BACKGROUND TO THE INVENTION The prior art is replete with water distribution systems of various types. These include once-through systems where water is delivered from a water tank or other source to a user outlet facility such as a tap, but only when a user demand occurs. The path of water flow may include devices such a filters, water purifiers, or the like that are designed to improve the quality of water passing through.

Prior art water distribution systems also include systems that incorporate means for recirculating water stored in a tank for the purpose of aeration or to prevent or counter the effects of stagnation. For example, see U. S. Pat. No. 5,032,290 granted to Yamagata et al. on July 16,1991, and U. S. Patent No. 5,351,337 granted to Deutsch on September 27,1994. In the case of Deutsch, a system is disclosed which may be selectively controlled to deliver water from a storage tank to a user outlet facility along a once-through path or, alternately, to recirculate water in a short loop that bypasses a substantial part of the water delivery path to facility. One of the indicated advantages of the recirculation loop is that it permits the safe long storage, even the freezing, of water in a water storage tank without algae formation or stagnation becoming a problem. Thus, it is implied that if water should freeze in the storage tank then, upon thawing, it may be rejuvenated by activating the recirculation loop. But, Deutsch is not concerned with the possible freezing of water while the system is operating in freezing conditions. Yamagata et al. are essentially concerne to recirculate stored water to avoid stagnation that may occur if water remains still for an extended period of time. They do not address the question of freezing.

The problems that can arise by reason of freezing are recognized by Deutsch, but only to a limited degree. In a more comprehensive sense, they are also recognized in U. S. Patent Nos. 5, 303,739 and 5,309,938 granted to Eligoth et al. on April 19,1994 and May 10,1994, respectively. Eligoth et al. describe a fresh water supply system for an aircraft where the exposure of water distribution lines in the aircraft to freezing temperatures is a recognized possibility. Eligoth et al. note that the conventional way to address the problem of freezing temperatures is to heat the water lines. They also note that such heating can be both complex and costly. They go on to note that sufficient recirculation can serve to prevent freeze-up, and that a pump may be used to achieve recirculation. But particulars of the pump are not described and, notwithstanding the desire to avoid having to heat the water lines, their system still calls for a limited degree of heating along a portion of the lines and for the provision of heat insulation along another portion.

The foregoing systems fail to recognize or take advantage of the full benefits that can be achieved with water recirculation.

A primary object of the present invention is to provide a method of water distribution and water distribution apparatus that has reduced sensitivity to the temperature of the surrounding environment.

A further object of the present invention is to provide a method of water distribution and water distribution apparatus operable for extended periods of time at temperatures below freezing, and to do so without the need for external heating.

A further object of the present invention is to provide a method of water distribution and water distribution apparatus that is able to improve the quality of or to impede the deterioration of water in a water distribution system, including substantial reduction of organic and inorganic contamination in the system by way of water and air supplied to the system.

SUMMARY OF THE INVENTION In a broad aspect of the method of the present invention, water is supplied to a water user outlet facility by directing a tappable flow of water in a recirculation loop that includes a pump that establishes and maintains the flow while imparting thermal energy to water within the loop, a water delivery path that extends from the pump to the outlet facility, a water return path that extends from the outlet facility back to the pump, and one or more water treatment devices for improving the potability of and imparting further thermal energy to water within said loop. The pump is configured to provide a relatively constant discharge pressure over a broad range of water usage rates and is operated at a water flow rate which is sufficient to avoid the freezing of water within the loop while any one or more of the parts of the loop is exposed for an extended period of time to an ambient temperature substantially below the freezing temperature of water. To make the system more adaptable to differing water usage rates, the pump is preferably a centrifugal pump that is driven by a substantially constant speed motor.

The flow in the loop can be controllably tapped at the outlet facility by a water user.

Any untapped portion of the flow is directed into the water return path.

The system may include only a single water user outlet facility. However, more typically, it is contemplated that it will include a plurality of such facilities located at intervals around the loop. In such cases, a part of the water return path for all but the last outlet facility in the loop will also be a part of the water delivery path for the one or more other facilities in the loop.

