CHAPTER 4. SCREENING ANALYSIS

TABLE OF CONTENTS

**Chapter 4.**  **Screening Analysis......................................................................................................4­i** 

**TABLE OF**  **CONTENTS..............................................................................................................4­I**

**CHAPTER 4.**  **SCREENING ANALYSIS** 

**.................................................................................. 4­1** 

**4.1 INTRODUCTION** 

**........................................................................................................... 4­1** 

**4.2 TECHNOLOGIES**  **THAT DO**  **NOT ENHANCE**  **EER AS**  **MEASURED...................... 4­2** 

**4.2.1 Variable**  **Speed Compressors** 

**............................................................................... 4­2** 

**4.2.2 Complex**  **Control Boards** 

**..................................................................................... 4­2** 

**4.2.3 Corrosion**  **Protection**

**............................................................................................ 4­3** 

**4.2.4 Clutched**  **Motor Fan** 

**............................................................................................. 4­3** 

**4.2.5 Thermal**  **Expansion Valve....................................................................................**  **4­3**

**4.3 SCREENED­OUT**  **TECHNOLGIES............................................................................... 4­4**

**4.3.1 Scroll**  **Compressors**

**.............................................................................................. 4­4** 

**4.3.2 Higher**  **Efficiency Fan**  **Motors**

**............................................................................. 4­5** 

**4.3.3 Microchannel**  **Heat Exchangers** 

**........................................................................... 4­5** 

**4.3.4 Material**  **Treatment of**  **Heat Exchangers** 

**.............................................................. 4­6** 

**4.3.5 Improved**  **Air Flow**  **and Fan**  **Design**

**.................................................................... 4­7** 

**4.3.6 Heat**  **Pipes**

**............................................................................................................ 4­8** 

**4.4 REMAINING**  **TECHNOLOGIES**

**................................................................................... 4­8** 

**4­i**CHAPTER 4. SCREENING ANALYSIS

4.1 INTRODUCTION

**This chapter**  **details the**  **screening analysis**  **that the**  **U.S. Department**  **of Energy**  **(DOE)**

**conducted in**  **support of**  **the ongoing**  **energy conservation**  **standards rulemakings**  **for packaged** 

**terminal air**  **conditioners (PTACs)**  **and packaged**  **terminal heat**  **pumps (PTHPs).** 

**In Chapter**  **3, the**  **market and**  **technology assessment**  **(MTA), DOE**  **presented an**  **initial list** 

**of technologies**  **that can**  **improve the**  **energy efficiency**  **of PTACs**  **and PTHPs.**  **The purpose**  **of**

**the screening**  **analysis is**  **to evaluate**  **the technologies**  **that improve**  **equipment efficiency**  **to**

**determine which**  **technologies to**  **consider further**  **and which**  **to screen**  **out. DOE**  **consulted with**  **a**

**range of**  **parties, including**  **industry, technical**  **experts, and**  **others to**  **develop a**  **list of**  **technologies**

**for consideration.**  **Some of**  **these technologies**  **can reduce**  **annual energy**  **consumption of** 

**equipment in**  **actual applications,**  **but may**  **not improve**  **the energy­efficiency**  **ratio (EER)**  **and**

**coefficient of**  **performance (COP)**  **of PTACs**  **and PTHPs**  **as measured**  **by the**  **Air­Conditioning**

**and Refrigeration**  **Institute (ARI)**  **310/380­2004** Standard for Packaged Terminal AirConditioners and Heat Pumps **(ARI 310/380­2004)**  **test procedure,**  **which DOE**  **has incorporated** 

**by reference**  **into its**  **regulations at**  **10 Code**  **of Federal**  **Regulations (CFR)**  **section 431.95.**  **DOE**

**removed from**  **consideration those**  **technologies that**  **do not**  **increase EER**  **and COP**  **per the**  **test**

**procedures. DOE**  **evaluated the**  **remaining technologies**  **pursuant to**  **the criteria**  **set out**  **in the** 

**Energy Policy**  **and Conservation**  **Act (EPCA),**  **as amended.**  **(42 U.S.C.**  **6311­6317)**

**Section 325(o)**  **EPCA establishes**  **criteria for**  **prescribing new**  **or amended**  **standards**

**designed to**  **achieve the**  **maximum improvement**  **in energy**  **efficiency. Further,**  **EPCA directs**  **the**

