NBS

PUBLICATIONS

NBS BUILDING SCIENCE SERIES 163

Potential Energy Savings in

Residential Oil-Fired Heating

TA ems in the U.S.

^135

,U53

iJo.163

293/1 ARTMENT OF COMMERCE • NATIONAL BUREAU OF STANDARDS

c. 2
/ he National Bureau of Standards' was established by an act of Congress on March 3, 1901. The

Bureau's overall goal is to strengthen and advance the nation's science and technology and facilitate their effective application for public benefit. To this end, the Bureau conducts research and provides: (1) a

basis for the nation's physical measurement system, (2) scientific and technological services for industry and

government, (3) a technical basis for equity in trade, and (4) technical services to promote public safety.

The Bureau's technical work is performed by the National Measurement Laboratory, the National

Engineering Laboratory, the Institute for Computer Sciences and Technology, and the Center for Materials

Science.

The National Measurement Laboratory

Provides the national system of physical and chemical measurement;

coordinates the system with measurement systems of other nations and

furnishes essentiaJ services leading to accurate and uniform physical and

chemical measurement throughout the Nation's scientific community, in- dustry, and commerce; provides advisory and research services to other Government agencies; conducts physical and chemical research; develops,

produces, and distributes Standard Reference 'Materials; and provides

calibration services. The Laboratory consists of the following centers:

• Basic Standards^

• Radiation Research

• Chemical Physics

• Analytical Chemistry

The National Engineering Laboratory

Applied Mathematics * Electronics and Electrical Engineering'

Manufacturing Engineering

Building Technology

Fire Research

Chemical Engineering'

and proposes new engineering practices; and develops and improves

mechanisms to transfer results of its research to the ultimate user. The

Laboratory consists of the following centers:

Provides technology and technical services to the public and private sectors to • address national needs and to solve national problems; conducts research in • engineering and applied science in support of these efforts; builds and maintains competence in the necessary disciplines required to carry out this • research and technical service; develops engineering data and measurement •

capabilities; provides engineering measurement traceability services; develops •

test methods and proposes engineering standards and code changes; develops •

The Institute for Computer Sciences and Technology

Conducts research and provides scientific and technical services to aid Federal agencies in the selection, acquisition, application, and use of computer technology to improve effectiveness and economy in Government

operations in accordance with Public Law 89-306 (40 U.S.C. 759), relevant Executive Orders, and other directives; carries out this mission by managing

the Federal Information Processing Standards Program, developing Federal ADP standards guidelines, and managing Federal participation in ADP

voluntary standardization activities; provides scientific and technological advisory services and assistance to Federal agencies; and provides the technical foundation for computer-related policies of the Federal Government. The Institute consists of the following centers:

Programming Science and

Technology

Computer Systems

Engineering

The Center for Materials Science

Conducts research and provides measurements, data, standards, reference

materials, quantitative understanding and other technical information fundamental to the processing, structure, properties and performance of materials; addresses the scientific basis for new advanced materials technologies; plans

research around cross-country scientific themes such as nondestructive

evaluation and phase diagram development; oversees Bureau-wide technical programs in nuclear reactor radiation research and nondestructive evaluation; and broadly disseminates generic technical information resulting from

its programs. The Center consists of the following Divisions:

Inorganic Materials Fracture and Deformation^

Polymers

Metallurgy Reactor Radiation

'Headquarters and Laboratories at Gaithersburg, MD, unless otherwise noted; mailing address

Gaithersburg, MD 20899. ^Some divisions within the center are located at Boulder, CO 80303.

^T nrprpH RmilHpr PO with <;nmp plpmpnf^ at riaithpr^hiirp MD
NBS BUILDING SCIENCE SERIES 163 "i^sSo^o^"

Potential Energy Savings in

Residential Oil-Fired Heating

Systems in the U.S.

Kelly, G.E., Didion, D.A.,

Quigley, D., and

Collins, B.

Center for Building Technology

National Engineering Laboratory

National Bureau of Standards

Gaithersburg, MD 20899

UBRAflY

, UC'6

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

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director

Issued December 1984
Library of Congress Catalog Card Number: 84-601145

National Bureau of Standards Building Science Series 163

Natl. Bur Stand. (U.S.), BIdg. Sci. Ser. 163, 58 pages (Dec. 1984)

CODEN: BSSNBV

U.S. GOVERNMENT PRINTING OFFICE

WASHINGTON: 1984

For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, DC 20402
ABSTRACT

Studies of the performance of residential oil-fired heating systems in the New

England area from 197A-1977 demonstrated that significant energy savings are achievable through better maintenance and simple system modifications. These

studies showed that annual tune-up of the furnace or boiler would Improve the

seasonal efficiency of most units, while considerable energy savings are possible

by reducing the firing rate of the burner. Reduction in nozzle size with

burner modification or with the installation of a new flame retention burner was found to reduce oil consumption substantially. In addition, more innovative

equipment modifications such as the use of stack dampers, sealed combustion

systems, and heat recovery devices also resulted in fuel savings, although to

a lesser extent. Both experimental field data and results from computer simulations

of furnace performance are presented.

Key words: Boiler; energy savings; firing rate; fuel efficiency; furnace;

nozzle size; oil-fired; residential heating; sealed combustion;

stack damper.

1

ill
TABLE OF CONTENTS

Page

ABSTRACT iii

LIST OF FIGURES vi

LIST OF TABLES vii

1. INTRODUCTION 1 1.1 Background 1 1.2 Scope 1

2. EFFICIENCY FACTORS IN RESIDENTIAL OIL-FIRED HEATING SYSTEMS 3

2.1 Overview 3

2.2 Determination of Steady-State and Seasonal Efficiency 3

3. EFFECTIVENESS OF TUNE-UPS ON THE PERFORMANCE OF OIL-FIRED FURNACES

AND BOILERS 9

3.1 Effect of Annual Tune-Ups on Steady-State Efficiency 9

3.1.1 Field Test Measurements and Tune-Up Procedures 9

3.1.2 Annual Tune-Up Test Results 11

3.2 Deterioration of Steady-State Efficiency Over a Series of

Heating Seasons 14

3.3 Variables Affecting Steady-State Efficiency 16

3.4 Conclusion 16

4. EFFECTIVENESS OF REDUCING FIRING RATES 17

4.1 The Problem of Oversized Heating Systems 17

4.2 Guidelines for Optimizing Nozzle Size Reductions 19

4.3 Fuel Savings Resulting from Combining Nozzle Size Reductions

with Burner Modifications 20

4.3.1 The New England Field Tests 20

4.3.2 Reduced Firing Rates with Burner Modifications 21

4.3.3 Reduced Firing Rates with New Burners 25

4.3.4 Tankless Coil Hot Water Systems 27

5. EFFECTIVENESS OF HEATING EQUIPMENT MODIFICATIONS 29

5.1 Suimnary of Field Tests 29

5.1.1 Objective and Scope of Tests 29

5.1.2 Description of Modifications 29

5.1.2.1 Stack Dampers 29

5.1.2.2 Sealed Combustion Systems 30

5.1.2.3 Heat Recovery Devices 31

5.1.3 Field Test Procedures 31

5.1.4 NBS-Developed Calculation Procedure 32

5.2 Effectiveness of Stack Dampers 33

5.3 Effectiveness of Sealed Combustion Systems 38

5.4 Effectiveness of Combined Stack Dampers and Sealed Combustion

Systems 40

5.5 Flue Gas Heat Reclaimers 41

iv
TABLE OF CONTENTS (Continued)

Page

6. CONCLUSIONS 42

6.1 Summary 42

6.2 Additional Research 43

7. REFERENCES 44

APPENDIX - Procedure for Optimizing Nozzle Sizes 46

V
I

I

I LIST OF FIGURES

Page

Figure 1. Schematic of furnace model 4

Figure 2. Temperature vs. time plots for a typical furnance 6

Figure 3. Typical smoke - CO2 characteristics for a residential oil

burner—with recommended air adjustment 10

Figure 4. Distribution of efficiency before tune-up 12

Figure 5. Distribution of efficiency after tune-up 13

Figure 6. Frequency distribution of percentage of overfired units 18

Figure 7. Minimum nozzle size 48

vi
LIST OF TABLES

Page

Table 1. Test Population Distribution for Field Test 9

Table 2. Summary of Efficiency Measurements 11

Table 3. Oil Burner Service lA

Table 4, Mix of Heating Systems 15

Table 5. Comparison of Serviced and Unserviced Units 15

Table 6. Type of Equipment in 1975-76 Test 20

Table 7. Effectiveness of Combustion Air Handling Equipment Modifications 22

Table 8. Change in Performance from Reduced Firing Rates and Burner

Modifications 24

Table 9. Change in Performance by Burner Type 25

Table 10. Change in Performance with New Burners 27

Table 11. Change in Performance of Hot Water Systems with the

Installation of Reserve Storage Tanks and Reduction in

Firing Rates 28

Table 12. Fuel Savings Resulting From the Installation of Motorized

Stack Dampers 34

Table 13. Fuel Savings as a Function of Equipment Type 35

Table 14. Installation and Operational Problems Associated with

Motorized Stack Dampers 37

Table 15. Summary of Fuel Savings for Sealed Combustion Systems 39

Table 16. Summary of Fuel Savings for Sealed Combustion Systems with

Stack Dampers 40

Table 17. Summary of Fuel Savings for Flue Gas Heat Reclaimers 41

vii

1. INTRODUCTION

1.1 BACKGROUND

As a result of the need for greater energy conservation in buildings generated

by the 1973 energy crisis, the Center for Building Technology (CBT) of the

National Bureau of Standards (NBS) conducted a series of studies on the performance of residential heating and cooling systems. This research included both

field studies of specific equipment modifications for improving performance

and mathematical modeling for simulating dynamic and seasonal performance.

The bulk of this NBS research was sponsored by the Department of Energy (DoE)

and its forerunners, the Federal Energy Office, the Federal Energy Agency, and

the Energy Research and Development Administration. This research formed the

part of the technical background and data base that was used by NBS to develop

the DoE test and rating procedures for residential heating and cooling equipment. These procedures were mandated in the appliance labeling, energy targets,

and minimum standards sections of the Energy Policy and Conservation Act (P.L.

94-163), the Energy Conservation and Production Act (P.L. 94-385), and the

National Energy Conservation Policy Act (P.L. 95-619).

1 .2 SCOPE

The present report summarizes the NBS studies of the performance of residential

oil-fired heating equipment. These studies, performed between 1974 and 1978,

focused on the energy performance of oil-fired furnaces and boilers used in

single family residences. They were concerned with a variety of measures for

improving the efficiency of these installations. Particular attention was paid

to the energy savings potential of annual maintenance, equipment modifications,

and the installation of add-on devices by qualified, trained personnel.

Work was conducted by a number of organizations under the direction of NBS.

These included the Walden Research Division of Abcor, Inc., Honeywell, Inc. and

Exxon Research and Engineering Company, The Walden Research Division performed

the series of field tests [1, 2]* on residential oil-fired systems in the New

England area during the winter heating seasons of 1974-75 and 1975-76. Field

tests on some new innovative energy saving devices [3] were also performed by

Walden during the 1976-77 heating season. The Honeywell Corporate Research

Center, using data gathered in the New England field tests, used their computer

model, HFLAME, to estimate seasonal efficiencies and potential energy savings

analytically [4, 5]. Exxon participated in laboratory studies of furnace

efficiencies under cyclic conditions [6]

In the following section, the operation of a furnace or boiler is discussed.

Both steady-state and seasonal efficiency are defined, along with some of the

factors affecting performance. In sections 3, 4, and 5, the results of field

tests of heating systems in New England with different modifications are presented. The modifications range from simple tune-ups to reductions in

* Numbers in brackets refer to references given in the reference section.

1
firing rate, to more innovative changes such as stack dampers and heat recovery

devices. In addition, field results are compared with data from a computer

simulation program modeling equipment performance. Conclusions are presented

in section 6, with results from the various modifications indicating the possibility of significant energy savings for oil-fired residential heating

equipment.

