Abstract:
The prompt hot water and water conservation system includes a hot water supply pipe connected to a hot water heater outlet. A discharge faucet is connected to the supply pipe. A return pipe is connected to the supply pipe and to a hot water tank drain. The return pipe carries cooled water to the drain for reheating. Reheated water circulates into the supply pipe. A flow control device, in the return pipe, includes a chamber that houses a sphere. Return water flow moves the sphere toward a stop and permits unimpeded movement of water into the tank drain for reheating. When the faucet is opened, water flows from the tank drain into the flow control device. The sphere is moved to contact a small end of the chamber and substantially stop flow through the return pipe. Water is circulated through the system by increased density of cooled water.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of the filing date of U.S. Provisional Application No. 61/485,122, titled PROMPT HOT WATER SYSTEM AND METHOD. Filed May 11, 2011. 
    
    
     TECHNICAL FIELD 
     The invention is in a convection hot water system that provides prompt delivery of hot water from a central water heater for use at one or more remote locations and conserves water. 
     BACKGROUND OF THE INVENTION 
     The hot water system in many homes, offices and other facilities includes a hot water heater that receives cold water from a water source, heats the water and delivers the heated water through pipes to a location where heated water is needed. The hot water heater is often located on a lower level of such facilities near where potable water is received. Kitchens and bathrooms are generally located on upper levels and may be remote from the hot water heater. 
     A hot water faucet is opened to obtain hot water from a hot water heater. Unless hot water was obtained from the faucet a short time earlier, water must run from the faucet for a sufficient time to remove all the cold water from the pipe between the faucet and the hot water heater plus heating the pipe. The cold water discharged from the hot water faucet passes into a drain pipe and to a sewer system. The quantity of water that is lost can be significant. Insulation on the pipe can keep hot water in the pipe and the pipe at least warm for some period of time. However, insulation will not keep the water and pipe hot for an extended period of time. 
     Potable water is generally pumped from a water source by pumps. The pumps also maintain pressure in a water system or elevate water to a storage tower. The water is generally filtered and treated with some chemicals to insure that water born organisms do not make people sick. In a few areas, salt water is evaporated and then condensed to provide potable water. This pumping, filtering and chemical treatment of water is expensive. The heat required to distill salt water is also expensive. Sanitary sewer systems, where available, are constructed and operated by fees added to water bills thereby further increasing the cost of water. 
     Instant or nearly instant hot water may be obtained by adding a flow through heater to the hot water pipe near the hot water faucet. These electric heaters work well to heat a relative small quantity of water for making a hot drink or some food products. Such heaters have relatively low capacity. The purchase, installation and operation of an instant or nearly instant hot water heater is expensive. However, such heaters may reduce water usage. Such reduction of water usage is probably more significant than most home owners believe. However installation and operating costs of a flow through heater are significant and may exceed the cost savings due to water use reduction. 
     Instant or nearly instant hot water may also be provided by a pump or pumps that circulate water through a hot water supply pipe and back to the hot water heater. Such pumps run constantly and require a significant amount of electricity. These water circulating systems are generally reliable. The water that is returned to the water heater has cooled somewhat in the hot water supply line. The return flow of water by the pump is through a cold water supply pipe in some pump systems. After the pump runs for a period of time, there is hot water in a portion of the cold water supply pipe. Opening a cold water faucet will in some cases result in the discharge of hot water. Hot water in the cold drinking water is undesirable. Some chemicals employed to treat potable water will become gases at an elevated temperature and atmospheric pressure. The gases will separate from the water. The separated gases may be harmful to people and animals. Although the need for hot water may only occur a few times each day, the pump circulates water continuously. 
     Pumps employed to return cooled hot water to a hot water heater produce pressure changes in a pipe system that may result in vibrations and noise. Noise generated by a pump resonates throughout the plumbing system and often is objectionable. Although the need for hot water may only occur a few times each day, the pump cycles, as required, 24 hours per day. 
     A recent innovation used to provide hot water is the high flow, point of use water heaters that can be placed adjacent to areas such as showers and laundries that require a large quantity of hot water in a very limited time. They produce hot water almost instantly by the rapid infusion of large quantities of energy. They work well, and reduce the amount of cooled hot water discharges to the drain. Often they are secondary serving only a portion of the building, the main source being a standard hot water heater. The purchase price may be two to three times the cost of a standard hot water heater. Infrastructure is expensive due to the required capacity of 180,000 B.T.U.s of energy at an instant as need basis. If the high capacity point of use heater is selected, there is additional cost to provide venting of exhaust gas, and a larger gas meter to provide that fuel. 
