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NBS

PUBLICATIONS

Rating Procedure for Mixed Air

Source Unitary Air Conditioners

and Heat Pumps Operating in the

Cooling Mode

Piotr A. Domanski

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Building Technology

Building Equipment Division

Gaithersburg, MD 20899

I

February 1986

Sponsored by:

-nr_L apartment of Energy

gton, DC 20585

100

• U56

86-3301

1986

NBS keseaech infosmatton CENTER

NBSIR 86-3301

4 • RATING PROCEDURE FOR MIXED AIR

SOURCE UNITARY AIR CONDITIONERS

AND HEAT PUMPS OPERATING IN THE

COOLING MODE

^6

I &0

U 5 (p

Piotr A. Domanski

U S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Building Technology

Building Equipment Division

Gaithersburg, MD 20899

February 1986

Sponsored by:

U.S. Department of Energy

Washington, DC 20585

U.S. DEPARTMENT OF COMMERCE, Malcolm Baldrige, Secretary

NATIONAL BUREAU OF STANDARDS, Ernest Ambler. Director

RATING PROCEDURE FOR MIXED AIR SOURCE UNITARY AIR CONDITIONERS AND

HEAT PUMPS OPERATING IN THE COOLING MODE

Abstract

A procedure is presented for rating split, residential air conditioners and

heat pumps operating in the cooling mode which are made up of an evaporator

unit combined with a condensing unit which has been rated under current

procedures in conjunction with a different evaporator unit. The procedure

allows calculation of capacity at the 95°F rating point and seasonal energy

efficiency ratio, SEER, without performing laboratory tests of the complete

system. This procedure has been prepared for the Department of Energy for

consideration in the rule making process.

Key Words: Air conditioner, central air conditioner, heat pump, mixed

system, mixed-matched system, rating procedure

iii
TABLE OF CONTENTS

Page

1. PURPOSE 1

2. SCOPE ..... 1

3. DEFINITIONS 1

4. PROCEDURE FOR RATING MIXED SYSTEM 3

4.1 Rating Correlations ....... 3

4.2 Indoor Coil Scaling Factor 5 4.2.1 Determination of the Indoor Coil Scaling Factor ... 5 4.2.2 Restrictions 6

4.2.3 Verification of Coil Capacity Determination Method . . 6

4.3 Expansion Device Scaling Factor 8

4.3.1 Determination of the Expansion Device Scaling Factor . 8

4.3.2 Restrictions 8

4.3.3 Equations for Calculating Expansion Device Scaling

Factor 11

4.4 Power Input to the Indoor Fan 13

4.4.1 Power Input to the Indoor Fan of the Matched System . 13

4.4.2 Power Input to the Indoor Fan of the Mixed System . . 14

4.5 Values of Ratings 14

4.5.1 Values of Capacity at Test A 14

4.5.2 Values of Seasonal Energy Efficiency Ratio, SEER ... 15

5. ALTERNATIVE RATING PROCEDURE FOR MIXED SYSTEMS 15

6 . REFERENCES 16

i v
1 . PURPOSE

The purpose of this report is to establish procedures for determining the

cooling performance ratings of air source unitary air-conditioners and heat

pumps consisting of a condensing unit and an evaporator which were not tested

together as a system. The performance ratings covered in this document are

the cooling capacity at Test A conditions and seasonal energy efficiency

ratio, SEER, defined by ARI Standard 210/240-84 [1], This rating methodology

is a composite of independent measurements and calculations made on an outdoor

unit in conjunction with a matched indoor coil, and a mixed indoor coil.

2 . SCOPE

This procedure applies to residential air-conditioning and heat pump systems

charged with Refrigerant 22 consisting of an indoor air-cooling coil assembly

and an outdoor single-phase, electric, air source unit whose matched system*

cooling capacity** is less than 65,000 Btu/h (19,050.0 V). This procedure

does not apply to systems employing multispeed compressors, or systems in

which compressor control strategy changes with load (e.g., cylinder unloads,

hot-gas bypass). Additional limitations as to the quantitative range of the

scope of this document are given in Sections 4.2.2 and 4.3.2.

3 . DEFINITIONS

All definitions included in or cited by ARI Standard 210/240-84 [1] shall be

considered part of this procedure in addition to the following definitions.

Refer to Section 3, Definitions.

