water heaters fall under the jurisdiction of the "Energy

Policy and Conservation Act" (Public Law 94-163) which mandated the

implementation of an energy conservation program for consumer products.

Under this law energy efficiency improvement targets for specified

appliances (including water heaters) were prescribed.

Maximum feasible improvements in the energy efficiency of covered

products were encouraged by P.L. 94-163- This concept extended not only to

manufacturing capabilities but also to the necessity for any improvements

to be "economically justified" as feasible. That is, the benefits of

reduced energy use and operating costs over the estimated average life of

the product must be greater than the added costs of the improvements plus

any associated increased costs of operation. These anticipated savings in

energy and operating costs may not be realized if the product efficiency

degrades during the life of the product; thus, a consideration of energy

efficiency degradation becomes important. A test program was initiated to

study the energy efficiency degradation of one of the products covered by

P.L. 94-163, the gas-fired water heater.

Water composition is the most important factor controlling water heater

degradation. Of particular importance are highly mineralized (hard) waters

that produce deposits in the forms of scale and sediment. The accumulation

of these deposits can affect water heater performance, reduce water heater

energy efficiency, increase service costs (e.g. electric water heater

element burnout), and reduce the water heater's operating life. For the case of a gas-fired water heater, the accumulation of these deposits on the

tank bottom (bottom head) and flue wall can affect the heat transfer from

the flame and the hot flue gases to the water, resulting in a reduction in

energy efficiency.

The primary purpose of the work covered in this report was to determine

the significance of the energy efficiency degradation due to mineral

deposit accumulation in typical gas-fired water heaters and to estimate the

magnitude of the occurrence and geographical distribution of mineral

deposit buildup. Water heaters using other fuels (oil, and electricity)

were not specifically covered by the results presented in this report.

#

Numbers in brackets refer to references on page 39-
Oil-fired water heaters with heat transfer systems comparable to those in

gas-fired water heaters would be similarly affected by mineral deposit

buildup; , while electric water heaters do not suffer from these same effects.

Used gas-fired water heaters were obtained from several known depositproducing areas around the country for this study. These water heaters were inspected for deposit formation and then tested in both a recovery and

standby mode of operation. In addition to energy efficiency degradation,

three other forms of degradation were identified: lifetime, safety, and

performance degradation. The causes and effects of each form of

degradation are discussed in this report. The effects of these "aging

processes" (degradation) of the water heater are considered in terms of the

improvements to energy efficient operation that might be realized by proper

maintenance and servicing of the water heater throughout its life.

This work was performed at the National Bureau of Standards in the

Product Engineering Division of the Center for Consumer Product Technology,

and was performed in conjunction with Federal Energy Administration

sponsored work on water heater test method development [2] that was also

performed at NBS. Sincere appreciation is extended to Robert Palla for his

helpful contributions throughout this experimental program, and to Rose

Massengill for manuscript preparation.

2. GAS-FIRED WATER HEATER CONSTRUCTION AND OPERATION

The residential gas water heater (Figure 1) is a relatively simple

appliance in terms of construction and operation. Typically it consists of

an insulated water storage tank (110 to 190 liter (30 to 50 gallon) K

; capacity), and a gas-fired burner (7.3 to 22 kW (25000 to 75000 Btu/h)

firing rate). Cold water enters the tank from the cold water supply

through a dip tube which carries the water to the bottom of the tank for

heating. This incoming cold water pushes hot water upward through the tank

outlet. A drain is provided about 5 cm above the edge of the convex tank

bottom for the purpose of tank flushing, cleaning, or draining. The

internal surfaces of the tank are usually protected from corrosive chemical

attack by a glass lining and a sacrificial magnesium anode (not shown in

Figure 1)

.

Heavy deposit accumulations on electric water heating elements may

reduce recovery rate (a performance penalty) but should not significantly

affect the energy efficiency of the electric water heater. All of the

energy from the heating element(s) will still be transferred to the water.

However, heavy scale deposits on electric water heating elements will

promote a reduction in operating lifetime through element burnout.

S.I. units have been used throughout this report. Customary units have

been included after the S.I. units for clarification in those cases where

they are normally encountered in common usage (e.g. 110 liter (30 gallon water

heater)

.

2
3

m FUEL

Figure ] Schematic of a typical gas-fired water heater.

3
In operation the water heater is designed to (1) heat cold water to a desired temperature, (2) store the hot water near that temperature, and (3)

deliver the hot water, in sufficient quantities to satisfy the users'

demands. The operating mode of each of these functions is termed (1)

recovery, (2) standby, and (3) performance^ 0

. A degradation in the energy

efficiency operation of a gas-fired water heater would principally affect

recovery.

In the recovery operation, gas enters the burner (Figure 2) from the

main supply through an orifice opening. The gas is mixed with the primary

air supply, ignited by the continuously burning pilot, and burned in the

presence of secondary air at the burner head. The burner, located in the

combustion chamber beneath the water tank, transfers energy to the water by

passing hot combustion gases from the burner over the tank bottom and

through the flue of the water heater. The transfer of heat is enhanced by

baffling in the flue and other restrictions to the secondary air supply

entering the combustion chamber. Current water heater designs provide

baffling and air supplies that result in flue gas temperatures of 290°C at

the flue exit with excess air levels (primary and secondary air in excess

of that required for complete combustion) greater than 50 percent. Under

these conditions, minimum recovery efficiencies of about 70 percent are obtained. A decrease in the recovery efficiency operation of the water

heater is equivalent to a decrease in the heat transfer ability of the

water heater. Such decreases can result from the presence of insulating

layers of scale on the bottom and flue wall of a water heater or deterioration in burner operation or water heater baffling.

3. LITERATURE SURVEY

A literature survey was conducted to determine the existence of

previously published information on the extent of a mineral deposit buildup

problem in terms of geographical distribution and severity, and to relate

this information to water heater energy efficiency degradation.

Information pertaining to water heaters, water heater efficiency, water

heater degradation, water quality, corrosion and scale, water treatment,

etc. was sought. This survey included texts, magazines, technical society

journals, published papers and reports, geological survey data, and

abstract collections. In addition, two data bases available through the

NBS Library computer retrieval systems (Lockheed DIALOG and ERDA/RECON) were searched for information in those subject areas. Collected data from

these sources, were compared and refined with respect to each source in

order to obtain an overall picture of the extent (numbers and geographical

distribution) of a potential deposit build-up problem and its resultant

effect on the energy efficiency of gas-fired water heaters.

