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CHAPTER 4. SCREENING ANALYSIS 

TABLE OF CONTENTS 

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

4.2 SCREENED-OUT TECHNOLOGY OPTIONS ............................................................. 4-1

4.2.1 Scroll Compressors .............................................................................................. 4-2

4.2.2 Heat Pipes ............................................................................................................ 4-2

4.2.3 Alternate Refrigerants .......................................................................................... 4-3

4.3 OTHER TECHNOLOGIES NOT CONSIDERED IN THE ENGINEERING 

ANALYSIS .................................................................................................................................. 4-5

4.3.1 Re-Circuiting Heat Exchanger Coils ................................................................... 4-5

4.3.2 Rifled Interior Tube Walls ................................................................................... 4-5

4.3.3 Microchannel Heat Exchangers ........................................................................... 4-6

4.3.4 Complex Control Boards ..................................................................................... 4-6

4.3.5 Corrosion Protection ............................................................................................ 4-6

4.3.6 Hydrophobic Material Treatment of Heat Exchangers ........................................ 4-7

4.4 REMAINING DESIGN OPTIONS ................................................................................. 4-7

4.4.1 Higher Efficiency Compressors ........................................................................... 4-7

4.4.2 Higher Efficiency Fan Motors ............................................................................. 4-8

4.4.3 Increased Heat Exchanger Area ........................................................................... 4-8

4.4.4 Improved Air Flow and Fan Design .................................................................... 4-8

LIST OF TABLES 

Table 4.2.1 Potential Substitutes for HCFCs in new Household and Light Commercial 

Air Conditioning Equipment.................................................................... 4-4

Table 4.4.1 Retained Design Options for PTAC and PTHP ....................................... 4-7
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CHAPTER 4. SCREENING ANALYSIS 

4.1 INTRODUCTION 

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

(DOE) of the technology options identified in the market and technology assessment (Chapter 3 

of this technical support document (TSD)) for packaged terminal air conditioners (PTACs) and 

packaged terminal heat pumps (PTHPs). In the market and technology assessment, DOE 

presented an initial list of technologies that can be used to increase the efficiency of the 

considered equipment. 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’s analysis as well as inputs 

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

advocates. Technology options that are judged to be viable approaches for improving efficiency 

are retained as inputs to the subsequent engineering analysis, and are designated as design 

options. Technology options that 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. The rationale for either screening out or retaining each 

technology option is detailed in the following sections. 

4.2 SCREENED-OUT TECHNOLOGY OPTIONS 

The following section details the specific technology options that were screened out prior 

to the engineering analysis, along with the rationale for elimination. 

 The technologies identified in the market and technology assessment were evaluated 

pursuant to the criteria set out in the Energy Policy and Conservation Act (EPCA). (42 United 

States Code (U.S.C.) 6291-6317) DOE consulted with industry, technical experts, and other 

interested parties in developing a list of design options. DOE then applied the following set of 

screening criteria to determine which design options are unsuitable for further consideration in 

the rulemaking: 

 (1) Technological feasibility. If it is determined that a technology has not been 

incorporated in commercial equipment or in working prototypes, then that technology will not be 

considered further. 

 (2) Practicability to manufacture, install, and service. If it is determined that mass 

production of a technology in commercial equipment and reliable installation and servicing of 

the technology could not be achieved on the scale necessary to serve the relevant market at the 

time of the effective date of the standard, then that technology will not be considered further. 
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 (3) Impacts on equipment utility to customers. If a technology is determined to have 

significant adverse impact on the utility of the equipment to significant subgroups of customers, 

or results in the unavailability of any covered equipment type with performance characteristics 

(including reliability), features, size, capacities, and volumes that are substantially the same as 

equipment generally available in the United States at the time, it will not be considered further. 

 (4) Safety of technologies. If it is determined that a technology will have significant 

adverse impacts on health or safety, it will not be considered further. 

 After reviewing the technology options to increase the efficiency of the covered 

equipment against the screening criteria, DOE eliminated the following technology options from 

consideration in its rulemaking analysis. 

4.2.1 Scroll Compressors 

Scroll compressors compress gas in a fundamentally different manner from traditional 

compressors—between two spirals, one fixed and one rotating. Scroll compressors may operate 

at higher efficiencies than the rotary compressors typically used in PTAC and PTHP 

applications. Though scroll compressors are less common in the capacity range associated with 

PTAC and PTHP equipment (6,000 to 15,000 Btu/h), several companies manufacture scroll 

compressors from 9,000 Btu/h and up. However, DOE is not aware of scroll compressor models 

at these lower capacities that would fit in a PTAC cabinet and that are more efficient than the 

same capacity of rotary compressor. The rotary compressors found in reverse engineering of 

PTACs and PTHPs in the 15,000 Btu/h class had efficiency ratings from 9.8 to 10.6 EER. By 

comparison, scroll compressors of similar capacity are rated from 7.2 EER to 11.0 EER, but 

most are too tall to fit in a 16” PTAC cabinet. 

