Reference

NBS

PUBLICATIONS

NAT'L INST. OF STAND & TECH

AlllDb D3mb2

NBSIR 85-3225

Laboratory Study of Gas- Fueled

Condensing Furnaces

Esher R. Kweller

Robert A. Wise

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Building Technology

Building Equipment Division

Gaithersburg, MD 20899

July 1985

•QC'

100

.1156

85-3225

1985

Prepared for LS. Department of Energy

of Building Energy Research and Development

iuilding Equipment Division

/ashington, DC 20585

V

NBSIR 85-3225

t i * LABORATORY STUDY OF GAS-FUELED

CONDENSING FURNACES

"yATIONAl' BUREAU

OF STANDARDS

LIBRARY

Qc

10

p

F'' A.

/y - '

Esher R. Kweller

Robert A. Wise

U S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Building Technology

Building Equipment Division

Gaithersburg, MD 20899

July 1985

Prepared for

U.S. Department of Energy

Office of Building Energy Research and Development

Building Equipment Division

Washington, DC 20585

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

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director
DISCLTUiMER

Any coiranercial equipment, instruments, or controls identified in this

report does not iitply recommendation or endorsement by the National Bureau

of Standards nor does it inply that the mterials or equipment identified

are necessarily the best available for the purpose.
TABLE OP CONTENTS

Page

1. Purpose 1

2. Objectives 1

3. Background 1

3.1 Issues Concerning New Test Procedures for Condensing

Furnace 3

3.1.1 Cyclic Testing for Condensate Collection 3

3.1.2 Steady State Test for Condensate Collection 4

3.2 Ainbient Test Room Conditions of Temperature and Relative

Humidity 4

4. Test Equipment and Procedures 6

4.1 Test Furnaces....... 6

4.2 Laboratory Test Eguipnent 6

4.3 Test Procedures 9

4.3.1 Condensate Collection 9

4.3.2 Control of Combustion Air Taiperature and Humidity

5. Test Results 11

5.1 Cyclic Testing 11

5.1.1 High Efficiency.. 11

5.1.2 Borderline Condensing Furnaces 12

5. 1.2.1 Variability of Condensate Collected 12

5. 1.2. 2 Effect of the Nuirber of Test Cycles 12

5.1.3 Discussion of Test Results 17

5.2 Effect of Variable Burner On/Oif Time 19

5.2.1 High Efficioicy Condensing Furnaces 19

5.2.2 Borderline Condensing Furnaces 22

5.3 Investigations of Steady State Testing 24

5.4 Effects of Ambioit Test Room Conditions 26

.1 Effects of Room Air Toiperature 26

.2 Test Room Humidity Effects 29

.3 Discussion of Test Results With Controlled Roan

Air Tenperature and Humidity 31

6.0 Summary 33

References
Appendix A - DOE Test Procedure for Direct Measurement of Condensate

Appendix B - Alternative Approaches to Bating Condensate Collection

Bate for Borderline Condensing Furnaces

Appendix C - Sanple Calculations

i^pendlx D - Weather Data Used for Bin Analysis of Condensate

Collection
1 . PURPOSE

This report is intended to serve as background information concerning

revisions made to test procedure for condensing furnaces and published by

the Department of Energy (DOE) as rules and regulations in the Federal

Register on March 28, 1984 [1]*.

2. OBJECTIVE

The objective of this study was to determine if the direct measurement

method of condensate collection that was developed during testing of a

condensing boiler would be adequate for direct measurement of the

condensate from forced warm air condensing furnaces.

Another objective of these tests was to quantify the effects of varying

test room ambient temperatures and relative humidity on the rate of

condensate collected with condensing furnaces,

3. BACKGROUND

The Department of Energy (DOE) test procedure for furnaces and vented

heating equipment was issued as a final rule in the Federal Register (FR)

on May 10, 1978 [2], The procedure was based on the NBS Report [3]

"Recommended Testing and Calculation Procedures for Determining the

Seasonal Performance of Residential Central Furnaces and Boilers." Tliose

procedures contained no provisions for testing furnaces that improve

efficiency by recovering some of the latoit heat by condensing the water

vapor in the flue gas. Heating units that incorporate such aiergy savings

means are known as condensing furnaces or boilers. In order to evaluate

and advertise the advantages of condensing units, industry requested that

provisions be made in the test procedure to accommodate such tests. In

* Nuirbers in brackets pertain to referoices listed on pages 35-36.

1
response, DOE published amendments to the test procedure on August 12, 1980

In the Federal Register (with correction notice on September 19, 1980) [4]

to Include special procedures for condensing furnaces and boilers, l^e FR

amendments were based on the recommendations In the NBS Report,

"Recommended Testing and Calculation Procedures for Estimating the Seasonal

Performance of Residential Condensing Furnaces and Boilers," [5] The

method consisted first of a mathematical analysis of the test results to

assure that condensation would occur and then a calculation of the amount

of condensation to be expected. The resultant heat recovery of the latent

heat of vaporization of water formed was then used to reduce the heat

losses and increase the seasonal efficioicy rating of the unit tested. The

method proposed by NBS in 1980 and adopted by DOE was based on analysis and

evaluation by NBS of the only unit commercially available at the time and

that was a condensing boiler [6]. The analytical method for determining

the credit due to recovery of latent heat is described in the NBS

Background report [3].

Following publication of the DOE test procedures [4] in 1980, a

manufacturer of condoising boilers (Hydrotherm) petitioned DOE for waivers

from those test procedures. The petition claimed that the prescribed

method either understated the amount of condensate or indicated that there

is no condensate when in fact a significant amount of condensate was

collected during the test [7]. DOE allowed that manufacturer to instead

use a method of direct condensate measurement for rating their equip«nent.

From that time through 1983 DOE received seven similar requests.

Subsequently, DOE allowed the use of a direct condensate measurement for

all manufacturers on March 28, 1984 [1].

2
3.1 ISSUES CONCERNING NEW TEST PRXEDURES FOR FTTPMArRq

3.1.1 Cyclic Testing for Measurement of Condensate OolLection

A direct method which was published as l^pendix C of NBSIR 80-2110 [5]

called for measuring the amount of condensate produced during three test

cycles of the furnace or boiler.

Prior to the March 1984 final rule, DOE published proposed rules in the

Federal Register [7] which included test provisions for condensing furnaces

and boilers. These proposed test methods were identical to the test method

of ^pendix C of [5] except that it specified a six cycle test instead of

three cycles. The need for six cycles was determined based upon testing at

NBS (see Section 5.1.2) which showed that with some types of condensing

furnace, the amount of condensate collected per cycle was highly variable

and the results of a three cycle test should be improved by doubling the

nunber of test cycles.

Several commentors to these proposed procedures objected to the need for

six test cycles in all cases and suggested that the test be reduced to

three cycles if it could be shown that the condensate collection rate for

the three cycles gave consisteit results, Ihe Gas i^pliance Manufacturers

Association (GAMA) suggested that if the standard deviation of condensate

collected for three cycles did not exceed more than 20 percent of the mean

value, the test should be stopped after three cycles. Another canmentor

suggested the standard deviation should not exceed 10% of the mean value in

order to stop at three cycles. None of the commentors recommended a

procedure if after six cycles the variation were still greater than 20% of

the mean value. In an analysis of these comments [8], NBS recommended to

DOE a procedure that allows a three cycle test and suggested alternatives

3
to extended testing if this variability was exceeded. (See Appendix A.)

DOE published its final rules for furnaces and boilers in the Federal

Register on March 28, 1984 [1] . These test procedures prescribed a three

cycle test for a furnace or boiler having a "repeatable condensate

collection rate" (i.e. standard deviation less than 20% of the mean over

three cycles). "For those furnaces which do not doionstrate a repeat^le

condensate collection rate in the three cycles, an additional three cycles

are required irrespective of variability." Sections of the DOE procedure

[1] v^ich ^ply to condensing furnace testing are included here as i^pendix

B.

3.1.2 Steady State Test for Condensate Collection

A petition for waiver from test procedures submitted by a furnace

manufacturer (Amana Refrigeration, Inc.) asked that in addition to annual

fuel utilization efficiency (AFUE) the steady state efficiency also be

adjusted by direct measurement of the condensate collected during the

steady state test. DOE granted that waiver and in the proposed test

procedure [7] specified a 60 minute test period for determining the weight

of condensate collected. After DOE proposed to include these provisions in

the test procedure, three commentors asked that this test time be reduced

to a thirty minute collection period. DOE acc^Jted this adjustment to the

testing period and published it in their final rules [1]. See Section 5.3

for discussion of test results on this subject.

