CHAPTER 4. SCREENING ANALYSIS

TABLE OF CONTENTS

4.1 INTRODUCTION ........................................................................................................... 4-1

4.2 SCREENED-OUT TECHNOLOGIES............................................................................ 4-2

4.2.1 Burner Derating ............................................................................................................... 4-2

4.3 TECHNOLOGIES THAT HAVE NEGLIGIBLE OR NO IMPACT ON 

THERMAL OR COMBUSTION EFFICIENCY AS MEASURED BY THE 

DEPARTMENT OF ENERGY TEST PROCEDURE.................................................... 4-3

4.3.1 Combustion Preheaters .................................................................................................... 4-3

4.3.2 Economizers..................................................................................................................... 4-3

4.3.3 Blow-down Waste Heat Recovery................................................................................... 4-4

4.3.4 Jacket Insulation Optimization ........................................................................................ 4-4

4.4 TECHNOLOGY OPTIONS FOUND IN BASELINE UNITS ....................................... 4-4

4.5 REMAINING TECHNOLOGY OPTIONS .................................................................... 4-5

LIST OF TABLES

Table 4.4.1 Technologies Found in Common Baseline Boiler Designs...................................... 4-5

Table 4.5.1 Design Options for Commercial Packaged Boilers Analyzed in the 

Engineering Analysis....................................................................................................... 4-5

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CHAPTER 4. SCREENING ANALYSIS

4.1 INTRODUCTION

This chapter discusses the screening analysis conducted by the U.S. Department of 

Energy (DOE) of the technology options identified in the market and technology assessment for 

commercial packaged boilers (CPBs). In chapter 3, the market and technology assessment DOE 

presented an initial list of technology options that can be used to improve the energy efficiency 

of CPB. The goal of the screening analysis is to identify any technology options that will be 

eliminated from further consideration in the rulemaking analyses. 

The candidate technology options are assessed based on DOE analysis as well as inputs 

from interested parties including manufacturers, trade organizations, and energy efficiency 

advocates. Technology options which are judged to be viable approaches for improving energy 

efficiency are retained as inputs to the subsequent engineering analysis. Technology options 

which are not incorporated in commercial equipment or in working prototypes, or that fail to 

meet certain criteria as to practicability to manufacture, install and service, as to impacts on 

equipment utility or availability, or as to health or safety will be eliminated from consideration in 

accordance with subpart C of Title 10 of the Code of Federal Regulations, Part 430 (10 CFR Part 

430, subpart C), under appendix A, section 4(a)(4)(i‒iv). Some of the technologies identified 

during the technology assessment can improve the overall efficiency of a CPB but may not 

improve the thermal and/or combustion efficiency of a CPB, as measured by the test procedure 

prescribed under 10 CFR 431.86. Such technologies are not passed on to the engineering 

analysis for consideration because they would not be implemented as a result of more stringent 

energy conservation standards. 

The technologies identified in the market and technology assessment were evaluated 

pursuant to the criteria set out in the Energy Policy and Conservation Act, as amended (EPCA or 

the Act). (42 U.S.C. 6291-6317) EPCA provides criteria for prescribing new or amended 

standards, which will achieve the maximum improvement in energy efficiency the Secretary of 

Energy determines to be technologically feasible. (42 U.S.C. 6313(a)(6)(A)(ii)(II)) It also 

establishes guidelines for determining whether a standard is economically justified. (42 U.S.C. 

6313(a)(6)(B)(ii)) In view of the EPCA requirements for determining whether a standard is 

technologically feasible and economically justified, appendix A to subpart C of 10 CFR Part 430, 

Procedures, Interpretations and Policies for Consideration of New or Revised Energy 

Conservation Standards for Consumer Products, section 5., Policies on Selection of Standards, 

sets forth procedures to guide DOE in the consideration and promulgation of new or revised 

residential product and commercial and industrial equipment efficiency standards under EPCA. 

