Patent Publication Number: US-8534310-B1

Title: Hot water circulation system

Description:
BACKGROUND AND SUMMARY OF THE INVENTION 
     This invention relates generally to hot water circulation systems that rapidly deliver hot water from a conventional water heater to a hot water faucet and, more particularly, to such a system employing a two-way check/bypass valve for increased efficiency and performance. 
     The need for and benefits of making hot water rapidly available at remote faucets in residential buildings is well known. However, minimal progress has been made over the years toward implementation of systems satisfying that need. It has been estimated that the average home in America wastes up to 10,000 gallons of potable water each year as homeowners run cool water down the drain while waiting for hot water to reach a faucet remote from the water heater. Since the wasted water was once hot, the heat energy it contained is also wasted. 
     The time required for hot water to reach a remote faucet depends on the length of the line from the water heater to the faucet. In many buildings, the delay amounts to a minute or more. At a typical faucet flow rate, five to six gallons of water can be wasted several times a day at a given faucet. 
     Tests have shown that water in an un-insulated ¾-inch diameter copper pipe at a temperature of 118° F. in an ambient environment of 70° F., will cool to 100° F. in about twenty minutes. If the supply line is ½-inch in diameter, the temperature will drop to about 95° F. Water at a temperature of 100° F. is warm to the touch, but cannot be considered hot. The reintroduction of heater-temperature water to the system is necessary to deliver hot water at a faucet. A simple solution to this waste of water and heat energy is to establish a circulation flow of hot water from the existing water heater through the normal hot water distribution line to the most remote hot water faucet on the plumbing branch, and back to the heater. This can be accomplished using a dedicated return line from the hot water faucet line typically located under the sink to the water heater, or by routing the return flow into the normal cold water supply line back to the water heater. Contrary to the belief of the average plumber, engineering tests and analyses have proven that circulation systems will conserve heat energy as compared to standard systems without circulation. 
     Water circulation can be accomplished either passively or actively. Passive circulation systems rely on convection forces resulting from differential temperatures between the hot and cold supply lines, whereas active systems incorporate an electric pump and possibly electronics connected to an electrical outlet to control the pump and a valve. Connections that must be made to the water piping are somewhat more complex in the case of active water circulation systems. 
     Passive water circulation systems operate on the principal of convective flow, by which hot water will rise and cool water will fall in a closed loop, without the need of a pump. Since hot water cools as it travels away from the heater and since cool water is denser than hot water, a higher pressure will exist in the cold line. This higher pressure will cause a low level circulation flow from the heater up to the high point in the loop at the remote hot water faucet, so long as a vertical separation of a few feet exists between the water heater and the faucet. This vertical separation exists in the normal home in which the water heater is in the basement and the faucets are on the main or a higher floor. This low level flow rate is sufficient to maintain hot water at remote faucets, and will operate continuously, day and night, without attention. Convective circulation systems require no electrical power, no gas, and no burner, and operate reliably with few moving parts, based upon the laws of physics. 
     Convective water circulation systems will cool by only 15-20° F. in the loop to and from the water heater at a flow rate of about 240 cubic centimeters per minute. This temperature loss represents a smaller heat energy loss than the combined heat energy loss resulting from allowing previously heated water to go down the sink drain while the user waits for hotter water to arrive and the energy required to heat the replacement water entering the water heater at about 50° F. 
     Active circulation systems employ a pump, control circuitry, and complex mechanisms that are expensive and require a source of electrical power and a professional installer. They are less reliable than passive circulation systems since they utilize more components. In active circulation systems, the pump will start at a preset water line temperature or elapsed time in order to restore hot water at the remote hot faucet. Typically, the time interval between pump cycles will be on the order of twenty minutes. At the end of each pump cycle, the water at the faucet will be hot and will then gradually cool before the pump starts again. 