Water heater performance is closely related to the recovery mode of the

water heater. As defined here, performance is also dependent on other

factors including: heat transfer rate from the source to the stored

water, the distribution of heated water in the tank, mixing of the

incoming cold water, flow rate, and tank volume.

4
AIR SHUTTER

PRIMARY

AIR OPENINGS

MIXER NIXING

TUBE

(VENTURI

)

MIXER FACE

AIR OPEMSHS

Figure 2 General design of an appliance gas burner

5
3.1 Water Composition and Scale Formation Tendency

To some extent, all water heaters undergo an internal attack (either

corrosive or scaling) that is caused by continuous contact with the water

and controlled by the mineral content of the water. Two measures of the

amount and nature of the mineral components in a water supply are the total

dissolved solids (TDS) content and the hardness level.

The TDS content is a measure of the mineral constituent dissolved in

the water. Typical values of TDS content in municipal water supplies range

from 0 to more than 1000 ppm. According to the U.S. Public Health Service,

water supplies with TDS levels greater than 500 ppm are undesirable for

drinking purposes [4]. Water heater lifetimes tend to decrease with

increasing dissolved solids levels [5,6].

Hardness is a more commonly recognized describer of water quality.

Hardness is a measure of the calcium and magnesium in water and is

commonly expressed as the equivalent amount of calcium carbonate (ppm) that

can be formed from these minerals in solution. Water hardness levels (both

low and high) are reported to effect plumbing system life [5,7,8] household

economics [5,8,9,10] and human health [11,12].

Hardness levels in finished public water supplies range from 0 to more

than 180 ppm. A hardness level of from 0 to 60 ppm is subjectively

considered "soft”, while hardness levels in excess of 120 ppm indicate

"hard" water. Hard water is generally conducive to scale formation.

Any reasonable, qualitative measure of the scale-forming tendency of a water supply is dependent on other factors in addition to hardness. The

Langelier Saturation Index [13] and the Ryznar Stability Index [14] each

provide a semi-quantitative measure of the tendency of a given water to

form scale. In the formulation of these indices both hardness and

dissolved soilds levels are used along with other water parameters, the pH,

alkalinity, and operating temperature, to provide an indication of the

scale formation tendency of the water.

Both the Langelier and Ryznar indices are based on the calculation of

the saturation pH (pH ) of the water. A tabulated form for calculating the

saturated pH of a water is given in Appendix A.

The Langelier Saturation Index (I

s

) is given as the algebraic

difference between the actual pH and saturation pH,

I s

= pH - pH

s

. (2)

For positive values of I scale formation is predicted.

O

The Ryznar Stability Index is given by

Stability Index = 2 pH - pH.

o (3)

6
Stability Index values less than 6 are scaling. From data in Reference 14

the stability index appears from field experience to predict not only

scaling tendency but also the relative amount of scale formation.

Both the Langelier and Ryznar indices were used to evaluate the scaleforming tendencies of finished municipal water supplies in order to select

areas from which scaled water heaters would most likely be obtained.

3.2 Extent and Effect of Scale Formation

Hard water is commonly cited as the chief cause of scaling problems in

plumbing systems and appliances. In the absence of the other water quality

parameters necessary for the calculation of both indices (equations 2 and

3), a hard water level of 120 ppm or greater was used to indicate scale

formation tendency for municipal water supplies. Using this assumption,

there are 20 states with a combined population of 94 million people (1970

census) that have, on an average statewide basis, hard and potentially

scale forming public water supplies [15], Figure 3. This large population

group has 24 million residential water heaters of which 17 million are gasfired [16]. Eighteen percent of this group soften their water [5],

therefore, 14 million water heaters are potentially subject to scaleproduced problems.

The widespread deposition of scale is not in itself a serious problem

since thin layers of scale can provide a beneficial buffer against plumbing

system corrosion. But reports of water heaters 10 to 70 percent full of

scale have been made [17,18]. Such large amounts of scale impose penalties

in reduced water storage capability in addition to any energy efficiency

degradation.

Estimated increases in fuel consumption (corresponding decrease in

energy efficiency) of 20 to 50 percent have been attributed to large

buildup of scale in boilers and water heaters [9,16,19,20,21] . For the

gas-fired water heater this degradation is due to the preferential buildup, on the flue and the bottom head of the water heater, of an insulating layer

of scale. (Scale as an insulator has a thermal conductivity value (k)

approximately equivalent to firebrick [21]). For 14 million affected water

heaters the extent, in terms of geographical distribution and severity of

scale occurence, is more than significant. However, no quantitative

experimental evidence relating scale accumulation to energy efficiency

degradation was found in the literature survey.

4. SPECIMEN COLLECTION

Based on information obtained in the literature survey (particularly

reference 22), 11 major metropolitan areas were identified as having

treated municipal water supplies with scale-forming tendencies. The scale

formation tendency of a given water supply was judged according to both the

Langelier (L) and Ryznar (R) indices of those waters at 60°C as given by

equations 1 through 3* A list of these 11 cities and the calculated

indices of their municipal water supplies are given in Table 1.

7
mWmi

5 8 fc

Figure

3

Hardness

of

Finished

Public

Water

Supplies
Table 1 - Cities Supplying Water With Scale-Forming

Tendencies (1962 Data)

City State L<a) R

(l

San Diego Calif. 1.7 5.3

San Jose Calif. 1.6 5.0

Lubbock Tex

.

1.0 5.2

1.0 5.1

0.8 5.6

Amarillo Tex. 0.9 5.5

0.6 6.0

South Bend Ind. 1.1 5.3

0.9 5.5

1.0 5.3

1.3 4.7

Indianapolis Ind. 0.6 6.0

0.9 5.5

Rockford 111. 1.3 5.0

1.3 4.9

Madison Wis. 1.4 4.8

1.5 4.8

1.3 5.0

Kansas City Kans. 0.9 5.9

Oklahoma City Qkla. 2.2 5.5

Lincoln Nebr

.

