GAS DISHWASHER AND BOOSTER HEATER …...Dishwashing machines and booster heaters are vital...

CEE/TR94-6 CM

GAS DISHWASHER AND BOOSTER HEATER

SAVINGS EVALUATION

Prepared by:

Center for Energy and Environment

100 North 6th Street, Suite 412A

Minneapolis, MN 55403-1520

Principal Investigators:

Mark W. Hancock

David L. Bohac

Essam S. Wahbah

December, 1994

Prepared for:

Minnegasco

800 LaSalle Avenue, Floor 11

PO Box 59038

Minneapolis, MN 55459-0038


SAVINGS EVALUATION

TABLE OF CONTENTS

EXECUTIVE SUMMARY ............................................................................................................ 1

INTRODUCTION .......................................................................................................................... 3

BACKGROUND ............................................................................................................................ 3

METHODOLOGY ......................................................................................................................... 4

Site and Equipment Operation Information ................................................................................ 4

Equipment Information ............................................................................................................... 4

Existing Electric Equipment ................................................................................................... 4

Replacement Gas Equipment.................................................................................................. 5

Monitoring System ...................................................................................................................... 6

RESULTS ....................................................................................................................................... 8

Measured Energy Use ................................................................................................................. 8

Normalized Energy Use ............................................................................................................ 12

Operating Costs ......................................................................................................................... 15

SUMMARY AND CONCLUSIONS ........................................................................................... 24

REFERENCES ............................................................................................................................. 26

Center for Energy and Environment Page 1

Gas Dishwasher and Booster Heater Savings Evaluation


SAVINGS EVALUATION

EXECUTIVE SUMMARY

Dishwashing machines and booster heaters are used in a wide variety of foodservice

establishments. These appliances are used to clean and sanitized dishes so that the foodservice

facility will be in compliance with the National Sanitation Foundation's Standard 3-82. The

introduction of gas fired booster heaters and dishwashing machines has made the economics of

retrofitting an existing electric warewashing system feasible under many circumstances. This

study monitored the energy consumption and heating load of an existing electric booster heater

and conveyor dishwashing machine and a replacement gas booster heater and gas fired conveyor

type dishwashing machine. Both systems had a nearly identical dishwashing capacity, but the

newer gas fired dishwashing machine had improvements to the wash and rinse cycles that reduce

water consumption. The warewashing system was located in a foodservice facility that provided

90% of the meals for residents of a 310 unit apartment style retirement community.

The annual operating costs were computed for the two warewashing systems and simple paybacks

were calculated based on the installed cost of the new warewashing system. The operating costs

included water and sewer charges and energy use and demand costs. Since it was not possible to

simultaneously monitor the warewashing system and building electric demand, it was not possible

to directly compute the contribution of the warewashing system to the total building demand.

Instead, low, average, and high "contribution factors" were estimated based on a previous study of

electric booster heaters (Sachi and Hewett 1990). Applying these factors to the measured peak

demand provided a range for the estimated peak demand charge. The actual value is most likely

midway between the average and high estimate.

The electric warewashing system had a estimated annual operating cost ranging from $8,316 to

$12,927 and the gas warewashing system had an annual operating cost of $3,494. The cost

savings are almost evenly split between electric demand and water use cost reductions. The

installed cost of the new gas fired booster heater and dishwashing machine was $25,000, which

resulted in paybacks for the new system ranging from 2.7 years to 5.2 years. The best estimate of

the simple payback is about 3 years. The data also showed that the gas warewashing system used

73% less source energy than did the electric warewashing system.

To account for a very large leakage rate that was present in the pre-retrofit electric system, the

pre-period operating costs were normalized to the water consumption measured in the post-

period. Normalized water consumption of the pre system was calculated based on manufacturer's

information of water consumption at 100% load. The ratio of the pre-period dishwashing

machine rated water use to that of the post-period was computed and then multiplied by the

measured post-period water consumption to compute an estimated water use for the pre-period.

The leakage rate was found to be 0.6 gallons per minute. Visual inspections and discussions with

kitchen staff indicated that this leakage rate was reasonable.



INTRODUCTION

Dishwashing machines and booster heaters are vital components of the foodservice industry.