     With an emphasis on simple installation, industry trends have moved toward the use of the cold water supply line as the return loop for circulation in both active and passive systems, thereby avoiding the costly and sometimes difficult installation of a dedicated return line. Circulation can be achieved through the addition of a crossover line between the hot and cold supply lines under the sink. The circulation path is from the water heater through the normal hot water supply line, through the crossover line, into the cold water supply line, and back to the water heater. The crossover line must also provide a means to prevent mixing of hot and cold water when a faucet is opened. 
     A review of prior art water circulation systems that utilize the cold water supply line as a return line reveals that most of them utilize a standard one-way check valve in order to prevent cold water from flowing into the hot side of the system when the hot faucet is opened. Some prior art systems utilize either a thermostatically-operated or solenoid-operated valve to prevent that situation. Other prior art systems, such as those described in U.S. Pat. No. 5,819,785 to Bardini, U.S. Pat. No. 5,323,803 to Bluemenauer, and U.S. Pat. No. 6,779,552 to Coffman, for example, address the above problem, but fail to recognize the need to prevent hot water from flowing into the cold side of the system when the cold faucet is opened. Solenoid valves operated on a timed basis may avoid the problem, but thermostatically-controlled valves may allow hot water to flow into the open cold water faucet during a portion of the valve&#39;s operating cycle as it responds to changes in water temperature. Moreover, these prior art systems fail to recognize, that unlike waiting for hot water to arrive at a remote hot water faucet in systems without circulation, cold water will never flow from the cold water faucets. Without some additional provision, hot water will flow through the bypass line into the cold water line, and lukewarm water will be delivered at the cold water faucet. Finally, each of these prior art valves contains free poppets with no provision to avoid a water hammer effect upon closing. 
     The system described in U.S. Pat. No. 2,842,155 to Peters describes a valve using a thermostatically-operated ball for controlling convective flow, primarily in the direction from hot to cold, and a free ball check to prevent cold to hot flow when the hot faucet and the thermostatically-controlled ball are open. No provision to avoid a water hammer effect is provided in this valve. 
     U.S. Pat. No. 4,391,295 to Stipe describes a one-way, gravity-operated cheek valve for use in a convective hot water circulation system. A slow-closing valve with gravity reseating provides damping of valve closures that are otherwise noisy and potentially damaging. The slow-closing valve is a one-way valve for use in systems employing a dedicated return line and is of no usein systems returning water through the cold water supply line. 
     The present invention provides a high-performance, inexpensive, maintenance-free passive hot water circulation system for use in both existing buildings and new construction that eliminates the need for an expensive dedicated hot water return line and that may be packaged in kit form for easy installation by a homeowner. It utilizes a two-way check/bypass valve that is connected between the hot and cold water supply lines at hot and cold water faucets that are located most distantly from the water heater in a plumbing branch of a building. The two-way check/bypass valve establishes and maintains convective hot water circulation at a low flow rate from the water heater to the most distantly located hot water faucet, through the cold water supply line of the plumbing branch, and back to the water heater, during the period of time when both the hot and cold water faucets are closed. When the hot water faucet is opened, hot water is nearly instantly available. The two-way check/bypass valve stops convective hot water circulation when either the hot or cold faucet is opened. It also prevents mixing of hot and cold water when either the hot or cold faucet is open and includes provision for dampening any water hammer effect. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a pictorial diagram illustrating the components of the convective hot water circulation system of the present invention. 
         FIG. 2  is a pictorial diagram of the under-sink components of the convective hot water circulation system of  FIG. 1 . 
         FIG. 3  is a pictorial diagram illustrating the details of connection of the under-sink components shown in  FIG. 2 . 
         FIG. 4A  is a front elevation pictorial diagram illustrating the structural details of the two-way check/bypass valve of  FIGS. 1 and 2 . 
         FIG. 4B  is a top view of the two-way check/bypass valve of  FIGS. 1 ,  2 , and  4 A. 
         FIG. 5A  is a front elevation view of one of the valve poppets employed in the two-way check/bypass valve of  FIG. 4A . 
         FIG. 5B  is a top plan view of the valve poppet of  FIG. 5A . 
         FIG. 6A  is a front elevation view of one of the movable valve seats employed in the two-way check/bypass valve of  FIG. 4A . 
