BACKGROUND INFORMATION The present invention relates to an apparatus and method for moderating or controlling air temperature, in particular to enhanced air conditioning systems. Air conditioning systems used in domestic, industrial and military settings typically contain a refrigeration device that transfers heat from incoming air to a refrigerant, such as an HCFC or HFC, thereby cooling the air prior to it being released into a space such as a room.

Known air conditioning systems can require considerable power to operate. Power generation, even where feasible, can be expensive, particularly for military deployments. In such operations, transporting supplies and equipment over long distances and/or in hostile conditions often is necessary. The supplies or equipment being transported often are expensive and may benefit from being maintained within a predetermined temperature range. For example, food supplies may need to be kept at around room temperature, and some electrical equipment can be damaged by or function inefficiently when exposed to unusually hot or cold conditions. When external day- and night-time temperatures vary significantly, air conditioning equipment needs to be sized to cope with the maximum temperature demands, which often means less-than-full utilization during cooler periods.

Temporary offices, living quarters, or other buildings often need to be provided in hostile climates, for example, for mobile personnel. Maintaining such buildings at a comfortable temperature is desirable.

Power for units as described above often needs to be generated by transportable means so that a housing structure or other container can operate at a comfortable temperature even in a remote area. This arrangement presents a number of practical problems. First, transporting sufficient quantities of fuel to enable air conditioning units to operate adequately can present logistical difficulties. Second, although evaporative cooling units can help to reduce fuel consumption, providing sufficient (clean) water supplies for operating those units can be problematic, especially in desert regions. Third, generators providing power to operate air conditioning units tend to emit significant heat which can

lead to easy identification because the thermal signatures of such equipment differ significantly from the thermal signatures of natural environments. Thermal imaging devices can recognize such equipment, and effective camouflage can be a significant problem. Phase change materials absorb or release heat at the operational temperature where they exhibit a phase change, which gives them thermal regulating properties. Such phase change materials have been used in textiles (for instance for military and sports clothing), surgical bandages and protectors for electronic components. They also have been embedded in linings which can be applied to walls to improve the thermal efficiencies of buildings; see, e.g., PCT publication WO 03/085346.

Providing means for cooling air that can mitigate or overcome such problems remains desirable.

SUMMARY OF THE INVENTION

In a first aspect is provided an apparatus for controlling air temperature in a defined space which enables improved efficiency. The apparatus includes an air conditioning unit, phase change material, and a system to circulate fluid so as to enable transfer of heat between the phase change material, the air conditioning unit and the air in the space. A method of cooling that employs such an apparatus also is provided.

The circulating system in a first mode can operate to pass fluid from the phase 'change material to the air conditioning unit and, in a second mode, to pass fluid from the air conditioning unit to the phase change material. The phase change material can undergo a first phase change in the first mode and a reverse phase change in the second mode; for example, the first phase change can be endothermic and the second exothermic.

The apparatus additionally can include a unit for controlling the circulating system. By providing the control unit with various inputs, such as the temperatures of external and internal air as well as phase change materials, the control unit can be enabled to switch between different modes of operation according to relevant conditions. For example, the control unit can be arranged to cause the circulating system to operate in a first mode during periods of

increased ambient temperatures (e.g., daylight) and in a second mode during periods of reduced ambient temperatures (e.g., nighttime). The first mode can involve the circulating system being arranged to pass fluid from (i.e., be in thermal communication with) the space to the phase change material, from the phase change material to the air conditioning unit, and from the air conditioning unit to the space. Air in the space thus can be cooled by action of both the phase change material and the air conditioning unit. The thermal communication preferably is conduction of heat between the two objects or volumes.

The fluid can be air, a (compressed) gas, a liquid, etc., or a plurality of fluids in different regions of the circulating system. The fluid between the air conditioning unit and the space preferably is a liquid.