**As defined by ARI Standard 210/240-84 [1]

.
3.1 ARI - Air Conditioning and Refrigeration Institute.

3.2 Air Source Unitary Air Conditioner or Air Source Unitary Heat Pump or

Unitary System - an outdoor unit combined with an indoor coil assembly.

3.3 Outdoor Unit - an assembly of refrigerating components designed to

compress and liquify a specific refrigerant. It consists of refrigerant

vapor compressor, air-cooled refrigerant coil, coil fan and motor,

and regularly furnished accessories. A liquid line solenoid valve and

other cyclic performance enhancing devices (excluding the expansion

device itself), if included in an air-conditioner or heat pump, are

considered to be a part of the outdoor unit.

3.4 Indoor Coil Assembly - an assembly consisting of a coil, condensate

collecting pan, and expansion device, and which may or may not include a

blower, motor and cabinet.

3.5 Matched Coil - an indoor coil which is a part of the matched

system.

3.6 Matched System - a unitary system which has been tested and

noted in accordance with ARI Standard 210/240-84 [1] and Part

430.23 of Title 10, Code of Federal Regulations [2].

3.7 Mixed Coil - an indoor coil which is used in a unitary

system instead of the matched ooil.

2
3.8 Mixed System - a unitary system which is not a matched

system.

3.9 Shall - where 'shall' or 'shall not' are used for a provision specified,

that provision is mandatory if compliance with the standard is claimed.

3.10 Should, Recommended, or It Is Recommended - 'should', 'recommended', or

'it is recommended' are used to indicate provisions which are not mandatory but which are desirable as good practice.

4. PROCEDURE FOR RATING MIXED SYSTEM

4.1 Rating Correlations

Mixed system capacity at DoE Test A condition, Qx

, shall be calculated using

equation 4.1. Mixed system Seasonal Energy Efficiency Ratio, SEERX

, shall be

calculated using equations 4.2, 4.3, and 4.4 (derivation of these

equations will be presented in a separate publication).

Q, =[«* + 3 - 413 ’ PF,m] ' Fc'

37 - Fe - 3 ' 413 ’ pF,x (4.1)

seek, - REe^ (4.2)

(V

) .

r +

3 .25 • ^al

\v L Qm J

(?*'\ - 0.8 * F®

14 * Fa

4 \Pm-182

c e

)ol s used in equations 4.1,

%

(4.3)

PF,m

(4.4)

3
Exponents

a = -0.15 for F

@ l 1

a = 0 for Fe

< 1

P = 0 for F

e 1 1

P = -0.2 for F < 1

Other Symbols

F„ = indoor coil scaling factor calculated as explained in section

c 4.2.1.

Fg = expansion device scaling factor calculated as explained in section

4.3.1.

RfXV = thermostatic expansion valve factor. (Shall be evaluated as shown in

Table 1).

Pp

m

= power input to the indoor fan of a matched system as defined in

Section 4.4.1 (watt).

Pp

x = power input to the indoor fan of the mixed system as defined in

Section 4.4.2 (watt).

Qjjj = capacity of the matched system at Test A as certified by its

manufacturer (Btu/h)

.

Qx = capacity of a mixed system at Test A, as calculated by equation

4.1 (Btu/h).

= ratio of capacities at Test B conditions of the mixed and

matched system.

= ratio of power inputs at Test B conditions of the mixed and

matched system.

SEEB^ = seasonal energy efficiency ratio of the matched system

(Btu/h * watt) as certified by its manufacturer.

4
SEER I = seasonal energy efficiency ratio of the mixed system (Btu/(h * watt))

as calculated by equation 4.2.

4 .2 Indoor Coil Scaling Factor

4.2.1 Determination of the Indoor Coil Scaling Factor

The indoor coil scaling factor, F . is defined by the following equation:

c

F - (4.5)

c Q^c ,m

where

Q„ _ = cooling capacity of a mixed coil at the air mass flow rate specified

for the mixed system. The air mass flow rate specified for the mixed

system shall satisfy conditions of section 5. 1.3. 3, ARI Standard

210/240-84.

