7-i

CHAPTER 7. ENERGY CONSUMPTI ON OF FURNACES AND BOILE RS TABLE OF CONTENTS 7.1 INTRODUCTION
................................................... 7-1 7.2 METHO D FO R NON -WEA THERIZED GA S FU

RNA CES
................... 7-1 7.3 VIRT UAL FURNACE MODE LS
....................................... 7-2 7.3.1 Ba sic Ac t ua l Fu r na ce Mo de ls

..................................... 7-3 7.3.2 In put C ap ac i

ty an d M ax i m um A i rf l ow .............................. 7-4 7.3.2.1 Non-w eath eri zed g as f urn ace s. ....................... 7-4 7.3.2.2 Other Product Cl ass es. .............................. 7-5 7.3.3 Bl ower Size

.................................................. 7-6 7.3.4 Moto r Size

................................................... 7-6 7.3.5 Supply

-Ai r Outlet Area

.......................................... 7-7 7.3.6 Power Consumpti on of Draf t Inducer

.............................. 7-11 7.3.7 Del ay

Tim es and Ign

itor Power

.................................. 7-11 7.4 ASS IGNIN G EXISTIN G EQUIP MENT TOSAM PLE HOUSES
.............. 7-11 7.4.1 Fu

rnac e I n pu t Ca pa ci ty
......................................... 7-11 7.4.2 A i rf l ow C ap ac i

ty
............................................. 7-13 7.4.3 Efficiency Char act er istics of E xisting E quip ment
..................... 7-13 7.4.4 Electri ci

ty Consum

ption of the Ex

is ting F urnace Bl ower ................ 7-14 7.5 CALC

ULATING FUR

NACE BLO WER ELECTRICITY CONSUMPTION
..... 7-14 7.5.1 System Curve s ............................................... 7-15 7.5.2 Furnace F an Curves ........................................... 7-16 7.5.3 Overal

l A ir-Movi ng Ef fi ci ency ................................... 7-17 7.5.4 Blow er -Mo t or Elec t ricit y Cons umpt ion

............................ 7-21 7.6 AN

NUA L HEA TING A ND CO OLIN G LO AD S IN SA MPL E HOUS ES
........ 7-21 7.6.1 An

nual House-Heating L oad

.................................... 7-21 7.6.2 An

nual House-Coo li

ng Load

.................................... 7-22 7.7 FURNA

CE ENERGY CONSUMPTION
................................. 7-23 7.7.1 Fuel

Consu m ption ............................................ 7-23 7.7.2 El ec tri ci

ty Con su m ption ........................................ 7-23 7.8 BOILER ENERGY CONSUMPTION
................................... 7-25 7.9 RESULTS
........................................................ 7-25 7.9.1 Non-Weatherized Gas Furnace Energy Use

......................... 7-25 7.9.2 Weatherized Gas Furnace Energy Use
........................ 7-28 7.9.3 Mobil

e Home Furnace Energy Use
................................ 7-30 7.9.4 Oil

Furnace En

ergy Us e ........................................ 7-32 7.9.5 Gas Boil

er Energy Use
........................................ 7-34 7.9.6 Hot -Water Oil Boil er Energy Use
................................. 7-367-ii LIST OF TABLES Tab l e 7.3.1 Ch ar ac t er ist ics o f Ba sic Fu r na ce Mo de ls

............................. 7-3 Tab l e 7.3.2 Vi

rtua l Model Fu rn ac es : C ap ac i

ty an d A i rf l ow ........................ 7-4 Tab l e 7.3.3 Rel evan

t Sizes of Virtual Models f or No n-Wea

therized a nd Weatheri zed Gas Furn

aces ....................................... 7-5 Tab l e 7.3.4 Rel evan

t Sizes of Virtual Models f or Mobile Home F

urnaces ............. 7-5 Tab l e 7.3.5 Rel evan

t Sizes of Virtual Models f or Oil -Fi red Furnaces

................. 7-5 Tab l e 7.3.6 A ss i gn

ed Bl owe r Si ze b y A i rf l ow C ap ac i

ty
........................... 7-6 Tab l e 7.3.7 A ss i gn

ed Mot or S i ze

b y A i rf l ow C ap ac i

ty
........................... 7-6 Tab l e 7.3.8 Supply

-Ai r Outlet Area (i

n Square Feet) f

or Virtual Non-Condensi

ng Ga s F ur na ce Mo de ls

........................................... 7-10 Tab l e 7.3.9 Supply

-Ai r Outlet Area (i

n Square Feet) f

or Virtual Conden

si ng Ga s F ur na ce Mo de ls

........................................... 7-10 Table 7.3.10 Val

ues f or Delay and Igni tion Ti me s .............................. 7-11 Tab l e 7.9.1 Non-Weatherized Gas Furnace Energy Use

......................... 7-26 Tab l e 7.9.2 Weatherized Gas Furnace Energy Use
............................. 7-28 Tab l e 7.9.3 Mobil

e Home Furnace Energy Use
................................ 7-30 Tab l e 7.9.4 Oil

Furnace Energy Use
........................................ 7-32 Tab l e 7.9.5 Hot -Water Gas Bo il er Energy Use
................................ 7-34 Tab l e 7.9.6 Oil

Boil er Energy Use
.......................................... 7-36

LIST OF FIGURES Figure 7.3.1 Nu

m b er of GA MA Li ste d Fur n ac e M ode l s b

y In pu t Ca pa ci ty
............. 7-3 Fi gure 7 .3.2 Supply

-Air Outlet Area for Non-Co ndensi ng Natural Gas Furnaces

........ 7-8 Fi gure 7 .3.3 Supply

-Ai r Outlet Area f

or Condensi

ng Natural Ga s Furna

ces ............ 7-9 Fi gure 7 .4.1 Pe rc en

t of Exi sti n g Fur n ac es b y In pu t Ca pa ci ty
...................... 7-12 Fi gure 7 .5.1 Samp le of S yste m Cur ves w ith a T ypical Fan Cu rve ................... 7-16 Fi gure 7 .5.2 Fan C

urves f or 800 cfm

Virtual Furnace Model

...................... 7-17 Fi gure 7 .5.3 Fan C

urves f or 1200 cfm

Virtual Furnace Model

..................... 7-17 Fi gure 7 .5.4 Fan C

urves f or 1600 cfm

Virtual Furnace Model

..................... 7-17 Fi gure 7 .5.5 Fan C

urves f or 2000 cfm

Virtual Furnace Model

..................... 7-17 Fi gure 7 .5.6 Overal

l A ir-Movi ng Ef fi ci ency of Exi stin

g Furnaces
................... 7-19 Fi gure 7 .5.7 Ov er all Air

- Mo ving E fficie nc y o f No n- Co nd en sing Vir t ua l Fu r na ce Mo de ls

. 7-20 Fi gure 7 .5.8 Ov er all Air

- Mo ving E fficie nc y o f Co nd en sing Vir t ua l Fu r na ce Mo de ls

..... 7-20 Fi gure 7 .9.1 Range of

An nual Gas Use, Non-We atherize d Gas Furn aces ............. 7-26 Fi gure 7 .9.2 Ran

ge of An nua l GasUsa ge b y Regi on, 90 p erce

nt A FUE, Non-Weatheri

zed Gas Furn

ace ................................... 7-277-iii

Fi gure 7 .9.3 Range of

Wi nter Electric ity

Use, Non-Weatheri

zed Gas Furn

aces ......... 7-27 Fi gure 7 .9.4 An

nual Gas Use, Weatheriz ed Gas Furn aces ......................... 7-29 Figure 7.9.5 Wi

nter Electr ici

ty Use, Weatherized Gas Furnaces

.................... 7-29 Figure 7.9.6 An

nual Gas Use, Mobi

le Home Furn

aces ........................... 7-30 Figure 7.9.7 Wi

nter Electric ity

Use, Mobile

Home Furn

aces ....................... 7-31 Figure 7.9.8 Range of

An nual Oil Use, Oi l F

urnaces ............................. 7-33 Figure 7.9.9 Range of

Wi nter Electric ity

Use, Oi l F

urnaces ....................... 7-33 Figure 7.9.10 Ran

ge of An nua l GasUse , Hot-Water Gas Boi l ers .................... 7-35 Fi gure 7 .9.11 R

an ge of Wi nter El ectrici ty U se, H ot-Water G as B oil ers ................ 7-35 Fi gure 7 .9.12 R

an ge of An nua l Oil Use , Hot-Water Oil

Boi l ers ...................... 7-37 Fi gure 7 .9.13 R

an ge of Wi nter El ectrici ty U se, H ot-Water O i l

Boi l ers ................ 7-377-1

CHAPTER 7. ENERGY CONSUMPTI ON OF FURNACES AND BOILE RS
7.1 INTRO DUCTI ON The f urnace an d boil er energy -eff ic ie ncy standards rul em

