1.  FIELD OF THE INVENTION
This invention relates to cooling of buildings, particularly to cooling by absorption and removal of heat from solar energy from the outer surface of buildings, thereby obviating the necessity of expensive and energy-wasting systems for removing such energy.  The invention further relates to a fail-safe design wherein any failure of a component of the system will not result in a catastrophic spillage of water on the surface being cooled. 
2.  DESCRIPTION OF THE PRIOR ART
The desire and need to provide cooling for buildings and structures is as old as the art of constructing human habitation.  Humans perceive xe2x80x9ccomfortxe2x80x9d over a very narrow temperature range.  Below about 18 degrees Celsius, the average person has the perception of cold.  Above about 27 degrees Celsius the average person feels uncomfortably warm.  From the very beginning, the concept of a habitable structure involved providing protection from the elements, including natural temperature variations beyond the foregoing comfortable range. 
From the earliest use of mud and leaves as insulation, humans have sought to perfect the environment by the use of habitats.  For much of the time, the consumption of resources and the use of power, was secondary to the achievement of a controlled environment.  The prior art clearly shows the desire for achievement of climate control, without consideration for the inevitable failure of the system components, or the consequences of such failures. 
As early as 1937, Holder, in U.S. Pat.  No.  2,069,150 (Jan. 26, 1937), recognized that not only was evaporative cooling of structures a desirable means of cooling, but just as importantly, various systems and devices that had previously been used for cooling roofs were found faulty in cost of maintenance, consumption of water and also by reason of mechanical defects.  While recognizing that mechanical defects were an impediment to the practical use of water for cooling roofs, neither Holder, nor any other prior art that I have found in the intervening fifty-six years addresses the issue of component or system failure. 
Any system applying water, or another fluid, to a roof for cooling purposes must consist of at least pipes to carry water, valves to apply or restrict the application of water, and a control system to operate the valves.  If a pipe failsxe2x80x94which can happen at any time since the most practical pipe to use is PVCxe2x80x94a material attacked by sunlight over timexe2x80x94water can be delivered to the roof in uncontrolled quantities.  A failed valve can deliver unchecked water, or fail to deliver water when required.  While solid-state electronics today are quite reliable, a control system cannot be presumed to be failure-free. 
Holder raises the possibility of xe2x80x9cmechanical defectxe2x80x9d, but does nothing to address the issue of what impact it might have when an inevitable failure occurs.  I believe that for this very reason, a concept that has been known for a century has never been accepted as a conventional means of structure cooling and energy savings. 
Another patent to Holder, U.S. Pat.  No.  2,266,321 (Dec. 16, 1941), addresses the xe2x80x9cprevention of excessive heat accumulation in exposed surfaces such as roofs.xe2x80x9d Importantly, Holder recognizes that evaporative cooling efficiently removes energy, while the excessive application of fluid on the surface decreases the effect.  In his ""150 patent, supra, Holder described a piping and spray system using a continuously applied spray of water.  By first describing continuous water spray, then adding an interrupted spray, Holder improved upon a basic concept of using water for cooling purposes.  While envisioning a thermostatically controlled valve to interrupt the flow of water, holder failed to contemplate the consequences of his own analysis. 
Holder correctly describes the xe2x80x9cinitially high roof cooling efficiencyxe2x80x9d as water is initially applied to the roof surface.  He then continues describing the action as it progressively and rapidly approaches the condition of low evaporative cooling efficiency where the main reliance is be placed on the cooling effect of the water per se.  One liter of water absorbs 570,000 Calories in the transition from liquid to a gas or vapor.  The heating of water to absorb energy absorbs only 1,000 Calories per liter of water, per degree Centigrade.  Holder then proceeds to describe a process wherein a valve is thermostatically controlled for the application of water to the roof.  Unrecognized is the effect of pooled water, rising to the temperature that is required to turn the valve on, thereby applying more water on water.  This is an effect already recognized as undesirable.  Holder fails to assure that water is applied without the possibility of accumulating water on the surface.  Under such condition, the accumulated water may not provide any cooling. 