2
2. EFFICIENCY FACTORS IN RESIDENTIAL OIL-FIRED HEATING SYSTEMS

2.1 OVERVIEW

Subsequent sections of the present report document the results obtained from

certain adjustments and modifications to oil-fired residential heating equipment. These changes were designed to improve the steady-state efficiencies

and seasonal performance of the system. Both warm air and hot water systems were studied in a series of field tests. Modifications included burner adjustment and tune-up, reduction of firing rates by reducing nozzle size, reduction

and modification or replacement of burners, the installation of hot water

reserve storage tanks on tankless coil systems, and the use of stack dampers,

sealed combustion systems and heat recovery devices. Data on the resulting

changes in steady-state and seasonal efficiency are presented along with predicted data from a series of computer simulations of equipment performance.

However, before presenting the results from the various studies, certain

background information will be discussed in this section.

2.2 DETERMINATION OF STEADY-STATE AND SEASONAL EFFICIENCY

Because there exist a number of different furnace efficiency definitions, it

is useful to define the meaning of the terms "seasonal efficiency" and "steady

state efficiency" as they are used in this report. Seasonal efficiency is

taken to be the ratio of the total useful heat delivered to the building by the

heating system, as a result of the combustion process, to the total fuel energy

used, over a full heating season. Steady state efficiency, on the other hand,

is defined as the rate of energy input to the furnace by the fuel minus the

rate at which energy is lost up the flue, divided by the rate of fuel energy

input, under steady state operating conditions. The latter definition assumes

that the combustion process itself is 100 percent efficient and that heat

losses through the furnace jacket contribute useful heat. Because residential

heating equipment operates on a cyclic basis, seasonal efficiencies are usually

less than their steady state efficiencies. The losses associated with the

operation of a furnace are discussed in greater detail below.

Figure 1 presents a schematic of the major components and processes common to

most oil-fired systems. These form the basis for the NBS equipment performance

modeling work [7, 8] , and help to explain the operation of the furnace as described herein.

Several factors related to the design and operation of residential oil-fired

heating equipment limit any real system from operating at 100 percent efficiency. First, for complete combustion, each fuel molecule must be in close

proximity to air (oxygen) molecules. Although the typical oil burner finely

atomizes the fuel and uses a blower to bring in and mix the fuel and combustion

air, the combustion process is invariably less than complete, unless excess outside air is used. This excess combustion air must be heated to the flue

gas temperature level, resulting in efficiency loss.

Another factor resulting in diminished efficiency is the heat lost up the

chimney from the combustion by-products. Although this loss could be reduced

3
«UF»»LYAm

STACK GAS

0,COMBUSTION PRODUCT

(Of Droti Aff)

COMBUSTION AIR

RELIEF AIR J

BLOWER

THERMOSTAT

,b,HEAT EXCHANGER

- e, CIRCULATING AIR

I BURNER

I CONTROL FUEL

BLOWER

^— RETURN AIR

) BLOWER

'control

I

ROOM thermostat

Figure 1. Schematic of furnace model

4
considerably by cooling the gas to room temperature, two practical limitations

occur. First the use of combustion chambers at close-to-atmospheric pressure

levels requires a certain flue gas temperature level above room temperature to

exhaust the combustion products safely up the chimney. Secondly, certain

condensables in the combustion gases, if allowed to cool, will liquify,

creating severe corrosion problems.

In addition to combustion air and flue gas losses, there is usually an increase in building air infiltration due to the combustion air and the relief

air required to maintain a constant draft condition in the combustion chambers.

Neither this loss, nor the losses from the furnace jacket and distribution

systems, are usually considered in a steady-state efficiency rating, although

they are often considered in seasonal performance definitions of heating systems. However, the major factor contributing to reduced seasonal efficiency

is the cyclic nature of residential heating systems. Unlike more expensive

industrial equipment, residential systems do not modulate the fuel and air to

meet changing load demands. Most residential systems operate either full on or full off. When heat is called for, the burner comes on at its full firing

rate with combustion heat being transferred to the furnace mass itself until

steady state equilibrium temperatures are reached. Once combustion stops,

residual heat contained within the unit's mass continues to be transferred to

any draft air flowing through the furnace and up the stack. Such draft losses

can be reduced through the use of a power burner or automatic stack closure.

These losses also become smaller if the percentage of off time is decreased by

reducing the furnace firing rate to more closely match the heating load of the

building. The effects of such modifications are discussed in subsequent sections.

Figure 2 provides a profile of changes in a typical residential furnace temperature as a function of time. Four different operational periods are identified.

During the first period (burner-on/blower-of f )

, the unit's heat exchanger is

brought to a temperature level that will maintain a comfortable supply air

temperature. Although a lot of the residual heat in the heat exchanger is

recovered during the third period, the amount recovered usually does not completely

offset the heat loss during period 1. During the second period (burner and

blower both on) the blower transfers heat from the heat exchanger (which is

still being heated) to the building. During the third period, the burner is

shut off and the blower continues to distribute heated air to the building in an attempt to recover the residual heat of the unit's mass. The limit of this

recovery process is timed so that the temperature of the supply air (water)

does not result in uncomfortable space temperatures. Finally, both burner and

blower are turned off. During both the third and fourth periods, the heat

exchanger loses heat to the air that passes through the combustion chamber and

up the chimney. The losses during the third and fourth periods described

above tend to be larger if the heating unit is oversized. Since most residential

furnaces in the United States tend to be at least 100 percent oversized, a large potential for energy loss exists. To reduce this loss and achieve the

best seasonal efficiency for a particlar system, adjustments can be made to

the furnace firing rate to match its output to the heating load of the residence.

5
IDQCD

<

UJ

Q.

Scale

change

- Burner on, blower (fximp) off 2 - Burner on, blower (fxjmp) on 3 - Burner off, blower (pump) on 4 - Burner off, blower (pump) off

TIME

Figure 2. Temperature vs. time plots for a typical furnace

6
The heating load may be estimated using its K-factor, which is defined as the

number of degree days occuring in a time period divided by the total number of

gallons of oil consumed during the same period.

This K-factor provides a good approximation of the heating load of the residence

under various conditions of outdoor temperature, wind condition, humidity, solar

radiation and occupant habits. It also provides a good approximation of the

seasonal efficiency of the heating system when the entire season is the time

period used to determine the degree days and gallons used.

The winter K-factor can be used to calculate the minimum firing rate to minimize

furnace off-period losses as follows:

FR = "

24 X K

where FR is the firing rate of the furnace in gallons/hour and ATp is the

average indoor balance point temperature* minus the outdoor design

temperature.

This formula assumes that the furnace output at steady-state operation matches

the heating load of the residence at its greatest load (i.e., when the outdoor

temperature equals the outdoor design temperature)

.

The use of the winter K-factor, therefore, serves as a guide toward which

firing rates can be successively reduced while attempting to maintain satisfactory

steady-state operation. As firing rates are reduced, the furnace efficiency

should increase and the building load decrease slightly due to reduced infiltration

losses. Hence, a new value for the K-factor may emerge which can become the

basis for further iterations. The method for determining optimum firing rates,

and the effectiveness of firing rate reduction procedures are described in

subsequent sections of this report.

Several computer simulations currently exist for evaluating furnace seasonal

performance and the effect of various design changes on annual energy consumption [7, 8]. One of these is HFLAME [9], developed by Honeywell Inc. This

model accounts for heat loss during both the on-cycle and off-cycle mode and

provides a method for predicting seasonal efficiency. It can predict the

effects of excess air, flue gas temperature, off-cycle draft losses, and variations

in firing rate upon seasonal efficiency. Other programs, developed at NBS,

include DEPAB and DEPAF [7, 8], which simulate the operation of fossil fuel

fired boilers and warm air furnaces under cyclic conditions. These programs

provide a detailed time history of temperatures in the combustion chamber/

stack, the heat exchanger and the heat distribution medium (air or water).

These programs allow furnace efficiency to be calculated for different load and

weather conditions. Estimates of building loads may also be obtained by using

such load determination programs as NBSLD [11], DoE-2 [12], or BLAST [13].

* Residential balance points are most often assumed to be 65°F (18°C); however,

they can be considerably lower in well-insulated homes. See Petersen [10].

7
In the following sections, various modifications for improving furnace

efficiency are presented. It should be noted, however, that the result of any

energy saving modification is often specific to the installation and operating

conditions of the individual heating system. As a result, prediction of

specific energy use for one installation is somewhat risky.

8
3. EFFECTIVENESS OF TUNE-UPS ON THE PERFORMANCE OF OIL-FIRED FURNACES

AND BOILERS

3.1 EFFECT OF ANNUAL TUNE-UPS ON STEADY-STATE EFFICIENCY

Steady-state efficiency measurements were carried out on 429 oil-fired heating

systems in the New England area during the 1974-75 heating season. Interest in

the steady-state efficiency of installed heating systems was promoted by the

possibility that annual oil consumption in the U.S. could be reduced if heating

systems were well maintained and serviced properly on an annual basis.

The tests were carried out on a rather large sample of installed units with the

consent and cooperation of the homeowners. Most types of oil-fired heating

systems were included in the sample, with the actual testing conducted by local

heating system serice personnel and supervised by technical personnel of the

Walden Research Division of Abcor. The structure of the test program and

results are described below.

3.1.1 Field Test Measurements and Tune-Up Procedures

The sample of installed units consisted of systems that had not been tuned for

approximately 1 year. The mix of types of units selected for testing is shown

in table 1.

Table 1. Test Population Distribution for Field Test

System Type

Burner Type Warm Air Hot Water Steam

Conventional 64 86 49

Shell Head 8 18 16

Flame Retention 17 65 31

Low Pressure 7 31 14

Rotary 9 8 6

Sub-total 105 208 116

Total 429

The distribution of units selected was based on statistical requirements,

consideration of the population mix for the New England area, the availability

of willing participants, and the growing use of flame retention burners.

9
Steady-State measurements were made on each of the 429 units before tune-up.

These measurements were made by regular maintenance personnel from five oil

distributors In the area. Steady-state efficiency was determined from the

measurement of CO2 and net stack gas temperature using a Bacharach Flue Finder

efficiency chart. Following the Initial steady-state efficiency measurements,

the unit was adjusted and tuned to "best" operating condition by visual inspection of the burner flame and smoke readings. The following procedure was

used:

• disassemble burner and clean. Change nozzle assembly if worn

• change oil filter

• lubricate draft adjuster

• vacuum clean heat exchanger, combustion area and vent pipes

• seal air leaks

• adjust draft regulator

• adjust combustion air

• change air filter on warm air systems

In addition to the tests performed by the regular service personnel, a more

rigorous combustion air adjustment procedure was also performed on 25 units.

This procedure was designed to assist in adjusting the ratio of excess air to

obtain the highest steady state efficiency with an acceptable level of smoke.

This procedure requires development of a plot of smoke as a function of CO2 over a range of air settings as indicated in figure 3.

Ptreent COt •« Flu« Gas Figure 3. Typical smoke —CO2 characteristics for a residential oil

burner—with recommended air adjustment

The purpose of the smoke —CO2 plot is to locate the "knee" of the curve (see

figure 3) where the smoke number begins to rise sharply as the amount of excess

air to the burner is reduced. The procedure is to adjust the air supply to a point on the curve slightly below the knee to provide a tolerance against

10
possible shifts in the setting over time. The smoke—CO2 plot can be quite

effective in air adjustments provided that care is taken in obtaining the data

points, and that other adjustment procedures, such as elimination of air leaks,

have been carried out properly. The characteristic plot of smoke—CO2 does,

however, vary according to burner type, making the identification of the point

of the "knee" more difficult for some types of burners.

The results of carrying out this more rigorous combustion air adjustment

procedure were not conclusive because of the small number of units involved and

the difficulty experienced in obtaining sufficiently smooth plots to identify

the "knee" of the curve. However, on the 22 units studied, the average efficiency was increased 1.2 percent over that obtained by the simpler adjustment

procedure usually employed. The average smoke number was reduced from 1.0 to

3.0. The development of a continuous-reading CO2 device could facilitate

the development of a more useful CO2 smoke plot for field installations, and

would probably be cost-effective in view of the higher efficiencies obtainable.*

3.1.2 Annual Tune-Up Test Results

Figures 4 and 5 show the distribution of steady-state efficiencies before and

after tune-up, respectively, for the 429 units tested. The average steadystate efficiency before tune-up was 74.2 percent and 76.1 percent after. The

median efficiency before tune-up was 74.8 percent and 76.5 percent after tuneup. In examining these distributions, however, it should be noted that 79.2

percent of the units were more than 70 percent efficient after tune-up. This

indicates that some 40 units were brought up to a more reasonable level of

steady-state efficiency as a result of tune-ups. It should also be noted that

this summary data includes 14 units that were determined to be in need of

replacement and could not be properly tuned.