The circulating system also can be operable in a third mode to pass fluid from the phase change material to the space. The control unit can be arranged to cause the circulating system to operate in the first mode during warmer times (e.g., daylight hours) and in the third mode during cooler times (e.g., nighttime hours) so as to warm air in the space.

The phase change material and the air conditioning unit can be provided in an integrated device. This can allow the apparatus to be compact and easily transportable. Alternatively, the phase change material and air conditioning units can be provided separately. This may be desirable where the phase change material unit is to be an add-on component to an air conditioning unit.

A thermionic heat transfer device also can be provided in the apparatus for heating or cooling the fluid. The air conditioning unit may be such a thermionic unit. The circulating system can have a first fluid carrier passing through the phase change material to transfer heat between the phase change material and fluid in the first carrier. The system also can have a second fluid carrier positioned so as to enable transfer of heat between fluid in the second carrier and air in the space. The second carrier can be provided with a relatively large surface area so as to enhance transfer of heat between fluid in the second carrier and air in the space.

In another aspect is provided a heat transfer unit including phase change material and having an inlet, an outlet and a fluid carrier for passing fluid from

the inlet through the phase change material to the outlet, thereby enabling heat transfer between the fluid and the phase change material. The outlet may be arranged for connection to an inlet or an outlet of an air conditioning unit.

In a third aspect is provided a fluid cooling unit that includes an inlet, a fluid carrier, phase change material, a fluid cooling device, and an outlet. The unit is arranged to receive fluid at the inlet, pass the fluid along the carrier through the phase change material, the fluid cooling device, and to the outlet, thereby enabling heat transfer between the fluid, the phase change material and the fluid cooling device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an embodiment apparatus for controlling air temperature in a housing structure;

FIG. 2 is a schematic view of a heat transfer unit including phase change material;

FIG. 3 is a schematic representation of a fluid cooling unit; and

FIG. 4 is a front perspective view of a mechanism for heat transfer between a liquid and a gas.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

An apparatus of the present invention is indicated generally by numeral 100 in FIG. 1. A soft-sided shelter 1 , such as a tent, is connected by pipes 4 and 6 to, respectively, a unit 2 that includes phase change material and an air conditioning unit 3. Fluid can be transferred between units 2 and 3 by means of pipe 5. Further pipes 7 and 8, which can constitute inlets or outlets, also are provided on units 2 and 3. Controller unit 20 can regulate or direct the flow of fluid within the pipes.

In one mode of operation, which is selectable by means of controller 20, warm air is drawn out of shelter 1 through pipe 4 and into unit 2 (the direction shown as A in FIG. 1). Air passes through the phase change material, which has gaps within it to allow air flow, and the operational temperature of phase change material is such that the phase change material absorbs heat from the passing air, thereby cooling it. For example, maintaining air temperature in the

shelter within a range up to about 32 ⁰ C might be desirable. A suitable phase change material then would be one with an operational temperature at around 32°C so that it absorbs heat until it reaches its operational temperature, at which point it absorbs such further heat as is required for it to change phase. Suitable phase change materials include hydrated metal salts such as calcium chloride hexahydrate and sodium sulfate decahydrate, waxes, parafins and fatty acids. In some situations, relatively dangerous or toxic materials such as lithium salts may be acceptable, in addition to or instead of more commonly used materials. (Some military applications may permit the use of relatively dangerous materials.)

If air in shelter 1 is at a temperature higher than the operational temperature of the phase change material, air in pipe 9 passing through phase change material 10 in unit 2 (shown in FIG. 2) is caused to cool as the phase change material absorbs some of its heat. Thus, air leaving unit 2 at pipe 5 is cooler than air entering unit 2 at pipe 4. When subsequently passed to air conditioning unit 3, the air is further cooled, expelled through pipe 6, and fed back into shelter 1. Because of the pre-cooling effect of unit 2, the amount of heat that must be removed by air conditioner unit 3, so as to expel the air at a desired temperature, is reduced. Thus, less power is required to operate air conditioning unit 3.