U.S. Pat.  No.  2,506,936 to Murray (May 9, 1950) continues the refinement of the cooling process by first reiterating the correct statement; xe2x80x9cIf only a small amount of water is placed on the roof, the evaporation is highly accelerated as compared to what would be if the roof surface were flooded with water.xe2x80x9d Murray""s solution is the addition of a time delay after a first application of water, before permitting a succeeding application of water.  At this point, the concept fails in several respects.  First, Murray describes a means of cooling the thermostat as water is applied to the roof.  If the thermostat is cooled by application of too great a flow of water, the roof receives to little water.  If the thermostat is cooled by too little water, the roof receives too much water.  In this procedure, the surface to be cooled is not directly sensed for the correct amount of water to achieve optimal cooling.  Murray, as all others, fails to address the problem of system or component failure, and the possible spillage of uncontrolled water. 
U.S. Pat.  No.  4,761,965 to Viner (Aug. 9, 1988) describes a very specific arrangement of an evaporative roof cooling system.  Viner describes a xe2x80x9cplurality of water distribution . . .  nozzles, a xe2x80x9cconduit meansxe2x80x9d, a solenoid valve, and a xe2x80x9ctemperature measurement means comprising a thermistorxe2x80x9d.  Viner, like his predecessors, espouses the need to apply water in a thin film, allow it to evaporate, and then repeat the application.  Also like his predecessors, Viner falls into the trap of presuming that a timed cycle of water on/ water off will achieve the goal of optimum application of water.  This timed sequence will never account for the variations in temperatures, variations of the water absorption of the roof material, variation in relative humidity, wind factor, as well as other factors that impact not only the rate of cooling of the roof, but also the rate of evaporation.  Consequently, Viner fails in his goal to apply an optimally thin film of water. 
Viner boasts xe2x80x9celectrical power usage for the system is essentially zeroxe2x80x9d, but describes an electrically operated solenoid control valve, which is continuously energized.  Viner neglects the power requirements of the valve, in addition to the costs associated with wiring the valve and control systems to the building wiring.  Viner, as before, does not address the possibility of failure of a component of his system. 
No known prior art that I have found, from as early as Crawford, U.S. Pat.  No.  964,464 (Jul. 12, 1910) through Strussion, U.S. Pat.  no.  6,112,538 (Sep. 5, 2000), has recognized the fact that water on the roof of a structure carries an intrinsic risk of damage to the structure.  Several possibilities contribute to that risk.  Much of the prior art discloses the use of a thin film of water to effect an evaporative cooling on the structure.  While early patents promote the use of moisture absorbing pads to keep a roof wet at all times, later, more advanced patents teach the deleterious effect of too much water.  Earlier patents expound the use of a control valve, with later patents expounding to the use of multiple valves to control different portions of a roof.  While the use of multiple valves where each valve is delivering water to only a portion of the roof may reduce the effects of a single valve failure, the risk of a catastrophic delivery of water is increased by the use of multiple devices, each prone to failure.  In particular, a valve can be damaged by normal wear, by abrasion of particulate matter moving through a valve, and by the deleterious effects of ultra-violet and infra-red radiation, each a contributor toward ultimate failure. 
U.S. Pat.  No.  4,064,706 to Stephens, Jr, Dec. 27, 1977, teaches the use of a moisture sensing system to apply water whenever the roof is dry.  This leads to another type of failure, one potentially dangerous to human health, as opposed to the structural damage following the uncontrolled flow of water on a roof.  If a roof is maintained in a wet condition for an extended time period, organic matter in the water, combined with airborne organisms, can reproduce and develop colonies of unwanted biological growth on the roof.  Over time, spores, bacteria, fungi and other human-immune attacking organisms can grow and produce a biological threat. 
There has been considerable promotion of the use of white, or light colored roofs, as a means of combating the heating effects of solar energy.  While a light-colored roof will have some effect in reducing the solar heating, during cold months it has the opposite effectxe2x80x94blocking some of the scant solar heat available during cold weather. 
My patent application, Ser.  No.  09/540/450, filed November 1999, shows a system that solves many of the potential failure modes of a roof-mounted cooling system, but does not completely negate all possible failure modes. 
