u ..........."v• •-'1.);;, ::.1..)UJo.+O Lv ;J,Jv:,,;.; I Lv f

Flonda Solar Energy Industries Assoc. In....

Exhibit _ (WTG-l)

Schedule 1

Electrical Use, Efficiency,

and Peak Demand of

Electric Resistance, Heat

Pump, Desuperheater, and

Solar Hot Water Systems

FSEC-PF-215-90

Tim Merrigan

Danny Parker

Florida Solar Energy Center

300 State Road 401

Cape Canaveral, Florida 32920

Published in

ACEEE 1990 Summer Study on

Energy Efficiency in Buildings.

Views and opinions expressed here represent

those of the authors and not necessarily

those of the Florida Solar Energy Center.

. .

EE-RM-90-201 COMMENT OOI5

U\Jl...h.L: •• -.u;;, ::1..,)UJo+O Lv :J, l\ .,) I L v f 

Flonda Solar Energy Industries Assoc , In ..... 

Exhibit _ (WTG-l) 

Schedule 1 

Electrical Use, Efficiency, 

and Peak Demand of 

Electric Resistance, Heat 

Pump, Desuperheater, and 

Solar Hot Water Systems 

FSEC-PF-21S-90 

Tim Merrigan 

Danny Parker 

Florida Solar Energy Center 

300 State Road 401 

Cape Canaveral, Florida 32920 

Published in 

ACEEE 1990 Summer Study on 

Energy Efficiency in Buildings. 

Views and opinions expressed here represent 

those of the authors end not necessarily 

those of the Florida Solar Energy Center. 
Docl\et Nos 930548-EG - 930551-EG

Florida Solar Energy Industries Assoc., Inc.

Exhibit_ (WTG-l)

SchedJlel

Page 2 of 12

ELECTRICAL USE, EFFICIENCY, AND PEAK DEMAND OF ELECTRIC

RESISTANCE, HEAT PUMP, DESUPERHEATER, AND

SOLAR HOT WATER SYSTEMS

Tim Merrigan and Danny Parker

Florida Solar Energy Center

Eighty single family residences in Florida were monitored for two years in order to

collect data on water heating electrical energy consumption, efficiency, and time-ofday demand. The homes were divided into equally sized samples of four different

water heating systems: conventional electric resistance, heat pump, desuperheater and

solar hot water systems.

Electrical consumption for electric resistance water heaters averaged 8.3 kWh per day

in Florida with an average water heating ~ystem efficiency of 82%. Desuperheaters

used an annual average of 7.4 kWh per day at an annual system efficiency of 110%

and heat pump water heaters used 6.1 kWh per day at an average system efficiency

of 153%. Electrical use of solar hot water systems averaged 2.7 kWh per day and

the average system efficiency was 235%.

Electrical demand taken at IS-minute intervals showed electric resistance water

heaters contribute approximately 1.1 kW of diversified demand to the utility winter

peak and at least 0.2 kW to the summer peak. Solar hot water systems exhibited the

most desirable demand profile relative to Florida utility coincident peak loads with

a 0.7 kW per customer reduction in the winter and a minimum 0.2 kW per customer

reduction in the summer. Desuperheaters have the same 0.2 kW minimum peak

demand reduction in the summer and 0.2 JeW per customer reduction in the winter.

Heat pump water heaters exhibited approximately half the peak demands of electric

water heaters in the winter but were unable to reduce swmner peak: demand by any

significant amount.

Since electric water heaters account for approximately 25 percent of the utility winter

peak demand per customer, encouraging the use of alternative water heating methods

is beneficial to a winter-peaking utility in Florida.

INTRODUCTION

Since 1982, Florida's electric utilities have sold more

electricity each year in the state than they have

produced (Florida Public Service Commission 1985.

1989). Fortunately. this situation is the planned

result of purchasing more economical power from

electric utilities in the neighboring states of Georgia

and Alabama. Since the purchased power is more

economical. the transmission lines that carry this

power from the neighboring states are generally at

full capacity. Unfortunately, when a high demand

for electricity occurs, Florida's utilities are severely

limited in their ability to increase capacity beyond

their own generation. Such a circwnstance recently

occurred on December 24, 1989 when a strong

winter cold front quickly passed through the

southeastern United States. The cold weather

created a peak demand for electricity that Florida's

utilities were unable to meet, in part because the

EE-RM-90-201 COMMENT OOI5

Dodlet Nos 930548-EG - 930551 -EG 

Florida Solar Energy Industries Assoc .. Inc. 

Exhibit _ (WTG-l) 

SchedJlel 

Page 2 of 12 

ELECTRICAL USE, EFFICIENCY, AND PEAK DEMAND OF ELECTRIC 

RESISTANCE, HEAT PUMP, DESUPERHEA TER, AND 

SOLAR HOT WATER SYSTEMS 

Tim Merrigan and Danny Parker 

Florida Solar Energy Center 

Eighty single family residences in Florida were monitored for two years in order to 

collect data on water heating electrical energy consumption, efficiency, and time-ofday demand. The homes were divided into equally sized samples of four different 

water heating systems: conventional electric resistance, heat pump, desuperheater and 

solar hot water systems. 

Electrical consumption for electric resistance water heaters averaged 8.3 kWh per day 

in Florida with an average water heating ~ystem efficiency of 82%. Desuperheaters 

used an annual average of 7.4 kWh per day at an annual system efficiency of 110% 

and heat pump water heaters used 6.1 kWh per day at an average system efficiency 

of 153%. Electrical use of solar hot water systems averaged 2.7 kWh per day and 

the average system efficiency was 235%. 

Electrical demand taken at IS-minute intervals showed electric resistance water 

heaters contribute approximately 1.1 kW of diversified demand to the utility winter 

peak and at least 0.2 kW to the summer peak. Solar hot water systems exhibited the 

most desirable demand profile relative to Florida utility coincident peak loads with 

a 0.7 kW per customer reduction in the winter and a minimum 0.2 kW per customer 

reduction in the summer. Desuperheaters have the same 0.2 kW minimum peak 

demand reduction in the summer and 0.2 leW per customer reduction in the winter. 

Heat pump water heaters exhibited approximately half the peak demands of electric 

water heaters in the winter but were unable to reduce summer peak demand by any 

significant amount. 

Since electric water healers account for approximately 25 percent of the utility winter 

peak demand per customer, encouraging the use of alternative water heating methods 

is beneficial to a winter-peaking utility in Florida. 

INTRODUCTION 

~ 

Since 1982. Florida' s electric utilities have sold more 

electricity each year in the state than they have 

produced (Florida Public Service Commission 1985. 

1989). Fortunately. this situation is the planned 

result of purchasing more economical power from 

electric utilities in the neighboring states of Georgia 

and Alabama. Since tile purchased power is more 

economical. the transmission lines that carry this 

power from the neighboring stales are generally at 

full capacity. Unfortunately, when a high demand 

for electricity occurs, Florida's utilities are severely 

limited in their ability to increase capacity beyond 

their own generation. Such a circwnstance recently 

occurred on December 24, 1989 when a strong 

winter cold front quickly passed through the 

southeastern United States. The cold weather 

created a peak demand for electricity that Florida's 

utilities were unable to meet. in part because the 
transmission of purchased power was already at full

capacity. The result was numerous large-scale

service interruptions due to rotated curtailments and

an understandable breakdown of overloaded

equipment. The state's largest utility, Rorida Power

and Light Company (FPL), experienced a demand of

close to 16,000 megawatts (MW), a level that was

not expected until 1998! FPL had forecast a 1989-

90 winter peak demand of approximately 13,500

MW -- based in part on the previous winter and

summer peak demands of 12,876 MW and 13,425

MW, respectively (FPL 1989).

Clearly, the ability to supply the winter peak demand

without service interruptions is of major concern to

Florida utilities. However, these utilities have

historically used summer peak demand as the basis

for determining a minimum capacity reserve margin.

Winter peak demand is generally only considered in

a loss-of-load probability analysis for determining

the need for new generating capacity (FPL 1989).

The 1989 Christmas Eve power shortfall, however,

emphasizes that any method to reduce peak demand

-- winter or sununer - should be imponant to a

utility's planning process, especially in a high

growth state like Rorida.

One area for utility peak load management lies in the

residential sector. Since 1970, residential electricity

consumption has been approximately 50 percent of

the total annual electricity use in the state of Florida.

In 1988, residential customers consumed over 63

million megawatt-hours with an annual growth rate

of over five percent for each of the preceding four

years (FPSC 1989). This growth rate exceeded the

population growth rate by at least two percent for

each of these years.

./ -~

Water heating accounts for approximatel~1 perceny

of the residential electricity consumption

(FPL 1978). Over 99 percent of this energy is due to

the use of electric resistance water heaters. Alternative water heating technologies - solar hot water

systems, heat pump water hearers, and desuperheater

units that recover the waste heat of the refrigerant

in a residence's air-conditioning equipment --

account for less lhan one percent of the domestic hot

water (DHW) systems in the state (Rorida

Governor's Energy Office 1981). Of course, these

water heatin~ alternatives still reQuire electricity

Docket Nos 930548-EG - 930551-EG

Florida Solar Energy Industries Assoc., Inc.

