Florida Solar Energy Industries Assoc. Inc.

EXhibil_ (WTG-1)

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 ot the authors and not necessarily

those of the Florida Solar Energy Center.

EE-RM-90-201 COMMENT OOR19

Florida Solar Energy Irldustnes Assoc . Inc. 

Exhibll_ (WTG- l ) 

&heW_ \ 

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 

Publi shed in 

ACEEE 1990 Summer Siudy on 

Energy Efficiency in Buildings. 

Views and opinions expressed here represen t 

those of the authors and not necessarily 

those ollhe Flori da Solar Energy Center. 
Dod<.el Nos 930548-EG - 930551-EG

Florida Solar Energy Industries Assoc., Inc.

Exhibit _ (WTG-l)

SchedJIe 1

Page2 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 bot 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 kW 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 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, Rorida'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 . ..

full capacity. Unfortunately, when a high demand

for electricity occurs, Florida's utilities are severely

limited in their ability to increase capacity beyood

their own generation. Such a circumstance 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

",ili,i.." Ul..r.. t1n2hlp tn nt_t in nllrt hecause the.

EE-RM-90-201 COMMENT OOR19

Dod<.et NOS 930548·EG - 930551 -EG 

Florida Solar Enefgy Industries Assoc .. Inc. 

E~hibit (WTG-I) 

Scheci.Ji91 

Page2 ot12 

ELECTRICAL USE, EFFICIENCY, AND PEAK DEMAND OF ELECTRIC 

RESISTANCE, HEAT PUMP, DESUPERHEATER, AND 

SOLAR HOT WATER SYSTEMS 

Tim Merrigan and DaDDY Parker 

Fklrida Solar EDergy CeDler 

£ighlY single family residences in Aorida were monitored fer- 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 elecDic resistance. beat pump, desuperheater and 

solar hot water systems. 

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

in Rorida with an average water heating system efficiency of 82%. Desuperbeaters 

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

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

of 153%_ Elecbical use of solar hot water systems averaged 2.7 kWh per day and 

the average system efficiency was 235%. 

Electric:al demand taken at IS-minute intervals showed electric resistance water 

heaters conuibute approximately 1.1 kW of diversified demand 10 the utility winter 

peak. and at least 0.2 kW to the summer peak. Solar bot wiler systems exlUbiltd the 

most desirable demand profile relative to Rorida 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. Desuperheatc:rs have the same 0.2 kW minimum peak 

demand reduction in the swruner and 0.2 kW per customer reduction in the winter. 

Heat pump water heaters exhibited approximately half the peak: demands of elecuic 

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

significant amount. 

Sinc:e elecuic water heaters iCC:Ount for approximately 2S percent of the utility winter 

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

is beneficial to a winter-peaking utilit), in Aorida. 

INTRODUCTION 

Since 1982. Rorida'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 

elecuic utilities in the neighboring states of Georgia 

and Alabama. Sinc:e the purchased power is more 

economical. the transmission lines that CatT)' this 

full capacity. UnfCl1UDately. when a high demand 

for elecuicilY occurs. Rorida's utilities are severely 

limited in their ability to increase capacity beyood 

their own generation. Such a circwnstance recently 

occurred on December 24. 1989 when a suong 

winter cold front quickly passed through the 

southeastern United States. The cold weather 

crealed a peak. demand for elccuicit)' that Florida!s 

",;t;,i ... ~ ..., ........ I1nllhl ... In """,.I in nlln "'cau~ the . 
transmission of purchased power was already at full

capacity. The result was nwnerous large-scale

service interruptions due to rotated cunailments and

an understandable breakdown of overloaded

equipment. The Slate's largest utility, Aorida 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 detennining 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 Chrisunas Eve power shortfall, however,

emphasizes that any method to reduce peak demand

-- winter or summer - should be imponant to a

utility's planning process, especially in a high

growth Slate like Florida.

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 Aorida.

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 approximatelNI perce~ of the residential electricity consumption Ui""FIOilda

(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 heaters, and desuperheater

units that recover the waste heat of the refrigerant

in a residence's air-conditioning equipment --

account for less i.han one percent of the domestic hot

water (DHW) systems in the state (Aorida

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

Dcx;;kel Nos 930548-EG - 930551-EG

Florida Solar Energy Industries Assoc., Inc.

EXhibtl_ (WTG-l)

SchedJIe 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 bot water delivered and the

actual water use of the residences's bousebold.

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 bad 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 coounission, FSEC collected time~ ..

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

June 1984) 011 four types of DHW systems:

1. Electric resistance water heaters (that met

ASHRAE Standard 9OA-1980)

2. Heat pump water beaters

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 bot water energy use. TIle systems were

located in single-family residences in four major

population areas of Florida: Jacksonville in nonb

Florida. OrlandolBrevard County in east central

Aorida, the Tampa Bay region in west central

EE-RM-90-201 COMMENT OOR19

b"ansmission of purchased power was already at full 

capacity. The result was numerous large-scale 

service interruptions due to rotated cunailments and 

an understandable breakdown of overloaded 

equipment. The Slate's largest utility, Aorida Power 

and Light Company (FPL). experienced a demand of 

close 10 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 

sununer peak demands of 12.876 MW and 13,425 

MW. respectively (FPL 1989). 

Clearly. the ability to supply the winter peak demand 

without service interruptiom is of major coocem 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 coosidered in 

a loss-of-load probability analysis for determining 

!he need for new generating capacity (FPL 1989). 

The 1989 Christmas Eve power shoruall, however. 

emphasizes that any method 10 reduce peak demand 

-- winter or sununer - should be importan! to a 

utility's planning process, especially in a high 

growth state like Florida. 

One area for utility peak load management lies in the 

residential sector. Since 1970. residential electricity 

comumption has been approximately SO percent of 

the total annual elecaicity use in the state of Florida. 

In 1988, residential customers consumed over 63 

million megawatt-hours with an armuaJ growth rate 

of over five percent for each of the preceding four 

years (FPSC 1989). nus growth rate exceeded the 

population growth rate by at least two percent for 

each of these years. 

