Abstract:
A hot water system includes cold water pipes, hot water pipes, a water heater, a pump, a pump control unit and a connection valve unit. The pump is used to increase the pressure of the hot water pipes to a preset higher level than the pressure in the cold water pipes. When hot water is needed, the connection valve unit at the user side is opened to connect the cold water pipes and the hot water pipes, and when the cold water pipes and the hot water pipes are connected, the water pressure difference between them will become smaller. When the pressure difference change is detected, the pump control unit will activate the pump to pump the water in the hot water pipes into the cold water pipes, so the water in the pipes starts to circulate, and the water will flow through the water heater and will be heated. When the heated hot water reaches the user, the pump is stopped. After the hot water is being served or when the water temperature drops down, the pump is again put into normal operation.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This Non-provisional application claims priority under 35 U.S.C. §119(a) on Patent Application No(s). 097115778 filed in Taiwan, Republic of China on Apr. 29, 2008, the entire contents of which are hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     This invention relates to a hot water system which uses the cold and hot water recirculation to provide a fast hot water supply and avoid the waste of water. 
     2. Related Art 
     Conventional domestic hot water supply system uses a water heater to heat up the water from the cold water pipes, and flows to the fixtures through hot water pipes, such as the faucets in the bathroom or kitchen. When using the hot water at the first time, there is a lot of cold water in the hot water pipes, the user has to open the faucet and drain the cold water before he gets the hot water. The user has to wait and the water is wasted. As for this water wasting problem, there are many inventions designed to solve this problem. 
     One of the most common hot water recirculation system at present time uses a pump installed under the sink, the pump inlet is connected to the hot water pipe under the sink, and its outlet is connected to the cold water pipe, the user has to push a start button to start the pump, and the cold water in the hot water pipes will be pumped into the cold water pipes and start the recirculation, when the recirculated water is heated by the water heater and returns to the pump through the hot water pipes, on the detection of a rising of water temperature, the pump will be stopped, and the user can now open the faucet and use the hot water. An example product is provided by the Dux Manufacturing Limited called READYHOT. But this kind of solution must install a pump under every sink that needs fast hot water, and for a shower room faucet there are problems in installation space and in the power supply safety. 
     There are other more complicated hot water supply systems, but most of them require the installation of a complicated control valves (for example, the U.S. Pat. No. 7,140,382), and some have to change the piping system layout (for example, U.S. Pat. No. 6,895,985 and U.S. Pat. No. 5,918,625). These solutions are basically not particle for an already built house. 
     SUMMARY OF THE INVENTION 
     Regarding the above-mentioned problems, it is an objective of the invention to provide an apparatus, which can provide a water recirculation without changing the layout of water piping systems. Thus, the user can enjoy fast hot water supply as well as saving the water. In this invention, there are cold water pipes, hot water pipes, a water heater, a pump, a pump control unit and a mix faucet with an outlet control valve. In the conventional water piping system, the cold water pipes connect to the water heater&#39;s inlet, and the hot water pipes connect to the water heater&#39;s outlet. The invention inserts a pump between the cold water pipes and the water heater, the pump control unit controls the pump to increase the water pressure in the hot water pipes, and the water pressure is kept at a higher preset level than the water pressure of the cold water pipes. The fixtures at the terminals of the piping system, which connects to both the cold water pipes and hot water pipes (such as the mix faucet with an outlet control valve), is used to form a closed channel for connecting the cold water pipes and the hot water pipes, and so to form a recirculation path. With the pump control unit which can detect the water pressure difference and the water temperature, and by detecting the water pressure difference change when the cold water pipes and hot water pipes are connected, the pump is controlled and able to recirculate the water in the pipes until the hot water is available. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will become more fully understood from the detailed description and accompanying drawings, which are given for illustration only, and thus are not limitative of the present invention, and wherein: 
         FIG. 1  is a system diagram showing a hot water system according to a preferred embodiment of the invention; 
         FIG. 2  is a functional flow chart of the pump control unit used by the preferred embodiment of the invention; 
         FIG. 3  is a water pressure and water flow chart of the hot water system according to the preferred embodiment of the invention; and 
         FIG. 4  is another system diagram of a hot water system according to the preferred embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention will be apparent from the following detailed description, which proceeds with reference to the accompanying drawings, wherein the same references relate to the same elements. 
