I AlllDO TfiTbDS

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^PUBLICATIONS

V NBSIR 80-2090

AlllOS 157^1

Estimating the Heating Seasonal

Operating Cost of Residential

Hybrid Heat Pump Systems,

Including Units Retrofitted to Oil,

Gas and Electric Furnaces

Peter Domanski and George E. Kelly

Mechanical Systems Group

Building Equipment Division

Center for Building Technology

National Bureau of Standards

U.S. Department of Commerce

Washington, DC 20234

July 1980

HlC

100

.U56

80-2090

1980

U.S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

nOJIAL BUREAU

0# 8TANDARU8

NBSIR 80-2090

ESTIMATING THE HEATING SEASONAL

OPERATING COST OF RESIDENTIAL

HYBRID HEAT PUMP SYSTEMS,

INCLUDING UNITS RETROFITTED TO OIL,

GAS AND ELECTRIC FURNACES

Peter Domanski and George E. Kelly

Mechanical Systems Group

Building Equipment Division

Center for Building Technology

National Bureau of Standards

U.S. Department of Commerce

Washington, DC 20234

July 1980

U.S. DEPARTMENT OF COMMERCE, Philip M. Klutznick, Secretary

Luther H. Hodges, Jr., Deputy Secretary

Jordan J. Baruch, Assistant Secretary for Productivity. Technology, and Innovation

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director
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.2
ESTIMATING THE HEATING SEASONAL OPERATING COST

OF RESIDENTIAL HYBRID HEAT PUMP SYSTEMS,

INCLUDING UNITS RETROFITTED TO OIL, GAS AND ELECTRIC FURNACES

by

Peter Domanskl and George E . Kelly

ABSTRACT

A method is presented for estimating the heating seasonal operating cost of a

residential, hybrid heating system consisting of an electric heat pump and a

warm-air furnace. The approach described is applicable to heat pump/control

system/gas or oil-fired furnace which is sold as a package or to a heat

pump/control system which is Intended to be added to an existing gas, oil or

electric furnace. Recommendations are made regarding how such systems can

be rated and the type of information that would assist consumers in comparing

the operating cost of a hybrid heat pump system with that of a conventional

heat pump or furnace. Different control strategies are accounted for and

examples are presented (in the appendix) for estimating the heating seasonal

operating cost of hybrid systems employing both single and two-speed compressors .

Key Words: Add-on heat pumps; furnaces; heat pumps; hybrid heat pumps;

hybrid systems; rating procedure; seasonal cost of operation

lil
TABLE OF CONTENTS

Page

1. INTRODUCTION 1

1.1 Reconmended Test Procedure 1

1.2 Description of Recommended Rating Procedure 2

2. CALCULATION OF THE HEATING SEASONAL OPERATING COST 4

2.1 Calculating the Heating Seasonal Operating Cost for a Hybrid System Employing a Single Speed Compressor 4

2.2 Calculating the Heating Seasonal Operating Cost for

Hybrid Systems with Two Speed Compressor or Two

Compressors 9

REFERENCES 16

APPENDIX A. Sample of Heating Seasonal Operating Cost Calculations

for a Hybrid System with a Single-Speed-Compressor 22

APPENDIX B. Sample of Heating Seasonal Operating Cost Calculations

for a Hybrid System with Two-Speed-Compressor or Two

Compressors 31

Iv
LIST OF FIGURES AND TABLES

Page

Figure 1. Heating Load Hours (HLH) for the United States 17

Table 1. Major Climatic Regions in the Continental U.S.A 18

Table 2. Standardized Design Heating Requirements (kBtu/h) 19

Table 3. Example of Information Which Would Assist a Consumer

in Purchasing a Heat Pump/Oil Furnace System 20

Table 4. Example of Information Which Would Assist a Consumer

in Purchasing an Add-on Heat Pump 21

Table Al. Sample Worksheet Used to Evaluate the Heating Seasonal

Energy Input to a Hybrid System with a Single-Speed

Compressor Heat Pump

Table A2. Heating Seasonal Operating Cost of Hybrid System

with an Oil-fired Furnace in Region V 29

Table A3. Heating Seasonal Operating Costs of Hybrid System

with Oil, Gas or Electric Furnace in Region V. 30

Table B1 . Sample Worksheet to Evaluate the Heating Seasonal

Energy Input to a Hybrid System with a Two-Speed

Compressor or with Two Compressors 37

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1 . INTRODUCTION

The test and calculation procedures recommended herein apply to residential,

hybrid heat pump systems. A hybrid heat pump system is defined in this

report as either (1) a heat pump/control system/gas or oil-fired furnace

which is sold as a package or (2) a heat pump/control system which is

intended to be added to a previously installed gas, oil or electric furnace.

This definition differs slightly from the usual definition of a hybrid

system by the inclusion of the case where a heat pump is added to an existing

electric furnace. This modified definition is adopted because it is felt

that distinguishing between fossil-fuel and electric furnaces in the heat

pump add-on application is largely academic, since both types of furnaces

will tend to be operated in the same manner. In addition, since a heat pump

retrofitted to an electric furnace will usually operate differently than a

heat pump sold with electric resistance heaters, it is important to have a

procedure for determining the heating seasonal operating cost of such addon systems.

1.1 RECOMMENDED TEST PROCEDURE

A hybrid heat pump system which is Intended to be sold with a particular

gas or oil-fired furnace, shall be tested in accordance with: the Department of Energy's "Test Procedures for Central Air Conditioners, Including

Heat Pumps" [1], and the Department of Energy's "Test Procedures for Furnaces and Vented Home Heating Equipment" [2]

The latter provides rating

data for the furnace; efficiency number, EFFY^, and an output capacity,

^Out» which are used in the calculation procedure described in Section

2 of this report to estimate the heating seasonal operating cost of the

hybrid system.

1
A hybrid heat pump system which is intended to be sold as an add-on to a

previously installed gas, oil, or electric furnace, need only be tested

with the Department of Energy's "Test Procedures for Central Air Conditioners,

Including Heat Pumps. " However, in the case of these add-on units, the

following furnace efficiencies, rip, shall be used in Section 2 to calculate

the heating seasonal operating cost of the hybrid system.

Type of Existing Furnace Assigned Furnace Efficiency, Up (%)

gas-fueled furnace 62

oil-fueled furnace 68

electric furnace 100

In addition, an output capacity of the furnace, Qp, is assumed in Section

2 to be equal to 1.7 x DHR (the design heating requirement), which is

equivalent to saying that the furnace is 70% oversized relative to the

heating requirements of the residence at the outdoor design temperature.