....----:::, 

Water heating accounts ror approximatelNJ perce~ of the residential electricity consumption lil'FTOfida 

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

the use of elecuic resisWlCe water heaters. Alternative water beating technologies - solar hoi water 

systems, heat pump water heaters. and desuperbeater 

units that recover the waste heal of the refrigerant 

in a residence 's air-conditioning equipment --

account for less ihan one percent of the domestic hot 

water (DHW) systems in the state (florida 

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

Oocl\et Nos 93054&EG - 930551-EG 

Florida Solar Energy Industries As$OC .. Inc. 

Exhibif _ (WTG- l ) -, 

Page 3 0112 

to operate or to supply backup water healing when 

neither solar nor waste heal is available. 

To evaluate the impact of alternative water heating 

technologies on the eledJic utility, it is necessary to 

measure the time-of -day electricity consumptioo or 

each system type in a number of occupied 

residences. However, the electrical consumption of 

any DHW method CIIl vary considerably depending 

on the temperature of (be hot water delivered and the 

actual water use of the residences's household. 

Unless a fairly large number of houses are measwed 

to eliminate the variance in these quantities. it is also 

necessary to measure !be bot water energy delivered 

by the DHW system. 'Ibis latter quantity can 

account for the variatioos in water temperature as 

well as volume and, therefore, can serve as a 

commoo ground for comparison. 

METHODOLOGY 

A Florida solar energy researcb and testing institute 

(FSEC) bas bad an active program in solar domestic 

hot water system field mcnitoring since 1978 

(McCluney 1980; Block 1983). In ceder 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 Rorida public 

utility regulatory coounission. FSEC collected time ~ 

of -day performance data for two years (July 1982 _ .. 

June 1984) 00 four types of DHW systems: 

I. Elecoic resistance water beaters (that met 

ASIlRAE Standard 9OA-I980) 

2. Heat pump water heaters 

3. Solar hot water systems (with collectors that met 

ASIlRAE SWldard 93-1977) 

4. Desuperheater water heaters. 

Twenty systems of eacb DHW type were instrumen&.ed to determine both their IS-minute electrical 

demand and hoi water energy use. TIle systems were 

located in single-family residences in four major 

population areas of Florida: Jacksonville in north 

Florida, Orlando/Brevard County in east cenual 

Florida, the Tampa Say regioo in west cenual 
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 (lOSS 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, controls, and/or

compressor of an alternative DHW system. Standard

single-phase 30 amp meters were used with pulse

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

A solid-state demand recorder accumulated contact

closure pulses from the kWh, Btu, and flow meters

and stored them in IS-minute totals in its internal

memory. These totals were routinely acquired by

UOC""II"iOS :;1-.1V::>4o-t;.u -- \J;)()::>::ll-t:.U

Florida Solar Energy Industries Assoc., Inc,

Exhibit _ (WTG-1)

Schedule 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 I lists the sample size, the average family size,

the daily average bot water use, the daily average

elecbic 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 elecbic and four beat pump water beaters were

omitted from these averages because of

instrumentation malfunctions or hot water system

equipment problems.) COP is defined as the bot

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 housebold bot 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 G..)!pay (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)

DesuperhealCf 20 3.6 58.6 7.4 1.10

Unit (222.1 )

EE-RM-90-201 COMMENT OOR19

Aorida. 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 fami ly sizes (Merrigan 1983). 

To measure the hot water energy delivered by the 

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

system. The heal 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 sensa 10 calculate the thermal energy 

change of the heated water befCl"e it is delivered to 

the household Lab«atory 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 (1055 k1) and I gal (3.8 L). 

A kilowatt-hour (kWh) meter was used 10 record the 

resistance element energy as well as any auxiliary 

energy used by the pumps, controls. amVor 

compressor of an alternative DHW system. Standard 

single-phase 30 amp meters were used with pulse 

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

A solid-state demand recorder accwnulated contact 

closure pulses from the kWh. Btu. and flow meters 

and stored them in 15-minute totals in its intemal 

memory. These tOLals were routinely acquired by 

W()(; UII'O~ ",..>U =>4o- l:l..> - \;IJO:>:> I. t;. l.:i 

Florida Solar Energy Industries Assoc .. Inc. 

Ed'libit _ (WTG- l ) 

""""'. 1 

Page 4 0112 

telephone interrogation of the demand recorders. 

b"ansferTed 10 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 bot water use, the daily average 

electric use, and a dimensionless coefficient of 

performance (COP) for !be four DHW 'ypes for !be 

two-year period luly I. 1982 to lune 30. 1984. 

(Two elecUic and four beat pump water beaters were 

omitted from these averages because of 

insrrumentation malfunctions or hot water system 

equi_g, problems.) COP is defmed as !be bot 

water energy use divided by the electrical energy 

consumption and is, therefore, a measW'e of the total 

DHW system efficiency. 

Figwe I displays the average daily electrical load 

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

DHW groups for !be lWO-year period. The hours 

displayed are clock times. rather lban the year-round 

standard time that is sometimes used in annual data 

acquisitioo projects subject 10 the hour offset of a 

sununer daylight savings period. This approach was 

taken since household bot wiler use generally 

corresponds to actual clock time, as seen by the 

apparent awakening of the florida groups around 

6:00 a.m. 

T.b,. 1. Florida Group Si:es. 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 

S~stems People Gal !1:llQa:l (kWh/Da~l Perronnance 

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 Healer (280.5) 

Solar Hot 20 3.1 53.8 2.7 2.35 

Water Heater (203.9) 

Desuperhcatcr 20 3.6 58.6 7.' 1.10 

Unit (222.1 ) 
UOCl\et Nos 930~-tG - 930551.EG

Florida Solar Energy Industries Assoc.. Inc.

Exhibit _ (WTG-1)

Sched.J1e 1

PageS of 12

Type 01 System

Florida average daily electrical demand

(July 1. 1982. - June 30.1984)

Load factor is a measure of how well the electtical

capacity demanded from the utility is utilized by the

load over a period of time.

for the same peak days. This bourJy coincident

demand is calculated by averaging &he four 1Sminute demands IbaI 0CCUJ'J'ed during the peak hour.

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

that FPL was unable to meet abe peak demand on

December 26, 1983 and bad to rotate CUJ1.Ijlments

throughout their service uea. Hence, abe FPL

system peak of &he winter of 1982-83 (January 13•

1983) bas been included in these tables.