Commercial establishments that commonly utilize dishwashing machines include restaurants,

hospitals, nursing homes, hotels, and dormitories. These sites make up 10% of the small

commercial sector (Dunsworth and Hewett, 1989). Foodservice operations use dishwashing

machines to comply with the National Sanitation Foundations (NSF) Standard 3-82, which

states that all dishes, pans, and serving containers that come in contact with the food must be

sanitized after every use. There are generally two means of sanitizing containers. The first is to

use a hot water rinse or high temperature method and the second is to use a chemical rinse or

low temp method. Booster heaters are used in the high temperature installations to supply water

at a elevated temperature (180°F) in order to kill any bacteria on the dishes after the wash and

rinse cycles. This study focused on a high temperature dishwashing machine and booster heater.

The purpose of this study was to evaluate the savings associated with the use of a gas booster

heater and a gas fired dishwashing machine in a foodservice location. Data was collected on an

existing electric booster heater and an electric dishwashing machine prior to the removal of the

equipment. A new gas booster heater and gas fired dishwashing machine were retrofitted in the

same establishment. Due to the regular use of the warewashing system, it was expected that a

valid comparison could be conducted using approximately one month of data for both the

electric and gas operated warewashing systems. The consumption by both systems was analyzed

and compared and the annual operating costs and savings were calculated.

BACKGROUND

Research on booster heaters and dishwashing machines has been well documented with regards

to performance and field monitoring of existing systems. Direct field measurements of pre-

retrofit and post-retrofit as presented in this report have not been published to a great extent. A

study of restaurant energy end uses was performed by Claar (1985) that documented all end uses

in the restaurant industry. Seven different categories of restaurant types were identified and five

different end use categories were monitored at each site. The end use categories included food

preparation, sanitation, refrigeration, lighting, and HVAC. The sanitation category included all

gas and electrical consumption for service water heating, dishwashing, laundry, and other

cleaning requirements. Claar found that sanitation was the third largest average end use for the

group of seven metered facilities. Sanitation consumed an averaged of 17.8% of the energy

entering the restaurants.

A study completed by Sachi (1990) looked at the potential for savings from the use of a gas

booster heater. This study monitored seven foodservice facilities that were equipped with

electric booster heaters. The total building electrical consumption was measured along with the

electrical consumption of the booster heater. Sachi found that for proper estimates of savings,

limited electric use monitoring must be performed. Data collected during the short monitoring

period could be used to identity the degree to which the booster heater demand was adding to

the building's peak consumption. Typically the booster heater's peak consumption occurred at a

Gas Booster Heater

r

120 F water building sery hot water

f r o m c e



dishwashing machine for both wash cycles and final rinse was supplied by the booster heater at a

temperature of 180°F. There was no separate water line to the dishwashing machine that supplied

120°F water from the buildings service hot water system for fills and skimming of the two tanks.

The water that was supplied to the booster heater was heated by a 72 gallon water heater that only

supplied hot water to the kitchen area.

Gas Booster -eater Con-F igurat ion

F = Flow Sensor T = Temperature Sensor

180 F water to dishwashing machine

Accumulator Aquastat

Pump

Figure 1 Gas Booster Heater Configuration

Replacement Gas Equipment

The retrofit involved the removal of both the electric booster heater and the electric dishwashing

machine. The new gas fired booster heater uses a Vanguard 250,000 Btu/hr instantaneous heater

with a 10 gallon accumulator (PowerPac 250). The equipment configuration of the PowerPac 250

is displayed in Figure 1. A pump is used to circulate water between the accumulator and the

heater. The pump is controlled by a aquastat located in the accumulator and the heater is



recorded by the data logger. Indicating relays were installed on the booster heater, wash tank,

and rinse tank elements. All the elements were controlled in an on/off operation. Power

measurements of each of the three heaters were performed using a Drantz model 808 power

analyzer. The power measurements were performed at different times during the pre-retrofit data

collection period to identify any drift in the electrical consumption. The fractional runtimes were

combined with the power measurements to give the energy consumption of the pre-retrofit dish

system. This method of computing electrical power consumption was accurate due to the

consistency of the power draw of resistance heating (i.e. the element electric use is nearly a step

function). The booster heater water consumption and inlet and supply temperatures were also

measured using a positive displacement water meter and T-type thermocouple thermowells

installed in the inlet and outlet water lines of the booster heater. Both non-weighted and water

flow rate weighted averages of the temperatures were computed and stored by the data logger2.

The booster heater thermal output was computed using the 15 minute average water

consumption and the flow weighted inlet and supply temperatures.