         FIG. 6B  is a right side elevation view of the movable valve seat of  FIG. 6A . 
         FIG. 7  is a graph of water temperature versus time illustrating the time required for heated water to reach a remote hot water faucet with and without the convective hot water circulation system of  FIGS. 1 and 2 . 
         FIG. 8  is a pictorial diagram illustrating a rolling ball alternative embodiment of the two-way check/bypass valve of  FIGS. 1 and 2 . 
         FIG. 9  is a pictorial diagram illustrating a variation in shape of the rolling ball embodiment of the two-way check/bypass valve of  FIG. 8 . 
         FIG. 10A  is a front elevation pictorial diagram illustrating the structural details of a gravity-operated alternative embodiment of the two-way check/bypass valve of  FIGS. 1 and 2 . 
         FIG. 10B  is a right-side elevation view of the two-way check/bypass valve of  FIG. 10A . 
         FIG. 11  is a front elevation pictorial diagram illustrating the structural details of a magnetically-operated alternative embodiment of the two-way check/bypass valve of  FIGS. 1 and 2 . 
         FIG. 12  is a pictorial diagram illustrating the details of connection of the under-sink components with a heat exchanger. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to  FIGS. 1 and 2 , there is shown the two-way check/bypass valve  10  of the present invention connected to a typical residential water delivery system that includes a conventional water heater  12 , usually positioned in a residential basement or crawl space area, for receiving cold water from a potable water source  14 , such as a public utility. Hot water produced by water heater  12  is conventionally piped to various appliances throughout the residence, such as a lavatory  16 , that allows the user to draw hot water from a hot water faucet  18 . Cold water from source  14  is likewise piped to various cold water faucets throughout the residence, including cold water faucet  20  of lavatory  16 . 
     Referring now to  FIG. 3 , there are shown the details of a typical connection of two-way check/bypass valve  10  to the existing hot and cold water supply lines  22 ,  24  within the enclosure of lavatory  16 , which represents the most remotely located of all of the building plumbing fixtures or appliances to which hot water is supplied. A conventional flexible or formed metallic line  30  serves to connect an inlet port  26  of two-way check/bypass valve  10  to hot water supply line  22 . An outlet port  28  of two-way check/bypass valve  10  is similarly connected by line  32  to cold water supply line  24 . Two-way check/bypass valve  10  may be mounted within the enclosure of lavatory  16  by means of a suitable bracket  34  to ensure that two-way check/bypass valve  10  is positioned horizontally in two axes. 
     Referring now additionally to  FIGS. 4A-B ,  5 A-B, and  6 A-B, two-way check/bypass valve  10  includes a housing constructed of a selected metal or plastic material and is formed to include a convection circulation cavity  36  within a lower portion of the housing. Two vertical cylindrical bores within the housing of two-way check/bypass valve  10  open at their lower ends into convection circulation cavity  36 , while their top ends terminate at inlet and outlet ports  26 ,  28 . The bore associated with inlet port  26  contains a one-way valve, illustrated in its open position, that includes a poppet  38 , a valve seat  40  positioned above poppet  38 , and a spring member  42  positioned between valve seat  40  and inlet port  26 . The bore associated with outlet port  28  also contains a one-way valve, illustrated in its closed position, that includes a correspondingly-positioned poppet  44 , a valve seat  46 , and a spring member  48 . Poppets  38 ,  44  are shaped to be non-cylindrical in cross-section, such as rectangular, triangular, grooved, or some other shape having a cross-sectional area that is smaller than the cross-sectional area of the associated cylindrical bore to permit water to flow around poppets  38 ,  44  when the respective valve is open. When that valve is in the open position, the bottom surface of the associated one of poppets  38 ,  44  contacts a shoulder  50  provided near the bottom of the cylindrical bores. Each of the valve seats  40 ,  46  contains a central water passageway  52  to permit water to flow through it when an associated one of poppets  38 ,  44  is in the down or valve-open position. Valve seats  40 ,  46  are shaped to include a lower shoulder portion  56  that is urged downward against a shoulder  54  of each of the cylindrical bores by respective ones of spring members  42 ,  48 . The upper ends of poppets  38 ,  44  are conically shaped to engage the central water passageway  52  in valve seats  40 ,  46  when one of the poppets  38 ,  44  is held in the up or valve-closed position by differential water pressure between inlet port  26  and outlet port  28  of two-way check/bypass valve  10  to thereby prevent the flow of water through the valve. In this embodiment, poppets  38 ,  44  are constructed of a material having a specific gravity greater than unity so that they will settle downward to the valve-open position when neither of the faucets connected to the ports  26 ,  28  of two-way check/bypass valve  10  is open. Thus, two-way check/bypass valve  10  will permit a low circulation flow rate of water through it, but will close off the high flow rate that would otherwise occur upon opening either hot water faucet  18  or cold water faucet  20  to which two-way check/bypass valve  10  is connected. 