1.2 DESCRIPTION OF RECOMMENDED RATING PROCEDURE

An analysis of the seasonal efficiency and seasonal operating cost for

hybrid systems has shown that for a system employing a fossil-fuel furnace, the seasonal efficiency is not necessarily consistent with seasonal

operating cost due to different control systems which may be employed

and the wide range of prices for electricity and fuel. For example, a

low-efficiency furnace may cost less to operate for the same heating done

than a high-efficiency heat pump, if the price of electricity is high

and the price of fuel low. This could result in a hybrid system with

a higher efficiency number costing more to operate than a hybrid system

with a low efficiency number, if the latter employs better system control

2
strategy. Since the consumer is primarily interested in what the cost

of heating his house will be, a seasonal efficiency number may be misleading. For this reason, it is recommended that only Heating Seasonal

Operating Cost (HSOC) be used to rate a hybrid heat pump system.

A procedure for calculating the HSOC for a hybrid unit is presented in Section 2. This calculation procedure recognizes that the hybrid heat pump

system can operate in different modes, depending on the control system

employed. Generally four modes of operation were found to be possible and

the recommended calculation procedure can be applied to the particular type

of control strategy used.* These four modes of operation are:

above balance point** - (1) heat pump operates alone, the furnace is off

below balance point - (2) heat pump is off, furnace operates alone

- (3) heat pump cycles with furnace to meet heating

load (e.g., when furnace is on, heat pump

is off and vice versa)

- (4) heat pump works continuously while furnace

cycles to meet the heating load.

Some simplifications are assumed in the recommended calculation procedure.

First, the effect of a heat pump timer which results in a minimum offperiod between compressor shut-off and start-up, is neglected. Second,

the performance degradation of the heat pump when it cycles with the

furnace is considered to equal the performance degradation of heat pump

cycling by itself. However, results of several detailed HSOC calculations

done without these two simplifications have shown that their effect on the

final results is negligible.

** The balance point is the outdoor temperature at which capacity of the

heat pump equals the building heating load.

3
2. CALCULATION OF THE HEATING SEASONAL OPERATING COST

The heating seasonal operating cost, HSOC, of a hybrid system is strongly

dependent upon the climatic region in which the unit operates, the type of

system employed (e.g., single-speed or variable-speed compressor, type of

A furnace control strategy etc.)> the design heating requirement of the

building relative to the heat pump's capacity at different outdoor temperatures, and the cost of fuel and electricity. Because of these factors,

it is recommended that the seasonal cost of operation of such a system be

determined in each climatic region at a number of different design heating

requirements and for a variety of different fuel and electric costs.

2.1 CALCULATING THE HEATING SEASONAL OPERATING COST FOR A HYBRID SYSTEM

EMPLOYING A SINGLE SPEED COMPRESSOR

Table 1 lists six major U.S. climatic regions and their associated heating

load hours, outdoor design temperatures, and fractional hours in each temperature bin. Figure 1 is a map of heating load hours (HLH) for the continental United States that may be used to locate these six regions. The

minimum and maximum design heating requirements of a residence in which a

hybrid system is likely to be installed will depend upon the climatic region

and the capacity of the heat pump. They may be obtained for each of

these six climatic regions by using the following equations:

The "design heating requirement" is the heating requirement that must be

met by the system at the 97-1/2 percent outdoor design temperature.

A consumer purchasing a heat pump which provides both heating and cooling

should be reminded to select a unit having a cooling capacity which will

satisfy his home's cooling requirements and maintain a comfortable indoor

level of relative humidity.

4
(minimum design heating requirement) ®= Qss(^7)

and

(maximum design heating requirement)

for regions I, II, III,

60 IV, and VI

Qgs(^7) for region V ( 2 . 1 )

2Q ss(47)

for regions I, II, III,

60

2.2Qgg(47), for region V

IV, and VI

( 2 . 2 )

and rounding the results off to the nearest standardized design heating

requirement given in Table 2 . In the above equations , "^OD is the outdoor

design temperature given in Table 1 for each major climatic region and

Qgs(47) is the heat pump capacity measured during the high temperature

performance test at 47®F.

Standard design heating requirements in a particular climatic region for

which calculations should be performed are those given Table 2 ranging

from the to the DHR^^y for the region.

For each climatic region and for each design heating requirement the

heating seasonal operating cost, HSOC, of a hybrid system employing a

single-speed compressor shall be determined using the following equation:

HSOC = HLH X C X DHR

Z "j BL(T .) j N

[

n. 6 (T.)X(T.)y(TP

J — E(T4)x

N PLF(X,y) J

$

cost

kWh

+

^ ^j[BL(Tj) - Q(Tj)6(Tj)X(Tj)Y(Tj)]^| x $

cost

unit of fuel

(2.3)

The first term on the right side of the above equation represents the

operating cost of the heat pump, while the second term is the operating

cost of the furnace. The ratio of (HLH x C x DHR) to (Z —j BL(T^)) is a N -J

5
scaling factor which allows the operating cost of the hybrid system to be

compared with that of a system employing either a single heat pump or a

single furnace.

The symbols used in eq. (2.3) have the following meaning;

j = 1, 2, 3, , n corresponds to the temperature bin

n = total number of non-zero temperature bins in the climatic region

Tj = 67 - 5j is the representative temperature of the bin, (“F)

I indicates the quantity following the symbol is to be summed over all

j

temperature bins

= the number of hours in the temperature bin divided by N = Z n^; ” .. rh ^ it is referred to as the "fractional hours in the j*-" temperature

bin" and values for it are given in Table 1 for each region

HLH = the number of heating load hours for the region as given in Table 1

DHR = the design heating requirement (kBtu/h)

Tqjj = the outdoor design temperature given in Table 1 for each major

climatic region, (**F)

C = 0.77, an experience factor which tends to improve the agreement

between calculated and measured building loads

K = the Btu content per unit of fuel (e.g. K = 100,000 Btu/therm if

cost/unit of fuel is given in dollars per therm)

Tip = the efficiency of the furnace, (%). For hybrid units sold with

a particular furnace, rip shall be set equal to EFFY^, as determined

by DOE "Test Procedure for Furnaces or Vented Home Heating Equipment" [2]

In a hybrid system intended to be added to an existing

gas, oil or electric furnace, the values assigned in Section 1.1

for Tip shall be employed.