In table 2 below, a summary of the before and after measurements for the

steady-state efficiency calculation is shown.

Table 2. Summary of Efficiency Measurements

Before Tune-Up After Tune-Up

Number of Units 429 429

Percent CO2 8.2 8.3

Net Stack Temperature 521°F 482°F

Mean Steady-State Efficiency 74.2 76.1

Smoke Reading 1.9 0.9

* Since the completion of this study, a continuous reading O2 and temperature

instrument equipped with a microprocessor for computing CO2 and efficiency has

been introduced onto the market.

11
32.6

STEADY-STATE EFFICIENCY. %

Figure 4. Distribution of efficiency before tune-up

12
40

37.5

STEADY-STATE EFFICENCY, %

Figure 5. Distribution of efficiency after tune-up

13
The effect of an annual tune-up was to increase the average efficiency by about

two percentage points, corresponding to a relatively small increase in CO2 (0,1

percent) and small decrease in net stack temperature (39°F), as shown in table

2. The effect of reducing smoke number from 1,9 to 0,9, however, was quite

dramatic.

Three months after the tune-ups had been performed, the steady-state efficiency

of 183 of the original 429 units was again measured. The objective of this

measurement was to determine if there had been any degradation in performance

during this time period. The average efficiency of the 183 units immediately after

tune-up was 76.5 percent, and the average efficiency three months later was also found to be 76.5 percent, indicating no deterioration in efficiency over

a 3 month period. Although these results indicated that the units had maintained

their efficiency levels for 3 months, the test performed on the original 429

units which had not been tuned-up for a year, would tend to indicated that

there is likely to be some degradation in steady state performance over the

entire heating season.

It is interesting to examine, at this point, the percentage of units in different

regions which receive annual tune-ups. Table 3 presents the results of a summary of oil distributor service [1, 3],

Table 3. Oil Burner Service

Annual Overhaul

Service Contract

Annual Overhaul

No contract

No Annual

Overhaul

New England 37% 45% 18

Metro New York 54 21 25

Other Mid-Atlantic 32 40 28

South Atlantic 24 26 50

Midwest 27 26 47

West 17 21 62

3,2 DETERIORATION OF STEADY-STATE EFFICIENCY OVER A SERIES OF HEATING SEASONS

The field tests to determine efficiencies before and after tune-up on 429 units

resulted in a small average increase in steady-state efficiency for this sample.

However, most of the units tested were regularly maintained by the oil distributor servicemen. It is of interest to know how well steady-state efficiency

is maintained over several heating seasons. In other words, are regular tuneups important to the maintenance of good steady-state efficiencies? To determine the change of steady state efficiency with time, 57 units in the New

England area that had not been tuned-up in the previous 3 years were selected

for tests. The mix of heating systems selected is shown in table 4,

14
Table 4. Mix of Heating Systems

System Type

Burner Type Warm Air Hot Water Steam

Conventional 11 14 7

Shell Head 2 4 2

Flame Retention 3 4 4

Low Pressure 1 3 2

For each installation the following measurements were taken:

• CO2 in dry flue gas • O2

• Draft over the fire

• Smoke number

• Net stack temperature

• Nozzle firing rate

The steady-state efficiency was calculated from the CO2 concentration and the

net stack temperature.

The results of these efficiency tests were compared to the measurements taken

before and after tune

results are shown in

-up on the 429

table 5.

units in the 1974-75 field tests . The

Table 5. Comparison of Serviced and Unserviced Units

Annually Serviced Units

After Tune-Up Before Tune-Up Unserviced

Number of Units 429 429 57

CO2 percent 8.3 8.2 7.4

Net Stack Temp. 482°F 52rF 590''F

Steady-State Eff. 76.1 74.2 69.9

Smoke No. 0.9 1.9 3.3

Unfortunately time and money did not permit the tune-up of the 57 unserviced

units. However, from the types of units in this study, there is no reason to

believe that a tune-up would not bring their average steady state efficiency

15
up to the same level obtained after tune-up for the 429 units. Assuming this

is correct, the data in table 5 is an indication of the general deterioration

over time of all the measured parameters. This deterioration in performance

is believed to result from the following factors;

• soot accumulation on the heat exchanger inhibiting efficient heat

transfer

• carbonizing of the nozzle tips interfering with the atomization and

spray angle of the fuel

• dust accumulation on air fans and air inlet shutter altering the airfuel ratio.

3 .3 VARIABLES AFFECTING STEADY-STATE EFFICIENCY

Extensive statistical analyses were performed on the steady-state efficiency

data for the 429 units tested in an attempt to relate efficiencies to variables

in the test population. The most significant variable, was burner type which

explained 10.9 percent and 14.5 percent of the total variance in the steadystate efficiencies before and after tune-up, respectively. However, these

small numbers, when compared with the small differences in average efficiencies,

appear to have little practical value.

3.4 CONCLUSION

Regular servicing of oil-fired furnaces and boilers is essential to maintaining

them at a high level of performance. The results of the field studies cited in

sections 3.1 and 3.2 would tend to indicate that the average unit's steady state

performance deteriorated at a rate of approximately two percentage points a year. While some units deteriorated faster than others, there does not appear

to be any significant relationship between steady state efficiency (or change

in steady state efficiency as a result of tune-up) and any of the variables

typically used to describe a heating system (e.g., burner type, type of system,

nozzle size, age, etc.).

Based upon these results, it is recommended that annual efficiency tests be

carried out on all oil-fired residential heating systems. (This could be

combined with a safety evaluation to assure that the units have not developed

any potentially dangerous malfunctions.) A low steady state efficiency or a significant drop in steady state efficiency from previous values should be the

criteria that is employed to determine if a tune-up would be cost effective.

16
4. EFFECTIVENESS OF REDUCING FIRING RATES

4.1 THE PROBLEM OF OVERSIZED HEATING SYSTEMS

The magnitude of the problem of oversized heating systems was determined in the

New England field tests conducted during the 1975-76 heating season. For each

of the 429 units tested, the magnitude of oversizing was determined by the

following formulas:

Design nozzle size = seasonal efficiency x AT design x 1

steady state efficiency 24 hr/day K

%Oversized = ( actual nozzle size - i ) x ICQ

design nozzle size

where

the design nozzle size = nozzle firing rate (in gph) required to meet

the heating load of the house at the outdoor

design temperature

K = average winter K-factor in degree days per gallon determined from

the oil supplier's record

AT design* = (indoor temperature - outdoor design temperature)

seasonal efficiency = assumed value of 60 percent

steady-state efficiency = unit's measured steady-state efficiency

Based upon the above, it was found that of the 429 units tested, 416 or 97

percent** were oversized with respect to the design heating requirement of the

building and that the average oversizing was 168 percent. Figure 6 shows the

distribution of the 429 units according to the percentage of oversized units.

Statistical analysis of the data showed that:

• the larger the heating system, the more likely it will be oversized,

• hot water systems are more likely to be oversized than warm air systems,

but steam systems are more likely to be oversized than either of these.

• Oversizing appears to be an industry-wide phenomenon regardless of the

oil distributer.

* Note that this definition of AT design differs slightly from the definition

of ATp given previously.

** Actually, a more detailed look at some of the units which were supposedly

under-sized or properly-sized revealed that almost all of these units were really oversized and that the oil supplier had underestimated the K-factors

for these installations.

17
CO

ISHi

I-co

>-COo

z

p

<

m

X

LLo

50

45

40

35

30

25

20

15

10

5

0

13

46 47 46

41

43

35

32 32

20 20

17 16

12

9

50 100 150 200 250

PERCENT OVERFIRED

300 350

Figure 6. Frequency distribution of percentage of oversized units

18
Another study of 40 units, in which the oversizing was determined from measured

values of on-time, daily average outdoor temperature, and average indoor temperature, resulted in an average oversizing of 208 percent. When the oversizing

was calculated for these same units using the oil supplier's K-factors and the

so-called properly-sized or under-sized units were eliminated, the average calculated oversizing was 200 percent and the average measured oversizing (based

on actual on-time) was 218 percent. This indicates that given the correct Kfactor, the formulas presented above give reasonably good results for determining which units are oversized and by what percent they are oversized.

4.2 GUIDELINES FOR OPTIMIZING NOZZLE SIZE REDUCTIONS

While the above findings provide a measure of the magnitude of the problem of

oversizing, they do not provide any information on the degree of reduction in

oversizing which can realistically be achieved in the field or on the potential

energy savings of such reductions. While it might in theory be desirable to

adjust the firing rate on all field installations to make them properly sized

or just slightly over-sized, in practice a reduction in firing rate will usually

alter other design factors, such as air-fuel ratio or heat transfer of the heat

exchanger, which may be only partially correctable, or perhaps correctable at

only a prohibitive cost. This section deals with these aspects as they relate

to reductions in nozzle size, while section 4.3 addresses the benefits of

combining simple burner modifications with nozzle size reductions.

Initial attempts to reduce nozzle sizes on furnaces and boilers in the New

England field tests quickly demonstrated the interactive effects of various

furnace design factors on both steady-state and seasonal efficiency. Therefore, field tests were carried out during the 1974-75 heating season to develop

sound procedures (see appendix) for reducing nozzle firing rates in order to achieve

the best seasonal fuel savings considering the cost of modifications to the

heating system. The effect of nozzle size reductions on steady-state parameters

was observed in the steady-state data collected for 27 units before and after

nozzle size reductions were carried out. The average values before and after

were:

Net Stack Steady-State

% CO9 Temperature Smoke No. Efficiency

Before Nozzle

Reductions 8,2 533°F 0.8 73.6

After Nozzle

Reductions 7.5 472°F 1.0 75,2

The observed reduction in average net stack temperature is to be expected,

based on the reduction in heat flow rate through the combustion chamber. This

reduction in temperature is responsible for the average increase in steady-state

efficiency, in spite of the increase in excess air as shown by the CO2 readings,

A more detailed analysis of the steady-state data demonstrated the importance

of reducing excess air when nozzle size is reduced. Fuel savings for those

19
units where the percent CO2 was actually decreased amounted to 1.8 percent,

compared to 7.8 percent savings for those units where the percent CO2 was maintained at the same level or increased. Excess air, therefore, is one

of the major parameters which must be watched when nozzle air reductions are undertaken. Procedures for reducing firing rates must address the problem of

adjusting the equipment to minimize excess air, while at the same time, assuring that the combustion efficiency is not adversely affected by excessive

firing rate reductions which result in a mismatch between the burner flame

and the size and/or shape of the combustion chamber.

4.3 FUEL SAVINGS RESULTING FROM COMBINING NOZZLE SIZE REDUCTION WITH BURNER

MODIFICATIONS

4.3.1 The New England Field Tests

Extensive firing rate reductions were carried out on 36 overfired heating

systems in the New England area during the 1975-76 heating season. These

tests were an extension of the 1974-75 heating season tests to evaluate the

energy savings of various firing rate reduction procedures. The 1974-75 tests,

as discussed in the previous section, involved reducing the nozzle size and

adjusting excess air without making any modifications to the burner, the combustion

air handling equipment, or the combustion chamber. The objective of the

1975-76 heating season tests was to evaluate the fuel savings resulting from

the following modification procedures:

• nozzle size reduction accompanied by modifications to combustion air

handling equipment and/or the combustion chamber as necessary

• installation of new burners with reduced firing rate

• addition of domestic hot water reserve storage tanks plus reduced firing

rates on hot water heating systems employing tankless coils to supply

domestic hot water.

The mix of the 36 heating systems selected for these tests is shown in table 6.

Table 6. Type of Equipment in 1975-76 Test

Heat System Type

Burner Type Warm Air Hot Water

Conventional 8 12

Shell Type 1 2

Flame Retention 3 9

Low Pressure 0 1

The field measurements were made by Walden Corp. technicians, with local oil

burner servicemen performing the actual modifications to the equipment.