**Secretary of**  **Energy to**  **determine whether**  **a standard**  **is technologically**  **feasible and** 

**economically justified.**  **(42 U.S.C.**  **6295(o)(2)(A), as**  **directed by**  **42 U.S.C.**  **6316(a)(1)­(3)).**

**EPCA also**  **establishes guidelines**  **for determining**  **whether a**  **standard is**  **economically justified.** 

**(42 U.S.C.**  **6295(o)(2)(B)) Appendix**  **A to**  **subpart C**  **of Title**  **10, Code**  **of Federal**  **Regulations,**

**Part 430**  **(10 CFR**  **Part 430),**  **“Procedures, Interpretations**  **and Policies**  **for Consideration**  **of New** 

**or Revised**  **Energy Conservation**  **Standards for**  **Consumer Products”**  **(the Process**  **Rule), sets**  **forth**

**procedures to**  **guide DOE**  **in its**  **consideration and**  **promulgation of**  **new or**  **revised equipment** 

**energy conservation**  **standards. These**  **procedures elaborate**  **on the**  **statutory criteria**  **provided in** 

**42 U.S.C.**  **6295(o) and,**  **in part,**  **eliminate problematic**  **technologies early**  **in the**  **process of** 

**prescribing or**  **amending an**  **energy efficiency**  **standard. In**  **particular sections**  **4(b)(4) and**  **5(b) of** 

**the Process**  **Rule guide**  **DOE in**  **determining whether**  **to eliminate**  **from consideration**  **any**

**technology that**  **presents unacceptable**  **problems with**  **respect to**  **the following**  **criteria:**

Technological feasibility. **Technologies incorporated**  **in commercial**  **equipment or**  **in**

**working prototypes**  **will be**  **considered technologically**  **feasible.**

Practicability to manufacture, install, and service. **If mass**  **production of**  **a technology** 

**in commercial**  **equipment and**  **reliable installation**  **and servicing**  **of the**  **technology could**  **be**

**achieved on**  **the scale**  **necessary to**  **serve the**  **relevant market**  **at the**  **time of**  **the effective**  **date of** 

**4­1 the**  **standard, then**  **that technology**  **will be**  **considered practicable**  **to manufacture,**  **install, and** 

**service.**

Impacts on equipment utility or equipment availability. **If a**  **technology is**  **determined**

**to have**  **significant adverse**  **impact on**  **the utility**  **of the**  **equipment to**  **significant subgroups**  **of**

**customers, or**  **result in**  **the unavailability**  **of any**  **covered equipment**  **type with**  **performance**

**characteristics (including**  **reliability), features,**  **sizes, 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.** 

Adverse impacts on health or safety. **If it**  **is determined**  **that a**  **technology will**  **have**

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

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

**unacceptable impacts**  **on the**  **policies stated**  **in section**  **5(b) of**  **the Process**  **Rule, 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.**  **Sections 4.2**  **and 4.3**  **document the**  **reasons for**  **eliminating any** 

**technology.**

4.2 TECHNOLOGIES THAT DO NOT ENHANCE EER AS MEASURED

**DOE eliminated**  **three technologies**  **because they**  **have no**  **effect on**  **or do**  **not increase** 

**EER or**  **COP as**  **measured by**  **the test**  **procedure since**  **the test**  **procedure measures**  **steady­state**

**energy efficiency.**  **However, these**  **features (i.e.,**  **variable speed**  **compressors, complex**  **control**

**boards, and**  **corrosion protection)**  **can reduce**  **the energy**  **consumption of**  **the PTAC**  **or PTHP**  **in**

**actual applications,**  **since they**  **affect the**  **cyclic operation**  **of the**  **equipment. 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**  **EER.**

4.2.1 Variable Speed Compressors

**Variable speed**  **compressors can**  **increase efficiency**  **over a**  **broad operating**  **range, but** 

**they do**  **not inherently**  **increase the**  **maximum efficiency**  **at the**  **compressor rating**  **point. Because** 

**the ARI**  **310/380­2004 test**  **procedure calls**  **for steady­state**  **conditions (i.e.,**  **no variability**  **in**

**inputs), the**  **speed of**  **the compressor**  **must remain**  **constant. If**  **the compressor**  **is to**  **maintain**