6
Q(Tj) = the heat pump's capacity at temp. Tj (kBtu/h)

E(Tj) = the heat pump's power at temp. Tj (kW)

BL(Tj) = the building load at temp. Tj (kBtu/h) as defined in eq. (2.6)

6(Tj) = the heat pump's cut-out factor due to low temperature or heat

pump/furnace control strategy as defined in eq. (2.7)

X(Tj) = the heat pump's heating-load factor at temp. Tj as defined in eq.

y(Tj) = the furnace-heat pump cycling factor at temp. Tj as defined in eq.

PLF(X,y) = the heat pump's part-load factor as defined in eq. (2.11).

( 2 . 8 )

(2.9)

The heat pump's capacity and power at temperature Tj shall be estimated

using the following formulas:

Q(Tj)

Qcca7) .

- Qssd?)) (Tj - 17)

5o

Tj > 45®F or Tj <. 17“F

A ,-,7. (W(35) - Qss( 17)) (Tj - 17)

17‘*F < Tj < 45“F

(2.4)

E(T^)

(Egs(47) - Ess( 17)) (Tj - 17)

rs

*

> 45“F or < 17“F - > J J

•“

17“F < Tj < 45°F

(2.5)

where Qgg (47) and Egg (47), Qpgp (35) and Epgp (35), and Qgg (17) and Egg

(17) are the capacities (in kBtu/h) and powers (in kW) measured during the

high temperature test, the frost accumulation test, and the low temperature

test, respectively.* The quantities BL(Tp, 6(Tj), y(Tj) and PLF(X,y) are

Refer to DoE's "Test Procedures for Central Air Conditioners, Including

Heat Pumps.” [1]

7
defined by the following equations:

BL(T^)

65 - T

65 - T

X C X DHR

OD

( 2 . 6 )

(O', < '^OFF

5(T J = < ^ ; W < T. < T

Q(T )a or =iY ’ ^OFF ^ _ ^ON

1 ; > foN

and

and

where Tq^j, and Tqjj denote:

(3.413)(E(Tj))

(3.413)(E(Tj))

(3.413)(E(Tj))

< 1

> 1

> 1

(2.7)

Tqff “ outdoor temperature at which the compressor is automatically

shut off (if no such temperature exists, Tj is always greater

than Tqpp and Tqjj) due to low teperature or heat pump/furnace

control strategy

Tqj^ = the outdoor temperature at which the compressor is automatically

turned on (if applicable) for units designed for low temperature

automatic shut-off or due to heat pump/furnace control strategy.

X(T.)

BL(T^)

1

Q(Tj ) > BL(Tj )

Q(Tj) < BL(Tj)

( 2 . 8 )

I Qf - BL(Tj)

1 Qp - Q(T^)

Y(Tj) =

when BL(Tj) > Q(Tj) and cycling

between the furnace & heat pump occurs at temperature T j

otherwise

Qout» which is defined in sections 4.7 and 4.10 of

i

Appendix N. Federal Register Vol. 43, No. 91,

May 10, 1978 (p. 20164)

(1.7)x(DHR) for a heat pump Intended to be sold as an add-on to previously installed furnace

(2.9)

( 2 . 10)

8
PLF(X,y) = 1 - Cp(l - (X)(y)) (2.11)

where Cp Is degradation coefficient which is either measured or assumed in

accordance with DOE's "Test Procedure for Central Air Conditioners, Including

Heat Pumps" [1]

The current (1980) recommended fuel and electricity price ranges for which

the above calculations are to be performed are:

electricity ($/kWh) .04, .06, .08, .10,

oil ($/gallon) .40, .60, .80, 1.00, 1.20 1.40

The above prices for oil give the same HSOC for the following prices

(in $/therm) of gas, respectively .26, .39, .52, .65, .78, .91 taking into

account the furnace efficiencies of =0.68 and = 0.62, as *oil ^Gas

assigned in Section 1.1.

It is recommended that all HSOC figures be rounded off to the nearest five

dollars and the information for each region be arranged in form similar to

Tables 3 and 4. Appendix A presents step-by-step sample HSOC calculations

according to the method described above.

2.2 Calculating the Heating Seasonal Operating Cost for Hybrid Systems

with Two-Speed Compressor or Two Compressors

The minimum and maximum design heating requirements of a residence in which

a heat pump is likely to be Installed, shall be determined for the six climatic regions listed in Table 1 using the same procedure outlined in Section

2.1 for units with single speed compressors. The only difference is that

Qgg^^~^^(47) (which is the capacity measured in the high temperature performance test at 47®F (+8.3 ®C) with the unit operating at the high compressor

9
speed or with both compressors in operation) shall be used in place of

in the equations (2,1) and (2.2) for the maximum and minimum

design heating requirements.

For each climatic region and for each standard DHR ranging from the

minimum to the maximum design heating requirement, the heating seasonal

operating cost, HSOC, shall be determined using the following equation:

HSOC = HLH X C X DHR V (T

^

)

E ^BL(TJ j N

'

j N

cost

kW

Ep(T .) 100 1000

u * ,, M I I N K

X i.

cost

unit of fuel]

where

Ejjp(T.) = energy used by a heat pump in the temperature bin

N

divided by the total number of bin hours, and

N

the heat supplied by a furnace in the temperature bin

divided by the total number of bin hours.

The terms PLF^“^ , PLF^“^, X^“^, X^“^, and which are used below, are

consistent with the definitions employed for single-speed compressor systems, but with their meaning expanded to including high speed or two compressor operation (k=2) or low speed or single compressor operation (k=l).

Ejjp(Tj) Ep^Tj)

These terms, along with the terms — and jj , are evaluated according to the four possible cases of heat pump operation denoted below.

CASE 1

a single compressor.

( 2 . 12 )

10
(2.13)

.k=l

E„p(T.) n. X (T.)

BL(TJU-6'(T,)]

N N

J J (2.14)

where tl^)

PLF

r^T.)

k.=l = 1 - C

k=l k=l

jj [1-X (Tj)]

(2.15)

(2.16)

6(T.)

Tj 1 Tqpp

"^OFF - "^ON (2.17)

CASE 2

k=i Jq»2

0 (Tj) < BL(Tj) < ^ heat pump alternates between high speed

or two-compressor operation (k=*2) and low speed or single-compressor operation

(k=l)

Eup(T.) n. k»l k»l k=2 k=2

M «"(T.) [E(T.) X(T .) + E(T J X(T J] (2.18)

N N J J J J J

Ep(T.) n. -^BL(T.) [1 - 6 ' (TJ]

iM J J (2.19)

.k=2

k=l Q t

where X (t J

= “H?