20
Steady-State and dynamic operating parameters were measured both before and

after the firing rate reductions and modifications were carried out.

The steady-state measurements included:

• Percent of CO2 in dry flue gas

• Net stack temperature

® Draft over the fire

® Smoke number

• Firing rate in gallons per hour from which steady-state efficiencies

The dynamic measurements included:

• Electrical usage of auxiliary equipment

• On and off-times

• Warm-up and cool-down flue gas temperature profiles

• Indoor temperature, 24 hour average

• Outdoor temperature, 24 hour average*

• Wind speed, 24 hour average*

® Solar radiation, daily average*.

The measured on-times and firing rate was used along with the outdoor

temperature data to calculate the K-factor before and after each modification.

The fuel savings resulting from each modification was then determined using:

In addition, under contract, Honeywell Inc. used their HFLAME (see section 3)

model to determine the estimated seasonnal efficiencies before and after a change. The results are described in the following sections.

4.3.2 Reduced Firing Rates with Burner Modifications

Firing rate reductions were carried out on 18 of the 36 units in the test

program. The study was performed in two phases. In the first phase, the

minimum firing rate that provided satisfactory combustion wihout modifying the

combustion air handling equipment was determined. In the second phase, the smallest

firing rate that provided satisfactory combustion with modified air handling

equipment was determined. These tests provided a comparison for evaluating the

effectiveness of air handling equipment modifications. The comparison is shown

in table 7, which shows the minimum firing rate achieved with and without air

handling equipment modifications.

* The outdoor temperature, wind speed, and solar radiation were measured at

several centrally located weather stations.

were calculated.

fuel savings = 100 ( K initial - K final

21
Table 7. Effectiveness of Combustion Air Handling Equipment Modifications

Minimum Nozzle Size Minimum Nozzle Size

System No. (without air Mod's) (with air Mod's)

4 1.20 gal/hr 1.00 gal/hr

5 1.10 0.75

7 1.10 0.85

8 — 0.85

11 1.10 0.75

15 1.00 0.85

19 1.75 1.35

20 1.10 1.00

21 1.10 0.85

22 1.20 1.00

23 0.90 0.65

24 — 0.85

25 1.20 0.85

29* 1.10 0.85

34 1.10 0.50

35 1 .00 0.60

37* 1.50 1.10

38 0.85 0.50

Average 1.14 0.84

* Combustion chamber liners were also installed on units 29 and 37 as a part

of the air handling equipment modification because both units could not

achieve the reduced firing rate criteria due to inadequate combustion chamber

design.

22
The nozzle size reductions in the first column amounted to an average 14.5

percent reduction in firing rate from the original nozzle size. The corre- sponding average reduction in firing rate with air handling equipment

modifications was 36 percent.

The combustion air handling equipment modifications were necessarily tailored to

the type of burner as follows:

Conventional High Pressure Gun Type

Installed flame retention end cones or available modernization kits to

improve the blast tube—air cone configuration.

Flame Retention Burners

Installed the appropriately sized end cone for the reduced nozzle size.

Shell Type Burners

Adjusted the primary air control ring which serves as a vacuum breaker

inside the cone.

Modification of the combustion air handling equipment allowed the percentage of excess air to be maintained or decreased as the firing rate was reduced. This

resulted in an increase in the steady-state efficiency, a longer burner on-time,

and an improved seasonal efficiency. The effect on these parameters is shown

in table 8.

As indicated in table 8, firing rate reductions with burner modifications

resulted in an average increase in the steady-state efficiencies of 10.7 percent. The average decrease in excess air was 1.4 percent, with a range of a 55.8 percent reduction to a 15.5 percent increase in excess air. The increase

in excess air occurred on unit number 35, which had a very high initial CO2

reading of 13 percent which produced excessive smoke (5 on the Bacharach smoke

scale). It was necessary to reduce the CO2 to 10 percent during the modification procedure to minimize this smoke problem.

The significant finding to note in table 8 is that fuel consumption was reduced

in all units. The fuel savings, as determined from the HFLAME model using the

dynamic test data as input, averaged 14.0 percent, which shows good agreement

with the 14.5 percent savings determined for the 10 day test period after

rates were reduced.

The relative change in seasonal fuel savings, steady-state efficiency, excess

air, and firing rate as a function of burner type is shown in table 9.

23
Table 8. Change in Performance from Reduced Firing Rates

and Burner Modifications

Unit No»

4

5

7

8

11

15

19

20

21

22

23

24

25

29

34

35

37

38

Steady-State

Eff. Increase %

8.6

11.4

7.0

15.8

9.6

2.9

0.9

3.4

10.0

4.3

19.1

27.2

5.3

0.6

17.0

7.9

21.9

19.2

Excess Air

Reduction %

0

24.3

13.6

23.2

11.9

0

(15.4

increase)

0

0

0

0

24.2

12.9

12.5

0

(15.5

decrease)

(32.9

increase)

55.8

Firing Rate

Reduction %

39.3

50.7

31.8

48.4

43.2

29.3

25.1

30.2

30.9

25.6

39.6

29.2

28.1

29.6

64.6

55.8

55.8

40.7

Fuel Savings %

10-day

Experiment

18.7

17.8

9.6

18.2

7.6

10.6

8.6

5.8

17.0

9.2

22.7

19.6

11.3

9.5

22.1

11.8

11.8

16.2

Predicted by

HFLAME

22.9

20.6

8.5

19.7

13.2

5.6

6.2

10.7

11.1

3.8

21.8

21.0

5.6

1.3

22.6

13.8

13.8

24.6

Average

Change 10.7 1.4 36.0 14.5 14.0

24
Table 9. Change in Performance by Burner Type

Burner

Type

No. of

Units

Conventional 10

Shell Head 1

Flame Retention 7

Steady-State

Eff» Increase

12.73;

2.9

8.9

Excess

Air

Decrease

9.6%

0

(17.3

increase)

Firing

Rate

Reduction

36.9%

29.3

41 .3

Fuel

Consumption

Decrease*

14.7%

5.6

14.2

Conventional burners showed the greatest increase in steady-state efficiency,

with an average reduction in fuel consumption of 14.7 percent. Although conven

tional burners are difficult to modify for improved burner air handling, their

relatively poorer condition and greater age offer significant potential for

improvement. Shell type burners offer limited possibility for air adjustment

(adjustment of the primary air control ring) and the one unit tested showed a fuel savings of only 5.6 percent. Flame retention burners facilitate relatively large reductions in firing rates due to the flexibility and ease in

modifying the air handling characteristics of these burners by simply changing

flame retention rings. The seven flame retention units tested showed an averag

fuel savings of 14.2 percent.

4.3.3 Reduced Firing Rates with New Burners

Installation of a new burner in a heating system is a major alteration which

costs considerably more than the modifications covered in the previous section.

The choice of the type of replacement burner involves consideration of not only

the size and range of the burner, but also the physical configuration of the

burner and the costs of mounting, rerouting electrical service, compliance with

fire codes, required modifications to the combustion chamber, etc. In practice

the decision by the homeowner to replace a bad burner is often based on economy

i.e., will the estimated fuel savings provide a reasonable payback period for

the cost of replacing the burner? In the tests described herein, the criteria

for selecting burners to be replaced were first developed. Then the new burner were installed and the firing rates reduced. Finally, the fuel savings was determined by comparing the fuel consumption during two ten day periods before

and after each burner replacement and by using the computer simulation model,

HFLAME. In this section, the criteria for burner replacement and subsequent

fuel savings are presented.

* Based on 10 day test period before and after burner modification.

25
The criteria for selecting burners for replacement were as follows:

• Low Combustion Efficiency

If the steady-state efficiency after adjustment and tune-up could not

be raised above 60 percent, the burner should probably be replaced.

Three units were selected on this basis.

o High Smoke Levels

If the steady-state efficiency after adjustment and tune-up is between

60 and 70 percent with a smoke number in excess of 3 on the Bacharach

scale, the burner should probably be replaced. Two units met this

criterion.

• Inability to Reduce Firing Rate

If the reduced firing rate procedure results in shifting to larger and

larger nozzle sizes until the original nozzle size was again reached,

the burner should probably be replaced. Five units were selected on

this basis.

After installation of a new burner, the procedures for calculating minimum

nozzle size and determining the minimum acceptable nozzle size based on CO2

level and steady-state efficiency were essentially the same as described in the

previous sections.

New burners were installed on 10 units and the steady-state and dynamic data

were measured as for the other firing rate reduction tests. Data for only seven of the units are presented here because the large distortions exhibited

in the data from three units resulted in unrealistic values for fuel consumption. The distortions in the results appeared to be due to weather factors

which could not be accounted for in either the manual or simulation model

(HFLAME) analytical procedures.

Table 10 shows the changes in steady-state parameters and fuel consumption for

the seven units.

As expected, all units showed an increase in steady-state efficiency and

reduction in excess air as the firing rates were reduced. Again, as in the

previous section, the fuel savings calculated by the HFLAME model using the

10-day dynamic measurements, corresponded quite closely to the fuel savings

calculated during the 10-day experimental run. The average firing rate reduction achievable was 42.8 percent and the average fuel savings measured was 29.2 percent, with a range of 44.8 to 14.2 percent. The fuel savings did not

appear to be dependent on the criteria used for deciding on burner replacement.

These results indicate that replacing bad burners while also reducing firing

rate offers significant potential for fuel savings.

26
Table 10. Change in Performance with New Burners

Fuel Savings %

Unit No.

Steady-State

Eff. Increase %

Excess Air

Reduction %

Firing Rate

Reduction %

10-day

Experiment

Predicted by

HFLAME

1 28.4 32.8 40.5 21 .6 43.1

2 54.5 66.7 44.9 38.1 36 .4

6 18.9 41 .2 42.7 28.7 31 .0

9 14.2 23.1 37.6 14.2 14.0

27 45.4 83.7 49.6 44.8 38.5

31 15.1 32.6 37 .7 18.3 23.7

36 24.2 83.7 46.9 38.5 25.9

Average 28.7 52.0 42.8 29 .2 30.4

4.3.4 Tankless Coll Hot Water Systems

The 1975-76 heating season field study also involved eight hot water systems

which provided domestic hot water by means of tankless coils located within

the heat exchanger of the furnace. Demand for domestic hot water caused the

burner to come on, irrespective of the demand for heat and prevented the firing

rate from being reduced by any significant amount. Reserve storage tanks were installed to satisfy the demand for hot water, while the firing rate of the system was reduced to more nearly match the heating load of the residence. The

change in performance of the eight boilers is shown in table 11.

Firing rate reductions averaging 33.6 percent were successfully carried out on all eight systems. It had been shown in previous field tests that firing rates

of at least 1.25 gallons per hour are necessary to provide enough hot water for

typical households with systems having tankless coils. The installation of the reserve hot water tanks permitted lowering of the minimum firing rate while

still providing sufficient hot water for a typical household. As noted from

table 11, the firing rate reductions for the eight systems ranged from 9.4 to

52.0 percent. The data demonstrate again, as in the previous firing rate reduction studies, that if excess air can be reduced with a consequent increase in

steady-state efficiency, then seasonal fuel savings will be realized. The fuel

savings measured during the tests averaged 13.4 percent, while that predicted

by HFLAME was 12.4 percent.

It should be noted that the fuel savings determined in these tests was for the

heating season only. Since domestic hot water is required year-round, it is

probable that reduced firing rates would also cause a reduction in fuel consumption during the summer months. This possibility was not, however, investigated

in the field program. Moreover, the effects of reducing the boiler water

27
I

Table 11. Change in

of Reserve

Performance of Hot

Storage Tanks and

Water Systems

Reduction in

with the Installation

Firing Rates

Unit No.

Steady-State

Eff. Increase %

Excess Air

Reduction %

Firing Rate

Reduction %

Fuel

Experiment

Savings %

HFLAME

10 1.7 0 9.4 7.5 3.9

12 8.2 33.8 31.8 6.5 14.6

13 8.2 0 40.2 6.4 18.2

14 3.2 34.4 33.1 41.0 6.1

16 9.2 0 52.0 1.1 16.7

17 12.9 13.6 28.3 10.4 16.2

26 12.6 15.2 42.7 34.2 21.7

30 0.2 79.5

(Increase)

31.4 0 1.4

Average 7.0 2.2 33.6 13.4 12.4

temperature, and the role of piping and tank insulation is critical and would

have to be carefully investigated in any future study to determine the effect

of this modification on summer fuel consumption.