There are often power shortages during hot periods of the year, when high-power-consuming air conditioners are running.  The above cooling systems do not provide a safe alternative to power-hungry air conditioners, while still providing reasonable comfort levels.  The problem of high-power-consuming air conditioners is presently especially acute in California and other areas which are experiencing energy shortages. 
Accordingly, one object of the present invention is to provide an improved system for a building to intercept and remove, with maximum efficiency, by evaporation of a fluid, solar energy impinging upon a building or dwelling. 
Other objects are to provide a self-diagnosing procedure capable of shutting off the water supply in the event of any component, system or power failure; to provide the comforts associated with cooler temperatures within a structure, while saving on the consumption of energy; to provide a water-based cooling system for a structure that avoids continuous wetting and organic growth, and to alleviate the problem of energy shortage, where a such problem exists. 
Additional objects are as follows:
To reduce the temperature shock and temperature excursions of the roofing materials, reducing the stress on those materials, thereby increasing the life of the roof;
To reduce the temperature of the roof and walls of a structure, thereby reducing the cost, in terms of dollars and resources, to maintain a building at a comfortable living and working level. 
To remove energy and reduce temperatures without the attendant risk applicable to having a water supply on the roof of a building;
To monitor the rate of flow of water being applied to a roof section, analyzing the flow rate to determine the condition of the spray heads, establish the frequency of maintenance required based on flow rate, without the necessity of a physical inspection;
To dDetect any system failure that could produce a continuous flow of fluid to one or more sectors of the structure, and stop the water supply before an excessive amount of unwanted water flow occurs. 
The current system, used in conjunction with the traditional black roof, provides benefit during all times of the year.  During hot months, the system maintains the roof at reasonable cool temperatures.  During cold months, a black roof will attract whatever solar energy is available, maintaining the roof at a higher temperature than would be had with a white or light-colored roof. 
The current system, when used in conjunction with recycled, reclaimed, or used water meets the generally accepted requirement that such water not be sprayed on a person without his knowledge or consent by disabling the system in the presence of any person within the spray area. 
Accordingly, still another object is to provide the above benefits at all times of the year. 
Still further objects and advantages will become apparent from the following description of the invention. 
This invention is directed to a system and method of using water to evaporatively cool residential, commercial, and industrial buildings to remove solar energy before it can infiltrate the structure, and detect any component or system failure that could lead to uncontrolled delivery of water.  Upon failure detection, the system then halts the flow of water until the failure can be corrected.  The system comprises a network of water delivery pipes, an array of fluid spray nozzles, sensors for measuring temperature of roof or wall areas, sensors for measuring remaining moisture on the roof or wall areas, electrical valves for applying water at appropriate intervals, and a master control valve capable of stopping all delivery of water to the system.  Further, the system comprises a control system capable of testing the conduit system for leaks or breaks, and additionally, testing the master control valve for proper operation.  Because of this series of self-tests, it would require the simultaneous failure of both the master control valve and one or more of the plurality of control valves to permit uncontrolled water flow.  Since a first failure would be detected immediately, and a simultaneous failure is a remote statistical possibility, the system is therefore substantially xe2x80x9cfail-safe.xe2x80x9d
The array of nozzles is arranged to cover respective areas of a roof or wall such that only a small number of nozzles are in operation at any one time.  This alleviates the need for large water delivery pipes.  One control valve covers each designated area, each valve being controlled by separate temperature and moisture sensors.  Thus, if one area of a roof or wall receives more or less solar energy, the system will deliver an appropriate amount of fluid to compensate for variations in solar energy coverage.  After each control valve completes its task, the system automatically self-tests for leaks, breaks or valve abnormalities, resulting in a frequent self-test, failure detecting system. 
The system is intended to use reclaimed, recycled, and reused water.  When such water is used, local laws generally require that water spray be prevented from unexpectedly reaching people.  The laws often permit informed interaction between people and water spray, but not the wetting of a person unaware of such a possibility.  The system includes a portable transmitter, carried on the person, which disables that portion of the system within the general vicinity of the person by transmitting a signal to all sensors within a reasonable range of the transmitter.