Q (Tj) - BL(Tj)

j) .k=2 .k«l

3 Q (Tj) - Q(Tj

j)

( 2 . 20 )

X^^ilj) = 1 - ( 2 . 21 )

11
Tj < Tqfp

6^(Tj) = Tqff - "^ON ( 2 . 22 )

Tj > Ton

CASE 3

. . . .k*2

Q (Tj) <BL(Tj) < Q (Tj) and the heat pump cycles on and off at high

compressor speed, or cycles both compressors on and off together (k*2)

%p(Tj)

N

Ep(Tj)

N

k=2

"1 ^ (Tj ) .k»2

^BL(Tj) [1 - «'(Tj)]

(2.23)

(2.24)

where

k-2 BL(Tj)

X (Tj) =

PLF Tj)

.k-2

Q (Tj)

k-2

1 - Cn (1 - k-2X (Tj))

(2.25)

(2.26)

Tj 1 Tqpp

6"(T.) =( i

:i I 2 Tqff Tj < Tqn (2.27)

CASE 4

Tj ^ Ton

.k-2

BL(Tj) > Q (Tj) and the heat pump alternates with the furnace, or the heat

pump works continuously while furnace cycles to meet building heating load,

or the furnace operates alone.

12
EHp(Tj)

*"(Tj) E tlj)

N N

PLF*^“^Tj)

Ep(T.) n. j^_2 ^-2

- [BL(Tj) - Q (Tj) 6"(Tj) y (T^)]

N

( 2 . 28 )

( 2 . 29 )

where Qp - BL(Tj) , when cycling occurs

“ between the heat pump

Qp

1

qk=2(xp and the furnace

otherwise

k«2 k=«2

PLF(Tj) = 1 - Cjj (1 - y(Tj))

( 2 . 30 )

( 2 . 31 )

0 ; £ **^OFF ikr— < 1 (3.413)(E (Tj))

6 (Tj) - 2

J Tqpp ^ Tj £ Tqjj and

.k=2 , Q (TJ

1 (3.413)(E (Tj))

( 2 . 32 )

1 ; ^

**'ON

.k=2

Q tT.)

(3.412)(E rXj))

In each of the above cases, the heating capacity Q(Tj), in kBtu/h, and the

power input fi (Tj), in kW, corresponding to low speed or single-compressor

operation (k»l), and high speed or two-compressor operation (k=2), shall

be calculated (when required) as follows:

13
.k=l .k=l

k=l IQ,,,; (62) - Q„ (47)1 (Tj - A7)

§ss (67) + 55 L___ : T, > AO-F

15

•k=l ^ . .k=l [QdEF^^^^

Qss

Qss^ 12)] (Tj - 17)

,k=l

t Oss (17) +

18

.k=l

; 17*F < Tj < A0“F (2.33)

QgS (17)] (T. - 17)

_!r 1—_; T. < 17®F

30

.k=*2

Q (Tj) =

U-, IQcI^A)) - Qcs^l7)] (T. - 17)

(17) +—55 1 ; Tj > A5'F orTj < 17 F (2.

bb 30

3A)

,k=2 [QdEf(^^^ “ ^SS (17)1 (l^j " 17)

Qss <i7) + ; 17*'F < T. < A5®F

18

.k=l . .k=l

e'^Itj)

• k=l

®SS (^7) +

.k=l

Egs (17) +

[Egg (62) - Egg (A7)] (T

j - A7)

.k=l

[Edef(^^)

15

Egs\l7)] (Tj - 17)

T. 2 A0*F

3

18

; 17“F 1 Tj < A0®F (2.35)

.k=l (^^)

^ss (1^)

Ess^(17)] (T. - 17)

i ; T,j < 17"F

30

^

u , IEc/(A7) - Ecc^l7)] (T, - 17)

Egs (17) + -55 -55 ^

; Tj > A5*F or Tj < 17»F

30

.k=

E ?Tj) = (2.36)

V=9 IEnFF(35) - 4s^( 17)1 (T-j - 17)

E^:^17) + — ; 17-F < Tj < A5-F

18

lA
k. Ic Ic • Ic • k • Ic where

• k .k

Qss(17) and Egg(17) are the capacities (in kBtu/h) and power (in kW) measured during the high temperature tests at 62 ®F, the high temperature tests

at 47®F, the frost accumulation tests at 35®F, and the low temperature tests

at 17®F, respectively. It should be noted that if these definitions of 0 (T-)

.k=2 J k Q (T *

and E (Tj) result in the quantity ^,5 being less than unity for

(3.413Kfi’‘-2(Tj))

a temperature Tj, then the value of 6”(Tj) used in the above HSOC calculation

are set equal to zero at this particular temperature T^. This avoids the

possibility of having an efficiency for the heat pump at an outdoor temperature Tj which is less than unity because of any errors introduced by the

straight line extrapolation of the measured capacities and power inputs

to low outdoor temperatures.

In the four cases described above, T^pp and Tqjj are, respectively, the outdoor temperatures at which compressor operation automatically stops and

automaticaly starts. If no such temperatures exists, then Tj is always

k=2

greater than and TQpp. The quantity Cp is the part load degradation

factor for the unit cycling at high compressor speed or with both compresk=l sors simultaneously cycling (if applicable), and Cjj is the part load

degradation factor for unit cycling at low compressor speed or with the

single compressor that normally operates at low heating loads (high outdoor

temperatures)

Appendix B presents a sample step-by-step calculation of the HSOC according

to the procedure described above.

Refer to DoE's "Test Procedure for Central Air Conditioners, Including

Heat Pumps." [1]

15
REFERENCES

1. "Test Procedures for Central Air Conditioners, Including Heat Pumps",

Federal Register, Vol. 44, No. 249, Dec. 27, 1979, pages 76700 through

76716.

2. "Test Procedures for Furnaces and Vented Home Heating Equipment",

Federal Register, Vol. 42, No. 91, May 10, 1978, pages 20147 through

20181.