aki ng consi ders the chan

ge i n l ifecy cl e cost (LCC) due to in

creased en

ergy ef fi ci ency of househ

old he ating e quipm

ent. Energy consum ption i s the key

part o f the operatin

g-cost input of the LCC c al cul ation. The en ergy cons um pti on of a f urn ace or boil er i

nc l udes ei ther g as or oi

l and el ectrici ty. In man y cas es, a furna ce blo wer op er at es o ut side t he hea t ing sea so n when t he air ha ndler is in use fo r c oo ling purpo ses, so DOE in

cluded this consum

ption in i ts calculations. In t he eng ineering analysis, t he De par t ment c alculat ed e ner gy co nsumpt ion o f baseline m ode l -s i ze d f

urn ac esan d b oi l ers us i ng the DO E test proc ed

ure f or th es e ty

pe s of eq ui pm en t. F or the LCC Anal

ysi s, DOE est im

ated energy consumption of furnaces an d boilers in actual h

ouses. To re pre sent a ctu al hou se s w i

th f urn ac esan d b oi l ers i n th e U ni ted State s, D OE u se d a

set of hou se s f rom DO E' s En

erg y In f orm ati on A dm i ni stra ti on ( EIA )’ s R es i de nti al En erg y Con su m ption Surv ey of 1 997 (R

ECS97 ). 1 For

ea ch hou se , RE CS 97 r

ep orts s pa ce -h ea ti ng en erg y con su m ption and spa ce-c ooli ng e l ectrici

ty c onsu m pti on, wh i ch are b ase d on the ex

i sti ng h ouseh old equi pm en t. Th e D ep ar

tmen t’s meth od e sti mate d th e en ergy con su m pti on of al ter n ati v e ( more -e f

f i ci en t) eq ui pm en t, i f th ey were us ed

i n ea ch h ous e i n pl ac e of th e e x i sti n g e qui pm en t. The Dep ar t ment d evelo ped t he met hod of c alculat ion d esc ribed in this cha pt er for nonwea t her ized g as fur nace s, t he mos t co mmon amo ng t he six pr od uct classe s in the ru lemaking anal ysi s. The Depart men

t generalized the energy

consumption cal culation f or t hi s prod uct class to th e oth er f ur n ac e p rod uc t cl as se s. Fu el con su m pti on ca l cul ati on s f or b oi l er s a

re si m i l ar to thos e f or th e f urn ac e p roduct c l as se s. The

el ec tri ci ty cal cu l ati ons f or b oi l ers are si m pler th an f or furn aces, beca use boile rs do not pr ovide

thermal dis tributi on for space cooli

ng as f urnaces of

ten do. 7.2 METHOD FOR NO N-WEATHERIZED GAS FURNACES To begin the anal ys is , the Department devel oped representative conce ptual f urnace m odel s. These

“v i rtual” m odel s i nc orporated ty

pical f eature s of curre ntl y -m arkete d f urn ace s. The Departmen

t based the vi

rtual f urnaces on m

odels se le cted from di

rector ie s and product li terat ure. The vi

rtual m odels capture the range of actual f urnace si zes. The an

al ys is assi gned an ap prop ri atevi

rtua l f urn ac e to e ac h s am

ple h ous e a s a wa y of mode l i ng en erg y con su m ption of alternative f

urnace designs. Estim ating the ann ual energy consum ption of al

ternative f

urnaces i n each house requi

red DOE t o e st imate t he hea t ing and c oo ling load s o f each ho use . T hese load s re pr ese nt t he amo unt of he at ing and c oo ling req uire d t o k eep a ho use co mfort able du ring a n ent ire year . T he Departmen

t estim ated the heatin

g and cooli

ng l oads from the h

eatin g and cooli

ng en ergy consum ption and the

assum ed characteri stics of

the exi stin

g furn ace and ai r conditi oner in

eacha

Fu rnac es are cap abl e of pr ovid in g seve ra l l evels of ai rfl ow. For heating operation, a low level of airflow is us ed. If the fu rnace prov

ides airflo w f or anair conditio

ner during coo ling ope

ration, it is typical ly set to provide a hi gher level of airflow w

hen th e air conditioner is operating. 7-2 sam ple house. The Departmen

t assign ed the characteri stics of

the exi stin

g equi pme nt to each sample ho use , d epe nding o n t he size a nd climate zo ne o f each ho use and t he ag e o f the heat ing eq ui pm en t. Th e e sti mati on of h ea ti n g l oad s a l so r eq ui re d c al cul ati on of th e e l ectri

ci ty co nsumpt ion o f the furna ce blo wer , since heat fro m the fu rna ce blo wer co nt ribut es t o he at ing t he hous e. To co mpl

ete the anal

ys is , the Department cal

cul ated how much

energy would be required by fu r na ce s w it h va r io us de sig n o pt io ns t o mee t t he sa me h ea t ing an d c o o ling lo ad o f ea ch sa mple house. 7.3 VIRTUAL FURNACE MOD ELS To co nduc t t he ana lysi s, t he De par t ment d evelo ped co ncep t ual fur nace mod els. T he De pa r t men t int en de d t he se ge ne r ic fu r na ce mo de ls t o r ep r es en t t ypic al fu r na ce s w it h ba sic feat ur es, but not t o d esc ribe sp ecific, e xisting fu rna ces . T he De par t ment d er ived t he char act er istics of t he virt ual fur nace mod els fro m existing “ba sic” fur nace mod els, a fte r e xamining directories a

nd product li

terat ure of existin

g furn aces. See Appen

dix 7.1, Reduced Set o f F

urnace Models, Database for more det ail s. As a st ar t ing po int fo r c hoo sing value s o f input cap acit y for t he virt ual fur nace mod els, t he Departmen

t looked at t he n

umb er of m

odels l is ted by in put capacity

in the Gas Appl

ia nce Manuf acturers Associ ation (GAM A) Di rector y of April 2002 2 (se e Figu re 7. 3. 1) . T he De pa rtm en t se l ec ted mode l s th

at w ere non -we atheri ze d ga s f urn ac es , th at w ere

not d es i gned f or mobile ho mes, a nd t hat wer e no t disco nt inued. Using t hese select ion cr iter ia, D OE re duc ed t he 36,032 gas furn

ace m odels i n the GA MA Di rector y to 15,881 model s. For vi rtual f urnaces, DOE select ed t welve inpu t cap acit ies t hat wer e t he mos t co mmon and t hat spa nned t he r ange on t he mark et . T he De par t ment mad e t hese select ions ba sed on t he as sumpt ion t hat t he sizes t hat have the m ost model s are

the m ost popular. The Departmen

t defi ned ai rfl ow capacity

as the nom

in al ma xi mum ai rfl ow at 0. 5 in

ches wa t er ga ug e ( in. w. g. ) ex t er na l st at ic p r es su r e, as list ed in t he pr o du ct lit er at ur e fo rea ch mo de l. a Ma nuf ac ture rs us ua l l y cod e th i s a i rf l ow c ap ac i

ty i n th e m ode l nu m be r (s eeA ppe nd i x 7 .2 on Decodin g of Man ufacturer Model N

umb ers, for more detail

s.) Most o f the f

urnaces f it i nto four ai rf l ow capa ci ty s i zes : 800 c

ubi c f eet per m i nute (cf m ), 1200cf m , 1600 c f

m , and 2000

cf m . These ai rfl ow capaciti es correspond to nomi nal ai r-conditi oner sizes of two to ns, three tons, four to ns, an d fi ve tons, respectiv

el y. The Departmen

t used the sam

e set of ai rfl ow and capaci

ty si zes for bot h non-condensi

ng and condensi

ng furnaces.7-3 Figure 7.3.1 Number

of GAMA Li sted Fur

nace Model

s by Input Capacity 7.3.1 Ba sic A ctu al Furn ace M ode ls The Departmen

t selected actual

furn ace m odels that represent the f

undam ental char act er istics of no n-c ond ensing a nd co ndens ing furna ces wit h no s pec ial featu re s. T he Depart men

t used t he characteristics l isted in Table 7.3.1 to select basi c furnace m

odels. These characteri stics a

re the most comm

on am ong model s on the m

arket (see Appendi

x 7.1, Reduced Set o f F urnace Model s Database). The Depa rtment sel ected several

dozen furn

ace m odels that have these f

eatures. It looked in

detail at these basi

c m odels to determi

ne speci fi c characteri stics to use f or creati ng v i rtual f urn ace s. Tabl e 7.3.1 Cha racte risti cs of B asic Furna ce M ode ls Non-Condensing Gas Furnace Condensing Gas Furnace si ngle stage burner si ngle stage 80% AFUE 90-92% AFUE pe rm an en t sp l i t ca pa ci tor (PS C) bl owe r m

