4- i 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 ENGINEERIN G 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 P THP ....................................... 4-74-1 CHAPTER 4. SCREENING ANALYSIS

4.1 INTRODUCTION

This chapter details the screening analysis conduct ed by the U.S. Department of Energy (DOE) of the technology options identified in the m arket and technology assessment (Chapter 3 of this technical support document (TSD)) for packa ged terminal air conditioners (PTACs) and packaged terminal heat pumps (PTHPs). In the marke t 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 ana lysis 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, tr ade organizations, and energy efficiency advocates. Technology options that are judged to be viable approaches for improving efficiency are retained as inputs to the subsequent engineerin g analysis, and are designated as design options. Technology options that are not incorporat ed 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 avai lability, or as to health or safety will be eliminated from consideration. The rationale for ei ther screening out or retaining each technology option is detailed in the following sect ions.

4.2 SCREENED-OUT TECHNOLOGY OPTIONS

The following section details the specific technolo gy options that were screened out prior to the engineering analysis, along with the rationa le for elimination.

The technologies identified in the market and tech nology assessment were evaluated pursuant to the criteria set out in the Energy Poli cy 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 o ptions. DOE then applied the following set of screening criteria to determine which design option s 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 s ervice. 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 n ecessary to serve the relevant market at the time of the effective date of the standard, then th at technology will not be considered further.4-2

(3) Impacts on equipment utility to customers. If a technology is determined to have significant adverse impact on the utility of the eq uipment to significant subgroups of customers, or results in the unavailability of any covered equ ipment 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 sig nificant 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 elimi nated 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 co mmon in the capacity range associated with PTAC and PTHP equipment (6,000 to 15,000 Btu/h), se veral companies manufacture scroll compressors from 9,000 Btu/h and up. However, DOE i s 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 comp ressors found in reverse engineering of PTACs and PTHPs in the 15,000 Btu/h class had effic iency 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 tha t the use of scroll compressors would improve the efficiency of PTAC and PTHP units, give n 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 e xchanger 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 evapora tor to the air leaving the evaporator. This allows the evaporator air exit temperature to be si gnificantly lower. Since the maximum possible moisture content of air increases with increasing t emperature, this also means that the reducedtemperature air at the evaporator exit would have l ower moisture content. The temperature of the air is then warmed by the post-evaporator portion o f 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, th us they do not improve EER of the equipment. Therefore, DOE screened out heat pipes a s a design option for improving the energy efficiency of PTACs and PTHPs.4-3

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) Significa nt New Alternatives Policy (SNAP) Program evaluates and regulates substitutes for the ozone-depleting chemicals (such as air conditioning refrigerants) that are being phased ou t under the stratospheric ozone protection provisions of the Clean Air Act (CAA) (42 U.S.C. 74 01 et seq.). The EPA’s SNAP Program currently lists 23 acceptable alternatives for refr igerant used in the Household and Light Commercial Air Conditioning class of equipment (whi ch includes PTAC and PTHP equipment). On July 9, 2014, the EPA issued a notice of propose d rulemaking proposing to list three flammable refrigerants as new acceptable substitute s, 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 substitu te refrigerants (including refrigerants that are already approved and refrigerants that are prop osed for approval) for use in new production in the Household and Light Commercial Air Condition ing class of equipment (which includes PTAC and PTHP equipment). DOE is not aware of any S NAP-approved refrigerants, or any refrigerants that have been proposed for SNAP appro val, 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 Progra m is available online at: http://www.epa.gov/ozone/snap/

.4-4

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 is sued July 9, 2014 HFC-32 Propane (R-290) R-441A

DOE is aware of initial research with drop-in appli cations (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 spl it-system application. Initial research shows that, in this application, R-32 had a higher capaci ty and similar efficiency as R-410A, but its discharge temperatures and pressures were significa ntly higher. 2 This suggests that R-32 might show efficiency comparable to R-410A in PTAC and PT HP applications, and the research is inconclusive regarding whether R-32 will reduce ene rgy 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 (2 013). “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 p1.4-5

aware of test results from the use of alternate ref rigerants in PTAC- or PTHP-specific applications that have been optimized for alternate refrigerants.

DOE is aware of initial research with drop-in appli cations (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 spl it-system application. Initial research shows that, in this application, R-32 had a higher capaci ty and similar efficiency as R-410A, but its discharge temperatures and pressures were significa ntly higher. This suggests that R-32 might show efficiency comparable to R-410A in PTAC and PT HP applications, and the research is inconclusive regarding whether R-32 will reduce ene rgy use and/or by how much.