     A common characteristic of check valves, especially free poppet valves like those described above, is that they will often cause a pressure spike known as water-hammer when closing in a pressurized water system. They will also occasionally spike sympathetically in response to the sudden closure of other valves in a system, such as a toilet, clothes washer, or dish washer. In addition to the attendant unpleasant sound, these pressure spikes can be damaging to other components of a water delivery system. This problem is solved by the present invention, in which the freedom of movement of valve seats  40 ,  46  against springs  42 ,  48 , when poppets  38 ,  44  contact the valve seats  40 ,  46 , serves to absorb the energy created when the flow of water is suddenly interrupted and thus dampen any water-hammer effect that may otherwise occur. 
     The two-way-check bypass valve  10  described above operates in three different modes in the process of providing continuous rapid hot water to faucets of a residence or other building. All modes are completely automatic in the system, with no action or maintenance required by the user. The first mode of operation is considered dominant since it is in effect most of the time. That is the time during which no water faucets in the plumbing system are open, and water is convectively circulating from water heater  12 , through the hot water distribution line  22 , to the two-way check/bypass valve  10 , and eventually back to the water heater  12  through the existing cold water supply line  24 . Convective flow rates of 200-400 cubic centimeters/second have been observed during testing. During this time, the circulating water will flow into the inlet or hot port  26  of two-way check/bypass valve  10 , past poppet  38 , through convection circulation cavity  36 , past poppet  44 , and out the outlet or cold port  28  to cold water supply line  24 . This convective circulation is very reliable so long as adequate vertical separation between water heater  12  and remote hot water faucet  18  exists, no external heat is applied to cold water supply line  24 , and no flow blockage is present in the system. Hot water is always available in the present system within seconds after opening a hot water faucet. It is recognized that the water in the cold water supply line  24  will tend to warm slightly during the convective circulation flow that is present during this first mode of operation. 
     The second mode of operation of two-way check/bypass valve  10  begins when a hot water faucet along hot water supply line  22  is opened. As hot water flows from the hot water faucet, the water pressure in hot water supply line  22  near two-way check/bypass valve  10  is lowered, and cold water will attempt to flow through cold water supply line  24  and through two-way check/bypass valve  10  to the outlet or hot port  26  of two-way check/bypass valve  10 , thereby reducing the temperature of the outflow water. The dynamic pressure of the water flowing through two-way check/bypass valve  10  will cause poppet  38  to rise against valve seat  40  and stop the flow of water through valve seat  40 . No water from cold water supply line  24  is allowed to enter hot water supply line  22 . When the previously-opened hot water faucet is closed, gravity will cause poppet  38  to fall to its position against shoulder  50 , as illustrated in  FIG. 4A , thereby opening the associated valve and allowing convective circulation flow to resume in accordance with the first mode of operation described above. 
     The third mode of operation of two-way check/bypass valve  10  is the reverse of the above-described second mode of operation, in order to prevent hot water from flowing through two-way check/bypass valve  10  into cold water supply line  24  when a cold faucet is opened. As hot water attempts to flow through two-way check/bypass valve  10  to the cold side thereof, poppet  44  will rise to contact valve seat  46  and thereby stop the flow through valve seat  46 . 