0.9 5.8

(a) Scale formation is predicted for L values positive - no quantititive

estimation of scale formation is provided

(b) R >7, plumbing system corrosion; 7>R>6, neutral; R<6, scale formation;

R<5, heavy scale

9
Efforts were made to obtain used water heaters from these and other

locations. Plumbers, general contractors, municipal and private solid

waste disposal personnel were asked to ship used water heaters containing

scale for test purposes. Private sources from the metropolitan District of

Columbia area and one of the two largest water heater manufacturers, State

Industries, were also asked to provide specimens for use in the test

program.

Twenty-six water heaters from various areas of the country were received for testing as a result of contacts in 4 of the 11 selected

cities, State Industries cooperation, and private sources in the

metropolitan District of Columbia area. One new 150 liter (40 gallon)

water heater was also obtained in order to establish benchmark data on energy efficiency and energy efficiency degradation experiments.

This group of water heaters, ranging in age from less than 5 years to

more than 20 years, included an external flue gas-fired water heater, an off-center flue gas-fired water heater, and one 24 year-old electric water

heater with several features apparently designed for energy efficiency

including an integral heat trap and a 7.5 crn thickness of insulation. None

of these water heaters, however, contained other than slight amounts of

sediment or loosened scale on the tank bottom.

Ten water heaters in this group were tested during this project. The

main physical characteristics of these 10 water heaters are presented in

Table 2.

5. LABORATORY FACILITIES

The test station established for the work on gas-fired water heater

degradation is shown in Figure 4. The necessary equipment and utilities

for testing one gas-fired water heater were available at this station. The

equipment consisted of: (l)a precision wet-test gas meter (1.8 rrr/h

capacity), (2) a multipoint temperature recorder with Type T or K

thermocouple readout capability (0 to 100°C temperature range), (3)

thermocouple probe(s), (4) a gas-pressure gage, (5) a gas-temperature

thermometer, (6) a water-pressure gage, (7) a flue-temperature thermometer,

and (8) an expansion tank, pump, and drain (not shown in the figure). The

general building supply of hot and cold water and natural gas were

available. Auxiliary equipment needed for the test program, namely a gas

calorimeter for continuously monitoring the incoming natural gas supply

heating value, an infared-analyzer to measure CO and CO2 levels in the flue

gas, a portable oxygen analyzer to determine excess air, and an electronic

barometer were readily accessible and were used when needed.

10
Table 2 - Water Heater Specimen Characteristics

Main

Tank Burner Pilot

Specimen Origin Age Volume Rate, q Rate

Years liter gal kW Btu/h W Btu/h

1 New 144 38.1 14.6 50xl0

3

230 800

2 (a) Wheaton,

MD

7 143 37.8 10.3 35xl03

290 980

3

(b) Arlington,

VA

17 107 28.3 8.8 30xl0

3

250 860

4 Rockville,

MD

15 141 37.3 8.5 29xl0

3

250 850

5 San Diego,

CA

12 142 37.6 11.4 39xl03

440 1500

6

(C) Madison,

WI

20 104 27.6 6.7 23xl03

230 790

7 Rockford

,

IL

- 105 27.8 9.7 33xl0

3 - -

8 Torrence,

CA

5 142 37.6 14.1 48xl0

3 210 700

9 Oceanside,

CA

5 144 38.0 14.4 49xl0

3 250 860

10 Huntington 7 185 49.0 15.8 54xl0

3

350 1200

Beach, CA

collapsed flue

off center flue

( c) external flue

11
12

Figure

4

Water

heater

laboratory

set-up.
6. TEST PROCEDURES

Recovery efficiency and standby loss tests were performed on used water

heaters in accordance with the Department of Energy (DOE), prescribed test

procedures that were developed at NBS [23]. A minor exception to the exact

procedure for recovery efficiency involved the use of tap water in the

range from 18 to 28°C due to seasonal variations in the incoming water

supply. The effects of this procedural change were not significant for the

large temperature differentials ( AT in excess of 40°C) between the

beginning and end of the recovery efficiency tests as shown in Figure 5.

Reduced recovery efficiency values for temperature differentials less than

20°C are probably the result of short burner-on times.

According to the test procedure, recovery efficiency (E ) is calculated

by:

r

E = ’PVW (4)

r Q

where

E^ = recovery efficiency,

V = tank capacity (L)

p = density of water

(0.989 kg/L),

0^ = specific heat of water (4180 J/kg°C),

T~ = final average tank water temperature

(°C),

T. = initial average tank water temperature

1 (°C) , and

Q = energy consumption (J).

Standby loss calculations are determined by:

VpC (T - T

2

) + Q

S = tVpC ( T - T ) p w a where

S standby loss as a fraction of the stored energy

lost per hour (h” 1

),

(5)

Q = energy consumed during the standby loss test (J),

13
14

WATER

TEMPERATURE

DIFFERENTIAL

(AT),°C
t = duration of standby test (h),

T, = average tank water temperature at start

of test (°C),

T?

= average tank water temperature at end of

test (°C),

T = average tank water temperature during test

(°C) (arithmetic average of cut-on and cut-out

temperatures), and

T = average ambient temperature during test

a (°C).

V,p,C and E

r are as defined previously for equation 4

A minimum standby period (t) of 48 hours with at least two complete

thermostat cycles after an equilibrium period of approximately 24 hours was

used for this test. (Note: Current DoE Test Procedure no longer requires

an equilibrium period.)

For the purposes of estimating the percent increase or decrease in

energy usage from water heater degradation or improvements, the daily

energy consumption of the water heater was calculated from the equation:

Daily Energy

Consumption =

E =

where

Main burner

input energy needed

j

L

' to raise U liters of

water from inlet to

outlet temperature

j

pC

p

ATl U E

| Energy required

to maintain V

liters of water

at an average

operating

temperature

above ambient

L

for a 24 hour

period

in burner

energy used

during the 24

hour period

i to recover from

|_hot water draws

+ 24VSp C At

2

_

fC UAT (pc AT )VS

P -L d

' ' ' " qC

'

E = energy consumption rate (J/day),

U = hot water usage rate (L/day),

AT^ = temperature rise of incoming water (°C),

AT^ = average temperature of stored water above ambient

during standby (°C),

15
q = energy input rate (kW), and

V, p,C ,E and S are defined previously in equations 4 and 5.

Equation 6 was originally developed by the American Gas Association [24].

Under the proposed test procedures for water heaters [231, an average

usage rate, U, of 1700 liters per week, (243 liters per day) and

temperature differentials, and AT2, of 50°C were prescribed. These

selections were used in calculating the daily energy consumption, E, and to

evaluate the magnitude of the energy degradation or improvements of the

water heaters tested in this program.