These procedures elaborate on the statutory criteria provided in EPCA and, in part, eliminate 

problematic technologies early in the process of revising an energy efficiency standard. Under 

the guidelines, DOE eliminates from consideration technologies that present unacceptable 

problems with respect to the following four factors: 

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1. Technological feasibility. DOE will consider technologies incorporated in commercial 

products or in working prototypes to be technologically feasible.

2. Practicability to manufacture, install, and service. If mass production and reliable 

installation and servicing of a technology in commercial products could be achieved on 

the scale necessary to serve the relevant market at the time the standard comes into effect, 

then DOE will consider that technology practicable to manufacture, install, and service.

3. Adverse impacts on product utility or equipment availability. If DOE determines a 

technology would have a significant adverse impact on the utility of the product to 

significant subgroups of consumers, or would result in the unavailability of any covered 

product type with performance characteristics (including reliability), features, sizes, 

capacities, and volumes that are substantially the same as products generally available in 

the United States at the time, it will not consider this technology further.

4. Adverse impacts on health or safety. If DOE determines that a technology will have 

significant adverse impacts on health or safety, it will not consider this technology 

further.

In summary, if DOE determines that a technology, or a combination of technologies, has 

unacceptable impacts based on the factors identified in 10 CFR 430, subpart C, appendix A, 

section 4(a)(4)(i-iv), it will be eliminated from consideration. If a particular technology fails to 

meet one or more of the four criteria, it will be screened out. Further, certain technology options 

may be removed from consideration if it is determined that (1) they do not impact the efficiency 

metric as measured by the current test procedure; (2) they are already found in baseline units; or 

(3) there is insufficient information documenting the efficiency benefits of the technology in 

CPB.

4.2 SCREENED-OUT TECHNOLOGIES

This section describes the technologies that DOE eliminated for failure to meet one of the 

following four factors: (1) technological feasibility; (2) practicability to manufacture, install, and 

service; (3) impacts on equipment utility or equipment availability; and (4) adverse impacts on 

health or safety. DOE eliminated one technology for failure to meet one of these criteria.

4.2.1 Burner Derating

Decreasing the burner size to increase the ratio of heat transfer area to fuel input, or burner 

derating, can increase the thermal efficiency rating of commercial gas and oil-fired boilers. 

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However, because heat output rate is directly related to burner size, derating also reduces the 

amount of heated air available to the consumer. This reduction in heat output adversely affects 

the utility to consumers. Therefore, DOE did not consider this technology option further in the 

rulemaking analyses.

4.3 TECHNOLOGIES THAT HAVE NEGLIGIBLE OR NO IMPACT ON 

THERMAL OR COMBUSTION EFFICIENCY AS MEASURED BY THE 

DEPARTMENT OF ENERGY TEST PROCEDURE

DOE further refined the list of technology options considered in the successive analyses 

stages by removing several technology options for which implementation would have minimal or 

no effect on thermal or combustion efficiency as measured by the DOE test procedure. Thus, 

DOE believes these technologies are unlikely to be implemented in response to changes to the 

DOE energy conservation standards. Although these options may not significantly improve rated 

efficiency of CPBs and are not included in the engineering analysis, DOE does not discourage 

their use by manufacturers, because of their potential to reduce energy consumption and increase 

efficiency. For each technology removed, DOE has provided an explanation of why the 

technology does not affect thermal and/or combustion efficiency.

4.3.1 Combustion Preheaters

Combustion preheaters capture heat from flue gases to preheat incoming combustion air. 

Although combustion preheaters effectively raise the operating efficiency of the boiler in the 

field, this efficiency is not measured or calculated directly by the test procedure. The test 

procedure requires that the inlet air be within ± 5°F of the room ambient temperature. Therefore, 

DOE eliminated this technology from the engineering analysis.