 As a result, DOE does not believe at this time that the use of scroll compressors would 

improve the efficiency of PTAC and PTHP units, given the size and capacity constraints of these 

units. For this reason, DOE did not consider scroll compressors further in the NOPR analyses. 

4.2.2 Heat Pipes 

Under humid ambient conditions, using heat pipes to pre-treat the entering air from the 

conditioned space can improve the evaporator heat exchanger performance. Heat pipes increase 

the latent cooling capacity (i.e., moisture removal) of an air-conditioner. They do this by 

transferring heat from the air entering the evaporator to the air leaving the evaporator. This 

allows the evaporator air exit temperature to be significantly lower. Since the maximum possible 

moisture content of air increases with increasing temperature, this also means that the reducedtemperature air at the evaporator exit would have lower moisture content. The temperature of the 

air is then warmed by the post-evaporator portion of the heat pipe. Heat pipes generally shift 

some of the cooling capacity of the equipment from reduction of air temperature to reduction of 

humidity, but do not increase the cooling capacity of an evaporator. They impose additional 

pressure drop that the indoor fan must overcome, thus they do not improve EER of the 

equipment. Therefore, DOE screened out heat pipes as a design option for improving the energy 

efficiency of PTACs and PTHPs. 
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4.2.3 Alternate Refrigerants 

Nearly all PTAC and PTHP equipment is designed with R-410A as the refrigerant. The 

Environmental Protection Agency’s (EPA’s) Significant New Alternatives Policy (SNAP) 

Program evaluates and regulates substitutes for the ozone-depleting chemicals (such as air 

conditioning refrigerants) that are being phased out under the stratospheric ozone protection 

provisions of the Clean Air Act (CAA) (42 U.S.C. 7401 et seq.). The EPA’s SNAP Program 

currently lists 23 acceptable alternatives for refrigerant used in the Household and Light 

Commercial Air Conditioning class of equipment (which includes PTAC and PTHP equipment). 

On July 9, 2014, the EPA issued a notice of proposed rulemaking proposing to list three 

flammable refrigerants as new acceptable substitutes, subject to use conditions, for refrigerant in 

the Household and Light Commercial Air Conditioning class of equipment. 79 FR 38811 (July 9, 

2014) 

Table 4.2.1 presents the list of potential substitute refrigerants (including refrigerants that 

are already approved and refrigerants that are proposed for approval) for use in new production 

in the Household and Light Commercial Air Conditioning class of equipment (which includes 

PTAC and PTHP equipment). DOE is not aware of any SNAP-approved refrigerants, or any 

refrigerants that have been proposed for SNAP approval, that are known to enable better 

efficiency than R-410A for PTAC and PTHP equipment.1 Hence, DOE did not consider alternate 

refrigerants for further analysis. 

 

1

 Additional information regarding EPA’s SNAP Program is available online at: http://www.epa.gov/ozone/snap/. 
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Table 4.2.1 Potential Substitutes for HCFCs in new Household and Light Commercial Air 

Conditioning Equipment 

Substitutes Approved by EPA SNAP Program 

HFC-134a 

ISCEON-59, NU-22, R-417A 

R-410A 

R-410B 

R-407C 

R-507, R-507A 

Ammonia Absorption 

Evaporative Cooling 

Desiccant Cooling 

R-404A 

R-125/134a/600a 

RS-44 

R-421A 

R-422D 

R-424A 

R-125/290/134a/600a 

R-422C 

R-422B 

KDD5, R-438A 

R-434A 

R-407A 

R-437A 

R-407F 

Substitutes Proposed by EPA SNAP Program in NOPR issued July 9, 2014 

HFC-32 

Propane (R-290) 

R-441A 

DOE is aware of initial research with drop-in applications (where an alternate refrigerant 

replaces the existing refrigerant in a system that is optimized for the existing refrigerant) using 

R-32 in place of R-410A in a residential ducted split-system application. Initial research shows 

that, in this application, R-32 had a higher capacity and similar efficiency as R-410A, but its 

discharge temperatures and pressures were significantly higher.2 This suggests that R-32 might 

show efficiency comparable to R-410A in PTAC and PTHP applications, and the research is 

inconclusive regarding whether R-32 will reduce energy use and/or by how much. DOE is not 

 

2

 This research was published in the journal ASHRAE Transactions, at: 

Biswas, Auvi; Barve, Atharva; Cremaschi, Lorenzo (2013). “An Experimental Study of the Performance of New 

Low Global Warming Potential (LGWP) Refrigerants at Extreme High Temperature Ambient Conditions in 

Residential AC Ducted Split Systems,” ASHRAE Transactions. 119(1), special section p1. 
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aware of test results from the use of alternate refrigerants in PTAC- or PTHP-specific 

applications that have been optimized for alternate refrigerants. 