16
2500

17

This

map

is

reasonably

accurate

for

most

parts

of

the

United

States

but

is

necessarily

highly

generalized

and

consequently

not

too

accurate

in

mountainous

regions

particularly

in

the

Rockies
Table 1. Major Climatic Regions In the Continental U.S.A. [1]

Region I II III IV V VI

Heating Load Hours, HLH 750 1250 1750 2250 2750 2750*

Outdoor Design Temperature,

Tqp for the region 37 27 17 5 -10 30

Fractional Hours, : N

Bin // Tj ("F)

j = 1 62 .291 .215 .153 .132 .106 .113

2 57 .239 .189 .142 .111 .092 .206

3 52 .194 .163 .138 .103 .086 .215

4 47 .129 .143 .137 .093 .076 .204

5 42 .081 .112 .135 .100 .078 .141

6 37 .041 .088 .118 .109 .087 .076

7 32 .019 .056 .092 .126 .102 .034

8 27 .005 .024 .047 .087 .094 .008

9 22 .001 .008 .021 .055 .074 .003

10 17 0 .002 .009 .036 .055 0

11 12 0 0 .005 .026 .047 0

12 7 0 0 .002 .013 .038 0

13 2 0 0 .001 .006 .029 0

14 -3 0 0 0 .002 .018 0

15 -8 0 0 0 .001 .010 0

16 -13 0 0 0 0 .005 0

17 -18 0 0 0 0 .002 0

18 -23 0 0 0 0 .001 0

* In Pacific Coast region

18
Table 2. Standardized Design Heating Requirements (kBtu/h)

5 25 50 90

10 30 60 100

15 35 70 110

20 40 80 130

19
Table 3. Example of Information Which Would Assist a Consumer in Purchasing a Heat Pump/Oil Furnace

System.

> °r)\

Heating Seasonal Operating

Cost ($)

^ < .80 1.00 1.20 1.40

REGION I

10

.04

.06

.08

.10

15

.04

.06

.08

.10

20

.04

.06

.08

.10

25

.04

.06

.08

.10

30

.04

.06

.08

.10

20
Table 4. Example of Information Which Would Assist a Consumer in Purchasing an Add-on Heat Pump.

21
Appendix A

Sample of Heating Seasonal Operating Cost Calculations for a Hybrid System

with a Single-Speed Compressor.

Sample calculations of Heating Seasonal Operating Cost for region V are given

below to show the sequence of calculating steps. The data employed is

for a fictitious hybrid system.

Rating Data for heat pump

Qss(^7®F) = 31.00 kBtu/h

Qdef( 35®F) = 24.00 kBtu/h

Qss( 17“F) = 17.00 kBtu/h

Cp = .25

Ess(47®F) = 3.430 kW

Egg(35*’F) = 3.150 kW

Ess( 17°F) = 2.770 kW

Rating data for furnace

Two examples are considered. The first assumes that a heat pump is added to

a previously installed gas, oil or electric furnace with Pp equal to 62%,

68% or 100% respectively and capacity Qp = 1.7 x DHR = 1.7 x 70 = 119,000

kBtu/h. The second example assumes that the hybrid system is sold with

a particular oil-fired furnace model of capacity = 119 kBtu/h and

an EFFY^ = 70% as determined from the DOE furnace test procedure.

Control information

The heat pump is the only source of heat as long as it can handle the

load alone. It thus supplies all the required heat above the balance

point. Below the balance point, it alternates operation with the furnace

down to the outdoor temperature T = 10“F, below which the heat pump is

22
turned off and the furnace satisfies the whole heating load. The heat

pump is turned on again at an outdoor temperature of T = 20®F

Thus Tqpp = 10®F and Tqn = 20®F.

Standard design heating requirements .

Using Equations (2.1), and (2.2) and Table 2, it is found for region V

that

°”^in " l^Btu/h

DHRjjjax = 2.2 QgsC^^^F) = 68.20 = 70.00 kBtu/h

The standard DHR's for which calculations shall be performed will thus be

30, 35, 40, 50, 60, 70 Btu/h as per Table 2.

Calculating Seasonal Operating Cost for DHR = 70 kBtu/h .

Table A1 presents sample worksheet for evaluation of the energy input to

the hybrid system for both considered cases for DHR = 70 kBtu/h in region V.

The number of heating load hours (HLH) and the design outdoor temperature

(Tod) were read from Table 1. An example showing how the figures in

the various columns were obtained is given below for the temperature bin

Tj = 27“F.

Column a, b and c : These values are read directly from Table 1

Column d : furnace capacity Qp, use eq. (2.10)

For example with a previously installed furnace

Qp = 1.7 X 709 = 119 kBtu/h

For example for the hybrid system sold with the

particular furnace Qp = Qout “ kBtu/h

23
Column e

column f

column g

so Qj. = 119 kBtu/h for both cases.

(Since the furnace capacities are equal, all calculations will be the same for both given examples

for DHR = 70 kBtu/h. In the calculations of the other

DHR's the capacity assumed for the previously Installed

furnace will be changed (Qp = 1.7 x DHR), while the

capacity of the second furnace will, of course, stay

= 119 Btu/h.)

heat pump capacity Q(Tj), use eq. (2.4)

Q(27) = Qgs(17) +

[QdEf(35) - Qss(17)] (27 - 17)

18

(24.00- 17.00) (27 - 17) = 17.00 + = 20.88 kBtu/h

18

: heat pump power E(Tj), use Eq. (2.5)

E(27) = Egg(17) +

[Ejjef( 35) - Egs(17)] (27 - 17)

18

(3.150 - 2.770) (27 - 17) = 2.770 + = 2.981 kW

18

: building load BL(Tj), use eq. (2.6)

BL(27) = X C X DHR = 65 - (-10) — X .77 X 70 = 27.31 kBtu/h

65 - (-10)

24
column h

column 1

column j

column k

column 1

column m

: heating load ^ BL(Tj)

BL(27) = .094 X 27.31 = 2.5671 kBtu/h

: low temperature cut-off factor, use eq. (2.7)

6(27) = 1

: heating load factor X(Tj), use eq. (2.8)

X(27) = 1

: furnace - heat pump cycling factor (2»9)

Qp - BL(27)

y(27) = Op - Q(27)

119.00 - 27.31

= .93

119.00 - 20.89

; part load factor PLF(X,y), use eq. (2.11)

PLF (X,y) = 1 - Cjj (1 - X(27) y(27)) =

= 1 - .25 (1 - 1 X .93) = .98

: heat pump energy Input

nj 6(27) X(27) y(27)

iT PLF (X,y)

E(27) =

(1)(1)(.93)

= .094 2.981 = .2662 kW

.98

25
column n : heating load handled by the furnace

-^[BL(27) - Q(27)5(27)X(27)y(27)] = N

kBtu

= .094 X [27.31 - 20.88 x 1 x 1 x .93] = .7319—

The above calculations must be repeated for each temperature bin. Then, to

obtain the heating seasonal operating cost, the sum of the results of column

h, m, n in Table A1 have to be applied as indicated by equation (2.3) along

with respective combinations of electricity and fuel prices. An example is

given below for electricity cost $.04/kWh, cost of oil $1. 00/gallon and cost

of gas $.26/therm.