4.3.2 Economizers

An economizer is a device that can be installed on a boiler to save energy by preheating 

supply water with boiler exhaust gases. Although economizers utilize otherwise wasted heat, and 

may improve the overall efficiency of the boiler, they have no impact on the thermal efficiency 

as measured by the DOE test procedure. This is because according to the test procedure, the inlet 

water has a set temperature. Therefore, DOE eliminated economizers from further consideration 

in the engineering analysis. 

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4.3.3 Blow-down Waste Heat Recovery

In large steam commercial boilers, salt and sediment residue gets left out in the water 

stored in the boiler. These dissolved solids are known as total dissolved solids and are removed 

from the boiler in a process known as blow-down. Depending on size of boiler, blow-down can 

either be a continuous, periodic, or a maintenance process. In any case, stored heat energy in 

blow-down water which would otherwise be wasted away in a drain can be utilized to preheat 

incoming water. This blow-down process may require a separator which separates water from 

steam. By integrating this technology, there is potential to reduce fuel requirement to achieve 

desired water temperature. This technique may also marginally increase efficiency levels as the 

stored heat derived from combustion gases is utilized to a greater extent. 

The DOE test procedure is performed in a laboratory setting on boilers which have not 

previously been commissioned for service in a building. Therefore, sediment, dissolved solids, 

and other deposits will not be present in the boiler, and therefore blow-down procedures will not 

be required, and blow-down is not captured in the current test procedure. Thus, an increase in 

efficiency from blow-down waste heat recovery would not be measured, thus this technology 

was not considered in the engineering analysis.

4.3.4 Jacket Insulation Optimization

For any equipment that is insulated to prevent energy loss, there exists a relationship 

between the overall increase in diameter (or external geometry) due to insulation thickness and 

the thermal resistance (depending on the thermal conductivity of the insulating material). The 

optimization of insulation thickness presents an opportunity to apply insulation of only the 

required amount and that is sufficient to prevent considerable heat loss.

From a review of literature and manufacturer interviews, DOE notes that a blanket 2-3 

inches insulation is typically used on many boiler models. Although there exists an opportunity 

to optimize the insulation, based on a review of product literature, DOE believes the potential 

gain in efficiency (combustion or thermal) is negligible. 

4.4 TECHNOLOGY OPTIONS FOUND IN BASELINE UNITS

After eliminating those technologies that do not increase thermal efficiency and screening out 

those technologies that do not meet the requirements of 10 CFR 430, subpart C, appendix A, 

section 4(a)(4)(i-iv), DOE identified the technologies that are already commonly found in 

baseline CPBs as listed in Table 4.4.1. Although DOE did not consider these technologies as 

options for improving the efficiency in comparison to the baseline, the costs of these components 

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was captured in the engineering analysis at the baseline efficiency level. For certain components, 

DOE lists multiple technologies if there is more than one type of component commonly found in 

baseline equipment.

Table 4.4.1 Technologies Found in Common Baseline Boiler Designs

Gas Valve: Single Stage, Two Stage, or Modulating

Primary Heat Exchanger: Cast Iron Sectional; Water Tube; Fire Tube; 

Copper Fin-Tube; Carbon Steel

Jacket Insulation

4.5 REMAINING TECHNOLOGY OPTIONS

After eliminating all the technology options by the methods described above, DOE considered 

the technologies listed in Table 4.5.1.

Table 4.5.1 Design Options for Commercial Packaged Boilers Analyzed in the Engineering 

Analysis

Addition of condensing, secondary heat exchanger

Increased primary heat exchanger surface area

Incorporation of heat exchanger surface features (such as dimples) and 

internal features (such as baffles, turbulators, micro-fins, corrugation, or 

rifling) with the purpose of inducing turbulent flow on either the air or 

water side of the heat exchanger

Flat, wavy or louvered tube heat exchanger with or without staggered fin 

configuration

Premix burners

Pulse combustion

Low pressure, air atomized oil burner

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