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Mobile Military CO2 Refrigeration


OBJECTIVE: Develop technology to enable mobile, military, containerized cold-storage assets that use carbon-dioxide as the refrigerant, for purposes of eliminating reliance on the more heavily regulated and expensive refrigerants currently used. DESCRIPTION: The result of chlorofluorocarbon (CFC) and hydrochlorofluorocarbon (HCFC) regulation in the 1990's was that road and rail transport refrigeration systems today use hydrofluorocarbons (HFCs) instead as their refrigerants. This includes all our military's existing and near-term mobile cold-storage assets. The issue is that HFCs are now under threat. In 2006, through the Kyoto Protocol, the international community, including the United States, came to an agreement that HFCs must eventually be phased out to help slow global climate change, because HFCs have a global warming potential (GWP) more than a thousand times greater than carbon-dioxide (CO2) . The first milestone -- phase-out of HFCs from automobiles in Europe beginning January 1, 2013 -- has passed. The next targets are supermarket and industrial refrigeration, then building air-conditioning, followed by road and rail container transport refrigerator/freezers, and domestic appliances. This trend has inspired Product Manager - Force Sustainment Systems (PM-FSS) and the Combined Arms Support Command (CASCOM) to ensure the Army is not disadvantaged by such regulation. The Army is therefore seeking advanced development of technologies that enable mobile military containerized cold-storage assets that use alternative refrigerants, namely CO2. Several major corporations initiated development ahead of the upcoming ban. Having concerns that ammonia, hydrocarbons, and the current hydrofluoroolefins (HFOs) are not suitable replacement candidates due to flammability and toxicity issues, researchers are investing in CO2 solutions. CO2 refrigeration is not new, but the need to eliminate refrigerants with high GWP, the necessity for greater efficiency to decrease energy consumption, and a desire for far lower refrigerant costs, is driving innovation. It is supported by recent advances in materials, processor-based electronic controls, and the advancement of computer-aided analysis tools and techniques, which in turn impact the designs of heat exchangers, compressors and other components, and enhance control over the process. The issues with CO2 refrigeration -- high pressures and/or increased component counts -- now appear to be surmountable with the emergence of these new technologies. Furthermore, the inherently high process pressures result in higher fluid densities, meaning reductions in weight and size are also possible -- given the same power requirements -- for various components including the compressor. The majority of work thus far has focused on vending machines (Danfoss and the Coca-Cola Co.), supermarkets (Hillphoenix, Hannaford Bros. and Sobey's), and recently Carrier has been developing for containerized transport refrigeration. While Carrier's containerized system is the closest to what we need, it is designed only for ordinary road, rail and ship transport conditions, not military application. And it is still in development, so commercial acquisition is not possible. As such, military investment is necessary. While small businesses may be able to leverage some of Carrier's technology, additional innovative development will address the fact that military assets require ruggedization for off-road transport, efficiency gains to minimize logistical burden, modification to power consumption levels to accommodate use with camp grids and gensets, the need for dual evaporators, compactness to create space for the inclusion of onboard gensets and fuel tanks, and adaptation to extremely hot environments - areas of deficiency in the Carrier unit. Concepts should target modular refrigeration units (RU) suitable to large containerized cold-storage. The weight objective for a system capable of cooling a 20'ISO container is<1200 lbs, with a threshold target of<1600 lbs -- including frame, onboard auxiliary power unit, and all ancillary components. The space available for the refrigeration mechanicals in such a frame is roughly 45"wide x 23"deep x 23"tall. At 135 degrees F ambient, the capacity required for simultaneously cooling 2/3rds of a 20'container to 38 degrees F and 1/3rd of the container to -5 degrees F is ~15,000 BTU/hr. The RU driving these temperatures should have a reserve capacity of 30% at this condition, and a target coefficient of performance of greater than 1 -- a reasonable goal for CO2 even in the most challenging climates. The annualized average power consumption target would be 2 kW in the Middle East. The design should lead eventually to a production cost of<$40k, the objective being<$25k. Respondents shall consider the two most common CO2 cycles, as well as alternative vapor compression cycles, and explain and justify their choice and safety considerations, especially with regard to cycles with extreme pressures. While it is expected that to limit scope the concepts will utilize the CO2 refrigeration compressors currently available (e.g., Carrier, Danfoss, Tecumseh, Daikin, etc.), development of new compressor technology will be considered if it does not jeopardize development of other technologies. Other technologies examined will be effective heat exchanger materials and geometries; efficient motors; variable-speed drives; algorithmic controllers employing process monitoring, logging and anticipatory software; and electrically or mechanically-pulsing evaporative control valves. PHASE I: During Phase I and the Phase I Option, offerors shall develop the initial concept design; demonstrate the practical and technical feasibility of their approach materially via scaled-down bench-top/breadboard fabrications of the most critical component technologies; then validate empirical results with modeling and simulation. Phase I deliverables will include progress and final reports detailing activities, description and rationalization of the design process and resulting concept, successes and failures, results of performance modeling and benchtop evaluation, safety, risk mitigation measures, MANPRINT, and estimated production costs. The final report shall specify how requirements will be met with a full-scale prototype in Phase II. Concepts will be judged on adherence to the quantitative and qualitative factors in the Description section above, and more generally on metrics such as cost, complexity, reliability, maintainability, size and weight. PHASE II: During Phase II, the researcher is expected to refine and scale-up the technology developed during Phase I, and further validate the concept and demonstrate how goals are being met by fabricating for delivery one or more fully-functional, full-size CO2 refrigeration units that have been subjected to various performance and environmental evaluation exercises representative of actual field conditions. The data deliverable shall be progress reports and a final report documenting the theory, design, safety, MANPRINT, component specifications, performance characteristics, and any recommendations for future enhancement of the equipment. PHASE III: During Phase III, the researcher is expected to perform final tasks necessary to polish the technology and through advanced testing prove it is capable of fulfilling the requirements necessary for technology transition and commercialization. Likely military applications will be containerized cold-storage assets such as the Tricon Refrigerated Container System (TRCS), the Multi-Temperature Refrigerated Container System (MTRCS), and the single-temperature Refrigerated Container System (RCS). The technologies developed will be applicable to the millions of refrigerated transport containers that travel road and rail across the our nation and the world.
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