3.2 AMBIENT TEST ROOM CONDITI(»JS OF TEMPERATURE AND RELATIVE HOMIDITy

These test room conditions were originally required to be within a range of

65°F to lOO^F. These test temperature tolerances were tightened in 1980

for condensing furnaces and boilers to a range of 65°F to 80°F [4]. The

4
wider range remains in effect for nonr-condensing furnaces or boilers.

In 1982, ASHRAE published ANSI/ASHRAE Standard 103 [9] which specified a

wider test room ambieit temperature range for condeising units of 65°F to

85®F (the range called for in i^pendix C of reference [4] ). These ASHRAE

specified room tenperatures for condensing furnaces were also referenced by

DOE with the latest published procoiure [1].

Since no condensing hot air furnaces were commercially available at the

time of publication of test procedures for condensing, boilers and furnaces

(1980) specifications for testing of warm air furnaces were based upon

information then available from industry. The effect of room air

temperature for air supply to the heat exchanger had not been quantified

until this stu(^ was begun.

Also the effects of relative humidity were not included in the 1980 test

procedures published by DOE [4]. Room air conditions were monitored in the

NBS stu<^ [6]

,

however, the variations reported in that stu<^ were focused

on the effects of boiler water terperatures only.

Although the proposed limits published by DOE [7] for room air tenperatures

of 65®F to 85®F and relative humidity of not more then 80% were prior to

the results of this study, those proposed limits were not contested by

industry and NBS did not believe it necessary to revise those proposed

ambient room test conditions for the final rules. Test results found in

laboratory tests are r^)orted in Section 5.4.1 and 5.4.2.

5
4. TEST EQUIPMENT AND PROCEDURES

4.1 TEST nmVTrES

Two gas fueled high efficiency condensing warm air furnaces were used in

these tests. Both of these furnaces have annual fuel utilization

efficienty (AFUE) ratings near 95%. Tvo warm air gas fueled furnaces with

AFUE ratings in the mid 80% range were also tested. These furnaces were

equipped with condensate drain lines but did qualify as condensing furnace

under the existing DOE test procedures [3]. These were: The two high

efficiency condensing furnaces are designated furnace "A" and "B" in this

r^x)rt and the borderline condensing furnaces are designated "C" and "D".

Hiree of the furnaces can be seen in Fig. 1.

4.2 LABORATORy TEST EQUIPMENT

Figure 1 shows an overview of furnace testing in the Combustion Equipment

Laboratory. Among the instrumeits shown in Fig. 1 are the non*-dispersion

type infra red analyzers used to measure caibon monoxide and cadoon dioxide

in combustion gases. Data collection equipment consisting of data logger,

strip chart recorder, and computer t^>e recorder is in the left foreground.

Figure 2 shows two dew point meters being used in a test with furnace B.

One of these meters is monitoring dew point of the combustion air supply

and the other is sampling and measuring the flue gas dew point.

Other equipment not shown included scales for measuring condensate. A

continuously recording calorimeter was used to measure gross heating value

of the pipeline natural gas fuel supply.

6
COMBUSTION ANALYZERS

7
FLUE PIPE

Figure 2. Test furnace "B" shown installed through wall of test room used for mixing

warm air and showing equipment used to supply conditioned combustion air

8
4.3 TEST PROCEDURES

4.3.1 Condensate Collection

Olie methods of test specified in i^pendix C of NBSIR 80-2110 [5] were used

in this study, (see ^pendix A, Section 3.6, "Direct Measurement of

Condensate"), The method for controlling combustion air teotperature and

humditity is described below.

4.3.2 Control of Combustion Air Temperature and Humidity

An environmental chamber was used to supply conditioned ccaibustion air at

various temperatures and relative humidities to the test furnaces. Test

furnace A has its combustion air supplied via a direct connection to the

furnace through an air intake pipe. The combustion air supply pipe of this

furnace was directly connected to the environmental chamber as shown in

Fig. 3.

Figure 3 shows a simplified overall schematic of the various flow paths

involved in the test of furnace "A" including a cross sectional viev/

through the furnace. Figure 4 shows a view of the test arrangement used to

adjust the return air temperature to the furnace by blending ambient room

air from outside the test room with partially recycled heated room air from

the furnace. Hie purpose of study this test was to the effect of elevated

return air temperature on condensate collection rate.

The furnace illustrated in Fig. 4 is shown in Fig. 2 installed through a

side wall of the room with the combustion air, fuel inlet, controls section

and flue pipe outside the room. The warm air discharge and return air inlet

are inside the room. This test room acts as a mixing chamber of partially

recycled heated room air with the ambient laboratory room air which was

9
—Room air —Conditioned air for combustion

Figure 3. Overview of laboratory testing equipment showing flue gas and

flow paths used for conditioning combustion air and return air.

Figure 4. View of test room showing method used to mix warm air from

furnace with ambient air for adjusting return air temperature.

10
approxinately 68°P (20°C) to 75^ (24°Q

In Fig. 4, the return air and discharge warm air from the furnace are for

reasons of clarity shown discharging to the left. However, in these tests,

return air Altered at floor level through a knockout opening in the base of

the blower conpartment and the furnace was mounted ^proximately 6 inches

off the floor. Also, discharge air was directed toward the rear wall in

this test.

Furnace B uses indoor room air for combustion. This air normally flows

through holes in the jacket of the furnace to the combustion air fan. In

order to supply conditioned combustion air to this furnace, the area vdiere

combustion air would be taken into the fan was surrounded by a box and a

flexible hose was connected to the box (see Fig. 2). Combustion air was

thereby supplied directly to the burner from the environmental chamber

through this flexible hose.

5. TEST RESULTS

5.1 CYCLIC TESTING

The objective of these tests was to determine if three test cycles were

sufficient in order to obtain repeatable test results of condensate

collection rate.

5.1.1 High Efficiency Condensing Furnaces ("A" and "B")

Test results with furnace A showed very repeatable results. Table 1 shows

these results for a series of 17 cycles. The standard deviation as a percentage of the mean value after three cycles was 1% or less for any

three consecutive cycles. These data show that three cycles are sufficient

11
with a high efficiency furnace. In these tests, the maximum theoretical

amount of condensate possible with this furnaces fuel firing rate was 149.8

grains per cycle. Therefore, approximately 75% of the theoretical amount of

water formed during combustion was condensed.* Similar repeatable results

were also found with test furnace "B".

5.1.2 Borderline Condensing Furnaces ("C" and "D")

5. 1.2.1 Variability of Condensate Collected

Table 2 (a) and 2 (b) shows the results found in testing furnace "C".

These results show the high variability of condoisate collection that is

possible with a borderline condensing furnace (i.e., AFUE rating of less

than 90%). In these cycles, the maximum condensation per cycle as a

fraction of the maxinum theoretically possible was 75%, the average was 13%

and the minimum was 0.0%. These data show a periodic high flow of

condensate every 3 to 4 cycles (i.e. No. 2, 5, 8 and 12). The reason for

the periodic flow of condensate was apparently due to a build up of this

condensed water in the heat exchanger. Additional test data were obtained

with variable burner on-off times and showed similar results. Those data

are discussed below in section 5.2.2.

5.1.2.2 Effect of the Number of Test Cycles

Table 2(b) shows data from a repeat test run of the cycling test reported

in Table 2(a). Data collection began following the heat-up to steady state

and cool-down tests. The first cycle began 12 minutes after the start of

the cool-down test.

* i^pendix C shows a calculation of the effect of condensate collection

rate on part load efficiency.

12
Table

1.

