CHAPTER 4. SCREENING ANALYSIS

TABLE OF CONTENTS

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

4.2 TECHNOLOGIES THAT DO NOT IMPACT AFUE OR STANDBY AND OFF MODE 

ENERGY CONSUMPTION ........................................................................................... 4-2

4.3 SCREENED OUT TECHNOLOGIES ............................................................................ 4-3

4.3.1 Pulse Combustion ............................................................................................................ 4-3

4.3.2 Control Relay for Models with Brushless Permanent Magnet (BPM) Motors (Standby/Off 

Mode) .............................................................................................................................. 4-4

4.4 REMAINING TECHNOLOGIES ................................................................................... 4-4

4.4.1 AFUE Efficiency Standards............................................................................................. 4-4

4.4.2 Standby Mode and Off Mode Power Consumption Standards........................................ 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 

residential boilers (chapter 3). In the market and technology assessment, DOE presented an 

initial list of technology options that can be used to reduce energy consumption of residential 

boilers. 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 information gathered during 

DOE research, as well as inputs from stakeholders 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 products or in working 

prototypes, or that fail to meet certain criteria as to practicability to manufacture, install and 

service, as to impacts on product utility or availability, or as to health or safety will be eliminated 

from consideration in accordance with 10 CFR 430, subpart C, appendix A, section 4(a)(4)(i-iv).

DOE uses the following four screening criteria to determine which technology options 

are suitable for further consideration in an energy conservation standards rulemaking: 

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 product 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.

.
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4.2 TECHNOLOGIES THAT DO NOT IMPACT AFUE OR STANDBY AND OFF 

MODE ENERGY CONSUMPTION

DOE eliminated 4 technologies that were identified in the technology assessment because 

they have no effect on or do not increase AFUE as measured by the DOE test procedure at 

Appendix N to Subpart B of 10 CFR Part 430. However, these features (i.e., Micro Combined 

Heat and Power, Improved Motor Efficiency, Positive Shut-Off Valve for Oil Burner Nozzles, 

and Heat Pump Boilers) can reduce the energy consumption of the residential boilers in actual 

applications. Although these technologies were not considered in the analyses, DOE does not 

discourage their use by manufacturers because of their potential to reduce annual energy 

consumption. For each technology removed for this reason, DOE provided an explanation of 

why the technology does not affect AFUE.

Micro Combined Heat and Power (Micro-CHP)

It is possible to use the heat generated by the boiler’s combustion system to generate 

electricity opportunistically. Self-generated electricity can be used to operate the electrical 

components of the boiler or can be sold back to the grid. Known methods of micro-CHP include 

fuel cell generators, thermophotovoltaic (TPV) generators, thermoelectric generators, and 

thermionic conversion. Other techniques use engines based on the Rankine cycle, Brayton cycle, 

Stirling cycle, or Otto cycle, where the engine drives an electrical generator or provides direct 

mechanical power and the waste heat from the engine is used for space heating. Neither the 

boiler’s electricity use nor the heat generated by its electrical components, however, contribute to 

the calculation of AFUE. Therefore, this technology will have no effect on AFUE. 

Improved Motor Efficiency

More-efficient electric motors could be used in hot-water boiler pumps and draft inducers. 

Most hot-water boiler pumps use a permanent split capacitor (PSC) design. PSC motors are 

reasonably efficient (above 70 percent) when operating at high speed; however, when these motors 

are operated at low speed, their efficiencies may drop into the 20 percent range. Energy 

consumed by the pump or other electrical components, such as draft inducers, is not accounted 

for by the AFUE calculation.

Positive Shut-Off Valve for Oil Burner Nozzles

One option for oil-fired boilers is a positive shut-off valve on the fuel nozzle, which 

reduces smoke and soot production during burner start-up and shutdown. This valve is generally 

installed directly in the nozzle tip and prevents oil from dripping into the combustion chamber. 

This option can also be retrofitted on existing burners. A positive shut-off valve in an oil burner 

nozzle does not affect the efficiency of the appliance, but plays a role as an emission-control 

device. 