Two immediate advantages derive from recirculation within the loop. Firstly, recirculation avoids or negates the consequences of stagnation and thereby impedes deterioration in the potability of the water. The formation of bacteriological colonies is deterred. Secondly, recirculation at a sufficient volume flow rate makes the recirculating loop and water within the loop materially less sensitive to the temperature of the surrounding

environment. In this regard, it will be recognized that the operation of the pump effectively adds thermal energy to the system and will therefore tend to maintain a continuous and uniform thermal level throughout the system. The added energy serves to balance heat energy loss to the surrounding environment. Thus, where water in a non-recirculating system will eventually freeze if the system is exposed for a sufficient length of time to freezing temperatures, it may be maintained in a liquid condition in the present system even though the water delivery path, the water return path, or other parts of the recirculation loop may be exposed to freezing temperatures for extended periods of time.

The inclusion of one or more suitable water treatment devices within the recirculation loop serves a dual purpose. Such devices not only serve to maintain or improve water quality, but advantageously impart further thermal energy to the system. Such devices may include a water purifier such as an ultra-violet lamp source to kill organic contaminants and to impart heat into the water, thus assisting in reducing the probability of freezing in harsh environments. They may also include a filter to remove inorganic material. Preferably, all such devices are located within the water delivery path of the loop and upstream from all water user outlet facilities. While such devices are generally well known in and of themselves, their effectiveness in treating the water is enhanced by the present system because any given control volume of water may pass through the devices many times before it is ultimately tapped by a user.

The avoidance of freezing can be achieved without the necessity to provide external heating for either the water delivery or the water return paths. Of course, there are limits depending upon the volume flow rate that can be maintained by the pump. Harsher environments may dictate a pump that is capable of adding more energy than a pump that would suffice for more moderate environments.

In a preferred embodiment of the present invention, the recirculation loop includes a water storage tank in which water is stored as a preliminary step. This embodiment is considered particularly suitable for vehicular applications, and especially applications such as

airborne applications where the system may be exposed to a wide range of environmental temperatures depending upon flight operations. In airborne operations, the system may be operated whether it takes operating power from the aircraft electrical system while in flight or from ground support facilities while on the ground with the aircraft engines shut down. It is noteworthy that since the water storage tank need not be pressurized as is typical in conventional aircraft, it may be shaped or configured to take better advantage of available space within the contours of the aircraft hull.

In another embodiment of the present invention, flow is maintained in the recirculating loop by adding make-up water into the loop to replace water tapped at the user outlet facility or facilities. This embodiment is considered to be suited for stationary applications where water is drawn from an external source such as a domestic water supply utility.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic representation of a water distribution system in accordance with the present invention where water for the system is carried in a water storage tank.

Fig. 2 is a schematic representation of a water distribution system in accordance with the present invention where water for the system is received as make-up water from an external source.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS The water distribution system shown in Fig. 1 is considered particularly suitable for, but not limited to vehicular applications. As shown, the system includes a water storage tank 10 that is initially filled with water through water inlet line 11 from an external source (not shown). The quantity of water received is controlled by a valve 12. Tank 10 also includes an air inlet vent 13 that serves to equalize pressure in the tank with that of the surrounding environment by allowing fresh air from the surrounding environment to enter the tank through a filter (not shown) that forms part of the inlet path.

Stored water is drawn from tank 10 through discharge pipe 14 which leads through a T-connection 15 to a drain pipe 16 and a delivery pipe 18, the latter of which feeds water pump 20. Pipe 16 includes a valve 17 that is normally closed to prevent drainage, but which may be opened if it is desired to empty tank 10.

Pump 20, is a centrifugal pump that is operated continuously by a substantially constant speed motor, and is configured to provide a relatively constant discharge pressure over a broad range of water usage rates. By way of example, one such pump that embodies such characteristics is the Model No. 2242 centrifugal pump available from Howden Fluid Systems of Santa Barbara, California. This pump has a rating of 3.5 gallons per minute at 35 psid and includes a substantially constant speed electric motor that operates on 115 VAC, 3 phase, at 400 HZ. Such electrical specifications make the pump compatible with and able to draw operating power from the on-board electrical system of many conventional aircraft.

In the Figures, pump 20 is schematically depicted as being connected by an electrical cable 80 to an electrical power source 81. For airborne applications, source 81 may be considered as representative of the on-board electrical system of an aircraft.

Of course, it will be understood by those skilled in the art that a suitable pump could be driven by other power sources such as compressed gases or fluids, or internal or external combustion engines.

