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25 escalation costs per unit of energy can be calculated and gas used at an airport. Within these two areas of high con- incorporated into payback analysis, potentially shortening sumption and energy cost come many of the opportunities for the payback term. significant energy efficiency savings through retrofit projects. Rate Adjustment with Advanced or Sub-Meters $ Heating--Hydronic (when meters are provided by utility) Solar Thermal $$ Utility companies around the country offer a number of rate- based programs aimed at improving the reliability of the elec- Solar thermal systems consist of roof-mounted panels through trical grid. Quite often advanced metering systems are required which water or a glycol/water mixture passes to gain ther- to enroll in these programs, which may be provided by the mal energy. This heated fluid is then pumped through a high-efficiency heat exchanger, which transfers energy utility. By utilizing advanced metering data, airport terminals to potable water to be used for space heating or domestic can have a greater understanding of their unique load charac- hot water. Although costs have dropped, solar thermal teristics and a more knowledgeable position when negotiat- heating systems and collectors have achieved significant ing rate-based programs (Sullivan et al. 2007, p. 7.67.7). increases in efficiency and reliability over the last 30 years Most rate-based programs work to incentivize off-peak use (DOE 2003). of electricity and reduce peak load demand. Specific pro- grams include time-of-use pricing, real-time pricing, and The use of solar thermal systems for hydronic heating (space load aggregation. or hot water) was largely absent at all airports surveyed, with only one respondent, DFW, indicating in the affirmative. About half of the survey respondents noted a negotiated Although a more proven technology than PV, solar thermal rate structure with their local utilities, including rates for bulk technology may only have limited applications for small energy users. airports. The best application of this technology may be for domestic hot water or snow-melt systems and not for pri- Cost/Payback/Savings: Low cost when meters are provided mary heating. Solar thermal can also be used to supplement by the utility. boiler systems (DOE 2008). Cost/Payback/Savings: DFW indicated a 2- to 5-year pay- Peak Load Shedding back and medium level cost. A method of energy management that can reduce the impact of peak demand rate increases is peak load shedding. The build- Central Boiler Upgrades $ - $$$ - ing automation system and meters are used to shed electrical loads or "turn-off" noncritical systems during peak demand Although boilers and associated components of a hydronic periods (CAP 2003a, p. 13; DOI 2006). Turner noted that this heating system vary owing to the size and complexity of an method of cost savings "works best at facilities with large airport terminal, it is generally assumed that replacement summer cooling loads, and it requires a dedicated O&M staff of major components in a heating/cooling system will be a and a favorable utility electric rate structure to be economically significant cost to any airport terminal. For older facilities, viable" (Turner et al. 2007). boilers are often oversized and inefficient. Replacement brings greater efficiency, multiple fuel options, and reduced main- Airports surveyed noted penalties in the form of peak-hour tenance costs (Turner et al. 2007, p. 13). Additional strategies demand charges associated with peak loads. may include replacing one boiler with multiple units and the addition of direct digital controls to increase boiler efficiency Cost/Payback/Savings: Paybacks of less than one year were (DOE 2008). reported by The College of New Jersey when metering and management were used to shed peak loads by cycling HVAC Of airports surveyed, boiler replacement was the primary equipment in multiple buildings (New Jersey Higher Educa- heating system improvement. Survey results varied depend- tion Partnership for Sustainability n.d.). ing on the size of the airport and type of system, with an over- all greater percentage of respondents indicating some type of MECHANICAL HEATING, VENTILATION, boiler replacement to improve efficiency. AND AIR CONDITIONING Cost/Payback/Savings: Airports surveyed reported that HVAC can consume greater than 40% of electrical energy boiler-related energy efficiency improvements provided a at airports, with most of that being used by air conditioning 0- to 5-year payback and could be achieved for a range of systems. With the exception of small systems such as domes- costs--from low to high. Literature noted payback ranges for tic hot water, HVAC systems consume nearly all the natural specific retrofit options including "oversized boiler replace-

