Patent Publication Number: US-2016223209-A1

Title: Hot Water Recirculation Control Unit and Method

Description:
CROSS-REFERENCE TO RELATED DOCUMENTS 
     The present invention claims priority to a U.S. provisional patent application 62/110,360, filed on Jan. 30, 2015 and entitled “Control system for using existing plumbing to signal a hot water recirculation pump to turn on”, disclosure of which is incorporated herein at least by reference, 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is in the field of hot water management and distribution and pertains more particularly to methods and apparatus for maintaining expedient hot water availability in a plumbing architecture. 
     2. Discussion of the State of the Art 
     In the field of hot water management and distribution, hot water heaters are often deployed in commercial or residential plumbing systems. In a typical installation a hot water heater has an incoming line (cold water) and an outgoing line (hot water). Water may be heated by burning propane or natural gas or by electrical means to attain a temperature suitable for the residence or commercial application. 
     One problem with typical water heater operation is when a draw occurs in the hot water plumbing after perhaps a long delay and the water in the pipes has cooled. Hence a period of wait time is needed after initial draw before the user actually has hot water available at the draw point in the plumbing. This causes water (cold draw) to be wasted until hot water from the water heater reaches the draw point. In an attempt to solve this problem, houses have been designed to have a hot water plumbing loop which passes near to all plumbing fixtures that use hot water. Water recirculation pumps were designed into the system to continually circulate hot water through the hot water plumbing loop and water heater. More particularly, the water flow may be constant through the hot water heater while the pump is running, thus ensuring that hot water is immediately available at any draw point in the building. 
     One problem with a hot water system using a recirculation pump that is always on is the energy that is wasted (gas and/or electricity) as heat is lost through the piping and for running the pump. But if the pump is turned off the pipes will cool until the pump is powered back on. In some installations timers are added to regulate the amount of time the pump is running in an attempt to conserve energy. However strict schedule requirements arise for the beneficiaries of the hot water such as using hot water only during a scheduled time window. And the energy saved by using a timer is negatively correlated with the convenience of having hot water. Another alternative is to install switches to power on the recirculation pump on demand. A problem here is that this requires wiring to all the desired draw-point fixtures. Therefore, what is clearly needed is a control system for managing hot water distribution in a plumbed system that eliminates or reduces the above problems. 
     BRIEF SUMMARY OF THE INVENTION 
     In one embodiment of the invention a hot water recirculation control unit is provided, comprising a housing, a standard male electrical wall plug integrated into a first wall of the housing, the male wall plug connected to hot, neutral and ground electrical conductors in electrical circuitry within the housing, an electrically-operable power switch in the circuitry of the controller, connected on an input side to the hot electrical conductor, a standard female electrical wall plug integrated into a second wall of the housing, connected to neutral and ground and to the output terminal of the electrically-operable power switch, control circuitry including a processor, connected to the electrical conductors, the control circuitry having an output enabled to switch the electrically-operable power switch, and one or more input signal ports enabled to receive signals from two temperature sensors and at least one flow sensor, the signal ports connected to the control circuitry. The control circuitry switches the electrically-operable power switch on or off, providing power to or disconnecting power from the standard female electrical wall plug, based on presence and value of signals received at the one or more input signal ports. 
     In one embodiment the control circuitry switches the electrically-operable power switch on, providing power to the standard female electrical wall plug, in response to a signal that the flow sensor senses positive flow, and a pre-set difference in temperature is sensed between the two temperature sensors. Also in one embodiment the unit further comprises a mechanism enabling adjustment of the preset difference in temperature . Also in one embodiment the unit further comprises a manual input enabled to switch the electrically-operable power switch on and off. And in one embodiment the control circuitry comprises one or more timing mechanisms for improving reliability of operation. 
     In another aspect of the invention a hot water recirculation system is provided, comprising a water heating source, a pipe loop from the water heating source supplying heated water to a plurality of draw points and returning to an input of the hot water heating source, a cold water supply line to the hot water heating source, a water pump in the pipe loop after the draw points and before the input to the water heating source, a flow sensor in the pipe loop to indicate positive flow of water, indicating a draw at one of the plurality of draw points, a first temperature sensor coupled to the pipe loop near the outlet of the water heating source, a second temperature sensor coupled to the pipe loop at a point after the plurality of draw points, and a controller having an electrical power input from a power source, an electrical power output to the water pump, and control circuitry enabled to switch power from the power source to the output to the water pump. Signals from the flow sensor and the first and second temperature sensors are coupled to the control circuitry and the control circuitry switches power from the power source to the power output to the water pump, based on presence and value of signals received from the flow sensor and the temperature sensors. 