otor PSC bl owe r m otor forward-curved i

mpe ll er blades forward-curved i mpe ll er blades up- f l ow or h ori zon tal ai r-f l ow dow

n- f l ow, u p-f l ow, or hor izon tal ai r-f l ow7-4

The basic fur nace mod els ar e liste d by bra nd and ser ies in Appe ndix 7. 3A, which co nt ains ba sic non-con

den si ng m odel data, an d A ppen di x 7.3 B, b asi

c non-con den si ng m odel data. 7.3.2 Input Capacity and Maximum Airfl ow 7.3.2.1 Non-w eathe ri

ze d gasfur

nace s. Fo r virt ual fur nace mod els, D OE select ed 2 5 co mbinatio ns (“bins” ) o f input cap acit y and ma xi mum ai rfl ow. The marked cel

ls in Table 7.3.2 refl ect the in put capacity

and n omi nal ma xi mum ai rfl ow for the vi

rtual f urnace m odels. The s el ection ref

le cts the most comm

on in put and n omi nal ma xi mum ai rfl ow capaciti es of m

odels i n the GA MA Di rector y A pril 2002, 3 in pr od uct liter at ur e, and list ed o n furna ce manu fact ur er web s ites . Mo st basic mo dels o n t he mar ke t fit int o t he 25 bins o f inp ut ca pa cit y and air flo w c ap ac it y. S o me mo de ls d o no t ex ac t ly match the b i ns , but th ei

r va l uesare c l ose en

ough th at DOE i nc l uded them i n one of the 2 5 bi ns . For exa m pl e, 40 kBTU/h

and 4 5 kBTU/h

model s are grouped

together in

to a sin gl e 45 kBTU/

h bi n. M ost bi

ns ha ve at l eas t two actual

model s. Tabl e 7.3.2 Virtual Model F urnaces: Capacity and Airf low Inp ut Cap acit y (kBT U/h)MaximumAirflow(at0.5"StaticPressure) 45 50 60 70 75 80 90 100 115 120 125 140 80 0 c fm (2 t ons) x x x 12 00 cfm (3 t ons) x x x x x x x x 16 00 cfm (4 t ons) x x x x x x x x 20 00 cfm (5 t ons) x x x x x x
The Departmen

t created o ne v

irtual model to represent all the m

odels as si gned to each bin. The Dep ar t ment u sed spe cificatio ns fro m the a ct ual mod els in each bin t o d et er mine the speci fi cations f or t he correspondi

ng vi rtual m odel. These s

peci fi cations i ncl ude bl ower size, mot or size, sup ply-air o ut let a re a, po wer co nsumpt ion o f the dr aft induce r a nd t he ignit er , a nd several del ay tim es. The speci

fi cations are des crib ed i

n the sections bel

ow.7-5

7.3.2.2 Other Product Classes . Be ca us e o f t he limit ed nu mbe ro f siz es av aila ble fo rmo bile h o me g as fur na ce s a nd o ilf i re d f ur n ac es , D OEse l ec ted

a s ub se t of th e 2 5 i n pu t an d ai rf l ow c ap ac i

ty com b i n ati on s to r ep r es en t ea ch pr o du ct cla ss . I n it s a na lysis o f we at he r ize d g as fur na ce s, DO E us ed t he sa me vir t ua l mo de ls a s it us ed in t he an alys is o f no n- we at he r ize d g as fur na ce s. Fo rmo bile h o me furnaces and oil-f

ired f urnaces, t he Department used a subset o f the 25 vi rtu al f urnace models, be caus e the

market i n those produ

ct class es is l

i m i ted to a sm

al l er n um ber of s izes

of f urn ace s. Tables 7.3.3-7.3.5 li st the relev ant si zes f or non-weatherized an

d weatherized gas, m

obil e hom e, and oil -fi red furnaces. Tabl e 7.3.3 Relevant Sizes of Virtual

Models for

Non-Weatherized and Weather ized Gas Furnaces Input Capac ity (kBtu/h)
Max. Air flow (tons) 45 50 60 70 75 80 90 100 115 120 125 140

2 X X X 3 X X X X X X X X 4 X X X X X X X X 5 X X X X X X
Tabl e 7.3.4 Relevant Sizes of Virtual

Models for

Mobile Home Furnaces Input C apaci

ty (k Btu/h))
Max. Air flow (tons) 60 70 75 80 90 100 115 120 125 140

2 X X X 3 X X X 4 X X X 5 X X X
Tabl e 7.3.5 Relevant Sizes of Virtual

Models for

Oil-Fire d Furnaces Input Capac ity (kBtu/h) Max. Air flow (tons) 45 50 60 70 75 80 90 100 115 120 125 140

2 3 X X X 4 X X 5 X X X7-6

7.3.3 Blo wer S ize The Departmen

t selected a b lower si

ze (li sted as nom

in al dia me ter in i nch es by nomi nal widt h in inches) fo r e ach virt ual fur nace mod el (T able 7. 3. 6) . T he blow er size is t ypical for t he basi c furn ace m odels i n each bi n. Blower size i

ncreases with a irf low capaci

ty, but not with i

nput cap acit y. The Dep ar t ment u sed fou r blo wer sizes— t he sa me one s for co ndens ing and no ncondensi ng vi rtual f urnace m odels. For the bl

ower sizes

of bas ic furn ace m odels, see Appendi x 7.3, Det ermi

nation of Basic Model Furnaces. Tabl e 7.3.6 Ass igned

Blow er Siz e by Air flow Capacity Airflow Cap acit y (cfm) Blower Size (inches) 2- t o n mo de ls ( 80 0 c fm) 9 X 8 3- t o n mo de ls ( 12 00 cfm) 10 X 8 4- t o n mo de ls ( 16 00 cfm) 10 X 10 5- t o n mo de ls ( 20 00 cfm) 11 X 10 7.3.4 Mo to r Si ze The moto rs for t he basi

c furnace m

odels are six-po le perm

anent spli t capacito r (PS C) i n du cti on motors . Th

e m otors i n th e b as i c f

ur n ac es com e w i th th re e to f i v e ta psth at a reus ed to set t he mot or spe ed. The Dep ar t ment a ssu med t hat , a t high spe ed, t he mot or s o per at e wit h a spe ed of 1075 r ev olu tion s per m

i nute (rpm ) to provide th e nomi

na l max i m um ai rf l ow at 0.5 in .w.g. Th e D ep ar

tmen t as si gn ed motor s ize

to v i rtu al f ur n ac e m ode l s, as sh own i n Ta b l e 7 .3. 7, t o re flect t ypical-size mot or s o f the basic fur nace mod els. M ot or sizes a re t he sa me for nonco ndens ing and c ond ensing fur nace s. T he larg er t he no minal m aximum airflow, t he larg er t he mo t o rsiz e. Fo rt he blo we rmo t o rsiz e a nd nu mbe ro f t ap s o n ba sic mo de l fur na ce s, se e A pp en dix 7.3 , Determ

i na ti on of Ba si c M ode l Fu rn ac es , wh

i ch l i sts the bl owe r-m otor si ze s a nd nu m be r of blower mot or t aps of basic furnace m odels. Tabl e 7.3.7 Ass igned

Motor Siz e by Air flow Capacity Airflow Cap acit y (cfm) Mot or Size (H P) 2- t o n mo de ls ( 80 0 c fm) 1/5 3- t o n mo de ls ( 12 00 cfm) 1/3 4- t o n mo de ls ( 16 00 cfm) 1/2 5- t o n mo de ls ( 20 00 cfm) 3/47-7

7.3.5 Supply-Air Outlet Ar ea T he su pp ly- air o ut let ar ea is t he o pe nin g f r o m t he fu r na ce t o t he su pp ly d uc t
. T he su pp lyai r outle t area f or bas i c f urn ace model s i ncreas es wi

th ai rf l ow capa ci ty a nd i npu t capac i ty. To cap t ur e t his tr end, DOE co nst ru ct ed a linear fit o f the sup ply-air o ut let a re a t o inp ut cap acit y and ai rf l ow c ap ac i

ty f or con de ns i ng an d n on- con de ns i ng f urn ac es(s eeA

ppe nd i x 7 .3, D ete rm

i na ti on of Ba sic Mo del Fu rna ces , fo r su pply-a ir o ut let a re as o f basic fur nace mod els). The Dep ar t ment use d t he fo llowing eq uat ions t o d et er mine the s upp ly-air o ut let a re a o f the non- co ndens ing and condensin g vi rtu al m odel furnace m

odels:

where: S = su

ppl y -ai r outle t area (s q. f

t.),; Q = no minal m

aximum airflow ( cfm) at 0. 5 in.w .g . st at ic pr essu re ,; a nd Qin = i

npu t capac i ty (k Btu/h ). Figures 7.3.2 and 7.3.3 show the data points f or supply -air outlet area f

or basi c furn

ace models an

d the li near plan e fi t used t o fit these points.7-8

Figu re 7.3.2 Supply-A ir Outlet Area for Non-Conden sing Natu ral Gas Furnaces7-9