     To overcome the delay in obtaining hot water, people often increase the thermostatic control on the hot water heater to the maximum or near maximum setting, thereby increasing the output temperature of water from a relatively safe one hundred and thirty degrees (130°) Fahrenheit to a potentially scalding temperature of one hundred and sixty degrees (160°). Skin exposure to 160° water can result in serious scalding in as little as one second. New regulations in some areas limit delivered water temperature through a faucet to 110 degrees Fahrenheit. The majority of grandfathered faucets in use today do not provide this protection, predictably resulting in many serious injuries. It will be years before all of the grandfathered faucets are replaced to prevent delivery of hot water above a regulation temperature. 
     SUMMARY OF THE INVENTION 
     The natural resource conserving prompt hot water system reduces potable water usage by reducing the quantity of cooled hot water discharged from a hot water faucet. The water conserving prompt hot system returns hot water that has cooled in a hot water pipe to the bottom of a hot water storage tank or hot water heater through a dedicated line without a pump and also limits the flow of cold water into the hot water supply system. The reduction in the quantity of cold water entering the hot water heater can reduce the energy required to heat water entering a home or building. 
     The natural resource conserving prompt hot water system, as described above operates without a pump with a normal temperature change in the hot water supply pipe and the return pipe and an elevation change as low as the distance between the hot water discharge opening and the drain pipe in a standard upright hot water heater. A two story building with a basement will have a substantially larger pressure change urging water flow in the return pipe. The return flow rate may be reduced by partially closing the metering valve. 
     The natural resource conserving prompt hot water system minimizes the quantity of water that is discarded, through a drain, before water at a desired elevated temperature is available. The system minimizes the energy required to reheat water returned to a hot water tank with partially cooled hot water. Energy is also reduced by substituting the quantity of cold water added to the hot water tank with partially cooled hot water. Energy is also reduced by insulating the hot water supply pipe and at least a portion of a return pipe. 
     The hot water tank includes a tank body, a tank top end and a tank bottom end. A water inlet opening in the hot water tank is connected to a water supply pipe. The water supply pipe generally supplies cold water from a water utility or a private water well. The water received from the water supply pipe is under pressure. 
     A hot water supply pipe has an inlet end connected to a hot water discharge opening in the hot water tank. The hot water supply pipe extends away from the hot water tank to a supply pipe remote end. This hot water supply pipe functions as a manifold. Pipe inside diameter depends on a number factors include maximum expected flow, pressure drops in the system and government ordinances. A manifold, for hot water in most residential construction in North America, employs half inch inside diameter pipe or three fourths inch inside diameter pipe. In some hot water systems there can be a change in the diameter of the hot water supply pipe between the inlet end and the remote end. 
     A plurality of point of use pipes are connected to the hot water supply pipe. A discharge faucet is connected to each point of use pipe and controls the flow of hot water from one of the point of use pipes. One or more discharge faucets can be open at a given time. In some hot water systems there may be only one point of use pipe. 
     A return pipe includes a return pipe inlet end that is connected to the hot water supply pipe or a nearby convenient branch. The connection is generally adjacent to the supply pipe remote end. However, the connection may be located in any chosen location where the connection can be made. A return pipe discharge end is connected to the drain opening in the tank body. Hot water tanks are provided with a drain opening near the tank bottom. The drain opening is provided for removing sediment from the tank. The drain opening is also used to empty the hot water tank if necessary. The return pipe discharge end may be connected to the drain valve. Drain valves have a threaded end for connecting a hose. It is generally possible to replace the drain valve and valve pipe with a short nipple. The return pipe discharge end may be connected to the nipple by suitable couplers if desired. 
     The hot water supply pipe, the return pipe and the hot water tank form a water circulation system. The water entering the return pipe from the hot water supply pipe is returned to the bottom of the hot water tank. Water removed from the hot water supply pipe, through the return pipe is replaced by hot water from the hot water tank. Water is circulated from the hot water discharge opening in the hot water tank, through the hot water supply tank, through the return pipe and back into the hot water tank. None of the recirculated water is lost. This water circulation results from the increase in water density as the temperature decreases as the hot water moves through the hot water supply pipe and return pipe and the decrease in elevation as the cooled water moves downward to the circuit bottom and into the drain opening. A pumpless circulation system is created that maintains hot water in the hot water supply pipe. The return pipe may have a return pipe inside diameter that is substantially the same or less than the supply pipe inside diameter to the hot water supply pipe. The relative large inside diameter of the return pipe is desirable to limit impedance to flow in the return pipe. However, an inside pipe diameter that is about sixty seven percent of the supply pipe inside diameter has been found to function well in some buildings. 