     In one embodiment the control circuitry switches power to the water pump in response to a signal that the flow sensor senses positive flow, and a pre-set difference in temperature sensed between the two temperature sensors. Also in one embodiment the system further comprises a mechanism coupled to the control circuitry enabling adjustment of the preset difference in temperature. Also in one embodiment the system further comprises a manual input to the control circuitry enabled to switch power to the water pump, overriding the control circuitry. And in one embodiment the control circuitry comprises one or more timing mechanisms for improving reliability of operation. 
     In yet another aspect of the invention a hot water recirculation method is provided, comprising providing a pipe loop from a water heating source to a plurality of draw points and returning to an input of the hot water heating source, providing a cold water supply line to the water heating source, providing a water pump in the pipe loop after the draw points and before the input to the water heating source, sensing flow by a flow sensor in the pipe loop to indicate positive flow of water, indicating a draw at one of the plurality of draw points, sensing a first temperature by a first temperature sensor coupled to the pipe loop near the outlet of the water heating source, sensing a second temperature by a second temperature sensor coupled to the pipe loop at a point after the plurality of draw points, monitoring flow indication from the flow sensor and temperatures sensed by the temperature sensors at a controller having an electrical power input from a power source, an electrical power output to the water pump, control circuitry enabled to switch power from the power source to the output to the water pump, and switching power from the power source to the power output to the water pump, causing recirculation in the pipe loop, based on presence and value of signals received from the flow sensor and the temperature sensors. 
     In one embodiment of the method the control circuitry switches power to the water pump in response to a signal that the flow sensor senses positive flow, and a pre-set difference in temperature sensed between the two temperature sensors. Also in one embodiment the method further comprises a step for adjusting the preset difference in temperature by a mechanism coupled to the control circuitry. In another embodiment the method further comprises overriding the control circuitry by a manual input to switch power to the water pump. And in one embodiment the control circuitry comprises one or more timing mechanisms for improving reliability of operation. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  is an architectural overview of a plumbed hot water system using a recirculation pump according to existing art. 
         FIG. 2  is an architectural overview of a plumbed hot water system using a hot water recirculation pump according to an embodiment of the present invention. 
         FIG. 3  is a process flow chart depicting steps for recirculation of hot water through a hot water loop according to an embodiment of the present invention. 
         FIG. 4  is a rear elevation view of the control unit of  FIG. 2  according to an embodiment of the present invention. 
         FIG. 5  is a front elevation view of the control unit of  FIG. 2 . 
         FIG. 6  is a bottom view of the control unit of  FIG. 2 . 
         FIG. 7  is an electrical diagram depicting control circuitry within the modular control unit of  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In various embodiments described in enabling detail herein, the inventor provides a unique system for managing the distribution of hot water in a plumbed system. The present invention is described using the following examples, which may describe more than one relevant embodiment falling within the scope of the invention. 
       FIG. 1  is an architectural overview of a plumbed hot water system  100  using a recirculation pump  104  according to existing art. System  100  includes a hot water heater (HWH)  101  that may be gas or electrically heated (heating apparatus not illustrated). A cold water line  102  is plumbed into HWH  101  delivering water into the tank to be heated. A hot water line or loop  103  is plumbed from HWH  101  and distributes hot water to hot water draw points in system  100 . 
     In this example, a hot water recirculation pump  104  is added to system  100  to constantly pull hot water through loop  103  and past draw points in the system. The draw points illustrated herein include a Tub/Shower unit  105 , a Faucet/Sink unit  106 , and a clothes washer unit  107 . In one example, one or more switches and wiring (not illustrated) are present for controlling power to pump  104 . In one example, a timer (not illustrated) may be included for automatic switch activation based on time of day, for example. The switches may be provided at draw points  105  through  107  or one switch at a central location to activate and run the recirculation pump. 
     In this example of existing art, pump  104  may be constantly on during an “active period” of hot water necessity that might be defined in a timer connected to the pump. In lieu of a timer, a manual switch or multiple switches may be activated from draw points or from a central location to start and stop pump  104  as described above. Either implementation is less than optimal from the standpoint of water and energy conservation. Loop  103  runs past draw points  105 ,  106 , and  107 , through pump  104  and into the incoming cold water line to HWH  101 . In either implementation the hot water availability at draw points  105  through  107  is not well regulated. 
