Residential Central

Air-Conditioner,

Small Duct,

High Velocity (SDHV)

Systems Standards

Rulemaking

Engineering Analysis

Draft Report for Review

Prepared for:

Building Technology Program

Office of Energy Efficiency and

Renewable Energy

U.S. Department of Energy

Prepared by:

Navigant Consulting, Inc.

1801 K St, NW

Suite 500

Washington, DC 20006

November 26, 2002

EE-RM-STD-02-330 COMMENT 01E
Foreword

The U.S. Department of Energy (DOE) issued a final rule on May 23, 2002 (67 FR

36368), increasing the minimum efficiency standards for most residential central air

conditioners and heat pumps to 12 SEER/7.4 HSPF. However, during the rulemaking process,

DOE received information indicating that the special characteristics of small duct, high velocity

(SDHV) air conditioner and heat pump systems make it unlikely that such systems could meet

minimum efficiency standards established for conventional products . Consequently, both the

SDHV manufacturers and the industry trade association , the Air-Conditioning & Refrigeration

Institute (ARI), supported the creation of a separate product class for SDHV systems and the

development of technologically feasible and economically justified standards for this product.

In the May 23, 2002 , final rule, DOE agreed that SDHV systems should not be subject

to the standards set for conventional products. DOE established a separate product class for

SDHV systems based on the following definition:

"Small duct, high velocitystem means a heating and cooling product that contains a

blower and indoor coil combination that: (1) Is designed for, and produces, at least 1 . 2 inches

of external static pressure when operated at the certified air volume rate of 220-350 CFMper

rated ton of cooling; and (2) When applied in the field, uses high velocity room outlets generally

greater than 1000 fpm which have less than 6.0 square inches of free area. "

In the May 23, 2002 final rule, DOE retained the 10 SEER / 6.8 HSPF standards

established under the National Appliance Energy Conservation Act (NAECA) for SDHV

systems, pending further study to establish appropriate higher standard levels. DOE also stated

its intention to publish a final rule for the test procedure in which minimum efficiency standards

for SDHV systems will be based on the testing requirements developed for SDHV systems in

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EE-RM-STD-02-330 COMMENT 01E
the air conditioning test procedure revision currently being finalized, or in a future revision

specifically aimed at SDHV products.

DOE determined that additional analysis on the cost and technical issues related to

SDHV air conditioner and heat pump products was needed to determine appropriate minimum

efficiency standards for this class of product. DOE's plan for establishing the manufacturing

cost and efficiency relationship for SDHV systems was to involve the manufacturers that

produce these products.

The intention of this report is to document the methodology and assumptions used in the

Engineering Analysis which develops the relationship between cost and efficiency for SDHV

systems. A separate spreadsheet' enables a user to reproduce the results of the Engineering

Analysis using the current assumptions or to revise the assumptions. The cost-efficiency

relationship from the Engineering Analysis is an input to the Life-Cycle Cost (LCC) Analysis

discussed in a separate report. A spreadsheet for the LCC Analysis' also allows a user to

reproduce the LCC results.

I http://www.eren.doe.gov/buildings/codes_standards/applbrf/central_air_conditioner.html

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EE-RM-STD-02-330 COMMENT 01E
TABLE OF CONTENTS

1. Introduction ............................................................................................................................ 6

1.1 SDHV Systems Description .................................................................................... 6

1.2 Comparison with Conventional Split Systems ......................................................... 7

1.2.1 Coil Geometry ............................................................................................ 7

1.2.2 Air Flow Rate ............................................................................................. 8

1.2.3 Blower Static Pressure ............................................................................... 8

1.2.4 System Power Consumption ...................................................................... 8

1.3 Industry ..................................................................................................................... 9

2. Engineering Analysis .............................................................................................................. 10

2.1 Data Sources ............................................................................................................ 10

2.2 Modeling SDHV System Performance .................................................................... 11

2.2.1 NIST Rating Method for Split Air Conditioning Systems ......................... 12

2.2.2 NIST Rating Method Specialized for SDHV Rulemaking ....................... 12

2.2.2.1 System Assumptions Specific for

SDHV Rulemaking Analysis ...................................................... 13

2.2.2.2 Other Assumptions ..................................................................... 14

2.2.2.3 Discussion of Assumptions ........................................................ 16

2.3 Description of Baseline SDHV System .................................................................... 19

2.4 Design Options ........................................................................................................ 19

2.4.1 Increased Efficiency of Blower Coil Components .................................... 20

2.4.2 Reduced Air Flow ..................................................................................... 21

2.4.3 Selection of Condensing Units .................................................................. 22

2.4.4 Use of Emerging Technologies ................................................................. 23

2.4.5 Max Tech .................................................................................................. 23

2.5 Conclusions on Design Options ............................................................................... 23

2.6 Estimated Cost Impacts ............................................................................................ 24

2.6.1 Increased Coil Size .................................................................................... 24

2.6.2 Higher Efficiency Condensing Unit .......................................................... 24

2.7 Distribution Chain Markups ..................................................................................... 26

2.8 Sensitivity Analysis .................................................................................................. 27

2.9 Heat Pumps .............................................................. ........ 29

2.10 Air-Distribution Systems and Installation Costs .................................................... 30

2.11 A Note on SDHV Cooling Capacity ....................................................................... 31

2.12 Summary of Results ................................................................................................ 32

Appendix A: NIST Method for Rating Mixed Air Conditioning Systems ................................ 34

Appendix B: Performance Equations .......................................................................................... 39

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EE-RM-STD-02-330 COMMENT 01E
LIST OF TABLES

Table 1: Physical Characteristics of Baseline Models ............................................................... 19

Table 2: Cost Allocation for Outdoor Unit ................................................................................ 25

Table 3: Condensing Unit Consumer Costs ............................................................................... 26

Table 4: Variability and/or Uncertainty Ranges for the Assumptions Considered in the

Sensitivity Analysis ........................................................................................................ 28

Table 5: Consumer Costs as a Function of SDHV Efficiency and Coil Size ............................ 33

LIST OF FIGURES

Figure 1: Distribution of Typical Fan Efficiencies for Small-Size Motors ............................... 17

Figure 2: Correlations Between Coil Size and Coil Capacity................................................... 18

Figure 3: Typical Crystal Ball Output for a SDHV Sample ...................................................... 29

Figure 4: Cost-Efficiency Curve ................................................................................................ 33

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EE-RM-STD-02-330 COMMENT 01E
1. INTRODUCTION

1.1 SDHV Systems Description

Small-duct, high-velocity (SDHV) systems are a type of air-cooled, split-system central

air conditioning and air conditioning /heat pump systems considered by DOE to be "spaceconstrained," thus requiring special consideration in determining the technical feasibility and

economic justification criteria required for a new efficiency standard.