     A directional flow control device is provided any place between the hot water supply pipe connection to the return pipe and the drain opening in the tank body. The directional flow control device substantially limits the flow of cold water through the return pipe and into the hot water supply pipe in response to the opening of one or more of the discharge openings from the hot water supply pipe. 
     The directional flow control device includes a body. The body includes an inlet bore that receives return water. A conical bore portion in the body includes an inlet end with an inlet bore that joins a small diameter end of the conical bore portion. A cylindrical bore portion in the body joins a large diameter end of the conical bore portion. A plug includes a plug tubular portion. An outlet bore passes through the plug tubular portion. A cylindrical plug portion is received in the cylindrical bore portion and fixed to the body to form a chamber. An axis of the directional flow control device is coaxial with the inlet bore, the conical bore portion, the cylindrical bore portion and the outlet bore through the plug. 
     A sphere positioned in the chamber of the directional control device is movable by water flow in a first direction toward at least one projection in the chamber. The projection limits movement of the sphere toward the outlet bore and permits free flow of water through the chamber. The sphere is movable by water flow in a second direction generally parallel to the axis and into the conical bore portion in response to opening one of the hot water discharge faucets. The sphere is moved, by water in the second direction, toward the small diameter end of the conical bore portion and substantially blocks the flow of water through the inlet bore and into the hot water supply pipe. 
     The conical bore portion includes a conical wall surface that extends from the small diameter end to the large diameter end of the conical bore portion at an angle relative to the axis of more than twenty degrees (20°). 
     There sphere may be a glass member with a high density. With the high density sphere, the inlet bore is at the same elevation as the outlet bore and the axis of the chamber is horizontal. Substantial water flow from a hot water discharge faucet may be required to move a high density sphere into the conical bore small diameter end. 
     A low density sphere made of a material such as nylon will move with water flow into the directional flow control device from the drain opening in the hot water tank or from the hot water supply pipe. The axis of the flow control device may be vertical, horizontal, or any position between horizontal and vertical. 
     A low density sphere may stick in the conical portion of the chamber due to the minimal density change with liquid water temperature change. The low density sphere remains free to move into and out of the conical bore portion by increasing the angle of the conical wall surface of the conical bore portion relative to the axis from twenty degrees to thirty degrees or more. 
     Cold water entering the chamber from the drain opening in the hot water tank may increase the pressure in the chamber and hold the sphere in the conical small end. A fluid bypass between the sphere and the conical bore portion equalizes pressure or the downstream side and the upstream side of the sphere. 
     The fluid bypass between the sphere and the conical bore portion is provided by three ridges on the conical bore portion surface. The ridges extend radially inward toward the axis a distance of up to thirty thousands of an inch. These ridges may extend only a portion of distance to the large diameter end of the conical bore. 
     A valve is provided to limit the quantity of cool water passing through the return pipe and into the hot water tank. 
     The device operates within a pressurized environment, and functions by sensing direction of flow, not pressure. The low convective pressure (0.006 PSI) generated is too low to reliably open, shift, or close a check valve. The natural resource conserving hot water device is never totally closed. 
     The function to be encouraged is from the hot end of the hot water supply to the cold end. Very low impedance is applied in this direction of flow. Flow from the cold side to the hot side, such as when a supply faucet is opened disrupts this balancing process; a small flow is permitted by higher impedance. Check valves are not used, as they do not operate reliably at the low convective pressure, and eventually cause the system to fail. 
     Thermal change is self-regulation. As the cooled hot water in the return line cools, the density of that water in the vertical component increases, slightly increasing the convective pressure moving additional hot water from the hot water line into the return line, and eventually back into the hot water heater. As the temperature of the water in the vertical component warms, its density becomes less, thus decreasing the convective pressure slowing the flow. The Low Impedance Directional Flow Control Device senses and restricts backflow. As demonstrated in the prototype system that has operated for an extended time, the temperature in the vicinity of the metering valve is virtually constant with a variance of a few degrees. 