The test procedures for recovery efficiency and standby loss are static

or "steady state" tests that place no hot water delivery demand on the

water heater. The ability to satisfy hot water delivery demand is

dependent on the rate of heat transfer from the heat source to the stored

and incoming water, the distribution of hot water in the tank and the

mixing of incoming cold water. As such, the hot water delivery performance

of a water heater is a usage or rate dependent attribute that is not

necessarily measured by test methods for recovery efficiency or standby

loss. In order to simulate use conditions and estimate the hot water

delivery performance, a dynamic test using computer-controlled water draws

was implemented. This method was used to calculate the effect of hot water

delivery decline on water heaters with damaged dip tubes.

For these tests a draw schedule using 243 liters of hot water per day was established. The draw schedule consisted of simulated hot water usage

for 2 showers, 1 dishwasher operation, 1 warm water clothes wash, and 12

sink uses. These events were spaced over a 24 hour period at intervals

that could be representative of a hot water usage pattern. No heavy or continuous draw demand was placed on the water heater. This draw schedule

is presented in Table 3-

A second draw schedule consisting of five 56.8-liter draws spaced every

600 seconds (water on for 300 seconds at 0.19 liters per second and off for

300 seconds) was used to deplete the supply of hot water in the tank. This

would simulate an unusually heavy demand schedule, e.g. five showers taken

sequentially.

Measurements of the energy content of delivered hot water were made

using the draw schedules. The delivered energy content of the water was calculated by

Ed

= i (Vpc ) (To

- T

±

) (7)

J =l J J

j

= 1,2,3 n and

16
Table 3 - Simulated Dally Demand Draw Schedule

Time of Rate of Durat ion Volume T

(a) Type

Day Draw of Draw of Draw of Draw

L/s gpm seconds liter gal

0701 0.09 1.5 24 2.3 0 .

6

1

0705 0.19 3.0 300 56.8 15.0 2

0725 0.09 1.5 24 2.3 0.6 1

0800 0.09 1.5 24 2.3 0.6 1

1000 0.25 4.0 120 30.3 8 . 0~

j ~ 3 1022 0.25 4.0 60 15.1 4.0_

1030 0.09 1.5 24 2.3 0.6 1

1200 0.09 1.5 24 2.3 0.6 1

1245 0.09 1.5 24 2.3 0.6 1

1600 0.09 1.5 24 2.3 0.6 1

1720 0.09 1.5 24 2.3 0.6 1

1800 0.09 1.5 24 2.3 0.6 1

1820 0.09 1.5 120 11.4 3 .0~

1828 0.09 1.5 120 11.4 3.0

1836 0.09 1.5 120 11.4 3.0 — 4

1844 0.09 1.5 120 11.4 3.0

1352 0.09 1.5 120 11.4 3.0_

2200 0.09 1.5 24 2.3 0.6 1

2205 0.19 3.0 300 56.8 15.0 2

2225 0.09 1.5 24 2.3 0.6 1

2330 0.09 1.5 24 2.3 0.6 1

(a) Type of Draw

1. sink use

2 . shower

3 . warm water clothes wash

4. automatic dishwasher
n = number of draws

where:

Ed

= energy content of the delivered water (J),

V r volume of draw (L),

P = average density of water at an average temperature (T + T. )/2

(kg/L), j j

C = specific heat of water (J/kg°C),

T = outlet temperature of delivered water (°C),

°J

o

Ih = inlet temperature of cold water supply ( C),

j

All of the water heaters tested using the recovery and standby

procedures were visually inspected prior to testing. The general condition

of each water heater was evaluated in terms of the amount of scale evident

from the inspection, and the known history (age and reason for removal).

When possible the more heavily scaled units were tested first.

The general test procedure consisted of testing the water heater in an "as received" condition for recovery efficiency and standby loss. Some

scaled water heaters were cleaned and retested to note any changes in their

operating characteristics. Adjustments to the primary air intake, the

pilot rate, or baffle length and design were made on several water heaters

to note their effects on water heater recovery efficiency and standby

losses. Measurements of the levels of carbon dioxide, carbon monoxide, and excess air, as well as, flue gas temperature were routinely made to

establish the range of operating values for these quantities in the used

water heaters. Several specimens were dissected for closer internal

inspection after the laboratory tests were completed.

7. RESULTS

The literature survey and experimental program combined to identify

four interrelated forms of degradation that can exist in gas-fired water

heaters. These forms have been labeled: (1) lifetime, (2) safety, ( 3 ) energy efficiency, and (4) performance degradation. The causes and

resulting effects, for each form of degradation are discussed below.

18
7.1 Lifetime Degradation

The average operating life of a water heater has been estimated at

approximately 8 to 10 years [25]. The range in operating lifetimes extends

from less than 3 to more than 20 years. Lifetime degradation is the

deterioration and ultimate failure of the water heater. Failure for the

gas-fired water heater is typically a water heater tank leak. The primary

normal failure mode is a corrosion induced leak.

Ignoring all other variables, the operating life (time to failure) of

water heaters has been related to the total dissolved solids (TDS) content

of a water supply [5,6]. Water heater lifetime as a function of TDS

content is shown in Figure 6. But, for a given TDS level, the failure

lifetime is basically temperature dependent. In the normal operating

temperature range for water heaters, 49 to 82°C the corrosion rate doubles

for every 11°C rise in temperature [26]. In this temperature range the

rate of scale formation also rapidly increases [27]. In the gas-fired

water heater any resultant accumulations of scale or sediment on the bottom

head will significantly increase the water heater surface temperatures,

[26] thus accelerating the corrosion process due to increased temperatures

.

Most water heaters are initially protected against this corrosive

attack on the tank through the use of a "glass” lining and a sacrificial

magnesium anode. With use, the anode is preferentially attacked (Figure

7). The disintegration of the anode without replacement allows the

corrosion process to attack the water heater tank through imperfections in

the glass lining and accelerate the lifetime degradation of the tank. Most

anodes in the water heaters tested were completely disintegrated. No

laboratory work on measuring the parameters affecting the rate of failure

or the lifetime phenomenon was undertaken in this program.