SDHV air conditioning systems currently marketed in the U.S . are similar to

conventional split system air conditioners that consist of an outdoor condensing unit and an

indoor coil unit, with or without an integral blower. A unique feature of SDHV systems is the

air distribution system. The air distribution system together with the blower-coil unit is usually

installed in attic spaces of older homes that were not designed for forced -air circulation heating

or cooling. Such homes lack conventional (i.e., large-size, low velocity) ducts, which are costly

and difficult to retrofit. Thus, installation of a SDHV system helps satisfy the air conditioning

needs for these older homes, replacing less efficient window air conditioners.

The air distribution system is comprised of a ceiling-mounted return grill and return air

duct which delivers room air to the blower-coil unit and a supply air system which delivers

conditioned air from the blower-coil unit to various spaces within the building . The supply

system consists of an insulated, rigid plenum, 7 to 9 inches in diameter, usually running the

length of the attic space. A series of flexible two-inch diameter branch ducts, which are small

enough to be concealed within wall spaces, are connected to the plenum . Each branch duct

terminates with a supply air outlet. The ceiling-mounted outlets deliver supply air at a velocity

of at least 1000 feet per minute (fpm) where the high velocity air enters, entraining and mixing

with room air.

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EE-RM-STD-02-330 COMMENT 01E
The outdoor condensing units used in SDHV systems are typically sourced from a full

line manufacturer of conventional split systems. These condensing units are identical to those

used by the full-line manufacturers in their product lines of conventional systems. A SDHV heat

pump system is comprised of a conventional outdoor heat pump unit and an indoor blower-coil

unit and duct system similar to that used for cooling, except that the blower-coil unit is equipped

with a larger coil for refrigerant management and a back-up heat source, such as a resistence

heating element or hot water coil, is added.

1.2 Comparison with Conventional Split Systems

The blower-coils used in SDHV systems are different from those used in conventional

split systems. The significant differences are discussed in this section.

1.2.1 Coil Geometry

The indoor coils of SDHV systems, while constructed of copper tubing and aluminum

fins and having design features similar to that of indoor coils for conventional systems, usually

have a smaller face area and contain more rows of coil. A key performance attribute for a SDHV

system is called its "core volume," which is the product of the number of coil rows and the coil

face area. Since the number of coil rows is a surrogate for coil depth, the product of coil rows

and face area is related to volume (and weight). As will be discussed in Sections 2.4.1 and

2.6.1, core volume has a major impact both on performance and cost. Indeed, the relationship

between core volume of SDHV systems and core volume of matched indoor coils, which can

vary over a wide range, has a major impact on SDHV system performance.

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EE-RM-STD-02-330 COMMENT 01E
1.2.2 Air Flow Rate

Conventional air conditioning systems are usually designed to operate with an indoor air

volumetric air flow rate per rated ton (12,000 Btu/h) of cooling capacity at 400 cubic feet per

minute (CFM) per ton. In contrast, SDHV systems are designed to operate at ranges from 50 to

70 percent of the nominal 400 CFM/ton of conventional systems, or 200 to 280 CFM per

nominal ton. However, matching an SDHV blower coil unit with a conventional outdoor unit

reduces its rated capacity by 10 to 20 percent. Therefore, the CFM per actual ton of a SDHV

system is in the range of 220 to 310 CFM/ton.

1.2.3 Blower Static Pressure

Because of the small duct size of SDHV systems, air velocity is much greater than with

conventional systems, resulting in higher frictional loss in the air distribution system. SDHV

systems are rated for performance with a minimum external static pressure of 1.20 inches of

water. Conventional systems are rated for performance with a minimum external static pressure

that ranges from 0.10 to 0.20 inches of water, depending on system capacity.

The air-side pressure drop across the SDHV indoor coil is approximately equal to that of

conventional systems, which for a wet coil is typically about 0.30 inches of water and for a dry

coil is typically about 0.20 inches of water.

1.2.4 System Power Consumption

The blower coil unit for SDHV systems operates with reduced air flow compared to

conventional air conditioning systems and supplies chilled air to the occupied space through a

system of small-size ducts. Because of the reduced volumetric rate of air flow through the

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EE-RM-STD-02-330 COMMENT 01E
blower coil units' evaporator, air temperature delivered to the conditioned spaces is lower (and

its humidity ratio is lower) than that of conventional systems. The reduced air flow through the

evaporator also decreases the refrigerant pressure leaving the evaporator and returning to the

compressor in the outdoor unit, which decreases the compressor's capacity and efficiency.

Also, the higher friction in the small ducts increases the work performed by the blower, which

increases the blower motor's power consumption. Because of the higher compressor and blower

power, a SDHV system usually operates with a lower efficiency and capacity than those of the

matched system. Thus, to achieve the current 10 SEER minimum efficiency, a SDHV blowercoil must often be matched with a condensing unit which is rated at higher efficiency and

capacity. Consequently, SDHV systems are less amenable than conventional systems to

increases in efficiency standards.

1.3 Industry

Two companies produce SDHV systems: Unico, Inc. and the SpacePak Division of

Mestek Incorporated. These companies typically out-source production of all components of the

blower coil units and function as assemblers. They also out-source production of most

components used in the duct distribution system, manufacturing only the components that are

unique to their designs. More information is available on the manufacturer web sites at

http://www.UnicoSystem.com and http://www.SpacePak.com.

The total market for SDHV systems is estimated to be less than 20,000 units/year2, or

about one-half of one percent of the total market for residential central air conditioning systems.

Because SDHV blower-coil components are currently outsourced, the impacts of increased

efficiency standards on the production facilities of SDHV manufacturers is likely to be small3.

2 Estimate based on private communications with manufacturers.

3 Determination of impacts of standards on SDHV manufacturers is not within the scope of this analysis.

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EE-RM-STD-02-330 COMMENT 01E
Z. ENGINEERING ANALYSIS

The Engineering Analysis develops the relationship between the efficiency and cost of a

central air conditioner or heat pump. This relationship serves as the basis for the subsequent

life-cycle cost analysis. Determining the cost-efficiency relationship involves analysis of the

options available to manufacturers for increasing the efficiency of a baseline product (i.e., one

that just meets the minimum efficiency standard). In general, the options available to SDHV

manufacturers which result in higher SDHV system efficiencies are limited to a) design changes

or operational constraints to blower coil units; b) pairing of existing SDHV blower coil models

with more efficient outdoor units; and c) a combination of options a and b. Because of the small

market share of SDHV blower coil units, unitary systems manufacturers do not have strong

incentives to redesign their outdoor units for optimal SDHV applications, therefore, outdoor unit

redesign is not considered a viable option.

2.1 Data Sources

The Engineering Analysis for SDHV systems used technical and cost data obtained from

both public and private sources. The public data used included published materials from

Chapter 4 of the Technical Support Document (TSD) produced for the Central Air Conditioning

(CAC) rulemaking4, data from the ARI certification data base, and materials published in

manufacturer catalogs. The private data included non-published information obtained by Arthur

D. Little, Inc., obtained under non-disclosure agreements with several air conditioner

manufacturers during the CAC rulemaking and data obtained by Navigant Consulting, Inc.,

under non-disclosure agreements with Unico Inc. and the Spacepak division of Mestek, the two

SDHV systems manufacturers.