Exhibit _ (WTG-l)

Schedule 1

Page 3 of 12

to operate or to supply backup water heating when

neither solar nor waste heat is available.

To evaluate the impact of alternative water heating

technologies on the electric utility, it is necessary to

measure the time-of-day electricity consumption of

each system type in a number of occupied

residences. However, the electrical consumption of

any DHW method can vary considerably depending

on the temperature of the hot water delivered and the

actual water use of the residences's household.

Unless a fairly large number of houses are measured

to eliminate the variance in these quantities, it is also

necessary to measure the hot water energy delivered

by the DHW system. This latter quantity can

account for the variations in water temperature as

well as volume .and, therefore, can serve as a

common ground for comparison.

METHODOLOGY

A Florida solar energy research and testing institute

(FSEC) has had an active program in solar domestic

hot water system field monitoring since 1978

(McCluney 1980; Block 1983). In order to compare

the measured performance of solar systems with the

performance of other types of domestic hot water

systems, the field monitoring program was expanded

in 1982. Under the sponsorship of the Florida public

utility regulatory commission, FSEC collected time~..

of-day performance data for two years (July 1982·'

June 1984) on four types of DHW systems:

1. Electric resistance water heaters (that met

ASHRAE- Standard 90A-1980)

2. Heat pump water heaters

3. Solar hot water systems (with collectors that met

ASHRAE Standard 93·1977)

4. Desuperheater water heaters.

Twenty systems of each DHW type were instrumented to detennine both their IS-minute electrical

demand and hot water energy use. The systems were

located in single-family residences in four major

population areas of Florida: Jacksonville in north

Rorida, Orlando/Brevard County in ea~t central

Rorida. the Tampa Bay region in west central

Rorida. and Broward/Palm Beach counties in south

EE-RM-90-201 COMMENT OOI5

transmission of purchased power was already at full 

capacity. The result was numerous large-scale 

service interruptions due to rotated curtailments and 

an understandable breakdown of overloaded 

equipment. The state's largest utility, Rorida Power 

and Light Company (FPL), experienced a demand of 

close to 16,000 megawatts (MW), a level that was 

not expected until 1998! FPL had forecast a 1989-

90 winter peak demand of approximately 13,500 

MW -- based in part on the previous winter and 

summer peak demands of 12.876 MW and 13,425 

MW, respectively (FPL 1989). 

Clearly, the ability to supply the winter peak demand 

without service interruptions is of major concern to 

Florida utilities. However. these utilities have 

historically used summer peak demand as the basis 

for determining a minimum capacity reserve margin. 

Winter peak demand is generally only considered in 

a loss-of-Ioad probability analysis for determining 

the need for new generating capacity (FPL 1989). 

The 1989 Christmas Eve power shortfall. however. 

emphasizes that any method to reduce peak demand 

-- winter or sununer - should be imponant to a 

utility's planning process, especially in a high 

growth state like Rorida. 

One area for utility peak load management lies in the 

residential sector. Since 1970, residential electricity 

consumption has been approximately 50 percent of 

the total annual electricity use in the state of Florida. 

In 1988, residential customers consumed over 63 

million megawatt-hours with an annual growth rate 

of over five percent for each of the preceding four 

years (FPSC 1989). This growth rate exceeded the 

population growth rate by at least two percent for 

each of these years. 

./ 

~ 

-~ 

Water heating accounts for approximatel~ 1 perceny 

of the residential electricity consumption ifii::'roi1da 

(FPL 1978). Over 99 percent of this energy is due to 

the use of electric resistance water heaters. Alternative water heating technologies - solar hot water 

systems, heat pump water hearers. and desuperheater 

units that recover the waste heat of the refrigerant 

in a residence's air-conditiOning equipment --

account for less lhan one percent of the domestic hot 

water (DHW) systems in the state (Rorida 

Governor's Energy Office 1981). Of course. these 

water heatin~ alternatives still reQuire electricity 

DOCket Nos 930548·EG - 930551-EG 

Florida Solar Energy Industries Assoc., Inc. 

Exhibit _ (WTG-l) 

Schedule 1 

Page 3 of 12 

to operate or to supply backup water heating when 

neither solar nor waste heat is available. 

To evaluate the impact of alternative water heating 

technologies on the electric utility. it is necessary to 

measure the time-of-day electricity consumption of 

each system type in a number of occupied 

residences. However, the electrical consumption of 

any DHW method can vary considerably depending 

on the temperature of the hot water delivered and the 

actual water use of the residences's household. 

Unless a fairly large number of houses are measured 

to eliminate the variance in these quantities. it is also 

necessary to measure the hot water energy delivered 

by the DHW system. This latter quantity can 

account for the variations in water temperature as 

well as volume . and, therefore, can serve as a 

common ground for comparison. 

METHODOLOGY 

A Florida solar energy research and testing institute 

(FSEC) has had an active program in solar domestic 

hot water system field monitoring since 1978 

(McCluney 1980; Block 1983). In order to compare 

the measured performance of solar systems with the 

performance of other types of domestic hot water 

systems, the field monitoring program was expanded 

in 1982. Under the sponsorship of the Florida public 

utility regulatory commission, FSEC collected time~ .. 

of -day perfonnance data for two years (July 1982 -' 

June 1984) on four types of DHW systems: 

1. Electric resistance water heaters (that met 

ASHRAE- Standard 90A-1980) 

2. Heat pump water heaters 

3. Solar hot water systems (with collectors that met 

ASHRAE Standard 93-1977) 

4. Desuperheater water heaters. 

Twenty systems of each DHW type were instrumented to detennine both their IS-minute electrical 

demand and hot water energy use. The systems were 

located in single-family residences in four major 

population areas of Florida: Jacksonville in north 

Rorida. Orlando/Brevard County in ea~t central 

Rorida, the Tampa Bay region in west central 

Rorida. and BrowardIPalm Beach counties in south 
Florida. The systems were selected both to achieve

a geographic balance of five systems of each type in

each population region and to reflect relatively

similar family sizes (Merrigan 1983).

To measure the hot water energy delivered by the

system. a heat (Btu) meter was installed on each

system. The heat meter utilized a flow meter located

in the cold water supply line to the hot water storage

tank, as well as both a cold and hot water

temperature sensor to calculate the thermal energy

change of the heated water before it is delivered to

the household. Laboratory tests on the flow meter

indicated flow accuracies within 2.5% of the true

mass flow over long time periods. Similar tests on

the heat calculation indicated an accuracy of within

5% of the true energy flow (Merrigan 1981), with

resolutions of 1000 Btu (l055 kJ) and 1 gal (3.8 L).

A kilowatt-hour (kWh) meter was used to record the

resistance element energy as well as any auxiliary

energy used by the pumps, conuols, and/or

compressor of an alternative DHW system. Standard

single-phase 30 amp meters were used with pulse

initiators that had a resolution of 1 watt hour (Wh).

A solid-state demand recorder accumulated contact

closure pulses from the kWh, Btu, and flow meters

and stored them in 15-minute totals in its internal

memory. These totals were routinely acquired by

UOC"l:!t 1'<05 :1.ju:>4o-t:1.> -- \:IJO:>:>l-cU

Florida Solar Energy Industries Assoc.. Inc.

Exhibil_ (WTG-1)

Sct1edJ1e 1

Page4 of 12

telephone interrogation of the demand recorders,

transferred to a microcomputer. and stored on

magnetic media for eventual data reduction.

RESULTS

Table 1 lists the sample size, the average family size,

the daily average hot water use, the daily average

electric usc, and a dimensionless coefficient of

performance (COP) for the four DHW types for the

two-year period July I, 1982 to June 30. 1984.

(Two electric and four beat pump water beaters were

omitted from these averages because of

instrumentation malfunctions or hot water system

equipment problems.) COP is dermed as the hot

water energy use divided by the electrical energy

consumption and is, therefore, a measure of the total

DHW system efficiency.

Figure 1 displays the average daily electrical load

profiles (based on IS-minute intervals) for the four

DHW groups for the two-year period. The hours

displayed are clock times. rather than the year-round

standard time that is sometimes used in annual data

acquisition projects subject to the hour offset of a

summer daylight savings period. This approach was

taken since household hot water use generally

corresponds to actual clock time, as seen by the

apparent awakening of the Florida groups around

6:00 a.m.

Table 1. Florida Group Sizes. Annual Daily Average Hot Water Use. Electric Use. and

Coefficient of Performance

Sample Size Family Hot Water Electric Coefficient

No. of Size Use Use of

Systems People Gal (L)/Day (kWh/Pay) Performance

Electric 18 3.6 55.7 8.3 0.82

Resistance (211.1 )

Heat Pump 16 3.9 74.0 6.1 1.53

Water Heater (280.5)

Solar Hot 20 3.1 53.8 2.7 2.35

Water Heater (203.9)

Desuperheater 20 3.6 58.6 7.4 1.10

Unit (222.1 )

EE-RM-90-201 COMMENT OOI5

Florida. The systems were selected both to achieve 

a geographic balance of five systems of each type in 

each population region and to reflect relatively 

similar family sizes (Merrigan 1983). 