     The natural resource conserving prompt hot water system is installable by a professional plumber or by a home owner. The system conserves water and may also conserve energy for heating the water. The system conserves water by reheating water in the water supply pipe that would be discharged to a drain pipe and sewer system without the reheating system. Energy may be saved by reducing the quantity of cold water entering the hot water heater from a source outside the home or other structure. If the hot water system is not to be used for an extended period of time, the reheating system and the primary water system can both be turned off. 
     The method for conserving water in a prompt hot water system includes connecting a return pipe inlet end of a return pipe to a hot water supply pipe in a position remote from a hot water discharge opening in a hot water tank. A return pipe discharge end of the return pipe is connected to a drain opening in the hot water tank. The drain opening of the hot water heaters is in a bottom portion of the hot water tank. Water is forced to flow from the return pipe and into the hot water tank through the drain opening entirely by an increase in water density due to a decrease in water temperature at the return pipe discharge end. 
     A sphere is moved in response to water flow through a direction flow device toward a position in which flow of water, in the return pipe, through the drain opening and into the hot water tank is unimpeded. 
     A faucet is opened to discharge water from the hot water supply pipe. Water moves the sphere, in response to water flow from the hot water tank through the drain opening and into the return pipe, into a position in which reverse flow of water through the directional flow device is substantially reduced. 
     Closing the faucet to block discharge of water from the hot water supply pipe results in returning the sphere, by water flow from the hot water supply pipe and into the return pipe, to the position in which flow of water through the directional flow device is unimpeded. 
     The maximum water flow rate of water through the return pipe is controlled to control the minimum temperature of water entering the hot water tank through the drain opening. The flow rate through the return pipe is controlled by a valve. A minimum temperature, of water returned to the water tank for reheating, that is twenty degrees Fahrenheit below the temperature of hot water discharged from the hot water tank through the hot water discharge opening provides satisfactory operation in most residential systems. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The presently preferred embodiment of the invention is disclosed in the following description and in the following drawings, wherein: 
         FIG. 1  is a perspective view of a water return connection to a hot water heater with parts broken away; 
         FIG. 2  is a sectional view of an injection molded plug of the directional flow control device; 
         FIG. 3  is a sectional view of an injection molded body of the directional flow control device; 
         FIG. 4  is an enlarged expanded sectional view of a low back pressure mono directional flow control device; 
         FIG. 5  is a schematic view of the prompt hot water system; and 
         FIG. 6  is a sectional view of an injection molded low back pressure mono directional flow control device. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A typical home or office hot water system  10  includes a hot water heater  12 . The hot water heater  12  includes a tank  14  with a cylindrical body  16 , a top end  18  and a bottom end  20 . The top end  18  includes a water inlet opening  22  and a hot water discharge opening  24 . The water inlet opening  22  is connected to a water supply pipe  26  that supplies unheated potable water under pressure from a remote water source or from a nearby well. An internal pipe  28 , in the tank  14 , is connected to the water inlet opening  22  and discharges water through an open end  30  near the bottom end  20 . A heater  32  heats water near the bottom end  20  of the tank  14 . A temperature control  33 , for adjusting maximum water discharge temperature is usually provided. Construction of the heater depends upon the heat source. An electric heat source would include a heater coil  21  inside the tank  14 . A natural gas source would include a burner in the heater  32  under the bottom end  20  and a fire tube or tubes (not shown) extending upward from the burner and through the bottom end  20  and through the top end  18 . Products of combustion discharged from a fire tube would be connected to a chimney by a pipe (not shown). A drain pipe  34  and valve  36  shown in  FIG. 3  is provided near the bottom end  20  of the tank  14 . The valve  36  is opened to drain water from the tank  14  and to remove any sediment collected in the tank. 
     The tank  14 , of hot water heater  12 , is substantially encased in insulation  38  as shown in  FIG. 5 . The cylindrical body  16  is generally fully encased in insulation  38  when water is heated electrically. The top end  18  is encased in insulation except for the water inlet opening  22  and the hot water discharge opening  24 . A metal cover  40  encases the insulation. 
     Hot water in the tank  14  tends to migrate toward the top end  18 . Cold water in the tank  14  tends to descend toward the bottom end  20  where it is heated. 
     A hot water supply pipe  42  is attached to the water discharge opening  24  in the top end  18  of the tank  14 . In homes and offices the supply pipe  42  is often copper. Pipes made from other material are also used. 