Qc m

= cooling capacity of a matched coil at the indoor-air volumetric flow

3 rate, CFJ^ (ft /min), at which matched system capacity, C^, was

measured. If CFJC information is not available, the value for the

indoor air volumetric flow rate shall be calculated as follows:

CFM = — ‘ 425 (ft3 /min) . (4.6) ^ 12000

Capacities of matched and mixed coils shall be obtained using the same

verified method (see Section 4.2.3). Coil capacities shall be obtained

at the following conditions:

5
inlet air conditions - 80°F dry bulb/67°F wet bulb

refrigerant saturation temperature at the evaporator outlet -

45°F

identical refrigerant superheat at the evaporator outlet

If coil capacities are obtained by means of a catalog or computer

simulation, the same catalog or computer simulation shall be used for

both coils. Coil material and geometry (e.g., inside tube diameter,

tube staggering, fin spacing, fin thickness, fin shape, and number of

tube depth rows) shall be accounted for by the method used. That is,

the methodology used must have these parameters as independent

variables

.

4.2.2 Restrictions

The acceptable range of values for the indoor coil scaling factor, F„, is from

0.8 to 1.3. This rating procedure shall not be used if the indoor coil

scaling factor is smaller than 0.8. If the ratio GL ,,/CL _ results in a value

v i x c p in greater than 1.3, the value of the indoor coil scaling factor, F

c

, shall be

1.3.

4.2.3 Verification of Coil Capacity Determination Method

A variety of methodologies exist for calculating the capacity of a coil based

on material and geometry data only. For example, several large heat exchanger

manufacturing companies publish catalogues of performance curves for their

specific products which are commonly used in a generic fashion. That is, the

capacity of coils of the same materials and of the same number of rows, tube

patterns and diameters, fin spacing, shape, and thickness is assumed to be the

6
same for all manufacturers. Similarily there exist many computer simulations

which are based either on regression analysis of the above mentioned catalogue

data or on first principles of the heat transfer phenomena involved. If a

specific methodology of either of these categories has at least the independent variables listed above, it may be used in this procedure to predict the

capacities of the coils (i.e., Q„ „ and CL J. However, the specific methoV ; A © 9 Juft dology chosen must be verified by test, in accordance with ASHRAE Standard 33-

78 [3] and ARI Standard 410-81 [4], to demonstrate that it is sufficiently

accurate to simulate the coil line which is being used in the mixed system

rating.

This verification requires that, for a given coil line, the capacity range

over which the methodology is being used to predict values must be straddled

by at least two tests which are within 5% agreement with the predictions. For

example; if a manufacturer produces a line of coils with six sizes having

capacities ranging from 20000 Btu/h to 33000 Btu/h and uses a single methodology (e.g., computer simulation) to predict the six individual capacity values,

the methodology must be within 5% agreement with the test values of a coil

from that line which is _< 20000 Btu/h and >. 33000 Btu/h. A similar pair of

tests straddling the matched coil is also required if the methodology has not

been previously verified for that line.

A coil line is defined as a group of coils which are of the same materials and

bonding procedure, configuration (i.e., flat or A-shape) , row staggering, fin

thickness, fin spacing, fin shape (i.e., flat, wavy, corrugated edge, etc.),

tube diameters and internal surface finish. If any of these parameters differ

then a new coil line has been defined and a new verification test pair is

7
required for the methodology.

It is recognized that different numbers of tube rows and circuitry are not

being considered as defining a new coil line; yet they probably have a

significant effect on performance, all other parameters being held constant.

However the state of the art of coil performance simulation or representation

is such that these variables are seldom considered. Some first principle

computer simulation programs, such as the one used to develop this standard,

do exist but they are not widely available and are usually so complex that

input errors are easily possible. It therefore appears unreasonable to

require this degree of sophistication for coil rating at this time.

4 .3 Expansion Device Scaling Factor

4.3.1 Determination of the Expansion Device Scaling Factor

The expansion device scaling factor, F. , depends on the types of matched and

mixed expansion devices involved. It shall be a determined using Table 1

which provides a value for the scaling factor or refers to an equation by

which the scaling factor shall be calculated.

4.3.2 Restrictions

This rating procedure shall not be used if:

a) the expansion device scaling factor, F

e

, calculated by the

recommended equation is less than 0.85, or greater than 1.35.

b) the matched system employs a thermostatic expansion valve and the

mixed system employs a capillary tube or an orifice.

8
c) the mixed expansion device consists of capillary tubes or orifices

connected in series.

d) the matched expansion device consists of capillary tubes or orifices

connected in series unless the mixed expansion device is a

thermostatic expansion device.