Figmes 2 through 5 present the average IS-minute

demand profiles for abe four DHW syBtcm types on

abe FPL wiD&er peak day of February 7. 1984.

Figures 6 1brough 9 presems the same time-of-day

profl1es for the Slimmer peak day of July 2S, 1983.

These two days were selected for presentation

because they represent-the bighest utility system

loads of all the FPlr peak days that did not have

service intemlptions.

ANALYSIS

Annual Electrical Use and Demand

The average electricity use of 8.3 kWh per day for

the electric resisWJCe water beater group - with an

average family size of 3.6 people - compares

f!lVorably with values oblained by other studies

performed in Florida. FPL determined in a 1976-77

study of 16S customers that a family of four used an

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

Power Corporatico detennined in a similar study lbat

a family 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 co electrical wilei'

bearers in order to meet the minimum beat lass rate

requiremcDlS of ASHRAE Standard 9OA-I980.

The shape of the average daily eleeuical dmwJd

profile for electric resistance water beaters as seen

in Figure 1 is also CXlOSisleDt wilb abe results of

previous SlUdies. 1be twin peats of mid- morning

and early eve:ning demand C:Ollespood to typical

residential bot waJa' ute patUms of sbowering, food

preparatiOl1, and cleanup (Perlman and Mills 1985;

Gladban and Wiebl 1986). As bot water is

withdrawn from the lUnge tank, the electric

element turns on wben the warer &emperature drops

Conventional electric

Heal pump water healer

Solar water heating system

Desuperheater water heater

Average Demand (kW)

Peak Demand (kW)

10 2 4 6 8 10

Noon Midnight

Average Daily Electrical Load Profile for

Four T)'Pes of Wattr Hearing Systems

.6

.2 .

.4

2 4 6 8

Midnight

Figure 1.

Load Factor (%) =

,-

Tables 3 and 4 indicate the FPL winter and summer

peak days, respectively. and the hoor mat 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

rD1 .,,,.,,pm nP-a-lc The diversified 6O-minute

The winter peak and sununer 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 balf of me systems were located in the service

areas of Florida Power Corporation. Tampa Electric

Company. and Jacksonville Elecaic Authooty.

These utilities either had the same winter and

summer peak load days as FPL or their Secondary

system peaks occurred on these days.

Table 2 presentS the daily average IS-minute

elecaical demand. the average IS-minute maximum

demand and the daily 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.

E..

';i .8

I/)"'"

;

Cl.

'0

c:

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E..

o

..

CII

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- 1.0

- -- 1 .1_:1••

EE-RM-90-201 COMMENT OOR19

~ 

Florida average daily electrical demand 

(Ju ly 1. 1982. 0 June 30. 1984) 

Type 01 Sy.tem 

~ 1.0 Con"enlionat eteC:lric 

Heat pump .aler healer 

Solar Wiler he aUng .ytle", 

Desuperh .. ler waler heller 

E 

• '; .8 ~ 

~ 

· • 

~ 

~ 

i .4 

E ". • Q 

: 0 ~ ~=~~"--::-T-:--=;=:---: ;.. 'WO o .' 

~-;;-~ c 2 • 6 8 10 2' 6 8 10 

Midnight HOOf! Midnight 

Figure 1. Averagt Daily £Itcrricaf Load P,ojilt fo, 

Four Typts of WaItT Htatillg SYSltms 

Table 2 presentS the diily average I5-minute 

electrical demand. the average IS·mioute maximum 

demand and !be daily load faclOr for the four DHW 

types for the twcryear period. Load factor is the 

ratio. expressed as a percent of the average kilOWlU 

demand over a designated period of time to the 

maximum demand occurring in that period. 

Load Factor (%) • Average Demand (kW) 

P,ak Demand (kW) 

Load factor is a measure of how well the elecuical 

capacity demanded from the utility is utilized by the 

load over a period of lime. 

The winter peak. and sununer peak. days chosen for 

dau 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 'Nert loclltd in the service 

areas of Acrida Power Corporation. Tampa Electric 

Company. and Jacksonville Electric Authaity. 

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 winLel' and summer 

peak. days. respectively. and the boor \hat the peak 

occurred. These same tables also contain each OHW 

system type's maximum lS·minute diversified 

demand that was coincident with the hour of the 

rDT ." .. ~I .. ", N':.Ilk. The diversified 6()..minute 

U<X.>\e1 Nos. 9JO:wB c~ - 930551 .EG 

FIoMa Solar Energy Industries Assoc .. Inc. 

Exnibit_ (WTG-l ) """"'. , 

Page 5 0112 

for Ihe same peak. days. 'Ibis bowiy coiodderu 

demand is calcula1ed by averaging lbc four IS· 

minute drmands 1Iw occwred during the peak bouT. 

It is imporwu to DOle in boCh Table 3 and Table 5 

that Fi'L was unable to meet the peak. demand 00 

December 26. 1983 IUd bad to rDCate cwujlmeolS 

tbrougbout Cbeir service uea. Heoce. lbe FPL 

sy.tem peIk of lbc winter of 1982·83 (JIDUIly 13. 

1983) bas _ iDcludcd in lbcse tables. 

Figuros 2 lhrougb 5 presem lbc avenge 15·miDute 

demand prof ties for lbc four DHW _ type. 011 

the FPL winIer peIk day of February 7. 1984. 

Filures 6 IIIrougb 9 praeDIS lbc same time-oC-day 

proflies for lbc .. ",,_ peak day of July 25. 1983. 

Tbese two days were ldecced fa preseorarioo 

beuuse they repn:sent ihe bighest utility system 

loads of all the FPL peIk days ihat did not bav, 

service inte:n'Uptioas. 

ANALYSIS 

Annual Electrical Use and Demand 

1be average elearicity use of 8.3 kWh per day for 

the electric resistance water beater group - with an 

average family size of 3.6 people - compares 

fllvorably with values obcained by other studies 

perform,d in Florida. FPL determined in. 1976-77 

study of 165 CIIstomen lbal I family 01 four used an 

Iverlg' 0110.2 kWh per day (FPL 1978). Aorida 

Power Corporatioo _ in I similar srudy tIW 

a f .. -nily of three used an avenge 01 8.4 kWh per 

day and I family of four wed 11.6 kWh per day 

(FPC 1974). BolIl studies .... n: performed befor, 

improved iDsulatioc was required 011 electrical water 

beaten in order to meet the minimum beaI: as rate 

nquin:meDls of ASHRAE $1_ 9OA·I980. 