**constant speed,**  **there is**  **no opportunity**  **for the**  **compressor to**  **increase the**  **measured EER**  **because**

**the power**  **input and**  **work output**  **are constant.**  **Therefore, DOE**  **did not**  **consider this**  **technology**

**in the**  **engineering analysis.** 

4.2.2 Complex Control Boards

**Fan motor**  **controllers can**  **reduce the**  **annual energy**  **consumption of**  **PTACs and**  **PTHPs**

**by adjusting**  **the air**  **flow over**  **the heat**  **exchangers to**  **changing indoor**  **and outdoor**  **conditions.**

**For example,**  **the PTAC**  **or PTHP**  **might only**  **need the**  **evaporator fan**  **motor to**  **be on**  **at half** 

**speed while**  **the condenser**  **fan motor**  **is at**  **full speed**  **to maintain**  **an indoor**  **air temperature.** 

**4­2 Because**  **the ARI**  **310/380­2004 test**  **procedure calls**  **for steady**  **state operating**  **conditions during** 

**the test**  **(i.e., no**  **variation in**  **the indoor**  **and outdoor**  **temperatures), there**  **is no**  **opportunity for** 

**varying the**  **speed of**  **the fan**  **motors to**  **impact the**  **EER calculation.**  **Consequently, DOE**  **did not** 

**consider this**  **technology in**  **the engineering**  **analysis.**

**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**  **setpoints 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**  **310/380­2004 test**  **procedure because**  **of the**  **steady**

**state test**  **conditions. Therefore,**  **DOE did**  **not consider**  **this technology**  **in the**  **engineering**

**analysis.**

**Heat pump**  **controllers can**  **reduce annual**  **energy consumption**  **of PTHPs**  **by adapting**  **the**

**operation of**  **the heat**  **pump cycle**  **and use**  **of supplemental**  **electric resistance**  **to changing**  **loads**

**and ambient**  **conditions. Because**  **the ARI**  **310/380­2004 test**  **procedure calls**  **for steady­state** 

**conditions, there**  **is no**  **opportunity to**  **account for**  **the adaptive**  **technology of**  **the heat**  **pump cycle** 

**to increase**  **EER. Therefore,**  **DOE did**  **not consider**  **this technology**  **in the**  **engineering analysis.** 

4.2.3 Corrosion Protection

**PTACs and**  **PTHPs are**  **designed to**  **have partial**  **exposure to**  **the elements**  **(i.e., a**  **section**

**exposed to**  **the outdoors).**  **While corrosion**  **protection materials**  **used in**  **PTACs and**  **PTHPs may** 

**reduce the**  **efficiency of**  **the heat**  **exchangers somewhat,**  **they also**  **protect the**  **equipment and** 

**prolong its**  **use when**  **it is**  **exposed to**  **chemically harsh**  **operating conditions.**  **Although it**  **is**

**beneficial for**  **the unit**  **to be**  **corrosion protected,**  **it does**  **not improve**  **the EER**  **as per**  **the ARI** 

**310/380­2004 test**  **procedure. Since**  **corrosion protection**  **only helps**  **maintain performance**  **and**

**does not**  **affect the**  **EER of**  **PTACs and**  **PTHPs, DOE**  **did not**  **consider this**  **technology in**  **the**

**engineering analysis.** 

4.2.4 Clutched Motor Fan

**DOE did**  **not consider**  **clutched motor**  **fan technology.**  **In theory,**  **these devices**  **would**

**work with**  **PTACs and**  **PTHPs to**  **reduce the**  **load on**  **a single**  **fan motor**  **used to**  **drive both**  **the**

**evaporator and**  **the condenser**  **fan blades**  **when the**  **refrigerating system**  **is not**  **operating by** 

**disengaging the**  **condenser fan.**  **In this**  **way, power**  **input could**  **be reduced**  **during times**  **when**

**only the**  **indoor blower**  **is running**  **to recirculate**  **air, or**  **when electric**  **resistance heating**  **is being** 

**provided. However,**  **the measure**  **of energy**  **use and**  **EER for**  **PTACs in**  **cooling mode**  **is based**  **on**

**full cooling**  **operation, in**  **which both**  **the indoor**  **blower and**  **the condenser**  **fan must**  **operate.**