Condensate

Collected

during

Cyclic

Testing

of

Furnace

"A”

(3.3

minutes

on,

13.3

min

off)

c

CO

(U S o

o

c

(Uo

(UM

Pm

U X V

6^

rHV

6^ 6^

X ui

cr> Qj

^ rHa

T3 O O

tM -H

to -u cn

X) to C <H -w

to > w

4J 0) CO cn Q iH

\£5 CN I I I CT^ o\ I I I CN O

• o

• III* I I I .H

0)

QJ

I—

I

<u o

=3

1—I o

to /-s > ro I X

^

C 4J

to cn

(U CO

COe

cO

0) 3

J-J bO

Cfl COC X

0) 01 X u

3 a

o 0) CJ f—

1

1—

o

CJ

\D 00 LO •

• • • 1 1 CO cn fO CO 1 1

< 1—

H

-H 1 1 »—

i

1—

1

1—

1

rH

QJ

CxO un to

• 3

CO 03 rH >

1—1 c

vO CO 00 o o

00 og CO CO CN <1"

1—1 1—1 1—

1

o rH 1—

1

rH

r-H 1—1 1—

H

1—1 tn pH rH rH

X) 0) 0) 0) M 4-1 3 I u I

I—I tH I 01 -Q 3 3

pH O

O

:z;

(U I—t ^cNro-crLDvor^cocn-d-LOvor^ CJ •“* ?—I *-M f-H (—

t

I U C3^

13

112.4

113 6

1.06
Table 2.-a .CONDENSATE COLLECTION

WATER COLLECTED PER CYCLE

FURNACE "C"

CYCLING TEST - 3 MIN., 52 SEC. ON

15 MIN., 20 SEC. OFF

(1) (2) (3) (4) (5) (6)

CYCLE

NUMBER

MEASURED

GRAMS

MEAN (x)

last three

cycles

MEAN (x)

last three

cycles

SAMPLE

STANDARD

DEVIATION (Sx)

(Last Six cycles)

PERCENT of

MEAN

100 (Sx-^ x)

Preheat 54.1*

(5 cycles)

1 0.2

2 80.3

3 1.0 27.2

4 0.0 27.1

5 58.3 19.8

6 1.0 19.8 23.5 36.2 +154%

7 0.0 19.8 23.4 36.2 +155

8 38.3 13.1 16.4 25.5 +155

9 1.0 13.1 16.4 25.5 +155

10 1.2 13.5 16.6 25.5 +153

11 2.6 1.6 7.2 15.3 +212

12 97.8 33.9 23.3 39.4 +169

13 0.1 33.5 23.3 39.4 + 169

Overall average per cycle 27.8 (excluding preheat)

* no condensate collected prior to the 5th cycle

14
Table 2. (b) Condensate Collected during Cycling Test

Repeat Test Furnace "C" Cycling @ 3 min 52 sec on; 15 min 20 sec off.

NOTE: Start of Test for calculating Averages begins with cycle (4)

(1)

Cycle

Number

123

(2)

Measured

Grams

0

0

0

(3)

Average

Last Three

(4)

Average

Last Four

(5)

Average

Last Five

(6)

Average

Last Six

4 65.3

n — — — — 3

6

u6.0 23.8 — — — 7 58.5 21.5 30.9 — — 8 0 21.5 16.1 24.7 — 9 0 19.5 16.1 10.7 21.6

10 0 0.0 14.6 10.7 10.7

11 64.4 21.5 16.1 24.6 21.5

12 0 21.5 16.1 12.9 20.5

13 0 21.5 16.1 12.9 10.7

14 0 0.0 16.1 12.9 10.7

15 67.2 22.4 16.8 26.3 21.9

16 0 22.4 16.8 13.4 21.9

17 0 22.4 16.8 13.4 11.2

18 0 0.0 16.8 13.4 11.2

19 63.7 21.2 15.9 26.1 22.4

X cycles (4)-(19) 20.3 17.1 17.3 16.8 15.8

Sx 30.4 9.3 4.1 6.4 5.6

X cycles (3)-(19) 19.1 16.3 17.3 17.4 16.3

X cycles (4)-(18) 17.4 15.6 17.4 15.9 15.1

15
The DOE procedure [1] calls for recording results of the first cycle for

direct measurement of condensate when "flue gas temperature at end of a

cycle is within 5°F (2.8°C) of each other for two consecutive cycles."

Flue tenperatures at the end of the first four cycles were as follows:

cycle (1) 70.0®C (3) 72.2®C

Cycle (2) 71.5 (4) 70.2

Tlie above temperature data shows that the third cycle could have beoi used

as the first cycle for these tests. However, the fourth cycle was used.

Results would have beai the same in either case over six cycles. The six

cycles would have been required for these data since the first three cycles

do not meet the DOE test for r^)eatability.

These data of Table 2(b) have been reduced to the average values calculated

for between three and six cycles. This set of data also shows (see column

3) that averaging over three cycles could result in a zero average reading

if for example the starting condition had been with cycles (8) (i.e.

average of cycles 8, 9 and 10). The overall average for the 16 cycles

(i.e. cycles (4) through (19)) was 20.3 grams with a standard deviation of

30.4, This is approximately 150% of the mean value.

This overall average over estimates the population average of these data

because it begins and ends with a large collection of condensate, A more

accurate reflection of the population mean would be found by either

starting with cycle (3) or by dropping cycle (19) and would result in

population average of 19,1 and 17.4 grams per cycle respectively. The true

picture of the population average for this data set is seen in column (2)

to include a series made up of one large collection and three small or zero

collection rates. Taking the value of 17.4 as the population mean (using

16
cycles 4 through 18) and comparing this to overall averages of the results

shown at the bottom of columns (3) through (6) shows that four cycles was

the most repeatable with a standard deviation of 4.1 v^ich is within 24% of

the mean value of 17.3 grams. If the first result (30.9) of this group

(which is atypical of the entire data set because it includes two high

readings in the set) is neglected, the standard deviation (0.61) is within

4% of the new group average of 16.1. The six cycle test that would be

required (column 6) shows the averages fall into two groups spaced almost

equally apart from the mean value of 15.1. These are the four low groups,

averaging from 10.7 to 11.2, and the six high groups (averaging from 20.5

to 22.4). Using the overall mean value of 17.4 as the b^t estimate of the

true population mean the largest error in the six cycle test is (17.4-10.7)

or 6.7 grams per cycle low. This amounts to an error in part load

efficiency of 0.4 percentage points, (see /^pendix C for this calculation).

5.1.3 Discussion of Test Results

As a result of testing with furnace "C", the DOE proposed test procedure

[7] specified that six test cycles be run for all condensing furnaces

instead of the three cycles previously specified in NBSIR 80-2110 [5] v^ich

was the procedure to be used if test procedure waivers were granted. Ilie

use of six test cycles should offer at least some improvement to this

highly variable rate of condensate collection. A first glance at the first

few test cycles in Table 2(b) does not show much improvement with the

initial six test cycles versus the first three. An explanation of the need

for more than three cycles can be seen by analysis of the data in Tables

2(a) and 2(b). Condensate drained from this heat exchanger in spurts.

Every fourth or fifth cycle resulted in a sudden flow (spurt) of

condensate, followed by two or three very small collections of condensate,

/^parently, there was either a reservoir of condensate being formed in the

17
heat exchanger that overflowed every few cycles or there was condensate

formed on the walls of the condensing heat exchanger section that became

wetted to the point where It flowed off all at once. In any case, and for

whatever reason the first cycle of condensate collected could be similar to

any one of those amounts shown between cycles 1 and 13 In Table 2(a),

Since the steady state, heat-up and cool-down tests may be run prior to

this test, there could be any number of starting conditions with respect to

the amount of condensate stored inside the heat exchanger. Therefore,

cycles 9, 10 and 11 (in Table 2(a)) could possibly represent the 3 cycles

used to measure condensate. This would give an average of 1,6 grams. If

starting conditions were such that the first cycle was cycle 10, and cycles

10, 11 and 12 were used to rate the unit (which averaged 33,9 gms) ; this

would have given an improvement in part load efficioicy of 1.4 percentage

points. The cycles 9, 10 and 11 would show less than 0,1 percent point

increase in part load efficiency, The six cycle test would help but would

not completely correct this discrepancy. Six cycles could possibly

overestimate the condensate collection rate because it may include two

longer collection cycles. However, it would not underestimate the

improvement as three cycles could with these data.

After DOE proposed a six cycle test for all condensing furnaces, several

manufacturers suggested that a three cycle test be allowed for units vAiich

gave repeatable results. This would reduce testing time and cost.

Repeatable results were suggested as those resulting in a standard

deviation for three cycles being with 20% of the mean value. Table 2 (a)

shows those limits of variability could not be achievable for this unit in

any of the six consecutive cycles, DOE agreed with the manufacturers and

specified either a three cycle or six cycle test d^)ending upon the results

on variability as described above, DOE further specified a maximum of six

18
cycles irrespective of the variability after six cycles. In the Analysis

of Comments [8], an alternate ^proach was suggested if variability were

greater than the 20% of the mean after six cycles. This approach is

included in i^pendix B,

5.2 EFFECT OF VARTART.R Fg ai/QFF TIMES

Ihe test procedure proposed by DOE for direct condensate measurement was

based on an assigned average burner on period of 3.8 minutes, and off

period of 13.3 minutes. These times were chosen in order to be consistent

with the test procedure previously used for non-condensing furnaces. Ihe

previous test procedure for non-condensing furnaces was based on the

finding that the efficiency calculated using one cycling rate and one

heating load corresponding to the average outdoor temperature would

approximate the weighted average for several on-off times representing

several outdoor temperature ranges through the heating season (e.g., a

Multi-Bin Analysis).

