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 1. Field of the Invention
 This invention relates to transport aircraft galley systems, and more particularly, to systems to cool food carts prior to service by the cabin attendants.
 2. Description of Related Art
 Aircraft galley systems for modern transport aircraft incorporate food carts which are cooled to prevent food spoilage prior to use by the cabin attendants for distribution of food to the passengers. These food carts have in the past been interfaced with cold air supply systems in the galley designed to cool the interiors of the food carts. Such cool air distribution systems were generally co-located with the balance of the galley and interface to the food carts by means of gaskets connecting the food carts to a plenum containing the cool air.
 As space in modern aircraft has become more at a premium and more efficient means of cooling the carts has become necessary, there has emerged a need for alternatives to such systems. Furthermore, recent FDA rulings have lowered the required temperature at which the interior of the food carts has to be kept in order to prevent food spoilage. Additionally, it has become more desirable to remove refrigeration equipment from the galley compartment and to find other means to properly cool the food carts without locating the entire refrigeration system in the galley area. In order to be compatible with modern transport aircraft requirements, it has become important to have an increased degree of safety and modularity for any aircraft system incorporating electronics or electric pumps, and it would be particularly desirable to locate at least a portion of such systems outside of the cabin area of the aircraft. In any event, it is important that any system that interfaces with either food or the cabin area is non-toxic and can be configured to provide a wide range of cooling capacity as a function of the food and food carts that are to be interfaced with such a system. The present invention satisfies these and numerous other requirements for transport aircraft.
 The present invention overcomes the shortcomings of previously known systems for cooling food carts in aircraft. The system of the invention serves to not only remove the bulk of the refrigeration system from the galley area but also obviates the need to accommodate bulky air ducts that would supply cooled air from refrigeration stations directly to the carts. Additionally, the system allows low temperatures to be readily achieved in a very controllable manner.
 In general terms, the invention employs an intermediate working fluid to transfer heat from a cart or carts to a remote chiller or chillers. In a presently preferred embodiment, the components of the system may be advantageously positioned in the aircraft and do not have to be contained in a single location. More specifically, the invention utilizes a plurality of heat exchangers to effect a cooling of the carts wherein heat from the food cart is first transferred to an airflow; heat from the airflow is then transferred to an intermediate working fluid which is circulated between a location immediately adjacent the food carts and a remote chiller; heat from the intermediate working fluid is subsequently transferred to the chiller working fluid; and finally, heat from the chiller working fluid is expelled to ambient air.
 While in the currently preferred embodiment, the chiller working fluid undergoes a phase change in order to transfer heat from the intermediate working fluid to the ambient air, the intermediate working fluid typically remains in its liquid phase throughout its circulation. A recirculation pump serves to circulate the intermediate working fluid through a distribution system that may link a plurality of chillers to a plurality of food carts. An expansion tank accommodates the expansion and contraction that the intermediate working fluid undergoes during its circulation. Each of the chillers cycles the associated chiller working fluid between a condenser and evaporator in a conventional manner whereby an expansion valve is relied upon to control the phase change therebetween.
 The temperature of the food cart is regulated by a combination of controls. The speed of a fan circulating air flowing over the heat exchanger for the intermediate working fluid and directing the air cooled in this manner through the food cart may be varied so as to influence the rate of heat transfer between the food cart and the intermediate working fluid. A variable flow valve may be used to control the flow of intermediate working fluid to each cart, while the flow velocity of the intermediate working fluid circulating in the entire distribution system may be controlled by varying the speed of the recirculation pump. Finally, each of the chillers may be turned on or off depending upon the temperature of the intermediate working fluid returning from the food carts. Temperature sensors and pressure sensors are positioned throughout the system to monitor these parameters at appropriate locations in order to allow the operation of the overall system to be properly controlled by the use of electronic controls such as programmable industrial controllers. (PIDs)
 Other features and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments in conjunction with the accompanying drawings, which illustrate, by way of example, the operation of the invention.
 The present invention is directed to a system for refrigerating food carts within an aircraft galley system. Generally, the system includes a set of remote chillers which remove heat from a distributed liquid refrigerant system, which in turn removes heat from one or more food carts to refrigerate the food carts. The entire system is electronically monitored and controlled to provide a sufficiently chilled environment within a potentially large number of food carts.
 More specifically, the present invention includes three distributed refrigeration subsystems, and an electronic control subsystem for monitoring and controlling the refrigeration subsystems. The first refrigeration subsystem includes at least one remote chiller, the second refrigeration subsystem includes at least one galley air cooling unit, and the third refrigeration subsystem includes at least one recirculation unit.
 Each remote chiller constitutes a self-contained refrigeration unit, which serves to remove heat from a liquid refrigerant, referred to as the intermediate working fluid. The intermediate working fluid is then distributed to the second refrigeration subsystem. The galley air cooling units each include a galley cart and a galley plenum. The chilled intermediate working fluid is distributed into and exits from a heat exchanger within the galley plenum. A blower or fan within the plenum blows air over the exchanger and through the galley cart. In this manner, the galley cart may be continually flushed with air chilled by the galley plenum heat exchanger.
 Upon exiting the galley plenum the intermediate working fluid is distributed to the third refrigeration subsystem. Each recirculation unit may include one or more liquid pumps and expansion tank or accumulator. The one or more pumps of the recirculation units pressurize the intermediate working fluid for redistribution to the remote chillers. The accumulators of the recirculation units allow for the storage and thermal expansion of the intermediate working fluid.
 The electronic control subsystem is also a distributed system which may monitor and control individual components of each refrigeration subsystem. Individual electronic devices may be used to monitor and control the temperature within each galley cart. The galley air cooling units may include a control valve to vary the amount of liquid refrigerant entering the galley plenum. The electronic devices monitoring the temperature of the air in the galley cart may be used to adjust the control valve. These same electronic devices may also be used to turn the fan in the galley plenum on and off.
 Other electronic devices may be used to monitor and control the recirculation units. These electronic devices monitor and control the recirculation units. These electronic devices may also be configured to monitor the pressure and volume within the expansion tank. The recirculation units may be controlled by turning the pumps on and off or by varying the speeds by which the pumps operate.
 Other electronic devices may also be used to monitor and control the remote chillers. By monitoring the pressure and temperature within the remote chiller the electronic devices can appropriately determine which remote chillers to operate at different times.
 The electronic subsystem may be powered by the aircraft electrical power systems. The electronic subsystem may also include any number of display systems and interfaces for control by the crew. An overall control system may operate each individual electronic device.
 The entire system and each individual component should be configured for operation within the unique environment presented by transport aircraft. Equipment used on commercial aircraft must meet strict requirements. In addition to maintaining food at safe temperatures, general aircraft operating requirements must be met. The size and weight of the system must be kept to a minimum. The reliability and ease of maintenance are key economic considerations. Fire suppression, non-toxicity and electromagnetic interference (EMI) shielding are key safety considerations. The present invention allows for these concerns, and others, to be met satisfactorily.
 As depicted in
 The heat exchanger
 A large number of the galley carts
 A proportional flow valve
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 From the compressor
 Associated with the evaporator
 A remote chiller unit
 The unchilled intermediate working fluid
 Within the recirculation unit
 Each recirculation unit
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 To circulate the intermediate working fluid
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 A chiller unit monitoring device
 A system monitoring and control device
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 It will be apparent to those of skill in the art that the exemplary systems described in this detailed description conform to the invention described. It will also be apparent to those of skill in the art that various modifications may be made to the exemplary systems while remaining within the scope of the invention. Thus, the invention is not intended to be limited to the examples described herein. The scope of the invention is described and limited only by the following claims.