The sbIpe of lbc Iverage daily eiOClricai demand 

profile for e~ resistlDC:e wlltr beaters IS seen 

in Figure 1 is also CODSiSCCDI with the results of 

previous llUdies. '!be !wiD peak> of mid- IIIOrDiag 

and Cltly evczUn& demand CUiespood to typical 

residential boc: waser ue patlans of sbowerin.g. food 

preparwoo. IUd cleanup ~ and Mills 1985; 

GladIwt and Wiebi 1986). As bot wiler is 

withdrawn frcm the aorage tank. !be electric 

element turns on wbeo &be water umpc::rarure I!rops __ _ .... ..1.:1 •• 
Docket Nos 930548-EG - 930551-EG

Florida Solar Energy Industries Assoc.• Inc.

Exhibit_ (WTG-1)

SchecilIe 1

Page 6 of 12

Table 2. Annual Average i5-MinUle Demand. Peak i5-MinuJe Demand. and Load Faclor by Type of System

Average Demand Peak Demand Load Factor

(leW) (leW) (%)

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 i5-MinUle Demand Coincident wilh FPL Winter P~ak 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 i5-Minule Demand Coincident with FPL Summer Peak Load (60-Minute Nel)

August 24, 1982 July 25, 1983

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

Electric Resistance 0.74 kW 0.34 kW

Heat Pump Water Heater 0.61 kW 0.37 kW

SoIlU' Hot Water System 0.08 kW 0.02kW

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.

LJ..... n,,",n UllltP1" hplItl"r~ had a similar load factor

average demand is approximately 25 percent less.

This reductioo is due to the higher annual average

system efficiency of the beat pump water beater --

approxin:lately twice that of the electric resistance

water heaters. However, seven of the 20 heat pump

EE-RM-90-201 COMMENT OOR19

Do:::Jo.eI Nos 93054&-EG - 930551-EG 

Florida Solar Energy Industries Assoc., Inc. 

Exhibil_ (WTG-l ) """""', 

Page 6 0112 

T4b~ 2. Annual Average 15-Minute Demand, Peak !5-Minule Demand, and wad Factor by Type of Syslem 

Average Demand Peak Demand Load Factor 

(!;Wl (!;Wl !%l 

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 

TtJb~ J. Average JS-Minute Demand Coincuunl with FPL Wimer Peak Load (60-Miruue 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 

Tab~ 4. Average JS-MinuJe Demand Coincichnz with FPL Summu Peak Load (60-MinuJe Nel) 

Augus' 24, 1982 July 25, 1983 

5-6 p.m. 

ElecU"ic Resistance 0.74 kW 

Heat Pump Water Heater 0.61 kW 

Solar HOI Water System 0.08 kW 

Desuperheater Unit 0.14 kW 

average demand of the element is exacUy one-half of 

its average peak demand, resulting in an annu31. 

average load factor of SO percenl. 

u ...... n ....... n w"'~r h ..... ' ... r" had a similar load factor 

5-6J2.m. 

0.34 kW 

0.37 kW 

0.02kW 

0.19 kW 

average demand is approximately 25 percent less. 

This reductioo is due to the higher annual average 

system efficiency of !.be beat pwnp water beater -

approximately twice that of the electric resistance 

waLer heaters. However, seven of the 20 heat pump 
i)OCl\tll Nos 930548 EG -- 930551·EG

Florida Solar Energy Industries Assoc.. Inc.

Exhibit _ (WTG·1)

Schedule 1

Page 70112

Tabu 5. Average 6O·Minute 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 O.64kW

• Unserved utility load of 666 MW

Tabu 6. Average 6O-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 0.58 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-term

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.

C'omhined with lhe 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.

Desuperbeater 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 performance 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 OOR19

iJoc"ul Nos 930~8 EG·· 93055I-EG 

Florida Solar Energy Industnes Assoc., Inc. 

El<.hibil_(WTG·I) """"" , 

Page 701 12 

Table S. A\"erage 6O·Minule Demand Coincident ·with FPL Winter Peak Load (60·Minule Net) 

lanuary 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 

Resistancc 

Heat Pump Water 0.48 kW 0.36 kW 0.68 kW 

Heater 

Solar Hot Water 0.24 kW 0.59 kW 0.44 kW 

System 

Desuperheater Unit 0.63 kW 0.30 kW 0.64 kW 

• Unserved utility load of 666 MW 

Table 6. Average 6O-Minult Demand Coincident with FPL Summer Peak Load (60-Minule Nel) 

Augusl 24. 1982 July 25. 1983 

5-6 p.m. 

Electric Resistance 0.58 kW 

Heat Pump Water Heater 0.51 kW 

Solar Hot Water System 0.06 kW 

Desuperheater Unit 0.04 kW 

failures. indicating a problem with long·term 

reliability in 1982-84. 

Solar hot water systemS operated with the highest 

average electrical system efficiency and had the 

10wesL average daily electrical demand p-ofile. 

However. the solar system's annual load factor of 

41 percent compares favorably with the electric 

resistance waler heater's load factor of 50 perceot 

This is surprising since the majority of solar system 

owners turned off their st(l"age 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 thcse systems was that of the solar circulation 

pump as can be secn in the summer day average of 

Figure 9 for the six-hour period around noon. 

C:nmhin~d with the occasional winter use of the 

5-6 p.m. 

0.23 kW 

O.!7kW 

om kW 

0.07 kW 

backup element. this electrical demand was 

consistent enough during the summer months to 

create a relatively high annual load factor. 

Desuperbeater unit owners also typically rumed off 

their backup electric clement during the sununer. 

However. these units would only supply hot waler 

when there was a need f(l" air conditioning or, for 

those eleven desuperheaters lhat were instaUed on 

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

considerable periods of time when neither mode of 

space conditioning is required. TIUs is reflected in 

the average two-year coeffacient of performance of 

1.10 for desuperheaters. Although this COP is 

beuer than unity, it is not much higher than the 

efficiency for UI electric resistance waler healer. 

The annual load factor of 54 percent and the average. 
Docket Nos 930548-EG - 930551·EG

Florida Solar Energy Industries Assoc., Inc.