**Hence, including**  **a clutched**  **condenser fan**  **would not**  **provide measurable**  **energy efficiency** 

**benefits.**

4.2.5 Thermal Expansion Valve

**DOE did**  **not consider**  **thermal expansion**  **valve (TXV)**  **technology for**  **PTACs or**  **PTHPs.**

**TXVs are**  **expansion devices**  **that meter**  **the flow**  **of refrigerant**  **from the**  **condenser to**  **the**

**4­3 evaporator**  **at a**  **rate equivalent**  **to the**  **amount of**  **refrigerant being**  **boiled off**  **in the**  **evaporator.**

**Typically, TXVs**  **are installed**  **in central**  **air conditioning**  **applications where**  **equipment is**  **rated**

**with the**  **seasonal energy**  **efficiency ratio**  **(SEER) metric**  **and testing**  **occurs at**  **various operating** 

**conditions and**  **temperatures. In**  **contrast, PTACs**  **and PTHPs**  **are measured**  **using the**  **EER**

**metric, with**  **testing occurring**  **at a**  **constant temperature**  **of 95**  **degrees F.**  **Therefore, the**  **energy**

**efficiency benefits**  **of a**  **TXV will**  **not affect**  **the EER**  **rating of**  **a PTAC**  **because the**  **orifice of**  **the**

**TXV and**  **the flow**  **of refrigerant**  **would remain**  **constant during**  **testing. Therefore,**  **DOE does**  **not**

**consider TXVs**  **to be**  **a technology**  **for improving**  **the EER**  **of PTACs**  **and PTHPs.** 

4.3 SCREENED­OUT TECHNOLGIES

**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 scroll**  **compressors, higher**  **efficiency fan**  **motors, microchannel** 

**heat exchangers,**  **material treatment**  **of heat**  **exchangers, improved**  **air flow**  **and fan**  **design, and** 

**heat pipes.** 

4.3.1 Scroll Compressors

**Although scroll**  **compressors are**  **currently used**  **in residential**  **and commercial**  **air**

**conditioning applications,**  **they have**  **not yet**  **penetrated the**  **PTAC and**  **PTHP market.**  **Scroll**

**compressors are**  **more difficult**  **to manufacture**  **than rotary**  **compressors, cost**  **more to** 

**manufacture, and**  **are also**  **physically larger**  **than rotary**  **compressors.**

**DOE determined**  **that manufacturers**  **typically produce**  **scroll compressors**  **with cooling** 

**capacities of**  **approximately 20,000**  **Btu/h or**  **higher, and**  **that the**  **majority of**  **equipment using** 

**scroll compressors**  **is typically**  **rated at**  **capacities higher**  **that 40,000**  **Btu/h. Manufacturers**  **also**

**produce scroll**  **compressors with**  **housings larger**  **than those**  **used for**  **compressors found**  **in**

**PTACs and**  **PTHPs. DOE**  **found that**  **scroll compressors**  **are typically**  **built to**  **be 16**  **inches or** 

**higher in**  **height and**  **that capacity**  **ratings do**  **not impact**  **scroll compressor**  **heights significantly.** 

**For example,**  **DOE found**  **that the**  **height of**  **a scroll**  **compressor only**  **decreases by**  **approximately**

**1.5 inches**  **when capacity**  **decreases from**  **80,000 to**  **20,000 Btu/h.**  **However, significant** 

**improvements in**  **efficiency, when**  **compared to**  **rotary compressors,**  **are generally**  **achieved with** 

**higher capacity**  **models. DOE**  **also found**  **that scroll**  **compressors typically**  **weigh 50**  **pounds or** 

**more, compared**  **with the**  **25 to**  **30 pounds**  **for a**  **PTAC/PTHP rotary**  **compressor found**  **in PTACs** 

**and PTHPs.** 

**Thus, cost,**  **weight, and**  **height hinder**  **the incorporation**  **of scroll**  **compressors in**  **PTACs**

**and PTHPs.**  **For PTACs**  **and PTHPs**  **to use**  **current market**  **scroll compressors,**  **the equipment’s** 

**wall sleeve**  **dimensions would**  **have to**  **increase and**  **other components**  **would have**  **to be**  **resized.**

**In addition,**  **currently available**  **scroll compressors**  **are not**  **rated for**  **the relatively**  **lower capacities** 

**(i.e., fractional**  **horsepower ratings)**  **required for**  **PTACs and**  **PTHPs. Since**  **it is**  **not currently** 