5.2.1 High Efficiency Condensing Furnace

This type of bin analysis was run using data obtained with furnace "A".

Table 3 shows the results found.

Burner on/off times were calculated by first selecting outdoor air

tenperature. These were selected so that the total heating season hours

between each temperature would be approximately the same number of hours

for each bin. Data by month were obtained from reference [11] and were

compiled in table format for the analysis in reference [12], One of those

tables of compiled data from [12] is included as i^pendix D for the city

used in this example (i.e. Charleston, West Virginia). This city was

selected because it has close to the national average number of degree days

used by the DOE procedure.

Ui
Table

3.

Multi

Bin

Analysis:

Furnace

"A*

rH

CO

>-C3 CO

u

•H X.

O1—1

03c r—1

0) CO T—1 o rH

<u It 5-1 CO

(U IS /—S

U-4cu 3 'w' pi P • c H vO

•rH Nw^ P

QJ

p rO II cO O

T3 P p

CJ to e O O ^ ^ CO p p

4-J P 0) CO o

CO QJ • • Xi

l>^ > C

TO

Q *H Q)

O QJ P3 £ X •rH 00 P •H QJ 4-i CO 03 C 00

vDo>

«—1

cp

C

O c

<)1 O

CO

QJCX

IX

on o £ C • p 03 4H

II < c Q) QJ > o QJ CO o /-N £ CO cO o

CO 0 c •H Nw/

QJ CO P c > p cO O Q) p) QJ rO <r P CO o to • • CO X m

cu

C P CN I—1 O QJ CJ P QJ Cu < D

cc3 03 P

QJ CiO 03 c

CJ> CO QJ QJ c

CO

O CO P Xi C c o I—t

QJ •r' 'w' >p QJ CO 03 E P p C II cU cO O O C3N P H CJ • u

CO QJ 0") 03 P £ 1—1

QJO CO • P -C P p 0) 00

QJ ip o • CO p •H P to 03 QJ

cO cO QJ 03 4-» QJ Q P QJ QJ

cO P *• CO

QJ iH CO

C

u QJ 3 £ O QJ •H P u •H CN XJ

CO 00 rH

p

C

CO QJ cO CO 0

CP

Q CJ

w

U

?n
Appendix D shows the cumulative degree-hours, degree-days and bin hours

beginning at 65°F (summing upward from the bottom of the last three

columns)

.

Equations used to calculate burner or\/off times are presented in ^pendix

C-2. From i^pendix D, note that the number of bin hours from 5^ to 9^ is

25 hours and from 10°F to 14°F is 69 hours. This totals 94 hours which is

shown in column 7 of Table 3. The last column in Appendix D is the

weighted average outdoor temperature between 64®F and the outdoor

temperature (tQ^). This city with averge 42,2°F over the heating season is

identical to the national average of 42®F used with DOE test procedure to

calculate the oiVoff times of 3.8 minutes and 13.3 minutes. In both cases

oversizing of 70% is assumed.

The bin analysis of Table 3 shows that a total of 1958 kg of condensate

would be collected over the heating season. In order to compare this with

the result from the DOE procedure for one bin (average on/off periods of

3.8 min and 13.3 min), the total hours per year is calculated as shown on

Table 3 to be 1116 hours, and condensate collected is calculated to be 1968

Kg. This is within 0.5% of the multi-bin analysis result. The adequacy of

the single bin ^proach is appareit from these results.

This calculation used a condensate collection rate obtained in the

laboratory with ambient conditions of approximately 70-75^ and relative

humidity of ^proximately 30-50%. If a more detailed analysis to represent

field conditions were to be run, it would be necessary to consider the

absolute humidity of the outdoor air for these various temperature bins.

The effect of the variation of humidity on condensate collection is

reported in section 5.4.2.

21
5.2.2 Borderline Condensing Furnace

Table 4 shows results of five cycling rates including for coirparison those

results reported in Tables 2(a) and 2(b) for the average on/off times

specified by the DOE test procedure. Data in Table 4 shows that as the

percentage of burner on time increased, there was a change in the pattern

of condensate collection. The frequency of cycles were no condensate was

collected fell off with increasing burner on periods.

The periodic changes that occur began to show a repeating pattern

particularly with the maxinum heating load factor (i.e, 100% equivaleit to

7.32 minutes on/S-i minutes off). Notice for test series no. 5 from cycles

(20) through (26) the grams of sarrple collected was practically a repeat of

cycles (7) through (13).

These results show very little effect of cycling rate on the rate of water

condensed. (See column of overall averages per minute of burner on time.)

A bin analysis using the Charleston, West Virginia data shown in i^pendix D

results in a weighted collection of 342 kg/year compared to 365 kg/year

using the single bin collection rate data for 3.8 min. on/13.3 min. off).

Again, the single bin gives a slightly higher value (7% higher). This is a

much smaller effect in terms of part-load efficiency effect since only 10

to 15% of the total possible condensate was actually condensed in these

tests. The total possible latent heat correction for conplete condensation

is 9.55 percentage points. Fifteen percent of the total possible condensed

therefore amounts to 1.5 percentage points of efficiency. A seven percent

variation in 1.5 points is only 0.1 point. These results confirm the

adequacy of a single burner on/off period for the direct condensate

measurement for both high efficiency and borderline types of condensing

22
Table

k

Effect

of

Burner

cycling

on

collection

(grams)

-

lest

Furnace

0 G Q)

<D *H tH

•O X ^

fl tg -H

0) 0) V4 Vrf > > 0) 3 O < cQ

fO CM 00

vO sD irt

.H 0» O H 00 >*

<0 CO o

00 m

CO m m

\D in o

CO CO m

I—I rH P*^ 00

<r O' CM -'.HO ON ON

vo tn CO

CO CO r-* « 00

CO m CO ON O <!• O *H ON m

o m in in

iH <1* rH m

-vP m p^ CO CO vO o ^ o

ON 00 in

S -H CHS O H

T3 a. 0

i-i u G o 3 H (D H

o <: H

CO (U H H (U (0 H 0> W 4-1

23
furnaces

No tests were run with furnace "D^ because that furnace, although equipped

with a condensate drain, did not produce any condensate in either steady

state or cyclic tests.

5.3 INVESTIGATION OF STEADY STATE TESTING

The objective of these tests was to determine the effect of condensate

collection test period on rate of condensate collected. These data were

obtained in order to respond to comments received from manufacturers

requesting that the total test time be reduced to 30 minutes from the 60

minute test as proposed by DOE in [7]. A reduced test time would reduce

testing costs.

Table 5 (a) shows the data obtained for three furnaces tested. Table 5 (b)

shows these data in terms of condensate collection rate after steady state

conditions were established (i.e. 30 minutes after start-up). The DOE

procedure [1] specifies that steady state conditions be established before

starting the collection of condensate. These data show that a 30 minute

test gave results equivaleit to the proposed sixty minute test. Condensate

collected with furnace "C" was slightly less during the first 30 minutes

compared to the proposed 60 minute test. However, the results after 30

minutes were obviously consistent with the extended test period of 90

minutes (i.e. average 4.9 g/min after 30 minutes and after 90 minutes for

furnace "C").

DOE published rules for condensing furnaces on March 28, 1984 [1] which

reduced the testing time period for this test to 30 minutes.

24
Table 5(a) — Effect of Testing Time on Direct Measurement

of Condensate for Steady State Test

Time interval Condensate Collected during time interval (grams)

(minutes) Furnace A Furnace B Furnace C 0-10 2Z9 298 0

10 - 20 Ilk 301 0

20 - 30 216 298 88.7

30 - 40 211* 294* 38.8*

40 - 50 205 295 31.1

50 - 60 208 293 78.2

60 - 70 207 294 55.3

70 - 80 207 293 41.2

80 - 90 213 294 68.4

90 - 100 212 295 19.5

100 - 110 211 293 81.4

110 - 120

*Start of Steady State

211

Conditions

295 24.0

Table 5(b) —

Length of

Condensation Collection

Test Period After Start

Rate (gm/minute)

of Steady State

vs

,

Test Period Furnace A Furnace B Furnace C

30 minutes 20.8 29.4 4.9

60 minutes 20.8 29.4 5.2

90 minutes 20.9 29.4 4.9

25
Additional test data including the effect of test room air conditions on

condensate collection rate at steady state conditions is included in

Section 5,4.

5.4 EFFECTS OF AMBIENT TEST ROOM OCM)ITiaJS

5.4.1 Effects of Roan Air Temperature

This study involved variation in temperature of the return air supply.

Combustion air was kept at ^proxiirately 70°F throughout these tests. In

order to obtain data at above the normal room air temperature of the

laboratory, the test room described in 3,3.2 was used in these tests.