While the Installation of reserve storage tanks accompanied by reduced firing

rates resulted in heating season fuel savings, the modification costs are con- siderably higher than for other modifications proposed. The higher costs and

the uncertainty of summer fuel savings currently leave these modifications in

question.

28
5. EFFECTIVENESS OF HEATING EQUIPMENT MODIFICATIONS

5.1 ADDITIONAL FIELD TESTS

5.1.1 Objective and Scope of Tests

A third field study was carried out on a mix of steam, hot water, and warm air

heating systems in the New England area during the 1976-77 heating system to

determine the potential fuel savings of several innovative technologies.

Among the new technologies investigated were:

• Stack dampers to close off the stack when the furnace is not firing and

thereby reduce the flow of warm air from the heat exchanger and draft

control device going up the stack during off-periods.

• Sealed combustion systems in which outside air is piped directly to

the furnace to provide air for combustion and draft control. This

incoming air may or may not be preheated by the exiting flue gases.

o Heat recovery devices to reclaim heat from the hot stack gases for

use in combustion air, or in direct heating of the residential space.

The three devices discussed above were studied in a variety of combinations.

The objective of the tests was to determine the seasonal fuel savings that

could be achieved by measuring fuel consumption before and after the modifications to the existing heating systems. A brief description of the innovative

devices tested and the test procedures employed are given below.

5.1.2 Description of Modifications

5.1.2.1 Stack Dampers

A stack damper is an automatically activated valve that can be readily installed

downstream from the draft control device on existing fossil fuel-fired heating

equipment. Its purpose is to reduce off-cycle convective flue loss and minimize

the contribution of chimney flow to building infiltration. Two types of electrically activated automatic stack dampers, having slightly different operating

modes, were evaluated in this study.

One of the models tested was spring-loaded in the open position and activated

to the closed position by de-energizing the burner controls. The unit used a 2.5 +_ 1 minute delay in closing the damper after burner shutdown to allow for

the evacuation of residual combustion products. When a call for heat occurred,

the gear motor was de-energized and the coiled spring drove the damper to the

open position. When the heat demand was satisfied, the burner controls were de-energized and the gear motor drove the damper to the closed position. If

power to the unit was disrupted for any reason, the damper would spring open.

This operation, when coupled with the burner operating switch, functioned as a fail-safe mechanism. A later modification, which was not included on the test

units, included optional 3/4" knockouts in the damper to help alleviate

potential odor problems.

29
The second type of automatic vent damper studied was a power-open/power close

device. It consisted of two primary components: the damper assembly and the

control box. The control box, which contained all of the necessary controls,

was mechanically connected to the cast aluminum casing and stainless steel

damper and shaft. The control assembly was activated when the burner controls were energized so that a high torque gear motor rotated the damper to a fully

open position. This caused a microswitch and relay to complete the burner circuit and allow the burner to fire. When the heat demand was satisfied, the

burner control was de-energized and the gear motor drove the damper plate to

the closed position, at which time the motor stopped. This unit incorporated a 15 second delay mechanism to allow for the evacuation of residual combustion

products. Unlike the first model, which completely covered the stack cross- sectional area (with the exception of the new knockouts), the second model

covered approximately 80 percent of the cross-sectional area thus allowing

continuous low flow exhaust of the flue products.

5.1.2.2 Sealed Combustion Systems

With the exception of the mobile home market, sealed combustion systems were

not, at the time of this study, in general use in the U.S. Nevertheless, such

systems offer the potential for reducing heating system losses. In sealed

combustion systems, outdoor air is piped directly to the furnace to provide

air for combustion and barometric draft control. By piping air directly from

outside the residence, two sources of potential heat loss are reduced. During

the on-period, the air infiltration into the residence, caused by replacing

the vented, heated flue gases, is reduced. During off-cycle, the convective

flow of air from inside the residence through the heat exchanger and draft

control device is eliminated. The extraction of heat from the warm heat

exchanger during the off-period may, however, be increased, since this heat

loss depends upon a difference in temperature and outdoor air is considerably

colder than inside air. In addition, the use of cold outdoor air for combustion

air reduces the overall efficiency of the combustion/heat exchanger process

during the on-period. Part of the purpose of this study was to bypass these

conflicting theories and actually measure the fuel savings from the installation

of several sealed combustion systems on existing oil-fired furnaces and boilers.

The sealed combustion systems employed in the program were designed and

fabricated by Walden personnel since no commercially available units could be

adapted to the unique configurations required at each residence. A total of

nine sealed combustion systems were installed, of which six incorporated a preheat device which transferred heat from the flue gases to the incoming combustion and draft control air by means of heat pipes. Outdoor air was passed

through a window pane via a smoke pipe to the barometric damper and burner. A

sheet metal Tee was used to bring the combustion air to a sealed metal box

surrounding the burner.

A pre-installation survey was required to measure the overall dimensions of the

burner, the size of a window, the distance from the window to the barometric

draft regulator, the distance from the barometric draft regulator to the burner,

and stack pipe diameter.

30
5.1.2.3 Heat Recovery Devices

Flue gas heat reclaimers recover waste heat from flue or stack gases through

the process of heat exchange. They can vary from simple air-to-air heat

exchangers to heat pipes, which use a vaporlzlng-condenslng fluid to transfer

heat from the flue to a supply air stream. The performance of three heat pipe

units and one alr-to-alr heat exchanger were analyzed In this study.

The heat pipe heat-recovery device Is designed with four or five heat pipes

which are Individually charged with a suitable transfer media and permanently

sealed. Heat from the flue gas evaporates the liquid in the heat pipes, and

the vapor flows to the other end of the pipe (room air or supply air), where

the lower temperature causes the vapor to condense. A wick transports the

fluid back to the evaporator end to complete the cycle. Since the method takes

advantage of the latent heat of vaporization, a relatively high rate of heat

transfer can be expected. For the units studied, the condenser end of the

pipes was located within a circular duct that housed a fan, which was activated

by a thermostat to move air over the heat transfer unit. The temperature sensor was located within the housing of the device so that the fan was controlled

by the temperature of the air after it was heated by the heat pipe heat

exchanger.

The air-to-air heat reclaimer was a homemade device designed for the residence

in which it was installed. It consisted of 3/4 inch electrical conduit, each

about 12" long, mounted in two flanges which were covered with shrouds. A fan

drew room air into the shroud and conduits, and then distributed the heated air

via ducts to the living space.

5.1.3 Field Test Procedures

Measurement of the steady-state operating parameters and dynamic flue gas

temperature rise and decay profiles were gathered on 21 selected residential

oil-fired heating installations. Fuel consumption and weather information was obtained for test periods, which were at least 10 days long, before and after

installation of the vent dampers. The rate of fuel consumed by each residence

was monitored in the following manner:

1) The oil flow rate to the nozzle tip was determined at each installation

by connecting an oil-filled graduated cylinder to the burner pump inlet

and measuring the oil flow for a limited time period. A two minute

start-up was provided prior to measurement to allow for stabilization

of oil flow rates.

2) The on-off cycling rate was monitored for each 10 day period with a voltage

recorder connected across the power supply to the burner. The strip chart

records were later digitized to obtain the dally burner operating time and

the number of burner operating cycles.

3) Indoor house temperature was monitored with circular temperature recorders

to note any disturbances to the normal routine and to provide daily average

indoor temperatures.

31
4) Outdoor weather data (daily temperature, wind speed, and insolation) were obtained throughout the measurement period at three meterological stations

located within the test region.

These data were then used to calculate daily K-factors for each 24-hour period

using the equation:

= (65°- average outdoor temp, in 24-hour period) x 60 min/hr

(total burner on-time in minutes in 24-hour period) x nozzle flow rate in gal/hr

The average K-f actor for each test period was then determined. Days which were overtly nonrepresentative of the average conditions existing during a test

period were excluded. The determination of the days to be excluded was based upon

records kept by the homeowner, meterological data and indoor temperature measurements. Days were excluded only when it was obvious that something extraordinary had happened (e.g., a homeowner went on vacation and lowered his

thermostat setting).

The experimental fuel savings attributable to each modification was then

determined using the formula:

% fuel savings =

where Kj^ and K2 are the average K-factor for the test periods before and after

a modification, respectively.

5.1.4 NBS-Developed Calculation Procedure

The use of the above procedure for determining the fuel savings resulting from

a furnace or boiler modification depends upon the existence of similar heating

loads and weather conditions during the before and after test periods. In order

to remove these effects and to generalize the results to weather conditions and

installation practices which are more typical of the nation as a whole, some of

the field results were also analyzed using procedures recommended by the

National Bureau of Standards for determining the seasonal performance of

residential central furnaces and boilers [14, 15].

The above mentioned procedures formed the basis for the test procedures published

by the Department of Energy in the Federal Register, Vol. 43, No. 91, May 10,

1978. These are currently used by manufacturers of residential furnaces and

boilers to test and rate their appliances. The test procedures require carrying out the following four tasks: 1) measuring the flue gas temperature and

CO2 concentration during steady-state operation, 2) obtaining data on the shape

of the flue gas temperature-vs-time curves as the unit cools down and warms up

from steady-state conditions, 3) assigning appropriate values to various factors

which describe the off-period air flow rates through the flue and stack, and

4) carrying out a step-by-step calculation procedure to determine the various

on-period and off-period losses and seasonal efficiency of a furnace or boiler.

32
The information for tasks 1) and 2) was measured during the field study, while

the factors assigned in task 3) were the values (recommended in reference 2)

for units equipped with power burners, barometric draft control devices, and

installed with or without automatic vent dampers. The part-load efficiency of

all the units was calculated for the average weather and oversize load conditions which existed during the test period. These results were then used to

predict the energy savings resulting from the installation of automatic stack

dampers and sealed combustion systems, which were then compared with the measured energy savings. In addition, the energy savings for these two devices

for conditions corresponding to an average national climate was also determined,

based upon the assumption that each furnace or boiler was oversized by 70

percent at an average outdoor design temperature of 5°F (-15°C).

To predict the heat reclaimed by the heat recovery devices and the percent

increase in seasonal efficiency attributable to these devices, a simulation

model was developed and employed by Walden [3]. The model used the results of

tests performed on each unit, together with weather information, to predict the

heat reclaimed over the entire heating season. Although the values used for

the initial seasonal efficiencies were approximate, the percent increase in

seasonal efficiency attributable to the heat reclaimer was relatively

insensitive to the exact value used,

5.2 EFFECTIVENESS OF STACK DAMPERS

As a result of the installation of 21 automatic vent dampers, the average

experimental fuel savings during the test period attributable to these devices

was found to be 6.5 percent. The predicted fuel savings during the same period

was 6.2 percent. The predicted fuel utilization efficiency averaged 69.9 percent in the test period prior to the modification and 74.4 percent in the test

period with the vent damper functioning. Table 12 provides a summary of the

individual fuel utilization efficiencies and the fuel savings based on both the

experimental determination and the NBS calculation procedure. Excluding unit

14, which had a wide variation in average outdoor temperature between the before

and after test periods, a regression analysis of the paired data (experimental

vs. predicted model results) yields a correlation coefficient of 0.862.

Since the predicted and measured fuel savings during the test periods were in

such good agreement, the calculation procedure was used to find the expected

annual fuel savings for an average U.S. climate. An average annual fuel

savings of 8.2 percent was calculated based upon the assumption that all units were 70 percent oversized.

As shown in table 13a, installations with the power-open/ power-close dampers

had average measured and predicted fuel savings for the test periods of 6.1 and

5.3 percent, respectively, whereas installations with the spring-loaded damper

test had average measured and predicted fuel savings during the test period of

7.7 and 9.1 percent, respectively. The average seasonal fuel savings associated

with the installation of the power-open/ power-close dampers and the spring

loaded dampers were predicted to be 7.5 and 10.5 percent, respectively, when

based on an average U.S. climate and a 70 percent oversizing factor.