**practical to**  **manufacture scroll**  **compressors in**  **the sizes**  **necessary for**  **use in**  **PTACs and**  **PTHPs,**

**DOE screened**  **out scroll**  **compressors as**  **a design**  **option for**  **improving the**  **energy efficiency**  **of**

**PTACs and**  **PTHPs in**  **the engineering**  **analysis.**

**4­4**4.3.2 Higher Efficiency Fan Motors

**Manufacturers of**  **PTACs and**  **PTHPs use**  **high efficiency**  **permanent split**  **capacitor (PSC)** 

**fan motors**  **due to**  **their modest**  **cost, high**  **efficiency, compact**  **design, and**  **durability. Developing** 

**more efficient**  **PSC motor**  **designs applicable**  **to PTACs**  **and PTHPs**  **is an**  **ongoing industry** 

**challenge, and**  **there have**  **been no**  **substantial gains**  **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.**  **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 due**  **to the**  **size constraints**  **of the**  **equipment and**  **because the**  **impact on**  **the EER**  **would**

**be low.**  **Therefore, DOE**  **believes that**  **it would**  **not be**  **practicable to**  **manufacture, install,**  **and**

**service this**  **technology on**  **the scale**  **necessary to**  **serve the**  **relevant market**  **at the**  **time of**  **the**

**effective date**  **of an**  **amended standard.** 

**Besides PSC­based**  **fan motors,**  **PTAC and**  **PTHP original**  **equipment manufacturers** 

**(OEMs) can**  **choose to**  **implement electronically**  **commutated permanent**  **magnet (ECM)**  **or**

**direct­current (DC)**  **motors. Both**  **ECM and**  **DC fan**  **motors typically**  **uses a**  **brushless permanent** 

**magnet (BPM)**  **design for**  **economy and**  **longevity. Such**  **motors may**  **offer higher**  **efficiencies**

**than PSC­based**  **fan motors,**  **but size**  **implementation and**  **cost issues**  **have so**  **far precluded**  **the**

**industry from**  **adopting them**  **in any**  **but a**  **handful of**  **units. Additionally,**  **because the**  **PTAC and** 

**PTHP industries**  **have a**  **relatively small**  **number of**  **annual shipments,**  **manufacturers typically** 

**have to**  **choose their**  **motors from**  **existing motor**  **lines, rather**  **than having**  **motors customized**  **for**

**their specific**  **needs. The**  **type of**  **motor and**  **its power**  **rating are**  **typically indicative**  **of its** 

**efficiency. For**  **example, shaded**  **pole motors**  **are generally**  **the lowest**  **efficiency motors**  **that are** 

**available, particularly**  **at very**  **low power**  **levels. By**  **contrast, the**  **electronically commutated** 

**motors (ECM)**  **or brushless**  **permanent magnet**  **motors (BPMs)**  **are typically**  **the most**  **efficient**

**motors for**  **the low**  **power levels.** 

**DOE determined**  **that the**  **PTAC and**  **PTHP industries**  **have not**  **adopted ECMs**  **or similar** 

**high efficiency**  **motors due**  **to size**  **and weight**  **constraints. The**  **size limitation**  **is particularly** 

**problematic when**  **given the**  **installation limitations**  **of the**  **sleeve sizes**  **for PTACs**  **and PTHPs,** 

**particularly for**  **non­standard PTACs.**  **Ultimately, DOE**  **screened out**  **high efficiency**  **motors as**  **a**

**viable design**  **option. DOE**  **found that**  **high efficiency**  **motors are**  **not available**  **in the**  **full ranges** 

**of sizes**  **needed for**  **the PTAC**  **and PTHP**  **industries making**  **it unlikely**  **that this**  **technology option** 

**could be**  **readily applied**  **to these**  **products. Therefore,**  **it would**  **not be**  **practical to**  **manufacture,**

**install, and**  **service this**  **technology on**  **the scale**  **necessary to**  **serve the**  **relevant market**  **at the**  **time**

**of the**  **effective date**  **of an**  **amended standard.**  **DOE did**  **not consider**  **BPM­based motors**  **as a** 

**design option**  **for improving**  **the energy**  **efficiency of**  **PTACs and**  **PTHPs.**

4.3.3 Microchannel Heat Exchangers

**DOE found**  **that microchannel**  **heat exchangers**  **are already**  **incorporated in**  **certain types** 

**of air**  **conditioning equipment.**  **Specifically, microchannel**  **heat exchangers**  **are presently**  **used in** 