Exhibit _ (WTG-1)

Schedule 1

Page8 of 12

Winter Peak Load Day: February 7, 1984

Solar water heating .y.tems

800 1200 1600 2000 2400

Hour of Day

400

-

7a 1800

"0 1600 -----.

; 1400

E 1200. -- _._- -.----- - III

o 1000 III

'; 800

.5::IE 600 - ----n-t--...-------

400 - --.,--

& 200- --iO- __M

III

> 0

<

Winter Peak Load Day: February 7, 1984

Conventional electric re.i.tance

o 400 800 1200 1600 2000 2400

Hour of Day

-

1800

;- 1600

; 1400

1200

1000

'; 800

c

j 600

It) 400 ...& 200

0 III

>

<

Figure 2. Average Winter Peale Day Electrical Load

Profile for Electric Resistance Water Heaters

Winter Peak Load Day: February 7, 1984

D..up.rh.at.r water heate,..

800 1200 1600 2000 2400

Hour of Day

400

Figun 4. Average Winter Peak Day Electrical Load

Profile for Solar Warers Heaters

-

- 1800 - ------------,---

;- 1600 - -----------------:

; 1400 - ---------~-__t---'

1200' ------------f!---

o 1000 - ----+-----_-...-.,...-' III

'; 800 - -----1j---.,.-------,f,'------:T._-zt:-

C

j 600

400- ---*-

& 200 - ~:"-'lb-..-t--f;ji.1II

0 - _ilIioW....._

III

0

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

Winter Peak Load Day: February 7, 1984

He.t pump water heater.

o 400 800 1200 1600' 2000 2400

Hour of Day

-

-III 1800·

"0 1600

c

III 1400

E

CII 1200

0 1000 III

'; 800

.5 600 ::IE

It) 400 ...

III 200 Cl

III 0 CII

>

<

Figure 3. Average Win/tr Peak Do)' Electrical Load

Profile for Heat Pump Waler Heaters

Figu"; 5. Average Winter PeaJc Day Electrical Load

Profile f,?r Desuperheater Units

daily electrical demand as seen in Figure I also

suggest that desuperbeater 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 peak demands for each of the DHW

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

vary considerably from one peak 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 wimer peak. as evideDccd by tbe fact Ihal FPL

system peak occurred at a different boar OIl eacb of

the three peat days. The peak day electrical demand

prof1les for each of the DHW system types (found

in Figures 2lbrwgb 9) also are higbly variable due

to tbe weather as well as the bot water use 00 tbat

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 OOR19

'" ;; 1800 ~ 

.; 1600 

~ 1400 

f. 1200 

C 

• 

1000 

'5 ••• .E ••• ,. 

~ 

- ••• 

• 2 •• 0> 

• • • • • 

.. 

Winler Puk L.oad Day: February 7. 1984 

Conv.ntional .I.ctric r •• i.'ance 

• 

t .. 

L . 

,. I" 

400 800 1200 1600 2000 2400 

Hour of Oay 

Fi,un 2. A~ragt Wimer Peak Day Elulricaf Load 

Profilt f or Eltctric Rtsistaflct Wattr Htattrs 

_ Win Ie, Pe.k 1.oad Day: February 7, 11184 

= H •• t pump wat.r h •••• ,. 

~ ;; ,. ... --- _ .--. ------------------

'D 1600 

e 1400 • E 1200 • C 1000 J!! 

, ••• .E ••• ,. 

~ 

- ••• 

• 2 •• 0> 

• • • • • 

.. i . . 

• ••• ••• 1200 1600' 2000 2400 

Hour of Oay 

ngurt J. Avtragt Winltr Ptak Day Eltclrical Load 

Profilt f or Htar Pump Wattr Htattrs 

daily electrical demand as seen in Figure 1 also 

suggest ahat desuperbuter units perform very sim.ilar 

to electric resistance water heaters on an annual 

basis. 

Peak Day Demand 

AJthough both the lS·minute and the 6()..minUle 

coincident peale demands for each of the: DHW 

system lypeS (found in Tables 3 through 6) appeu to 

vary considerably (rom one peale day to another 

within the same season, it is important to note that 

these demands are highl y dependent on the: weather 

Docket Nos 9Xl548·EG - 9Xl5St ·EG 

Fbrida Solar Energy Industries Assoc .. Inc. 

hibit (WTG· 1) 

SctI9d.Jiii1 

Page 8 01 12 

:F 

.. Winter Peak 1.oad Day: February 7, 1984 

Sol.r .at.r h.aUng ayat.ma 

~ 1800 

'a 1600 

e 

E 1400 

1200 • c 1000 

J!! 

• •• ~. ·------rrt ~i-------~---­

.... --~-, 

~ 200 · -,.---~ 

~ . . ....... ....JJ 

C • 0 400 100 1200 1100 2000 2400 

Hour ot Day 

Firun 4. AwrD,t Winler Ptak Day Electrical Load 

Profilt lor Solar WattrS Heatlrs 

Wint.r P.ak Load Day: Februlry 7, 1884 

i' D .. uperh •• t.r •• ter h ....... 

!. .. , •••. ---------c------------- ----- ~ 1~0 ~------------------------_c 

; 1400 - -------- ------------_r---O 

E 1200 · --------,----------'------f,---- ~ 10~ ------~~------~--_f~T" 

~ 100 ' -------c+-,-~~c_--_. 

:i 

~ 

-

t 

• • 

.. 

••• 

••• . -----,-0-

200 · ~ti!j; • . E 

• ... .oo 1200 1100 2000 2400 

Filurt S_ Awra,t Winttr Ptak. Day Eltctrical Load 

Profilt 10/ DtsuptrMDttr Units 

foc each day_ 1bi.s is especially true in the case of 

!he wiDIu peak. IS eviclcoccd by !he flCl that FPL 

system peak occuned II • diffe=t boor 00 eacb of 

lhc three peak da}'$. The peak day electrical dem,nd 

prom .. for cacb of tile DHW system l)'JJes (found 

in FiglRS 2 lbroulb 9) _ ... bilhly variable due 

10 &be we&tber u well IS (be bot water use 00. tba1 

day. 