     The hot water supply pipe  42  for hot water may extend upward to the bottom of floor joists for an upper floor and then extend to a far end of the building. The hot water supply pipe  42  is supported by the floor joists and pipe hangers. Point of use pipes  44 ,  46  and  48  are connected to hot water supply pipe  42 . Pipes  44  and  48  supply water from the hot water supply pipe  42  to a floor directly above the hot water heater  12 . Pipe  46  supplies hot water from the hot water supply pipe  42  to a point of use at the same elevation as the hot water heater  12 . 
     A faucet  50  on the point of use pipe  44  may for example supply water to a kitchen sink or a dish washer. A faucet  52  on the point of use pipe  46  may for example supply water to a laundry washing machine on the same floor as the water heater  12 . A faucet  54  on the point of use pipe  48  may for example supply water to a bathroom on the same floor as the kitchen. 
     A building with a second floor above the floor directly above the hot water heater  12  may be supplied with water through a vertical extension  56  to the hot water supply pipe  42  and a point of use pipe  58  as shown in  FIG. 5 . A faucet  60  on the point of use pipe  58  can for example supply water to a bathroom on the second floor. 
     The pipe  42  may have a diameter of one half inch (0.5 inch), however the plumbing code in many states requires a diameter of three fourths of an inch (0.75 inch). The larger three fourths inch diameter is often used in the hot water supply pipe  42  that becomes a manifold, to reduce the pressure drop when a faucet  50 ,  52 ,  54  or  60  is opened. 
     The water in the hot water supply pipe  42  cools over a period during which there is no demand for hot water. To obtain hot water from the hot water heater  12  after a period of non use, it is necessary to drain the water between the faucet from which hot water is desired and the hot water discharge opening  24  in the hot water heater  12 . These pipes hold a significant quantity of water. The quantity of water in the supply pipe  42  is increased if the pipe diameter is larger than one half inch. 
     Water contracts and becomes denser from a temperature at which there is a change from steam to a temperature at which water becomes ice. A return pipe  64  connected to the hot water supply pipe  42 , at a location near a remote end of the hot water supply pipe, and the bottom end  20  of the hot water tank  14  will create a natural return flow of cooled water to the tank  14  through the return pipe. The rate of return flow through the return pipe  64  depends on water temperature differences and the change in vertical elevation between the return pipe inlet end  66  and the return pipe discharge end  68 . A temperature decrease increases water density. A vertical drop in elevation increases the pressure at the discharge end  68  of the return pipe  64 . 
     A vertical column of water that is ninety six inches long loses 0.000288 pounds per square inch (PSI) for each degree centigrade of temperature increase. The convective system head change is 0.00576 pounds per square inch with a twenty degree centigrade temperature change. This pressure change is relatively small. The pressure change is however sufficient to create convective fluid flow due in part to the inside diameter of the return pipe  64  providing low flow impedance. 
     The rate of return flow through the return pipe depends on water temperature differences and the change in vertical elevational changes as stated above. There are a number of other factors that change the rate of return convection flow. These factors include the flow restrictions in the hot water supply pipe  42  and in the return pipe  64 . Temperature changes in the convective fluid due to friction in the pipes  42  and  64  also change flow rates. The movement of relatively cold water from the point of use pipes  44 ,  46  and  48  and movement of hot water from the hot water supply pipe  42  into the point of use pipes also changes the temperature of water entering the return pipe  64 . These other factors have a less significant affect on water flow in the return pipe  64  than water temperature differences and elevation changes between the inlet end  66  and the discharge end  68  of the return pipe  64 . The elevation change between the hot water discharge opening  24  and the drain pipe  34  in the hot water heater  12  is sufficient to provide some return flow. 
     The return pipe  64  is a flexible Chlorinated Poly Vinyl Chloride (CPVC) water conveying plastic pipe, commonly called PEX. PEX is resistant to scale and chlorine, doesn&#39;t corrode or develop pinholes, can be installed quickly, and has a maximum service temperature of 200 degrees Fahrenheit. However, the return pipe  64  could also be copper or other material. The return pipe  64  may have the same inside diameter as the hot water supply pipe  42 . A return pipe  64  with an inside diameter of one fourth of an inch will provide adequate flow in some hot water systems  10 . 
     Two different plumbing assemblies exist for connecting the return pipe  64  to the bottom portion of tank  14 . The plumbing assembly shown in  FIG. 1  would most likely be used by the home owner or a semi skilled installer. The plumbing assembly shown in  FIG. 5  would probably be used by the professional plumber. 