DOE is aware of initial research with drop-in applications (where an alternate refrigerant 

replaces the existing refrigerant in a system that is optimized for the existing refrigerant) using 

R-32 in place of R-410A in a residential ducted split-system application. Initial research shows 

that, in this application, R-32 had a higher capacity and similar efficiency as R-410A, but its 

discharge temperatures and pressures were significantly higher. This suggests that R-32 might 

show efficiency comparable to R-410A in PTAC and PTHP applications, and the research is 

inconclusive regarding whether R-32 will reduce energy use and/or by how much. 

DOE is not aware of test results from the use of alternate refrigerants in PTAC- or PTHPspecific applications that have been optimized for alternate refrigerants. DOE requests feedback 

on the efficacy of alternative refrigerants in PTAC and PTHP equipment. 

4.3 OTHER TECHNOLOGIES NOT CONSIDERED IN THE ENGINEERING 

ANALYSIS 

Typically, energy-saving technologies that pass the screening analysis are evaluated in 

the engineering analysis. However, some technologies are not included in the analysis for other 

reasons, including: (1) available data suggest that the efficiency benefits of the technology are 

negligible; (2) data are not available to evaluate the energy efficiency characteristics of the 

technology; or (3) the test procedure and EER or COP metric would not measure the energy 

impact of these technologies. Accordingly, DOE eliminated the following technologies from 

consideration in the engineering analysis based upon these three additional considerations. 

4.3.1 Re-Circuiting Heat Exchanger Coils 

Manufacturers of PTAC and PTHP heat exchangers may improve the heat transfer 

efficiency across the heat exchanger by rearranging the refrigerant’s path through the various 

tubes inside the heat exchanger. Manufacturers can rearrange the refrigerant path by “recircuiting” the heat exchanger, either by splitting the refrigerant path into new circuits or rerouting the existing circuits. One objective of re-circuiting is to optimally pair air and refrigerant

at every location in the heat exchanger. DOE believes that PTACs are a very mature industry and 

that engineers have already optimized the number of circuits for heat transfer. Thus, DOE 

believes that the efficiency benefits of the technology are negligible and DOE has eliminated 

heat exchanger re-circuiting as a potential avenue for efficiency improvement. 

4.3.2 Rifled Interior Tube Walls 

Heat exchangers using rifled interior tube walls (also known as “microgrooves”) to 

enhance energy efficiency by improving heat transfer across the heat exchanger. With this 

technology, the internal face of heat exchanger tubes is rifled with small grooves that increase 

the interior surface area of the tube and induce turbulence in the refrigerant flow. Having 

observed that microgroove technology was used in the majority of baseline units disassembled in 

the engineering analysis, DOE believes that microgroove technology is currently being used in 

baseline equipment today. Thus, DOE believes that the efficiency benefits of the technology are 
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negligible and DOE has eliminated rifled interior tube walls as a potential avenue for efficiency 

improvement. 

4.3.3 Microchannel Heat Exchangers 

Microchannel heat exchangers in air conditioning applications are heat exchangers in 

which refrigerant fluid flows in confinements with typical hydraulic diameter of less than one 

millimeter. Microchannels may improve unit efficiency by improving the efficiency of heat 

transfer between refrigerant and air across the heat exchanger. Currently, microchannel heat 

exchangers are in the development stage for PTAC and PTHP applications and are not proven 

for consistent, field installed equipment performance in PTACs and PTHPs. DOE notes that the 

engineering analysis was based on efficiency levels and, because units with microchannels are 

not commercially available, DOE cannot estimate the increase manufacturing costs associated 

with whatever efficiency gains such units may offer. 

DOE is aware that Zess, Inc. Industries is developing an integrated microchannel 

refrigeration system for applications in PTAC units. Zess, Inc. Industries has indicated that this 

application may achieve efficiencies as high as 15 EER in PTACs. DOE requested more 

information from Zess, Inc. Industries regarding prototype units and test results. 

At this point, DOE does not have information regarding these prototype tests that would 

allow assessment of the efficiency improvements associated with the specific microchannel 

technology and/or the costs associated with its implementation. DOE eliminated microchannel 

heat exchanges from the NOPR analysis because data are not available to evaluate the energy 

efficiency characteristics of the technology. 

4.3.4 Complex Control Boards 

Digital energy management control interfaces can reduce annual energy consumption of 

PTACs or PTHPs by optimizing the operation of the equipment under varying operating 

conditions. For example, they may allow operation managers in hotels to remotely turn off or 

change temperature set points of units throughout a building. Although this technology can 

reduce peak energy demand and also reduce overall energy consumption throughout the year, it 

does not increase the EER under the ARI 310/380-2004 test procedure. The test procedure 

requires that units be tested at steady state test conditions and DOE believes that complex control 

boards do not help steady state performance in PTAC and PTHP applications. 