Understandably. the coosumption of bot wat.c:r IDd, 

therefore the demand for electricity, was greater in 

the winter than in the summer. For instlDCe. the 

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

Florida Solar Energy Industries Assoc.. Inc.

Exhibit _ (WTG-1)

Sched.de 1

Page9 of 12

o

400

200

____--.1. • __

800 1200 1600 2000 2400

Hour of Day

400

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

Summer Peak Load Day: July 25. 1983

Solar water heating .y.'ems

600 -

400 - ---------

200 - r-;__••Iba_~__ 0- 1lj b

o

800- -----

ClI

en

CIlI

...

ClI

:-

<

-.:2

-; 1200

;- 1000 - - ---------

c:

III

E

GI

C

ClI

'S

.5

It!

...

..

Summer Peak Load Day: July 25. 1983

Conventional electric resistance

o 400 800 1200 1600 2000 2400

Hour of Day

800

600

-

";

1200

- 1000 III

E

ClI

c

ClI

'S

.=

It!

...

ClI

en

III

...

ClI

>

<

Figure 6. Average Summer Peak Day Electrical Load

Profile for Electric Resistance Water Heaters

Figure 8. Average S~r Peak Day Electrical Load

Profile for Solar Walers Healers

Summer Peak L.oad Day: July 25. 1983

- Heat pump water heater .ystems

-; 1200------- -

!

__w'; t\~Lj'jfl. 400 800 1200 1600 2000 2400

Hour of Day

'C 1000 - . c:

CIlI

E 800 - GI

C 600 - GI

'S

.5 400

:IE

It!

... 200·

GI

en

CIlI 0- ...

GI

:- 0

<

Summer Peak Load Day: July 25.1983

-; De.up.rh••'er water h••t.,.

i 1200- ---------.,.------

-

!

- -;-t~-- :

800 1200 1600 2000 2400

Hour of Day

o 400

800

600

400

ClI

en

III

...

ClI

>

<

1000 -

III

E

ClI

c

ClI

'S

.=

It!

...

Figure 7. Average Summer Peak Day Electrical Load

Profile for Heat Pump Water Heaters

Figure 9. Average SlU'J'JIner Peak Day Electrical Load

Profile for Desuperheater Units

electtic resistance water heaters on the winter peak

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

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

during the previous summer. FurthennCl'e. the

average electtical consumption used to heat each

gallon of bot water shows large differences between

winter and summer peak days. On the winter peak

day. February 7. 1984. electrical resistance systems

used an average of 175 Wb 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

2iven volume of water on the winter peak day. Most

of the difference in electrical consumption is due to

the seasonal variatioo in inlet water temperature to

the bot water tank. Data recorded over the last two

years at FSEC show that iDlet Wiler temperatures in

Central Florida vary by more than 14 OF throughout

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

beaters are loclleCl in larqeB in FlOOda, lower

ambient temperab.lres 00 winter peak days iDcrease

tank: standby losses and add 10 the daily bot water

beating electtical consumption.

'to evaluate the peak demand reduction potential of

the alternative water heating technologies. it is

EE-RM-90-201 COMMENT OOR19

F 

;; 

~ 1200 

~ 1000 

• 

~ 800 

o 

600 

~ 400 

~ 

~ 

• 

~ 

• • • • " 

200 

o 

Summer Peak Load Day: July 25, 1983 

Conventional electric re.iatance 

o 

. ;. 

jI 

400 800 1200 1600 2000 2400 

Hour ot Day 

Figur, 6. Alltrogr S~r Ptok Day Electrical Load 

Profile/ or Electric Resistance Wattr Heaters 

-• 

~ 1200 

~ 

't:I 1000 c 

• e 800 • o 

• ;; 

.E 

:I 

~ 

~ 

~ • 

• :;; 

• " 

600 

400 

200 

o 

SUmmer Peak Load Day: July 25, 1983 

H •• t pump water h •• ter arstem. 

.. _ .. _---

o 400 800 1200 1600 2000 2400 

Hour 01 Day 

Figure 7. Avtrage Summer Pta); Do)' Electrical Load 

Profile for Heal Pump Wattr Heaters 

elecb'ic resistance water heaters on the winter peak 

<lay in 1984 (66.3 gallons or 251 L) was 27% gre...,r 

!han !he use on the peal< day (52.3 gallons or 198 L) 

during the previous swnmer. Furthermore, the 

average electrical consumption used to beat each 

gaUoo of bot water shows large differences between 

winLet and summer peak days. On Ihe winter peak 

day, February 7. 1984. electrical resistance sySlc:mS 

used an average of 175 Wb to beat each gallon of 

water, whereas only 119 Wh were used to heat each 

gallon on July 25. 1983. the summer peak day. Thus. 

electrical conswnption was 47% greater to heat a 

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

-

" ;; 

;J 

.., 

c 

• E 

• 0 

• ;; 

c 

i 

~ 

~ 

• .. 

• • • • " 

1200 

Dod<.ec Nos 93()548.-EG - 93055 H G 

Florida Solar Energy lna..stries Assoc., Inc. 

Exhibit _ (WTG-1) """""', 

Page 9 0112 

Summ.r P •• k Lo.d D.y: July 25. 1183 

Solar .ater h •• tlng .,.t.me 

._-_ .. - - - - - ._- . .. _._ --

1000 . - - - - - -- .. .- - . 

100 · 

600 · .. - .-

400 · 

200 · 

• L, O · 

0 400 100 1200 1600 -- 2000 2400 

Hour of D.y 

Fitllrt 8. Awragt SJunmLr PtDk Day Eitctrical Load 

Profilt for Solar Wattrs Htaltrs 

-

" .. 1200- ------.,-------

~ .., 1000 - ' 

c 

• E .00 · 

• 0 600 - ~ 

• c 400 i 

~ 200 · 1.., U;, tlLtL ~ 

.. • 

O · • • • 0 400 100 1200 1800 2000 2'00 • " Hour of D.y 

Fi,urt 9. !.'1tragt S~r Peak. Day Eltclricai Load 

PraftJt for DtSllptrhetUtr Uniu 

of the diffeJCDCe in e1ectric:a1 ccosumptioo is due to 

the seuooal variatioo iD iDlel water aempenture 10 

the bot w_ WIlt. n... rocudod over the lISt two 

years It FSEC sbow dI.at iDld water temperatuJcs in 

Ceulral Flori<la vory by ""'" IIwI 14 OF Ihrougbout 

IIIe year (Parter 1989). AlIa, IiDce '""'" 1>01 water 

beaI<rs .. loc:_ in I...,.. in Florida. lower 

ambient lempenlllreS OIl .n- peak days iD=as<: 

WlI: sundby losses IDd odd to the daily bot wiler 

beating electrical coosumptioo.. 

