Handbook for Evaluating Emissions and Costs of APUs and Alternative Systems (2012)

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64 C h a p t e r 4 Beyond the calculated emissions and costs, there are various qualitative issues that need to be addressed to allow proper assessment of alternative systems. For example, implementation of an alternative system could result in emissions reductions compared to the use of APUs, but if adoption of the alternative system by the airlines is uncertain or if funding is uncertain, the envi- ronmental benefits of the alternative systems may be outweighed by other factors. Also, there are finer levels of assessments not appropriate at the planning stage that should still be qualitatively considered since they can help to further define the advantages and disadvantages of each type of alternative system. These types of important issues need to be addressed and/or resolved at the planning stage before finer assessments can or should be conducted. 4.1 Infrastructure Requirements and Comparisons The issue of infrastructure requirements encompasses many issues such as the availability of an electrical system to support the implementation of alternative systems. For example, Level 1 and Level 2 electric infrastructures refer to the availability of electrical feeders, breakers, bus taps, distribution panels, etc., that are necessary before POU systems can be used. Such infrastructures are also included as part of central system basic installation packages. Infrastructure issues also include the potential to move loading bridges/aircraft parking posi- tions to new locations and how that will affect the current or planned implementation of alter- native systems. Structural and electrical support necessary to install POU systems or AHUs and gate boxes at new locations must be considered during the planning phase for alternative systems. The structural integrity of the PBB will also need to be considered when installing these types of equipment. The overall impacts on reliability and maintenance will need to be carefully considered (at least qualitatively) when changes to these systems are introduced. When considering the implementation of alternative systems, airport operators also need to consider the locations where aircraft would be provided ground power and/or PCA. For exam- ple, electricity could be provided at remain over night (RON) and cargo aircraft parking posi- tions, whereas it would be unusual to provide PCA at these locations, except in colder climates. At general aviation airports or at general aviation facilities that are located at commercial service airports, suitable locations need to be identified to properly mount fixed alternative systems since aircraft are typically not accessed by loading bridges. For remote RON locations, a reason- able choice would be to use portable diesel units to provide electricity and PCA. These types of issues are important to consider when selecting the appropriate alternative system. It should also be understood that if an APU is used at RON locations, it will generally not be used all night. In contrast, if an alternative system is available at RON locations, it will likely be used all night. As such, different usage times (different TIM values) may need to be used when calculating emissions for remote aircraft parking positions. Qualitative Evaluations

Qualitative evaluations 65 An often overlooked item that should be considered when evaluating different alternative ground power/PCA systems is the installation location of the PCA and ground power equipment mounted on the PBB. The GSE industry manufacturers have designed equipment to be mounted at various locations on or near the PBB. Experience has shown that ground power system equip- ment mounted beneath the cab of the PBB will invariably suffer more damage from mobile ramp equipment than will equipment mounted at the rotunda or side of the PBB (ASE 2011). Typically, a POU unit (PCA or ground power), is mounted at the cab end of an apron drive bridge. Having the refrigerant and the compressors located in this environment significantly increases the risk of refrigerant leaks and endangers the useful life of the compressors. Typically, the compressors used in the POU units are for light commercial applications and are designed to be mounted in a stationary unit with a small horsepower blower motor. Past studies and expe- rience have shown that a compressor subjected to the airport ramp environment will typically have to be replaced within the first 5 to 10 years of operation (ASE 2011). Damage to POU units can be caused by ramp equipment, routine movement of the bridge, and/or increased wear and tear due to the demanding application. Central system equipment, such as AHUs and gate boxes, can be mounted at the rotunda end of an apron drive bridge with a side mounted telescoping air duct and on the side of the PBB with a dogleg assembly, respectively. This arrangement affords greater protection from damage by mobile equipment on the ramp/apron. The ramp environment is dangerous for any piece of equipment, regardless of type. In a central system, the compressors and the refrigerant sys- tem reside in a more controlled environment accessed only by maintenance personnel, thereby eliminating the possibility of damage due to the ramp environment. POU system equipment typically weighs substantially more than central system gate equipment. The POU air conditioning equipment can weigh approximately 9,000 pounds for wide body gates and approximately 12,000 lbs for jumbo-wide body aircraft gates. The impact to the opera- tion and maintenance of the PBB should be researched before making a decision to implement POU systems, especially when the airport operator is retrofitting older, existing PBBs. While a POU system may cause some PBB-related weight issues, it does have greater mobil- ity than a central system. Should an owner move his/her gates from one concourse/terminal to another, the POU system equipment are simply relocated as well. On a central system, the gate equipment mobility is governed by whether the new facility has central equipment or not (e.g., central plant, electrical infrastructure, etc.). If it does not, the owner must consider selling the equipment, or possibly transferring it to another of the owner’s facilities. Related to the issue of operation and maintenance is that of equipment/system reliability. An apparent advantage of a POU system is that if one unit fails, it only affects one gate, whereas a central system failure may affect all aircraft gates served by the central system. Although this is primarily true, it is rare for a problem to completely disable an entire central system, and often the central plant continues to operate while repairs are being made. For example, if a chiller fails, today’s central systems are generally equipped with thermal storage which will essentially replace the failed chiller during the peak cooling hours, allowing repairs to take place. There are levels of redundancy which can be incorporated to further ensure the systems remain online, but in the past, the redundant systems have typically been considered unnecessary. The components utilized in central systems are all industrial-rated equipment that can reliably operate for longer life cycles and are typically utilized in large factories for comfort cooling and industrial processes. Essentially, they are utilized in processes and situations where downtime is detrimental to deliv- ering products and services, and therefore, reliability is of utmost concern. In contrast, POU equipment is typically manufactured with commercial grade components. These components are generally used in such applications as convenience stores or small office buildings.