Figu re 7.3.3 Supply-Air Outlet Ar ea for C ondensing Natural Gas F urnaces7-10

Ta bles 7. 3. 8 and 7. 3. 9 sho w t he value s DO E u sed for sup ply-air o ut let a re as fo r no ncondensin g and condensin

g vi rtu al gas f urnaces. The sup ply-air o ut let a re a is larg er for co ndens ing mod els. T he larg er op ening com pensates f or the i ncreas ed pre ssu

re drop du

e to the s econ

dary , conden si ng h eat ex ch anger. This lar ger sup ply-air o ut let a re a r edu ces t he pr essu re dr op acr os s t he fur nace , so t hat t he pr es su r e r ise fo rco nd en sing fur na ce s is t he sa me a s no n- co nd en sing mo de l fur na ce s a t t he sa me ai rfl ow. Tabl e 7.3.8 Supply-Air Outlet Ar ea (in Square Feet) for Virtual Non-Condensing Gas Furna ce M ode ls Input Capa city (kBT U/h) 45 50 60 70 75 80 90 100 115 120 125 140MaximumAirflow(at0.5"StaticPressure)800cfm(2tons) 1.58 1.62 1.711200cfm(3tons) 1.78 1.82 1.91 2.00 2.04 2.08 2.17 2.261600cfm(4tons) 2.20 2.24 2.29 2.37 2.46 2.59 2.63 2.682000cfm(5tons) 2.57 2.66 2.79 2.83 2.88 3.01
Tabl e 7.3.9 Supply-Air Outlet Ar ea (in Square Feet) for Virtual Condensing Gas Furna ce M ode ls Input Capa city (kBT U/h) 45 50 60 70 75 80 90 100 115 120 125 140MaximumAirflow(at0.5"StaticPressure)800cfm(2tons) 1.72 1.76 1.831200cfm(3tons) 1.94 1.98 2.05 2.13 2.16 2.20 2.27 2.351600cfm(4tons) 2.35 2.39 2.42 2.50 2.57 2.68 2.72 2.752000cfm(5tons) 2.06 2.79 2.90 2.94 2.97 3.087-11

7.3.6 Power C onsumption of Draf t Inducer A c o mmo n va lue fo rt he po we rco nsu mpt io n o f t he dr aft ind uc er , PE , fo rba sic non-condens in

g model furn aces i s 75 watts, and the average val ue i s about 75 W, so DOE sel ected 75 W f

or all the non-conden si

ng m odels. The De

partment f

ound no correlation b etween t he PE and inpu t cap acit y or bet wee n PE and a irflow c apa city. Fo r c ond ensing fur nace s, t he De pa r t men t us ed a P E o f 90 W, wh ich clo se ly mat ch es t he mea n fo rt ha t gr o up . Se e A pp en dix 7. 3, De t er minat io n o f Ba sic Mo de l Fu r na ce s, fo rt he po we rco nsu mpt io n o f t he dr aft ind uc er in the basic m

odels. 7.3.7 Delay Tim es and Ignitor Powe r Pre-pu rge an d post-pur

ge ti mes a re the l en gths of ti me the draf t in duce r operates be f ore and af ter a fi rin g cy cl e. On-del ay

is the am ount o f ti me the bl ower waits to begin

operating af

ter the b urn er starts

f i ri ng. O f f -del ay i s the tim e the bl ower ke epsoperati

ng a f ter the b urn er turn s of

f

. Ign i tion tim e i s the l ength of tim e the hot surf ace i gni tor is on b ef ore gas i s se nt to the b

urn er. Pre-purge, po st-purge, o n-delay , and off -delay tim es are not related to airfl

ow or in put cap acit y. The Dep ar t ment s elect ed c ommo n values for t he de lay and ignitio n t imes of co ndens ing and n on-condensi

ng vi rtual f urnace m odels (Tabl

e 7.3.10). For these data on basi c furn ace models, see A

ppendix 7.3, D eterminati on of Basic Model F urnaces. Table 7.3.10 Values f

or Del ay and Ignition Times Pre-P urge Post-Purge On-Delay Off-Delay Ignition 15 seconds 5 seconds 30 seconds 120 seconds 37 seconds

7.4 ASSIGNING EXISTING EQUIPMENT TO SAM PLE HOUSES To estima te the heatin

g and cooli

ng l oad of each sa

mpl e house, DOE assi

gned the i nput ca pa cit y, a irflo w c ap ac it y, a nnu al fu el u t iliza t io n e fficie nc y (A FU E ) , an d fo rt he air co nd it io ne r( if t he ho use has o ne) , t he se aso nal ener gy-e ficiency rat io ( SE ER ). As pa rt of t he hea t ing- a nd coolin g-load cal cul ations, DOE esti

ma ted the electri ci

ty consum

ption and e ff

ic ie ncy of the f urnace b l owe r m otor. Th e D ep ar

tmen t us ed th e i n pu t ca pa ci ty an d n om i n al max i m um ai rf l ow c ap ac i

ty assigne d t o t he exist ing furna ce t o c hoo se t he virt ual fur nace mod el for t he ho use , fo r u se in t he rest o f the LCC anal

ysi s. 7.4.1 Fur

nace Input C apaci

ty Th e D ep artm

en t as si gned an i np ut c ap ac i ty f or th e e xi sti ng f urn ac e of ea ch hou se ba se d on an al gorithm that cor relates i

nput capaci

ty wi th the house si

ze, the ye ar the furn

ace was i nstalle d, and t he dist ribut ion o f input cap acit y of new fu rna ces so ld t he year t he fur nace was insta lled. T he foll owing steps describe the assi gnm ent pro cess.7-12

Figu re 7.4.1 Per

cent o f Ex

istin g Fur

nace s by I nput Capacity (1) Th e D ep ar

tmen t ra n ke d al l th e R EC S9 7 h ous es i n as cen di n g order by

si ze (s qu ar e f oot) and c alculat ed t he pe rc ent ile rank of e ach ho use using t he st at istica l weight of e ach o f the sampl e recor ds. (2) The Departmen

t construct ed percenti le

table s by in put capacity

of f urnaces s old each

ye ar f or 1997 a nd pri or y ears , ba sed

on the histori cal sh i pm en t in f orma tion f or each year. 4 (3) Afte r se lect ing a ho use fro m the R EC S9 7 da t abas e du ring e ach M ont e Ca rlo iter at ion, DOE noted t he si

ze of the sel

ected house and determ

in ed the percentile

rank f rom Step 1. (4) T o av o id

a o ne - t o - o ne de t er minis t ic r ela t io n be t we en t he ho us e s ize an d i np ut ca pa cit y, DOE added a random

term to t he percen

tile i dentif ie d in Step 3 so t hat the correlation wa s not perf ect. The Dep artm

en t used a norm al di stri buti on to ch arac terize th e ran dom term
. Th e r an dom ter m h as a m ea n of zero a n d a sta n da rd de v i ati on of 8 p ercen t. (5) Usi

ng the percen

tile from Step 4, DOE looked up t he i nput capaci

ty f rom the i nput capa ci ty p erce nti l e tab l e i n Step 2 f or the ag e of

the e qui pm en t. (6) Figur e 7. 4. 1 sho ws t he pe rc ent of e xisting fu rna ces by input cap acit y assigned t o t he sampl e houses.