4 http://www.eren.doe.govibuildings/codes standards/applbrf/central_air_conditioner.html

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EE-RM-STD-02-330 COMMENT 01E
All the assumptions, results and formulas used in the Engineering Analysis, with the

exception of data covered by non-disclosure agreement, are available for stakeholders' review in

the form of a worksheet posted on the DOE web site.' The worksheet is designed such that

users can verify assumptions, analyze sensitivities, review methodologies and submit comments.

Additional information is contained in the worksheet itself.

2.2 Modeling SDHV System Performance

System performance, along with cost estimates, is one of the two key factors in the

Engineering Analysis. To estimate SDHV system performance, DOE took advantage of an

existing rating method that is currently available for use by industry to rate split-system air

conditioners. The rating method is particularly useful for the intended purpose because its use

avoids the need for testing, computer simulation or equipment teardown.

In rating split-system air conditioners and heat pump systems for efficiency, DOE

requires a unitary system manufacturer to test the highest likely sales volume combination of

indoor and outdoor units they produce. For other indoor-outdoor unit combinations produced

by the same manufacturer, or in part by a component manufacturer using the same outdoor unit,

DOE allows the efficiency rating to be determined by an alternative rating method. The

alternative rating method, which must be requested by a manufacturer and approved by DOE,

must be supported by test data, as specified in the Code of Federal Regulations. One such rating

method, developed by the National Institute of Standards and Technology (NIST), is accepted

by DOE.

' http://www.eren.doe.gov/buildings/codes_standards/applbrf/central air_conditioner.htmI

6 10 CFR part 430, section 430.24(m)(2)

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EE-RM-STD-02-330 COMMENT 01E
2.2.1 NIST Rating Method for Split Air Conditioning Systems

The NIST rating method for air conditioning systems is described in the U.S.

Department of Commerce Report, NISTIR 89-40717. The NIST rating method uses measured

performance data for a "matched system" or tested combination of outdoor and indoor units and

calculates the performance with a different indoor unit substituted for the tested indoor unit.

The non-tested combination is called a "mixed system." The technical basis for the NIST rating

method is described elsewhere.' The stated purpose of the NIST rating method is to account for

the interaction of three components deemed most likely to be changed in a matched system: the

indoor evaporator coil, the indoor fan, and the expansion device. Specific equations and

constraints for the NIST rating method are excerpted from the 1989 NIST report and provided in

Appendix A.

2.2.2 NIST Rating Method Specialized for SDHV Rulemaking

This section describes the specific assumptions made in the Engineering Analysis for the

purpose of estimating the performance (capacity and efficiency) of a mixed system consisting of

a SDHV blower-coil combined with a conventional condensing unit. These assumptions

specialize the general equations of the NIST method and are coded as equations and data in an

accompanying spreadsheet. Because of the restrictive nature of these assumptions and the

specificity of the data, use of the spreadsheet is not recommended for purposes other than that of

the rulemaking.

7Domanski, Piotr A., "Rating Procedure for Mixed Air-Source Unitary Air Conditioners and Heat Pumps in

the Cooling Mode-Revision 1, May 1989.

8Domanski, Piotr A., "Rating of Mixed Split Air Conditioners", Proceedings of 5"' Annual Symposium on

Improving Energy Efficiency in Hot and Humid Climates, Houston, TX; September, 1988.

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EE-RM-STD-02-330 COMMENT 01E
2.2.2.1 System Assumptions Specific for SDHV Rulemaking Engineering Analysis

Matched system:

1. Air flow rate 400 CFM/nominal ton

2. External static pressure 0.15 in. H2O

3. Coil air side pressure drop 0.3 in. H2O

4. Blower/motor efficiency 45 percent (Default)

5. Indoor fan power 0.365 W/CFM

SDHV (mixed) system:

6. Air flow rate 220-350 CFM/rated ton

7. External static pressure 1.2 in.H20

8. Coil air side pressure drop 0.3 in. H2O

9. Blower/motor efficiency 65 percent

Matched and mixed systems:

10. Both equipped with similar type thermostatic expansion valves,

11. Both have similar part load efficiency factors, CD,

12. Both indoor coils use similar coil technology, e.g., same tube materials, geometries,

enhancements; and same fin materials, geometries, and enhancements.

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EE-RM-STD-02-330 COMMENT 01E
2.2.2.2 Other Assumptions

The distinguishing feature of the SDHV methodology is the manner in which values for

the indoor fan power, Pr„X and indoor coil scaling factor, F. = QC X/Q^ m, are determined for use in

the NIST equations (Appendix A). In this section the assumptions are refined and differences

with the NIST method are noted. In section 2.2.2.3, the rationale behind these assumptions is

discussed.

SDHV Fan Power. PFC.

Since most SDHV blower coils are paired with matched systems which are rated based

on a cased indoor coil (i.e., coil only), the matched system indoor fan power is provided by the

default value as:

PF,n = 0.365 x CFM,,,,, (2.1)

where CFM. is the nominal volumetric air flow rate of the matched system, given by

CFM,,, = 400 x Q,,, /12, 000. (2.2)

Note that equation 2.2 differs from NIST equation 4.6 (see Appendix A) because 400

CFM/ton is the nominal volumetric air flow in general use by industry when rating coil-only

systems where the air flow is supplied by furnaces.

Blower motors convert electrical energy into work done on the air stream. For blower

motors used in heating, ventilation and air conditioning (HVAC) applications, work is

proportional to the product of the volumetric air flow rate and the fan total pressure rise. The

14

EE-RM-STD-02-330 COMMENT 01E
ratio of the work done on the air stream to the electrical energy input to the motor is the blowermotor's "wire-to-air" efficiency, rl. For the SDHV system and the matched system, the total

pressure of the fan is the sum of the static pressure losses in the coil and in the supply ducts.

Thus, the SDHV system fan power is determined from the matched system fan power by:

P,,,,n x [CFMx x (ESP. + CPD)]/[CFM,,, x (ESP,,, + CPD,)Jx elm/Tlx (2.3)

where:

CFMX is the selected indoor air volumetric flow rate of the mixed (SDHV) system,

ESPm is the external static pressure imposed on the indoor unit of the matched system

prescribed by rating standards (listed in section 1.2.3),

ESPX is the external static pressure imposed on the indoor unit of the mixed (SDHV)

systems,

CPDm is the air side pressure drop of the wet indoor coil for the matched system,

CPDX is the air side pressure drop of the wet indoor coil of the mixed system,

rlX is the combined blower and motor efficiency of the SDHV system,

Tlm is the combined blower and motor efficiency of the matched system.

Indoor coil scaling factor, =QC,.a,,,

The NIST method requires the capacities of the matched and mixed coils be obtained

using a "verified method" at the same set of thermodynamic conditions for the air and

refrigerant. The air side flow rates are required to be the same as those specified for the mixed

and matched systems. Verified methods include manufacturers' test data or computer

simulations based on fundamental principles of heat transfer phenomenon.