In normal operation, cooling system 100 is disabled when the outside air temperature falls (e.g., at night). If the shelter is positioned in a region in which the night-time temperature is not sufficiently cool for the phase change material to revert spontaneously to its initial phase (i.e., the outside temperature does not fall below the operational temperature of the phase change material), the phase change material will not function optimally the following day to absorb heat from air inside shelter 1. In such situations, it may be desirable to run air conditioning unit 3 at night to pass air cooled by air conditioner 3 into phase change material unit 2 to allow the phase change material to change phase in preparation for operation the following day. Additional pipes 7 and 8 can be provided in units 2 and 3 so that outside air can be drawn through pipe 8, in direction B, into air conditioning unit 3 at night, fed through pipe 5 into unit 2, and subsequently released through pipe 7. Although this mode involves extra running costs during

periods of lower temperatures, it can be more efficient to use these two modes, illustrated in FIG. 1 as A and B, sequentially than to run air conditioning unit 3 at a higher power during hot times and disabling it when cooler (e.g., night). Air conditioning unit 3 might not need to pass cooled air to unit 2 throughout the night and, instead, merely to run air along path B. Controller 20 can be arranged to determine the temperature of phase change material 10 and to switch off air conditioning unit 3 when phase change material 10 has cooled to below its operational temperature. Controller 20 additionally or alternatively can include a timer so that air conditioning unit 3 automatically can be switched on or off or adjust the direction of flow of air within system 100 according to the time of day. Controller 20 also can be arranged to measure outdoor air temperature and modulate or regulate system 100 accordingly.

A further possible mode of operation involves passing external air through unit 2 and into shelter 1 during cooler periods, e.g., at night. This could be effective at heating the internal air in situations where the night-time temperature is unpleasantly cold. Thermal energy stored in phase change material 10 can be released into the shelter when the external temperature cools below the operational temperature of phase change material 10. This can reduce or avoid the need for additional heating equipment. If system 100 is intended to be used in this manner, providing a radiator inside shelter 1 to achieve heat transfer from liquid in pipe 4 traveling towards shelter 1 from unit 2 might be desirable. Pipe 4 can supply a radiator with warm liquid (e.g., water) for heating the internal air by convection and radiation. A design with a high surface area can be preferable for the radiator to improve heat transfer. FIG. 3 shows an alternative apparatus in which phase change material and standard air conditioning functionality are incorporated within the same unit 12. Air can enter unit 12 through pipe 11 and pass through a phase change material component 13 before entering the air conditioning section 14 and leaving device 12 at pipe 15. Fluid passing through the pipes of the various embodiments described need not be air. An alternative way of operating apparatus would be to pass a liquid such as water, an HFC, an HCFC, etc., through some or all of the pipes, which might achieve improved heat transfer. FIG. 4 shows a pipe design 30

which can allow the fluid type to be changed at a point within the overall system. A fluid, preferably a liquid such as water, can flow through helically arranged pipe 16 and air can be passed along the inside of the helix, thereby exchanging heat between fluid and air passing by pipe 16. An advantage of the described apparatus and method is that contaminated external air can be kept from entering shelter 1. Shelter 1 can be sealed against the outside and air can be made to circulate according to route A in FIG. 1. Alternatively, introducing outside air into shelter 1 might be desirable but, if such air is contaminated, it could be directed through a filter for removing the contaminants before being passed into shelter 1.

While the foregoing description has been based on a system designed to cool air, the ordinarily skilled artisan easily can envision a heating system that employs a furnace or other heat generator in place of air conditioning unit 2 as well as the modifications (if any) in direction of fluid flow through system 100. Each individual feature described herein is disclosed in isolation and any combination of two or more such features, to the extent that such features or combinations are capable of being carried out based on the present specification as a whole in the light of the common general knowledge of a person skilled in the art, also are disclosed irrespective of whether such features or combinations of features solve a problem disclosed herein. Aspects of the present invention may consist of any such individual feature or combination of features. Various modifications may be made within the scope of the invention.