To measure the hot water energy delivered by the 

system, a heat (Btu) meter was installed on each 

system. The heat meter utilized a flow meter located 

in the cold water supply line to the hot water storage 

tank, as well as both a cold and hot water 

temperature sensor to calculate the thermal energy 

change of the heated water before it is delivered to 

the household. Laboratory tests on the flow meter 

indicated flow accuracies within 2.5% of the true 

mass flow over long time periods. Similar tests on 

the heat calculation indicated an accuracy of within 

5% of the true energy flow (Merrigan 1981), with 

resolutions of 1000 Btu (l055 kJ) and I gal (3.8 L). 

A kilowatt-hour (kWh) meter was used to record the 

resistance element energy as well as any auxiliary 

energy used by the pumps. conuols. and/or 

compressor of an alternative DHW system. Standard 

single-phase 30 amp meters were used with pulse 

initiators that had a resolution of 1 watt hour (Wh). 

A solid-state demand recorder accumulated contact 

closure pulses from the kWh. Btu. and flow meters 

and stored them in 15-minute totals in its internal 

memory. These totals were routinely acquired by 

vQ(;"~I S :1.:1U04o - t:u -- \:KlOool-t:U 

Florida Solar Energy Industries Assoc., Inc. 

Exhibit _ (WTG-l) 

SctledJIe 1 

Page4 of 12 

telephone interrogation of the demand recorders. 

transferred to a microcomputer, and stored on 

magnetic media for eventual data reduction. 

RESULTS 

Table 1 lists the sample size. the average family size. 

the daily average hot water use. the daily average 

electric use. and a dimensionless coefficient of 

performance (COP) for the four DHW types for the 

two-year period July 1. 1982 to June 30, 1984. 

(Two electric and four heat pump water heaters were 

omitted from these averages because of 

instrumentation malfunctions or hot water system 

equipment problems.) COP is defined as the hot 

water energy use divided by the electrical energy 

consumption and is. therefore. a measure of the total 

DHW system efficiency. 

Figure 1 displays the average daily electrical load 

proflles (based on IS-minute intervals) for the four 

DHW groups for the two-year period. The hours 

displayed are clock times. rather than the year-round 

standard time that is sometimes used in annual data 

acquisition projects subject to the hour offset of a 

summer daylight savings period. This approach was 

taken since household hot water use generally 

corresponds to actual clock time. as seen by the 

apparent awakening of the Florida groups around 

6:00 a.m. 

Table 1. Florida Group Sizes, Annual Daily Average Hot Water Use , Electric Use, and 

CoeffiCient of Performance 

Sample Size Family Hot Water Electric Coefflcient 

No. of Size Use Use of 

S~stems People Gal (LllDa:z:: !kWh/Da:z::l Performance 

Electric 18 3.6 55.7 8.3 0.82 

Resistance (211.1 ) 

Heat Pump 16 3.9 74.0 6.1 1.53 

Water Heater (280.5) 

Solar Hot 20 3.1 53.8 2.7 2.35 

Water Heater (203.9) 

DesuperheatCf 20 3.6 58.6 7.4 1.10 

Unit (222.1 ) 
LJOCl\et Nos 930!:>48-~G - 930551-EG

Florida Solar Energy Industries Assoc.. Inc.

Exhibit _ (WTG-1)

ScheciJle1

Page 5 of 12

Type 01 System

Florida average daily electrical demand

(July 1. 1982.· June 30.1984)

Figures 2 through 5 present the average IS-minute

demand profiles for the four DHW system types on

the FPL winter peak day of February 7, 1984.

Figures 6 tbrough 9 presents the same time-of-day

profiles for the summer peak day of July 25, 1983.

These two days were selected for presenlation

because they represent the bighest utility system

loads of all the FPL peak days that did not have

service interruptions.

The average electricity use of 8.3 kWh per day for

the electric resistance water heater group - with an

average family size of 3.6 people -- compares

f~vorably with values obtained by other studies

performed in Florida. FPL determined in a 1976-77

study of. 165 customers that a family of four used an

average of 10.2 kWh per day (FPL 1978). Florida

Power Corporation determined in a similar study that

a f:mrily of three used an average of 8.4 kWh per

day and a family of four used 11.6 kWh per day

(FPC 1974). Both studies were performed before

improved insulation was required" on electrical water

heaters in order to meet the minimum beat loss rate

requirements of ASHRAE Standard 9OA-1980.

for the same peak days. This hourly coincident

demand is calculated by averaging the four 15-

minute demands Ihat occurred during the peak hour.

It is important to note in both Table 3 and Table 5

that FPL was unable to meet the peak demand on

December 26. 1983 and bad to rotate curtailments

throughout their service area. Hence. the FPL

system peak of the winter of 1982-83 (January 13•

1983) bas been included in these tables.

ANALYSIS

Annual Electrical Use and Demand

The Shape of the average daily electrical demand

profile for electric resistance Wiler beaters as seen

in Figure 1 is also c:oosisteDt with the results of

previous studies. 1be twin peaks of mid- morning

and early evening demand correspond to typical

residential bot water use patterns of showering, food

preparation. and cleanup (Perlman and Mills 1985;

Gladhart and Wiehl 1986). As bot Wiler is

withdrawn from the storage tank. the electric

element turns on when the water temperature drops

.....Inw thl' Lank thermostat setting. The annual daily

Convenlio'nal electric

Heal pump water heater

Solar water healing system

Desuperheater water heater

-'- .,.-.,...................

8 10 2 4 6 8 10

Noon Midnight

Average Daily Electrical Load Profile for

Four Types o/Water Heating Systems

.6

.2 .

.4

246

Midnight

Figure 1.

Table 2 presents the daily average IS-minute

electrical demand. the average IS-minute maximum

demand and the daiIy load factor for the four DHW

types for the two-year period. Load factor is the

ratio, expressed as a percent, of the average kilowatt

demand over a designated period of time to the

maximum demand occurring in that period.

Load Factor (%) = Average Demand (kW)

Peak Demand (kW)

Load factor is a measure of how well the electrical

capacity demanded from the utility is utilized by the

load over a period of time.

The winter peak and summer peak days chosen for

data reduction are the actual peak load days of

Florida Power and Light Company. in whose service

territory half of the 80 systems were located. The

other half of the systems were located in the service

areas of Florida Power Corporation. Tampa Electric

Company, and Jacksonville Electric Authority.

These utilities either had the same winter and

summer peak load days as FPL or their secondary

system peaks occurred on these days.

Tables 3 and 4 indicate the FPL winter and summer

peak days, respectively. and the hour that the peak

occurred. These same tables also contain each DHW

system type's maximum IS-minute diversified

demand that was coincident with the hour of the

FPL system peak. The diversified 6O-minute I.- -- ._..1.:_ T ..""'Ar' " ~nA f-.

EE-RM-90-201 COMMENT OOI5

Florida average daily electrical demand 

(July 1. 1982.· June 30.1984) 

Type 01 System 

~ 

~ 1.0 Convenlio'nal electric 

Heat pump water heater 

Solar water heating system 

Desuperheater water heater 

I\> 

DI 

'" 

-'- .,.-., ............... .... t Ol+-~~~--~-r~~~~--~ 

~ 2 4 6 8 10 

Midnight 

Figure 1. 

Noon Midnight 

Average Daily Electrical Load Profile for 

Four Types o/Water Heating Systems 

Table 2 presents the daily average IS-minute 

electrical demand. the average IS-minute maximum 

demand and the dai ly load factor for the four DHW 

types for the two-year period. Load factor is the 

ratio. expressed as a percent. of the average kilowatt 

demand over a designated period of time to the 

maximum demand occurring in that period. 

Load Factor (%) = Average Demand (kW) 

Peak Demand (kW) 

Load factor is a measure of how well the electrical 

capacity demanded from the utility is utilized by the 

load over a period of time. 

The winter peak and summer peak days chosen for 

data reduction are the actual peak load days of 

Florida Power and Light Company, in whose service 

territory half of the 80 systems were located. The 

other half of the systems were located in the service 

areas of Florida Power Corporation, Tampa Electric 

Company, and Jacksonville Electric Authority. 

These utilities either had the same winter and 

summer peak load days as FPL or their secondary 

system peaks occurred on these days. 

Tables 3 and 4 indicate the FPL winter and summer 

peak days, respectively, and the hour that the peak 

occurred. These same tables also contain each DHW 

system type's maximum IS-minute diversified 

demand that was coincident with the hour of the 

FPL system peak. The diversified 6O·minute I . - --____ ._..I!_ 'T' .. "'Ar' ( ~nA f-. 

LJOCl\et Nos 930!:>48·~G - 930551·EG 

Florida Solar Energy Industries Assoc., Inc. 

Exhibit _ (WTG·1) 

Sc:heciJ1e1 

Page 5 of 12 

for the same peak days. This hourly coincident 

demand is calculated by averaging the four 15· 

minute demands Ihal occurred during the peak hour. 