       FIG. 2  is an architectural overview of a plumbed hot water system using a hot water recirculation pump  204  according to an embodiment of the present invention. A hot water heater (HWH)  201  is provided having a cold water line  202  plumbed thereto for water inflow and a hot water loop or line  203  plumbed therefrom for hot water distribution to flow points  205  (Tub/Washer),  206  (Faucet/Sink), and  207  (Clothes Washer). HWH  201  may be electrically or gas heated or with a tank or tankless without departing from the spirit and scope of the present invention. 
     An electronic control apparatus  208  is provided to control the distribution of hot water from HWH  201 . Control unit  208  may be located at a point that may be proximal to HWH  201  and recirculation pump  204  such as within the space of a utility closet housing the components, for example. In a preferred embodiment, recirculation pump  204  plugs into control unit  208  for power. In this embodiment, control unit  208  is adapted to turn on or turn off power to a female AC plug receptacle (not illustrated) on control unit  208  that recirculation pump  204  plugs into. In this example connections to control unit  208  are logically depicted. In a preferred embodiment, control system  208  plugs into a wall electrical outlet and the recirculation pump is plugged into the control unit. It should be noted herein that in one implementation, pump  204  may be plugged in elsewhere and a control line may be provided from the control unit to an on/off switch (not illustrated) on the pump. Similarly, sensors may communicate over separate communication lines or over a single line or cable without departing from the spirit and scope of the invention. 
     Control unit  208  in one implementation includes a micro-processing unit (MPU), a memory (MEM), a power supply (PS), and circuitry adapted for actuating the pump wiring specifically based on sensor input received at the control unit in real time over another connection, such as a computerized communications port such as Universal 
     Serial Bus (USB) port. In this embodiment a first temperature sensor (TS  1 )  210  is provided and connected to the hot water output line ( 203 ) of HWH  201 . TS  1  is adapted to measure the temperature of the water in pipe  203  where it egresses HWH  201 . TS  1   210  is electrically wired to control unit  208  and may constantly or periodically report the current temperature of the hot water leaving the water heater. 
     In one embodiment, TS  1   210  is an active sensor that takes temperature readings periodically and reports those to control unit  208 . In another embodiment, TS  1   210  is a passive sensor that may be accessed periodically by the control unit to access the current temperature reading at egress of the water heater. TS  1   210  may, in one implementation be installed within the water line or plumbing fixture connected at egress and has direct contact with the hot water. In another implementation, TS  1   210  is installed over or onto the pipe exiting the hot water heater and actually measures the temperature of the pipe. It is sufficient to say that TS  1   210  measures the temperature of the output of the hot water heater. 
     A second temperature sensor (TS  2 )  209  is provided and connected to a portion of loop  203  just before cold water ingress line  202  junction where the re-circulated hot water may mix in with incoming cold water into the water heater. TS  2   209  may be identical in some embodiments to TS  1   212 . TS  2  measures the temperature of returning hot water just before it junctions with cold water line  202 . In the course of operation it is expected that the temperature at hot water egress from HWH  201  will be greater than the temperature of hot water ingress into cold water line  202 , especially after recirculation pump  204  has been off for a period of time allowing the water in hot water loop  203  to cool down. The difference in temperature may, in one embodiment, be used to define a temperature range window that may be specified in an algorithm to determine whether recirculation pump  204  will be powered on or off. 
     A flow sensor (FL S)  211  is provided in this embodiment to sense a draw of hot water through hot water loop  203 . Control unit  208  may continuously or periodically monitor flow sensor  211  to determine if there is a draw on hot water loop  203  via one or more hot water line draw points ( 205 - 206 ). In one implementation, the control system includes an Arduino Micro™ micro-controller, 2 Thermal Probe DS 18B20 sensor devices, a SEN-HZ43WB G3/4″ water flow sensor, a 15 amp relay, and a 5 volt power supply. 