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26 ment"--6 to 8 years; "high efficiency boiler replacement"-- 8 to 12 years (Turner et al. 2007, p. 14). Box 14 Building Ventilation Systems Exhaust ventilation systems are common in almost every commercial and institutional building, and therefore one Energy Recovery Systems of the most common sources of wasted energy. Two airports Heat recovery units increase heating and cooling efficiency had specific examples of the often unseen but significant by capturing or "recovering" energy from exhaust air or chiller impact of inefficient exhaust ventilation systems. water that would otherwise be lost. Systems transfer heat One airport reported that the restroom exhaust was con- from warmer air to cooler air in heating or cooling modes, trolled with the restroom lights, which were historically left reducing these loads depending on the season. Air-to-air heat on continuously. The air handling equipment of the HVAC exchangers, classified as "heat recovery," remove only heat, system was also controlled by these lights, to provide make- whereas others, classified as "energy recovery," remove both up air for the exhaust fans. By replacing the lighting controls heat and water vapor from the air stream (Turner et al. 2007, with occupancy sensors, savings were created in all three p. 13; DOE 2009b). Various materials are used in the air-to- systems: lighting, exhaust, and HVAC. air heat exchanger, with some requiring greater maintenance than others. Systems typically achieve transfer efficiencies of Another airport reported that their best efforts at promoting 70% to 80% (DOE 2009b; Commonwealth of Pennsylvania energy efficiency were often circumvented by human actions: n.d., p. 43). Tenant employees of concessionaires would open their doors to the terminal when their kitchen became hot, effectively adding a commercial kitchen to the terminal's air condition- Plate and Frame (Fluid) Heat Exchangers $$ ing load as the commercial exhaust hood would draw in cool air from the terminal. By implementing independent High-efficiency plate and frame heat changers transfer energy make-up air for the kitchen exhaust, the airport is able keep over a greater surface area than traditional fluid heat exchang- these functional ventilation zones separate and operate the ers, greatly increasing the speed of the process. This type of terminal more efficiently. heat exchanger is used as a component of the cooling system chiller. Plate and frame heat exchangers installed at Seattle Tacoma International Airport (SeaTac) in 2004 were notable because Cooling of their projected savings of more than $1,000 per day and installation by engineering staff in "the equivalent of a week- Primary energy efficiency improvements in the area of end." Payback based on projections was less than one year cooling by airports surveyed consisted of replacement or (CAP 2004). upgrades to central chillers and rooftop air-handlers and/ or split systems. Life expectancy for mechanical systems serving commercial buildings is widely variable--ranging Air-to-Air Heat Exchangers $$ - from as little as 10 years to as long as 50 years in the case of ground-source heat pumps (DOE 2008). When replace- Air-to-air systems use a film or plate over which the air passes ment occurs as a result of age, it is very likely that it will to transfer energy between supply and exhaust airstreams. Sys- result in energy savings simply because of improvements tems are modular and adaptable for a range of air stream capac- to the technology. ities and should be considered where design conditions require continuous exhaust and make-up air (Commonwealth of Penn- sylvania n.d., p. 43). Systems work best in extreme climates Central Chiller $$ - where temperatures outside are significantly different from indoor temperatures. In mild climates, the energy consumed by Much like boilers, chillers and other components of the cool- continuous powered exhaust may offset any gains found using ing system are often oversized or have become oversized heat recovery technology. Also, in cold climates, systems are owing to reduced cooling loads generated by lighting retrofits. typically equipped with frost control measures (DOE 2009b). Replacement with properly sized units that more closely match cooling loads will bring reduced energy costs. Conversely, Survey respondents noted limited implementation of heat if chiller size is deemed inadequate, improvements reducing recovery systems. Primarily used by larger facilities, the tech- cooling loads may be less than the cost of additional chillers. nology holds promise for many small airports, and may be A limited number of airport respondents noted some form of considered as a component of mechanical retrofit. chiller replacement, with one noting a full replacement for a terminal (see Figure 9). Cost/Payback/Savings: Medium level implementation costs were noted by survey respondents. Literature noted a payback Cost/Payback/Savings: The 2- to 5-year payback for the of 8 to 10 years (Turner et al. 2007, p. 14). one large airport (PHX) indicated that a full replacement