     A fourth mode of operation of two-way check/bypass valve  10  may be identified as relating to the availability of cold water at the temperature of water source  14  at a cold water faucet that prior art water circulation systems utilizing a one-way check valve system cannot support. This is accomplished by opening the cold faucet and allowing the warm water to flow down the drain until the warm water is replaced by water from the cold water source  14  through cold water supply line  24 , similar to the process of obtaining hot water in a system that does not employ circulation. This fourth mode of operation is made possible by employing two-way check/bypass valve  10  that will not allow hot water into the cold line at the high flow rate, but is impossible when using a prior art one-way check valve. 
     In the first mode of operation of two-way check/bypass valve  10  described above, hot water at faucet  18  will reach a temperature in the range of 105-115° F., with a water heater setting of 120° F., within one to three seconds. Hot water faucets located closer to water heater  12  will produce hotter water than may be obtained at remotely located hot water faucet  18 . The provision of insulation on hot water distribution line  22  between water heater  12  and remote hot water faucet  18  will result in hotter water at hot water faucet  18 . The water temperature will rise to near the temperature of water at the outlet of water heater  12  within a short time after opening hot water faucet  18 .  FIG. 7  graphically illustrates the typical residential hot water temperature variation after opening a hot water faucet in a water distribution system employing convective circulation, as in the present invention, as compared to the same system without circulation. The difference between the two graphs that are illustrated reflects the loss of water, the loss of heat energy, and the waste of the user&#39;s time while waiting for hot water to arrive from the water heater. 
     Referring now to  FIG. 8 , there is shown an alternative embodiment  80  of the two-way check/bypass valve  10  described above. Alternative two-way check/bypass valve  80  employs a single spherical rolling ball  82  retained in an upwardly-curved passageway of circular cross section. Fittings  84 ,  86  are provided at each end of the upwardly curved passageway for connection to the hot and cold supply lines at remote faucets of a building water distribution system. Water attempting to flow from the hot supply line to the cold supply line or vice versa at a rate higher than required to support a convective flow of water in the system will be stopped as the rolling ball  82  is driven up the curved passageway to one of two circular valve seats  87 ,  88 . This will occur when one or the other of the hot and cold faucets is opened, and the static pressure in the associated supply line is reduced. When that faucet is then closed, rolling ball  82  will roll, by gravity, to the lowest or neutral position along the curved passageway, at which position a larger cross-sectional area of the curved passageway will allow water to continue to flow through two-way check/bypass valve  80  at the low convective flow rate. 
     Referring now to  FIG. 9 , there is shown an alternative embodiment  90  of two-way check/bypass valve  80  of  FIG. 8  wherein the circular passageway in which rolling ball  82  is positioned is formed to be V-shaped, extending upward and outward from valve seats  87 ,  88  and terminating at fittings  84 ,  86 . Operation of two-way check/bypass valve  90  is the same as described above in connection with two-way check/bypass valve  80  of  FIG. 8 . 
     Referring now to  FIGS. 10A-B , there are shown front and right side elevation views of an alternative embodiment  100  of two-way check/bypass valve  10  described above in connection with  FIGS. 4A-B ,  5 A-B, and  6 A-B. In the embodiment of  FIGS. 10A-B , the convective flow of water moves past poppets  102 ,  104  in adjacent water bypass channels  101 ,  103  that terminate above poppets  102 ,  104  when in the down or valve-open position. As either one of the poppets  102 ,  104  is forced upward to the valve-closed position by dynamic water pressure when a faucet is opened, it covers a bottom surface of an associated one of inlet and outlet ports  106 ,  108 , thereby stopping the flow of water through two-way check/bypass valve  100 . Each of the water bypass channels  101 ,  103  is inwardly tapered at its upper end to effect a slower closing action in order to minimize any water hammer effect. Each of the poppets  102 ,  104  is returned to its down or valve-open position by gravity to thereby permit the convective flow of water through two-way check/bypass valve  100 . 