DOE is not aware of test results from the use of al ternate 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 ENGINEERIN G ANALYSIS

Typically, energy-saving technologies that pass the screening analysis are evaluated in the engineering analysis. However, some technologi es 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 CO P metric would not measure the energy impact of these technologies. Accordingly, DOE eli minated the following technologies from consideration in the engineering analysis based upo n 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 believ es 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 techno logy 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 (a lso known as “microgrooves”) to enhance energy efficiency by improving heat transfe r across the heat exchanger. With this technology, the internal face of heat exchanger tub es is rifled with small grooves that increase the interior surface area of the tube and induce tu rbulence in the refrigerant flow. Having observed that microgroove technology was used in th e majority of baseline units disassembled in the engineering analysis, DOE believes that microgr oove technology is currently being used in baseline equipment today. Thus, DOE believes that t he efficiency benefits of the technology are4-6

negligible and DOE has eliminated rifled interior t ube walls as a potential avenue for efficiency improvement.

4.3.3 Microchannel Heat Exchangers

Microchannel heat exchangers in air conditioning ap plications are heat exchangers in which refrigerant fluid flows in confinements with typical hydraulic diameter of less than one millimeter. Microchannels may improve unit efficien cy by improving the efficiency of heat transfer between refrigerant and air across the hea t exchanger. Currently, microchannel heat exchangers are in the development stage for PTAC an d PTHP applications and are not proven for consistent, field installed equipment performan ce 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 developi ng 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 pr ototype units and test results.

At this point, DOE does not have information regard ing these prototype tests that would allow assessment of the efficiency improvements ass ociated with the specific microchannel technology and/or the costs associated with its imp lementation. 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 re duce annual energy consumption of PTACs or PTHPs by optimizing the operation of the e quipment 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 e nergy consumption throughout the year, it does not increase the EER under the ARI 310/380-200 4 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 effic iency option because the test procedure and EER or COP metric would not measure t he energy impact of these technologies.

4.3.5 Corrosion Protection

Corrosion protection materials used in PTACs and PT HPs protect the equipment and prolong its use when it is exposed to chemically ha rsh operating conditions. DOE believes that corrosion protection has a negative impact on stead y state operation to some degree, but that corrosion protection may help improve the overall u nit performance over several years of operation. Although it is beneficial for units in harsh environments to be corrosion protected,4-7

corrosion protection does not improve the EER as me asured by the test procedure. Therefore, DOE did not consider this technology in the enginee ring analysis.

4.3.6 Hydrophobic Material Treatment of Heat Exchangers

Material treatment of heat exchangers (also known a s “plasma treatment”) allows the condensate that forms on the fins to be repelled an d drained faster than on non-treated heat exchangers. Hydrophobic treatments are used to redu ce 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 sh own 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 the rmal expansion valves (TXVs) would not improve the energy efficiency of PTACs or PTHPs, be cause there is only one condition for which the fixed-orifice expansion device can be opt imized. DOE has insufficient information to know whether testing at multiple conditions would m ake 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 technol ogies will be evaluated (consistent with equipment available on the market) further in the s ubsequent engineering analysis.

Table 4.4.1 Retained Design Options for PTAC and PT HP Compressor Improvements

• Higher Efficiency Compressors Condenser and evaporator fan and fan motor improvem ents:

• 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 hi gh efficiency compressors, into their designs. DOE observed in reverse engineering analysis that P TAC and PTHP manufacturers use several different compressor models with a wide range of ef ficiency ratings.4-8

4.4.2 Higher Efficiency Fan Motors

Manufacturers of baseline PTACs and PTHPs use perma nent split capacitor (PSC) fan motors due to their modest cost, compact design, an d durability. More efficient PSC motor designs applicable to PTACs and PTHPs are an ongoin g industry challenge, and there been no substantial gain in efficiency in recent years. PS C 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 constraint s 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 origina l 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. Seve ral 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 effi ciency 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 ar e 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 manufa cturer has incorporated bent heat exchanger coils to increase the heat exchanger face area whil e remaining inside the standard size unit constraints.

4.4.4 Improved Air Flow and Fan Design

Manufacturers of PTACs and PTHPs currently use seve ral techniques to shape and direct airflow inside PTAC and PTHP units. Manufacturers m ay improve unit efficiency by optimizing air paths and fan blade designs, and by selecting a ppropriate fan and motor combinations.