Test results by linear regression analysis of data for room temperatures

versus rate of condensate collected (gran\/min) are shown in Fig, 5.

These results are for furnace "A". Test results are shown for both cyclic

and steady state tests. With the cyclic tests the blower input air

temperatures used for Fig, 5 were obtained during the furnace fan on

period. During burner off periods, test room air temperature became the

ambient laboratory temperature of 70°F because the air supply fan remained

on throughout the burner oiVoff periods. Therefore, return air temperature

or "blower input air temperature" in Fig. 5 on start up was approximately

70®F for each test. However, this air temperature rose rapidly on start up

of the burner, since this test room was small (362 cubic ft) compared to

the warm air discharge rate of the furnace, (roughly 1000 cfm). As a

result of this reduced roan temperature starting condition of approximately

70®F, the effect of high ambient room air temperature reported here are

conservative. If it had been possible to maintain a constant return air

temperature during these cyclic tests, we could expect to see a greater

drop off in condensate collection rate at the elevated temperature (i.e„ a

26
BLOWER

INPUT

AIR

TEMPERATURE

°F

-a

(U -M

• • * * • o ru uD CO «s> 'T ro iTJ ^

^InNu\/s^^JVijC) Noiio^nnoo d3ivAA

27

ao.00

a3.00

36.00

39.00

33.00

35.00

BLOWER

INPUT

AIR

TEMPERATURE.

DEG.

C
greater slope to the curve of cyclic tests). Alternatively, if the average

room tQiperature were used in plotting the data of Fig. 5, the slope of the

cyclic test line would have been greater because data points for a given

ordinate value would have beei shifted to the left.

This cyclic curve would be expected to be parallel to the steady state

curve with the above adjustments to these test data on test conditions.

The effects of a lower average air torperature on the air side of the heat

exchanger is also the reason vdiy the condensate collection rate for cyclic

tests is greater than the steady state tests.

From the data shown in Fig, 5, it is seen that running a steady state test

with room air temperature at 75°F would give the same result as a cyclic

test run at 85®F (i.e., by following a line from 75°F down to the steady

state line, to the right to the intersection at 85°F of the cyclic test

line)

,

These test results show that effects of the test room tenperature on direct

condensate measurement and part load efficiency are significant. The

difference in these tests on part load efficiency with each 10°F of room

tenperature amounted to 1,1 percaitage points in part load efficiency and

1,6 percentage points in steady state efficiency. In other words, a

maximum effect of part load efficiency with a return air tenperature at the

lower allowable limit of 65°F conpared to 85°F at the upper limit could be

3.2 percentage points. These changes in part load efficiency are

approximate and cannot be used to predict actual part load efficiency

changes under rating conditions, because the tenperature rise of the warm

air in these tests was not readjusted with each change of inlet tenperature

to achieve the manufacturers rated maximum tenperature rise as specified by

28
the DOE procedures. Also in these tests the laboratory air temperature

could not be adjusted below 70®F, therefore, these results were

extr^x>lated from 70®F to 65^.

However, these data may be used to predict what the maximum allowable

variation in room air temperature could mean in terms of its relative

effect on part load efficiency. The allowable variation in room air

teirperature could mean a change in reproducibility of 1,1 percentage points

in part load efficiency with this test furnace,

5.4.2 Test Hoorn Humidity Effects

Ambient conditions of humidity are of concern only for the ccatibustion air

supply. There were no controlled conditions of humidity for the return air

side during these tests and there is no reason to expect any significant

change of heat transfer through the heat exchanger due to humidity of the

return air. Since one of the combustion products of fossil fuels which

contain hydrogen is water, there is reason to believe that condensate

collection would be effected by humidity in the air supplied for

combustion. In these tests, conditioned air was supplied to the burner

from an environmental chamber as described in 4.3.2. Test results are

shown in Fig. 6 both for the cyclic tests and the steady state tests.

These results with cyclic tests show that a change from 10% to 90% relative

humidity results in an increase of 7.6 g/min of water condensed. This is

equivalent to 0.2 percentage points of part load efficiency for each 10

percQit change in relative humidity. In these tests air supplied both for

combustion and return air to the furnace fan was constant at 72°F (22°C)

and at 92®F (33°C), The data for the steady state tests show approximtely

29
CONDENSATE

COLLECTION

Z

UJU

a:u

0.

i’

q:a

<

z

g>—

(/) D

m

5

o

o

3inNI/S/Si^Vd0 ‘3iVd N0II031103 d3LVM

30

Figure

6.

Effect

of

relative

humidity

of

test

room

air

at

constant

room

temperature

on

rate

of

condensate

collected

-

Using

test

furnace

"A"
the same change in condensate collection rate (i.e„ 1.0 percentage points

increase in efficiency for an increase of 60 percentage points increase in

relative humidity).

5.4.3 Disucssion of Test Results With Controlled Room Air Temperature

and Hiaiddity

In the calculation of steady state efficiency by the flue loss method, flue

temperature is measured in terms of the temperature rise above room

temperature. Similarly, the calculations of part load efficiency are

related to temperature rise above room temperature. Therefore, a wide

range of test room air tenperatures have beai allowed with ncxv-condensing

furnaces. With this direct measurement of condensate there is no

correction for roan tenperature and the airount of condensate collected is

used as measured in adjusting the credit for part-load efficiency.

A narrow ambient room temperature range of 65®F to 75®F was proposed in

1977 [13] for furnaces. Industry objected to that narrow range and cited

the cost of expensive refrigeration equipnent that would be needed in order

to meet that proposed room tenperature condition [14]. Several coramentors

suggested various tenperature ranges of 65°F to 85°F or; 65®F to 95®F; or

65°F to 100°F. DOE published their procedure [2] specifying 65®F to 100^

for non-condensing furnaces. The proposed range of 65°F to 85®F for

condensing furnaces would, therefore, be within a range originally

recommended by the Industry that would not require the air conditioning of

testing facilities.

The allowable 80% relative humidity in the range of 65^ to 85°F means the

allowable dew point is between 61°F and 80®F. These extreme conditions are

unlikely to exist, (see Fig. 7 for weather maps showing maximum dew point

31
Figure 7, Weather maps showing

dewpoint readings in

two of the extreme months for maximum

the United States ( From ref. 15)

32
cx>ntour lines)

.

In view of the past objections to a tighter test room temperature

specification and because there were no commentors objecting to the

proposed procedures during the public comment period, NBS did not recommend

changes to the proposed room temperature specification [14],

It should be understood, that test parameter effects such as room air

tenperature and humidity are a concern regarding the ability to reproduce

test results in the laboratory, either within the same laboratory (i.e.,

r^atability of results) or between laboratories (i.e., r^roducibility of

results). These test parameters do not pertain to the differences between

laboratory and field conditions. Several designs of condensing furnaces

use outdoor air which is piped to the furnace through an outside wall and

through roughly 25 feet of 1.5 inch diameter plastic pipe. Therefore,

actual temperature and humidity conditions of the combustion air will

depend upon the outdoor tenperature and the degree of heat transfer to rocan

air that results before combustion air enters the furnace. With respect to

return air temperature in the home during the heating season, that will

depend upon the users thermostat setting and overall heating system design

with respect to the return air duct work location, surface area and

insulation. Specifying a return air teooperature that would reflect in use

conditions is beyond the scope of this stu(^.

6.0 SUMMARY

It is shown that a single cycling rate representing the heating season

average typical burner on/off times (as currently used in the DOE test

procedures) would also be adequate for use in the direct condensate

measuremsit test under cyclic conditions.

33
Under this cyclic test for direct condensate measurement, it is also shown

that a three cycle test would be adequate for the high efficiency

condensing furnace because that type of furnace resulted in a highly

r^atable rate of condensate formation and collection. With borderline

condensing furnaces, it is shown that the amount of condensate collected

would be so variable that a test for r^>eatability would be difficult or impossible under the guidelines suggested by several commenters to the

proposed procedures.

In the direct condensate measurement test under steady state conditions, it

is shown that a thirty minute collection period provides sufficient

information regarding the condensation rate and can r^lace the originally

pressed sixty minute test period.

The effect of ambient room return air temperature over the allowable range

is found to be significant in terms of its effect on condensate collected.

For of part-load efficiency the effect can be up to three percentage points

over the range of allowable room tenperatures. Effects of humidity are

considerably less than the effect of return air temperature, being only 0.2

percentage points per 10% change in relative humidity.