     Referring now to  FIG. 11 , there is shown yet another alternative embodiment  110  of two-way check/bypass valve  10  described above in connection with  FIGS. 4A-B ,  5 A-B, and  6 A-B in which a single horizontal poppet bore  112  replaces the two vertical poppet bores illustrated in  FIG. 4A . The housing of two-way check/bypass valve  110  is constructed of a non-magnetic material. Poppet bore  112  terminates at its distal ends in inlet and outlet ports  120 ,  122 . A spherical ball poppet  114 , constructed of a water-compatible magnetic material, is centrally positioned within poppet bore  112 , midway between the distal ends of poppet bore  112 . Moveable valve seats  116 ,  118 , like valve seats  40 ,  46  illustrated in  FIG. 4A , are positioned within poppet bore  112  on opposite sides of ball poppet  114 . Like valve seats  40 ,  46 , each of the valve seats  116 ,  118  contains a central water passageway  130  to permit water to flow through it. A spring member  124 , like spring member  42  illustrated in  FIG. 4A , is positioned between valve seat  116  and inlet port  120 . Similarly, a spring member  126  is positioned between valve seat  118  and outlet port  122 . Like shoulder portion  56  of valve seats  40 ,  46 , each of the valve seats  116 ,  118  is shaped to include a shoulder portion  132  at the distal ends thereof that is urged, by spring members  124 ,  126 , against a corresponding shoulder formed along the inner cylindrical wall of poppet bore  112 . A permanent magnet  128  is imbedded in the housing of two-way check/bypass valve  110  adjacent poppet bore  112  at a position midway between the distal ends of poppet bore  112 . When all faucets are closed, permanent magnet  128  maintains ball poppet  114  at its central position, where the cross-sectional area of poppet bore  112  is greater than its cross-sectional area on either side of ball poppet  114  to permit water to convectively flow around ball poppet  114  and, thus, through two-way check/bypass valve  110 . When a faucet is opened, the differential pressure created thereby causes ball poppet  114  to roll either left or right from its central position and to engage the central water passageway  130  of one of the valve seats  116 ,  118  to stop the flow of water through two-way check/bypass valve  110 . When that faucet is closed, permanent magnet  128  returns ball poppet  114  to its central position that permits water to again flow convectively through two-way check/bypass valve  110 . 
     Referring now to  FIG. 12 , there is shown the two-way check/bypass valve  10  of  FIGS. 1 ,  3 , and  4 A-B with the addition of a heat exchanger  120  connected between two-way check/bypass valve  10  and cold water supply line  24 . Using the cold water supply line  24  as the return line to water heater  12 , in accordance with the present invention, offers significant advantages over prior art systems that require running a costly separate return line to the water heater. In some buildings, installation of a separate return line is nearly impossible, even at significant cost. A minor drawback to using the cold supply line  24  as a return line is that some heating of the water in cold supply line  24  will result in a wait time of several seconds after remote cold faucet  20  is opened, if truly cold water is desired. However, this wait time is considerably shorter than the wait time required for hot water to reach a remote hot water faucet in prior art water distribution systems. The minor limitation just described should not be of concern since most remote hot water faucets in residences are located in bathrooms where instant cold water is rarely required. The use of a small (¾″×2½″×3″) water-to-air heat exchanger  120  that is readily commercially available has been shown to reduce the temperature of water that would otherwise enter cold supply line  24  from two-way check/bypass valve  10  by three to five degrees F. during periods of normal convective circulation. A larger (¾″×5″×10″) heat exchanger  120  resulted in reducing the temperature of water otherwise entering cold supply line  24  by five to nine degrees F. These seemingly small reductions in the temperature of water entering cold water supply line  24  will result in shorter wait times and less wasted water, when truly cold water is required at remote faucet  20 . The heat exchanger  120  may be similarly connected to and employed with alternative two-way check/bypass valves  80 ,  90 ,  100 ,  100  of  FIGS. 8 ,  9 ,  10 A-B, and  11 .