N251-061 TITLE: Carbon Dioxide Modular Refrigeration System

OUSD (R&E) CRITICAL TECHNOLOGY AREA(S): Sustainment

The technology within this topic is restricted under the International Traffic in Arms Regulation (ITAR), 22 CFR Parts 120-130, which controls the export and import of defense-related material and services, including export of sensitive technical data, or the Export Administration Regulation (EAR), 15 CFR Parts 730-774, which controls dual use items. Offerors must disclose any proposed use of foreign nationals (FNs), their country(ies) of origin, the type of visa or work permit possessed, and the statement of work (SOW) tasks intended for accomplishment by the FN(s) in accordance with the Announcement. Offerors are advised foreign nationals proposed to perform on this topic may be restricted due to the technical data under US Export Control Laws.

OBJECTIVE: Develop a non-hydrofluorocarbon (HFC), shipboard modular refrigeration system (MRS) using carbon dioxide (CO2/R-744) as the refrigerant.

DESCRIPTION: Shipboard refrigeration systems are used to store perishable foods and operate at temperatures between 41°F (5°C) and 33°F (-0.6°C) for chilled food storerooms and 0°F (-17.8°C) and -4°F (-20°C) for freeze food storerooms. The Navy currently relies on R-404A and R-407A for its MRSs sized for 0.75 and 1.5 tons-refrigeration (rTons) at freeze conditions. Each MRS consists of a modular refrigeration unit (MRU) located in the refrigerated storeroom (hung from the ceiling), a control panel with programmable logic controller (PLC), and a condenser located external to the refrigerated storeroom cooled with 44°F (6.7°C) chilled water. Each MRU contains a compact scroll compressor, refrigerant suction accumulator (receiver), motorized impeller to circulate air from the space through dual evaporators configured in a horizontal vee, controlled by two thermal expansion valves, a pressure regulating valve, and a solenoid valve to allow either chill or freeze operation. Each refrigerated storeroom contains at least two MRSs with integrated electrical defrost cycles (one installed as a spare) . Production and import of hydrofluorocarbons (HFC) are now being phased down in a step wise fashion due to their high global warming potentials (GWP), as mandated by the Kigali Amendment to the Montreal Protocol and the American Innovation and Manufacturing (AIM) Act of 2020 culminating in an 85% phase-down by 2036.

R-744/CO2 has reemerged as a credible very low GWP (GWP = 1) natural refrigerant, particularly for refrigeration systems that have condensers cooled by chilled water. But the use of CO2 is a far greater technical challenge than fluorinated refrigerants requiring additional engineering expertise to incorporate additional components of greater complexity with more complex controls. The toxicity and pressure safety aspects of CO2 are far more complex than fluorinated refrigerants. A R-744 MRS would need to be designed for transcritical operation to account for shutdown conditions, as well as transients that are inherent to a Naval combatant. Transcritical compressors are commercially available, but they are typically reciprocating designs, about three-times larger/heavier than scroll compressors. Developmental prototypes are necessary to fully understand the benefits and issues required for a CO2-MRS to be successful shipboard. The objective of this SBIR topic is to explore potential opportunities surrounding a non-HFC, shipboard transcritical carbon dioxide (CO2/R-744) MRS.

PHASE I: Design a compact 0.75 rTons MRS. Verify feasibility using modeling and/or component demonstration. Perform rough size, weight, electrical power, reliability, operating charge, and manufacturing cost analysis. Develop a Phase II plan.

PHASE II: Demonstrate a working prototype of the system and test in a laboratory environment. Validate analytic models developed in Phase I and scale design to a 1.5 rTon application. Complete a cost analysis of concepts established to ensure the selected technology is competitive with current approaches.

PHASE III DUAL USE APPLICATIONS: Optimize the concept design for manufacturability, performance and military requirements using the knowledge gained during Phases I and II. Develop the next generation of MRS that meets unique military requirements, such as shock and vibration. Explore similar commercial applications such as retail and supermarket refrigeration systems.

REFERENCES:

1. Frank, M.; Spector, M. S. and Antin, N. "Investigating Low Global Warming Potential (GWP) Alternatives for Navy Refrigeration Systems." ASNE Advanced Machinery Technology Symposium, 2024. https://navysbir.com/n25_1/N251-061-Reference-1-AMTS_Paper_Investigating_Low_GWP.pdf

2. "Naval Refrigeration Equipment." Leonardo DRS. https://www.leonardodrs.com/what-we-do/products-and-services/navy-refrigeration-equipment/

3. "ASHRAE Standard 15, Safety Standard for Refrigeration Systems and ANSI/ ASHRAE Standard 34-2022, Designation and Safety Classification of Refrigerants.

KEYWORDS: refrigeration; carbon dioxide; low global warming potential; vapor compression

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