66 handbook for evaluating emissions and Costs of apUs and alternative Systems Although POU system components may have shorter life spans, they still provide the con- venience of modularity when either upgrading or replacing older equipment. Individual units can be modified without affecting the other units. New technologies and hardware can be inves- tigated without making major capital investments as may be necessary with central systems. This type of flexibility may be more desirable to an airport than having lower operating and maintenance costs. 4.2 Operational Considerations and Comparisons The operational differences between POU and central systems are mainly based on operat- ing strategies that can improve energy efficiencies and/or maintenance strategies. The inherent differences in these systems offer noticeable operational tradeoffs that need to be considered. In general, central systems are more efficient than a distributed POU system in providing cooled air to aircraft (ASE 2011). This holds true for centralized PCA systems located in office complexes as well. Central systems at airports are mainly water-based. Water is heated or cooled at a central location and then transmitted to the gate location where it is used to heat or cool air that is then transmitted into the aircraft. A centrally located, water-cooled chiller system is more efficient than multiple air-cooled, direct expansion air conditioning units since water is more thermally conductive than air, has a higher specific heat, and has a higher density. These factors indicate that for the same mass flow, water can absorb and remove a greater amount of heat than air. By utilizing the thermally superior heat transfer properties of water, a central system can be designed to be more energy efficient than a POU system. Another factor to consider is the price of electricity during peak periods. Many electricity pro- viders charge a premium for electricity usage during the provider’s daily peak periods. This sug- gests a possibility to significantly reduce utility charges by utilizing thermal storage during peak periods. This does not imply that the PCA system capacity should be reduced such that thermal storage is necessary to meet the peak cooling loads. It does suggest, however, that although the central system should be sized to provide the necessary peak cooling demands, during the utility provider’s peak periods, thermal storage could be used to reduce the system’s power consump- tion. This could also ensure a lower overall system electricity demand for the system’s owner. The key is being able to target this peak demand period, which has been attempted in the past with varied levels of success. However, by utilizing modern control systems, targeting the utility’s peak demand period can be accomplished with minimal additional programming. This pro- gramming could include software routines that monitor the plant’s actual demands, and when changes are detected in the loading, peak usage periods can be automatically redefined. Proper usage of thermal storage systems can easily save thousands or hundreds of thousands of dollars a year depending on the size and electricity requirements of the PCA system. This design principle is not possible with the use of a POU system. These types of differences in operating costs and potential for efficiencies tend to be beyond the scope of assessments conducted at a planning level, but need to be considered in the decision-making process since they could noticeably increase the difference in operating costs between POU and central systems. Central systems that use heat from existing airport boilers benefit from lower operating costs due to the lower cost of natural gas-derived heat energy. The cost calculations presented in Section 3.3 illustrate the difference in operating costs between a central system using electrically- generated heat and boiler (natural gas)-generated heat. One potential refinement to the operational cost data that is beyond the scope of a planning- level assessment is the concept of discount rates. This refers to the potential use of savings from capital costs that can be invested to help pay for utility costs in future years. That is, if a POU