1:.0 evalualt the peak demand reduction poc.eotial of 

the ah.emative water heating teChnologies. it is 
necessary to frrst 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.

ResullS 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 detennine the difference in coincident

peak demand between each technology and a base

technology - the conventional electric resistance

water heaters. Table 7 presenlS 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 cunailmenlS 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 15-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 leW per customer.

Heat pump water heaters contribute approximately

0.6 leW per customer reduction to winter peak

demand. while desuperheaters are responsible for at

least a 0.2 leW 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 waler heaters may be

Dochel Nos 930548-EG -- 930551-EG

Florida Solar Energy Industries Assoc., Inc.

EXhibil_ (WTG-1)

Schedule 1

Page 100112

as low as 0.25 leW per customer. one cannot claim

more than a 0.2 leW 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 ooIy 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 oulSide

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 common electric resistance water

heater contributes approximately 1.1 leW per

customer to the utility winter peak and at least 0.2

leW 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 pea.ks was 4.2 leW (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

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

become more important 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 leW per

customer in the winter and a minimum of 0.2 leW

per customer in the summer. Solar systems perform

EE-RM-90-201 COMMENT OOR19

necessary to nrsttest whether the winter and sununer 

peak day electrical prolile of each technology was 

statistically diffcrenI 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 prontes. 

Results show«1 that the peak day prontes 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 leChnology and a base 

technology - the conventional electric resistance 

waler 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 cunailments 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 ami 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 S. 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 bot 

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 presents a similar analysis as Table 7 except 

that the diversified sununer coincident peak demands 

from Tables 4 and 6 are used to detennine 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 thaI the 6O.minute COincident peak 

demand for electric resiSlance waier heaters may be 

DocJ,.m Nos 930 S- · 930551·EG 

Florida Solar Energy Industries Assoc .. Inc. 

Exhibit _ (WTG· l ) """"'. , 

Page 10 01 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 waler heaters. 

However. it is important to note that this analysis 

considers the peak demand reduction due to water 

heating roly and does DOt consider any increase or 

reduction that may occur if the space conditioning 

load is affected by the water beater operation. While 

most beat pwnp water heaters were located outside 

of the conditioned space of a bouse. there were some 

that were located inside such that their operatioo 

would increase the heating load in the winter and 

decrease the cooling load in the summer. This 

analysis does not consider any effcct that this 

contribution may have had on overall residential 

peak demaod. 

CONCLUSIONS 

Residential water heating offers a significant 

potential for Rorida electric utility load management 

because of the increasing level of residential 

.elecDicity consumption and the ability of alternative 

water heating technologies to reduce coincident peak 

demand. The conunon elecDic resistance water 

heater contributes approximately 1.1 kW per 

customer to the utility winter peak and at least 0.2 

kW per CUSIOmcr 10 the summer peak. In 1988. the', 

total peak demand per customer at the time of both 

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

J 989). Heoce, electric water heaters are responsible 

for approximately 25 percent of the utility winter 

peak demand ami ooIy about 5 percent of the utility 

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

become more important than the sununer peak in 

determining the need for new generating capacity. 

FCX1Unately. alternative water heating teChnologies 

offer a means to reduce winter and sununer peak 

demand wilhout requiring controlled utility 

intervention or even significantly reducing load 

factor. 

Solar hot water systems exhibit the highest 

coincident peale demand reduction of 0.7 kW per 

customer in the winter and a minimwn of 0.2 kW 

per customer in the summer. Solar systems perfonn 
Do<::ket Nos 930548-EG - 930551-EG

Florida Solar Energy Industries Assoc., Inc.

Exhibit _ (WTG-1)

SchedJIe 1

Page 11 ot 12

Table 7. Diversified J5-Minule 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 IS·Minute and 60-Minute Summer Peak Demond Reduction (kW per Customer)

Electric Resistance

Heat Pump Water Heater

Solar Hot Water System

Desuperheater Unit

August 24, 1982 July 25, 1983 Swnmer Peak

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

IS-minute Base IS-minute Base IS-minute Base ••• aM ••••• -_......... ------ 60-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 arulUal 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.

Desuperheater units can also provide the potential of

reducing coincident summer peak demand by a w'" __ . __ .:_ .L._

winter, only those units that are installed 00 beat

pwnps 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

.....""hl\! turic-,. lluIl of an electric resistance water

EE-RM-90-201 COMMENT OOR19

Doc:kel Nos 93Q548·EG - 930551 ·EG 

Florida Solar Energy Industries Aswc., Inc. 

Exnibil _(WTG. l j 

""""'. 1 

Page 11 at 12 

Tabu 7. Divf'rsijif'd 15-Miflwf' and 60-Minute Wintf'r P~ak D~mand R~ductiofl (kW per Cu.nomer) 

January 13. 1983 February 7. 19S4 WinLer Peak 

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

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

Electric Resistance ------- ----- --------- 6O-minute Base 6O-minute Base 6O-minute Base 

0.61 0.61 0.61 

Heat Pump Water Heater ---

0.59 0.50 O.SS 

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 

Tabu 8. Div~rsified J5 Miflut~ and 60-Miflut~ Summer Peak DemtJnd Reduction (kW per Cuswmer) 

August 24. 1982 

5-6 IZ.m. 

15-minute Base 

Electric Resistance 

6O-minute Base 

0.13 

Heat Pump Water Heater 

0.07 

0.66 

Solar HOl Water System ---

0.52 

0.60 

Desuperheater Unit ---

0.54 

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 SO 

percent. 

Desuperheater units can also provide the JX)tenlial of 

reducing coincident summer peak demand by a 

July 25. 1983 Sununer Peak 

5-6 IZ.m. Average 

IS-minute Base IS-minute Base 

--- 6O-minute Base 6~minute Base 

.o.Q3 0.05 

0.06 0.07 

0.32 0.49 

-- --

0.22 0.37 

0.15 038 

0.16 0.35 

winter. mly those wtits lhat are installed 00 beat 

pumps are capable of reducing electrical demand. 