7.4.2 Airflow Capacity Th e D ep artm

en t cl as si f i ed f urn ac esby nom i na l max i m um ai rf l ow i n c f m at 0 .5 i n. w.g . of ex tern al sta ti c p res su re. Th e D ep artm

en t as si gned the ai rf l ow c ap ac i

ty of ex i sti ng f urn ac esf or houses that had ai

r conditi oners i

n a si mi la r man ner that it assi

gned f urnace i nput capaci

ty. Larger air co nd it io ne r s g o t o lar ge rho us es , ac co r din g t o t he dis t r ibu t io n o f siz es o f air co nd it io ne r s s o ld7-13

the year the ai

r conditi oner was i

nstalle d in that house. The Department used the ai r conditi oner nomi nal si ze of two, t hree, f

our, o r fi ve tons to set t he ai

rfl ow capacity

with a ratio of 400 cf

m pe r to n of cooli

ng. The steps were: (1) Base d o n t he hist or ical shipment informat ion o f resid ent ial cent ra l air co ndit ioner s by ca pa cit y, D OE co nst ruc t ed t he air flo w c ap ac it y pe r ce nt iles t ab les fo rair co nd it io ne r s s o ld i n 19 97 an d pri or y ears . The

Depa rtme nt restricted the

ai rf l ow si zes to two, t hre e, f

our, o rfive t o ns— t he eq uiv ale nt o f 80 0, 12 00 , 16 00 , o r20 00 cfm a t 0. 5 in

. w. g. st at ic pres sure . The

va ri ati on of the d i stri buti on of the f our ai rf l ow si zes over th e y ears i s sm al l

. Mo st o f t he an nu al s ale s o f r es ide nt ial c en t r al a ir c o nd it io ne r s fr o m 19 76 t o 19 94 ar e in these airfl ow sizes. (2) Since t her e ar e no available shipment dat a o n t he airflo w ca pac ity o f furnac es, t he De pa r t men t us ed t he air flo w c ap ac it y o f r es id en t ial c en t r al a irco nd it io ne r s a s a pr o xy. Using t he ad

just ed p er cent ile of ho use size fro m St ep ( 4) in the I nput Cap acit y sect ion, DOE det er mined t he airflo w ca pac ity by loo king u p t he pe rc ent ile in the co rr esp ond ing dist ribut ion o f nominal air co ndit ioner size fo r t he ag e o f the co oling eq uipment . T he Departmen

t selected a v

irtual model with the i

dentif ie d ai rfl ow capacity . If no vi

rtual mod el with t he ident ifi

ed a irflow c apa city wa s ava ilable, t he De par t ment s elect ed t he vi rtual m odel wi th the sam

e i nput capaci

ty an d the cl osest airf

low capaci

ty as a s ubsti tut e. (3) I f t he RE CS r ec o r d in dic at ed t ha t t he ho us e d id n o t ha ve an air co nd it io ne r , DO E st ill used the procedure from s tep (2) t o determin

e the ai rfl ow capacity . In this

case, DOE us ed th e a ge of th e h ous e ( or 3 0 y

ea rs i f th e h ous e w as ol der than

30 yea rs ) a s a su b sti tute f or the ag e of

the c ooli ng e qui pm en t. 7.4.3 Eff

iciency C harac

teris tics of

Existing Equipm ent GAMA shipment s da t a indicat e t hat hou ses in co lder re gio ns re ceive mo re -e ffi cient furnaces. 4 Theref

ore, DOE co rrelated the AF UE of existin

g furn aces wi th the heati

ng degree da ys ( HD D) t o ba se 65 °F a ss o cia t ed wit h e ac h sa mple ho us e. T he fo llo win g s t ep s d es cr ibe t his pro cess: (1) The Dep ar t ment s or t ed t he RE CS ho use s in asce nding o rd er of H DDs , a nd ca lculat ed t he percentil e rank of ea

ch h ouse by HDD usi ng the statistical

wei ght of each

sam ple house. (2) Based on the h

is to rical furn ace shi pme nt in form ation sorted by

AFUE, DOE constructed percentile tables by

AFUE shi

pmen ts o f f urnaces for 1997 and prior years. (3) Afte r D OE select ed a hou se fro m the R EC S d at abas e du ring e ach M ont e Ca rlo iter at ion, i t note d the H DD of

the se l ec ted hou se . The D ep artm

en t l ooke d up

the pe rce nti l e ra nk of that house f

rom th e HDD perce nti l e tab l e dev

eloped i n Step (1). (4) The Departmen

t added a random un

certainty term to t he HDD percen

tile found i

n Step (3) to account for vari abi

li ty wi thin the sam ple . The Departmen

t used a normal dist ribut ion t o c har act er ize t he unc er t ainty t er m. The dist ribut ion o f values o f the un certa i n ty ter m h as a m ea n of zero a n d a sta n da rd de v i ati on of 8 p ercen t.b A v

ery sma ll s hare o f ex is ting

furna ces use b elt-dr ive blow ers with sh aded-pole motors. T hat arr angem ent was less ef fi ci ent than direct-drive

n PSC moto

rs, but the airf

low from the se o ld mode l furnaces was less , so e

lectric ity consum ption was not si gni fican tly reduced when t hi s techn ology became obsolete. 5 7-14 (5) Using t he ad

just ed H DD p er cent ile from St ep ( 4) , D OE det er mined t he AFUE by loo king it u p fro m the AF UE per cent ile table fr om S t ep ( 2) co rr esp ond ing t o t he ag e o f the exi stin g equi pme nt in the house. Hou se s wi

th cen tra l ai r c on di ti on er s u se

th e c i rc ul ati n g- ai r b l owe r i n th e f ur n ac e to ci rculate the condi

tioned ai r durin g the cooli

ng seas on. If a house h

ad an ai r conditi oner, DOE assigne d it a SE ER level. U nlike AFUE , S EE R wa s no t co rr elat ed w ith any o t her hou sing fact or s. T he De par t ment c ons t ru ct ed S EE R dist ribut ions fo r a ll y ear s fro m histo rical shipment da t a; it r an do mly se lec t ed a S E E R fr o m t he dis t r ibu t io n fo rt he yea ro f t he ag e o f eq uip men t in eac h h ouse. 7.4.4 Electr

icity Consumption of the Existing Fur nace Blower All fu r na ce s ma nu fac t ur ed sinc e a bo ut 19 80 us e fo r wa r d- cu r ve d imp elle r s d r ive n d ire ct ly by a P SC mo t o r . T hu s, mo st ex ist ing fur na ce s ha ve a b lo we ran d b lo we rmo t o rsimila rt o t ho se in the virtual f

urnace models. b The re for e, in assigning t he elec t ricit y cons umpt ion o f the exist ing furn ace bl ower for each house, DOE assum ed that the electri ci

ty use of the exi stin

g furn ace was equi va l en t to t he electrici ty u se of the v i rtual f urn ace model des cri be d i n s ection 7.2. The Depart men

t calculated electrici

ty use by the existi ng furnace f

rom the fan curves, overall eff ic ie ncy , airpower, and tim

e del ay s of the v

irtual furn ace m odel of the s am

e i nput capa ci ty a nd a i rf l ow capa ci ty.
7.5 CALCUL

ATING FURNA CE BLOWE R ELE CTRIC ITY CO NSUMPTI ON The elect ricit y cons umpt ion ( and o ver all effi ciency) o f a blow er mot or dep ends on t he spe ed at wh

i ch the m otor operates, the

ex terna l stati c pres sure

di f f eren ce acrossthe b l ower, and the ai rfl ow thro ugh the b lower. To calcul ate bl ower-moto r electrici ty consum

ption, DOE det er mined t he o per at ing co ndit ions ( t he pr essu re and a irflow) at which a p ar t icular furna ce in a par t icular hou se w ill

op er at e. The se o per at ing co ndit ions c an be g ra phically displayed as t he inter sec t ion o f a syst em cur ve o f the duc t s in the hou se ( which plo t s t he st at ic pr essu re acr os s t he su pp l y an d r etu rn ai r d uc ts a s a f un cti on of ai rf l ow) wi th th e f an cu rv e of th e f ur n ac e (wh i ch pl ots the static pressure across the f urnace as a

fun ction of ai rfl ow). T he i

ntersection of the se two curves is the static pressure an d the ai rfl ow at which

the furn ace will operate in that house. Fur nace fan cur ves, re po rt ed a s t ables o f sta t ic pr essu re rise ve rsu s airflo w t hro ugh t he furna ce, ar e ava ilable from manufac t ur er s in the pr od uct liter at ur e fo r e ach fur nace . O ne o f the7-15

manufact ur er s also sup plies blow er -mo t or input po wer as a funct ion o f airflow t hro ugh t he f urn ace . Ai r po wer is cal

culated from the air speed throug h the furnace and the pressure rise across t he fur nace . T he o ver all air-mo ving efficiency is air po wer divided by t he elec t ric p ow er t o t he bl ower moto r. Al l the e le ctric power of the bl ower moto r eventual

ly is converted to heat t hat contributes to meeti

ng the b uil din g heati ng l oad. 7.5.1 System Curves T he sys t em c ur ve o f t he air