**condensers of**  **automobile air**  **conditioners and**  **have been**  **demonstrated in**  **field tests**  **of**

**prototypes of**  **commercial unitary**  **air conditioners.**  **Micro­channel heat**  **exchangers have**  **a**

**rectangular aluminum**  **cross­section containing**  **several small**  **channels through**  **which refrigerant** 

**4­5 passes.**  **Aluminum fins**  **with a**  **corrugated shape**  **are brazed**  **at a**  **90­degree angle**  **between the** 

**rectangular tubes.**  **Micro­channel heat**  **exchanger designs**  **provide more**  **heat transfer**  **per volume** 

**of heat**  **exchanger core,**  **can provide**  **more heat**  **transfer per**  **unit of**  **face area,**  **and have**  **lower**

**airside pressure**  **drop.**

**DOE determined**  **that micro­channel**  **heat exchangers**  **have inherent**  **problems with** 

**performance and**  **condensate removal**  **when installed**  **in PTAC**  **equipment. In**  **particular,**

**manufacturers observed**  **that the**  **smaller airflow**  **passages between**  **plate fins**  **are subject**  **to**

**clogging in**  **installations where**  **debris is**  **present, which**  **can affect**  **both the**  **heat exchanger**  **and**

**fan motor**  **performance. Additionally,**  **for PTACs**  **and PTHPs**  **operating in**  **cooling mode,** 

**condensate buildup**  **on the**  **evaporator of**  **the installation**  **may result**  **in icing,**  **which is**  **harder to** 

**remove from**  **small horizontal**  **micro­channel heat**  **exchanger passages**  **than from**  **the vertical**  **fins**

**found in**  **the currently**  **used tube**  **and fin**  **heat exchangers.** 

**For the**  **reasons stated**  **above, manufacturers**  **have chosen**  **not to**  **install micro­channel**  **heat**

**exchangers in**  **PTAC and**  **PTHP designs.**  **DOE determined**  **that this**  **technology has**  **not yet** 

**penetrated the**  **PTAC and**  **PTHP industry**  **and that**  **design challenges**  **still exist.**  **At this**  **time,**

**DOE believes**  **microchannel heat**  **exchangers are**  **technologically infeasible**  **in PTAC**  **and PTHP** 

**applications. DOE**  **understands that**  **manufacturers are**  **conducting research**  **into the**  **use of**  **micro**

**channel heat**  **exchangers in**  **their PTACs**  **and PTHP**  **design at**  **this time.**  **However, DOE**  **does not** 

**have definite**  **knowledge of**  **whether their**  **research efforts**  **will be**  **successful, of**  **when mirco** 

**channel heat**  **exchangers could**  **appear in**  **either prototypes**  **or equipment**  **designs, and**  **what the** 

**contribution to**  **system performance**  **would be.**  **Because this**  **technology is**  **in the**  **research stage** 

**for the**  **PTAC industry,**  **it is**  **also not**  **possible to**  **assess whether**  **it will**  **have any**  **adverse impacts** 

**on equipment**  **utility to**  **customers or**  **equipment availability,**  **or on**  **customer health**  **or safety.** 

**DOE believes**  **it would**  **not be**  **practicable to**  **manufacture, install**  **and service**  **this**

**technology on**  **the scale**  **and in**  **the timeframe**  **necessary to**  **serve the**  **relevant market**  **at the**  **time**

**of the**  **effective date**  **of an**  **amended standard.**  **Also, because**  **this technology**  **is in**  **the research** 

**stage, it**  **is not**  **possible to**  **assess whether**  **it will**  **have any**  **adverse impacts**  **on equipment**  **utility to** 

**customers or**  **equipment availability,**  **or any**  **adverse impacts**  **on customers'**  **health or**  **safety.**

**Therefore, DOE**  **screened out**  **microchannel heat**  **exchanger as**  **a design**  **option for**  **improving the** 

**energy efficiency**  **of PTACs**  **and PTHPs.** 

4.3.4 Material Treatment of Heat Exchangers

**Material treatment**  **of heat**  **exchangers significantly**  **improves their**  **efficiency by**  **allowing**

**the condensate**  **that forms**  **on the**  **fins to**  **be repelled**  **and drained**  **efficiently. Using**  **material**

