N221-052 TITLE: Low Hazard Heat Pump for Distributed Cooling

OUSD (R&E) MODERNIZATION PRIORITY: General Warfighting Requirements (GWR)

TECHNOLOGY AREA(S): Materials / Processes

OBJECTIVE: Develop an affordable point-of-use water-to-water heat pump using a low hazard refrigerant or solid-state device with a small footprint, low weight, low vibration, high reliability, and low maintainability cost.

DESCRIPTION: Electronics are an increasingly prominent part of ship systems and weapons. The standard U.S. Navy cooling system provides 44°F chilled water throughout the ship. However, electronics equipment typically require 67°F cooling water to prevent condensation, short circuit, shock hazards, and corrosion. This (a 23°F) delta creates condensation conditions that can present an electrical hazard and accelerate corrosion. Raising the temperature of the 44°F chilled water at point-of-service (for multiple electronics cooling loads) is less efficient than lowering only for specific loads. However, raising temperature requires a heat exchanger while lowering requires a heat pump. The U.S. Navy seeks an innovative heat pump to support development of a distributed cooling architecture and topology where centralized chillers provide 67°F cooling water (instead of the 44°F chilled water). The water temperature is then reduced at point-of-service to 42-44°F (where needed) for air conditioning purposes. The net result is a more efficient cooling system onboard.

The U.S. Navy seeks heat pumps with innovative solutions to minimize environmental impact and meet volume, weight, power, noise, and refrigerant charge requirements. The global warming potential requirement limits the refrigerants used to carbon dioxide, air, water, and a short list of other compounds. Solid-state thermoelectric cooler devices or other unconventional refrigeration systems will be considered in this SBIR effort.

Operational requirements of proposed heat pumps include:

• Chilled water supply and return flow rate of 12 GPM
• Electrical power input is limited to 2 kW at 3 Phase / 450 VAC
• Total volume and weight of the system are limited to 3 ft3 and 150 lbs
• Must fit down a standard Navy hatch (36 in. x 36 in.)
• Noise limit is 65 dB
• Global warming potential of the refrigerant, if used, must be less than or equal to 1
• Maintain the 42°F water outflow temperature within ±2°F using internal controls
• User-configurable thermostat setpoints capable of turning the system ON and OFF based on external temperature and humidity sensor input
• Maximum refrigerant charge is .66 lb (0.3 kg)
• Mean time to failure > 200,000 hours
• Ability to operate in cooling and heating mode
• Meet relevant qualification testing including shock, vibration, electromagnetic interference (EMI), humidity, and temperature in product at end of Phase II

The proposed solutions shall be initially targeted for transition to backfit opportunities where the technology provides a solution to HVAC challenges in existing systems. Other transition targets include the Future Large Surface Combatant program DDG(X), the amphibious transport dock (LPD), and potential use in submarines.

The low Global Warming Potential (GWP) requirement in the solution will provide the ability to transition commercial and residential heat pumps away from high GWP refrigerants such as R-134a and R-12. This addresses the California governmental push for transitioning away from high GWP refrigerants; specifically the requirement for centrifugal chillers to move away from R-134a by January 1, 2024 [Ref 1]. One of the available refrigerants in the solution is carbon dioxide. This effort will push the limit of carbon dioxide heat pump development that has seen little to no commercial or residential application in the United States. Another potential solution is solid-state thermoelectric cooling devices. The efficiency requirement of this effort will push the limits of thermoelectric device coefficient of performance to that of only cutting edge developments relating to ZT factor (main figure of merit in thermoelectric efficiency). [Ref 2].

Current platforms are not able to integrate advanced radar, electronic weapons, and lasers due to the limited capacity of the chilled water system. The Navy transition to electric drive presents issues as the chilled water demand will reach levels that are unsustainable with existing chilled water architecture designed around 44°F. Designing the shipboard distribution system for 67°F chilled water doubles the capacity of existing chillers without any size, weight or power increases, and the temperature allows for direct cooling of equipment with chilled water removing the need for cooling equipment units. The tradeoff in the removal of the cooling equipment units is the integration of the distributed heat pumps throughout the ship.

PHASE I: Develop a design for a low hazard heat pump as described in the Description. The Phase I final report shall be supported by predicted data from a subscale design of the proposed system. This subscale design must be capable of reducing a primary/internal chilled water loop from 67°F to 42°F by rejecting heat to cooling water supplied at 52°F. Proposed solution shall provide a thermodynamic analysis of the solution, estimate of the anticipated total volume and weight of the system referencing weights and volumes of individual components, documentation of estimated noise level, estimate of total refrigerant charge, evidence supporting the mean time to failure, estimate of power use, and an estimate of global warming potential of proposed refrigerant. Identify risks and mitigations, as applicable.

The Phase I Option, if exercised, will include the initial design specifications and a capabilities description to build a prototype solution in Phase II.

PHASE II: Develop and deliver a full-scale prototype designed around 12 GPM of water flow with scaled power, weight, volume, and refrigerant charge (if applicable). Work with the Navy to develop requirements and demonstrate system performance through evaluation in a laboratory environment over the required range of agreed upon requirements. Refine the heat pump design and fabrication process to manufacture consistently in hundreds of units. Calculate a preliminary return on investment. The final product shall be designed to meet all relevant qualification testing including shock, vibration, electromagnetic interference (EMI), humidity, and temperature. Support the development of documentation including, but not limited to; technical manuals, parts lists, drawings, training guides, and logistics documents. Prepare a Phase III development plan to transition the technology for Navy and potential commercial use.

PHASE III DUAL USE APPLICATIONS: Support the Navy in transitioning the system to large surface combatant and amphibious ships.

Transition opportunities for this technology include commercial ship and offshore systems that could benefit from efficient, low condensation cooling systems for electronics.

REFERENCES:

1. California Air Resources Board, "Hydrofluorocarbon (HFC) Prohibition in California," 19 11 2020. [Online]. Available: https://ww2.arb.ca.gov/resources/fact-sheets/hydrofluorocarbon-hfc-prohibitions-california.
2. Attar, Alaa "Dissertation: Studying the Optimum Design of Automotive Thermoelectric Air Conditioning," Western Michigan University, 2015. https://scholarworks.wmich.edu/cgi/viewcontent.cgi?article=2165&context=dissertations.

KEYWORDS: Heat Pump; Chilled Water; Thermal; Carbon Dioxide; Thermoelectric; Thermal Management