7.2 Safety Degradation

Properly installed, the gas-fired water heater is a reliable and safe

appliance that will adequately perform throughout its lifetime. But

occasionally safety related failures do occur.

Of the water heaters received for testing, two specimens (2 and 6) were

found that had degraded in a manner that posed potential safety problems.

Specimen 6 (see table 2), a 20 year old external-flue gas water heater, had

been removed from service because of a thermostat malfunction that allowed

the burner to remain on past the temperature cutout point. This

malfunction produced excess water temperatures and pressures which

activated the properly acting pressure-temperature relief valve (PTRV).

The proper reaction of the PTRV to this situation prevented any serious

safety problem. In addition to the PTRV many modern gas-fired water

heaters are now equipped with high temperature limit switches to

automatically shut off the gas supply in the presence of high water

temperatures.

19
SNVBA

1 3311 N31V3H HBiVM

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01

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u

ei

4-1 cO X

0)

J-i

60

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tu

on

TOTAL

DISSOLVED

SOLIDS

,(

ppm)
21

Figure

7

Stages

of

anode

deterioration

from

new

(bottom)

to

complete

disintegration

(upper

right)
The other water heater (specimen 2) had been removed from service after

only 7 years because of a "flue blockage". Initial tests showed a low

recovery efficiency, long recovery time, evidence of occasional flame

rollout (flames extending outside of the combustion chamber), and carbon

monoxide (CO) levels in the flue gas in excess of 500 ppm. The exact cause of this deterioration, a collapsed flue (Figure 8), was not discovered

until dissection. The collapse of the flue was apparently the result of

the flue wall deterioration due to corrosive action of the hot flue gases

on the flue of the water heater. (The flue wall thickness had decreased to

about 25 percent of its original value.) This water heater without

evidence of tank leakage, was fortunately replaced before the degraded

operational characteristics, particularly CO concentration, produced any

tragic results. Flue collapse can also result from temporarily high

pressures produced by inoperable pressure-temperature relief valves.

Neither of these failures were typical of other service failures

encountered in this investigation.

7.3 Energy Efficiency Degradation

Prior to 1975 gas-fired water heaters had a baseline recovery

efficiency of approximately 70 percent^ [28] with the remaining 30

percent lost to the surroundings, mainly through flue losses. Any

reduction in the transfer of heat from the combustion gases to the water

storage tank should reduce the operating efficiency of the water heater,

increase the flue losses, and should be reflected directly in a lower

recovery efficiency number. This reduction is "energy efficiency

degradation"

.

The degradation in energy efficiency is primarily the result of reduced

heat transfer capability arising from insulating layers of loose scale

(sediment) on the tank bottom, insulating layers of adherent scale on the

tank bottom and flue wall, burner malfunction or misadjustment, and a degradation in the heat transfer system (e.g. baffle deterioration, rust

and soot accumulation in the flue, and flue blockage).

Nine of the 26 old water heaters and one new water heater were tested

in accordance with the established procedures for recovery efficiency and,

where possible, standby loss. The results of these tests are given in

Table 4. Excluding specimens 1 and 2 (the new water heater and the water

heater with the collapsed flue) the average recovery efficiency for these

water heaters as received was 65 percent. This figure represents an average recovery efficiency degradation from a "new" condition of about 4

recovery efficiency percentage points. Efforts to determine the cause of

this decrease were undertaken.

This value for recovery efficiency is based on a recovery efficiency

test method using a preheated tank according to standards in effect before

1977. The use of a cold start recovery efficiency test would decrease

this baseline number by about one percent to 69 percent. The cold start

recovery test method was used in this test program.

22

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7.3*1 Sediment and Scale Accumulation

Approximately 50 percent of the heat input to a gas-fired water heater

is transferred through the tank bottom [29]. The accumulation of an insulating layer of scale or sediment should affect the heat transfer

process and degrade the energy efficiency of the water heater.

The effect of loose sediment on the recovery efficiency of a gas-fired

water heater was demonstrated in tests on a new water heater to which sand was added. Recovery efficiency dropped linearily from 74 to 69 percent as 9-9 liters of sand (an average depth of about 10 cm) were deposited in the

tank, Figure 9. Relatively little degradation in energy efficiency was

noted in agreement with Reference 29. This volume of sand was at least

five times the accumulation of sediment (loose scale) found in any of the

26 water heaters received for testing. Removal of the sand restored this

water heater's recovery efficiency to its original value, but the removal

of sand was a laborious and probably not cost effective task. The

recommended practice of draining the tank "until the water runs clear" is

ineffective because it does not remove large amounts of sand and sediment

in the tank.

In addition to specimen 1, repeat tests for recovery efficiency and

standby loss were also made on specimens 3, and 8 after sediment removal.

Recovery efficiencies improved slightly for these specimens, while standby

losses increased for specimens 1 and 3 after removal of the insulating

layer of sediment. The overall effect of sediment removal for specimens 1 and 3 would increase the energy consumption of the water heater due to the

increased standby losses, according to equation 6.

7-3-2 Burner System Adjustments

Water is heated in the typical gas-fired water heater by passing hot

combustion gases from the burner over the tank bottom and through the water

heater flueway. The transfer of heat is enhanced by baffling in the flue

and other restrictions to the air supply traveling through the flue. A

degradation in the heat transfer capability of the burner, combustion, and

flue system would result in an energy efficiency degradation for a water

heater. The degree of improvement in water heating efficiency obtained

through servicing or minor adjustments to the burner-combination system of

old, in-service water heaters can provide an estimate of energy efficiency

degradation as a result of burner-combustion system misad justment . Such

improvements require either an increase in heat transfer capability or a reduction in energy consumption without a corresponding reduction in water

heating performance.

The burner, Figure 2, is the most conspicuous part of the burner

system. In the typical burner primary air is premixed with the gas supply

in the mixing tube and burned in the presence of secondary air at the ports

in the burner head. Other parts of the burner system include the

continuous pilot, used primarily for main burner ignition, the orifice spud

25
Figure

9

Effect

of

sediment

accumulation,

on

the

bottom

of

gas-fired

water

heaters,

on

water

heater

recovery

efficiency.
and pressure regulator, which determine the gas flow rate, the thermostat

valve, which controls the burner on-off operation according to sensed water

temperature, and manual on-off switch. The pressure regulator, thermostat

valve, and on-off switch are generally physically located together in a packaged "thermostat" control (not shown in Figure 2).