For the purpose of the SDHV Engineering Analysis, simplifying assumptions are

15

EE-RM-STD-02-330 COMMENT 01E
essential because meeting the exact specifications of the NIST method for verification is not

considered practical. Based on "rules of thumb" frequently used by design engineers, DOE

assumes that the indoor coil scaling factor is given by:

FF = [(CFM/CFM„) x (FA x Rows)./(FA x Rows)jos (2.4)

Where:

(FA x Rows)X /(FA x Rows), is the ratio of "core volumes " ( product of face area and

number of rows) for the SDHV coil to that of the matched system indoor coil.

2.2.2.3 Discussion ofAssumptions

SDHV Fan Power, PFD

As previously discussed, most matched systems at the low to mid range of efficiency

levels considered for SDHV applications are of the "coil-only" type, so matched system fan

power is based on the "default" value of 0.365 Watts/CFM. Matched systems are also typically

rated with a nominal air flow of 400 CFM/ton. SDHV systems differ because while the default

value for fan power can be used for the matched system, the rating method requires use of the

actual SDHV fan power. Therefore, to estimate the SDHV fan power from the known

information, an assumption regarding blower-motor efficiencies is needed9.

The default value of 0.365 Watts/CFM is based on data obtained many years ago from

residential forced air heating systems. At that time, furnace blowers used either shaded pole

motors or split capacitor motors less efficient than those made today. The actual value of

9 Measured fan power from ARI certification test data were not useful because either the static pressures

were not available or not at the 1.2 in. H2O required.

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EE-RM-STD-02-330 COMMENT 01E
default fan power is a matter of some controversy, with some arguing that the value is too high,

and others taking the opposite position. SDHV blowers and blower motors use technologies

such as permanent split capacitor (PSC) motors, which generally have higher efficiency. Absent

specific efficiency data, the efficiency corresponding to the default fan power of a conventional

system is assumed to be 45 percent. Analysis of data shown in Figure 1 for more recent

commercially available blowers show a range of blower motor efficiencies from 50 to 80

percent, with a mean of about 65 percent. Consequently, this is the value selected for the SDHV

analysis.

Os

0.4

0.1

0

5 50£E 65-70

E9cl$r (^+I

70-75 ITS

Figure 1: Distribution of Typical Fan Efficiencies for Small-Size Motors (from

publicly available data).

Indoor coil scaling actor. F,=a,Qcin

In the NIST rating method, described in Appendix A, F, is the ratio of indoor coil

evaporator capacities of the mixed (SDHV) and the matched systems at their respective CFM.

Establishing suitable indoor coil scaling factor presents a challenge to predicting mixed system

performance ratings, because of the wide variety of matched coil design in current use.

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EE-RM-STD-02-330 COMMENT 01E
In the technical paper describing the basis of the NIST rating method, system capacity

ratio at 95 °F is proportional to F°° 37 and system capacity ratio at 82 °F is proportional to F°0.35

System efficiency, or Seasonal Energy Efficiency Ratio (SEER), is directly proportional to the

capacity ratio at 82 °F and inversely proportional to the compressor power ratio at 82 °F. Since

the F° exponents for capacity ratio and power ratio at 82 °F are 0.35 and 0.14, respectively, the

system efficiency is approximately proportional to F.0-21 Note that, for coil sizes that are

typically found in SDHV systems, the correlation predicts system cooling capacity within ±2

percent and SEER within ±l percent. This is well within testing accuracies.

The use of equation 2.4 is believed to be suitable for the SDHV analysis because it is

based on empirical relationships used by designers in predicting heat exchanger performance

when changes are made to a coil of known performance, either of coil size or airflow or both.

For example, a 10 percent increase in CFM results in a 5 percent increase in coil capacity, and a

10 percent increase in face area with the same CFM also results in a 5 percent increase in coil

capacity. Figure 2 demonstrates that the 0.5 exponent in equation 2.4 is reasonable, based on

coil manufacturer catalog data.

7

;gu

0

5116" G. D. GROOVED

TUBE -Ix0A25

Coal subset A STAGGERS -

L OUVERED FIN - 14 FM

MPM

fl^

In

E14

11 5m '® 133 3113 25M 0

rrf7' 'FAM n,c

Coil subset B

0

313" O.D. GRO OVED

TUBE - 1 x0266

STAGGERED -

LOUVERED FIN- 14FP1

1® 1^m 1ID

Ckll"fiffW.'4

Figure 2: Correlations Between Coil Size and Coil Capacity.

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EE-RM-STD-02-330 COMMENT 01E
2.3 Description of Baseline SDHV System

The starting point for the analysis of efficiency standards is the definition of a baseline

system, which just meets the current minimum efficiency standard of 10 SEER. An examination

of certified performance ratings in the ARI directory indicates that a significant number, if not

most SDHV systems, just meet the current 10.0 SEER standard. Rather than selecting an actual

system, which is considered arbitrary, DOE defined a baseline system assuming the attributes

described in Table 1.

Product SDHV Delivered SDHV SDHV Coil SDHV Matched Coil Features of

Group Efficiency SDHV Airflow Size Blower Size Matched

(SEER / Capacity Rate (Face Area Motor (Face Area Condensing

HSPF) (Btu/hr) (CFM) (sqft x Rows) Efficiency (sqft x Rows) Unit

12.0 SEER -

Air 10.0 30,000 800 2 x 4 65% 4 x 3 36,000

Conditioners

Table l: Physical Characteristics of Baseline Model.

2.4 Design Options

A SDHV manufacturer has several options available to improve system efficiency.

These consist of. a) changes to the design and/or operation of current SDHV blower-coil units;

and b) changes to the set of currently available condensing units. In the category of changes to

the SDHV unit, the Department includes design changes which a) increase blower motor

efficiency; and b) increase coil size. In the category of operation changes, DOE includes

adjusting SDHV air flow. In the category of changes to currently available condensing units, the

Department includes: a) selecting higher efficiency condensing units; and b) restricting the type

of condensing units to those whose matched systems performance ratings are not obtained

through use of excessively large indoor coils.

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EE-RM-STD-02-330 COMMENT 01E
While it is theoretically possible to redesign a condenser unit to optimize the

performance for the reduced indoor air flows associated with SDHV systems, the small market

share of such systems makes condenser unit redesign an unlikely option.

In the following section DOE discusses in a qualitative sense each of these options and

then estimates the costs associated with those options that make sense from a basis of efficiency

improvement.

2.4.1 Increased Efficiency of Blower Coil Components

Changes to certain SDHV components can increase the efficiency of a SDHV system.

These include improved blowers and improved coils. The efficiency of the blower can be

increased in several ways, typically by: 1) substituting a higher efficiency, electronically

commutated motor (ECM) for the current permanent split capacitor (PSC) motor; 2)

substituting a blower with air foil or backward-inclined blades for the current blower; 3) simply

replacing the existing coil in each SDHV blower coil model with a larger coil (either larger face

area or more rows).