9
Table 1. Evaluation of the Expansion Device Scaling Factor, F

Q

, and tbe

Thermostatic Expansion Value Factor,

Expansion Device

17 fTXV

Matched System Mixed System

TXV. no bleed TXV, no bleed* 1.0 1.000

TXV, no bleed TXV, w/bleed* 1.0 0.975

TXV, w/bleed TXV, no bleed* 1.0 1.025

TXV, w/bleed TXV, w/bleed* 1.0 1.000

Capillary

or Orifice

TXV, no bleed** 1.0 1.050

Capillary

or Orifice

TXV, w/bleed** 1.0 1.025

Capillary Capillary eq. 4.7 1.000

Capil lary Orifice eq. 4.8 1.000

Orifice Capillary eq. 4.9 1.000

Orifice Orifice eq. 4.10 1 .000

*the mixed TXV shall have equivalent capacity and same superheat setting as the matched TXV.

**the mixed TXV shall have equivalent capacity as the matched expansion device

10
4.3.3 Equations for Calculating Expansion Device Scaling Factor

The expansion device scaling factor, Fg, is the ratio of refrigerant mass flow

rates through the mixed and matched expansion devices at the same operating

conditions.

This section provides equations for calculating the expansion device scaling

factor, F0

. Subscripts i and j in all equations below correspond to the

V number of parallelly connected capillary tubes or orifices in the mixed and

matched expansion devices, respectively. Symbol D denotes the inner diameter

(inch) and symbol L denotes the length (inch) of a capillary tube or an

orifice. Subscripts x and m refer to mixed and matched expansion devices,

respectively. If inner diameter or length is required in the recommended

equation, it should be measured by methods providing precision of + 1.5%.

If a matched expansion device and a mixed expansion device consist of

capillary tubes, the following equation shall be used:

where (J>x and <£> m

are flow factors for capillary tubes employed in the mixed and

matched expansion devices, respectively, determined based on their geometry

with the aid of the ASHRAE Handbook, Equipment Volume, 1983, Chapter 20,

Figure 38 [5]

.

If a matched expansion device consists of capillary tubes and a mixed expansion

device consists of orifices the following equation should be used:

(4.7)

11
(4.8)

10976

3>x.l + $x.2 + + ®x.i

109 . 6(^1 + 3>m#2 + ... 3> ffi>j

)

where

n2

* = 7220Q D x

x Lt 0.5

(0.58 + 0.008

(Jjju = flow factor for a capillary tube employed in a matched expansion

device, and determined based on geometry with the aid of ASHRAE

Handbook, Equipment Volume, 1983, Chapter 20, Figure 38 [5].

If a matched expansion device consists of orifices and a mixed expansion

device consists of capillary tubes the following equation should be used:

= 109 - 6 ’I>x.i = 109.6(3^ + <t>x , 2 + + $x .j ) 2>... s> . + 4 A +

m, 1 ^m,2 + <i>, (4.9)

®, j

where

- flow factor for a capillary tube employed in a mixed expansion

device, and determined based on geometry with the aid of ASHRAE

Handbook, Equipment Volume, 1983, Chapter 20, Fig. 38 [5].

- = 72200

y 0 5

(0.58 + 0.008 —

D„

12
If a matched expansion device consists of orifices and a mixed expansion

device consists of orifices the following equation should be used:

F - Xfex.i = Q.l + ^x.2 + $x,i

6 XfonJ $m,l + <^m,2 + •* ,<J)m,j

where

3> = L 0.5

(0.58 + 0.008

*

L 0.5

(0.58 + 0.008 -2)

D_

4.4 Power Input to the Indoor Fan

4.4.1 Power Input to the Indoor Fan of the Matched System

Power input to the indoor fan. Pp m

shall be measured in accordance with the

ARI Standard 210/240-84 [1] at the indoor-air volumetric flow rate, CFM . at which m capacity of the matched system, C^, was measured. If CFMjq information is not

available, the value for the indoor-air volumetric flow rate shall be

calculated by equation (4.6). If the indoor fan is not supplied with the

system, Pp shall be evaluated by the equation:

PF,m " °-3«5 ‘ CTM* (4.11)

3 where CFMju (ft /min) is a volumetric flow of air through the matched

indoor coil at which system capacity, G^, was measured.