It is important to note in both Table 3 and Table 5 

that FPL was unable to meet the peak demand on 

December 26, 1983 and bad to rotate curtailments 

throughout their service area. Hence, the FPL 

system peak of the winter of 1982-83 (January 13, 

1983) bas been included in these tables. 

Figures 2 through 5 present the average 1S-minute 

demand profiles for the four DHW system types on 

the FPL winter peak day of February 7, 1984 . 

Figures 6 tbrough 9 presents the same time-of-day 

profiles for the SU11lIDeI' peak day of July 25, 1983. 

These two days were selected for presenlation 

because they represent the bighest utility system 

loads of aU the FPL peak days that did not bave 

service interruptions. 

ANALYSIS 

Annual Electrical Use and Demand 

The average electricity use of 8.3 kWh per day for 

the electric resistance water beater group - with an 

average family size of 3.6 people -- compares 

f~vorably with values obtained by other studies 

performed in Florida. FPL determined in a 1976-77 

study of. 165 customers that a family of four used an 

average of 10.2 kWh per day (FPL 1978). Florida 

Power Corporation determined in a similar study that 

a f:mrily of three used an average of 8.4 kWh per 

day and a family of four used 11.6 kWh per day 

(FPC 1974). Both studies were performed before 

improved insulation was required' on electrical water 

heaters in order to meet the minimum beat loss rate 

requirements of ASHRAE Standard 9OA-1980. 

The sbape of the average daily electrical demand 

profile for electric resistance Wiler beaters as seen ~ 

in Figure 1 is also c:oosisteDt with the results of 

previous sbldies. The twin peaks of mid- morning 

and early evening demand correspond to typical 

residential bot water use patterns of showering, food 

preparation. and cleanup (Perlman and Mills 1985; 

Gladbart and Wiehl 1986). As bot Wiler is 

withdrawn from the storage tank, the electric 

element turns on when the water temperature drops 

..... Inw thl' tank thermostat seuing. The annual daily 
Docket Nos 930548-EG - 930551-EG

Florida Solar Energy Industries Assoc.. Inc.

Exhibit _ (WTG-1)

SChedJIe 1

Page60f12

Table 2. Annual Average I5-Minute Demand. Peak IS-MinUle Demand. and Load Factor by Type of System

Average Demand Peak Demand Load Factor

(leW) QsW) (%)

Electric Resistance 0.34 0.68 50

Heat Pump Water Heater 0.25 0.48 52

Solar Hot Water System 0.11 0.27 41

Desuperheater Unit 0.31 0.57 54

Table 3. Average IS-Minute Demand Coincident with FPL Winter Peak Load (60-Minute Net)

January 13, 1983 December 26, 1983 February 7, 1984

9 a.m. 9-10 a.m.· 7-8 a.m..

Electric 1.14 kW 1.26 kW 1.36 kW

Resistance

Heat Pump Water 0.53 kW 0.56 kW 0.75 kW

Heater

Solar Hot Water 0.46 kW 0.88 kW 0.73 kW

System

Desuperheater Unit 0.94 kW 0.62 kW 1.11 kW

• Unserved utility load of 666 MW

Table 4. Average IS-Minute Demand Coincident with FPL Summer Peak Load (60·Minute Net)

August 24, 1982 July 25, 1983

5-6 p.m. 5-6 p.m.

Electric Resistance 0.74kW 0.34 kW

Heat Pump Water Heater 0.61 kW 0.37 kW

Solar Hot Water System 0.08 kW 0.02 kW

Desuperheater Unit 0.14 kW 0.19 kW

average demand of the element is exactly one-half of

its average peak demand. resulting in an annual

average load factor of 50 percent.

Heat pump water heaters had a similar load factor . .

average demand is approximately 25 percent less.

This reduction is due to the higher annual average

system efficiency of the beat pump water beater --

approximately twice that of the electric resistance

water heaters. However, seven of the 20 heat pump

Ul"IM hp"lpr~ in thi~ ~I\ldv exnerienced comoressor

EE-RM-90-201 COMMENT OOI5

Docket Nos 930548-EG - 930551·EG 

Florida Solar Energy Industries Assoc .. Inc. 

Exhibit _ (WTG-1) 

SchedJ\e 1 

Page60f12 

Table 2. Annual Average I5-Minute Demand. Peak IS-MinUle Demand. and Load Factor by Type of System 

A verage Demand Peak Demand Load Factor 

(!W} (!W} !%} 

Electric Resistance 0.34 0.68 50 

Heat Pump Water Heater 0.25 0.48 52 

Solar Hot Water System 0.11 0.27 41 

Desuperheater Unit 0.31 0.57 54 

Table 3. Average IS-Minute Demand Coincident with FPL Winter Peak Load (60-Minute Net) 

January 13, 1983 December 26, 1983 February 7, 1984 

9 a.m. 9-10 a.m.· 7-8 a.m .. 

Electric 1.14 kW 1.26 kW 1.36 kW 

Resistance 

Heat Pump Water 0.53 kW 0.56 kW 0.75 kW 

Heater 

Solar Hot Water 0.46 kW 0.88 kW 0.73 kW 

System 

Desuperheater Unit 0.94 kW 0.62 kW 1.11 kW 

• Unserved utility load of 666 MW 

Table 4. Average IS-Minute Demand Coincident with FPL Summer Peak Load (60-Minute Net) 

August 24, 1982 July 25, 1983 

5-6 p.m. 5-6 p.m. 

Electric Resistance 0.74kW 0.34 kW 

Heat Pump Water Healer 0.61 kW 0.37 kW 

Solar Hot Water System 0.08 kW ~ 0.02 kW 

Desuperheater Unit 0.14 kW 

average demand of the element is exactly one-half of 

its average peak demand, resulting in an annual 

average load factor of 50 percent. 

Heat pump water healers had a similar load factor . . 

0.19 kW 

average demand is approximately 25 percent less. 

This reduction is due to the higher annual average 

system efficiency of the beat pump water beater --

approximately twice that of the electric resistance 

water heaters. However, seven of the 20 heat pump 

\1I"IM hp~lpr~ in Ihi~ ~I\ldv exnerienced comoressor 
Uocl\el Nos 930548 EG -- 930551·EG

Florida Solar Energy Industries Assoc., Inc.

Exhibit _ (WTG-1)

Schedule 1

Page 7 of 12

Table 5. Average 60-MinUle Demand Coincident with FPL Winter Peak Load (60-Minute Net)

January 13, 1983 December 26, 1983 February 7, 1984

8-9 a.m. 9-10 a.m.· 7-8 a.m.

Electric 1.07 kW 0.90 kW 1.18 kW

Resistance

Heat Pump Water 0.48 kW 0.36 kW 0.68 kW

Heater

Solar Hot Water .0.24 kW 0.59 kW O.44kW

System

Desuperheater Unit 0.63 kW 0.30 kW 0.64 kW

• Unserved utility load of 666 MW

Table 6. Average 6O-Minute Demand Coincident with FPL Swnmer Peak Load (60-Minute Net)

August 24, 1982 July 25, 1983

5-6 p.m. 5-6 p.m.

Electric Resistance 0.58 kW 0.23 kW

Heat Pump Water Heater 0.51 kW 0.17 kW

Solar Hot Water System 0.06 kW 0.01 kW

Desuperheater Unit 0.04 kW 0.07 kW

failures, indicating a problem with long-tenn

reliability in 1982-84.

Solar hot water systems operated with the highest

average electrical system efficiency and had the

lowest average daily electrical demand profile.

However, the solar system's annual load factor of

41 percent compares favorably with the electric

resistance water heater's load factor of 50 percent

This is surprising since the majority of solar system

owners turned off their storage tank's backup

electric element and relied on the solar system to

supply whatever hot water they needed during the

summer months. The only electrical consumption

for these systems was that of the solar circulation

pump as can be seen in the summer day average of

Figure 9 for the six-hour period around noon.

Combined with the occasional winter use of the

backup element, this electrical demand was

consistent enough during the summer months to

create a relatively high annual load factor.

Desuperheater unit owners also typically turned off

their backup electric element during the summer.

However, these units would only supply hot water

when there was a need for air conditioning or, for

those eleven desuperheaters that were installed on

heat pumps, a need for beating and/or air conditioning. Surprisingly, even in Florida, there are

considerable periods of time when neither mode of

space conditioning is required. This is reflected in

the average two-year coefficient of perfonnance of

1.10 for desuperheaters. Although this COP is

better than unity, it is not much higher than the

efficiency for an electric resistance water heater.

The annual load factor of 54 percent and the average

EE-RM-90-201 COMMENT OOI5

Uocl\el Nos 930548 EG·· 930551·EG 

Florida Solar Energy Industries Assoc., Inc. 

Exhibit _ (WTG-1) 

Schedule 1 

Page 7 of 12 

Table 5. Average 60-MinUle Demand Coincident with FPL Winter Peak Load (60-MinUle Net) 

January 13, 1983 December 26, 1983 February 7, 1984 

8-9 a.m. 9-10 a.m.· 7-8 a.m. 