     Referring to  FIG. 1 , the hot water system of the invention consists of cold water pipes  11 , hot water pipes  12 , a water heater  13 , a pump  14 , a pump control unit  15 , a mix faucet  16  and water mains  17 . The water heater  13  has a cold water inlet  131  and a hot water outlet  132 . The pump  14  has a water inlet  141 , a water outlet  142  and a power supply input  143 . The pump control unit  15  has a water pressure detector  151 , a water temperature detector  152 , a water flow detector  153  and a pump control circuit  154 . The mix faucet  16  has a cold water inlet  161 , a hot water inlet  162 , a cold water control valve  163 , a hot water control valve  164 , an outlet control valve  165 , a water outlet  167  and a water mix chamber  166 . The hot water inlet  162  connects to the hot water pipes  12 , and the cold water inlet  161  connects to the cold water pipes  11 . The outlet control valve  165  can stop the water in the mix faucet  16  from flowing out of the water outlet  167 , and force the water from the hot water pipes  12  to flow back into the cold water pipes  11  through the water mix chamber  166  of the mix faucet  16 . The pump  14  increases the water pressure in the hot water pipes  12  and makes the water pressure higher than the water pressure in the cold water pipes  11 . The cold water pipes include a first cold water pipe  111  and a second cold water pipe  112 . The first cold water pipe  111  connects to the cold water inlet  161 , and the second cold water pipe  112  connects to the pump  14  and the first cold water pipe  111 . The hot water outlet  132  of the water heater  13  connects to hot water pipes  12 , the cold water inlet  131  of the water heater  13  connects to the water outlet  142  of the pump  14 , the inlet  141  of the pump  14  connects to cold water pipes  11 , the water pressure detector  151  of the pump control unit  15  connects to the water inlet  141  and the water outlet  142  of the pump  14 , the water temperature detector  152  connects to the water inlet  141  of the pump  14 , the water flow detector  153  connects to the water outlet  142  of the pump  14 , the inputs of the pump control circuit  154  connect to the outputs of the water pressure detector  151 , the water temperature detector  152  and the water flow detector  153 , the output of the pump control circuit  154  connects to the power supply input  143  of the pump  14 , the cold water inlet  161  of the mix faucet  16  connects to the cold water pipes  11 , the hot water inlet  162  of the mix faucet  16  connects to the hot water pipes  12 , and the cold water pipes  11  connects to the mains  17 . 
     Referring to  FIG. 1 , in the embodiment, the pump control unit  15  controls the pump  14  to increase the water pressure of the hot water pipes  12 , and to keep the water pressure difference between the hot water pipe  12  and cold water pipe  11  at a preset value. When the cold water control valve  163  and the hot water control valve  164  of the mix faucet  16  are both opened, and the outlet control valve  165  is closed, the water from the cold water pipes  11  and hot water pipes  12  will be injected into and mixed in the water mix chamber  166 , as a result the cold water pipes  11  and hot water pipes  12  will be connected and their water pressure difference will be decreased. When the water pressure detector  151  detects the water pressure difference drop, the pump control unit  15  will start the pump  14  to increase the water pressure in the hot water pipes  12 , as a result the water in the hot water pipes  12  will flow into the cold water pipes  11  through the water mix chamber  166 , and flow back to the pump  14  to form a recirculation. The recirculated water will flow through the water heater  13  and will be heated to become hot water, the hot water will flow to the mix faucet  16  and to the cold water pipes  11  and finally to the pump  14 . When the water temperature detector  152  detects that the water temperature starts to rise at the pump  14 , the pump control unit  15  will stop the pump  14  to stop the water recirculation, and waits for the user to use the hot water in the hot water pipes  12 . When the user opens the outlet control valve  165  of the mix faucet  16  to use the hot water, the cold water from the mains  17  will flow through the cold water pipes  11  to the mix faucet  16  and the pump  14 . When the water flow detector  152  detects that water is flowing from the water inlet  141  to the water outlet  142  of the pump  14 , or when the water temperature detector  152  detects the water temperature has dropped to a certain level, the pump control unit  15  will start the pump again to increase the water pressure of the hot water pipes  12  or start the recirculation again to re-heat the water in the pipes. 
     Furthermore, the outlet control valve  165  can be a temperature controlled valve which will open when the water temperature rises. When the outlet control valve  165  is closed and the water recirculation starts, the heated water will flow by the outlet control valve  165 , by using a temperature controlled mechanism the outlet control valve  165  can be opened automatically to let the hot water flow out of the water outlet  167 , and so when the water recirculation is started and the heated hot water arrives the mix faucet  16 , the hot water will be automatically released by the outlet control valve  165  through the water outlet  167 , and the water recirculation will be stopped, the user can then uses the hot water, also preventing the hot water from entering the cold water pipes  11 . 
     Referring to  FIG. 1 , in the embodiment, the pump control unit  15  can further include an operating time control function, which can protect the pump  14  from endless recirculation condition when the water heater  13  is not working or when the hot water pipes  12  are having a leak. The operation time control function can further be used to set the time limit for every recirculation operation to prevent too much hot water from flowing into the cold water pipes  11 . 