The energy consumption of the gas warewashing system was measured using a gas meter and two

indicating relays. Indicating relays were installed in parallel with the signals to the gas valves of

the fixed input rate burners on the dishwashing machine wash and rinse tanks. The input rate of

both burners was measured at the beginning and end of the monitoring to assure an accurate

measure of the input rate and that it did not change over the monitoring period. The consumption

of the dishwashing machine was computed by multiplying the fractional run time of each burner

by the burner's measured input rate. Previous studies have shown that this is an accurate method of

measuring the consumption of a fixed input gas burner (Lobenstein et al. 1992). The method of

control for the booster heater did not allow it to be monitored by an indicating relay. Instead, a

single gas meter3 measured the gas consumption of the booster heater and the dishwashing

machine combined. A pulse pickup was installed on the lowest resolution dial (1/2 cubic feet per

revolution) on the meter index. The sensor generated ten pulses per revolution resulting in a

resolution of 0.05 cubic feet per pulse. A constant multiplier of 1.12 was used to correct for the

gas line pressure. A subtraction method was used to split out the gas consumption between the

booster heater and the dishwashing machine. The booster heater gas consumption was computed

by subtracting the dishwashing machine consumption from the total consumption as read from the

meter. The positive displacement meter and T-type thermocouple thermowells from the pre-

retrofit monitoring period were left in place to measure the supply water temperature and thermal

output of the new booster heater and the water consumption of the dishwashing machine.

The measured consumption rate values used to convert fractional runtime into energy

consumption are listed in Table 2 for both the pre and post-periods. Except for the rinse tank

element for the pre-period, all input rate measurements were within 10% of the name plate

data. The low readings of the rinse tank heater was attributed to a malfunctioning heating

element in the tank.

2 flow rate weighted averages provide a more accurate indication of the average temperature of the water supplied to

the dishwashing machine.

3 this gas meter was also used for the single time measurements of the dishwashing machine burner inputs.

Center for Energy and Environment Page 9 Gas Dishwasher and Booster Heater Savings Evaluation

Weekdays 16 2246 (300) 190 (24) 204 (9) 394 (28)

Saturday 3 2337 (348) 200 (33) 211 (18) 411 (49)

Sunday 3 2161 (416) 186 (27) 191 (15) 377 (42)

Total Period 22 2247 (311) 191 (24) 203 (12) 394 (32)

Daily averages from the pre-period were separated into weekdays, Saturdays and Sundays in

order to determine if there were significant differences in the level of consumption for each type

of day. Table 3 displays the averages and standard deviations of the energy use for the different

types of days. A statistical' test of the daily average data indicated that there is not a statistically

significant difference in the use for the three different day types (p-value = 0.475). This is

somewhat expected, since about the same number of meals are served on each day. For the

following analysis all days of data are considered together and are not separated by day type.

Table 3 Comparison of Weekday and Weekend Pre-retrofit Daily Averages

note - values in ( ) are standard deviations

The post-retrofit monitoring period spanned from day 134 to 195 yielding 54 days of usable

data. Daily averages of water consumption, gas consumption by the booster heater, dishwashing

machine, and the two combined are displayed in Figure 3. As in the pre-period, the daily

consumption in the post-period is relatively stable.

4 analysis of variations

5 p-value represents the probability of observing a test result of a given magnitude in the absence of any real

relationship. A smaller p-value indicates greater confidence that there is a real difference between the average

consumption for the different day types. A p-value less than 0.05 is conventionally accepted as indication of a real

difference.



section. The gas booster heater efficiency was computed to be 48.4% - almost half of that

achieved by the electric booster.

Table 4 Comparison of Pre/Post Energy Use

e erio s e d

Number of days 22 54

Water Consumption (gal/day) 2,250 1,070

(310) (110)

Volume Weighted Inlet Temperature (F) 147.3 142.7

(1.2) -(2.2)

Volume Weighted Outlet Temperature (F) 183.7 174.5

(1.6) (4.0)

Booster Heater Energy Output (Btu/hr) 25,490 9,810

(3,410) (1,040)

Booster Heater Input Energy: Site (Btu/hr) 27,180 20,070

(3,460) (2,400)

Booster Heater Site Efficiency 93.8 % 48.9 %

Booster Heater Input Energy : Source (Btu/hr) 87,690 20,270

(11,170) (2,420)