Electric 1.07 kW 0.90 kW 1.18 kW 

Resistance 

Heat Pump Water 0.48 kW 0.36 kW 0.68 kW 

Heater 

Solar HOl Waler .0.24 kW 0.59 kW O.44kW 

System 

Desuperheater Unit 0.63 kW 0.30 kW 0.64 kW 

• Unserved utility load of 666 MW 

Table 6. Average 6O-Minure Demand Coincident with FPL Swnmer Peak Load (60-Minute Net) 

August 24, 1982 July 25, 1983 

5-6 p.m. 

Electric Resistance 0.58 kW 

Heat Pump Water Heater 0.51 kW 

Solar Hot Waler System 0.06 kW 

Desuperheater Unit 0.04 kW 

failures, indicating a problem with long-tenn 

reliability in 1982-84. 

Solar hot water systems operated with the highest 

average electrical system efficiency and had the 

lowest average daily electrical demand profile. 

However. the solar system's annual load factor of 

41 percent compares favorably with the electric 

~ resistance water heater's load factor of 50 percent 

This is surprising since the majority of solar system 

owners turned off their storage tank's backup 

electric element and relied on the solar system to 

supply whatever hot water they needed during the 

summer months. The only electrical consumption 

for these systems was that of the solar circulation 

pump as can be seen in the summer day average of 

Figure 9 for the six-hour period around noon. 

Combined with the occasional winter use of the 

5-6 p.m. 

0.23 kW 

0.17 kW 

0.01 kW 

0.07 kW 

backup element, this electrical demand was 

consistent enough during the summer months to 

create a relatively high annual load factor. 

Desuperheater unit owners also typically turned off 

their backup electric element during the summer. 

However. these units would only supply hot water 

when there was a need for air conditioning or. for 

those eleven desuperheaters that were installed on 

heat pumps, a need for beating and/or air conditioning. Surprisingly, even in Florida, there are 

considerable periods of time when neither mode of 

space conditioning is required. This is reflected in 

the average two-year coefficient of perfonnance of 

1.10 for desuperheaters. Although this COP is 

better than unity, it is not much higher than the 

efficiency for an electric resistance water heater. 

The annual load factor of 54 percent and the average 
Dod<.et Nos 930548-EG - 930551-EG

Florida Solar Energy Industries Assoc., Inc.

Exhibit _ (WTG-l)

Sd1edu1e 1

PageS of 12

800 1200 1600 2000 2400

Hour of Day

400

Winter Peak Load Day: February 7. 1984

Solar water heating ayatem• -.

.!!

0; 1aoo. !."Cl 1600· ---'--

1400

e 1200. __ 4_ •• _ -.------

QI

o 1000 QI

'E aoo

.E 600 - --~__i_T+-__!__-------

400- --~­

200- --+-

E 0 - ....._-.1 QI < 0

I " !-

"

,

f:

,.

Winter Peak Load Day: February 7, 1984

Conventional electric realatance

o 400 800 1200 1600 2000 2400

Hour of Day

-.

1800

:; 1600

1400

1200

1000

'E aDo c

ii 600

It) 400

- 200

0 111

>

e:r:

Figure 2. Average Winter Peak Day Electrical Load

Profilefor Electric Resistance Water Healers

Figure 4. Average Winter Peale Day Electrical Load

Profile for Solar Waters Healers

800 1200 1600 2000 2400

Hour of Day

400

Winter Peak Load Day: February 7, 1984 -.

.!! De.uperheater water heatera

0; 1800 - -------------.--

:; 1600 - ---------....,..-----

I; 1400 - ----....,..-------"-----t--

1200- -----------+---

C 1000 - ----+-----..----W--.-' QI

:i 800 - -----th,--~-----:T_~&:_ C

i 600

It) 400 - ---f!-

- 200 - ~b-l.-l;i!i-tt

E 0 - EiliI.iU"-:;;U;;O

QI < 0

r .~

-'._- _...__._---------

.------- --_....__.._-----

Winter Peak Load Day: February 7, 1984

Heat pump water heater.

c=':,."f.!£l:~~_Ii

o 400 800 1200 1600' 2000 2400

Hour of Day

-.

0; 1800 ' !.

"Cl 1600

c

III 1400

E\I) 1200

0 1000 111

'E 800

.E 600

It) 400

-111 200 Cl'l

III 0 111

>

e:r:

Figure 3, Average Winter Peak Day Electrical Load

Profile for Heat Pump Water Heaters

Figure 5. Average Winter Peak Day Electrical Load

Profile for Desuperhealer Units

daily electrical demand as seen in Figure I also

suggest that desuperheater units perfonn very similar

to electric resistance water heaters on an annual

basis.

Peak Day Demand

Although both the IS-minute and the 6O-minute

coincident peale demands for each of the DHW

system types (found in Tables 3 through 6) appear to

vary considerably from one peale day to another

within the same season, it is important to note that

these demands are highly dependent on the weather

for each day. This is especially ttue in the case of

the winter peak, IS evidenced by the fact that FPL

system peak occurred at • different hour 00 each of

the three peak days. 1be peak day electrical demand

profiles for each of the DHW system types (found

in Figures 2 tbrough 9) also are highly variable due

to the wel1her IS well as the bot water use 00 that

day.

Understandably, the consumption of bot water and,

therefore the demand for electricity. was greater in

the winter than in the summer. For instance, the

average hot water consumption associated with

EE-RM-90-201 COMMENT OOI5

--

~ 

'i 1800 

:; == 1600 

; 1400 

~ 1200 

o 1000 CI 

'E aoo 

.: 600 ::E 

It') 400 

-CI 200 01 

III 

.. 0 CI 

> 

<I: 

Winter Peak Load Day: February 7, 1984 

Conventional electric real.tance 

0 400 800 1200 1600 2000 2400 

Hour of Day 

Figure 2. Average Winter Peak Day Electrical Load 

Profile for Electric Resistance Water Healers 

-

~ 

'i !. 1800 · 

"CI 1600 

; 1400 

~ 1200 

~ 1000 

'E 800 

.E ::E 600 

400 

~ 200 

~ 0 CI 

> <I: 

Winter Peak Load Day: February 7, 1984 

Heat pump water heater. 

o 400 800 1200 1600' 2000 2400 

Hour of Day 

Figure 3. Average Winter Peak Day Electrical Load 

Profile for Heat Pump Water Heaters 

daily electrical demand as seen in Figure I also 

suggest that desuperheater units perform very similar 

to electric resistance water heaters on an annual 

basis. 

Peak Day Demand 

Although both the IS-minute and the 6O-minute 

coincident peale demands for each of the DHW 

system types (found in Tables 3 through 6) appear to 

vary considerably from one peak day to another 

within the same season, it is important to nOle that 

these demands are highly dependent on the weather 

.!! --

Dod<.et Nos 930548-EG - 930551 -EG 

Florida Solar Energy Industries Assoc., Inc. 

Exhibit _ (WTG-l) 

Sd1edu1e 1 

PageS of 12 

'i 1800 . !. 

Winter Peak Load Day: February 7, 1984 

Solar water heating .y.tem • 

"CI 1600 · --_ ._. 

; 1400 

f 1200 · 

o 1000 CI 

'E 800 

.E ::E 600 - --~~~---~------------

It') 

-

~ 200 - --+-

E 

CI O - ...... -~ 

~ 0 400 800 1200 1600 2000 2400 

Hour of Day 

Figure 4. Average Winter Peak Day Electrical Load 

Profile for Solar Waters Heaters 

Winter Peak Load Day: February 7, 1984 

-.!! De.uperheater wat.r h.at.r. 

'i 1800 ----------------------~----

~ 1600 -------------~------­ ; 1400- --------~--------~--~---­

E 

CI 

o 

CI 

'S 

c 

j 

It') 

-CI 

01 

«I 

... 

CI 

> 

<I: 

1200 -

1000 -

800 · 

600 

400 -

200 -

0-

0 400 800 1200 1600 2000 2400 

Hour of Day 

Figur, S. Average Winter Peak Day Electrical Load 

Profile for DesuperiJeater Units 

for each day. This is especially ttue in the case of 

the winter peak, IS evidenced by the fact that FPL 

system peak occuned at • different hour OIl each of 

the three peak clays. 1be peak day electrical demand 

profiles for each of the DHW system types (found 

in Figures 2 through 9) also are highly variable due 

to the weather IS well IS the hot water use 00 that 

day. 

Understandably, the consumption of bot water and, 

therefore the demand for electricity, was greater in 

the winter than in the summer. For instance, the 

average hot water consumption associated with 
Docket Nos 930548--EG - 930551-EG

Florida Solar Energy Industries Assoc., Inc.

Exhibit_ (WTG-1)

Schedule 1

Page 9 of 12

---....:.----_.-~--- ...