33
Table 12. Fuel Savings Resulting from the Installation of Motorized Stack Dampers

Seasonal Fuel Predicted

Predicted Fuel Utilization Seasonal

Utilization Fuel Savings Experimentally Efficiency Fuel Savings

Efficiency for Prediction for Determined for Average for Average

Unit Test Period^ (%) Test Period! (%) Fuel Savings (%) U.S. Climate2 (%) U.S. Climate^ (%)

With With

As Stack As Stack

Found Damper Found Damper

1 65.2 75.4 13.5 10.0 67.9 74.8 9.2

2 72.4 77 .0 6.0 7 .8 72 .

1

76 .5 5.8

3 64.2 69.7 7 .9 5.3 64.5 69.2 6.8

4 55.6 62.6 11 .2 12.5 53.9 64.0 15.8

5 70.3 73.5 4.4 2.2 67 .4 74 .5 9.5

6 63.7 67.2 5 .2 4 .6 63.6 67.9 6.3

7 62.0 67.6 8.3 8.6 60.6 68.2 11.1

8 69 .3 71.5 3.1 5.7 65 .6 70.6 7.1

9 61 .4 63.7 3.6 5.6 58.1 63.8 8.9

10 75.1 77.0 2.5 3.5 73.7 77.8 5.3

11 70.7 72.9 3.0 3.4 68 .3 76.6 10.8

12 75.9 78.7 3 .6 3 .5 77.0 82.8 7 .0

14 75.4 77.1 2.2^ 8.93 75.8 81 .0 6.4

15 63.2 70 .8 10.7 8 .6 60.7 70 .2 13.5

16 82.2 83.7 1 .8 2.4 83.1 86.7 4.1

17 80.4 81.2 1.0 5.3 78.3 83.3 6.0

18 66.3 73.7 10.0 9.5 65.8 73.9 11.0

20 59.7 68.3 12 .6 11.2 62.9 69.7 9 .8

21 79.8 82.1 2.8 3.2 78.5 83.9 6.4

22 81 .6 85.7 4.8 6.2 82.2 86.2 4.6

23 73.0 82.4 11.4 8.1 75.6 81.6 7.4

Avg. 69.9 74.4 6.2 6.5 69.3 75.4 8.2

Predicted by the NBS calculation procedure using average measured values of outdoor temperature,

indoor temperature, and on-and off-cycle times for test periods.

Predicted by the NBS calculation procedure using an average U.S. climate and assuming that all

units were oversized by 70 percent at an outdoor design temperature of 5'*F (-15°C).

For this unit the average outdoor temperatures during the before and after test periods were considerably different. This tends to explain the large discrepancy between measured and

predicted fuel savings.

34
Table 13. Fuel Savings as a Function of Equipment Type

13a. Fuel Savings as a Function of Damper Type

Number

Damper Type of Units

Fuel Savings for

Test Periods (%)

Experimental NBS

Data Procedure

Predicted

Seasonal Fuel

Savings for Average

U.S. Climatel(%)

Power open/power close 16

Spring Loaded 5 6.1 5.37.7 9.1

7.5

10.5

13b. Fuel Saving

Number

System Type of Units

!;s as a Function of System Type

Fuel Savings for

Test Periods (%)

Experimental NBS

Data Procedure

Predicted

Seasonal Fuel

Savings for Average

U.S. Climatel(%)

Steam 6

Forced Hot Water 9

Forced Warm Air 7

8.9 8.7

5.9 6.8

4.72 2.72

10.3

8.0

6.5

13c. Fuel Savings

Number

Burner Type of Units

5 as a Function of Burner Type

Fuel Savings for

Test Periods (%)

Experimental NBS

Data Procedure

Predicted

Seasonal Fuel

Savings for Average

U.S. Climatel(%)

Flame Retention 8

Conventional 13

6.5 6.8

6.5 5.8

7.5

8.7

Predicted by tbe NBS calculation procedure using an average U.S. climate and assuming

tbat all units were oversized by 70 percent at an outdoor design temperature of 5°F

(-15°C).

Excluding unit 14, tbe average experimental and predicted fuel savings for forced warm

air systems during the test period were 4.0 and 2.8 percent, respectively.

35
The slightly lower fuel savings associated with the power-open/ power-close

damper could be due to longer off-cycle convective losses, since the damper

plate did not completely cover the stack area. The spring loaded units,

operating with a post-purge period to evacuate combustion products, employed a damper plate that effectively covered the stack area and thus eliminated most

off-cycle convective losses. However, odors caused by unburned hydrocarbons

might be more likely to occur with this latter type of automatic damper. Perhaps as a result of this, the spring-loaded dampers are now being produced with

knockout holes in the damper plate to eliminate odors.

Similarly, it was found that the fuel savings also varied as a function of the

heating plant configuration, as shown in table 13b. The average measured and

predicted fuel savings resulting from the installation of automatic vent dampers

was highest for steam boilers, somewhat lower for forced hot water boilers, and

lowest for warm air furnaces. Warm air furnaces operate with a low, purgeable

thermal mass so that off-cycle heat transfer from the heat exchanger is smaller

and more rapid. Boilers, however, function with a large stored thermal mass,

so that off-cycle heat transfer is continuous and more substantial.

It was thought that the burner type might affect the fuel savings potential of

automatic vent dampers; however, this was not evident from the results of this

field study (see table 13c). The average measured fuel savings resulting from

the installation of automatic vent dampers on units with flame retention burners

and units with conventional burners was the same, 6.5 percent. It was expected

that automatic vent dampers might produce greater fuel savings in heating plants

with conventional burners than in heating plants with flame retention burners.

This expectation was based upon the belief that the combustion head on a flame

retention burner might tend to choke the air stream at the air tube outlet,

thereby reducing the off-cycle convective flue flow. However from the results

of this study alone, it is not clear whether other factors such as stack height,

boiler/furnace configuration, heating plant type, or other unmeasured parameters

may have played a more significant role in the determination of relative fuel

savings which could overwhelm the effect of burner type.

Information was also obtained from this field test on problems associated with

the installation and operation of automatic vent dampers on oil-fired heating

equipment. It was found that the proper installation of these devices is critical to the long-term, maintenance-free, and safe operation. Old or partially

deteriorated flue pipes cannot support the additional weight of the damper

assembly, and should be replaced with new flue pipe, securely fastened with

sheet metal screws and firmly supported with wire or perforated metal strapping

ceiling loops. Under cyclic operation, the flue pipe and damper assembly were

found to resettle due to contraction and expansion which caused a shifting of

the damper plate alignment. If, during the installation, the flue pipe and

damper assembly were not securely supported, the likelihood of "no heat" calls

was significantly increased. During the field study, six service calls were

required to release damper plates that hung up on the flue pipe. Table 14

summarizes the operational problems encountered in this study that were associated with the automatic stack dampers. These were all the result of

inadequate installation procedures.

36
Unit

1

Table

Odor problems

Installation and Operational Problem Associated

with Motorized Stack Dampers

Yes - severe

Yes - slight

Yes - slight

Yes - moderate

No

No

Other Problems

Yes - smoke pipe collapsed as a result of weight of stack

damper.

Yes - insulation on stack damper motor control leads melted and burned out damper transformer

No

Yes - control relay field, damper plate hung up on flue pipe

No

Yes - damper plate hung up on fire pipe

Yes - damper plate hung up on flue pipe.

Comments

Supported flue from ceiling, strengthened flue pipe with

sheet metal screws. Continued

to operate damper after test.

Drilled holes and cut ends of damper plate, dropped baro- metric damper below flue pipe, installed solenoid on oil line. Disconnected damper after test due to odor problem

Disconnected damper after test due to odor problem

Continued to operate damper

after test

Disconnected damper after test due to odor problem

Continued to operate damper

after test

Continued to operate damper

after test

Smoke pipe strengthened with

sheet metal screws and sup- ported flue from celling. Continued to operate damper

after test

Yes - moderate

12

14

Yes - severe

Yes - slight

Yes - very slight

Yes - very slight

Yes - damper plate hung up on flue pipe

Yes - damper plate hung up on flue pipe

Installed solenoid in oil

line. Disconnected damper

after test due Co odor problem

Continued to operate damper

after test

Continued to operate damper

after test

Disconnected damper after

test due to odor problem

Dropped barometric damper, sealed flue pipe and leaks. Disconnected damper after

test due to odor problem

Continued to operate damper after test

Continued to operate damper

after test

17 No Continued to operate damper

after test

Yes - moderate

Yes - moderate.

Disconnected damper after

test due to odor problem

Installed solenoid on oil line , sealed smoke pipe

.

Disconnected damper due to odor problem, test discontinued

Yes - damper plate hung up on flue pipe and casting

Continued to operate

damper after test

Disconnected damper

after test at owner's

request

Continued to operate

damper after test

Continued to operate

damper after test

37
In addition to problems associated with the installation of automatic vent

dampers, certain operational concerns developed during the program. Two

electrical failures occurred; one resulting from motor control leads shorting

out, which in turn burned out the damper transformer, and one failure of the

control relay. But more significantly, following installation of the stack

dampers, 11 residences experienced some level of odor ranging from very slight

traces to severe, noxious odors. Ultimately, eight out of the 23 stack dampers

initially installed were disconnected or removed due to odor problems which

could not be eliminated and two of these eight disconnections resulted in

incompleted tests.

It is believed that the odor is caused by oil in the nozzle and jet tube

expanding from the heat of the combustion chamber after burner shut-down. The

oil then drips out of the nozzle and into the hot chamber, where it vaporizes

and produces unburned hydrocarbons. Since the draft has been significantly

reduced or entirely removed by the motorized stack damper, the natural escape

route up the chimney is closed off. The unburnt hydrocarbons then escape out

of any hole, especially the draft regulator.*

A portable hydrocarbon analyzer was employed in the field to ascertain the

particular locations in the heating system where leaks occurred. The primary

sources of leaks were the barometric damper, the connection between the flue

pipe and boiler/furnace, and any obvious holes or loose seams. Several

attempts were made to eliminate or at least reduce the odor. The first procedure entailed patching all visible leaks with furnace cement and asbestos rope.

Partial success was encountered with this procedure. The second method was to

modify the draft regulator positioning by adding a 2-foot extension and droping the regulator below the flue pipe. No change was noticeable from this

alteration. Finally, solenoid valves were installed on the oil line to interrupt the oil flow to the nozzle when power to the burner ceased. Again, this was not overly successful.

5.3 EFFECTIVENESS OF SEALED COMBUSTION SYSTEMS

The experimental field data and NBS predicted values for the fuel savings

resulting from the installation of nine sealed combustion systems showed poor

correlation. The results are presented in table 15. Unit No. 7 was excluded

from the average because of the large unaccountable discrepancy between

predicted and experimental data.

Extreme variations in the estimated seasonal fuel savings were generally

obtained for both the predicted and experimentally determined fuel savings.

These discrepancies resulted from unique characteristics inherent in each

calculation procedure. In the case of the experimental data, if similar test

parameters (in particular, outdoor temperature and indoor temperature) were maintained during the before and after test periods and if these parameters

* Since the completion of this study, it has been common practice to install

solenoid valves in the fuel line to the burner, with the installation of the

stack damper, to immediately stop the fuel flow when the damper closes.

38
Table 15. Summary of Fuel Savings for Sealed Combustion Systems

Unit

Preheat

Unit

Fuel Savings

PtpHi pt'pH fni" Test Period

\ la )

Experimentally

Hp f" p T*Tn "f npH

Fuel Savings

2 Yes -1 1 s

A No -1 fS

5 10 7 1 4

*7 Yes -11.5 30 .6

8 Yes 5 6 9 4

9 No 1.9 11.7

14 No 5.4 11.0

16 Yes 4.3 4.5

17 Yes 6.1 -9.6

Average 4.6 1.8

* Not included in average

were typical of winter conditions, then the experimentally determined fuel

savings based upon the before and after measured K - factors tend to provide a good approximation of seasonal fuel savings. This required that similar heating

loads be experienced during the two test periods. In the NBS tests, however,

outdoor temperature variations of 20°F or more occurred for the two test periods.

Hence, the fuel savings predictions based on the measured K-factors may really

reflect significant differences in seasonal efficiency of the furnaces or boilers under different heating loads and not the effect of installing a sealed

combustion system.