In this relatively simple system, adjustments are limited to the (a)

primary air supply, (b) secondary air supply, (c) pilot rate, and (d) main

burner rate. The effects of adjusting the primary air supply and pilot

rate on several water heaters were determined.

(a) Primary Air Supply

Primary air is the air that is premixed with the gas before it enters

the burner head. This air supply is adjustable within limits by means of

an air shutter at the burner mixer face on older water heaters. The

primary air supply was adjusted on specimens 2,3,6, and 7 in an effort to

improve the recovery efficiencies of these water heaters. Recovery

efficiency changes of 5 and 3 percentage points were recorded for specimens

2 and 3 while no beneficial effects were observed from the primary air

adjustments to specimens 6 and 7- Under normal use conditions, once properly installed and adjusted, adjustments to the primary air supply are

generally unnecessary. Current industry trend is to produce burners with

preset non-ad justable primary air supplies.

(b) Pilot Rate

The continuous pilot in a gas appliance is a major consumer of energy.

In the water heater it contributes heavily to the standby loss. The

effect of pilot-rate on the standby loss was demonstrated on specimens 3

and 10.

Specimen 3, a nominal, 114 liter (30 gallon) water heater with an offcenter flue was tested in a standby mode with pilot rates of 250 (as

received) and 110 W (800 and 360 Btu per hour). The corresponding standby

losses were 8.6 and 7.3 percent per hour. Using equation 6 and the

estimated average use conditions this reduction in pilot rate produced a five percent reduction in total energy consumption for the water heater.

Specimen 10, a conventional water heater with a nominal capacity of 189

liters (50 gallons) was tested in a standby mode with pilot rates of 350

(as received) and 120 W (1200 and 400 Btu per hour). The standby loss

rates for these tests were 6.4 and 6.0 percent per hour. Using equation 6

and the average use conditions, a 3 percent savings in total energy usage

was predicted for this pilot rate reduction.

The results for specimens 3 and 10 are given in Table 4. These results

are in general agreement with other pilot-rate reduction tests run at NBS

on new water heaters [30] and with other reported estimates of a 2 percent

27
energy savings that can be obtained through pilot rate reduction on a typical 151 liter (40 gallon) water heater [16].

7.3*3 Flue Baffle Effect

The burner does not work alone in the process of heating water. The

combustion chamber, flue, and flue baffle provide the path for the hot

combustion gases and promote the transfer of heat from the gases to the

water. Current gas-fired water heater designs provide baffling, and

primary and secondary air supplies which result in flue gas temperatures of

about 290°C, at the diverter, and excess air levels (i.e., primary and

secondary air in excess of the air required for complete combustion)

greater than 50 percent. Both the exit flue temperature and excess air

level are higher than required for safe and proper combustion; reductions

in each of these parameters would result in an increase in water heater

efficiency (heat transfer capability) and a corresponding reduction in flue

loss. Safe lower limits for these parameters are a 220°C flue gas exit

temperature and 25 percent excess air. The net effect of reduction to this

lower flue temperature and excess air level is a decrease in flue loss from

24 to 18 percent, as shown on the nomograph, Figure 10.

Flue baffling can be increased through length increases, added air flow

restrictions , or baffle pattern redesign. However, the harsh environment

of the flue of the gas-fired water heater is capable of destroying the

baffle's lower end, effectively decreasing the baffle length and

eliminating any added air flow restrictions at that point. The net result

of this destruction would be a decrease in water heater recovery efficiency — energy efficiency degradation.

The effect of baffle length on water heater recovery efficiency was demonstrated by tests on specimen 3 in which several baffles of various

lengths and configurations were installed in place of the original baffle.

The results of these tests are presented in Table 5 and Figure 11. For

this off-center flue water heater, recovery efficiency appears to be a linear function of baffle length, independent of the baffle pattern, Figure

12. In all of the specimens examined during this project baffle length

destruction was limited to the bottom 3 cm of the baffle. Based on Figure

11 a decrease in baffle length of 3 cm produces less than a 1 percentage

point degradation in water heater recovery efficiency.

The off-center flue design of specimen 3 is not typical of most gasfired water heaters. However, a design of this type is more efficient in

transferring heat from the burner to the water [29] and, as a result, use of the original baffle (No. 2), which was 40 cm shorter than the flue,

resulted in the commonly encountered flue temperature and excess air

level. For specimen 3 significant improvements to the water heater

recovery efficiency were made by increasing baffle length alone. In the

center-flue water heaters tested (8,9, and 10) typical baffle lengths were

28
TEMPERATURE

DIFFERENCE

,

FLUE

GASES

—

ROOM

Figure 10 Flue loss alinement nomograph (31)

29

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FLUE

GASES
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31

BAFFLE

LENGTH

(cm )
32

assess

effect

of

baffle

length

on

water

heater

Recovery

Efficiency.
within 15 cm of the flue column length and significant improvements in

recovery efficiency were brought about by baffle modifications other than

increased baffle length.

Recovery efficiency tests were run on specimens 8, 9, and 10 using two

to six similar baffles, Figure 13. Baffle length, width, and pattern were

all similar; the major difference between baffles was the presence of a flow restricting disk or plate normal to the flue column axis at the bottom

edge of baffles 7 and 9, and the use of a disk at the bottom edge, plus a tab located 30 cm from the bottom tip of baffle 11. The results of these

tests are also presented in Table 5. The use of restrictions on the bottom

edge of a baffle produced recovery efficiency improvements from 6 to 9

percentage points. Based on recorded flue temperatures, even higher

recovery efficiency improvements are attainable through further baffle

modifications. The resultant increases in heat transfer from the

combustion gases to the water offer a significant energy savings at a relatively small price.

The inclusion of air flow restrictions at the baffle end do not insure

increased operating efficiency throughout the water heater's operating

life. Loss of such restrictions from environmental factors would suddenly

and significantly degrade the water heater's energy efficient operation.

7.4 Performance Degradation

The fourth form of degradation is in the area of performance. Water

heater performance is closely related to the operating efficiency of the

water heater; a degradation in energy efficiency generally results in a degradation in performance. Performance deterioration is specifically

defined here as a decrease in the ability of the water heater to deliver a desired quantity of water at a desired temperature. The ability to satisfy

hot water demand is dependent on the rate of heat transfer from the heat source to the stored water, the distribution of hot water in the tank,

mixing of the incoming cold water, hot water flow rate, and the tank

volume. As such, performance is a usage or rate dependent attribute that

is not readily measured or determined by a test method for recovery

efficiency or standby loss.