Booster Heater Source Efficiency 29.1 % 48.4 %

Dishwashing Machine Input Energy: Site (Btu/hr) 28,900 28,810

(1,680) (2,950)

Dishwashing Machine Input Energy: Source (Btu/hr) 93,240 29,100

(5,420) (2,980)

Warewashing System Energy Input: Site (Btu/hr) 56,090 48,880

(4,591) (4,847)

Warewashing System Energy Input: Source (Btu/hr) 180,930 49,370

(14,810) (4,900)

note - values in ( ) are standard deviations

For comparisons of gas and electric systems it is important to not only consider the energy used

at the site, but also the equivalent source energy of the raw products used to deliver the

commodity consumed at the site. For this analysis it was assumed that the conversion efficiency

for electricity is 31%6 and 99% for gas

7. With these conversion factors, the pre-period booster

heater source energy consumption increases to 87,690 Btu/hr and the post-period increases to

20,270 Btu/hr. As a result, the electric booster efficiency is computed to be 29.1% and the

efficiency of the gas is 48.4%. Thus, when the use of source energy is considered, the efficiency

of the gas booster heater is 66% greater than that of the electric heater.

The lower half of Table 4 includes the energy use results for the dishwashing machine and for

the entire warewashing system (i.e. dishwashing machine and booster heater combined). The

two dishwashing machines used approximately the same amount of energy per day. The electric

system used an average of 28,900 Btu/hr and the gas system used 28,810 Btu/hr. However, a

6 this includes power plant conversion and distribution efficiency.

1% losses are typically due to leaks in the gas distribution system.

Ele

ctri

cal

Use

(k

wh/d

ay)



500

450

400

350

300

250

—

200

150

100

50 —

0

x X_

_x—xx. — — —53R

+ +

x

x — — x

x— —

x

-

y = 0.0907x + 189.98

+ ++ ++ y= 0.0209x

+-I. +

+ 155.88

1500 1700 1900 2100 2300 2500 2700 2900

Water Use (gal/day)

+ Dishwashing Machine X Warewashing System — — — Linear (Warewashing System) ________ Linear (Dishwashing Machine )

Figure 4 Variation in Energy Use With Water Use for the Pre-Retrofit Period

The regression equations and the adjusted pre-period water consumption of 1,270 gal/day were used to compute the normalized daily average energy use values displayed in Table 5. Since the

electric dishwashing machine energy use is relatively insensitive to changes in water

consumption, the 44% reduction in estimated water use results in only a 10% reduction in energy use. The normalized electric dishwashing machine use is 10% less than that of the gas

machine, but the source energy use by the electric machine is still considerably higher (187%)

than that for the gas machine. The reduction in system water use results in a relatively large 37%

reduction in total energy use. The water use normalized consumption of 35,450 Btu/hr is 28% below that for the gas system. However, the normalized source energy use of the electric system

is 132% higher than that for the gas system.

Table 6 Heating Load Normalized Consumption of the Pre-Retrofit Booster Heater

PtOeriod: :

as-16stie0d.:.

e OW Normalized

st,Tgife

s..M00iii

Booster Heater Energy Output (Btu/hr) 25,490 9,810 9,810

(3,410) (1,040)

Booster Heater Energy Input: Site (Btu/hr) 27,180 11,260 20,070

(3,460) (2,400)

Booster Heater Site Efficiency 93.8 % 87.1 % 48.9 %

Booster Heater Energy Input: Source (Btu/hr) 87,690 36,330 20,270

(11,170) (2,420)

Booster Heater Site Efficiency 29.1 % 27.0 % 48.4 % note - values in ( ) are standard deviations

Operating Costs

The operating costs of the two warewashing systems was computed by summing the annual

energy demand, energy use, and water use costs. The energy and water use costs can be directly

computed using the results of the earlier sections. However, estimates of the electric demand

cost requires an evaluation of the contribution of the warewasher system electric demand to the

total building demand. The first step in this process was to determine the peak 15 minute electric

use. Results from a previous study were then used to estimate the percentage of the warewasher

peak demand that contributes to the total building peak demand.

Figure 5 shows the maximum 15 minute electric demand of the dishwashing machine, booster

heater, and warewashing system for each day of the monitoring period. From the graph it can be

seen the dishwashing machine has a constant peak that is equal to 100% of its rated capacity.