- dis t r ibu t io n sys t em is a g r ap hic al r ep r es en t at io n o f t he st at ic pr essu re dr op gene ra t ed a cr os s t he su pply and r et ur n duc t s in a ho use for different airflow s. T he ai rf l ow a nd pre ss ure dropat w

hi ch the f urn ac e w i l l ope rate ca n b e d ete rm

i ne d by the i nte rs ec ti on of the sy stem curv e of the h ouse a nd th e f an curv e of the f urn ace ci rcul ati ng a i r bl ower. 4 The Departmen

t modele d system curves as quadrati c curves, wh ic h i s standard i

n he ating, ventil ation, and air conditioni

ng (HVAC) design an

d fan sel ection handbooks. 6 The

curv es a re base d o n Ber nou lli ’s eq uat ions fo r fluid flow and a re expr esse d as t he fo llowing eq uat ion:

where: P = stati

c pres sure (i n.w .g.),; " = a constant coeff ic ie nt, and Q = ai

rf l ow (cf m ). The Depa rtme nt se l ected th

e coef f i ci en t in the sy stem

curv e equ ati on f or each hous e. It randoml y s am ple d a coeff

ic ie nt from one of f our distrib

utions, depen

din g on the nomi

nal ma xi mum ai rfl ow of the vi

rtual m odel f urnace sel ected for that house. The Department desi gned eac h dist ribut ion so t hat 10 p er cent of sa mples wo uld have st at ic pr essu re s belo w 0. 5 in.w .g ., and 1 percent of the sam

ple s would h

ave static pres sures greater than 1 i n.w.g at the nomi

nal max im um ai rflow. This i

s in li ne wi th several f

iel d studies. 7 To ke ep the

sy stem cu rv esf rom clumping at t he higher pr essu re s, t he De par t ment u sed a log -no rmal dist ribut ion o f values o f the coeff ic ie nt. See Fi gure 7.5.1 for an exam ple of a pl ot of sy stem curves i

ntersectin g a furn ace f an curve.
7.5.2 Furnace F an Curves De pe nd ing o n t he r es ist an ce ( mea su r ed as st at ic p r es su r e) o f t he su pp ly and r et ur n a ir du ct s, a fu r na ce will mo ve mo r e o rles s a ir. Whe n t he se pr es su r e v alu es ar e p lo t t ed gr ap hic ally agai ns t ai rf l ow, they are re f erred to as f an curv es.7-16

The Dep ar t ment a ssigned t hre e fan cu rve s t o e ach virt ual fur nace mod el: o ne fo r c oo ling operation, one for heatin

g, and a thi

rd for the low-f

ire h eatin g operation of m

odulatin g design option s. In

cool i ng ope rati on, the

f an curv e pas ses through the n omi na l max i m um ai rf l ow at 0.5 in.w. g. ext er nal st at ic pr essu re . D ur ing no rmal heat ing o per at ion, airflow is 80 p er cent of t he nominal maximum airflow at 0. 5 in.w .g . e xt er nal st at ic pr essu re . T he airflo w fo r lo w- fire hea t ing operation at 0.5 in.w.g. static pressure i s 2/3 of the n omi nal ma xi mum ai rfl ow at t he sam

e external static pressure.

Figu re 7.5.1 Sample of Sys tem Curves with a Typical Fan Curve T he De pa r t men t de ve lo pe d fa n c ur ve s fo rt he vir t ua l fur na ce mo de ls a s d et aile d in Appen dix 7.4, Furnace Fan

Curves. Fi

gures 7.5.2–7.5.5 show t he f an curve s f

or t hat vi rtual furn ace m odels. From

the le ft, the li

ne cl osest t o vertical

axi s shows a f

an curve for that vi

rtual furn ace m odel operating i

n l ow-fi re mode, the m

iddl e l in e i s f or t he v irtual furn ace m odel operating i

n he ating m

ode, and the li

ne f urthest to the righ

t, which passes through 0.5 i

n. w.g. st at ic p r es su r e a t t he no minal ma ximu m o f air flo w, is t he fan cu r ve fo rt he vir t ua l fur na ce mo de ls operating i

n cooli ng m ode.7-17

Figu re 7.5.2 Fan Cu rves for 800 cfm Virtual F urnace Model Figu re 7.5.3 Fan Cu rves for 1200 c fm Virtual F urnace Model

Figu re 7.5.5 Fan Cu rves for 2000 c fm Virtual F urnace Model Figu re 7.5.4 Fan Cu rves for 1600 c fm Virtual F urnace Model

7.5.3 Overal

l Air -Moving Efficiency The ove ra ll air-moving e ffi ciency is t he air p ow er divided by t he elec t ric p ow er use d by the b l ower m

otor. Air po wer (a ir ho rse po wer , o r AH P) , t he po wer add ed t o t he air be cau se o f its mo t ion and pressure increase as i

t is forced thro ugh the furnace, is cal culated as: 8

where:c The

v el oc ity pre ss ure is the inc rea se in pr es su re c aus ed b y the mo tio n o f air. 7-18 = ai r power (w atts), = ai rf l ow (cf m ),

= a conversion f

acto r to express air horsepower in watt s,
= a c o nve r sio n fa ct o rt o ex pr es s t he ve lo cit y pr es su r e o f st an da r d a ir i n w .g., c = ext er nal st at ic pr essu re (in.w .g .) , a nd = cross-sectional

ai rfl ow area defi

ned as the s

upply -air outlet area (sq.f t.). In addi tion to airf

low at a range of e

xternal static pressures, one m

anuf acturer repo rts fan mot or elect ricit y cons umpt ion. 9, 10, 11, 12, 13, 14 Thi s al lowed DOE to calcul

ate the overall

eff ic ie ncy f rom d ata i n that man

uf acturers’ product l

i terature.

where:

= o ve r all a irmo vin g e ffic ien cy, = fan mot or elect ricit y cons umpt ion ( W), and = ai r power (W

). The Departmen

t calcul ated air power and overal l e ff ic ie ncy for each poi

nt in the fan op er at ing t ables fo r e ach o f the mod els. T o g ener alize t his relat ion o f ove ra ll air-moving ef f i ci en cy to ai rf l ow, th e D ep artm

en t transf orm ed ai rf l owsto pe rce

nta ge s of ai rf l ow a t f ree f l ow for all the fu rna ces . T he De par t ment d id t his calcu latio n sep ar at ely for c ond ensing a nd no ncondensi ng f urnaces. The trans form

ation of ai rfl ow to fracti on-of-airf

low-at-free-f

low al lowed DOE t o p lot all of t he cu rve s o f ove ra ll air-moving e ffi ciency t og et her (a s an e xample o f the trans f orme d data, s ee F i gures

7.5.6–7 .5.8). Th e D ep artm

en t f i t the se cu rv esto a s i

ng l e e qua ti on of ove ral l ef f i ci en cy asa f un cti on of the rat io of ai

rflow t o free airfl

ow as foll ows:

where:7-19 = overall

ai r movi ng ef fi ci ency ,

= ra t io o f airflow t o fr ee flow , a nd

= empi

rical ly deter mi ned coeffi cien ts. Figur es 7 .5 .7 and 5 .7 .8 sho w t he cu rve fit for high-fire he at ing and lo w- fire hea t ing, a nd coo li ng for non-condensin

g and condensin

g furnaces. Fo r d et ails of t he o ver all air-mo ving efficiency and t ables o f co efficients fo r e ach o f the vir t ua l fu r na ce s a nd o pe r at ing mo de s, se e A pp en di x 7
. 6, Ov er all A ir

- Mo vin g E ffic ien cy.

Figu re 7.5.6 Overal

l Air -Moving Efficiency of Ex isting Furnaces7-20 Figu re 7.5.7 Over all

Air-Moving

Eff iciency o f Non-Con densing Virt ual Fu rnace Mo dels

Figu re 7.5.8 Overal

l Air -Moving Efficiency of Condensing Vir tual Furna ce M ode ls7-21

7.5.4 Blower

-Motor El

ectr icity Cons umption The circulating-air bl

ower- moto r electrici

ty consumption i

n steady-stat e at full

load is a fun ction of ai rfl ow ( Q ), external

static pressure (

P), and t he o ver all air-mo ving efficiency of t he furn ace ( 

### 0 overall ). For a b as el i ne mode l f urn ac e, th e D ep artm

en t cal cu l ate d the c i

rcu l ati ng -ai r f an-m otor ele ct r icit y co nsu mpt io n fo rt he fo r wa r d- cu r ve d imp elle rwit h a dir ec t
- dr ive PS C mo t o ras t he air power di vi ded by the overa l l ai r-mov i ng ef fi ci ency of the bl ower and b l ower moto r:

where:

= bl ower m otor ele ctri ci

ty c onsu m pti on (W ),

= air p ow er (W) , a nd

= o ve r all a irmo vin g e ffic ien cy.
7.6 ANNUAL HEATING AND CO OLING LOADS IN SA MPLE HOUSES 7.6.1 Annual House-Heating Load The ann ual house-heati

ng l oad (HHL) is the total am ount o f h eat out put from the f

urnace tha t the hou se ne ed s d uri ng the he ati ng se as on. Thi s i

nc l ude s h ea t f rom the bu rn er a nd he at f rom the b l ower an

d the bl ower m otor. Burner operating h

ours (BOH), t he n

umb er of hours the f

urnace b urner i s on durin

g a year, is a ke y variable in t he ca lculat ion o f HHL. The Dep ar t ment c alculat ed B OH fo r t he exi sting f urnace as:

where:

= bur ner operati

ng h ours (h rs/y r), = annual

fuel consumption for heating the house , f rom RE CS9 7 ( kBt u/ yr), and = i npu t capac i ty of the existi ng f urn ace (kBtu/h r).7-22

The Dep ar t ment d et er mined HHL for eac h sampled hou seho ld, ba sed on t he BO H and t he characteristics of the assign ed exis ting f urnace, using the followin g calcul ations:

where:

= i npu t capac i ty of ex i sti ng f urn ace (kBTU /hr) ,

= AFUE of

exi stin g furn ace, 3.412 = constant to conv ert kW to kBTU/h

r, = ratio of bl

ower on-t im

e to burner on-time

in the heati ng m ode (fro m DOE t est pr oc edu re ), and = power c onsu

m pti on of the b l ower m

otor (kW). The po wer co nsumpt ion o f the blowe r mo t or dep ends on t he st ead y-st at e o per at ing condi tions (the pressure an

d ai rfl ow) for the furnace. Th

is cal cul ation i s expl

ai ned i n section 7.5, Cal cul ati ng F urn ace Blower Electrici

ty C onsu m pti on. 7.6.2 Annual House-Cooling Load The annual

house-co olin

g load (HCL) is the to tal amount of coo li ng provided to the house for t he ent ire co oling se aso n. I t includes t he co oling p ro vided by t he exist ing air c ond itio ner , a nd ac cou nts f or th e h ea t f rom the bl owe r an d b l owe r m

otor. Th e D ep artm

en t cal cu l ate d H CL

f rom t he co o ling en er gy c o nsu mpt io n r ep o r t ed in RE CS 97 an d t he SE E R o f t he as sig ne d e xist ing air conditioners:

where:

= an nua l hous e-cooli

ng l oad (kB tu/h/

y r),

= ann

ual house-cooli

ng el ectrici ty consum

ption, from

RECS97 kWh/yr ), and = SEER of

the existi ng a i r cond i tion er (kB tu/h/

kW ).7-23

7.7 FURNA CE ENE RGY CONSU MPTION On ce th e h ea ti n g a n d c ooli n g l oad s of each sa m pl e h ous e a rekn own , i t i s p oss i b l e to estim ate what the energy

consum ption of al

ternative (m

ore-effi ci ent) furna

ces would b e i f m

oreeff ic ie nt furn aces, rather than the ex

is ting equi pme nt, were used i

n each house. 7.7.1 Fuel Consum

ption Fo r e ac h de si gn opti on , B OH i s d i f f er en t, s i n ce th e A FU E a n d b l owe r-m otor e l ec tri

ci ty con su m pti on ar e d i f f er en t. Th er ef ore , e ach de si gn opti on re qui re s a dif f er en t ope ra ti n g ti me to heat the same house. The Depart men t calculated BOH as:

where:

= i npu t capac i ty of ex i sti ng f urn ace (kBTU /h);

= AFUE of

design option or eff

ic ie ncy le vel bei ng consi dered; 3.412 = a co nst ant t o c onve rt kW t o k BT U/h;

= t he r at io o f blowe r o n-t ime to bur ner on- t ime (heat ing mod e) ; and = the p ower con sum pti on of the b l ower m

otor (kW). The BE va ri eswi th a i rf l ow a nd sta ti c p res su re, wh i ch are de term i ne d by the i nte rs ec ti on of the furn ace f an curve and the duct sy

stem curve. The Dep ar t ment c alculat ed t he fur nace fuel co nsumpt ion fo r e ach d esign o pt ion and eff ic ie ncy le vel usi ng the f oll owing f ormul a:

where:

= bur ner op er at ing ho ur s (h) , a nd

= i npu t capac i ty of ex i sti ng f urn ace (kBTU /h). 7.7.2 Electr

icity Consumptiond Th e DOE an d ASHRAE test procedur es do not coun t th e electri city usedby controls w

hen th e furnace is not f

irin g.

e The AS H RA E te st pro ce dure

do es no t de al w

ith i gnitor ene

rgy co nsu mption. 7-24 Th e D ep ar t ment ca lcu lat ed fur nac e e lec t ric it y co nsu mpt io n fo r t he b lo we r, t he d ra ft i ndu cer, a nd th e igni ter. d The bl

ower moves h

eated air through the house wh enev er the furn

ace burner is on (and the h

eat exchan

ger has reach

ed a certain

set-point temperature). It al so operat es in the cooli ng seas on (summ

er) if the house i s ai

r-conditi oned. The el ectrici ty use cal cul ation was ca rri ed out s ep ar ate l

y f or w i n ter an d sum mer . Th e D ep ar tmen t ca l cul ate d th

e w i n ter el ec tri ci ty consumption as:

where:

= bur ner operati

ng h ours (h ), = ratio of bl

ower on-t im

e to burner on-time , = power c onsu

m pti on of the b l ower m

otor (kW),
= ratio of i

nduced-draf

t blower on-tim

e to burner on-time , = power c onsu

m pti on of the d raf t-in duce r bl ower-m otor (kW), = ra t io o f ignito r o n-t ime to bur ner on- t ime, and
= power c onsu

m pti on of the i gni tor (kW). The ra t io o f blowe r o n-t ime to bur ner on- t ime and t he r at io o f induced dr aft blowe r o nt ime to bur ner on- t ime are fr om t he America n So ciet y of Hea t ing, R efrige ra t ing and Ai r-Condi tion i ng En gi ne ers (A SHRA

E) test proce dure 15 usi

ng del ay tim es f or t he v irtual model f urn ace s. The ratio of i

gni tor on-tim

e to burn er on-ti me com es f rom th e DOE tes

t procedur

e 16 and the igni

tion time of the vi

rtu al m odel furnaces. e Su mmer ele ct r icit y us e is du e t o t he fur na ce cir cu lat ing

- air blo we rt ha t mo ve s t he air cooled by the ai r conditi oner. During c oolin g mode, the bl

ower moto r wil

l operate at a hi gh speed, so the airf

low an d static pressure condi

tions wi ll be diff erent from

the heati ng m ode conditions. The Depart men t calculated summ

er electrici

ty use as:

where:

= air- co ndit ioner op er at ing ho ur s (h/ yr), and = power c onsu

m pti on of the b l ower-m

otor in cool i ng m ode (kW ).7-25

T he de t ails fo rca lcu lat ing en er gy c o nsu mpt io n o f mo du lat ing fur na ce s a pp ea rin Ap pe nd ix 7.7, G as and Electrici

ty Use for Modulating Furnaces.
7.8 BOILER E NERGY C ONSUMPTI ON To assign t he input cap acit y for t he ene rg y cons umpt ion ca lculat ion fo r ho t -w at er gas and oil b oilers, the Depart men t used t he i

nput capacities of the vi

rtu al m odel furnaces f

or bo il ers, weight ed a cco rd ing t o t he shipment dat a fro m GAMA. 3 The Dep ar t ment c alculat ed t he hea t ing l oad f or th e h ous e a nd the en erg y con su m ption of dif f ere nt m ode l de si gn s i n a si m i l ar m an ne r f or furna ces . T he po wer co nsumpt ion o f the circu lating pump mot or is 62 w at t s for t he bas eline mod el des ign. 17 7.9 RESULTS Thi s s ec ti on pres en

ts a nn ua l ga s or oi l con su m ption a nd wi nte r el ec tri ci ty con su m ption f or selected design

opt ions i n each product class. 7.9.1 Non-Weat herized Gas Furnace Energy Use The ave rage ann ual household energy

use f or each desi

gn option f

or non-weatherized gas fur na ce s is sho wn in T ab le 7

. 9. 1. T he r an ge o f an nu al g as us e fo rea ch de sig n o pt io n is s ho wn in Figur e 7. 9. 1. Figur e 7. 9. 2 sho ws t he r ange of g as u se fo r t he 90 per cent AFUE co ndens ing furn ace across the di ff

erent regions

of the country. Fi

gure 7.9.3 shows the range of wi nter elect ricit y cons umpt ion.7-26 Figu re 7.9.1 Range of Annual Gas Use , Non-Weatherized Gas Furnace s Tabl e 7.9.1 Non-Weat herized Gas Furnace Energy Use Design Option Average Annual Gas Us e (MMBtu) Average Winter Electr icity Use* (kWh) 78% 66.5 487 80% 64.9 476 80% 2-stage Mod. 63.5 492 81%, 8% C at. III 64.1 470 81% 2-stage M od, no Ca

t. III 62.8 487 82% 63.3 464 82%2-stag e M od 62.0 481 83% 62.6 459 90% 57.9 421 92% Incr. HX Area 56.6 412 96% St ep Mod E CM 54.0 226 * The av erage su mme r el ec tric ity us e ( fo r the b low er)is 15 6 k