34
REFERENCES

1, Federal Register Vol. 49, No, 61, pp. 12148-12178, March 28, 1984,

2, Federal Register Vol. 43, No, 91, pp, 20158-20180, May 10, 1978,

3, Kelly, G„ et,al„ "Recommended Testing and Calculation Procedures for

Determining the Seasonal Performance of Residential Central Furnaces

and Boilers," NBSIR 78-1543, October 1978, National Bureau of

Standards, Gaithersburg, MD 20899,

4, Federal Register Vol, 45, no, 157, pp, 53714-53748, August 12, 1980

and Vol, 45, No, 184, pp, 62417-62418, Correction Notice S^ember 19,

1980,

5, Kelly, G,E„ and Kuklewicz, M,E„ "Reccanmended Testing and Calculation

Procedures for Estimating the Seasonal Performance of Residential

Condensing Furnaces and Boilers," NBSIR 80-2110, i^ril 1981, National

Bureau of Standards, Gaithersburg, MD 20899,

6, Kelly, G,E, and Kuklewicz, M,E,, "A Laboratory Study of a Gas-Fired

Condensing Boiler," NBSIR 80-2094, November 1980, National Bureau of

Standards, Gaithersburg, MD 20899,

7, Federal Register Vol, 48, No, 118, Proposed Rules, pp, 28014-28046,

June 17, 1983,

8, Kweller, E,R,, "Analysis of Public Responses to Proposed Department of

Biergy Test Procedures for Furnaces, Boilers, and Household Heaters,"

National Bureau of Standards Letter Report to Department of Energy,

February 7, 1984,

9, ANSI/ASHRAE Standard 103-1982, "Methods of Testing for Heating

Seasonal Efficiency of Central Furnaces and Boilers," ASHRAE, Atlanta,

GA 30329,

10, Federal Register Vol. 47, No. 233, pp. 54530-54531,

35
11. "Engineering Weather Data," D^rtment of the Air Force APM 88-29, Hie

Army (TM 5-785) and the Navy (NAVFACP-89) , July 1978, Washington,

DC 20330,

12. Kweller, E.R. and Thomas, F., "An Analysis of United States Weather

Data for the Calculation of Average Outdoor Teitperatures and

Fractional Heating Loads for Furnaces and Boilers Equipped With Fuel

Modulating Controls," NBS Letter Report to Department of ESiergy, 1982,

13. Federal Register Vol. 42, No. 155, pp. 40826-40845, August 11, 1977.

14. "Technical Analysis of Public Heating Testimony Regarding Proposed

Energy Efficiency Iirproveroent Targets for Furnaces," NBS Letter Report

prepared for Departmait of Energy, March 23, 1978,

15. "Climate ATLAS of the United States," Department of Commerce,

Environmental Science Service Administration, Environmental Data

Service, Washington, DC, June 1968.

36
APPENDIX A, B, C, D

A, DOE Test Procedure for Direct Measurement of Condensate

B. Alternative Method of Rating Condensate Collection Rate

for Borderline Condensing Furnace

C. Sample Calculations

1. Part Load Efficiency Effect With Condenste

Collection Rate

2. Calculation of Burner On/Qff Time

D, Weather Data Used for Bin Analysis of Condensate Collection
mt *»!. *i. »’'4ieiWL«pj*»)eM^^ itj' 1»7^

^ t i tia tyf

1<M:. •/ 'gp • M’ L.I- <if fc*

' "• »

—rt
12160 Federal Register / Vol. 49, No. 61 / Wednesday, March 28, 1984 / Rules and Regulations

boiler hall be started simultaneously with

the main bumerfg| The water How rate shall b« the same as that maintained during the steady-state test described in section 9.1 of ANSl/ASHRAE 103-82. During the heat-up

test for oil fired boilers maintain the draft in the flue pipe within ± 0.01 inch of water column of the manufacturer's recommended

on-period draft. Record the measured

temperatures.

3.6 Direct measurement of condensate. For condensing furnaces and boilers, the condensate heat loss shall be determined

either by the method specified in section

11.2.33 of ANSI/ASHRAE 103-82 or by the following test procedures: Control devices shall be installed to allow

cyclical operation of the unit and return water or air flows as described in sections 9.2 and 9.3 of ANSI/ASHRAE 103-82 and

sections 3.2, 3.3, 3.4 and 3.5 of this appendix.

The test unit shall be leveled prior to test. Operating times and beginning and end of condensate collection shall be determined by

a clock or timer with a minimum resolution of one second. Humidity of the room air shall, at no time, exceed 80 percent. Control of on or off operation actions shall be within ± 6 seconds of the scheduled time. Condensate drain lines shall be attached to the unit as specified in -the manufacturer’s

installation instructions. A c6hfiriubfi8“‘‘- downward slope oT drmn lines from the unit hall be maintained. Additional precautions

shall be taken to facilitate uninterrupted flow

of condensate during tbeteat.

' ' —

The flue pipe installation must not allow condensate formed in the flue pipe to flow back into the unit. An initial downward slope from the unit's exit, an offset with a drip leg, annular collection rings, or drain holes must

be included in the flue pipe installation without disturbing normal flue gas flow, as

specified in section 7.2.2 of ANSI/ASHRAE

103-82. Flue gases should not flow out of the drain with the condensate.

Collection-containers must be glass or polished stainless steel, so removal of interior deposits ccn be easily made. The collection- container shall have a vent opening to the atmosphere.

Jhe scale for measuring the containers and

sample condensate mass shall be calibrated with an error no larger than ± 0.5 percent over the range of interest. The condensing furnace or boiler shall be

tested by the flue loss method in accordance

with the provisions for condensing units, as

specified in section 9 of ASNI/ASHRAE 103-

82 and section 3 of this appendix. The

condensate collection-containers shall be

dried prior to each use and shall be at room

ambient temperature prior to a sample

collection. Tare weight of the collection- container must be measured and recorded

prior to each sample collection. The unit should be operated in a cyclical manner until flue gas temperatures at the end

of each on-cycle are within 5° F (2.8° C) of each other for two consecutive cycles. Oncycle and off-cycle times are listed in Table 2

of this appendix. Begin three test cycles. Return air temperature for furnaces shall be

as specified in section 9 of ANSI/ASHRAE

103-^2 and section 3 of this appendix. Return water temperature for boilers shall be as

specified in section 2.3 of this appendix.

X)peratidn ofThrfUmace blower oi faollfer pump shall conform to the time delay

requirements specified in sections 9.2 and 9.3 of ANSI/ASHRAE 103-62 and sections 3.2, 3.3, 3.4, and 3.5 of this appendix for cool down and heat up tests. Operation of the

boiler pump shall conform to the time delay

requirements specified in section 3.3 of this appendix.

Begin condensate collection at one minute

before the on-cycle period of the first test cycle. The container shall be removed one

minute before the end of each off-cycle period of the sixth test cycle. Condensate mass shall be measured for each test cycle. Fuel input shall be recorded during the

entire test period starting at the beginning of

the on-time period of the first cycle to the beginning of the on-time period of the second

cycle, etc., for each of the test cycles. Fuel

higher heating value (HHV), temperature and

pressures necessary for determining fuel energy input (QJ shall be recorded. The fuel quantity and HW shall be measured with

errors no greater than one percent. Determine

the mass of condensate for each cycle (mj in pounds. If at the end of three cycles, the sample standard deviation is within 20% of

the mean value for 3 cycles use total condensate collected in the three cycles as

m«, if not, continue collection for an

additional three cycles and use the total condensate collected for the six cycles as nOc. Determine the fuel energy input during the

three or six test cycles (QJ expressed in Btu. Begin a steady-state condensate collection

after steady-state conditions have been

achieved as specified in section 8 of ANSI/

ASHRAE 103-62 and section 2 of this appendix. The steady-state collection period

shall be 30 minutes. Condensate mass shall be measured immediately at the end of the /Jr

collection period to prevent evaporation loss^

| from the sample. Fuel input shall be recorded

for the one hour steadv-state test period. ^el

Higher Heating Value (HHV), temperature

and pressures necessary for determining fuel energy input Qc.ss will be observed and

recorded in Btu's. The fuel quantity and HHV

shall be measured with errors no greater than one percent. Determine the mass of condensate for the steady-state test, mc.ss. in pounds by subtracting the tare container weight from the total container and

condensate weight measured at the end of

the 30 minutes test period.