Hybrid system sold with an oil furnace with Pp = 70%

HSOC = 2750 X .77 X 70

21.3084

1.6314 X .04 + 9.6934

100

70

1000

X

140,000

X 1.00] = $1142

Hybrid system added to an existing gas-fired furnace

HSOC = 2750 X .77 x 70

21.3084

[1.6314 X .04 + 9.6934

100 1000

X X

62 100,000

.26] = $737

Hybrid system added to an existing electric furnace. In the case of heat

pump being added to an existing system, the Heating Seasonal Operating Cost

becomes:

HSOC = 2750 x .77 X 70

21.3084

[1.6314 X .04 + 9.6934 x

1000

X

3413

.04 ] = $1220

The above calculation procedure was also performed for other standard

design heating requirements applicable to the analyzed system in region V

eq . 30, 35, 40, 50 and 60 kBtu/h. The final results for region V, rounded

26
off to the nearest $5 are shown In Tables A2 and A3. Table A2 presents

results for a heat pump sold with a particular furnace of efficiency

Dp - 0.70. Table A3 contains results for the same heat pump sold as an

add-on to a previously Installed oil, gas or electric furnace. Furnace

efficiencies employed In the latter case are respectively rip ^ 0.68,

0.62 and !•
Table A1

Sample Worksheet Used to Evaluate the Heating Seasonal Energy Input to a

Hybrid System with a Single-Speed-Compressor Heat Pump

CO o 0) ti •H •rn e C

Nw*' 'W' 'w' •w

(Uo

4-1 d

0) •r~i •H d

> H •HIz O •v) d

•H C 1 CO H CO t2 4-1 T) >4-; 0) (2. O CO d CO

n) V4 i-H CO • cy hJ O & O

(U 4-1 d d CO O D- O: 1-3 a d hJ 42 d u d d B ^ B bC /—

E *H B 0) rt o d (U 42 d -d 42 d d 42 W 42 >- d bO 'd 42 0 (0 d •H o O O, -H — o. •H "

d ^ O- d <u c a) (U 4-1 42 CO d a d d T3 *r-d •H d /—V /-*s X bO •H r—4 d

0^ O d 4J d CO -u 4-1 d) iH H 4-1 4J 4-1 •r-} •m '—' 4-1 d /—

>

4-1 T3 4-1 c a. B d d d PQ (0 a PQ CO •H PQ CO PQ H H H Fl^ CO <U IS CO d PQ •H 0) 0) d •H d <U CO 4«S <U o S d h4 4*1 <U 4<i Nw' 1-3 <U d 4<S QJ CO PQ pp; 4J Fi. 42 pt(. Cr w P2 O fC PQ PQ ^ CC to X Fd p~! <U v-x 32 42

1 62 .106 38.00

2 57 .092 35.67

3 52 .086 33.33

4 47 .076 31.00

5 42 .078

6 37 .087 24.78

7 32 .102 22.83

8 27 .094 20.89

9 22 .074 18.94

10 17 .055 17.00

11 12 .047 14.67

12 7 .038 119

13 2 .029

14 -3 .018

15 -8 .010

16 -13 .005

17 -18 .002

18 -23 .001

Region V

HLH = 2750

I^OD

" -10“F

DHR = 70 kBtu/h

3.760 2.16 .2285 1 .06

3.650 5.75 .5289 1 .16

3.540 9.34 .8034 1 .28

3.430 12.94 .9831 1 .42

3.298 16.53 1.2892 1 .62

3.192 20.12 1.7506 1 .81

3.087 23.72 2.4190 1 1 2.981 27.31 2.5670 1 1 2.876 30.90 2.2867 1 1 2.77 34.50 1.8972 .5 1 2.66 38.09 1.7901 .5 1 2.55 41.68 1.5839 0 1 45.27 1.3130 0 1 48.86 0.8796 0 1 52.46 0.5246 0 1 56.06 0.2803 0 1 59.65 0.1193 0 1 63.24 0.0632 0 1

21.3084

Z BL(T.) = 21.3084

j N V

, MTj) X(Tj) y(T.

j

N PLF(X.y)

1 .76 .0295 -

1 .79 .0684 -

1 .82 .1040 -

1 .85 .1273 -

1 .91 .1759 -

1 .95 .2366 -

99 1 .3127 .1118

93 .98 .2662 .7319

88 .97 .1931 1.0528

83 .96 .0659 1.5099

77 .94 .0513 1.5228

1 1 .0 1.5839

1 1 .0 1.3130

1 1 .0 0.8796

1 1 .0 0.5246

1 1 .0 0.2803

1 1 .0 0.1193

1 1 .0 0.0632

1.6314 9.6934

kBtu/h

- E(Tj) = 1.6314 kW

Z

j

^ [BL(Tj) - Q(Tj) 6(Tj)X(Tj)Y(Tj)] =

= 9.6934 kBtu/h

28
Table A2

Heating Seasonal Operating Cosj^ of Hybrid System with an Oil-fired Furnace in Region V.

V Heat pump + oil furnace

OyV

^ N. .80 1.00 1.20 1.40 \ \

.04 435 475 515 560

.06 570 610 655 695

30 .08 705 750 790 830

.10 845 885 925 965

.04 500 550 600 650

.06 655 705 755 800

35 .08 810 860 905 955

.10 965 1010 1060 1090

Region V .04 570 630 685 740

.06 740 795 855 910

40 .08 910 965 1025 1080

.10 1080 1135 1195 1250

.04 710 785 865 945

.06 905 980 1060 1140

50 .08 1100 1180 1255 1335

.10 1295 1375 1450 1530

.04 855 960 1065 1175

.06 1065 1175 1280 1385

60 .08 1280 1385 1495 1600

' .10 1495 1600 1705 1815

.04 1005 1140 1280 1415

.06 1230 1370 1505 1645

70 .08 1460 1595 1735 1870

.10 1685 1825 1960 2100

Tip = 0.70

29
Table A3

Heating Seasonal Operating Cost of Hybrid System with Oil, Gas or Electric Furnace* in Region V.

