N231-064 TITLE: Reversible Replenishment Air Conditioning System

OUSD (R&E) CRITICAL TECHNOLOGY AREA(S): General Warfighting Requirements (GWR)

OBJECTIVE: Develop compact and energy efficient technologies to reduce the latent loads of outside air entering the ship during the summer while providing heat during the winter.

DESCRIPTION: The heating, ventilation, and air conditioning (HVAC) system is critical to the functionality of the ship�s combat and damage control systems, in addition to ensuring the comfort and health of the crew. Navy ships operate in salt-latent humid environments. Latent loads from outside air, or replenishment air, entering the ship typically represents 10 to 20% of the total cooling load during the summer, while sensible heating from heaters during the winter season creates a significant electrical demand. Evolving battle-space doctrine, emphasizing operations in both the littoral and arctic, as well as changing climate conditions, are further increasing these loads. Technologies are sought to condition the outside air entering the ship to reduce the air conditioning latent load and improve system efficiency. Compact, non-hazardous, and efficient solutions are desired which minimize airside pressure loss while reducing size, weight, and electrical power consumption of the shipboard HVAC systems.

In a typical system, weather air enters the ship through a wire-mesh screen prior to entering a moisture separator or a vertical lift in ductwork, followed by a preheater directly upstream of a vane axial fan, which supplies the various shipboard spaces with fresh air. Typical air velocities through this ventilation system ranges from 1500 to 2500 feet per minute. The weather air is supplied to various recirculation systems, where it mixes with return air, prior to entering a filter directly upstream of the chilled water cooling coils, which provides sensible and latent cooling when applicable. Exhaust systems balance replenishment air but typically exhaust warm and often very humid air from spaces like laundry, scullery, showers, toilet areas, electronic cabinets, and flammable storage lockers. Design temperature for outside weather air during the summer is 90 degrees Fahrenheit (�F) and 10�F during the winter. The design relative humidity during the summer condition is 69%. Preheaters typical heat the air during winter conditions from 10�F to between 45�F and 55�F. Moisture entrainment within the airstream is not desirable and moisture should be disposed of by an appropriate drainage systems.

PHASE I: Develop an innovative, compact, and energy efficient approach to reduce air conditioning latent loads and power consumption associated with bringing outside air into the ship. The air-side pressure drop should be minimized and not exceed 1 inch of water gauge. Validate design performance through analytical modeling or subscale demonstration of components as appropriate.

PHASE II: Demonstrate a working prototype of the system sized for an airflow of 2000 cubic feet per minute device sized for 10-tons of cooling when exposed to design summer conditions and 30 kilowatts of heat when exposed to design winter conditions. Experimentally validate the unit�s performance over a variety of flow rates and inlet dry-bulb and wet-bulb temperatures at and between design routines. 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. Improve the effectiveness of the shipboard HVAC system to reduce size, weight, and power of military and commercial HVAC systems as well as other specialized thermal management systems.

REFERENCES:

4.       Frank, M. and Helmick, D. "21st Century HVAC System for Future Naval Surface Combatants � Concept Development Report." Naval Surface Warfare Center Report NSWCCD-98-TR-2007/06 (2007).

5.       Frank, M. and Spector, M.S. "Next-Generation Thermal Management Architecture for Future Surface Combatants." ASNE Advanced Machinery Technology Symposium (2016).

6.       Labban, O.; Chen, T.; Ghoniem, A.F.; Lienhard V, J.H. and Norford, L.K. "Next-Generation HVAC: Prospects for and Limitations of Desiccant and Membrane-Based Dehumidification and Cooling." Applied Energy, 200:330�346 (2017). https://doi.org/10.1016/j.apenergy.2017.05.051

 

KEYWORDS: thermal management; air-conditioning; dehumidification; heating; energy efficiency

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