3.7 Direct measurement of off-cycle losses testing method. Reserved.

3.8 Direct measurement of the S/Ffactors for oil furnaces and boilers. For oil furnaces and boilers that are marketed and sold with

attached barometric dampers, the S/F factor

shall be determined either by using assigned

factors in Table 2 of ANSI/ASHRAE 103-82

or by the following test procedure: To directly measure the S/F factor, seal the barometric damper plate in the closed

position. Operate the furnace or boiler until steady-state temperatures are attained. Adjust the draft in the flue within one foot of

the heat exchanger exit to be between 0.075 and 0.085 inch water column. A mechanical

draft inducer or a natural draft developed by

adjusting the height of the test stack may be

used. Remove the seal from the barometric

damper and adjust the damper gate to achieve proper draft, as specified by the manufacturer. If the draftnver the fire is specified as a range, adjust the draft to the mid-point of that range. After steady-state conditions are again achieved with the draft adjusted as specified, measure COi before and aher dilution at points marked A and B in Figure 2 of this appendix. To ensure that the sample is well mixed after dilution obtain a representative

sample of stack gas by sampling from several points on a horizontal plane through the cross section of the stack. The test setup shown in Figure 2 enhances the mixing of dilution air and flue gases. Alternatively, a straight length of stack or other flue piping

arrangement may be used with stack samples

taken sufficiently downstream after dilution

in order to obtain a well-mixed sample.

3.9

Furnaces and boilers that includes small air passages in the flue. For furnaces and boilers that includes small air passages

in the flue where such passage serves a

utility other than for draft relief, the air passage shall be open during all tests and the

test data shall be reduced as specified in section 4 of this appendix.

These units shall be considered as direct exhaust systems, for the purposes of this test procedure. These provisions shall not apply

to systems which allow for air flow through

the air passage in excess of 10 percent of maximum steady state total flue flow; in these cases, such passages are to be

considered as draft diverters or draft hoods.

4.0 Calculations. Calculations shall be as

specified in section 11 of ANSI/ASHRAE

103-62 with the exception of section 11.2.6, and the inclusion of the following additional

calculations:

4.1 Annual fuel utilization efficiency for

electric furnaces and boilers. The annual fuel utilization efficiency for electric furnaces and

boilers (AFUE) is equal to the heating seasonal efficiency for electric furnaces and

boilers (Effyh, ,) as defined in section 11.1 of ANSI/ASHRAE 103-82.

4.2. Average ratio of stack gas mass flow

rate to flue gas mass flow rate at steady-state

operation. The following paragraphs are in place of the requirements specified in section

11.2.6 of ANSI/ASHRAE 103-82: For gas furnaces and boilers with integral draft diverters, calculate the average ratio of stack gas mass flow rate to flue gas mass

flow rate at steady-state operation (S/F] defined as: S/F =1.3 Rr.g/Rr.r wherer* Rt.s= 89 defined in 11.2.3 of ANSI/ASHRAE

103-82

RT.r = as defined in 11.2.2 of ANSI/ASHRAE

103-82 For gas furnaces and boilers equipped with

draft hoods determine the S/F by the method

set out above or use the assigned value of 2 4 This alternative method may be used until 24 months from the effective date of the amendment. After that date, the assigned value may not be used and only the method

set out above may be used. For oil furnaces and boilers. S/F shall bs

1.40 for units not shipped with barometric
Federal Register / Vol. 49,

dampers or for units shipped with barometric dampers. S/F shall b6 either 1.40 or determined by: S/F= Rt s/Rx.r where;

Rt.s = bs defined in 11.2.3 of ANSI/ASMRAE

103-82 in which the value of CO2

measured in the stack in 3.8 of this appendix is used RT.F=as defined in 11.2.2 of ANSl/ASHRAE

103-82 in which the value of COj

measured in the flue in 3.8 of this appendix is used

4.3 Optional direct condensate measurement method. For condensing

furnaces and boilers for which the direct measurement of condensate is used, as

specified in section 3.6 of this appendix,

calculate the part-load efficiency (tJu) and the steady-state efficiency (tjss) expressed as a percent and defined as;

TK, = Effyh,-*-Lc-Lc

ijss = Effyss -t- Lo.ss ~ Lc.ss where;

Effyn,= heating seasonal efficiency for non- condensing furnaces and boilers, as defined in 11.2.34 of ANSI/ASHRAE 103-

82

L«=: latent heat gain under part-load

conditions, as defined in 4.3.1 of this appendix Lc= part-load heat loss due to the condensate

going down the drain and corrected for the fact that the condensate did not go up • the flue as heated vapor, as was

assumed in determining Lg.ss.A, os

defined in 4.3.2 of this appendix

Effyss = steady-state efficiency for non- condensing furnaces and boilers, as defined in 11.2.5 of ANSI/ASHRAE 103-

82

Lc.ss = latent heat gain under steady-state

conditions, as defined in 4.3.3 of this appendix

Lc.ss = steady-state heat loss due to'the condensate going down the drain and

corrected for the fact that the condensate

did not go up the flue as heated vapor, as was assumed in determining Lg.ss.A, ss defined in 4.3.4 of this appendix

4.3.1 Latent heat gain under part-load

conditions. Calculate the latent heat gain under part-load conditions (Lq) expressed as

a percent and defined as; Lc = 100(1053.3) m*/Q,

where:

100 = conversion factor to express a deciroal as a percent

1053.3 = latent heat vaporization of water, Btu

per pound

m« = a8 defined in 3.8 of this appendix

Qc = as defined in 3.6 of this appendix

4.3.2 Part-had heat loss due to the condensate. Calculate the part-load heat loss due to the condensate going down the drain and corrected for the fact that the condensate

did not go up the flue as heated vapor, as was

assumed in determining Lg.ss.A (Lc) expressed

as a percent and defined as; Lc = lHi[10(Tr.s,-70)-

0.45(Tp.sg- 42) 1/1053.3 where:

P b \K A (Co AfTiti M

No. 61 / Wednesday, March 28, 1984 / Rules and Regulations 12161

L<;=as defined in 4.3.1 of this appendix

1.0= specific heat of water (liquid), Btu per pound -°F

Tr.ss = as defined in 11.2.4 of ANSI/ASMRAE

103-82

70 = assunied average indoor air temperature,

“F

0.45 = specific heat of water vapor, Btu per pound -°F

42 = average outdoor temperature

corresponding to 5,200 degree day

location, °F —

1053.3— Latent heat of vaporization of water. Btu per pound

4.3.3 Latent heat gain under steady-state

conditions. Calculate the latent heat gain under steady-state conditions (Lc.ss) expressed as a percent and defined as:

Lg.ss =100(1053.3)m<;.ss/Qc.ss where: loq= conversion factor to express a decimal

as a percent

1053.3

=

latent heat of vaporization of water, Btu per pound

mc.ss = as defined in 3.6 of this appendix,

pound

Qc.ss=as defined in 3.6 of this appendix, Btu

4.3.4 Steady-state heat loss due to the condensate. Calculate the steady-state heat

loss due to the condensate going down the drain (Lc.ss) expressed as a percent and

defined as:

Lc.ss = Lc.ss(l •0(Tr.ss ~ 70) —0.45(Tf,ss — 42)/ 1053.3 where:

Lc.ss = as defined in 4.3.3 of this appendix

1.0=specific heat of water (liquid), Btu per pound-'

F

l'p.ss = a8 defined in 11.2.4 of ANSI/ASHRAE

103-82 70= assumed average indoor air temperature, •F

0.45 = specific heat of water vapor, Btu per pound—' F 42= average outdoor temperature

corresponding to 5200 degree day

location, * F

1053.3= latent heat of vaporization of water, Btu per pound

4.4 Direct determination of off-cycle losses for furnaces and boilers equipped with

stack dampers. Reserved

4.5 Modulating controls.

4.5.1 Weighted-average part-had

utilization efficiency. For furnaces and

boilers equipped with two stage thermostats,

calculate the weighted-average part-load

utilization efficiency at each dest^ heating

requirement (ttu.wr) expressed as a percent and defined as: qo.WT = Xi1)v.||H> + XiTIu.iiax where:

Xi = fraction of heating load at reduced

operating mode, as defined in 4.5.2 of this appendix

RiD = the part-load efficiency at the reduced fuel input rate and is defined as

the heating seasonal efficiency (Effyiu) in

11.2.34 of ANSI/ASHRAE 103-82, measured at the reduced fuel input rate and calculated by using the appropriate on and off times as specified from Table

2 of this appendix

Xg= fraction of heating load at maximum

operating mode, as defined in 4.5.3 of this appendix

v?v.MAX = lhe part-load efficiency at the maximum fuel input rate and is defined

as the heating seasonal efficiency (Effy^.) in 11.2.34 of ANSI/ASHRAE 103-82. measured at the maximum fuel input rate and calculated by using the appropriate on and off times as specified from Table

2 of this appendix

For furnaces and boilers equipped with step-modulating thermostats, calculate Hi' wr

expressed as a percent and defined as; WT~X, nil RKI)''' X^ ’’tlT NHH) where:

Xi = as defined in 4.5.2 of this appendix

ihJ.REo=es defined in 4.5.1 of this appendix

%=as defined in 4.5.3 of this appendix

»hj.iioD= average part-load efficiency for the modulating mode, as defined in 4.5.8 of

this appendix

4.5.2 Fraction ofheating had at reduced

operating mode. Determine the fraction of heating load at the reduced operating mode

(Xi) expressed as a decimal and listed in either Figure 4 or Table 3 of this appendix for appropriate values of the balance point

temperature (Tc). Tc is defmed in section 4.5.4 of this appendix.