Wh f or all o f the de si gn o pti ons sho w n.7-27 Figu re 7.9.2 Range of Annual Gas Usage by Region, 90 percent AFUE , Non-Weatherized Gas F urnace

Figure 7.9.3 Range o f Winter Ele ctricity Use, No nWeatheriz ed Gas Furnace s7-28

7.9.2 Weatherized Gas Furnace Energy Use T he av er ag e a nnu al e ne r gy u se fo rea ch de sig n o pt io n fo rwe at he r ize d g as fur na ce s is shown i n Tabl e 7.9.2. The range of an

nual gas use f or weatherized gas f

urnaces f or each desi

gn option i s sh own i n F i gure 7 .9.4. F i gure 7 .9.5 sh ows the ran ge of wi nter e l ectrici

ty c onsu m pti on. Tabl e 7.9.2 Weatherized Gas Furnace Energy Use Design Option Average Annual Gas Us e (MMBtu) Average Winter Electr icity Use* (kWh) 78 % AFU E - Ba se line M o de l 40.3 298 80% AFUE - Incr. HX A rea 39.3 291 80%AFU

E - Im prov ed In sul ati on 39.1 290 80% AFUE - Im

proved Heat Xfer 39.3 291 81% AFUE - Incr. HX A rea 38.8 288 81%AFU

E - Im prov ed In sul ati on 38.7 286 81% AFUE - Im

proved Heat Xfer 38.8 288 82% AFUE - Incr. HX A rea 38.3 284 82%AFU

E - Im prov ed In sul ati on 38.2 283 82% AFUE - Im

proved Heat Xfer 38.3 284 83% AFUE - Incr. HX A rea 37.9 281 83%AFU

E - Im prov ed In sul ati on 37.8 280 83% AFUE - Im

proved Heat Xfer 37.9 281 * The av erage su mme r el ec tric ity us e ( fo r the b low er)is 37 2 k

Wh f or all o f the de si gn o pti ons sho w n.7-29 Figure 7.9.4 Annual Gas Use , Weatherized Gas F urnaces

Figure 7.9.5 Winter El ectricity Use, Weather

ized Gas Furnaces7-30

7.9.3 Mobi le Home Furnace Energy Use The ave rage ann ual energy use f or each desi

gn option f

or mobile home furn aces i s shown i n T ab l e 7 .9.3 . F i gur

e 7 .9.6 sh owsthe ran geof an nu al ga s u se . F i gur

e 7 .9.7sh owsthe ran geof wint er elect ricit y cons umpt ion. Tabl e 7.9.3 Mobi le Home Furnace Energy Use Design Option Average Annual Gas Use (MMBtu) Average W inter El ectr icity Use (kWh )* 75 % AFU E - Ba se line M o de l 51.0 374 80% AFUE - Incr. HX A rea 45.2 405 80%AFU

E - 2 -s tag e M od 44.0 415.4 81% AFUE - Incr. HX A rea 44.7 400 81%AFU

E - 2 -s tag e M od 43.5 410.6 82% AFUE - Incr. HX A rea 44.1 395 90% AFUE - Co ndens ing 40.4 360 * The av erage su mme r el ec tric ity us e ( fo r the b low er)is 22 9 k

Wh f or all o f the de si gn o pti ons sho w n.

Figure 7.9.6 Annual Gas Use, Mobile Home F urnaces7-31 Figure 7.9.7 Winter El ectricity Use, Mobile Home F urnaces7-32

7.9.4 Oil Furnace Energy Us e T he av er ag e a nnu al e ne r gy u se fo rea ch de sig n o pt io n fo ro il fur na ce s is sho wn in T ab le 7.9.4. Th e ran ge of an nua l gasuse f or each des i gn opti

on i s sh own i n F i gure 7 .9.8. F i gure 7 .9.9 show the ra

nge of wi nter e l ectrici

ty c onsu m pti on. Tabl e 7.9.4 Oil Furnace Energy Use Design Option Average Annual Gas Use Average Winter

Electr icity Use* 78 % AFU E - Ba se line M o de l 87.8 787 80% AFUE- Incr. HX A

rea 85.7 768 81% AFUE- Incr. HX A

rea 84.7 759 81% AFUE A

to m B urner 2-stage Mod. 82.6 870 82% AFUE- Incr. HX A

rea 83.7 750 82% AFUE A

to m B urner 2-stage Mod. 81.6 860 83% AFUE- Incr. HX A

rea 82.7 741 83% AFUE A

to m B urner 2-stage Mod. 80.7 850 84% AFUE- Incr. HX A

rea 81.7 733 84% AFUE A

to m B urner 2-stage Mod. 79.8 840 85% AFUE- Incr. HX A

rea 80.8 724 85% AFUE A

to m B urner 2-stage Mod. 78.9 831 * T he ave ra ge s ummer e lect ricit y use ( for t he blow er ) is 71 kWh.7-33 Figure 7.9.8 Range of Annual Oil Use, Oil Fur

naces

Figure 7.9.9 Range of Winter Electr icity Use, Oil Furnaces7-34

7.9.5 Gas Boiler E nergy Use The ave rage ann ual energy use f or each desi

gn option f

or hot -water gas boil

ers i s shown i n Ta bl e 7.9.5 . The

ran ge of an nua l gasuse f or each des i gn opti

on i s sh own i n F i gure 7 .9.10. Fi gure 7 .9.11 shows

the ra nge of wi nter e l ectrici

ty c onsu m pti on.
Tabl e 7.9.5 Hot-Wa ter Gas Boiler Energy Use Design Option Average Annual Gas Use (MMBtu) Average Winter

Electricity Use (kWh) 80 % AFU E Ba se line M o de l 93.5 382 81% AFUE Imp H t Xfer / E lec. Ig n 88.8 384 81 % A FU E 2 -s t ag e mo d. + I ndc Dr aft 87.4 572 82% AFUE Imp H t Xfer / E lec. Ig n 87.7 379 82 % A FU E 2 -s t ag e mo d. + I ndc Dr aft 86.4 565 83% AFUE Imp H t Xfer / E lec. Ig n 86.7 375 83 % A FU E 2 -s t ag e mo d. + I ndc Dr aft 85.4 559 84% AFUE Imp H t Xfer / E lec. Ig n 85.7 371 84 % A FU E 2 -s t ag e mo d. + I ndc Dr aft 84.4 552 88% AFUE 81.8 354 91% AFUE 79.3 304 99% AFUE 73.0 2807-35 Figure 7.9.10 Range of Annual Gas Use, Hot-Water Gas Bo ilers

Figure 7.9.11 Range of Winter Electr icity Use, Hot-Water Ga s B oi lers7-36

7.9.6 Hot-Wa ter Oil Boiler Energy Use The av erage an nua l hous ehold

en ergy use f or each des i gn opti

on f or hot-water oi

l boi l ers i s sh own i n Ta bl e 7.9.6 . The

ran ge of an nua l gasuse f or each des i gn opti

on i s sh own i n F i gure 7.9.12. F i gure 7 .9.13 shows the ra nge of wi nter e l ectrici

ty c onsu m pti on.
Tabl e 7.9.6 Oil Boiler Energy Use Design Option Average Annual Gas Use (MMBtu) Average Winter

Ele ctricity Use (k

Wh) 80 % AFU E Ba se line M o de l 108.6 418 81%A FUE 107.3 413 81%AFUE A

to m B urner 2-stage Mod. 105.7 625 82%A FUE 106.0 408 82%AFUE A

to m B urner 2-stage Mod. 104.4 618 83%A FUE 104.7 402 83%AFUE A

to m B urner 2-stage Mod. 103.2 611 84%A FUE 103.5 398 84%AFUE A

to m B urner 2-stage Mod. 102.0 604 86%A FUE 101.1 389 86%AFUE A

to m B urner 2-stage Mod. 99.7 590 90%AFUE 97.0 303 95%AFUE 91.9 2877-37 Figure 7.9.12 Range

of Annual

Oil Us e, Hot-Water

Oil Bo ilers

Figure 7.9.13 Range

of Winter

Ele ctricity Use, Hot-Wa ter Oi l Bo ilers7-38 REFERENCES
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