     In one embodiment, SW  213  and or firmware (FW) may be provided in MEM on control unit  208  that provides instruction for the control unit to monitor flow sensor  211  for any draw events. SW  213  may be further adapted to read temperature measurements at or sent to control unit  208  by temperature sensors TS  1  and TS  2 . SW  213  may determine, based on the temperature readings whether the temperature difference is larger than or falls within a preset temperature range. If there is a hot water draw event, as long as the temperature difference between the two sensors remains within a preset temperature range or window, the recirculation pump may remain in off mode. If there is a hot water draw event and the temperature difference between the two sensors (TS  1 , TS  2 ) is larger than the threshold range then the recirculation pump may be powered on by control system  208  to begin circulating hot water through loop  203  and back to cold water ingress line  202 . In this way, as long as there are hot water draw events, the water circulated through loop  203  is prevented from cooling beyond a certain temperature defined within the temperature range making user access to the hot water more efficient and economical. Hot water loop  203  may include more draw points or access points, such as points  205  through  207  without departing from the spirit and scope of the present invention. Hot water loop  203  may in one embodiment include more than one recirculation pump. Hot water loop  203  may also include more than two temperature sensors without departing from the spirit and scope of the invention. In one embodiment of the invention, control unit  208  may be adapted to control more than one recirculation pump on one or more than one hot water loop that may share HWH  201 . In the case of two separate hot water loops, the loops may be isolated from one another by an electronically operated valve such as a ball valve (not illustrated). Such implementation may be useful in a commercial environment such as a multiple floor hotel with multiple rooms on each floor. 
     In one embodiment control system  208  may be adapted to accept user input from an authorized individual whereby such individual may program which of more than one hot water loops will be isolated from or shut off from the other hot water loop(s) in the plumbed system, and which one or ones of the loops will be active and recirculating hot water. In the example of a hotel, there may be one hot water loop at each floor level wherein if room occupation by patrons is controlled to specific floors, only the loops covering the occupied floor may be activated for hot water recirculation. In this way it is possible to conserve resources (water, energy) by only using recirculation on a single loop. It will also be apparent that there may be more than one water heater with a tank or tankless present in a plumbed system without departing from the spirit and scope of the present invention. The number of temperature sensors and flow sensors may vary without departing from the spirit and scope of the present invention. 
       FIG. 3  is a process flow chart  300  depicting steps for recirculation of hot water through a hot water loop according to an embodiment of the present invention. There is a delay period as a period of not immediately starting the pump when a draw is registered. By way of explanation assume the system has been off for quite some time, such that water in the hot water loop is cold. If someone draws hot water and then relatively quickly shuts the hot water off, that action may not draw enough hot water to the temperature sensor on the outlet side of the water heater to trigger a significant temperature difference, so the pump will not turn on. To account for this situation a delay period is triggered each time the control unit returns to monitoring the flow sensor. Then, with the sensing of a draw, the pump will turn on immediately only if the delay period has expired. In one embodiment a delay period of ten minutes is reasonable, but other periods may be set depending on the installation. This operation allows the temp sensor to heat up while the unit is checking for a temperature differential which it does for say  10  seconds after a draw event occurs. The delay period is continually reset every time the control unit returns to monitoring the flow sensor via steps  315  and  309  after hot water hot water is drawn, so this immediate turning on of the pump only happens after the there has been no hot water drawn for the length of the delay period. 
     Following the flow in  FIG. 3 , at step  301  the control unit is monitoring for draw (flow sensor) and the pump is off. At step  302  if there is no draw control loops back to step  301 . If at step  302  a draw is recognized the controller checks at step  303  if the delay period has expired. If so, the pump is turned on at step  304 . If not, the temperature at the temperature sensors is checked at step  305 , which has a time period. In one embodiment ten seconds is reasonable. At step  306  the system determines the temperature difference between the two sensors. At step  307 , if the difference is smaller than a preset threshold the system checks at step  308  to see if the temperature check period has expired. If the temperature check period has not expired control loops back through the temperature check step  305 . If, however, the temperature check period has expired, the pump is turned off at step  316  if it was turned on in step  304 , and the delay period timer is reset at step  309 . Control reverts to step  301 . 
     If at step  307  the temperature difference is larger than the preset threshold the pump is turned on (or left on as a result of step  304 ) at step  310 . The system then rechecks temperatures at step  311 , calculates difference at step  312 . If the difference is above the threshold value at step  313  control loops back through step  311 . If at step  313  the difference is less than or equal to the preset value the pump is turned off at step  314 , and the delay timer is reset at step  315 , returning control again to step  301 . 
