CHAPTER 4. SCREENING ANALYSIS TABLE OF CONTENTS 4.1 4.2 INTRODUCTION ........................................................................................................... 4-1 TECHNOLOGIES THAT DO NOT IMPACT EER AS MEASURED.......................... 4-2 4.2.1 Variable Speed Compressors ............................................................................... 4-2 4.2.2 Complex Control Boards ..................................................................................... 4-3 4.2.3 Corrosion Protection ............................................................................................ 4-3 SCREENED-OUT TECHNOLGIES............................................................................... 4-3 4.3.1 Scroll Compressors .............................................................................................. 4-4 4.3.2 Higher Efficiency Fan Motors ............................................................................. 4-4 4.3.3 Microchannel Heat Exchangers ........................................................................... 4-4 4.3.4 Material Treatment of Heat Exchangers .............................................................. 4-5 4.3.5 Improved Air Flow and Fan Design .................................................................... 4-5 4.3.6 Heat Pipes ............................................................................................................ 4-6 REMAINING TECHNOLOGIES ................................................................................... 4-7
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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 energy-efficiency ratio (EER) and coefficient of performance (COP) of PTACs and PTHPs as measured by the Air-Conditioning and Refrigeration Institute (ARI) 310/380-2004 Standard for Packaged Terminal AirConditioners and Heat Pumps (ARI 310/380-2004) 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. 6311-6317) 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
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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 steady-state 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 310/380-2004 test procedure calls for steady-state 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.
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Because the ARI 310/380-2004 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 310/380-2004 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 310/380-2004 test procedure calls for steady-state 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 310/380-2004 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. 4.3 SCREENED-OUT 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 (as much as 50 percent greater in height and weight). Thus, cost, weight, and height hinder the incorporation of scroll
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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. 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. 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. 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 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 PSC-based fan motors, PTAC and PTHP original equipment manufacturers (OEMs) can choose to implement electronically commutated permanent magnet (ECM) or direct-current (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 PSC-based fan motors, but size implementation and cost issues have so far precluded the industry from adopting them in any but a handful of units. Due to PTAC and PTHP size constraints and the technical difficulty in implementing BPM-based motors into the design, DOE did not consider BPM-based 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. Currently, microchannel heat exchangers are in the research stage for applications in PTACs and PTHPs. There have been inherent problems in the performance of the heat exchanger and condensate-removal from the fins. Although microchannel heat exchanger technology shows promising results in increasing EER, it has not yet penetrated the PTAC and PTHP market. Therefore, 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
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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. 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 “squirrel-wheel” 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. Single-fan 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 single-fan 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 dual-fan motor) for each heat exchanger so energy can be conserved under varying operating conditions. Dual-fans in PTACs or PTHPs allow the OEM to optimize a fan blade and
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motor for each heat exchanger. Dual-fan units can also address variable conditions better by reducing the speed of or even switching off a fan motor. Because the ARI 310/380-2004 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 dualfan 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 single-fan 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. 4.3.6 Heat Pipes
Under humid ambient conditions, using heat pipes to pre-treat the entering air from the conditioned space can improve the evaporator heat exchangers performance. Heat pipes pre-cool 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.
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Higher efficiency compressor. Increase heat exchanger area (extension of surface area or addition of coil rows). Re-circuiting heat exchanger coils.
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