In addition, the large variations shown between the experimental fuel savings

and the NBS model predictions may be due to the off-cycle air flow rates.

Tracer gas measurements on two sealed combustion systems showed flue and stack

volumetric flow rates vastly different from those for units without sealed com- bustion. Thus, the validity of the air-flow rate factors used in the NBS prediction procedure may be questionable for sealed combustion systems. For these

reasons, little confidence can be placed on the data in table 15 predicting

fuel savings attributable to sealed combustion systems. Further field and

laboratory testing of these types of systems should be carried out.

39
Table 16. Summary of Fuel Savings for Sealed Combustion Systems and

Stack Dampers

Unit

Preheat

Unit

Fuel Savings

Predicted for

Test Period

(%)

Experimentally

Determined

Fuel Savings

(%)

2 Yes 11 .3 -10.2

4 No 12.0 13.0

5 Yes 12.6 2.2

7 Yes 10.9 8.6

8 Yes 10 .1 12.8

9 No 7.8 12.2

14 No 6.6 20.2

16 Yes 6.2 4.6

17 Yes 7.1 6.6

Average 9.4 7 .8

5.4 EFFECTIVENESS OF COMBINED STACK DAMPERS AND SEALED COMBUSTION SYSTEMS

As shovm in table 16 , the measured and predicted average fuel savings resulting

from the use of sealed combustion systems and stack dampers were found to be

7.8 percent and 9.4 percent, respectively.

While these average savings are in fair agreement and appear reasonable, it is

likely that this is due to the large savings resulting from the use of stack

dampers. The same problems that arose with the determination of seasonal fuel

savings attributable to sealed combustion systems alone also appeared to exist

for the data on the combined effect of stack dampers and sealed combustion systems. The experimental data were obtained during test periods for which large

differences in temperature occurred. Tracer gas measurements also indicated

that the off-cycle flow factors for the type of system studied were not in

agreement with the NBS factors. Again, it is concluded that there is considerable

uncertainty regarding the applicability of the inverse K-factor comparison

method of calculating seasonal fuel savings for this set of data because of

the weather variations encountered during the test periods in question.

40
Table 17. Summary of Fuel Savings for Flue Gas Heat Reclaimers

Relative Change in

Seasonal Efficiency

Flue Temperature % Based on Based on Average Heating

TTn-i 1- Qt p aAfj—^t at p ° V WV c 1 o X ^ tz U 6 bins Dcaboii icuipc r a L ur e I jJ

I 1 n s

5 620 85 6.5 6.6

7 740 275 6.7 6.6

17 455 5 2.7 3.4

Average 6.6 6.7

5.5 FLUE GAS HEAT RECLAIMERS

The estimated seasonal fuel savings from the installation of four flue gas heat

reclaimers are shown in table 17. Unit 3 was the air-to-air heat exchanger,

while the others used heat pipes to recover heat from the flue gases.

The calculated seasonal efficiency increase, resulting from the installation of

the four heat recovery devices, averaged 6.6 percent, with a range of 2.7 to

10.5 percent. Using the average existing efficiency for units 3, 5, 7, and 17

of 69.2 percent, the efficiency increase would correspond to an average fuel

savings of approximately 8.7 percent. The results reported in the table also

indicate that minimal difference results from calculating the efficiency

improvement by using six temperature bins as opposed to using the average

heating season temperature.

It should be pointed out that the installation (unit 17) that yielded the lowest

efficiency increase (only 2.7 percent) also had the lowest initial steady-state

flue temperature. Since this unit was not wasting as much heat up the stack as the others, it would be expected that the heat recovered by the heat reclaimer

would be less.

It appears that heat reclaimers can recover significant quantities of heat when

the steady-state flue temperature significantly exceeds some minimum value

(approximately 400°F). Heating systems that are running efficiently initially

(i.e., with low flue temperatures) are not likely to incur significant fuel

savings by the addition of such devices. On the other hand, inefficient units

with high flue temperatures may benefit substantially.

41
6. CONCLUSIONS

6.1 SUMMARY

Field studies of the performance of oil-fired residential heating equipment

during New England winters demonstrated the feasibility of equipment modifications for reducing fuel consumption. A number of different types of modifications were made and the resulting improvement in both equipment efficiency

and fuel use was determined.

Annual tune-ups were shown to increase steady-state efficiency of oil-fired

heating systems (measured by determining the amount of CO2 and the net stack

gas temperature) by about 2 percent. Although improvements in efficiency

levels were demonstrated to last for at least three months, other data

indicated general deterioration in performance over longer periods of time,

A more serious problem, in terras of the amount of fuel used, is that of

oversizing. Measurements of heating systems taken during the winter of 1975-

1976 indicated that at least 97 percent of the units were oversized by an average

of 168 percent. To reduce the problem of oversized units, procedures for optimizing (reducing) nozzle size were developed and implemented. In a second phase,

reductions in firing rate were combined with modification of the air handling

equipment of the burners. This change resulted in a 14 percent average reduction in fuel use, depending on the type of burner modified. In some cases the

burner was in such poor shape that it was replaced, resulting in an average

fuel savings of 29 percent when combined with the reduction in firing rate.

Use of reserve storage tanks on hot water systems using tankless coils also

resulted in fuel savings when combined with reduced firing rate. The observed

improvements in fuel consumption for the different modifications were in good

agreement with the computer model calculations, thus providing some predictive

validity for the simulation.

Finally, the fuel savings potential of several innovative heating equipment

modifications was examined during the 1976-1977 heating season. These included

stack dampers, sealed combustion systems, and heat recovery devices. Of the

three, the stack damper offered the best potential fuel savings of about 6 to

8 percent, although some problems of electrical failure and noxious odors

developed. Data from the sealed combustion systems were inconclusive, while

the heat recovery devices appeared to be most effective for heating systems

which were not running efficiently.

The data obtained in the course of field tests on residential oil-fired heating

equipment over three New England winters indicated that modifications to this

equipment can result in substantial improvements in equipment efficiency and

reductions in fuel use. In addition to regular tune-ups and maintenance, reduction of firing rate through optimizing nozzle size and modifying the burner

offers the greatest likelihood of reducing energy consumption. Furthermore,

these equipment modifications can be made by local oil-company service personnel. Data obtained in these tests were also verified by computer simulation

of equipment performance, demonstrating the value of simulations for predicting

fuel savings nationally for a variety of equipment modifications.

42
6.2 ADDITIONAL RESEARCH

An obvious omission from the studies reported here is the type of furnace or boiler that is designed to cool the flue gas below its condensation temperature

before leaving the heat exchanger to reclaim the latent and sensible heat.

Although such equipment was not available at the time these studies were con- ducted, prototype models for gas-fired furnaces have since been evaluated by

NBS [16]. The test procedures developed for DOE have been revised to include

condensing units [17]. Because such units have seasonal efficiencies which are very similar to their steady-state efficiency, and which are on the order of

90 percent or more, the modifications and devices reported herein would not

result in the same savings and might not even be mechanically feasible.

The cost-effectiveness of the various modifications was deliberately omitted

because of the rapidly changing nature of fuel and equipment costs. A case study by NBS provides some calculations of the effects of equipment

modifications on life-cycle operating costs [18], however.

In addition, since these field studies were done, NBS has conducted additional

research on the effect of various design options on the performance of heating

equipment through a mixture of laboratory, field, and computer modeling research.

Nevertheless, the data presented in the present report clearly demonstrate the

effectiveness of annual maintenance and firing rate reductions, relatively

simple modifications which can be made by local oil-service personnel, in

reducing annual fuel consumption.

43
7. REFERENCES

1. Katzman, L. and D'Agostino, R. , "A Study to Evaluate the Effect of

Performing Various Energy Saving Procedures on Residential Oil Burner

Installation In the New England Area and to Gather Information on the

Steady-State and Dynamic Performance of These Installations", DoC

Contract No. 5-35781, September 1975.

2. Katzman, L. and Weltzman, D., "A Study to Evaluate the Effect of

Reducing Firing Rates on Residential Oil Burner Installations", DoC

Contract No. 6-35738, July 1976.

3. Katzman, L. and Monat, J., "Study to Evaluate the Energy Efficiency

Improvement of Residential Heating Equipment Modifications", DoC

Contract NO. 7-35747, May 1978.

4. Bonne, U. , Johnson, A. E., Glatzel, J., Torborg, R. , "Analysis of

New England Oil Burner Data Effect of Reducing Excess Firing Rate on Seasonal Efficiency." Contract No. NBS-514736, August 29, 1975.

5. Bonne, U. and Glatzel, J., "Analysis of Boston Oil Burner Data, Phase II",

Final Report, P.O. No. 26148.

6. Pepper, M. and Turne, D. , "Test Methods to Evaluate Annual Operating

Costs of Oil-Flred Heating Units", EXXON Research and Engineering Co.,

DoC Contract No. 6.35839.

7. Chi, J. S. W. , "Computer Simulation of Fossil-Fuel-Flred Hydronic Boilers,"

Second NBS/ASHRAE HVAC Equipment Conference, Purdue University, Lafayette,

Ind., April 1976.

8. Chi, J., "DEPAF - A Computer Model for Design and Performance Analysis of

Furnaces", AICHE - ASME Heat Transfer Conference, Salt Lake City, Utah,

ASME Paper NO. 77-HT-ll, August 1977.

9. Bonne, U. and Johnson, A. E., "Thermal Efficiency in Non-Modulating

Combustion Systems," First NBS/ASHRAE HVAC Equipment Conference, Purdue

University, Lafayette, Ind., October 1974.

10. Petersen, S. R., Economics and Energy Conservation in the Design of New

Single Family Housing, NBS, NBSIR 81-2380, August 1981.

11. Kusuda, T., NBSLD, Computer Program for Heating and Cooling Loads in

Buildings, NBSIR 74-574, 11-74.

12. DoE-2 User's Guide, Version 2, Lawrence Berkely Laboratory Report LBL-8698

,

May 1980.

13. Hlttle, D. C, The Building Loads Analysis and System Thermodynamics (BLAST)

Program, Version 2.0; User-Manual , Tech. Rep. E-153, Construction Engineering

Research Laboratory, 1979.

44
14. Kelly, G. E,, Chi, J., and Kuklewicz, M. , "Recommended Testing and

Calculation Procedure for Determining the Seasonal Performance of

Residential Central Furnaces and Boilers," NBS, NBSIR 78-1543, October

1978.

15. Chi, J., and Kelly, G. E., "A Method for Estimating the Seasonal

Performance of Residential Gas and Oil-Fired Heating Systems," ASHRAE

Transactions, Vol. 84, Part 1, 1978.

16. Kelly, G. E. and Kuklewicz, M. E., Laboratory Study of a Gas-Fired

Condensing Boiler, NBS, NBSIR 80-2094, November 1980.

17. Kelly, G. E. and Kuklewicz, M. E., Recommended Testing and Calculation

Procedures for Estimating the Seasonal Performance of Residential

Condensing Furnaces and Boilers, NBS, NBSIR 80-2110, April 1981.

18. Petersen, S. R. and Kelly, G. E., An Economic Analysis of Efficiency

Improvements to Residential Gas- and Oil-Fired Central Heating Equipment,

NBS, NBSIR 80-2079, July 1980.

19. ASHRAE Handbook of Fundamentals, 1972.

20. Exxon's "Guide for Optimizing Firing Rates."

21. Letter from Mr. Lone W. Nelson, Staff Engineer, Honeywell, Inc. to

Mr. Mickey Horn, California Energy Commersion, dated October 1978

amplifying data presented at 5 October 1978 Workshop on Furnace Oversizing.

22. Locklin, D. and Barrett, "Guidelines for Residential Oil-Burner

Adjustments", EPA Report No. EPA-6001 2-75-069a , October 1975.

45
Appendix - Procedures for Optimizing Nozzle Sizes

The following procedures for reducing nozzle sizes in oversized forced warm air

or forced hot water heating systems were developed from the test results and

experience gained in the New England field test program, (These procedures are

not recommended for use on steam heating systems).

Step 1

Repair and Tune-Up the Heating System

The heating system should be thoroughly checked and repaired before optimizing

the nozzle size. All air leaks into the combustion chamber should be sealed

and the oil burner given a regular tune-up. Optimizing the nozzle size should

be done in addition to regular servicing, not as a substitute for regular

servicing.