The peak for the dishwashing machine is typically set during the first wash cycle of the day. The

heat for the water in the tanks is lost to the dishes during the first cycle and the heating elements

are activated to replace the heat and maintain 160°F in the wash and rinse tanks. The tank

heating elements in the dishwashing machine often operated for entire 15 minute periods in

order to keep the tank water at the setpoint temperature.

Table 7 displays the maximum, minimum, and average peak demand for the 22 days of data for

the booster heater, dishwashing machine, and warewasher system. The booster heater peak

demand varies between 50% to 100% of its measured full rated consumption of 50.5kw. The

average booster heater peak demand for a day is 72% of the full measured demand. The peaks

occur at different times in the day depending on the number of racks of dishes the dishwashing

machine is processing. The booster heater peak typically occurs after a breakfast, lunch, or

dinner serving period. The booster heater is the largest electrical draw and the key component

that drives the peak consumption of the warewashing system. The warewasher peak demand

varies from 61% to 100% of the measured full rated consumption and averages 78% of the full

rated. Since the dishwashing machine often operates continuously for 15 minute periods and the

booster heater peak demand for a day averages 72% of the full rated demand, it is likely that the

warewashing system will contribute a high percentage, perhaps 80%, of the system full rated

demand to the building demand.

Center for Energy and Environment 0 Page 15




1 14.2 7.5 0.53

2 4.9 4.5 0.92

3 9.9 1.9 0.19

4 14.6 3.0 0.21

5 37.7 30.4 0.81

6 15,5 10.6 0.68

7 30.5 8.8 0.29

High 0.92

Average 0.52

Low 0.19

es

a,

4.)

it

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0

• •

0 • •

a •

a •

•

a

• • • • •❑

a a

• • •

•

a

13 18 23 28 33 38 43

Julian Date

a Booster Heater • Wareveashing System

Figure 6 Ratio of Afternoon Peak Demand to Daily Peak Demand

A previous study conducted by Sachi and Hewett (1990) computed the ratio of the electric

booster heater peak for an entire month to the booster heater demand that occurred during the

building peak demand period. This analysis was conducted for seven different foodservice

facilities. Table 8 displays the data and shows that the demand ratio varies from 0.19 to 0.92

with an average value of 0.52.

Table 8 Ratio of Booster Building Demand Contribution to Maximum Booster Demand

Data from Sachi and Hewett (1990)



$ 914 Annual Operating Cost: Average

$4,514

$6,329 Annual Operating Cost: High

Energy Use*

Energy Demand: Low*

Energy Demand:

Average Energy Demand:

High

Annual Operating

Cost: Low

69,650 (kwh/yr.)

9.6 (max. kw/month)

26.2 (max. kw/month)

46.4 (max. kw/month)

sy

1,758

(ccf/yr.)

N/A

era n ............

$ 914

N/A

N/A

N/A

$2,159

$ 863

$2,355 N/A

$4,170 N/A

$3,022

Table 9 Operating Cost Comparison of Pre and Post-Retrofit Warewashing Systems: As Measured

e-Retrofit POWRetrOfit:

er

Onsumptian

Intl 04. .4 figinifftiou„„:..

nu

Energy Use* 143,708

(kwh/yr.)

$4,455 4,282

(ccf/yr.)

N/A

$2,227

N/A Energy Demand:

Low**

13.3

(max. kw/month)

$1,195

Energy Demand:

Average

36.5

(max. kw/month)

$3,281 N/A N/A

Energy Demand:

High

64.6

(max. kw/month)

$5,806 N/A N/A

Water & Sewer***

(gal/yr.)

820,155 $2,666 389,820 $1,267

Annual Operating

Cost: Low

$8,316

Annual Operating

Cost: Average $10,402 $3,494

Annual Operating

Cost: High $12,927

* Operating costs were calculated with $0.03 l/kwh and $0.52/ccf

** Demand charges were calculated with and average demand charge for the entire year of $7.49/kw

*** Water and sewer charges were calculated with $3.25 per 1000 gallons of water used,

Table 10 Operating Cost Comparison for Booster Heater: As Measured

Operating costs were calculated with $0.03 l/kwh and $0.52/ccf

http://max.kw/month)





** Demand charges were calculated with and average demand charge for the entire year of $7.49/kw




year or 53%. The simple payback for this retrofit is 6.4 years. While this is a relatively long

payback for most commercial customers, this retrofit, or upgrade, will most often be considered

only at times of equipment purchase. In that situation, only the incremental cost of the system

over the less efficient option should be considered and the actual payback will be much lower

than 6.4 years. A payback based on incremental cost was not considered for this study, but would

be a straightforward calculation.