Design option 1 could potentially be cost effective in modulating systems, because

ECMs are substantially more efficient than baseline permanent split capacitor (PSC) motor at

partial load. However, because SDHV systems must deliver air to the terminal outlets at a

prescribed velocity (to ensure proper mixing with room air) modulation of the blower is not

considered to be a reasonable approach and the small efficiency improvement at full load does

not justify the much greater cost of the ECM. Option 2 could provide an increase in blower

efficiency where space is not an issue, but backward-inclined blowers are considerably larger

than conventional forward-inclined blowers and are not a good choice for space-constrained

applications, such as SDHV systems. Therefore, DOE did not consider blower-motor design

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EE-RM-STD-02-330 COMMENT 01E
changes as viable options for the purpose of this analysis.

One of the simplest design options which increases SDHV system efficiency is to

enlarge the coil's face area. Since current SDHV coil designs are either 4 row or 6 row coils,

and the tube and fm designs have near optimal features and configurations, adding face area is

the only viable design option. A larger coil has a beneficial effect on both efficiency and

capacity. Since current SDHV models have coils which fill available cabinet or module space,

the cabinets themselves require enlarging as does the cabinet insulation and external drain pans.

Of course, there is a practical limit to how much the indoor cabinet can be increased in size and

still stay within field installation limitations.

2.4.2 Reduced Air Flow

For a nominal 3-ton system, the indoor airflow quantity of SDHV systems will range

from about 600 to 840 CFM. In principle, when the airflow of the SDHV system is decreased,

the F,, ratio also decreases and compressor power decreases. Thus, as airflow is decreased from

840 CFM to 600 CFM, the SEER of the SDHV system increases by about 0.2 SEER, but the

system with the lower airflow has a reduced capacity.

Major changes to the range of 600 to 840 CFM for indoor airflow rates at that cooling

capacity level should not be considered for SDHV systems. The airflow rates cannot be

increased by any substantial amount because the pressure drop through the small ducts would

become excessive. The airflow rates cannot be decreased by any substantial amount because the

high velocity that is required to properly enter and mix with room air would not be available.

Also extending the range in either direction could cause the CFM per rated-ton of the SDHV

system to drift outside the mandated limits of 220 to 350 CFM per rated ton.

21

EE-RM-STD-02-330 COMMENT 01E
2.4.3 Selection of Condensing Units

In the category of changes to currently available condensing units, the option available to

SDHV manufacturers to increase SDHV efficiency is to either select more efficient condensing

units or to restrict the selection of condensing units to those whose matched ratings will not

significantly degrade SDHV efficiency.

In the SDHV rating method, if all parameters are kept constant, equation B.2 in

Appendix B shows that SDHV efficiency is directly proportional to that of the matched system:

SEER, = SEER,,, X (QJQ,,,)8, / (P/P,,,)

Therefore, increasing the SEER of the matched system by changing the condensing unit

from say a 12 SEER to a 13 SEER, increases the SDHV by 8.33 percent. Since the baseline

system has a condensing unit SEER of 12 and an SDHV SEER of 10, a new SDHV system with

a 13-SEER condensing unit will have an efficiency of 10.83. However, the capacity ratio and

the power ratio are not necessarily constant with SEER, so the coil scaling factor, F, must also

be considered. Thus, if the improved SEER for the matched system is achieved by use of a

larger indoor coil, the improvement in SDHV performance will be lower.

Another option is to be more selective about the matched system indoor coil size. It is

possible to select condensing units that achieve matched system SEERs with relatively small

indoor coils and thus increase the value of F, the coil scaling factor. Similarly, it is possible to

avoid condensing units that achieve matched system SEERs with relatively large indoor coils

which decreases the value of F., ratio. However, DOE believes that limiting the selection of

condensing units might cause distributors to move away from SDHV products. Therefore, this

option negatively impacts SDHV manufacturers in terms of marketing and sale opportunity and

22

EE-RM-STD-02-330 COMMENT 01E
is not considered further in the analysis.

2.4.4 Use of Emerging Technologies

DOE did not consider other emerging technologies in this analysis, due to the small size

of the small duct, high-velocity system industry. With regards to microchannel heat exchangers,

SDHV systems are constrained by the size of the evaporator, which is not currently being

considered as a viable application for microchannel technology because of condensate removal

concerns.

2.4.5 Max Tech

DOE estimates that the maximum technologically feasible efficiency for SDHV systems

is 13.4 SEER. This maximum performance was calculated based on the following two

considerations: 1) Condensing units with very high efficiency have features that are unsuitable

to SDHV systems. The most efficient condensing units that can be successfully coupled with

SDHV blower-coils have a 14-SEER rating; 2 ) Coil size is limited by the physical constraints

that SDHV blower-coils face. Therefore, SDHV coils cannot be larger than the largest coil

currently on the market.

2.5 Conclusions on Design Options

Two design options were selected for this analysis : 1) Increased indoor coil size and 2)

Higher efficiency condensing unit.

23

EE-RM-STD-02-330 COMMENT 01E
2.6 Estimated Cost Impacts

DOE relied on several sources to estimate the manufacturing costs of the two selected

design options: the Residential Air-Conditioner Engineering Analysis; confidential information

obtained under non-disclosure agreements between Navigant Consulting , Inc. and the SDHV

manufacturers, and estimates based on industry expertise and "rules of thumb".

2.6.1 Increased Coil Size

As coil size increases, more materials and labor are needed and the cost increases.

While coil material cost is essentially proportional to the coil size, other components experience

cost increases in a similar fashion, including cabinet panels, cabinet insulation and the external

drain pan provided in all attic installations. Based on confidential information submitted by the

SDHV manufacturers to DOE's contractors, this cost in terms of cost increase per increase in

the (Face Area x Rows) value is established. Because of the confidential nature of this data,

DOE is not disclosing manufacturer cost increases for larger coil sizes. In the sensitivity

analysis, discussed in section 2.8, the impact of incremental coil cost on the cost-efficiency

curves are analyzed.

2.6.2 Higher Efficiency Condensing Unit

To estimate the cost of more efficient condensing units, DOE relied on the analysis

performed for the residential air conditioner rulemaking . First, DOE evaluated the high volume

production costs of 12 , 13, and 14 SEER condensing units. In the residential air conditioner

analysis, the costs were divided into costs allocated to the outdoor unit, to the indoor unit and to

overhead (see Appendix B of the TSD). To determine the costs of the outdoor unit only, DOE

added a fraction of the overhead costs, in proportion to the direct costs, to the direct cost of the

24

EE-RM-STD-02-330 COMMENT 01E
outdoor unit. For example, if the direct cost of the outdoor unit is 78 percent of the total direct

cost, the overhead cost for the outdoor unit is also 78 percent of the total overhead cost. The

same procedure was followed for 13 and 14 SEER. The results are presented in the Table 2.