**treatment of**  **heat exchangers**  **to enhance**  **the heat**  **transfer properties**  **is currently**  **a patented** 

**technology and**  **only used**  **by one**  **PTAC and**  **PTHP manufacturer.**  **Mass production**  **of the** 

**patented technology**  **is not**  **practical and**  **can not**  **be achieved**  **on the**  **scale necessary**  **to serve**  **the**

**PTAC and**  **PTHP market**  **at the**  **time of**  **the effective**  **date of**  **the standard**  **because it**  **is proprietary** 

**to only**  **one manufacturer.**  **Therefore, DOE**  **screened out**  **material treatment**  **of heat**  **exchangers as** 

**a design**  **option for**  **improving the**  **energy efficiency**  **of PTACs**  **and PTHPs.** 

**4­6**4.3.5 Improved Air Flow and Fan Design

**Insulation material**  **is commonly**  **used in**  **air conditioning**  **equipment because**  **it reduces** 

**heat transfer**  **between component**  **sections. PTAC**  **and PTHP**  **manufacturers already**  **apply small** 

**quantities of**  **insulation between**  **the indoor**  **and outdoor**  **section of**  **the PTACs**  **and PTHPs.** 

**However, the**  **primary purpose**  **of this**  **insulation is**  **for soundproofing**  **rather than**  **for heat**  **transfer**

**application. The**  **volumetric constraints**  **of PTACs**  **and PTHPs**  **severely restrict**  **the amount**  **of**

**insulation that**  **can be**  **added. Because**  **only a**  **small amount**  **of insulation**  **can be**  **applied, the**  **heat**

**transfer benefits**  **are negligible**  **and therefore**  **do not**  **improve efficiency.** 

**While tangential**  **fan systems**  **may offer**  **marginally better**  **heat exchanger**  **performance**

**(i.e. the**  **same cooling**  **effect at**  **a higher**  **average heat**  **exchanger temperature),**  **volumetric**

**restrictions preclude**  **their use.**  **Tangential fans**  **require slightly**  **larger fan**  **motors than**  **propeller**

**or “squirrel­wheel”**  **fan designs**  **and require**  **the use**  **of separate**  **fan motors**  **for each**  **heat**

**exchanger. The**  **marginal EER**  **gain by**  **a tangential**  **fan may**  **be negated**  **by the**  **extra heat** 

**produced by**  **the larger**  **fan motors**  **required for**  **tangential blowers.**  **Tangential fan**  **designs also** 

**require different**  **fan plenum**  **shapes, which**  **can decrease**  **the space**  **that can**  **be used**  **to increase** 

**the heat**  **exchangers area.**  **Increasing the**  **heat exchanger**  **area has**  **significantly larger**  **EER gain** 

**than increasing**  **fan efficiency.** 

**Single­fan units**  **limit the**  **design to**  **one fan**  **axis, which**  **limits the**  **design to**  **either**

**propeller or**  **blower fans.**  **Manufacturers already**  **optimize propeller**  **or blower**  **fans to**  **suit each** 

**motor power**  **rating by**  **maximizing air**  **flow while**  **minimizing the**  **material used.**  **This**

**optimization allows**  **for minimum**  **possible fan**  **shaft power**  **to be**  **delivered to**  **the fan**  **while**

**generating the**  **required airflow.**  **All PTACs**  **and PTHPs**  **units having**  **single­fan designs**  **use the** 

**“slinger” design**  **fans to**  **improve efficiency**  **by spraying**  **collected condensate**  **on the**  **condenser**

**coil. Because**  **PTACs and**  **PTHPs have**  **size constraints,**  **the fan**  **dimensions are**  **also constrained,** 

**which limits**  **the improvement**  **in efficiency.**  **Also, more**  **efficient fan**  **designs are**  **an ongoing** 

**industry challenge,**  **and there**  **has not**  **been a**  **substantial gain**  **in efficiency**  **in recent**  **years.**

**In some**  **PTACs and**  **PTHPs, manufacturers**  **have designed**  **the unit**  **to have**  **separate fan** 

**motors (or**  **dual­fan motor)**  **for each**  **heat exchanger**  **so energy**  **can be**  **conserved under**  **varying**