Summer Peak Load Day: July 25, 1983

Soler water heating systems

800 1200 1600 2000 2400

Hour of Day

400

ca 1200 .-----.------.--- .-'"-- ' .... '._.0_.. '- -

!.'t:l 1000 - ------.-.---- ~.----.

c

E 800- CII

600 - -----,-----

:;

.E 400 - ----------

:1:

~enCII 200------~ ,

ell 0 - __W~;;;_'fiiRa"'_--:.__ t 0 ,.

<

2000 2400

Summer Peak Load Day: July 25. 1983

- Conventional electric resistance

iii 1200 :=

't:lc 1000 co

E

CII 800

0

CII 600 :;

c

:1: 400

L/')

... 200 CII

en

co

.. 0 CII

>

<

Figure 6. Average Summer Peak Day Electrical Load

Profilefor Electric Resistance Water Heaters

Figure 8. Average SJI11Uner Peak Day Electrical Load

Profile for Solar Warers Heaters

Summer Peak Load Day: July 25, 1983

- Heat pump water heater systems

iii 1200 -. --.----- . --..-----

Summer Peak Load Day: July 25, 1983

'jjj' De.uperheater water he.te"

i 1200· ---------,,--------,

:=

-

o

800 1200 1600 2000 2400

Hour of Day

400

't:l 1000· . C

ell

E 800· CII

0 600. CII

'S

.E 400

:IE

L/')

... 200 -

CII

en

ell 0- ..

CII

,. 0

<

800 1200 1600 2000 2400

Hour of Day

o 400

800

200

600

400

1000

co

E

CII

o

CII

:;

.E

:1:

L/')

...

Figure 7. Average Summer Peak Day Electrical Load

Profile for Heat Pump Water Heaters

Figure 9. Average SJI11Uner PeoJc Day Electrical Load

Profile for Desuperhealer Units

electric resistance water heaters on the winter peak

day in 1984 (66.3 gallons or 251 L) was 27% greater

than the use on the peak day (52.3 gallons or 198 L)

during the previous summer. FurtherrnCl'e. the

average electrical consumption used to heat each

gallon of hot water shows large differences between

winter and summer peak days. On the winter peak

day. February 7, 19.84, electrical resistance systems

used an average of 175 Wh to heat each gallon of

water. whereas only 119 Wh were used to heat each

gallon on July 25.1983, the summer peak day. Thus.

electrical consumption was 47% greater to heat a

£iven volume of water on the winter peak day. Most

of the difference in electrical consumption is due to

the seasonal variatiOll in iDlet water temperature to

the bot water tank. Data recorded over the last two

years at FSEC show that iDlet water temperatures in

Central Florida vary by more than 14 OF throughout

the year (Parker 1989). Also, since most bot water

heaters are located in ganges in Florida. lower

ambient tempetJtures OIl winter peak days increase

tank standby losses and add to the daily bot water

heating electrical coosumption.

To evaluate the peak. demand reduction potential of

the alternative water heating technologies. it is

EE-RM-90-201 COMMENT OOI5

-

~ 

iii 

:= 

't:I -

c 

10 

E 

CII 

0 

CII 

:; 

c 

:l: 

L/') 

... 

CII 

en 

10 

... 

CII 

> 

< 

1200 

1000 

800 

600 

400 

200 

0 

0 

Summer Peak Load Day: July 25. 1983 

Conventional electric re.istance 

400 800 1200 1600 2000 2400 

Hour of Day 

Figure 6. Average Summer Peak Day Electrical Load 

Profile jar Electric Resistance Water Healers 

Summer Peak Load Day: July 25. 1983 

-~ Heat pump water heater systems 

iii 1200 -. --.----- . --.. -----

~ 

~ 1000 10 

E 800 CII 

o 

CII 

:; 

.E 

:l: 

L/') 

... 

600 

400 

200 

o 

o 400 800 1200 1600 2000 2400 

Hour of Day 

Figure 7. Average Summer Peak Day Electrical Load 

Profile jor Heat Pump Water Heaters 

electric resistance water heaters on the winter peak 

day in 1984 (66.3 gallons or 251 L) was 27% greater 

than the use on the peak day (52.3 gallons or 198 L) 

during the previous summer. FurtherrnCl'e. the 

average electrical consumption used to heat each 

gallon of hot water shows large differences between 

winter and summer peak days. On the winter peak 

day. February 7. 19.84. electrical resistance systems 

used an average of 175 Wh to heat each gallon of 

water. whereas only 119 Wh were used to heat each 

gallon on July 25.1983. the summer peak day. Thus. 

electrical consumption was 47% greater to heat a 

£iven volume of water on the winter peak day. Most 

~ 

Docket Nos 930548--EG - 930551-EG 

Florida Solar Energy Industries Assoc .• Inc. 

Exhibit_ (WTG-1) 

Schedule 1 

Page 9 of 12 

Summer Peak Load Day: July 25. 1983 

ca 1200 .------------.--- .-'"-- "-,- .. _.0_ .. '- -

!. 't:I 1000 - ------.--.---- ~.----. 

c E 800- , . ---.....:.----. -~-- - ... 

CII 

~ 600- --------~-------- :; 

.E 

:l: 

400- -----------------

~ 200-------4~--r· --~'-------~----

g o. __ ~Lui~==n.' •. ~~ __ ~_ t 0 400 800 1200 1600 2000 2400 

Hour of Day :0-

< 

Figure 8. Average SU11IIner Peak Day Electrical Load 

Profile for Solar Waters Heaters 

Summer Peak Load Day: July 25. 1983 

., Desuperheater water he.ters 

i 1200·------------------~------~ := 

't:I -

C 

10 

E 

CII 

0 

CII 

'S 

.E 

:IE 

L/') 

.. 

CII 

en 

10 

... 

CII 

> 

< 

1000· . 

800· 

600. 

400 

200 -

O· 

0 400 800 1200 1600 2000 2400 

Hour of Day 

Figure 9. Average SU11IIner PeoJc Day Electrical Load 

Profile jor Desuperhealer Units 

of the difference in electrical consumption is due to 

the seasonal variatiOll in inlet water temperature to 

the bot water tank.. Data recorded over the last two 

years at FSEC show that inlet water temperatures in 

Central Florida vary by more than 14 OF throughout 

the year (Parker 1989). Also, siDee most bot water 

heaters are Iocared in ganges in Florida, lower 

ambient tempetatures OIl winter peak days increase 

tank standby losses and add to the daily bot water 

heating electrical coosumption. 

To evaluate the peak. demand reduction potential of 

the alternative water heating technologies. it is 
necessary to ftrst test whether the winter and summer

peak day electrical profile of each technology was

statistically different from the same peak day

electrical profile of the electric resistance water

heaters. Since the distributional shapes of the

electrical demand are non-normal, a Wilcoxon ranksum test was performed to compare the profiles.

Results showed that the peak day profiles of the

alternative technologies were statistically different

from conventional resistance systems at the 99.99

percent confidence level.

To calculate actual peak demand reduction, it is

necessary to determine the difference in coincident

peak demand between each technology and a base

technology - the conventional electric·resistance

water heaters. Table 7 presents this calculation for

both the IS-minute and 6O-minute coincident winter

peak demands found in Tables 3 and 5. (The winter

peak day of December 26, 1983 is omitt.ed from

Table 7 because of the service curtailments that

occurred on this day.) Table 7 also includes the

average value of the coincident peak demand

reductions of the two fully-served FPL winter peak

days of 1983 and 1984.

As evident from Table 7, the coincident peak

demand reduction on the two winter peak days is

much more consistent than the individual winter

peak demands of Tables 3 and 5. While the

coincident peak demand reduction based on 60-

minute intervals varies slightly from the IS-minute

value, this is simply the result of averaging over a

longer time period. Table 7 indicates that solar hot

water systems exhibit the largest winter demand

reduction of approximately 0.7 kW per customer.

Heat pump water heaters contribute approximately

0.6 kW per customer reduction to winter peak

demand, while desuperheaters are responsible for at

least a 0.2 kW per customer reduction.

Table 8 presenlS"a similar analysis as Table 7 except

that the diversified summer coincident peak demands

from Tables 4 and 6 are used to determine the

demand reduction for each alternative DHW system

type. Table 8 indicates that both solar hot water

systems and desuperheaters are able to reduce

summer peak demand considerably. However, since

Table 6 reveals that the 6O-minute coincident peak

demand for electric resistance water heaters may be

Doc"et Nos 930548-EG -- 930551-EG

Florida Solar Energy Industries Assoc" Inc.

Exhibit _ (WTG-1)

Schedule 1

Page 10 of 12

as low as 0.25 kW per customer, one cannot claim

more than a 0.2 kW summer peak reduction potential

for these technologies.

Table 8 also indicates no significant summer peak

reduction potential for heat pump water· heaters.

However, it is important to note that this analysis

considers the peak demand reduction due to water

heating only and does not consider any increase or

reduction that may occur if the space conditioning

load is affected by the water heater operation. While

most beat pump water heaters were located outside

of the conditioned space of a house, there were some

that were located inside such that their operation

would increase the heating load in the winter and

decrease the cooling load in the summer. This

analysis does not consider any effect that this

contribution may have had on overall residential

peak demand.