t5

0

0

M

Coil Materials

Coil Labor

Electrical Materials

Electrical Labor

Miscellaneous Labor

Miscellaneous Materials

731 Plum binci Labor

Fan Materials

Fan Labor

Cabinet Materials

Cabinet Labor

Plumbing Materials

Compressor Materials

Compressor Labor

Refrigerant l0atl

Fefrioerant Labor

Irriirert Labor

In^ire^ t,1aterial

Ea'.rir_,m ert [: er'redation

Builrlirn_r 1:1e ,rrci._tion

r:iainterr•:inr_r

I n:.ararn_

F rri ittt-Cut

12 13 14

4 J5; 4.92 x.40

1.99 3-'-.22 535:17

.1 .07 1 07 $1 .07

66 `x.95 :;6.30

1. 1.75 ;1. _

:4.47 .11 $4.556

:5I25 $112S $0.25

:i18.5:J 20 ._5 .1 1 i -

2.45 51

11 -3,2, ;1 14.4F_i

_ 3.99 4.21

.;152 3.7 ;10767,5 $167 78

1i 5.65 $0150 :1;0.65

5.60 .;6.11 : ;.0_;

$136 Ti $03'6

12.74 ;12.8-5- ;1 6=

: x1 1 2 _' $10.52 $11 .62

$6.59 7.47

:j;1 1.70 13.59 15.47

-=.07 $3.20 -'.41

'1;3 - 4.36 4:95

' 4. 1 $4.76; $5.29

=.74 $423 $4.70

:545.21 5 03 .9 1 :$6.31

'406.30 $462.91 1 500.49

Table 2: Cost Allocation for Outdoor Unit.

However, these costs were obtained assuming that a new standard would be set at the

analyzed level and, therefore, do not account for lower production volumes and higher margins

that are typical of high-efficiency products. In order to estimate the actual cost of 13- and 14-

SEER condensing units, DOE applied additional correction factors, based on our knowledge of

the industry. In particular, correction factors of 1.05 and 1.10 were applied to the 13- and 14-

SEER condensing units respectively to account for lower production volumes. Also, different

gross margins were applied across the efficiency levels, since higher-efficiency units are

typically sold at a premium. Gross margins were estimated to be 15, 25 and 35 percent

25

EE-RM-STD-02-330 COMMENT 01E
respectively for 12-, 13- and 14-SEER condensing units. Average markups were then applied to

estimate the consumer costs. The results of this analysis are summarized in Table 3.

CONDENSING UNIT EFF ICIENCY -----------------

Production cost for high volume production rates

Ad i ustment for actual production rate s

Adjusted production cost

Gross Margin, Percent

Manufacturer's Markup

Selling Price to Distributor

Distributor Markup

Selling Price to Dealer

Dealer Markup

Dealer Selling Price

Sales Tay

Consumer Cot

... 12

13 14

$4[I5,E1[l X462.91 6[1ft49

1.CIn 1.0S 1.19

: ,4 06. 51[ I f4116.06 $551_I.54

15.DC1 5.00 35.CICI

1.19 1 1.54

$47 H, 59 64u.[I7 , R4 9E:

1.-17 1. 1.27

; ;6 [17.51 : 23.05 $1,075.67

1..10 1.30 1.3

#;7 90.15 $1 I161-4.9i1 Ifl 39a 7

1 ill 1 i17 J .f17

246.5 $1144.9 $1496.3

Table 3: Condensing Unit Consumer Costs.

In the sensitivity analysis, discussed in section 2.8, the impact of different assumptions

on the cost-efficiency curves have also been analyzed.

The cost estimates illustrated in the table above were then validated and confirmed

through confidential data submitted by the SDHV manufacturers.

2.7 Distribution Chain Markups

SDHV systems are typically sold in the replacement market. The typical distribution

chain for these products is identical to the distribution chain for conventional products in the

replacement market. Manufacturers sell products to a distributor (wholesaler), the distributor

sells it to the contractor (dealer) and the contractor sells and installs the product to the

consumer. Therefore, the total distribution chain markup is the product of four factors:

manufacturer markup, distributor markup, contractor markup and sales tax.

SDHV manufacturer markups tend to be higher than markups on conventional systems.

26

EE-RM-STD-02-330 COMMENT 01E
Through its contractors and under non-disclosure agreements , the Department gathered

confidential information and estimated a SDHV manufacturer markup . Similarly, the

Department estimated other distribution markups, although they are very similar to conventional

product markups. Because of the confidential nature of the data, the Department is not

disclosing markup values.

2.8 Sensitivity Analysis

The Process Rule requires the Department to consider uncertainty . The initial

cost-efficiency relationship does not portray the uncertainty and variability in the assumptions.

Uncertainty arises when the precise model parameters cannot be determined . Variability arises

when the precise values can be determined, but when they vary among manufacturers , suppliers,

or processes. To quantify the uncertainty and variability in the consumer price estimates, DOE

used Crystal Ball ProTM to run Monte Carlo simulation analysis.

Distributions were defined for eleven of the assumptions. All other assumptions were

considered point values, either because of low uncertainty , or because any variation would not

have significant impact on the results. Uniform distributions represent the assumption that no

single value predominates across the range of possible values. Triangular distributions represent

that assumption that a particular value does predominate , and that other values are increasingly

less likely the farther they are from that value. Table 4 summarizes the ranges considered in the

sensitivity analysis.

27

EE-RM-STD-02-330 COMMENT 01E
Variable Min Mean Max Type of Distribution

Matched Coil Size (FA x Rows), 10 12 14 Normal

Blower Efficiency (1 bloi,,,) 50% 65% 80% Triangular

Indoor Airflow Rate of Matched System (CFM/Ton),,, 400 412.5 425 Uniform

Incremental Coil Cost ($) CONFIDENTIAL

Actual Condensing Unit Production Rate Factor at 13 SEER 1.0 1.05 1.1 Triangular

Actual Condensing Unit Production Rate Factor at 14 SEER 1.05 1.1 1.15 Triangular

Condensing Unit Manufacturer Gross Margin at 13 SEER 20% 25% 30% Triangular

Condensing Unit Manufacturer Gross Margin at 14 SEER 30% 35% 40% Triangular

SDHV Distribution Markups ±20% - CONFIDENTIAL

Table 4: Variability and/or Uncertainty Ranges for the Assumptions Considered in the Sensitivity Analysis.

To run a Monte Carlo simulation analysis, Crystal Bal1TM selects inputs randomly

according to the distributions and tracks the effects on price and efficiency. Since two final

results were tracked, a new Price/SEER parameter that combines the two values was defined.

The result is a bell-shaped probability distribution for the Price/SEER value of each sample.

Rather than predicting a single consumer price, the distribution describes the likelihood that the

actual consumer price is equal to a predicted value. Thus, the uncertainty in the consumer price

estimates can be quantified. Figure 3 illustrates a typical Crystal BaITM output.

28

EE-RM-STD-02-330 COMMENT 01E
Forecast: Price/SEERx

35

30 --------------------------------------------------------------------

25 -I-------------------------

20 1----------------- ---

15 -------------- --n

10 -- -----

0

186 196 205

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

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

i

d

14-

214 224

Figure 3: Typical Crystal Ball Output for a SDHV Sample.

On average, Price/SEER values were well within 20 percent of the predicted values with

a 95 percent confidence. Therefore, the Department applied a 20 percent uncertainty to the costefficiency curve. This uncertainty will be considered in the course of the Life-Cycle-Cost

analysis.