Pump 20 discharges into a water distribution pipe 21 that leads firstly to a first water treatment device or water filter 30 that serves to remove inorganic material, then to a second water treatment device or water purifier 31 such as a lamp source that irradiates flowing water with ultraviolet radiation to kill organic contaminants, then to an accumulator 32, then to the first of three water user outlet facilities 41,42,43 that are interconnected in succession by pipe segments 22,23. Each outlet facility includes an associated tap valve 44,45,46 controllable by water users, and an associated non-return valve (check valve) 47,48,49. A water return pipe 24 leads from the last of the three outlet facilities 43 back to tank 10.

Return pipe 24 is shown as including an orifice 50. Orifices are well known elements, the purpose being to maintain system pressure and provide a desired pressure drop.

In the case of water returning to tank 10, it is contemplated that in many cases pipe 24 itself may be sized to provide a sufficient pressure drop but, if not, then an orifice such as orifice 50 may be used. The actual need for an orifice will depend upon overall system design and design principles well known to those skilled in the art.

By definition, pipe 21 and the appliances (viz. filter 30, conditioner 31 and accumulator 32) connected along the line of pipe 21 define a water distribution path from pump 20 to the first of the three outlet facilities 41. This path, combined with the path through outlet facility 41 and pipe segment 22 defines a water distribution path from pump 20 to outlet facility 42. Likewise, the foregoing combined path further combined with the path through outlet facility 42 and pipe segment 23 defines a water distribution path from pump 20 to outlet facility 43.

Similarly, each outlet facility has a defined water return path extending from the facility to pump 20. In the case of outlet facility 41, the return path comprises pipe segment 22, outlet facility 42, pipe segment 23, outlet facility 43, return pipe 24 (with or without an orifice 50), tank 10, discharge pipe 14 and delivery pipe 18. Return paths for the remaining two outlet facilities may be similarly defined.

In operation tank 10 is first filled with water. Then, with valve 17 closed, pump 20 drawing power from source 81 is operated to establish and maintain a continuous flow of water in the recirculating loop defined by the water delivery and water return paths described above. While the flow continues, water is delivered from pump 20 to each outlet facility 41, 42,43 along an associated water delivery path. Concurrently, water may be independently tapped by users at any one or more of the facilities by using tap valves 44,45 46. At any given facility, water that is not tapped is directed into a water return path associated with the facility. When one or more of the tap valves is controlled to an open or a partially open

position, associated check valves 47,48,49 will serve to prevent system contamination by external or reverse water or air flow into the recirculating loop through the tap valves.

Typically, the demand at any given outlet will be random in character. But, from time-to-time peak flow conditions may arise. If such conditions are of relatively short duration, then the water flow capacity of pump 20 will be augmented by accumulator 32 without any significant loss of pressure at the outlet facilities. The alternative would be to use a higher rated pump, but it may be considered undesirable to carry a larger pump that is rarely called upon to deliver peak capacity.

From Fig. 1 and the foregoing description, it will be apparent that the bulk of water within the system will have little opportunity to stagnate so long as pump 20 is maintained in operation. Further, the potability of the water is improved as it repeatedly passes through filter 30 and purifier 31. Moreover, as the operation of the system introduces heat energy to the water, the system may be operated in environments where stagnant water might otherwise freeze.

The water distribution system shown in Fig. 2 is very similar to the system shown in Fig. 1, the essential difference being that there is no stored water in the system. Instead, make-up water is added to the recirculating loop described above.

More particularly, there is no storage tank 10 as in the case of Fig. 1. In the system of Fig. 2, a water return pipe 25 extends in place of return pipe 24, storage tank 10, and drain pipe 14 of Fig. 1. Make-up water is delivered to the system through inlet pipe 60, T-connection 70 and pipe section 19, and is added to the recirculating loop at T-connection 15. Pipe 60 is connected to an external source of water (not shown) and includes a valve 61 to control the quantity of water supplied. Further, pipe 60 includes a check valve 62 to prevent back flow.

When the system of Fig. 2 is in operation, water cycles in the recirculating loop in essentially the same manner as the system of Fig. 1. The basic difference is that new water

will be added to the loop at T-connection 15 to make-up for any water that is drained at outlet facility 44,45 or 46. Generally, the same advantages as may be realized with the system of Fig. 1 may also be realized with the system of Fig. 2.

Various modifications and changes to the embodiments that have been described can be made without departing from the scope of the present invention, and will undoubtedly occur to those skilled in the art. The invention is not to be construed as limited to the particular embodiments that have been described and should be understood as encompassing all those embodiments that are within the spirit and scope of the claims that follow.