4.5.3 Fraction ofheating load at maximum operating mode. Determine the

fraction of heating load at the maximum

operating mode (Xi) expressed as a decimal and listed in either Figure 4 or Table 3 of this appendix for appropriate values of the balance point temperature (Tc). 4.5.4 Balance point temperature. Calculate the balance point temperature (Tc) which represents a temperature used to apportion the annual heating load between

the reduced input cycling mode and either the modulation mode or maximum input cycling mode. Tc is defined as: Tc=85— (ATofl'anHs) [Qout.ii*d/Qoct.IIAxl) where: 65= average outdoor temperature at which a

furnace or boiler starts operating, 'F ATo=the difference between the outdoor air temperature where heating is typically required and the outdoor design

temperature, the national average

temperature difference is 65’ F—5’ F or

60‘ F 5=outdoor design temperature aDHa= oversize factor at each design heating

requirement, as defined in 4.5.5 of this appendix

Qovr.sso=heat output rate at the reduced fuel input rate, as defined in 4.5.6 of this appendix

QouT.MAx==heat output rate at the maximum

fuel input rate, as defined in 4.5.7 of this appendix

4.5.5 Oversize factor at eoch design

heating requirement. Calculate the oversize

factor at each design heating requirement

(ooHiO expressed as a decimal and defined as: Odhr = (Qout.uax/DHR) — 1 where:

Qout.i«ax°>o* defined in 4.5J7 of this appendix

DHR= typical design heating requirements,

as listed in Table 1 of this appendix
APPENDIX B

Cyclic Testing (the following discussion is from reference 8)

A three cycle test would be sufficient for the very high efficiency

condensing furnace. This can be defined in the terms recommended by the

coiTimentors. If the sample standard deviation after a series of three

cycles is coirpleted were not greater than 20% of the mean value for those

three cycles, the testing may be terminated after three cycles. This test

procedure will require weighing the condensate collected after each cycle

(which is not now required). If these guidelines were not met, three

additional cycles would be run and the mean and variability results

calculated based on six cycles.

If after six cycles, the test results were not within the specified

limits of varibility additional testing would be required. Ihis additional

testing presents a potential problem of extended testing that would be

considered excessively costly for certification. Uie extreme variability

of the furnace data shown in Table 2 shows that it would be iitpossible to

meet these guidelines of variability even after 18 cycles. In order to

reduce the possibility of extended testing time by independent laboratory

certifiction of the unit, the following options would be involved:

(1) The manufacturer should be permitted to submit a rated mean value for

the unit that would apply for that basic model. If after the three

additional test cycles were run (for a total of six), the sanple mean

value for six cycles were within ±30% of the manufacturers rated mean

value, testing would be terminated. The rated value would then be

either of:

the manufacturers rated mean value; or the

measured value vAiichever were the lowest.
DOE may wish to expand on this to consider alternatively allowing the

manufacturers claimed rating to apply (since it would be based on a

larger number of cycles). This variance of £30% from the mean is not

very significant in terms of the overall efficienty for the furnace

described here in Table 2(a). An increase of 30% in condensate

collected amounted to only 0.3% increase in steady state efficiency

for this furnace.

(2) If after six cycles, the sample mean were outside these limits

specified above, then additional testing would be necessary. For

example, it may be that a small amount of condensate does form during

each cycle but does not drain from the furnace during any of the first

six cycles but then drains out in a later cycle. The option of

running three or more additional cycles for certification testing

beyond six should then be permitted. The rating would then be based

on the total number of cycles using the guideline of being within ±30%

of the manufacturers rated mean value. In the example given here

(Table 2(a)), the sample mean was within the ±30% of the population

mean value after the seventh cycle and remained within that range

thereafter
APPENDIX C-1

Sairple Calculation of Part Load

Efficiency Effect of Condensate Collection Rate

Example: Furnace C. With 6.7 grams per cycle difference in condensate,

collected or (6.7 4

. 3.8 minute) = 1.76 gram per minute.

o Input rate of furnace is 57.5 cubic feet per hour. Using methane as

typical carposition for stoichiometric calculation (this natrual gas

is 96% methane)

CH^ + 2O2 CO2 + 2H2O

o One cubic foot (ft^) of fuel forms two ft^ of water vapor. This water

is equivalQit to 0.1 lb or 45.4 grams

(2 ft^ r 360 ftVlb mol) x 18 Ig/lb mol = 0.1 lb.

o 'Hiis furnace consumes 57.5 cubic feet of natural gas per hour or 0.96

cubic feet per minute and forms 43.6 grams/minute of water v^x>r. Of

this total v^por formed 1.76 grams/minute is condensed.

o The total latent heat of vaporization of water in combustion of

natural gas is assigned 9.55% as the part load lateit loss.

o The equivalent in latent heat recovery percentage points for 1.76

grams/minute of condensate is (1.76 r 43.6) x 9.55 = 0.39 percentage

points in efficiency.
Appendix C - 2

Example of calculation for buner on and

off times presented In Table 3

Ton

60x _ 60 j ^ 60 _

_ _ 60 ( 1-x)

4Nx(l-x) 4N(l-x) ° (4) (N) (x) (1-x) 4Nx(l-x)

60

4Nx

Where x is the load factor fraction N is the furnace number of cycles at half

loads set equal to 5 for furnaces and 2 for boilers.

The calculation of load factor x is from the equation:

X = 65-Toa

65-5

Where: a is the oversize fraction and 5 F is the Average design temperature,

The calculation of Ton and Toff is from reference (12)

Example: Outdoor Temperature of 42 F and an oversize fraction of 70% («- .7)

65-42

60

= 0.225

Ton = 60(0.225)

4(5) (0.225)(0.775)

60

4(5)(0.225)(0.775)

3.87 min

Toff 3.87 = 13.33 min
Outdoor

temperature

data

of

’

total

hours

in

temperature

ranges

of5

degrees

during

heating

season

for

Charleston

W

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NBS-H4A (REV. 2-BO) U.S. DEPT. OF COMM. 1. PUBLICATION OR 2. Performing Organ. Report No, 3. Publication Date BIBLIOGRAPHIC DATA

REPORT NO.

SHEET (See Instructions) NBSIR 85-3225

4. TITLE AND SUBTITLE

Laboratory Study of Gas Fueled Condensing Furnaces

S. AUTHOR(S)

Esher R. Kweller, Robert A. Wise

6. PERFORMING ORGANIZATION (If joint or other than NBS, see Instructions)

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

7. Contract/Grant No.

8. Type of Report & Period Covered

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

Department of Energy

Office of Conservation and Renewable Energy

Washington, D.C. 20585

10. SUPPLEMENTARY NOTES

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

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

bibliography or literature survey, mention it here) The objective of this study was to determine if the direct measurement method of

condensate collection that was developed during prior testing of a condensing boiler

would be adequate for direct measurement of the condensate from gas fueled forced warm

air condensing furnaces. Results of these tests were for purposes of supporting a test

procedure proposed by the Department of Energy and responding to questions raised in

comments to the proposed procedures. Another objective of these tests was to quantify

the effects of varying test room ambient temperatures and relative humidity in the

rate of condensate collected with condensing furnaces. These test results with a high

rate of condensate collected with condensing warm air furnace show that:

• each 10 F decrease of room temperature amounted to an Increase of 1.1 points in part

load efficiency and 1.6 points in steady state efficiency.

• an increase of 0.2 percentage points in cyclic operating efficiency was found for

each 10% rise in relative humidity (with constant room temperature)

.

Results that were used by the Department of Energy in resolving questions raised by

commenters Included:

• A thirty minute period was found to be acceptable in place of a one hour test under

Steady State test conditions.

• Three test cycles were found to be sufficient for high efficiency furnaces having

repeatable condensate collection rate.

12. KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicolon s) Annual Efficiency; Condensing Furnace; Cyclic Efficiency; Part load efficiency;

Test Procedures; Gas Fueled.

13. AVAILABILITY

Unlimited

I I For Official Distribution. Do Not Release to NTIS

I I 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

15. Price

USCOMM-DC 8043-P80