     The return pipe inlet end  66  of the return pipe  64  is connected to the hot water supply pipe  42  by a T-coupler  70  shown in  FIG. 5 . If there is a vertical extension  56  to the hot water supply pipe  42 , the T-coupler  70  may be moved to a position adjacent to the point of use pipe  58 . The vertical extension  56  in some buildings may be inside walls and not available for connection to the return pipe  64 . The pipe discharge end  68  of the return pipe  64  is connected to the drain valve  76 . The metering valve  130  is connected to the hot water input end  88  of the directional flow device  82 . The discharge end  84  of the directional flow device  82  is connected to the coupler  91 . The coupler  91  is connected to the T-coupler  78 . The T-coupler  78  is connected to the drain valve  80 . The drain valve  80  is also connected to the return valve  76 . The drain valve  36  as shown in  FIG. 1  is connected to the hot water discharge drain pipe  34  of the hot water heater  12 . Adequate flow rate in the return pipe  64  insures that the water in the hot water supply pipe  42  is nearly the same as the temperature of hot water leaving the hot water heater  12  through the hot water discharge opening  24 . Significant heat loss can occur in the hot water supply pipe  42  and in the return pipe  64 . To limit heat loss it is desirable to insulate the hot water supply pipe  42  and the return pipe  64 . The insulation reduces heat loss and reduces the load on the heater  32  of the hot water heater  12 . The hot water heater  12  maintains the temperature of water passing through the water discharge opening  24 . Heat is added, by the heater  32  or the heater coil  21 , to water returned by the return pipe  64  to maintain the temperature of water entering the hot water supply pipe  42  from the hot water heater  12 . It is therefore desirable to return water to the hot water heater  12  from the return pipe  64  with a relatively high temperature. A decrease in the temperature difference between hot water passing through the discharge opening  24  and the water entering through drain pipe  34  or nipple  74  will decrease the pressure drop and the flow rate. 
     The return pipe  64  can be connected to the drain pipe  34  and drain valve  36  of the hot water heater  12  as shown in  FIG. 1 . The drain pipe  34  is a return water entry port. However, the drain valve  36  and the drain pipe  34  may be removed if desired. A short nipple  74 , shown in  FIG. 5 , is screwed into the tank  14  where the original drain valve  36  and drain pipe  34  were located. A return valve  76  is attached to the nipple  74 . The nipple  74  is a return water entry port. The return water entry port is a drain opening  75  in the hot water tank. A T-coupler  78  is connected to the return valve  76 . A drain valve  80  is connected to the T-coupler  78 . The drain valve  80  is connectable to a hose  81  with a female hose connector  83 . The return pipe  64  is also connected to the T-coupler  78 . The return valve  76  permits the flow of water from the return pipe  64  to be opened or closed. The drain valve  80  can be opened to drain water from the tank  14  when the return valve  76  is also open. The drain valve  80  is also opened to discharge air from the return pipe  64  when the return valve  76  is closed. 
     The return pipe  64  is connected to the hot water supply pipe  42  through the T-coupler  70  inserted into the hot water supply pipe  42  in a selected position as described above. A directional flow control device  82  may be connected to the supply pipe T-coupler  70 . However, the return pipe  64  is connected to the T-coupler  78  as shown in  FIG. 1 . An inlet end  88  of the directional flow control device  82  is connected to a metering valve  130  and to the return pipe  64 . The discharge end  84  of the directional flow control device  82  is connected to the short nipple  74  through a coupler  91  the T-coupler  78  and the return valve  76  shown in  FIG. 5  or the drain valve  36  shown in  FIG. 1 . A stem elbow  126  and a female hose connector  128  connect the T-coupler  78  to the drain valve  36  as shown in  FIG. 1 . The drain valve  36  is also a metering valve as shown in  FIG. 1 . 
     Without the directional flow control device  82  the water supply pipe  42  and the return pipe  64  would both supply water to an open faucet  50 . The water passing through the open faucet  50 , or any other open faucet in a hot water supply system, could pass a mixture of hot water from the top end  18  of the tank  14  and cold water from the bottom end  20  of the tank. Cold water entering the bottom end  20  of the tank  14  through the internal pipe  28  would reduce the temperature of water flowing through the return pipe  64 . The flow rate through the hot water supply pipe  42  would most likely be different than the water flow rate through the return pipe  64 . The two flow rates would most likely change relative to each other depending upon which faucet  50 ,  52 ,  54  and  60  in the system is open and the number of faucets that are open. 