The deterioration in performance can be qualitatively observed by the

water heater user as a decline (either sudden or gradual) in the quantity

of hot water available for large draws.

One cause of such performance degradation is the broken or damaged dip

tube, Figure 14. A water heater with a damaged dip tube introduces cold

water near the top of the tank. This cold water mixes with and tempers the

stored hot water already present in the tank. This mixing prevents the

exit flow of large quantities of hot water to the point of use. Using the

two draw schedules outlined in Section 6, Test Procedures, the performance

of a 200 liter (52 gallon) electric water heater^ was measured using both

its original dip tube and the broken dip tube identified in Figure 14.

(e)

An electric water heater was used for this test for convenience because

it was already being monitored on computer control. The effect of dip

tube deterioration is similar to that for gas water heaters (see later).

33
U

<u>oo

Q)MU

0)

4-1 n)0) X

l-i <u

4-1 n)3Co

cocoO6

rOMOe

•He

M-lO

0) 4=

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CO Cl) Q) iH H O

cd 14-4 m <u

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oo

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34
35

Figure

14

Deteriorated

dip-tubes.

Upper

dip

tube

piece

was

used

in

simulated

draw

tests.
Specimen 1 was tested under the normal draw schedule with and without a dip

tube (limiting case of a broken dip tube).

Under the normal draw schedule, a 7 percent reduction in delivered

energy content for the electric water heater and 21 percent reduction in

delivered energy content for the gas water heater (specimen 1), were

observed in test comparisons between good and broken dip tubes. Under the

heavy demand draw schedule a 12 percent decrease in delivered hot water

energy content from the electric water heater was measured with the broken

dip tube. These reductions signify water heater performance degradation.

The reduction in energy content in the delivered hot water is a result

of mixing incoming cold water throughout the tank volume and delivering

tempered hot water. No thermal stratification was observed in the water

heater tests with the broken dip tube shown in Figure 14. The use of a good dip tube promotes stratification between the incoming cold water and

the delivered hot water. Mixing occurs primarily at the boundary of these

The stored hot water is essentially pushed, with little mixing, from the

tank bottom to the top through the hot water outlet.

With the assumption of a constant daily water usage (243 liters per

day) , the energy consumption of the water heater decreases because of the

broken dip tube. But hot water demands are not solely made on a constant

volume basis. Personal use demands showers, baths, and sink uses, are usually based on the delivered energy content of the water. Thus, under

the normal-use draw schedule, the broken dip tube test requires a 7 percent

increase in delivered energy content to satisfy the personal use (energy

content demands) for hot water. This is accomplished by either increasing

the volume of heated water delivered or increasing stored water

temperature; either action would increase energy consumption. For

constant-volume demands (clothes and automatic dish washing) the reduction

in energy content from the broken dip tube could affect the operational

performance of the clothes or dishwasher and produce unsatisfactory

results.

8. CONCLUSIONS

The aim of this project was to estimate the magnitude of the energyefficiency degradation of gas-fired water heaters caused by the

accumulation of mineral deposits, and the operating efficiency

improvements that can be made by proper adjustments or maintenance. The

typical used water heater tested at NBS contained a small amount of

sediment and possibly service related deterioration to the burner and

baffle. The average degradation in recovery efficiency performance (as

measured by water heater recovery efficiency) was 4 percentage points from

an assumed value, as new, of 69 percent.

The comparison of recovery efficiency results for used water heaters

tested before and after sediment removal indicated that in the amounts

36
present, loose mineral deposits (sediment) on the tank bottom have

relatively little effect on water heater recovery efficiency. Larger

sediment amounts and insulating layers of adherent scale on water heater

flue walls should produce significant decreases in water heater recovery

efficiency. These conclusions are in general agreement with the results of

simulated tests in Reference 29. No water heaters containing large

quantities of mineral deposits or adherent scale were received for testing.

In general, the operating efficiency of the used water heaters tested

did not suffer from the lack of proper burner maintenance either.

Adjustments to the burner that could improve the efficiency or performance

of a water heater were not dependent on degraded water heater performance

but were applicable to most existing gas-fired water heaters. Beneficial

burner adjustments were confined to lowered pilot rates which are now offered on current ’’energy efficient" water heater models. The effects of

baffling on water heater recovery efficiency were demonstrated and the

benefits to be derived from increased baffling appear to offer a significant energy savings at a relatively small price.

Three other forms of water heater degradation were specifically

identified: lifetime, safety, and performance degradation. Each of these

forms were evident in some of the used water heaters received for testing.

Performance is closely related to the operating efficiency of a water

heater and in preliminary tests the possibility of a performance decline in excess of 10 percent was demonstrated.

37
Appendix A

Calculation Procedure for Water Supply Saturation pH,

Saturation Index (Langelier) and Stability Index (Ryznar)

1. Saturation pH = pHs - , * (9.30 + A + B) - (C + D) U)

2. Saturation Index = I

g = pH^^- pH

g 3. Stability Index = 2pH

g - pH

(a) A,B,C, and D are based on water

supply characteristics. Values for

A,B,C, and D are obtained from the

appropriate tables.

(b) pH of water supply

A

Total Solids

in ppm

B

Temperature* in ileureva l-'nhrrnhelt UNITS

0 2 4 0 8 30 2 00 2 57 2.54 2 51 40 2.48 2.45 2 43 2 40 2 37 50 2 34 231 o O

2 CO 2.20 2 17 2 14 2 11 2 09 1 70 2 06 2.04 2 03 2.00 1 97 80 1 .95 1 .92 1 90 1 RS 1 SO

j 2

W 90 1.84 1 .82 1 80 1 78 1.70 j H

100 1.74 1.72 1.71 1.09 1 07 110 1 .05 1 04 1.02 1 00 1 5S

120 1.57 1.33 1.53 1.51 1 50 . 130 1.48 1 .40 1.44 1.43

I 1.41 140 1.40 1.38 1 37 1.35 1.34 150 1.32 1.31 1 29 1.28 1.27 100 1.26 1.24 1.23 1.22 1 21 170 1.19 1.1S 1.17 1 10

c

Calcium hardness expressed as ppm CaCOi

(For 3 to 209 rpm CaCOi. ure upper table) (For 210 to 990 ppm CaCOi. use lower table)