Table 12 Operating Cost Comparison of Warewashing System: Normalized by Water Consumption

irra .0 ... ... . ..... ro ... .. . .... .... .. ..

n s u f t

0 In 0

Energy Use* 90,830

(Kwh/yr.)

$2,816 4,282

(ccf/yr.)

N/A

$2,227

N/A Energy Demand:

Low* 12.7

(max. kw/month)

$1,141

Energy Demand:

Average

34.6

(max. kw/month)

$3,110 N/A N/A

Energy Demand:

High

61.3

(max. kw/month) $5,510 N/A N/A

Water & Sewer***

(gal/yr.)

461,981 $1,501 389,820 $1,267

Annual Operating

Cost: Low

$5,458

Annual Operating

Cost: Average $7,427 $3,494

Annual Operating

Cost: High $9,827

* Operating costs were calcula ed with $0.031/kwh and $0.52/ccf

** Demand charges were calcu ated with and average demand charge for the entire year of $7.49/kw *** Water and sewer charges were calculated with $3.25 per 1000 gallons of water used,

Table 13 compares the water use normalized pre-retrofit dishwashing machine annual operating

costs to those of the post-retrofit machine. The water use normalization results in a 24%

reduction of the pre-period system total cost from $5,888 to $4,490. The reduced costs are largely

due to the reduction in energy and water use costs. With the reduced pre-period costs, the savings

for the gas dishwashing machine is at least $1,900 per year or 43%.





period (183.7 °F - 147.3°F = 36.4°F). Multiplying the ratio of 31.8/36.4 by the adjusted

demand of 39.5 results in an estimated demand for the pre-period of 34.5kw.

The peak demand was then multiplied by the high, average, and low demand contribution ratios

found earlier to compute the normalized demand costs shown in Table 14. For an average

contribution ratio of 0.52, the gas booster heater costs $1,592 less per year to operate than the

electric heater. This is a savings of about 64% and is almost entirely due to eliminating the

electric demand charges. For this installation the cost of the booster heater installation was not

determined separately from the entire cost of the warewashing system so it was not possible to

compute a simple payback on the cost savings. However, a previous study (Sachi and Hewett,

1990) estimated an installed cost of $2,100 to $5,300. Depending on which combination of

equipment cost and operating savings are used, the simple payback for this installation varies

from 0.7 to 9.2 years. However, using an average contribution ratio of 0.52 and a installation

cost of $3,000 yields a simple payback of 1.9 years. The payback is reduced to less than one

year if the analysis is conducted using the incremental cost of a gas booster heater compared to

an electric booster heater (installed cost of approximately $1,750).

Table 14 Operating Cost Comparison for Booster Heater: Normalized by Heating Load

rmal ze

11SUMp ................ era ................ s u mp t eras n ..........

Energy Use* 28,950

(kwh/yr.)

$ 897 1,760

(ccf/yr.)

$ 914

Energy Demand:

Low**

6.6

(max. kw/month)

$ 593 N/A N/A

Energy Demand:

Average 17.9

(max. kw/month)

$1,609 N/A N/A

Energy Demand:

High

31.7

(max. kw/month)

$2,849 N/A N/A

Annual Operating

Cost: Low

$1,490

Annual Operating

Cost: Average $2,506 $ 914

Annual Operating

Cost: High $3,746

* Operating costs were calculated with $0.03 l/kwh and $0.52/ccf ** Demand charges were calculated with and average demand charge for the entire year of $7.49/kw






gas warewashing system resulted in a 73% reduction in source energy use when compared to

an electric system. Even when the results are normalized for water consumption, the gas

system still uses 57% less source energy than the electric system.

The lower portion of Table 15 also shows the operating cost comparison and simple payback

for a gas booster heater compared to the electric booster heater under similar heating loads.

The payback ranges from 1.1 to 5.2 years and is expected to be about 1.5 years. If only the

incremental cost of the gas booster heater is considered, the payback is reduced to less than

one year. Thus, a gas booster heater is a highly cost effective alternative to an electric booster

heater. The heating load normalized analysis also shows that the source energy use of the gas

booster heater is 44% less than that of the electric booster heater.

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