     Check valves are used in some systems to control the flow of water between two flow paths. Check valves will not work in the hot water system described above. The pressure differentials due to the changes in water temperature and water elevations are too small to reliably open or close a check valve in a pumpless system. 
     The directional flow control device  82  includes a device body  86  made of CPVC or other suitable material. The directional flow control device  82 , as shown in  FIG. 4  is machined from blocks. The directional control device  82 , as shown in  FIGS. 2 ,  3  and  6 , is injection molded. An inlet end  88  of the device body  86  includes an inlet bore  90  in a tubular portion  89  and a cylindrical outer surface  93 . The interior of the device body  86  includes a conical bore portion  96  and a cylindrical bore portion  98 . The tubular portion  89  joins the small diameter end  97  of the conical bore portion  96 . The large diameter end  95  of the conical bore portion  96  joins the cylindrical bore portion  98 . A plug  100  has a cylindrical portion  102  with a diameter that is the same as the diameter of the cylindrical bore portion  98  in the device body  86 . The cylindrical portion  102  of the plug  100  is telescopically inserted into the cylindrical bore portion  98  until a radial surface  104  on a flange  106  engages an end surface  108  on the device body  86 . An outlet bore  110  through a plug tubular portion  100  is coaxial with the inlet bore  90  in the inlet end  88  of the device body  86 . The conical bore portion  96 , the cylindrical bore portion  98  and the bore  110  through the plug  100  have a common central axis  111 . 
     A sphere  114  of a material such as nylon is inserted into the conical bore portion  96  and the cylindrical bore portion  98  before the plug  100  is telescopically inserted into the cylindrical bore portion  98  as explained above. An adhesive may be employed to hold the plug  100  in the cylindrical bore portion  98  and retain the sphere  114  in the device body  86 . If the plug  100  and device body  86  are made from a material that cannot be joined by adhesives, a different joining system is employed. 
     The sphere  114  has a diameter that is larger than the inlet bore  90 , the small diameter end  97  of the chamber  116  defined by the conical bore portion  96 , and the outlet bore  110 . The sphere  114  also has a sphere diameter that is smaller than the large diameter end  95  of the conical bore portion  96 . A plurality of projections  118  on the end surface  120 , of the plug  100  facing the conical bore portion  96 , are adjacent to the outlet bore  110 , and extend away from the end surface  120 . These projections  118  contact the plastic sphere  114  and prevent the sphere from closing the outlet bore  110 . The projections  118  are spaced apart and extend axially toward the chamber  116  so that the sphere  114  does not impede the flow of water through the return pipe  64  and into the lower portion of the water tank  14 . The cross section area of the cylindrical bore portion  98  is at least two times the cross section area of the sphere  114  to insure that the sphere does not impede flow through the cylindrical bore portion. The projections  118  have sphere engaging surfaces  119  that maintain sufficient space between the sphere  114  and the outlet bore  110  to insure that the sphere does not impede flow into the outlet bore through the plug  100 . There may be two projections  118  separated by a slot  121  as shown in  FIG. 2 . The slot  121  has a slot width normal to the central axis  111  that nearly as large as the diameter of the outlet bore  110 . 
     The return pipe  64  has a capacity that insures there is return water flow to the tank  14  due to temperature changes in the hot water supply pipe and the return pipe. A ¾ inch diameter hot water supply pipe  42  and a ½ inch diameter return pipe  64  work well. Pipes with other inside diameters will most likely work if they provide adequate flow rates. When one or more of the faucets  50 ,  52 ,  54  and  60  are opened, to dispense hot water for use, water flows out of the system and cold water flows into the system through the water inlet  22 . The water in the tank  14  of the hot water heater  12  tends to be forced out of the tank through both flow passages including supply pipe  42  and return pipe  64  connected to the hot water heater  12 . As a result cold water tends to exit the tank  14  through the return pipe  64 . Flow through the return pipe  64  is reversed. Flow through hot water discharge opening  24  and into the hot water supply pipe  42  is reduced. The dual flow paths could result in cold water and hot water mixing and warm water passing through one of the faucets. The dual flow paths could also result in cold water flowing through one of the faucets and hot water flowing through another one of the faucets. The sphere  114  of nylon is moved toward the inlet end  88  by back flow from the tank  14 . The sphere  114  engages the conical bore portion  96  and restricts flow through the directional flow control device  82  including the chamber  116 . 