2.9 Heat Pumps

Section 4.8.1 of the TSD discusses the relationship between cooling efficiency (SEER)

and heating efficiency (HSPF) in air conditioning heat pump systems. Based on heat pump

performance data from the Spring 1998 ARI Unitary Directory, DOE proposed the following

relationship for heat pumps with cooling efficiencies between 10 SEER and 14 SEER:

HSPF = 6.8 + 0.3 x (SEER - 10)

In previous proposed and final rules, DOE explained the rational for accepting this

relationship. In the May 23, 2002, final rule, DOE adopted this relationship for split system and

29

EE-RM-STD-02-330 COMMENT 01E
single packaged heat pumps and for split system and single package through-the-wall air

conditioners and heat pumps.

As previously discussed, a SDHV blower coil unit can be operated as a heat pump

system by substituting a reverse-cycle heat pump outdoor unit for an air conditioning outdoor

unit and by providing the indoor unit with a backup heat source. Currently, one SDHV

manufacturer offers a heat pump option. In this case, the coil unit has the same face area but a

six-row coil is substituted for a four-row coil to provide the refrigerant management function

needed for a heat pump. DOE has no data on the market share of SDHV heat pumps. However,

since the common application for SDHV air conditioning systems is in retrofits to existing

homes, and since these homes are usually equipped with a hydronic or radiant baseboard heating

system, DOE believes that SDHV heat pump market share is small. Consequently, DOE

believes that the above SEER vs HSPF relationship adopted for conventional heat pumps and

for through-the-wall air conditioners and heat pumps is valid for the purpose of SDHV heat

pump standards.

2.10 Air-Distribution Systems and Installation Costs

In our analysis we assume that air-distribution systems and installation costs are constant

for all efficiency levels. The Department obtained confidential data from manufacturers and

price lists and concluded that the total consumer cost for air-distribution systems is $2720. This

cost includes distribution markups and sales tax. In addition, the Department is using the same

installation cost that was used for the analysis of conventional systems ($1279).

30

EE-RM-STD-02-330 COMMENT 01E
2.11 A Note on SDHV Cooling Capacity

Previous sections discussed how SDHV manufacturers can improve SDHV system

efficiency by increasing the blower-coil size. However, it was not discussed how these changes

affect the delivered cooling capacity of the SDHV system. The purpose of this section is to

describe how to address the issue of variability in SDHV cooling capacity in our analysis to

produce the final cost-efficiency curves.

If a manufacturer simply substituted an existing SDHV coil with a larger coil and kept

all other variables constant, the capacity would increase significantly. This is a very basic

scenario and is illustrated in the `Fixed CFM Ratio' (scenario 1) spreadsheet in the published

workbook. In this situation, a manufacturer would set the airflow rate at a certain value and let

the capacity increase as the coil size increases. DOE used this method to estimate performance

values in the baseline case by fixing the SDHV airflow rate to 800 CFM (or, alternatively, fixed

the CFM ratio to 2/3).

However, as one increases the size of the coil, there is now extra-capacity that is not

needed. In this case, the best approach is to fix the SDHV capacity (at the 30,000 Btu/hr

baseline) and let the SDHV airflow rate vary to meet this requirement. SDHV SEER values are

typically higher than the `Fixed CFM Ratio', because the extra-capacity is re-used to increase

efficiency. Conversely, costs are lower at a given SEER. This scenario is illustrated in the

`Fixed SDHV Capacity' spreadsheet (scenario 2).

However, by increasing the coil size above a certain value (the threshold varies

depending on other assumptions), using the `Fixed SDHV Capacity' approach, CFM/Ton values

fall outside of the definition of SDHV systems (SDHV systems have an airflow rate between

220 and 350 CFM/Ton). Therefore, when hitting the 220 CFM/Ton barrier, the CFM/Ton value

31

EE-RM-STD-02-330 COMMENT 01E
was kept constant and all other variables are free of constraints. This scenario is illustrated in

the `Fixed SDHV CFM/Ton' spreadsheet (scenario 3). The capacity will increase as well, but is

accounted for in the fact that the manufacturer has no way to charge for this capacity surplus.

Therefore, using a combination of three different scenarios and a combination of the two

design options, a cost-efficiency curve was obtained and is shown in section 2.12.

2.12 Summary of Results

The cost-efficiency relationships are summarized in Table 5 and Figure 4. In Table 5,

the results are presented in terms of consumer prices at different efficiency levels. A given

efficiency level can be reached with different combinations of condensing unit efficiency, which

varies from left to right, and SDHV coil size, which varies from top to bottom. For each

efficiency level, the least expensive combination, was selected. Grey areas represent

combinations that are not cost effective. For each combination, the minimum, average and

maximum consumer prices are reported.

32

EE-RM-STD-02-330 COMMENT 01E
Cords- Unit SEER ----------- 12 13 1 14

rrow Price f$I Consume Price 31 Cons rrer Price f$I

Coil Size (Face A'rea[ft) x Rove ) SEER Nin Aye NW SEER Mn Ave Max SEER Mn Ave

8 1010[) 0 0 0

8.5 10 . 15 21 .1 263 31 . 6 11.00 250 5 3252 390.9

9 1029 422 52.7 63.2 11.15 281 .7 352.1 422.5

as 10 .41 532 79. 1 94.9 11.27 3222 3785 464.2 12.14 583.9 729.8 875.8

10 10 51 84.3 105.4 1265 11.39 323,9 4042 435.8 12.25 605.0 753. 2 907.4

105 10,59 105.4 131 .8 168.1 11.43 344.9 4312 517.4 12.36 625.0 782. 5 939.1

11 10.65 125.5 163.1 189.7 11.54 263 9 4575 549.0 12.43 647. 1 803.9 970.7

115 10 .71 147.0 184.5 221 3 11.60 387 .1 4839 635.6 12.60 668.2 835.2 1002.3

12 10.77 183.0 210.8 253.0 11.65 4082 5102 612.3 12.55 689.3 861.6 1033.9

125 1082 189.7 237.2 284.6 11.72 992 5351 643.9 12.62 710.4 887.9 1085.5

13 1087 210.8 263.5 3152 11.78 450.2 562.9 675.5 12.68 731.4 9143 1037.2

135 1002 231 .9 289. 9 347.0 11.83 471 .4 5892 707.1 12.74 752.5 910.6 1128.8

14 1097 253.0 318. 2 37x9:4 11.88 A92 B 6155 738.7 12.83 773.0 967.0 1160.4

145 11 .93 513.6 642.0 770.4 12.85 794.7 993. 3 1192.0

15 11 . 98 534.6 6683 802.0 12.97 815.8 1019.7 1223.6

155 12. 03 555 .7 694.7 833.6 12.95 836.8 10409 1255.3

16 12.03 576 D 721.0 865.2 13.00 852.9 10722.4 1288.9

165 11,1Z,,"ZZ11 ,'11,11 13.05 879. 0 10987 1318.5

17 13. 10 900.1 1125.1 131.1

176 13. 14 921.2 1151 .4 1381.7

18 13. 19 942. 2 1177.8 1413.4

185 .1 14E.0

19 J9 L1476.6

195

20 13.36 1026 5 12832 15328

Table 5: Consumer Costs as a Function of SDHV Efficiency and Coil Size.