13
4.4.2 Power Inpat to the Indoor Fan of the Mixed System

Power inpat to the indoor fan, Pp

x

, shall be measured in accordance with the

ARI Standard 210/240-84 [1] at the indoor volumetric air flow rate, CFMX

, at which

capacity of the mixed system, Qt

, is evaluated. If the indoor fan is not

supplied with the system, Pp

x shall be evaluated by the equation:

PF,x

= °- 365 * CFM

x (4.12)

where CFM

s (ft /min) is the volumetric flow of air through the mixed indoor

coil at which the capacity of the mixed system, Qz

, is to be evaluated.

4 .5 Values of Ratings

4.5.1 Values of Capacity at Test A

The capacity at Test A shall be expressed in of Btu/h (W) in multiples

of:

Capacities Multiples

Btu/h (W)

Less than 20,000 (less than 5,900)

20.000 up to 38,000 (5,900 up to 11,000)

38.000 up to 65,000 (11,100 up to 19,000)

65.000 and above (19,000 and above)

Btu/h (V)

100 (30)

200 (60)

500 (150)

1,000 (300)

The capacity value shall not exceed Qx value as calculated

by equation (4.1).

14
4.5.2 Values of Seasonal Energy Efficiency Ratio, SEER

The Seasonal Energy Efficiency Ratio, SEER, shall be expressed in mnltiples

of 0.05. The Seasonal Energy Efficiency Ratio shall not exceed SEER£

as

calculated by equation (4.2).

5. ALTERNATIVE RATING PROCEDURE FOR MIXED SYSTEMS

The large number of variables and the complexities of their interactions

associated with an air conditioner always make theoretical or quasi-empirical

rating procedures less certain than a whole system test. Therefore, an

acceptable alternative to this entire methodology is a formal certification

program in which a significant number of the mixed systems created by the use

of a single coil line is measured. At this time, the ARI Unitary Certification Program for Coil Manufacturers is the only known program with the objectivity and technical sophistication to be accepted in lieu of this rating

procedure. However, other test programs may develop in the future and they

should be submitted for consideration.

15
6 . REFERENCES

1. Air-Conditioning and Refrigeration Institute, Standard 210/240-84,

Standard for Unitary Air-Conditioning and Air Source Heat Pump Equipment,

Arlington, Virginia, 1984.

2. Code of Federal Regulations, Title 10, Part 430.23, Washington, D.C.,

1985.

3. American Society of Heating, Refrigerating, and Air-Conditioning

Engineers, Inc., Standard 33-78, Method of Testing Forced Circulation AirCooling and Air-Heating Coils, New York, NY 1978.

4. Air-Conditioning and Refrigeration Institute, Standard 410-81, Standard

for Forced-Circulation Air-Cooling and Air-Heating Coils, Arlington, Virginia,

1981.

5. American Society of Heating, Refrigeration, and Air-Conditioning

Engineers, Inc., ASHRAE Handbook, Equipment Volume, Chapter 20, Fig. 38,

Atlanta, GA, 1983.

16
NBS-1 14A IHEV. 2-80

U.S. DEPT. OF COMM. 1. PUBLICATION OR 2. Performing Organ. Report No. 3. Publication Date BIBLIOGRAPHIC DATA

SHEET (See instructions)

REPORT NO. 86-3301 FEBRUARY 1986

4. TITLE AND SUBTITLE

K il in.; Procedure for Mixed Air Source Unitary Air Conditioners and Heat Pumps

Operating in the Cooling Mode

5. AUTHOR(S)

Domanski, P.A.

6. PERFORMING ORGANIZATION (If joint or other than NBS, see in struction s) 7. Contract/Grant No. national bureau of standards

DEPARTMENT OF COMMERCE 8. Type of Report & Period Covered

WASHINGTON, D.C. 20234

9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street, City, State, ZIP)

U.S. Department of Energy

Washington, D.C. 20585

10. SUPPLEMENTARY NOTES

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

11. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here)

A procedure is presented for rating split, residential air conditioners and

heat pumps operating in the cooling mode which are made up of an evaporator unit

combined with a condensing unit which has been rated under current procedures in

conjunction with a different evaporator unit. The procedure allows calculation

of capacity at the 95 F rating point and seasonal energy efficiency ratio, SEER,

without performing laboratory tests of the complete system. This procedure has

been prepared for the Department of Energy for consideration in the rule making

process

.

12. KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicolons)

air conditioner; central air conditioner; heat pump; mixed system; mixed-matched

system; rating procedure

gvA. ^

A

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