 DOE eliminated complex control boards as an efficiency option because the test 

procedure and EER or COP metric would not measure the energy impact of these technologies. 

4.3.5 Corrosion Protection 

Corrosion protection materials used in PTACs and PTHPs protect the equipment and 

prolong its use when it is exposed to chemically harsh operating conditions. DOE believes that 

corrosion protection has a negative impact on steady state operation to some degree, but that 

corrosion protection may help improve the overall unit performance over several years of 

operation. Although it is beneficial for units in harsh environments to be corrosion protected, 
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corrosion protection does not improve the EER as measured by the test procedure. Therefore, 

DOE did not consider this technology in the engineering analysis. 

4.3.6 Hydrophobic Material Treatment of Heat Exchangers 

Material treatment of heat exchangers (also known as “plasma treatment”) allows the 

condensate that forms on the fins to be repelled and drained faster than on non-treated heat 

exchangers. Hydrophobic treatments are used to reduce mineral build up and corrosion on heat 

exchanger fins, to improve long-term performance of the unit. Although enhanced long term 

performance is beneficial, this treatment is not shown to improve the EER as per the test 

procedure. Thermostatic Expansion Valves 

Thermal expansion valves (TXVs) control the flow of refrigerant into the evaporator 

based on a temperature feedback. DOE notes that thermal expansion valves (TXVs) would not 

improve the energy efficiency of PTACs or PTHPs, because there is only one condition for 

which the fixed-orifice expansion device can be optimized. DOE has insufficient information to 

know whether testing at multiple conditions would make sufficient efficiency improvement to 

justify the increased test time. Therefore, DOE did not consider this technology in the 

engineering analysis. 

4.4 REMAINING DESIGN OPTIONS 

Table 4.4.1 lists the technology options that were retained by DOE and subsequently 

designated as design options. Each of these technologies will be evaluated (consistent with 

equipment available on the market) further in the subsequent engineering analysis. 

Table 4.4.1 Retained Design Options for PTAC and PTHP 

Compressor Improvements 

• Higher Efficiency Compressors 

Condenser and evaporator fan and fan motor improvements: 

• Higher Efficiency Fan Motors 

Increased Heat Exchanger Area 

Improved Air Flow and Fan Design 

The remaining technology options in Table 4.4.1 are briefly described below. 

4.4.1 Higher Efficiency Compressors 

Manufacturers can improve the energy efficiency of PTAC and PTHP units by 

incorporating more efficient components, such as high efficiency compressors, into their designs. 

DOE observed in reverse engineering analysis that PTAC and PTHP manufacturers use several 

different compressor models with a wide range of efficiency ratings. 
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4.4.2 Higher Efficiency Fan Motors 

Manufacturers of baseline PTACs and PTHPs use permanent split capacitor (PSC) fan 

motors due to their modest cost, compact design, and durability. More efficient PSC motor 

designs applicable to PTACs and PTHPs are an ongoing industry challenge, and there been no 

substantial gain in efficiency in recent years. PSC manufacturers can improve efficiency by 

increasing the surface area of rotors, although the overall size of the PSC motor would increase 

in that case. PTACs and PTHPs have size constraints that do not allow an increase in motor size 

to a level which would have a significant impact on energy efficiency. DOE believes any further 

gains in PSC fan motor efficiency will be difficult to achieve, and has thus eliminated 

improvement of PSC fan motors as a potential avenue for efficiency improvement. 

Besides PSC-based fan motors, PTAC and PTHP original equipment manufacturers 

(OEMs) can choose to implement permanent magnet (PM) motors. Such motors typically offer 

higher efficiencies than PSC-based fan motors, but these improvements come with increased 

costs for the motor unit and control hardware. Several manufacturers use DC motors in their 

higher-efficiency PTAC and PTHP models. 

4.4.3 Increased Heat Exchanger Area 

Manufacturers of PTACs and PTHPs increase unit efficiency by increasing heat 

exchanger size, either through elongating the face of the heat exchanger or increasing the number 

of heat exchanger tube rows. Standard-size PTACs are dimensionally constrained and, because 

of these constraints on unit size, there are limits to the efficiency gains that may be had by 

increasing heat exchanger size. At least one manufacturer has incorporated bent heat exchanger 

coils to increase the heat exchanger face area while remaining inside the standard size unit 

constraints. 

4.4.4 Improved Air Flow and Fan Design 

Manufacturers of PTACs and PTHPs currently use several techniques to shape and direct 

airflow inside PTAC and PTHP units. Manufacturers may improve unit efficiency by optimizing 

air paths and fan blade designs, and by selecting appropriate fan and motor combinations.