The points of Table 5 can then be connected to build the final consumer cost-efficiency

curve, as shown in Figure 4.

Cost-Efficiency Curve

1400 ,

1200

'8

a

1000

w

50 800

C

0

600

40L1

200

12

S OHV SEER

13 14

Figure 4: Cost-Efficiency Curve.

33

EE-RM-STD-02-330 COMMENT 01E
APPENDIX A: NIST METHOD FOR RATING MIXED AIR CONDITIONING SYSTEMS

To explain the NIST method for rating mixed air conditioning systems, relevant sections have

been excerpted from Chapter 4 of NISTIR 89-4071, retaining all the notation and equation

numbering:

"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.

Qx = [Qm + 3.413 • PF,,m]

• Fe° 37 • Fa - 3.413 Pr„X (4.1)

Mixed system Seasonal Energy Efficiency Ratio, SEER,, shall be calculated using

equations 4.2, 4.3, and 4.4 (derivation of these equations is presented in [2]).

SEERX = SEER„ [Qx/Qm 82 / [Px/Pm] 82 ` • FTXV (4.2)

[Qx/Qm]sz = [1+ (3.25 • PF„m/Qm)] •

Feoss .Fea 3.25 • PF„x/Qm (4.3)

[Px/Pm]82 = 0.8 • F,- 14 • Fea + 0.1 • Pr„x / PF„m

+ 0.1 (4.4)

Symbols used in equation 4.1, 4.2, 4.3 and 4.4 are explained below.

Exponents

a= -0.15 for Fe>_ 1

a=0forFe<1

34

EE-RM-STD-02-330 COMMENT 01E
(3=0forFe>_ 1

(3 = -0.2 for Fe < 1

Other Symbols

Fe = indoor coil scaling factor calculated as explained in section 4.2.1

Fe = expansion device scaling factor calculated as explained in section 4.3.1

F,x,, = thermostatic expansion valve factor. (Shall be evaluated as shown in Table 1).

Pr.,,,, = power input to the indoor fan of a matched system as defined in section 4.4.1

(watt).

PF.,X = power input to the indoor fan of the mixed system as defined in section 4.4.2

(watt).

Q,„ = capacity of the matched system at Test A as certified by its manufacturer (Btu/h).

QX = capacity of a mixed system at Test At as calculated by equation 4.1 (Btu/h).

[Qx/Qm]82 = ratio of capacities at Test B conditions of the mixed and matched system.

[PX/Pm]az = ratio of power inputs at Test B conditions of the mixed and matched system.

SEER,,, = seasonal energy efficiency ratio of the matched system (Btu/(h- watt) as

certified by its manufacturer.

SEER, = seasonal energy efficiency ratio of the mixed system (Btu/(h-watt) as

calculated by equation 4.2.

4.2 Indoor Coil Scaling actor

4.2.1 Determination of the Indoor Coil Scaling Factor

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

35

EE-RM-STD-02-330 COMMENT 01E
F,=Qc,x/Qc;m

where:

Qc,.X = 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

Appendix M to Subpart B of [6].

Q, „1= cooling capacity of a matched coil at the indoor-air volumetric

flow rate, CFMm (ft3/min), at which matched system capacity,

Qm, was measured. If CFMm information is not available, the

value for the indoor air volumetric flow rate shall be calculated

as follows:

CFMm. = Q. • 425/ 12000 (ft3/min) . (4.6)

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:

- 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

rows) shall be accounted for by the method used. That is, the methodology used must have

36

EE-RM-STD-02-330 COMMENT 01E
these parameters as independent variables.

4.2.2 Restrictions

The acceptable range of values for the indoor coil scaling factor, Fc, 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 QC,x/QC,111 results in a value greater than 1.3, the value of the indoor coil scaling factor, Fc,

shall be 1.3.

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, Pfm shall be measured in accordance with Appendix M to

Subpart B of [6], at the indoor-air volumetric flow rate, CFMm at which capacity of the matched

system, Qm, was measured.

If CFMm 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, Pfm shall

be evaluated by the equation:

Pfm 0.365 • CFMm (4.12)

where CFMR1 (ft3/min) is a volumetric flow of air through the matched indoor coil at

which system capacity, Q11, was measured.

37

EE-RM-STD-02-330 COMMENT 01E
4.4.2 Power Input to the Indoor Fan of the Mixed System

Power input to the indoor fan, PfX shall be measured in accordance with Appendix M to

Subpart B of [6], at the indoor volumetric air flow rate, CFMX, at which capacity of the mixed

system, Qx, is evaluated.

If the indoor fan is not supplied with the system, PfX shall be evaluated by the equation:

= 0.365 • CFMX (4.13)

where CFMX (ft3/min) is the volumetric flow of air through the mixed indoor coil at

which the capacity of the mixed system, Qx, is to be evaluated."

38

EE-RM-STD-02-330 COMMENT 01E
APPENDIX B: PERFORMANCE EQUATIONS

In this section (and in the spreadsheet), nomenclature and terminology used in the NIST

method are retained, except the equations are renumbered . As with the NIST method, the

subscript notation `m' indicates the matched system and the subscript `x' indicates the mixed

(SDHV) system. Similar to performance equations 4.1 to 4.4 in NISTIR 89-4071 (Appendix A),

the following equations are used:

Qx(95): Cooling capacity of the mixed (SDHV) system (at 95 °F ambient temperature)

Qx(95) _ [Qm + (3.413X PF„m)] X F°0.37 - (3.413X PF„X ), (B.1)

Note that F°, the expansion device scaling factor in NIST equation 4.1 is assumed equal

to unity.

SEER,: SEER efficiency of the mixed (SDHV) system

SEER, = SEER,,, X (Qx/Qm)82 / (Px/Pm)82

(B.2)

Note that FTXV, the thermostatic expansion valve factor in NIST equation 4.2 (Appendix

A) is assumed equal to unity.

(Qx/Qm)82: Ratio of cooling capacities of the mixed (SDHV) system and the matched at

82 °F ambient temperature.

(Qx/Qn)82 = [(1 + 3.25 X PF.,,m /Qm)

X F

°0.35] - [3.25 X PF„x /Qmd (B.3)

39

EE-RM-STD-02-330 COMMENT 01E
(Px/Pm)82: Ratio of power inputs of the mixed (SDHV) system and the matched system at

82°F ambient temperature.

(PX/Pm.)82 = (0.8 x F,,°'4) + (0.1 x PF,X/PF,m) + 0.1 (B.4)

Note that the above expressions for capacity ratio and power ratio are identical to those

in the NIST method.

All these equations, along with the assumptions discussed in section 2.2 of this

document are included in a calculation spreadsheets that is available on the DOE web site

(http: //www.eren. doe. gov/buildings/codes_standards/notices/notc0049/index.html).

40

EE-RM-STD-02-330 COMMENT 01E