CONCLUSIONS

Residential water heating offers a significant

potential for Florida electric utility load management

because of the increasing level of residential

,electricity consumption and the ability of alternative

water heating technologies to reduce coincident peak

demand. The conunon electric resistance water

heater contributes approximately 1.1 kW per

customer to the utility winter peak and at least 0.2

kW per customer to the summer peak. In 1988, the' C'

total peak demand per customer at the time of both

FPL's winter and summer peaks was 4.2 kW (FPL

1989). Hence, electric water heaters are responsible

for approximately 25 percent of the utility winter

peak demand and only about 5 percent of the utility

summer peak demand. However, recent circumstances in Florida indicate that the winter peak may

become more imponant than the summer peak in

determining the need for new generating capacity.

Fortunately, alternative water heating technologies

offer a means to reduce winter and summer peak

demand without requiring controlled utility

intervention or even significantly reducing load

factor.

Solar hot water systems exhibit the highest

coincident peak demand reduction of 0.7 kW per

customer in the winter and a minimum of 0.2 kW

per customer in the ·summer. Solar systems perform

EE-RM-90-201 COMMENT OOI5

necessary to ftrst test whether the winter and summer 

peak day electrical profile of each technology was 

statistically different from the same peak day 

electrical profile of the electric resistance water 

heaters. Since the distributional shapes of the 

electrical demand are non-normal, a Wilcoxon ranksum test was performed to compare the profiles. 

Results showed that the peak day profiles of the 

alternative technologies were statistically different 

from conventional resistance systems at the 99.99 

percent confidence level. 

To calculate actual peak demand reduction, it is 

necessary to determine the difference in coincident 

peak demand between each technology and a base 

technology - the conventional electric· resistance 

water heaters. Table 7 presents this calculation for 

both the IS-minute and 6O-minute coincident winter 

peak demands found in Tables 3 and 5. (The winter 

peak day of December 26, 1983 is omitted from 

Table 7 because of the service curtailments that 

occurred on this day.) Table 7 also includes the 

average value of the coincident peak demand 

reductions of the two fully-served FPL winter peak 

days of 1983 and 1984. 

As evident from Table 7, the coincident peak 

demand reduction on the two winter peak days is 

much more consistent than the individual winter 

peak demands of Tables 3 and 5. While the 

coincident peak demand reduction based on 60-

minute intervals varies slightly from the IS-minute 

value, this is simply the result of averaging over a 

longer time period. Table 7 indicates that solar hot 

water systems exhibit the largest winter demand 

reduction of approximately 0.7 kW per customer. 

Heat pump water heaters contribute approximately 

0.6 kW per customer reduction to winter peak 

demand, while desuperheaters are responsible for at 

least a 0.2 kW per customer reduction. 

Table 8 presenlS"a similar analysis as Table 7 except 

that the diversified sununer coincident peak demands 

from Tables 4 and 6 are used to determine the 

demand reduction for each alternative DHW system 

type. Table 8 indicates that both solar hot water 

systems and desuperheaters are able to reduce 

summer peak demand considerably. However, since 

Table 6 reveals that the 6O-minute coincident peak 

demand for electric resistance water heaters may be 

Doc"et Nos 930548-EG -- 930551-EG 

Florida Solar Energy Industries Assoc., Inc. 

Exhibit _ (WTG-1) 

Schedule 1 

Page 10 of 12 

as low as 0.25 kW per customer, one cannot claim 

more than a 0.2 kW summer peak reduction potential 

for these technologies. 

Table 8 also indicates no significant summer peak 

reduction potential for heat pump water· heaters. 

However, it is important to note that this analysis 

considers the peak demand reduction due to water 

heating only and does not consider any increase or 

reduction that may occur if the space conditioning 

load is affected by the water heater operation. While 

most beat pump water heaters were located outside 

of the conditioned space of a house, there were some 

that were located inside such that their operation 

would increase the heating load in the winter and 

decrease the cooling load in the summer, This 

analysis does not consider any effect that this 

contribution may have had on overall residential 

peak demand. 

CONCLUSIONS 

Residential water heating offers a significant 

potential for Florida electric utility load management 

because of the increasing level of residential 

. electricity consumption and the ability of alternative 

water heating technologies to reduce coincident peak 

demand. The conunon electric resistance water 

heater contributes approximately 1.1 kW per 

customer to the utility winter peak and at least 0.2 

kW per customer to the summer peak. In 1988, the' c' 

total peak demand per customer at the time of both 

FPL's winter and summer peaks was 4.2 kW (FPL 

1989). Hence, electric water heaters are responsible 

for approximately 25 percent of the utility winter 

peak demand and only about 5 percent of the utility 

summer peak demand. However, recent circumstances in Florida indicate that the winter peak may 

become more imponant than the summer peak in 

determining the need for new generating capacity. 

Fortunately, alternative water heating technologies 

offer a means to reduce winter and summer peak 

demand without requiring controlled utility 

intervention or even significantly reducing load 

factor. 

Solar hot water systems exhibit the highest 

coincident peak demand reduction of 0.7 kW per 

customer in the winter and a minimum of 0.2 kW 

per customer in the ·summer. Solar systems perform 
Docket Nos 930548-EG - 930551-EG

Florida Solar Energy Industries Assoc., Inc.

Exhibit_ (WTG-1)

SchedJIe 1

Page 11 of 12

Table 7. Diversified IS-Minute and 60-MinUle Winter Peak Demand Reduction (kW per Customer)

Electric Resistance

Heat Pump Water Heater

Solar Hot Water System

Desuperheater Unit

January 13. 1983 February 7, 1984 Winter Peak

8-9 a.m. 7-8 a.m. Average

IS-minute Base IS-minute Base IS-minute Base

.-------- .--.------ ---------

60-minute Base 60-minute Base 6O-minute Base

0.61 0.61 0.61

------ ---- -----

0.59 0.50 0.55

0.68 0.63 0.66

------ --- ----

0.83 0.74 0.79

0.20 0.25 0.23

------ ------ ---- 0.44 0.54 0.49

Table 8. Diversified I5-Minute and 60-Minute Sununer Peak Demand Reduction (kW per Customer)

Electric Resistance

Heat Pump Water Heater

Solar Hot Water System

Desuperheater Unit

August 24, 1982 July 25, 1983 Summer Peak

5-6 p.m. 5-6 p.m. Average

IS-minute Base 15-minute Base IS-minute Base

------.-- -------- ---------

6O-minute Base 60-minute Base 60-minute Base

0.13 -0.03 0.05

------ ---- ------

0.07 0.06 0.07

0.66 0.32 0.49

------ ---- -----

0.52 0.22 0.37

0.60 0.15 0.38

----- -- ----

0.54 0.16 0.35

with an average coefficient of performance of 2.35

and have an annual load factor of 41 percent. In

comparison, an electric resistance water heater has

an average COP of 0.82 and a load factor of 50

percent.

Desu.perheater units can also provide the potential of

reducinJ:t coincident summer peak demand by a

winter, only ltlose units that are installed on beat

pumps are capable of reducing electrical demand.

This winter peak demand reduction is determined to

be at least 0.2 kW per customer. Desuperheaters

also have an average COP of 1.10 and an annual

load factor of 54 percent.

Heat pump water heaters have a system efficiency

_L'-_ .. _-~-- """'_t _r "_ 1Io1~h"i,.. r~ci4::t~nrp water

EE-RM-90-201 COMMENT OOI5

Docket Nos 93054B-EG - 930551-EG 

Florida Solar Energy Industries Assoc., Inc. 

Exhibit _ (WTG-l) 

Sched.J1e 1 

Page 11 of 12 

Table 7. Diversified IS -Minute and 60-Minute Winter Peak Demand Reduction (kW per Customer) 

January 13. 1983 February 7, 1984 Winter Peak 

8-9 a.m. 7-8 a.m. Average 

15-minute Base 15-minute Base 15-minute Base 

Electric Resistance .-------- .--.------ ---------

60-minute Base 60-minute Base 6O-minute Base 

0.61 0.61 0.61 

Heal Pump Water Heater ------ ---- -----

0.59 0.50 0.55 

0.68 0.63 0.66 

Solar Hot Water System ------ --- ----

0.83 0.74 0.79 

0.20 0.25 0.23 

Desuperheater Unit ------ ------ --- 0.44 0.54 0.49 

Table 8. Diversified I5-Minute and 60-Minute Sununer Peak Demand Reduction (kW per Customer) 

August 24, 1982 

5-6 Q.m. 

15-minute Base 

Electric Resistance ------.--

60-minute Base 

0.13 

Heat Pump Water Heater ------

0.07 

0.66 

Solar Hot Water System ------

0.52 

0.60 

Desuperheater Unit -----

0.54 

with an average coefficient of perfonnance of 2.35 

and have an annual load factor of 41 percent. In 

comparison, an electric resistance water heater has 

an average COP of 0.82 and a load factor of SO 

percent. 