V

"

\

V

\

\

V\

\ V \

Add-on heat pump +

gas or oil furnace

Add-on

heat pump

+

electric

furnace

.26 .39 .52 .65 .78 .91

.40 .60 •

00 o 1.00 1.20 1.40

.04 355 400 440 480 525 565 505

.06 490 535 575 620 660 705 760

30 .08 625 670 710 755 795 840 1015

.10 765 805 850 890 930 975 1265

.04 405 460 510 560 610 660 590

.06 560 610 660 710 765 815 880

35 .08 715 765 815 865 915 965 1175

.10 870 920 970 1020 1070 1120 1470

.04 460 515 575 635 695 755 670

.06 625 685 745 805 865 925 1005

Region V 40 .08 795 855 915 975 1035 1095 1345

.10 965 1025 1085 1145 1205 1265 1680

.04 555 635 720 800 885 965 850

.06 750 830 915 995 1080 1160 1270

50 .08 940 1025 1105 1190 1270 1355 1695

.10 1135 1220 1300 1385 1465 1550 2120

.04 645 755 865 975 1090 1200 1040

.06 860 970 1080 1195 1300 1410 1560

60 .08 1070 1180 1290 1400 1515 1625 2085

.10 1285 1385 1505 1615 1725 1835 2605

.04 735 880 1020 1160 1305 1445 1220

.06 965 1105 1245 1390 1530 1675 1830

70 .08 1190 1335 1475 1615 1760 1900 2440

.10 1420 1560 1700 1845 1985 2125 3050

* “ .68, .62, 1 for oil, gas and electric furnace respectively.

30
Appendix B

Sample of Heating Seasonal Operating Cost Calculations for a Hybrid System

with a Two-Speed Compressor.

Sample calculations of Heating Seasonal Operating Cost for region IV are

given below to illustrate the steps involved.

Rating data of add-on heat pump .

k-1 k=2

kBtu/h 35.00 -(!)-

Qss kBtu/h 28.50 46.00

kBtu/h 21.00 37.00

kBtu/h 14.00 26.00

(62®F) kW 3.00 -(!)-

(47"F) kW 2.70 4.70

fi^Ep(35-F) kW 2.40 4.30

E^ (17*F) kW 1.80 3.90

C^ .25 -(2)-

(1) - not required

(2) - depending on control system, may be required. Not required

in control case presented here.

31
Rating Data for Furnace

The heat pump is assumed to be added to an existing gas, oil or electric

furnace. Since no furnace test procedure data is available, Pp are

assumed to be 62%, 68% and 100%, respectively, for the gas, oil and electric furnace.

Control Information

The heat pump is the only source of heat down to an outdoor temperature

35®F (1.67"C). Below this temperature it is shut off and furnace is

operated. The heat pump will restart after being shutoff [and furnace

will cease to operate] when outdoor temperature rises 10“F above the

cut-off temperature.

Thus Tqpp = 35"F (l.by^C) and Tqjj = 45“F (12.4"C)

Also subject to above stipulation the heat pump is designed to cycle between low

speed (k = 1) to high speed (k *• 2) when the building load is less than the

high speed capacity but greater than the low speed capacity.

Standard design heating requirements

Use equations (2.1), (2.2) and Table 2.

For region IV

= Q*^r^(47"F) -----QQ = 46.00 = 46.00 » 50.00 min '^ss ^

^ 60 60

65“T 65*“5

°^^max " 2 ~60~^ “ ^ ”6o“

' kBtu/h

From Table 2 the standard DHR will then be; 50, 60, 70, 80, 90 kBtu/h.

32
Calculating Heating Seasonal Operating Cost for DHR = 90 kBtu/h

Table B1 presents sample worksheet for evaluation of HSOC for

DHR “ 90 kBtu/h In region IV.

The number of heating load hours (HLH) and design outdoor temperature

(Tqj)) were obtained from Table 1.

HLH = 2250h Tqq = 5“F

Examples of calculations for bln temperature T = 42 ®F are shown below. ' M. I j

column a, b and c; obtain from Table 1.

column d

column e

: Since In this case a heat pump Is being added to an

existing furnace, Qp = 1.7 x DHR = 1.7 x 90 = 153 kBtu/h.

: the heat pump low speed capacity Q^~^(T.), use eq. (2.33)

k=l k=l

0

1^=1 _ . [Qss(62)- Q3 s(47)](42-47)

(42)" +

15

column f

_ (35.00 - 28.50) (-5) , = 28.50 +- —— 26.33 kBtu/h

15

k=2

: the heat pump capacity at the compressor's high speed, (Tj),

use eq. (2.34)

18

[37.00 - 26.00] X 25

= 26.00 + i 41.28

18 h

column g : the heat pump power at the compressor's low speed, E„|^~^(T 4 ), ' SS J use eq. (2.35)

33
column h

I l-^ss (62 )-Esg(47 )] [42-47 ] ss

13-00 - 2.70H-5) „ = 2.70 +- —— 2.60 kW.

15

: the heat pump high speed power, E^“'^(Tj), use eq. (2.36)

gk=2^/|0^ _ gk.=2Qy^ [Edep(35) - EggCl^)] [42-17]

18

o . [^.30 - 3.90] X 25 , ,, kBtu

18 h

column i ; the building load, BL(Tj), use eq. (2.6)

BL(42) =||^x C X DHR = x .77 x 90 = 26.57

65—5 65 — 5 h

column j : the heating load, —iBL(T-), is evaluated using columns

N J

( i ) and ( c )

iLlBLd.) = .100 X 26.57 = 2.6565 kBtu/h

N J

column k • Qoe^^2) < BL(42) < Q„„ (42), according to control information

the heat pump will cycle between low and high speed. This

implies case 2.

column 1 : The compressor cut-off factor ^(Tj)

use eq. (2.22)

<S'(42) = ^

34
column m the heating load factor with the compressor operating

column n

column o,p.

column r

column s

on low speed. for case 2 use eq. ( 2 . 20)

.k=2

Q (42) - BL(42)

41.28 - 26.57

41.28 - 26.33

: the heating load factor with the compressor operating on

k=2

high speed, X (Tj), for case 2 use eq. (2.21)

k=2 k=l

X (42) = 1 - X(42) = 1 - 0.98 = 0.02

: not appropriate in case 2

; the energy used by a heat pump in bin temperature

divided by the total number of bln hours, ,

use eq. (2.18):

n. k=l k=l k=2 k=2

= 6'(42) [E(42) X (42) + E (42) X (42)] = N N

= .100 X .5 X [2.60 X .98 + 4.46 x 0.02] = .1314 kW.

I_ U

: the heating load handled by a furnace in bin temperature

E (42)

divided by the total number of bin hours, — , for case

N

2 use eq. (2.19)

Ep(42) n.

= BL(42) [1 - 6(42)] = N N

kBtu

= 2.6570 X [1 - .5] = 1.3285

h

35
Once the worksheet calculations are finished heating seasonal operating

cost can be evaluated for each combination of electricity and fuel costs

for the given region and DHR using equation (2.12).