     Furthermore, the water heater  13  can be designed to output a lower temperature warm water at the beginning of the heating process, the lower temperature warm water has a higher temperature than the cold water, but it will not damage the cold water pipes which are mostly made of PVC (for example, a  40  degree C. warm water), and uses a timer to calculate the lower temperature warm water&#39;s travel time from leaving the water heater  13 &#39;s outlet to back to the water heater  13 &#39;s inlet, after the traveling time is obtained, the water heater  13  can then start to power up to heat the water to a preset high temperature and start to count the time until about half of the obtained traveling time, by then the high temperature hot water should be able to travel to the faucet of the user, and now the water recirculation can be stopped and wait for the user to use the hot water. 
     Referring to  FIG. 2 , the flowchart of the hot water system  1  is shown, first the system checks whether the water pressure difference is enough or not between the hot water pipes  12  and the cold water pipes  11 , if not enough, the pump  14  will be started to increase the water pressure of the hot water pipes  12 . At the same time the system will check whether the water temperature is rising or not, when the water temperature rises to a preset temperature, the system will stop the pump  14 . If the water temperature is not rising, the system will count the pump  14 &#39;s operation time and stop the pump  14  after a time limit is reached. Before the time limit the system will check the water pressure difference and the water temperature repeatedly until either one condition is met. After the time limit is reached or the water temperature is rising and the pump  14  is stopped, the system will then check for the water temperature drop and the water flow in the pump  14 , if the water temperature has dropped or there is water flowing through the pump  14 , the system will start the pump  14  again, and back to the previous process of checking the water pressure difference, water temperature and operation time limit. 
     Referring to  FIG. 3 , the water pressure change in the cold water pipes and the hot water pipes are shown. At time T 1  the pump  14  is started and the hot water pipes  12 &#39;s water pressure is increased. At time T 2  the pump  14  is stopped and the hot water pipes  12 &#39;s water pressure is kept at P HOT . At T 3 , the hot water pipes  12  and the cold water pipes  11  are connected and the water pressure of both will become P MIX . At time T 4  the pump  14  is started to run the heating recirculation, and the water temperature in the hot water pipes rises. At time T 5  the heating process is completed and the pump  14  is stopped. At T 6  the user start to use the water by opening the faucet, and the water in the hot water pipes  12  and the cold water pipes  11  starts to flow out of the faucet, and the water pressure in both pipes will drop. After detecting the water flow at T 7  the pump  14  is started again to pump water into the hot water pipes  12  until time T 8  the faucet is closed, and time T 9  when the water pressure reaches P HOT , the pump  14  is stopped. 
     Referring to  FIG. 4 , the hot water system of the invention, in comparison to the system in  FIG. 1 , further consists of a terminal control valve unit  21 . The terminal control valve unit  21  has a valve  211 , a water inlet  211   a , a water outlet  211   b  and a button  213 , a valve controller  212 . The valve controller  212  has a water temperature detector  212   a  and a timer  212   b.    
     Referring to  FIG. 4 , the water inlet  211   a  of the terminal control valve unit  21  connects to the hot water pipes  12 , the water outlet  211   b  connects to the cold water pipes  11 , the water temperature detector  212   a  connects to the hot water pipes  12 , the button  213  connects to the valve controller  212 , and the output of the valve controller  212  connects to the valve  211 . In normal condition the valve  211  is closed and the hot water pipes  12  and cold water pipes  11  are isolated. When the user wants to use hot water, the button  213  is pressed by the user and makes the valve controller  212  to open the valve  211 , the hot water pipes  12  and cold water pipes  11  are connected through the valve  211 , as a result the water pressure difference between the hot water pipes  12  and the cold water pipes  11  is decreased, when the pump control unit  15  detects the decrease in the water pressure difference, the pump  14  will be started to recirculate the water in the pipes, when the water is heated by the water heater  13  and flows back to the terminal control valve unit  21 , the water temperature detector  212   a  will detect the water temperature change, accordingly the valve controller  212  will close the valve  211 , as the recirculation path is closed by the valve  211 , the water pressure in the hot water pipes  12  will rise, so the water pressure difference between the hot water pipes  12  and the cold water pipes  11  will increase, finally when the water pressure difference has reached to a certain level, the pump control unit  15  will stop the pump  14 , the recirculation process is completed and the hot water is now ready to use. 
     In summary, the hot water system of the invention has the following advantages of:
         1. It uses the existing piping system, which makes it applicable to every existing house.   2. It uses the water pressure difference change to detect the user command, no extra or remote controller needed.   3. It can use the existing mix faucets to form the recirculation path, which is very simple, low cost and accessible at every end facilities.   4. It saves the waiting time and the water.       

     Although the invention has been described with reference to specific embodiments, this description is not meant to be construed in a limiting sense. Various modifications of the disclosed embodiments, as well as alternative embodiments, will be apparent to persons skilled in the art. It is, therefore, contemplated that the appended claims will cover all modifications that fall within the true scope of the invention.