Heat Pump Boilers
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Heat pump boilers use heat pump technology to extract heat from the surroundings for 

heating hot water. For electric boilers, this is an alternative to resistive heating. Since heat does 

not naturally transfer from a low temperature to a higher temperature, a mechanical system 

consisting primarily of a closed refrigeration loop containing a refrigerant vapor compressor, an 

evaporator (a type of heat exchanger), a condenser (another heat exchanger), and an expansion 

device is used to transfer the heat. The working fluid in the loop, the refrigerant, extracts heat 

from the surrounding air. Typically, the evaporator captures heat from the ambient air, and the 

condenser delivers this heat to the water inside of the boiler. The pump and expansion device

facilitate pressure and phase changes to allow for these heat transfer processes. This technology 

does not improve AFUE, as the test procedure currently sets the AFUE at 100% for indoor 

electric boilers. Gas-fired absorption heat pump boilers also use a refrigeration loop to transfer 

heat to the water, and similarly, this technology does not improve AFUE as it is not captured by 

the test method. 

4.3 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 product utility or product availability; and (4) adverse impacts on

health or safety. DOE eliminated Pulse Combustion and Control Relay’s for Brushless 

Permanent Magnet Motors.

4.3.1 Pulse Combustion

Pulse combustion burners operate on self-sustaining resonating pressure waves that 

alternately rarefy the combustion chamber (drawing a fresh fuel-air mixture into the chamber) 

and pressurize it (causing ignition by compression heating of the mixture to its flash point). Pulse 

combustion systems feature high heat transfer rates, and have high combustion efficiency. 

However, manufacturers have indicated that pulse combustion boilers have had reliability issues 

in the past, and therefore, they do not consider this as a viable option to improve efficiency. 

Further, manufacturers indicated that similar or greater efficiencies to those in pulse combustion 

boilers can be achieved using alternative technologies. For this reasons, DOE is not including 

pulse combustion as a technology option as it would reduce customer utility. 
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4.3.2 Control Relay for Models with Brushless Permanent Magnet (BPM) Motors 

(Standby/Off Mode)

During testing of standby and off mode components performed for the DOE furnace and 

central air conditioner rulemakinga, DOE found that BPM motors and their associated controls 

consume power while in standby and/or off modes, while PSC motors did not have any standby 

or off mode power draw. Therefore for those boilers that utilize them, the BPM motor and 

associated controls could be disconnected while the system is in standby mode or off mode 

through the use of a control relay to further reduce a system’s standby/off mode power 

consumption. A typical control relay activates a switch when current runs through it and when 

there is no current a spring holds the switch in the open position. However, manufacturer 

feedback in the furnace rulemaking (which was reconfirmed during interviews for the boiler 

rulemaking) indicated that ECM motors are subjected to large currents upon start up and using a 

control relay to completely depower them could reduce the lifetime of the motors, leading to a 

reduction in utility of the product. Manufacturer feedback at the framework public meeting also 

indicated that this feature would reduce the lifetime of the motors. For this reason, DOE is not 

including control relays as a technology option. 

4.4 REMAINING TECHNOLOGIES

After eliminating those technologies that have no effect on improving the rated AFUE or

reducing the standby and off mode energy consumption, and screening the other technologies

using the four criteria listed above, DOE passed the remaining technologies to the engineering 

analysis for consideration in developing the cost-efficiency relationship.

4.4.1 AFUE Efficiency Standards

For its AFUE standards analysis, DOE considered the following technology options: 

• Heat Exchanger Improvements

• Burner Derating

• Modulating Operation

• Direct Vent

• Delayed Action Oil Pump Solenoid Valve

• Premix Burners

• Low Pressure Air Atomizing Oil Burner

 

a

See:http://www1.eere.energy.gov/buildings/appliance_standards/residential/residential_furnaces_cac_hp_final_rule

.html
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DOE also considered Dampers and Electronic Ignition, but found that they are already 

incorporated in baseline products. 

4.4.2 Standby Mode and Off Mode Power Consumption Standards

Because DOE is required by EPCA, as amended by EISA 2007, to include a descriptor for 

standby mode and off mode energy consumption for residential boilers, a separate screening analysis 

was conducted for standby and off mode design options. (42 U.S.C. 6295(gg)(2)(A))

DOE considered the following design options that are capable of reducing the standby and 

off mode electrical power consumption of residential boilers: 

• Transformer Improvements

• Switching Mode Power Supply