N112-164 TITLE: Advanced Fan Coil Unit

TECHNOLOGY AREAS: Ground/Sea Vehicles

ACQUISITION PROGRAM: PMS 320 Electric Ships Office

OBJECTIVE: Develop and demonstrate durable, long-life, advanced fan coil unit (FCU), while improving efficiency, lowering noise levels, maintaining weight/volume requirements, providing greater standardization and lowering overall life cycle costs. An intermediate sink water system (ISWS) loop supplying 68°F water (1.8 gallons per minute per cooling ton) can be used by the FCU to reject heat during cooling applications and perform useful cooling during heating applications. The dry and wet bulb temperatures of the air exiting the FCU shall be less than 55°F, requiring the use of active refrigeration.

DESCRIPTION: Thermal Management is a critical requirement for future warships with electronic, propulsion, weapon, and sensor systems. Electronic advancements are resulting in distinct differences in the distribution of shipboard thermal loads, in which electronic cooling requirements are becoming more pronounced. Cooling equipment thermal loads using legacy naval design practices will result in systems which are inefficient, heavy, voluminous, and require significant manpower to operate/maintain. Incorporation of an ISWS loop, at a notational 68°F, for cooling the HVAC equipment loads and the non-HVAC chilled water loads is an alternative thermal management strategy which provides significant benefits in energy efficiency, equipment reliability, equipment availability, commonality and maintenance. Since the thermal loads requiring air conditioning duty are relatively modest, other strategies like the advanced FCU can be utilized to satisfy this cooling requirement with dramatically less power. Development of this technology will be a key enabler for deploying the ISWS.

Fan coil units are generally located within the space served, reducing the requirement for fan rooms and providing an effective ventilation approach for recirculation air systems. FCUs are designed for horizontal mounting in the overhead, or vertical mounting on bulkheads, minimizing the deck area required for installation. A typical FCU consists of a fan/motor, motor controller, air filters, inlet and outlet grills, thermal/acoustic insulation, chilled water cooling coil, and an electric heater. Ductwork may be connected to inlet and outlet openings on some units. The fan-coil unit cabinet is designed to permit ready connection of a power supply, chilled water supply and return lines, and a condensate drainage line. The fan-coil unit draws air through the inlet and the air filters, through the fan, into and through the cooling coil, through the heater and discharges the air through the supply outlet. Since FCUs are installed in manned spaces, air-borne noise must be minimized.

Innovative research is sought to produce the next generation of FCUs. Improved reliability and reduced noise levels are primary design considerations. Weight, volume and energy savings are important but secondary design considerations. Goals for the coefficient of performance (useful heat transferred divided by the input energy) are 6.5 for cooling applications and 4.5 for heating applications. This calculation ignores the pump power to circulate the water, as well as the power to circulate the air through the FCU. During heating application, heat from the ISWS will be absorbed so useful cooling can be conducted elsewhere within the ISWS loop. The ability of the FCU to switch from heating to cooling shall be automatic and require no assistant from personnel. The fan shall be designed for continuous operation, equipped with variable speed controls and have a minimum efficiency of 80 percent. Fan efficiency is the ratio of the ideal (isentropic) fan power divided by the product of the actual fan motor input power times the motor efficiency. Maximum water-side pressure drop is 12 psid across the heat exchanger.

PHASE I: Develop advanced concepts for the next generation of Naval FCUs meeting requirements above. Evaluate the feasibility of concepts through analytical modeling. Define strategies to reduce air-borne noise and improve component reliability. Determine the size and weight expectations over existing components. Determine coefficient of performance for cooling and heating applications as well as identifying water-side pressure drop and fan performance expectations. Identify risks and mitigations, as applicable.

PHASE II: Design and manufacture a full scale next generation FCU H3 unit (1.3 cooling tons capacity, 5.25 kW heating). Performance data shall be collected at a variety of flow rates (both air and water), air temperatures/humidity, and water temperatures. Air-borne and structure-borne noise testing shall be conducted. Validate and expand analytic models developed in Phase I. Investigate the scalability of design and identify commonality efforts. Refine calculation and estimates provided in Phase I.

PHASE III: Design and develop the next series of advanced FCUs using the knowledge gained during Phases I and II. This series of advanced FCUs must meet Navy unique requirements, e.g. shock, vibration and EMI.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: Advanced FCUs developed here would be suitable for use in commercial and home HVAC systems. Technology is ideal for integrating with a geothermal system to conserve much needed energy.

REFERENCES:
1. NSWCCD-98-TR–2007/06 of September 2007, "21st Century HVAC System for Future Naval Surface Combatants – Concept Development Report", Matthew Frank and Dick Helmick.

2. MIL-PRF-24775A - Performance Specification, Air Conditioning Fan-Coil Units, Horizontal and Vertical Types, Naval Shipboard.

KEYWORDS: Thermal Management; Cooling Coils; Heating, Ventilation and Air Conditioning (HVAC); Fan Coil Unit

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