**operating conditions.**  **Dual­fans in**  **PTACs or**  **PTHPs allow**  **the OEM**  **to optimize**  **a fan**  **blade and** 

**motor for**  **each heat**  **exchanger. Dual­fan**  **units can**  **also address**  **variable conditions**  **better by** 

**reducing the**  **speed of**  **or even**  **switching off**  **a fan**  **motor. Because**  **the ARI**  **310/380­2004 test** 

**procedure calls**  **for steady**  **state test**  **conditions, there**  **is no**  **opportunity for**  **varying the**  **operation**

**time of**  **each motor**  **and therefore**  **both motors**  **would need**  **to be**  **on. DOE**  **understands that**  **dual**

**fan PTACs**  **and PTHPs**  **have motors**  **that are**  **equally power**  **rated and**  **that the**  **sum of**  **the energy** 

**consumed by**  **both motors**  **is fairly**  **equal to**  **that of**  **a single­fan**  **PTAC or**  **PTHP fan**  **motor.**

**Although separate**  **fan motors**  **for each**  **heat exchanger**  **conserve energy**  **in real**  **world situation,**  **it**

**does not**  **improve EER**  **under the**  **ARI’s test**  **procedures. For**  **the technical**  **reasons outlined** 

**above, DOE**  **screened out**  **improved air**  **flow and**  **fan design**  **as a**  **design option**  **for improving**  **the**

**energy efficiency**  **of PTACs**  **and PTHPs.** 

**4­7**4.3.6 Heat Pipes

**Under humid**  **ambient conditions,**  **using heat**  **pipes to**  **pre­treat the**  **entering air**  **from the** 

**conditioned space**  **can improve**  **the evaporator**  **heat exchangers**  **performance. Heat**  **pipes pre­cool** 

**the entering**  **air (i.e.,**  **remove some**  **sensible heat**  **and increase**  **the relative**  **humidity level),**  **which**

**means the**  **evaporator heat**  **exchanger has**  **to remove**  **less heat**  **from the**  **air. By**  **reducing the**  **need**

**for heat**  **removal by**  **the evaporator**  **heat exchanger,**  **less work**  **is required**  **by the**  **compressor and** 

**energy is**  **conserved. A**  **draw back**  **to heat**  **pipes is**  **that they**  **partially block**  **the airflow**  **to the** 

**evaporator heat**  **exchanger, which**  **actually decreases**  **the performance**  **of the**  **evaporator heat** 

**exchanger and**  **therefore decreases**  **the EER**  **of the**  **equipment. Although**  **heat pipes**  **have the** 

**potential of**  **reducing energy**  **consumption in**  **humid conditions,**  **in standard**  **conditions they**  **have**

**the potential**  **to decrease**  **EER. Also,**  **the use**  **of heat**  **pipes in**  **PTAC and**  **PTHP design**  **is currently** 

**patented technology**  **and only**  **used by**  **one manufacturer**  **of PTACs**  **and PTHPs.** 

**Because heat**  **pipes have**  **the potential**  **to decrease**  **EER in**  **certain conditions,**  **it is**  **not**

**practical to**  **implement them**  **into PTAC**  **and PTHP**  **design. Also,**  **mass production**  **of the** 

**patented technology**  **is not**  **practical and**  **can not**  **be achieved**  **on the**  **scale necessary**  **to serve**  **the**

**PTAC and**  **PTHP market**  **at the**  **time of**  **the effective**  **date of**  **the standard**  **because it**  **is proprietary** 

**to only**  **one manufacturer.**  **Therefore, DOE**  **screened out**  **heat pipes**  **as a**  **design option**  **for**

**improving the**  **energy efficiency**  **of PTACs**  **and PTHPs.** 

4.4 REMAINING TECHNOLOGIES

**After eliminating**  **those technologies**  **that have**  **no effect**  **or do**  **not increase**  **EER and** 

**screening out**  **those technologies**  **that that**  **do not**  **meet the**  **requirements of**  **sections 4(a)(4)**  **and**

**5(b) of**  **the Process**  **Rule, DOE**  **is considering**  **the technologies**  **in the**  **following list.** 

• **Higher efficiency**  **compressor.**

• **Increase heat**  **exchanger area**  **(extension of**  **surface area**  **or addition**  **of coil**  **rows).**

• **Re­circuiting heat**  **exchanger coils.** 

**4­8**