     In one aspect it is possible that there is no hot water, therefore the temperature at both sensors would be the same. In that case the recirculation pump may be kept off by default. If the water is heated by the water heater, then the temperature sensor at the water heater will be hotter than the temperature at the end of the recirculation loop prior to the junction where the returning hot water mixes with incoming cold water before entering the water heater provided there has been a draw on the hot water loop as measured by the flow sensor and identified as a hot water draw by the control unit. Therefore in periods of no draw the recirculation pump stays off. After initial draw, the system kicks in to manage hot water accessibility for the users. 
       FIG. 4  is a rear elevation view of control unit  208  of  FIG. 2  according to an embodiment of the present invention.  FIG. 5  is a front elevation view of unit  208 .  FIG. 6  is a bottom view of unit  208 . Referring now to  FIG. 4  Unit  208  may be of the form of a plug-in module. In this respect control unit  208  is modular and may be plugged into a wall outlet near the hot water heater via standard male AC power plug  401 . Unit  208  may therefore reside within the local proximity of the hot water heater such as within a utility closet enclosing the tank. Unit  208  includes a multiple port  402  connecting input from the flow sensor and temperature sensors and providing power to the sensors. 
     Referring now to  FIG. 5 , opposite male AC power input plug  401  is a female AC power output plug  501  adapted to accept a male AC power plug from the recirculation pump. Module or unit  208  may be housed within a utility grade polymer housing. Referring now to  FIG. 6 , Port  402  is a multiple port connector serving +5 V, GND, flow sensor and temperature sensors. In one embodiment, unit  208  receives sensor data from the flow and temperature sensors via port  402 . The recirculation pump may be plugged into female receptacle  501 , while the unit itself is plugged into a standard wall outlet. It is noted herein that all of the control circuitry is housed within modular unit  208 . 
     A switch  403  is provided that, when closed, places the unit into a setup mode. Setup mode is useful for installations wherein the unit does not reliably start the pump when a faucet is opened and closed, indicating that the sensitivity of the flow sensor needs to be increased, which may be done via adjusting a potentiometer. Switching into setup mode causes the pump to turn on for about ten seconds and then to turn off regardless of the temperature values. This way the sensitivity of the flow sensor can be set without having to unplug the unit to reset it and even if the loop is up to temperature. This adjustment may also be used if the unit turns on when a cold water faucet is closed abruptly as, for example, when a toilet finishes filling. Sometimes this is enough to send a pulse through the plumbing and trigger the flow sensor if it is too sensitive. 
     In an alternative embodiment circuitry shown in  FIG. 7  may also include Bluetooth circuitry and code to allow updating logic for the controller and to adjust values for timer and temperature settings and the like via a computerized device such as a laptop computer or a smart telephone. In yet another variation WiFi circuitry and code may be included to allow updating logic for the controller and to adjust values for timer and temperature settings and the like via a computerized device such as a laptop computer or a smart telephone. 
     In some embodiments a manual on-off switch is included in the modular unit to over-ride the controller in the unit, so the recirculation pump may be powered on and off regardless of sensed conditions. Such a switch is depicted in  FIGS. 4, 5 and 6  as element  403 . 
       FIG. 7  is an electrical diagram depicting one possible arrangement of control circuitry  700  within modular unit  208  of  FIG. 2 . It will be apparent to the skilled person that there may be many alternatives to this circuitry, while still accomplishing the purposes. Logic for circuitry  700  in this particular example is based on a microprocessor  701  receiving input from flow sensor  211 , temperature sensor (1)  210  and temperature sensor (2)  209 . The microprocessor is powered by a 5 V DC power supply connected to input from wall plug  401 , and controls an electronic switch  703  to switch the main line from wall plug  401  to output  501  which powers pump  204 . 
     It will be apparent to one with skill in the art that the recirculation pump control system of the invention may be provided using some or all of the mentioned features and components without departing from the spirit and scope of the present invention. It will also be apparent to the skilled artisan that the embodiments described above are specific examples of a single broader invention that may have greater scope than any of the singular descriptions taught. There may be many alterations made in the descriptions without departing from the spirit and scope of the present invention. 
     It will also be apparent to the skilled person that the arrangement of elements and functionality for the invention is described in different embodiments in which each is exemplary of an implementation of the invention. These exemplary descriptions do not preclude other implementations and use cases not described in detail. The elements and functions may vary, as there are a variety of ways the hardware may be implemented and in which the software may be provided within the scope of the invention. The invention is limited only by the breadth of the claims below.