D

Alkalinity expressed as ppm CaCOi

(For 1 to 209 ppm CaCOi. use upper table) (For 2)0 to 990 ppra CaCOi. use lower table) UNITS 0123456789 0 0.08 0.20 0 30 0 38 0 43 0 51 0 56

10 0 00 0 01 0 08 0 72 0 75 0 78 0.81 0.S3 0.80 0 88 20 0.90 0.92 0.94 0 90 0 98 1 .00 1.02 1.03 1.C5 1 00 30 1 08 1.09 1.11 1.12 1.13 1.15 1.1C 1.17 1.18 1.19 40 1.20 1.21 1.23 1.24 1.25 1.26 1.20 1.27 1.28 1.29 50 1.30 131 1.32 1.33 1.34 1.34 1.35 1.30 1.37 1.37 00 1.38 1.39 1.39 1 .40 1.41 1.42 1.42 1.43 1.43 1.44 70 1.45 1.45 1.46 1.47 1.47 1.48 1.48 1.49 1.49 1.50 80 1.5'. 1.51 1.62 1.52 1.53 1.53 1.54 1.64 1.55 1.55 90 1.50 1.50 1.57 1 57 1.58 1.58 1.58 1.39 1 59 1.60 100 1.00 1.01 1 01 1.01 1.62 1.02 1 63 1.03 1 04 1 64

1 10 1.64 1.05 1 05 1 00 1 66 1 00 1 07 1.67 1 07 1 68

120 1.08 1.08 1.09 1 09 1.70 1 70 1 70 1.71 1.71 1.71 130 1.72 1.72 1.72 1.73 1.73 1 .73 1.74 1.74 1.74 1.75 140 1 75 1 .75 1 75 1 70 1 76 1 .70

. _ 1.77 1.77 1.77 1 78

150 1.78 1.78 1.78 1.79 1 .79 1.79 1.80 1.80 1.60 1.80 100 1.81 1.61 1.61 1 81 1.82 1 62 1 82 1.82 1.83 1.83 370 1 83 1.84 1 84 1.84 1.84 1 .85 1.85 1.85 1.85 1.86 180 1 80 1.80 1.80 1 .80 1.87 1.87 1.87 1.87 1.88 1.88 190 1.88 1.88 1 89 1.89 1.89 1.89 1.89 1.90 1.90 1.90 200 1.90 1.91 1 91 1.91 1.91 1.91 1.92 1.92 1.92 1.92

TENS

0 10 20 30 <0 50 00 70 80 90

200 1.92 1 94 1 96 1 98 2 W 2 02 2.03 2.05 2 00

C/5 a 3oo 2 08 2.09 2 1 1 2 i o 2.13 2.15 2.10 2.17 2.18 2.19

OS 4(JU Q

2 JO 2 21 2 23 2 21 2 25 2 20 2.20 2 27 2 28 2.29 Z 6<K) 2.30 2 31 2 32 2 33 2.34 2 31 2 35 2 30 2 37 2.37

55 WO 2 38 2 39 2 39 2 40 2.41 2 42 2 42 2 43 2 43 2 44 700 2 45 2 4 *» 2 40 2 47 2.47 2 18 2 48 2 19 2 49 2 50

[ 800 2 51 2 51 2 32 2 32 2.53 2.53 2 34 2 54 2.55 2 55 909 2.56 2 50 2 57 2 57 2 r, h 2 58 2.-3, 2 59 2 59 2 00

$
REFERENCES

1. Hoskins, Robert A. and Hirst, Eric, "Energy and Cost Analysis of

Residential Water Heaters," Oak Ridge National Laboratory,

0RNL/C0N-10, June, 1977.

2. Wan, C. A. and Pierson, R., "Test Procedures for Water Heaters,"

NBSIR, to be published.

3. American Gas Association Laboratories, "Fundamentals of Gas

Combustion," January, 1973.

4. U.S. Public Health Service Drinking Water Standards, 1962.

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ASCE - Journal of the Hydraulics Division, October, 1973.

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September, 1968.

8. Black and Veatch, Consulting Engineers, "Economic Effects of Mineral

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13. Langelier, W. F., "The Analytical Control of Anti-Corrosion Water

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14. Ryznar, J.W., "A New Index for Determining the Amount of Calcium

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15. Garaghty, J. J., et . al., "Water Atlas of the United States," Water

Information Center, Port Washington, New York, 1973.

39
16. Arthur D. Little, Inc., "Study of Energy Saving Options for Refrigerators

and Water Heaters," May, 1976.

17. Miller, P. D. , Stephan, E. F., Boyd, W. K., "Prevention of Corrosion

and Burnout of Electric - Water - Heater Tanks and Heating Elements,"

Battelle Memorial Institute, 1966.

18. Digurda, P., Rheem, Private Communication.

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21. Nordell, E., Water Treatment for Industrial and Other Uses,

Pheinhold Publishing Corporation, New York 1961.

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Paper 1812, 1964 .

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40
NBS-114A (REV. 7-73)

U.5. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO. NBSIR—78—1460

2. Gov’t Accession

No.

3. Recipient's Accession No.

4. TITLE AND SUBTITLE

The Degradation of Gas-Fired Water Heaters

5. Publication Date

6. Performing Organization Code

7. AUTHOR(S) George F> Sushinsky 8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/Worlc Unit No.

11. Contract/Grant No.

12. Sponsoring Organization Name and Complete Address (Street, City, State, ZIP)

Same as No. 9

13. Type of Report & Period Covered

Final

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.)

The energy efficiency degradation of gas-fired water heaters was measured in

laboratory tests of old water heaters collected from different sections of the

country. Three other forms of degradation (lifetime, safety, and performance

degradation) were also identified. The causes and potential effects of each

degraded condition were assessed through literature surveys. Supplementary

laboratory evaluations were conducted in the areas of energy efficiency and

performance degradation. Reductions in the recovery efficiency of water heaters

of 5 percentage points were measured, while simulated performance declines in excess of 20 percent were noted. Larger decreases in recovery efficiency are

expected for water heaters containing significant deposits of scale or sediment

.

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

)

Degradation; energy efficiency; mineral deposits; performance degradation;

test methods; water heaters (gas-fired)

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