Step 2

Measure the Steady-State Efficiency and Smoke Concentration

Steady-state efficiency should be determined by measuring flue gas temperature,

the percentage of CO2 in the flue gas, and the smoke concentration (smoke num- ber on a Bacharach Smoke Scale of 0 through 9). It is usually necessary to

wait at least 15 minutes after start-up for a unit to reach a steady-state

operating condition. Units should operate with steady-state efficiencies at or above 75 percent. If the steady-state efficiency is less, or the smoke number

is greater than y/2. Step //I has not been satisfactorily carried out, or the

burner or heat exchanger needs replacement.

Step 3

Determine First Trial Nozzle Size

Using the local outdoor design temperature for the area^ and the winter Kf actor for the residence^ (degree days per gallon), determine the "minimum

nozzle size" by using either:

]J If this is not known, refer to chapter 33 of the ASHRAE Handbook of

Fundamentals [19]. Use the 97.5 percent values for the nearest weather

station listed.

2J The winter K-factor should be the average value derived over one or more

complete heating seasons. The K-factor for a residence is defined as the

number of degree days occurring in a time period divided by the total

number of gallons of oil used during the same period to maintain a house

at its normal thermostat setting.

46
(1) the graph displayed in figure 7

(2) a calculator such as in [20] or

(3) the formula:

minimum nozzle size = (65 - Tp)

(K-factor)(24)

where Ty) is the local outdoor design temperature in °F and the K-factor is in

degree days per gallon of oil. Thermostat setback is encouraged as an additional energy conservation measure. If the owner plans to practice thermostat

setback, insure adequate indoor temperature recovery after setback by increasing

the minimum nozzle size found above by adding a value in gallons per hour

equal to the product of the heated house floor area in square feet and the

pickup capacity factor (PCF) divided by 105,000 Btu/gallonl, where PCF is given

by the following table [21]:

The minimum nozzle size selected should be at least:

0.5 gph for warm air systems;

0.65 gph for hot water systems not supplying domestic hot water;

0.85 gph for hot water systems with aquaboosters; or 1.20 gph for hot water systems using tankless coils without a storage tank.

The first trial nozzle should be selected to give the same spray pattern and

angle as the nozzle presently installed in the unit and should never be larger

than the present nozzle.

J_/ Based upon approximatey 140,000 Btu's per gallon of fuel oil and on assumed

steady state efficiency of 75 percent.

2J Based upon 10°F thermostat setback and 2 hour pickup time as given in

Outdoor Design Temperature, °F

Pickup Capacity Factor^

Btu/hour-sq-foot floor area

40

30

20

10

0

-10

-20

9.5

13.0

14.9

15.8

17.0

17.7

18.8

[21].

47
I

K-FACTOR FOR THE RESIDENCE

IN DEGREE DAYS PER GALLON

Figure 7. Minimum nozzle size

48
Step 4

Install Trial Nozzle and Nfake Required Adjustments

Install the trial nozzle and see if the flame fits the combustion chamber. If

it does not, a nozzle with a different spray pattern and angle may be needed.

Using a smoke measuring device, adjust the oil burner to the "best" operating

condition using either the "eyeball" inspection approach or the procedure

outlined in reference [22]. This "best" condition will generally correspond

to the smallest opening in the air shutter (least amount of excess air) which

will allow the burner to operate with an oil-free (non-yellowed) smoke spot

having a smoke number of //I or less on the Bacharach Smoke Scale. Check the

draft and readjust the draft regulator if necessary. The fire should be

uniformly distributed in the combustion chamber and must not touch any metal

surfaces. There should be no delayed ignition, visible flame instability or pulsation noise.

Step 5

Remeasure the Percentage of CO? and the Flue Gas Temperature

The percentage of CO2 and the flue gas temperature should be remeasured. The

percentage of CO2 in the flue gas should be equal to or higher than the reading

obtained with the original nozzle. As a general rule, the final CO2 reading

should not be allowed to fall below the reading obtained with the original

nozzle by more than 0.2 percentage points for each 10 percent reduction in

firing rate.

In addition, the smoke number must be less than or equal to #1 on the Bacharach

Smoke Scale. The- temperature of the combustion gases before entering the draft

regulator should be above 370°F in order to avoid the possibility of corrosion.

Satisfying the above conditions should result in a steady-state efficiency not

significantly lower than with the original nozzle. As a check, recalculate the new steady-state efficiency and compare it with the original. If the new efficiency is not below the original efficiency by more than 2 or 3 percentage

points, the new nozzle is the proper one and you may skip step #6. If this is

not the case, one or more additional nozzles should be tried. This is

discussed in step #6.

Step 6

Trying Additional Nozzles

If the conditions discussed in step #5 have not been meet, repeat steps #4

and #5 using other nozzle sizes. It is not possible to give a hard and fast

rule for selecting the successive nozzles. It may be desirable to try one or more additional nozzles of the same size but with different spray patterns or angles or it may be necessary to go to a larger size nozzle. The only generalization which can be made is that if after installing a trial nozzle, the

flame pattern looks good but the excess air has to be increased considerably

49
in order to keep the smoke equal to or below #1 on the Bacharach Smoke Scale,

the next nozzle size should probably be halfway between the newly installed

size and the original nozzle size. Experience will be the best guide in

selecting the successive trial nozzles.

Step 7

Record Results

Carefully record the following information and leave a copy with the owner or place a tag on the equipment:

• date of servicing

• the original nozzle size and type

© the final nozzle size, type, and spray angle

» the number and size of each nozzle tried (include the final nozzle in

this count)

© the initial and final CO2 , stack temperature, and smoke readings.

This information will be helpful for future servicing of the unit and could be

invaluable in trouble-shooting any problems which might arise immediately after

a reduction in firing rate.

Step 8

Repeat Nozzle Optimization Procedure

If the procedure in step //3 resulted in the proper nozzle size in step #5, the

nozzle size should be re-evaluated after one heating season. The reason for

this is that the K-factor used in step #3 to calculate the minimum nozzle size

is dependent upon the seasonal efficiency of the heating system. Reducing the

firing rate should increase the seasonal efficiency, leading to a larger

K-factor, This new K-factor should then be used to find a new minimum nozzle

size.

50
NBS-n4A (REV. 2-ec) U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET (See instructions)

1. PUBLICATION OR

REPORT NO,

NBS/BSS-163

2. Performing Organ. Report No. 3. Publication Date December 1984

4. TITLE AND SUBTITLE

POTENTIAL ENERGY SAVINGS IN RESIDENTIAL OIL-FIRED HEATING SYSTEMS IN THE U.S.

5. AUTHOR(S)

George Kelly, David Didion, Donald Quigley, Belinda Collins

6. PERFORMING ORGANIZATION (If joint or other than NBS. see /n struct/on s) 7. Contract/Grant No. National Bureau of Standards

U.S. Department of Commerce 8. Type of Report & Period Covered

Gaithersourg, MD 20399 Final

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

U.S. Department of Energy

1000 Independence Avenue, SW

Washington, DC 20585

10. SUPPLEMENTARY NOTES

Library of Congress Catalog Card Number: 84-601145

[^J Document describes a computer program; SF-185, FlPS Software Summary, is attached.

11. ABSTRACT (A 200-word or less factual sumnriary of most significant information . if document includes a si gnifi cant bibliography or literature survey, mention it here)

Recent studies of the performance of residential oil-fired heating systems in

the New England area from 1974-1977 demonstrated that significant energy savings

are achievable through better maintenance and simple system modifications. These

studies showed that annual tune-up of the furnace or boiler would improve the

seasonal efficiency of most units, while considerable energy savings are possible

by reducing the firing rate of the burner. Reduction in nozzle size with burner

modification or with the installation of a new flame retention burner was found to

reduce oil consumption substantially. In addition, more innovative equipment

modifications such as the use of stack dampers, sealed combustion systems, and heat

recovery devices also resulted in fuel savings, although to a lesser extent. Both

experimental field data and results from computer simulations of furnace performance

are presented.

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

boiler; energy savings; firing rate; fuel efficiency; furnace; nozzle size;

oil-fired; residential heating; sealed combustion; stack damper.

13. AVAILABILITY

Unl imited

I I For Official Distribution. Do Not Release to NTIS

^

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

20402.

' Order From National Technical Information Service (NTIS), Springfield, VA. 22161

14. NO. OF

PRINTED PAGES

58

15. Price

1 USCOMM-DC 6043-P80

Technical Publications

Periodicals

Journal of Research—The Journal of Research of the National Bureau of Standards reports NBS research and development in those disciplines of the physical and engineering sciences in which the Bureau is active. These include physics, chemistry, engineering, mathematics, and computer sciences. Papers cover a broad

range of subjects, with major emphasis on measurement methodology and the basic technology underlying

standardization. Also included from time to time are survey articles on topics closely related to the Bureau's

technical and scientific programs. As a special service to subscribers each issue contains complete citations to

all recent Bureau publications in both NBS and non-NBS media. Issued six times a year.

Nonperiodicals

Monographs—Major contributions to the technical literature on various subjects related to the Bureau's scientific and technical activities. Handbooks—Recommended codes of engineering and industrial practice (including safety codes) developed in cooperation with interested industries, professional organizations, and regulatory bodies.

Special Publications—Include proceedings of conferences sponsored by NBS, NBS annual reports, and other

special publications appropriate to this grouping such as wall charts, pocket cards, and bibliographies.

Applied Mathematics Series—Mathematical tables, manuals, and studies of special interest to physicists,

engineers, chemists, biologists, mathematicians, computer programmers, and others engaged in scientific and

technical work.

National Standard Reference Data Series—Provides quantitative data on the physical and chemical properties

of materials, compiled from the world's literature and critically evaluated. Developed under a worldwide pro- gram coordinated by NBS under the authority of the National Standard Data Act (Public Law 90-396).

NOTE: The Journal of Physical and Chemical Reference Data (JPCRD) is published quarterly for NBS by

the American Chemical Society (ACS) and the American Institute of Physics (AIP). Subscriptions, reprints,

and supplements are available from ACS, 1155 Sixteenth St., NW, Washington, DC 20056.

Building Science Series—Disseminates technical information developed at the Bureau on building materials,

components, systems, and whole structures. The series presents research results, test methods, and perfor- mance criteria related to the structural and environmental functions and the durability and safety

characteristics of building elements and systems.

Technical Notes—Studies or reports which are complete in themselves but restrictive in their treatment of a

subject. Analogous to monographs but not so comprehensive in scope or definitive in treatment of the subject

area. Often serve as a vehicle for final reports of work performed at NBS under the sponsorship of other government agencies.

Voluntary Product Standards—Developed under procedures published by the Department of Commerce in Part 10, Title 15, of the Code of Federal Regulations. The standards establish nationally recognized re- quirements for products, and provide all concerned interests with a basis for common understanding of the

characteristics of the products. NBS administers this program as a supplement to the activities of the private

sector standardizing organizations.

Consumer Information Series—Practical information, based on NBS research and experience, covering areas of interest to the consumer. Easily understandable language and illustrations provide useful background

knowledge for shopping in today's technological marketplace.

Order the above NBS publications from: Superintendent of Documents, Government Printing Office,

Washington, DC 20402. Order the following NBS publications—FIPS and NBSIR 's—from the National Technical Information Service, Springfield, VA 22161.

Fedei-al Information Processing Standards Publications (FIPS PUB)—Publications in this series collectively constitute the Federal Information Processing Standards Register. The Register serves as the official source of

information in the Federal Government regarding standards issued by NBS pursuant to the Federal Property

and Administrative Services Act of 1949 as amended. Public Law 89-306 (79 Stat. 1127), and as implemented

by Executive Order 1 1717 (38 FR 12315, dated May 11, 1973) and Part 6 of Title 15 CFR (Code of Federal

Regulations).

NBS Interagency Reports (NBSIR)—A special series of interim or final reports on work performed by NBS

for outside sponsors (both government and non-government). In general, initial distribution is handled by the sponsor; public distribution is by the National Technical Information Service, Springfield, VA 22161, in paper copy or microfiche form.
U.S. Department of Commerce

National Bureau of Standards

Gaithersburg, MD 20899

Official Business

Penalty for Private Use $300