The following examples are given for electricity cost of $.05/kWh, cost

of oil $1. 00/gallon and cost of gas $. 26/therm:

Hybrid system added to a gas furnace

HSOC

2250 X .77 X 90

27.6333

100 1000

[.8504 ' X .05 + 19.5792 x x x

62 100,000

.26] =

= $703 = $705

Hybrid System added to an oil furnace

2250 X .77 X 90 100 1000

HSOC = [.8504 X .05 + 19.5792 x x — x 1.00] = $1400

27.6333 ' 68 140,000

Hybrid System added to an electlc furnace

2250 X .77 X 90 1000

HSOC = [.8504 X .05 + 19.5792 x x .05] = $1858 = $1860

27.6333 ' 3413 *

The above calculation procedure should be repeated for all standard DHR

(given in Table 2) ranging from the minimum to the maximum DHR.

The final results may be also displayed in the format presented in Table 3.

36
Table

Bl.

Sample

Worksheet

to

Evaluate

the

Heating

Seasonal

Energy

Input

to

Hybrid

System

with

a

Two-Speed

Compressor

or

with

Two

Compressors

(s)

(^)

(•’)

« (d)

(O)

(«)

(m)

(T)

(^)

(P)

(T)

(«1)

(8)

(?)

(*)

(P)

(=)

w

(»)

(M/n38M) —

(•D-^a

(M^)

T-^

JTd

d'la

(^1)9

3SV0

(H/nia^)igr^

(M/nia^)(^I)ig

(M^)

(q/n3a>i)(^i)^^^b

(q/maq)

sjnog niq 'dmaj^

XBUoxqoBjj

(do) ‘dmax

joop^no

niq djn^Bjadmax

o O O O lA tA -4- tA CO tA 00 tA o CO

« • • • 00 CM CM 00 tA -H o sO p«^ •4* o o O o CM sO O CO ON ON r*» CO tA 00

CO 00 00 r*- ON tA 00 -4* O

(O CM o O o o

so <}• 00 mT CO o o O O o o O o o O o sO ON • • • • • • • • *A sO ON CO ON o o o o o o o o o O kM

c < <! < •< < a a z a a a

rs. CM r-. CO < <! < < <5 < < < < < < r** OO 00 ON a a a a a a a a a a a • * • • < < < < < < •-H a a a a z a

< < c < CM < < < < <! < < < < a a a a O NO z a a a a a a a a

o a o> CO 00 sO <«! < < < < ••i: < < < CM ON CO a a a z a a a a a • • ' *

lA lA o o o o o o o o o • •

CM CM •4- '4- '4- '4'

cn SO lA <*• O O Mt tA 00 tA 00 lA O CO lA sO CO P*«. lA CM CO tA o sO P^ •4* >A CM CO lA CM O CO ON ON r- CO tA 00 O lA ON SO tA 00 CO ON tA 00 -4- o

CM CO CO CM o o O o

r*^ -a- CM ON r«* •4- CM ON px. «4* CM ON r«- -4* CM

CM O lA CO CO SX> '4* CM ON p*«. tA CO

• • • • • • • • • • • CO o> lA O sO CM 00 CO ON tA so CM 00 <r

CM CM CO CO «4* -4* tA SO so P^ P««. 00

o CO O SO CO CM O sO CO O CO Os CO -O CO CM o ON sO lA CO CM

• • • • « • • • • • lA -4- •4- CO CO CO CO CO CO

O o o o o so O CO r>* o tA o tA o tA O o> 00 r«s so CO ON 00 N^ tA CO CM O

CO CM CM CM CM CM CM CM

lA O lA o CO CM r«* sD o sO CO o sO CO

CM tA o CM CM O o sO CO o SO CO

• • • • • • • • • o\ A* \0 CO lA CM ON sO CM ON so CM o\ lA CO CO CO CM CM CM

O CO sO o CO 00 CO ON *4* o 00 tA CO CM o 00 so lA CO r«. «0 CO ON o tA P^ CO ON

lA CM O CO so ON tA Mf ON sO CO CO CO CM CM CM

CO

tA

CM CO CO o ON sO r>. tA sO SO CO sO CM »—

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NBS-114A (REV. 9-76)

U.S. DEPT. OF COMM. 1. PUBLICATION OR REPORT NO. i, '/ / ';4 BIBLIOGRAPHIC DATA

SHEET NBSIR 80-2090

4. TITLE AND SUBTITLE 5. Publication Date Estimating the Heating Seasonal Operating Cost of Residential

Hybrid Heat Pump Systems, Including Units Retrofitted to Oil,

Gas and Electric Furnaces

July 1980

Rtjffdtming Organization Code

. ^ .

. m.

7. AUTH0R{S)

George E. Kelly and Peter Domanski

8. Performing Organ. Report No. NBSIR 80-2090

9. PERFORMING ORGANIZATION NAME AND ADDRESS

• * < NATIONAL BUREAU’OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, DC 20234

11. Contract/Grant No.

12. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS CSfroer. city, St^te. ZIP)

Department of Energy

20 Mass . Ave. , NW

Washington, D.C. 20585

13. Type of Report & Period Covered

15. SUPPLEMENTARY NOTES

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

16. ABSTRACT (A 200-word or leas factual summary of most significant information. If document includes a significant bibliography or

literature survey, mention^it here,)

A method is presented for estimating the heating seasonal operating cost of a residential, hybrid heating system consisting of an electric heat pump and a warm-air

furnace. The approach described is applicable to a heat pump/control system/ gas or oil-fired furnace which is sold as a package or to a heat pump/control system which is

intended to be added to an existing gas, oil or electric furnace. Recommendations

are made regarding how such systems can be rated and the type of information that

would assist consumers in comparing the operating cost of a hybrid heat pump system

with that of a conventional heat pump or furnace. Different control strategies are accounted for and examples are presented (in the appendix) for estimating the heating

seasonal operating cost of hybrid systems employing both single and two-speed

compressors.

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name;

separated by semicolons)

Add-on heat pumps; furnaces; heat pumps; hybrid heat pumps; hybrid systems; rating

procedure; seasonal cost of operation

18. AVAILABILITY S3 Unlimited

I I For Official Distribution. Do Not Release to NTIS

I I Order From Sup. of Doc., U.S. Government Printing Office, Washington, DC

20402, SD Stock No. SN003-003-

[in Order From National Technical Information Service (NTIS), Springfield, VA. 22161

19. SECURITY CLASS

(THIS REPORT)

UNCLASSIFIED

20. SECURITY CLASS

(THIS PAGE)

UNCLASSIFIED

21. NO. OF

PRINTED PAGES

42

22. Price

$ 6.00

USCOMM-DC

7

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