This winter peak demand reduction is determined to 

be al leasl 0.2 kW per customer. Desuperheaters 

also have an average COP of 1.10 and an annual 

load r actor of 54 percent. 

Heal pwnp water heaters have a system efficiency 

........ hlv lwi ... ", IhM of an electric resistance wa~r 
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 kW per customer.

UnConunately, 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 perfonned in 1982 to 1984. If these problems

have been resolved. heat pump waters also offer

significant potential for reducing electric utility

winter peak demand.

ACKNOWLEDGEMENTS

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 projectstaff - 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 Patzseh 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. ANSIIASHRAE Standard 93·/977,

"Methods of testing to determine the thennal

perfonnance of solar collectors." American Society

of Heating, Refrigera~g, and Air-Conditioning

Engineers, Inc., Atlanta, Georgia.

ASHRAE. 1980. ANSIIASHRAE Standord 90A·

1980, "Energy conservation in new building design."

American Society of Heating, Refrigerating, and Air·

Conditioning Engineers, Inc., Atlanta. Ge<xgia. '

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

system four-year perfonnance results." ProCt!~tJjngs

ofthe 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.

'-',",,-"t;lll~uS ::;';V::"Hl-!:l.i - 930551-EG

Florida Solar Energy Industries Assoc.• Inc

EXhibit_ (WTG-1)

SChedule 1

Page 1201 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

Deparunent. "Statistics of the Florida Electric Utility

Industry 1984," Tallahassee, Florida.

Florida Public Service Commission. 1989. Research

Depanment, "Statistics of the Florida Electric Utility

Industry 1988," Tallahassee, Florida.

Gladhart. P.M., and Wiehl, I.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, Pan 2, pp. 657-679, Atlanta,

Georgia.

EE-RM-90-201 COMMENT OOR19

heater and operate at a load factor of 52 percent. 

.The winter peak. coincidem demand is approximately 

half that of in electric water heater so its winter 

demand reduction p:1tential is 0.6 kW per customer. 

Unfortunately. in the sununer. the: coincidtm peak. 

demand reduction of heat pwnp water heaters is 

negligible. Heat pump water heaters also 

demonstrated reliability problems when me study 

was performed to 1982 to 1984. If these problenu 

have been resolved. beat pump waters also offer 

significant po&ential for reducing electric utility 

winter peak. demand. 

ACKNO~DGEMENTS 

The sponsorship of the Florida Public Service 

Commission, the support of the Florida Solar Energy 

Center management, and lhe cooperation of Florida's 

elecDic utilities are grl1etully acknowledged. The 

FSEC project stall' - Charles Beach. Omar Hancock. 

Ross McCluney and Tom Tiedemann - &Iso deserve 

both credi' and thanics for their considerable worIc at 

the projecl The dedicated assistance of comultants 

Don PalZSCh and Timothy Stryker. as well as 

numerous FSEC graduate assiswus. is also 

acknowledged. Finally. the participating 

homeowners deserve special gratitude for their 

cooperation. Wi!bout their assistance. the project 

would not have been possible. 

REFERENCES 

ASHRAE. 1977. ANSJlASHRAE SIDNlDrd93-1977. 

"Methods of testing to detennine the thermal 

performance of solar collectors." American Society 

of Heating. Refrigera~g. and Air..cooditioning 

Engineers. Inc .• Atlanta. Georgia. 

ASHRAE. '980. ANSJlASHRAE SIDNlDrd 9OA1980. "Energy comervatioo in new building design. .. 

American Society of Heating, Refrigerating. and AirConditiooing Engineers. Inc .• Atlanta, Geagia ... 

Block. D. L. 1983. "Solar domestic hoc: water 

syslem fOUT-year performance results." 'prou~dings 

o/tht /983 Annual Muting. A~r;can Solar EMrgy 

Soci~ty. Vol. 6. pp. 235·240. Minneapolis. MN. 

Florida Governor's Energy Office. 1981. "Florida 

Energy Data: 1960-1981 ." Tallahassee. Aorida. 

.... """""" I~"'~ ~~o [;\,i - 930551 ·EG 

Florida Solar Energy Industries Assoc" Inc 

El(hibit_(WTG-l ) -, 

Page 12d 12 

FPC. 1974. FJorida Power Corporation. "Water 

Heater Test Data," Technical Information No. 37. 

St Petersburg. Florida. 

FPL. 1978. Florida Power and Light Company. 

"1978 Residential ElecDic Waler Heater Study." 

Miami. Florida. 

FPL. 1989. Florida Power and Light Company. 

"Petition to Determine Need fer Electrical Power 

Plant: 1993-1996." Miami. florida. 

Florida Public Service Commission. 1985. Research 

Depatanent. "Statistics of the florida Electric Utility 

Indusl/)' 1984," TaUahass ... Florid>-

Florida Public Service Commission. 1989. Research 

Department. "Statistics of the Florida Electric Utility 

Indusl/)' 1988," Tallahassee. Florid>-

Gladhart. P.M .. and Wiehl. 1.5. 1986. "Morul",e<! 

hot water use: A seasonal analysis. " Procudings -

)986 SlU11IMr Sludy on En~rgy Effici~ncy jn 

BUildings. American COWlcil for an Energy-Efficient 

Economy. pp. 1.90-1.103. 

Merrigan. T. 1983. "Residential conservation 

demmstration: Domestic hot water. Final repon." 

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

Canaveral. Flcrida. 

Merrigan, T .• and Wang. M. 1981. "BnJ meler 

dynamic "st. Final "pen." FSEC-CR-81-29(RD). 

Florida Solar Energy Center, Cape Canaveral, 

florida. 

McCluney. R. 1980. "Annual perfonnlDCe of 20 

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

4, Florida Solar Energy Cemer. Cape: Canaveral. 

Florida. 

Parker. D.S. 1989. "Hot Wa"r Study: PI1ase I 

Final report." FSEC.cR-295-89. Florida Solar 

Energy Center. Cape Canaveral. Florida. 

Periman. M .• and Mills. B. "Development of 

residential hOl waler use patterns." ASHRAE 

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

Georgia.