Des~perheater units can also provide the potential of 

reducinJ:t coincident summer peak demand by a 

July 25, 1983 Summer Peak 

5-6 Q.m. Average 

IS-minute Base IS-minute Base 

-------- ---------

60-minute Base 60-minute Base 

-D.03 0.05 

---- ------

0.06 0.07 

0.32 0.49 

---- -----

0.22 0.37 

0.15 0.38 

-- ----- 0.16 0.35 

winter, only ~ose units that are installed on beat 

pumps are capable of reducing electrical demand. 

This winter peak demand reduction is determined to 

be at least 0.2 kW per customer. Desuperbeaters 

also have an average COP of 1.10 and an annual 

load factor of 54 percent. 

Heat pump water heaters have a system efficiency _L'- _ .. -- ~-- ,,\..._. _t" "_ a.l~t-r'r-- r~4::iCl:t!lnrp water 
heater and operate at a load factor of 52 percent.

.The winter peak coincident demand is approximately

half that of an electric water heater so its winter

demand reduction potential is 0.6 leW per customer.

Unfonunately, in the summer, the coincident peak

demand reduction of heat pump water heaters is

negligible. Heat pump water heaters also

demonstrated reliability problems when the study

was performed in 1982 to 1984. If these problems

have been resolved. heat pump waters also offer

significant potential for reducing electric utility

winter peak demand.

ACKNO~DGEMENTS

The sponsorship of the Florida Public Service

Commission. the suppon of the Florida Solar Energy

Center management. and the cooperation of Florida's

electric utilities are gratefully acknowledged. The

FSEC project staff - Charles Beach. Omar Hancock.

Ross McCluney and Tom Tiedemann -- also deserve

both credit and thanks for their considerable work on

the project The dedicated assistance of consultants

Don Patzsch and Timothy Stryker. as well as

numerous FSEC graduate assistants. is also

acknowledged. Finally. the participating

homeowners deserve special gratitude for their

cooperation. Without their assistance. the project

would not have been possible.

REFERENCES

ASHRAE. 1977. ANSIIASHRAEStandard93-/977,

"Methods of testing to detennine the thermal

performance of solar collectors." American Society

of Heating. Refrigerating, and Air-Conditioning

Engineers, Inc.• Atlanta. Georgia.

ASHRAE. 1980. ANSI/ASHRAE Standard 90A1980. "Energy conservation in new building design."

American Society of Heating. Refrigerating. and AirConditioning Engineers. Inc.• Atlanta, Georgia.

Block. D. L. 1983. "Solar domestic hot water

system four-year performance results." Procee(/jngs

o/the 1983 Annual Meeting, American Solar Energy

Society, Vol. 6. pp. 235-240, Minneapolis, MN.

Florida Governor's Energy Office. 1981. "Florida

Energy Data: 1960-1981," Tallahassee. Florida.

v",,""'I~US ",JUOOll:H:::G - 930551-EG

Florida Solar Energy Industries Assoc.• Inc.

Exhibit _ (WTG-1)

Schedule 1

Page 12 eX 12

FPC. 1974. Florida Power Corporation, "Water

Heater Test Data," Technical Information No. 37.

St Petersburg, Florida.

FPL. 1978. Florida Power and Light Company.

"1978 Residential Electric Water Heater Study."

Miami. Florida.

FPL. 1989. Florida Power and Light Company.

"Petition to Detennine Need for Electrical Power

Plant: 1993-1996." Miami, Florida.

Florida Public Service Commission. 1985. Research

Department. "Statistics of the Florida Electric Utility

Industry 1984." Tallahassee. Florida.

Florida Public Service Commission. 1989. Research

Department. "Statistics of the Florida Electric Utility

Industry 1988." Tallahassee. Florida.

Gladhan, P.M.• and Wiehl, ].S. 1986. "Monitored

hot water use: A seasonal analysis." Proceedings -

1986 Summer Study on Energy Efficiency in

Buildings. American Council for an Energy-Efficient

Economy. pp. 1.90-1.103.

Merrigan, T. 1983. "Residential conservation

demonstration: Domestic hot water. Final report"

FSEC-CR-90-83. Florida Solar Energy Center, Cape

Canaveral, Florida.

Merrigan. T.• and Wang. M. 1981. "BTU meter

dynamic test. Final report" FSEC-CR-81-29(RD),

Florida Solar Energy Center. Cape Canaveral.

Florida.

McCluney. R. 1980. "Annual performance of 20

solar water heaters in central Florida." FSEC-RM-80-

4. Florida Solar Energy Center. Cape Canaveral,

Florida.

Parker. D.S. 1989. "Hot Water Study: Phase I

Final repon." FSEC-CR-295-89, Florida Solar

Energy Center. Cape Canaveral. Florida.

Perlman, M.. and Mills, B. "Development of

residential hot water use patterns." ASHRAE

Transactions. Vol. 91, Part 2. pp. 657-679. Atlanta.

Georgia.

EE-RM-90-201 COMMENT OOI5

heater and operate at a load factor of 52 percent. 

.The winter peale coincident demand is approximately 

half that of an electric water heater so its winter 

demand reduction potential is 0.6 kW per customer. 

Unfonunately, in the summer. the coincident peale 

demand reduction of heat pump water heaters is 

negligible. Heat pump water heaters also 

demonstrated reliability problems when the study 

was performed in 1982 to 1984. If lhese problems 

have been resolved. heat pump waters also offer 

significant potential for reducing electric utility 

winter peak demand. 

ACKNO~DGEMENTS 

The sponsorship of the Florida Public Service 

Commission. the suppon of the Florida Solar Energy 

Center management, and the cooperation of Florida's 

electric utilities are gratefully acknowledged. The 

FSEC project staff - Charles Beach, Omar Hancock, 

Ross McCluney and Tom Tiedemann -- also deserve 

both credit and thanks for their considerable work on 

the project The dedicated assistance of consultants 

Don Patzsch and Timothy Stryker. as well as 

numerous FSEC graduate assistants, is also 

acknowledged. Finally. the participating 

homeowners deserve special gratitude for their 

cooperation. Without their assistance, the project 

would not have been possible. 

REFERENCES 

ASHRAE. 1977. ANSIIASHRAEStandard93-1977, 

"Methods of testing to detennine the thermal 

performance of solar collectors." American Society 

of Heating, Refrigerating, and Air-Conditioning 

Engineers. Inc., Atlanta, Georgia. 

ASHRAE. 1980. ANS/IASHRAE Standard 90A1980, "Energy conservation in new building design." 

American Society of Heating, Refrigerating, and AirConditioning Engineers, Inc .• Atlanta, Georgia. 

Block. D. L. 1983. "Solar domestic hot water 

system four-year performance results." Proceedjngs 

o/the 1983 Annual Meeting. American SoJar Energy 

Society, Vol. 6. pp. 235-240, Minneapolis. MN. 

Florida Governor's Energy Office. 1981. "Florida 

Energy Data: 1960-1981," Tallahassee. Florida. 

v"'"'''',, I~US ::tJUOOII:)-t::G - 930551-EG 

Florida Solar Energy Industries Assoc .• Inc. 

Exhibit _ (WTG-l) 

Schedule 1 

Page 12 eX 12 

FPC. 1974. Florida Power Corporation. "Water 

Heater Test Data," Technical Information No. 37. 

St Petersburg. Florida. 

FPL. 1978. Florida Power and Light Company. 

"1978 Residential Electric Water Heater Study." 

Miami. Florida. 

FPL. 1989. Florida Power and Light Company, 

"Petition to Determine Need for Electrical Power 

Plant: 1993-1996." Miami. Florida. 

Florida Public Service Commission. 1985. Research 

Department. "Statistics of the Florida Electric Utility 

Industry 1984." Tallahassee, Florida. 

Florida Public Service Commission. 1989. Research 

Department. "Statistics of the Florida Electric Utility 

Industry 1988," Tallahassee, Florida. 

Gladhan, P.M., and Wiehl. ].S. 1986. "Monitored 

hot water use: A seasonal analysis." Proceedings -

1986 Summer Study on Energy Efficiency in 

Buildings. American Council for an Energy-Efficient 

Economy. pp. 1.90-1.103. 

Merrigan. T. 1983. "Residential conservation 

demonstration: Domestic hot water, Final report" 

FSEC-CR-90-83. Florida Solar Energy Center, Cape 

Canaveral. Florida. 

Merrigan. T .• and Wang. M. 1981. "BTU meter 

dynamic test. Final report" FSEC-CR-81-29(RD). 

Florida Solar Energy Center. Cape Canaveral. 

Florida. 

McCluney, R. 1980. .. Annual performance of 20 

solar water heaters in central Florida." FSEC-RM-80-

4. Florida Solar Energy Center. Cape Canaveral, 

Florida. 

Parker. D.S. 1989. "Hot Water Study: Phase I 

Final repon," FSEC-CR-295-89, Florida Solar 

Energy Center, Cape Canaveral. Florida. 

Perlman. M.. and Mills. B. "Development of 

residential hot water use patterns." ASHRAE 

Transactions. Vol. 91. Part 2. pp. 657-679. Atlanta. 

Georgia.