Qualitative evaluations 67 system with noticeably lower capital cost is selected, the difference (the money saved) in capital cost between the POU system and a central system can be grown through some investment options to help offset future growth in utility costs. To improve the overall energy consumption and, therefore, cost estimates, the distribution of ambient conditions needs to be as accurate as possible. Assuming the default distribution of 25% cold, 50% neutral, and 25% hot conditions for airports in areas that are predominantly in one condition could have a significant impact on the calculated results. 4.3 Local and Corporate Airline Support With the implementation of alternative systems, airlines must also have trained personnel to properly use the equipment (i.e., know how and when to connect ground power and PCA to the aircraft). In general, all airlines (at least at the corporate level) support the use of these systems as they represent a win-win situation where aircraft fuel consumption, emissions, and APU maintenance costs can be reduced. However, there are situations where airline pilots will use their APUs even though alternative systems are available. In addition to the issue of personnel training (or availability), there may be other reasons why APUs are used when ground power/PCA systems are available. For example, on quick turnaround flights, the use of APUs may be considered easier and less disruptive than switch- ing to alternative systems. Some airports have rules in place to try to force airlines to use the systems if an aircraft is parked at the gate longer than a designated amount of time. Unless an airline constantly monitors the activities of its pilots and crews, it may be difficult for the airline to enforce the use of the alternative systems. Ultimately, it may depend on the pilot’s willingness to shut down the APUs. It is also possible that there could be some overlap in the use the APUs and alternative sys- tems when one is turned on and the other is slow to turn off. In addition, some gates with non- working alternative systems would require the use of APUs, hence giving the impression that APUs are being used when alternative systems are available. Although there can be many reasons why alternative systems are not used (or may not appear to be used), it is clear that airlines need to agree to have their personnel (pilots, ground workers, etc.) follow protocols to use these systems. There needs to be good communication between airport operators and airlines to ensure support of alternative systems at the corporate level, and communication between corporate airline staff and flight crews and ground personnel at each airport. Indeed, airport operators should place more emphasis on ensuring local airline personnel agree to the use of alternative systems. 4.4 Ownership of Emissions and Fuel Consumption Reductions Although currently not a major consideration, there is an evolving concern over the ownership of greenhouse gas emissions reductions. With the development of airport greenhouse gas emis- sions inventories and airport climate action plans, a question will likely come up: who takes credit for the reduction in aircraft APU emissions? The airlines will likely say that they should receive any ERCs. Airport operators may argue that since they invested in the alternative systems, they should receive the credits. Based on the World Resource Institute’s (WRI’s) scope definitions, APUs are owned by the airlines and so are APU-related emissions. Hence, any reductions thereof should be claimed by the airlines. However, airport operators have been developing greenhouse

68 handbook for evaluating emissions and Costs of apUs and alternative Systems gas inventories based on the airport community as a whole (i.e., “airport sources” include sources owned by the airport, tenants, and the public). Although airport operators acknowledge they do not own aircraft APUs, different airports have used varying definitions of control to justify taking credit for APU emissions reductions. One possibility is to award the reductions on the basis of monetary contribution to the devel- opment of the alternative system. That is, the reductions could be split between an airport and an airline using the alternative system if both parties contributed to the development of the system. This is a difficult issue and one that will likely not be resolved in the near future. It will continue to evolve as airports and airlines continue to look for opportunities to reduce their carbon footprints. Regarding the ownership of the emissions due to airport electricity usage (i.e., electricity used by alternative systems), the evolving approach appears to be based on who receives the “bill” and pays for the electric energy. That is, even if the tenants (airlines) pay an airport through sub-metering, the airport’s control over the payment to the utilities is used as the reason for allocating the resulting indirect emissions to the airport. 4.5 Equipment Noise In general, noise levels generated by aircraft APUs and alternative systems are relatively low such that their impact on local communities is negligible. However, in a few cases, APU noise can actually cause a disturbance if a community is located in close proximity to the airport and if a clean line-of-sight exists between the source of the noise and the receiver (i.e., no structural obstructions to impede the noise). Therefore, while noise from APUs is not a primary concern of most airport noise abatement officers, airport management needs to be cognizant of where com- munities are in relation to aircraft parking areas and other locations where APUs are operated. As there is very little information on APU and alternative system noise (Tam 2005; Kwan 2010), a noise measurement program was conducted at San Francisco International Airport (SFO) in December 2010 to determine the relative differences between APU and alternative system noise levels. The APU noise measurements were conducted at a distance of 50 ft from the APU exhaust (i.e., at aircraft tail points) for various aircraft types. Because of background noise levels on the ramp (e.g., nearby aircraft operating on main engines), it was difficult to obtain reliable noise measurement data for alternative system equipment. Therefore, manufacturer noise specifica- tions data for alternative systems were used as the basis for propagating noise levels to the same location used for APU noise measurements. With the exception of AHUs, noise levels generated by alternative system components are generally lower or negligible compared to either the noise generated by APUs or background noise levels at busy commercial service airports like SFO. Central plant chillers and boilers are generally enclosed in a building and accessible only to maintenance staff and hence are not a major contributor to noise levels on the ramp. Therefore, the conclusion from the limited noise investigation conducted for this research project is that alternative systems are generally quieter than APUs. The only exception is with the AHUs associated with centralized systems which generate noise levels that are comparable to the lower end of the APU noise levels. However, since the AHU noise levels were derived from manufacturer specifications for maximum levels, the actual AHU noise levels could be lower. This assessment was conducted at a hypothetical distance of 50 ft from the tail end of parked aircraft. Higher fidelity noise measurement studies could potentially be conducted to include the impact of airport structures and other features (e.g., roadways and vegetation) in order to better determine potential impacts to local communities.