     Three ribs  140 ,  141  and  143  are provided on the conical bore portion  96 . The ribs  140 ,  141  and  143  are spaced apart 120° from each other about the axis  111  as shown in  FIGS. 3 and 6 . Each rib  140 ,  141  and  143  is radially spaced from the axis  111  and parallel to one of three planes that include axis  111 . The conical bore portion  96  has inside surfaces that extend from the device bore  90  at an angle  150  of thirty degrees from the axis  111  as shown in  FIG. 3 . Each rib  140 ,  141  and  143  has a radial height of less than 0.030 inches. The ribs  140 ,  141  and  143  permit some water to bypass the sphere  114  when one of the faucets  50 ,  52 ,  54  and  60  is opened. The ribs  140 ,  141  and  143  insures that a pressure differential does not lock the sphere  114  in the small diameter end  97  of the conical bore portion  96 . The angle  150  of the conical bore portion  96  shown in FIG.  3 , insures that friction does not hold the sphere  114  is the small diameter end  97  of the conical bore portion. The slight leakage between the sphere  114  and the conical bore portion  96  when a faucet  50 ,  52 ,  54  or  60  is open has minimal effect on the temperature of hot water passing through open faucets. One or more grooves  146  may provide the same function as the ribs  140 ,  141  and  143 . The groove  146  is shown in  FIG. 4 . 
     Closing the open faucets  50 ,  52 ,  54  and  60  will stop the flow of potable water through water inlet opening  22 . The force of water equalized on both sides of the sphere  114  by water will permit the sphere  114  to move to an open position with the assistance of gravity or water flow. 
     The sphere  114  made of nylon or a similar plastic member is relatively light weight and can be moved by water with a low flow rate. As a result, the low impedance directional control device  82  may be in a vertical position, a horizontal position or a position between horizontal and vertical. The low impedance directional control device  82  may also be mounted in any position in the return pipe  64 . 
     A sphere  114  may also be made from a material such as glass. With a glass sphere, the central axis  111  of the directional flow control device  82  should be nearly horizontal. A glass sphere  114  will require somewhat more water flow to be moved into a flow reducing position adjacent to the small diameter end  97  of the conical bore portion  96  than a lighter weight sphere. 
     The angle  150  can vary from thirty degrees. However, a sphere  114  has stuck in the position adjacent to the small diameter end  97  of the conical bore portion  96  when the angle  150  was twenty degrees. The angle  150  should therefore be larger than twenty degrees. There is a maximum angle  150 . A sphere  114  may not move to a position coaxial with the central axis  111  if the angle  150  is ninety degrees. 
     A metering valve  130 , shown in  FIG. 5  is connected to the inlet and  88  of the directional flow control device  82  and the return pipe  64  as shown in  FIG. 5 . The metering valve  130  is preferably a CPVC valve with integral connectors for connection to the return pipe  64  and to the directional flow control device. The metering valve  130  is employed to control the rate of water return flow through the directional flow control device  82  and into the bottom end  20  of the hot water heater  12 . The return flow rate is self regulating to some extent in that as the temperature of return water to the bottom of the tank  14  increases the pressure difference decreases. If the temperature of water returned to the tank  14  is the same as hot water passing out through the discharge opening  24 , the flow of water through the return pipe  64  will stop. However, an attempt to hold the return water close to the hot water discharge temperature from the hot water tank  14  will require the addition of substantial heat. In most homes, maintaining a water flow rate that maintains a water temperature drop of 20° F. between the return pipe inlet end  66  and the return pipe discharge end will provide satisfactory results. If a home owner is to be away for some time the return valve  76  or metering valve  130  can be closed. The metering valve  130  is positioned in a relatively easy place to reach. The return valve  76  is close to the bottom of the hot water heater  12  and may be more difficult to adjust or close. The metering valve  130  can be closed to prevent the entry of air into the return pipe  64  when discharging water from the bottom end  20  of the hot water heater  12  through the open return valve  76  and the open drain valve  80 . 
     The directional flow control device  82  can be located anyplace in the return pipe  64 . It is however generally desirable to mount the flow control device near the hot water heater  12  where most of the system components are located. 
     The water conserving prompt hot water supply system  10  can be added to most existing home, office and other facilities. These systems  10  can be sold as kits. Each kit might contain a hot end assembly including one T-coupler, and a cold end assembly, including one metering valve  130  connected to one directional flow control device  82 , connected to one elbow  126 , connected to one T-coupler  78 , to which is connected one drain valve  80 , and either one female hose connector  128  or one ¾ inch male NPT threaded connector. Additional fittings and pipe can be added to the supply system if desired.